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Decline of the Mara woodlands : the role of fire and elephants 1986

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DECLINE OF THE MARA WOODLANDS: THE ROLE OF FIRE AND ELEPHANTS by HOLLY T. DUBLIN B.A., A n t i o c h C o l l e g e , Y e l l o w S p r i n g s , O h io, 1976, M . S c , U n i v e r s i t y of Washington, S e a t t l e , Washington, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA November 1986 ( c j H o l l y T. D u b l i n , 1986 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Z O O L O G Y The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date 23 •hecvmWor ISSlo DE-6(3/81) S u p e r v i s o r : D r . A . R . E . S i n c l a i r ABSTRACT The Masai Mara Game Reserve of sout h w e s t e r n Kenya forms the northernmost e x t e n s i o n of the S e r e n g e t i ecosystem and p r o v i d e s the c r i t i c a l d r y season range f o r a p p r o x i m a t e l y 1.5 m i l l i o n m i g r a t o r y w i l d e b e e s t . Over the pas t 100 y e a r s , major e c o l o g i c a l changes have o c c u r r e d . The a r e a has e x p e r i e n c e d a t r a n s f o r m a t i o n from open g r a s s l a n d t o dense woodlands and back. T h i s study a d d r e s s e d the t r a n s i t i o n i n the Mara woodlands from b o t h an h i s t o r i c a l and a contemporary p e r s p e c t i v e . The study f o c u s e d on two c e n t r a l q u e s t i o n s : 1) what f a c t o r (or f a c t o r s ) were r e s p o n s i b l e f o r the d e c l i n e of the woodlands i n the 1960s? And 2) what f a c t o r ( o r f a c t o r s ) a r e c u r r e n t l y r e s p o n s i b l e f o r i n h i b i t i n g woodland r e g e n e r a t i o n ? In the 1880s an i n t r o d u c e d d i s e a s e , r i n d e r p e s t , decimated w i l d and domestic u n g u l a t e s i n the S e r e n g e t i - M a r a r e g i o n . L o c a l p a s t o r a l i s t s , dependent on t h e i r l i v e s t o c k f o r s u r v i v a l , succumbed t o d i s e a s e and s t a r v a t i o n . E l e p h a n t numbers had a l s o been g r e a t l y reduced by i n d i g e n o u s h u n t e r s . E x p l o r e r s , s l a v e t r a d e r s , and h u n t e r s d e s c r i b e d t h e a r e a as an open g r a s s l a n d by 1900. In the f o l l o w i n g decades, c o n d i t i o n s were c o n d u c i v e t o the e s t a b l i s h m e n t of woodlands; b u r n i n g r a t e s were low and e l e p h a n t b r o w s i n g was n e g l i g i b l e . By the 1930s, the ar e a was co v e r e d by dense woodland. These woodlands began a steady d e c l i n e s e v e r a l decades l a t e r . U n u s u a l l y h i g h r a i n f a l l , h i g h g r a s s p r o d u c t i v i t y , and severe f i r e s c h a r a c t e r i z e d the p e r i o d of g r e a t e s t d e c l i n e (1961 1967). A l t h o u g h woodland l o s s e s were i n t i a l l y viewed as " e l e p h a n t p r o b l e m s " , f i n d i n g s f r o m t h i s s t u d y s u g g e s t t h a t f i r e was t h e p r i m a r y f a c t o r i n t h e d i s a p p e a r a n c e o f w o o d l a n d s , w h i l e e l e p h a n t s m e r e l y a c c e l e r a t e d t h e r a t e o f d e c l i n e . E l e p h a n t s p r e f e r r e d o p e n g r a s s l a n d s , s w a m p s , a n d r e l i c t t h i c k e t s i n t h e we t s e a s o n . H o w e v e r , i n t h e d r y s e a s o n , e l e p h a n t s s e l e c t e d w o o d e d h a b i t a t s . A v e r a g e g r o u p s i z e was s i g n i f i c a n t l y h i g h e r i n t h e we t s e a s o n t h a n t h e d r y . M a r a e l e p h a n t s f i t t h e same f e e d i n g p a t t e r n s r e p o r t e d f o r many A f r i c a n e l e p h a n t p o p u l a t i o n s . E l e p h a n t s c o n c e n t r a t e d on g r a s s e s a n d h e r b s i n t h e r a i n y s e a s o n a n d b r o w s e i n t h e d r y s e a s o n . I n g e n e r a l , m a l e s b r o w s e d more t h a n f e m a l e s , w h i l e f e m a l e s a t e more d i v e r s e d i e t s c o n t a i n i n g more h e r b a c e o u s m a t t e r . E l e p h a n t s u t i l i z e d s e e d l i n g s u n d e r 1m more t h a n a n y o t h e r h e i g h t c l a s s o f t r e e s t h r o u g h o u t t h e y e a r . T h i s p a t t e r n o f s e l e c t i v e f e e d i n g s i g n i f i c a n t l y r e d u c e d s e e d l i n g s u r v i v o r s h i p . L a r g e - s c a l e f i e l d e x p e r i m e n t s s u b j e c t e d p l a n t s t o t h r e e t r e a t m e n t s : b r o w s e d o n l y , b r o w s e d a n d b u r n e d , a n d n e i t h e r b r o w s e d n o r b u r n e d . A l t h o u g h f i r e , a t c u r r e n t f u e l l o a d i n g s a n d i n t e n s i t i e s , p r o d u c e d a n a l m o s t t o t a l t o p k i l l , t h e m a j o r i t y o f b u r n e d i n d i v i d u a l s r e s p r o u t e d w i t h i n s i x m o n t h s . E l e p h a n t s r e m o v e d a s i g n i f i c a n t p r o p o r t i o n o f s e e d l i n g s a n d s e v e r e l y damaged o t h e r s . W i l d e b e e s t i n h i b i t e d s e e d l i n g g r o w t h t h r o u g h t r a m p l i n g , t h r a s h i n g , a n d a c c i d e n t a l b r o w s i n g . O n l y t h o s e s e e d l i n g s p r o t e c t e d f r o m b o t h b u r n i n g a n d b r o w s i n g i n c r e a s e d i n h e i g h t . W o o d l a n d d y n a m i c s i n t h e M a r a a r e c u r r e n t l y more a f f e c t e d by e l e p h a n t s , w i l d e b e e s t , a n d o t h e r b r o w s e r s t h a n by i v f i r e . E l e p h a n t s c a n be c o n s i d e r e d a " k e y s t o n e " s p e c i e s i n t h i s s y s t e m . I c o n c l u d e d t h a t e l e p h a n t s w e r e n o t c a p a b l e o f i n i t i a t i n g t h e w o o d l a n d d e c l i n e s w h i c h s t a r t e d o v e r two d e c a d e s a g o . H o w e v e r , o n c e t r e e d e n s i t i e s h a d b e e n r e d u c e d by p r e v i o u s p e r t u r b a t i o n s ( s u c h a s i n c r e a s e d b u r n i n g r a t e s f o l l o w i n g a r e d u c t i o n i n w i l d e b e e s t n u m b e r s a n d a n i n c r e a s e d f r e q u e n c y o f man-made f i r e s ) , e l e p h a n t s a c c e l e r a t e d t h e r a t e o f d e c l i n e . My f i n d i n g s d i d n o t s u p p o r t C a u g h l e y ' s " s t a b l e l i m i t c y c l e " h y p o t h e s i s . T o d a y , e l e p h a n t s a r e h o l d i n g t h e M a r a i n a g r a s s l a n d p h a s e , d e s p i t e l o w b u r n i n g r a t e s . T h i s p a t t e r n s u g g e s t s t h a t t h e M a r a may h a v e two l o c a l l y s t a b l e s t a t e s , w o o d l a n d o r g r a s s l a n d , a n d t h a t a n e x t e r n a l f a c t o r s u c h a s f i r e i s n e c e s s a r y t o move t h e s y s t e m b e t w e e n t h e t w o . E l e p h a n t s , a l o n e , a p p a r e n t l y c a n n o t move t h e s y s t e m f r o m one s t a t e t o a n o t h e r , b u t o n c e i t i s i n t h e g r a s s l a n d p h a s e , t h e y c a n h o l d i t t h e r e . V TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES x LIST OF FIGURES x i i ACKNOWLEDGEMENTS X V CHAPTER 1. GENERAL INTRODUCTION 1 CHAPTER 2. THE SERENGETI-MARA WOODLANDS: AN HISTORICAL PERSPECTIVE 10 I n t r o d u c t i o n 10 Methods 12 The Q u a l i t a t i v e and Eyewi tness E v i d e n c e of V e g e t a t i o n Changes 12 The D i r e c t Ev idence of V e g e t a t i o n Changes 13 The A c a c i a woodlands 16 The C r o t o n t h i c k e t s 17 R e s u l t s 19 V e g e t a t i o n Changes from 1880 to 1980: the q u a l i t a t i v e ev idence 19 V e g e t a t i o n Changes from 1950 to 1982: the d i r e c t ev idence 30 The Acac i a woodlands 30 The C r o t o n t h i c k e t s 34 D i s c u s s i o n 39 Summary 47 CHAPTER 3. HABITAT SELECTION AND GROUP SIZE OF ELEPHANTS IN v i THE MASAI MARA GAME RESERVE 49 I n t r o d u c t i o n 49 Study Area 50 C l i m a t e 51 P l a n t Communities 53 Geology and Hydro logy 58 Methods 59 Wet and Dry Season T o t a l Counts of E l e p h a n t s 60 Monthly Census C i r c u i t s 62 R e s u l t s 63 H a b i t a t S e l e c t i o n 63 Group S i z e 67 D i s c u s s i o n 69 H a b i t a t S e l e c t i o n 69 Group S i z e 74 Summary 77 CHAPTER 4. FEEDING ECOLOGY OF ELEPHANTS IN THE MASAI MARA GAME RESERVE 7 9 I n t r o d u c t i o n 79 Methods 81 R e s u l t s 85 F e e d i n g d i f f e r e n c e s between males and females 85 D i e t c o m p o s i t i o n 85 D i e t d i v e r s i t y 90 Lengths of f e e d i n g bouts 99 C h a r a c t e r i s t i c s of p l a n t s i n the d i e t 99 Female f e e d i n g p a t t e r n s 102 D i e t c o m p o s i t i o n 102 D i e t d i v e r s i t y 103 Lengths of f e e d i n g bouts 106 C h a r a c t e r i s t i c s of p l a n t s i n the d i e t 106 Male f e e d i n g p a t t e r n s 108 D i e t c o m p o s i t i o n 108 D i e t d i v e r s i t y 111 Lengths of f e e d i n g bouts 111 C h a r a c t e r i s t i c s of p l a n t s i n the d i e t 112 D i s c u s s i o n 113 E f f e c t s of food q u a l i t y 114 E f f e c t s of the w i l d e b e e s t m i g r a t i o n 117 E f f e c t s of s e a s o n a l change 122 E f f e c t s of woodland d i s a p p e a r a n c e 125 Summary 127 CHAPTER 5. THE EFFECTS OF ELEPHANTS, FIRE, WILDEBEEST AND BROWSERS ON THE ACACIA WOODLANDS 129 I n t r o d u c t i o n 129 Background I n f o r m a t i o n 130 Methods 133 Me a s u r i n g Browsing E f f e c t s 136 M e a s u r i n g B u r n i n g E f f e c t s 137 Data A n a l y s i s 141 R e s u l t s 142 The L a r g e - s c a l e F i e l d E x p e r i m e n t s 142 M o r t a l i t y of Trees and S e e d l i n g s 142 S e e d l i n g I n h i b i t i o n 143 v i i i S e e d l i n g Growth 150 The M u l t i p l e - b u r n Exper iments 156 The Seed G e r m i n a t i o n Exper iments 158 D i s c u s s i o n 158 E l e p h a n t s 160 F i r e 164 W i l d e b e e s t 169 Other Browsers 170 Summary 171 CHAPTER 6. DYNAMICS OF THE MARA WOODLANDS: PAST, PRESENT, AND FUTURE 173 I n t r o d u c t i o n 173 The Model 176 The Assumptions 176 E l e p h a n t s 176 F i r e 177 W i l d e b e e s t 178 R e s i d e n t Browsers 178 C o n s t a n t s and V a r i a b l e s i n the Model 179 The Tes t C o n d i t i o n s 182 R e s u l t s 184 Woodland D e c l i n e s in the 1 960s 184 Woodland Dynamics in the 1980s 189 Woodland Dynamics in the 1890s 191 Escapement Rates of T r e e s 193 D i s c u s s i o n 195 The 1 960s and 1 970s 1 95 ix C u r r e n t Dynamics 196 The F u t u r e 1 99 Management I m p l i c a t i o n s 202 LITERATURE CITED 204 APPENDIX A . THE WOODLAND DYNAMICS MODEL 224 X LIST OF TABLES T a b l e 2 . 1 . D e s c r i p t i o n of the a e r i a l photography 14 T a b l e 3 . 1 . Percent of h a b i t a t types in the Mara Reserve . . . 61 T a b l e 3 . 2 . Average herd s i z e by h a b i t a t type and season i n the Mara Reserve 68 T a b l e 3 . 3 . Average herd s i z e for o ther A f r i c a n e l ephant p o p u l a t i o n s 75 T a b l e 4 . 1 . Number of f o c a l a n i m a l s , t o t a l r a i n f a l l , and mean monthly r a i n f a l l f or each sampl ing p e r i o d 82 T a b l e 4 . 2 . Comparison of female and male d i e t c o m p o s i t i o n . 88 T a b l e 4 . 3 . Comparison of a b s o l u t e d i e t d i v e r s i t y between females and males by season 94 T a b l e 4 . 4 . Comparison of r e l a t i v e d i e t d i v e r s i t y between females and males by season 97 T a b l e 4 . 5 . Mean l e n g t h of f o r a g i n g bouts a c r o s s a l l forage types by month and season 100 T a b l e 4 . 6 . Comparison of d i e t c o m p o s i t i o n for females and males between seasons 105 T a b l e 4 . 7 . Comparison of l e n g t h of f o r a g i n g bouts for females and males between seasons 107 T a b l e 4 . 8 . Comparison of f e e d i n g h e i g h t p r e f e r e n c e s for females and males between seasons 109 T a b l e 5 . 1 . S e e d l i n g d e n s i t i e s f or f i v e sample p l o t s 134 T a b l e 5 . 2 . C h a r a c t e r i s t i c s of l a r g e - s c a l e e x p e r i m e n t a l f i r e s 140 x i T a b l e 5.3. ANOVA r e s u l t s f o r the l o s s of stems a c r o s s seasons, s i t e s , and t r e a t m e n t s 145 Tab l e 5.4. ANOVA r e s u l t s f o r stem damage a c r o s s s i t e s and t r e a t m e n t s 148 Tab l e 6.1. C o n s t a n t s i n the model 180 Ta b l e 6.2. Parameters i n the model 181 Ta b l e 6.3. Test c o n d i t i o n s f o r the 1 960s and 1980s 183 Tab l e 6.4. Woodland r e c r u i t m e n t r a t e s w i t h f i r e , e l e p h a n t s , and browsers i n the 1960s 185 Tab l e 6.5. Woodland r e c r u i t m e n t r a t e s w i t h f i r e , e l e p h a n t s , b r o w s e r s , and w i l d e b e e s t i n the 1980s 190 x i i LIST OF FIGURES F i g u r e 1 .1 . Map of the S e r e n g e t i - M a r a ecosystem 2 F i g u r e 1.2. Map of the Masai Mara Game Reserve 3 F i g u r e 2 . 1 . Narok r a i n f a l l - f i v e - y e a r averages 27 F i g u r e 2 . 2 . Changes i n the mean cover d e n s i t y of Acac i a woodlands from 1950 to 1982 31 F i g u r e 2 . 3 . A b s o l u t e r a t e of cover l o s s i n the Acac i a woodlands 32 F i g u r e 2 . 4 . R e l a t i v e r a t e of cover l o s s i n the Acac i a woodlands 33 F i g u r e 2 . 5 . Cover d e n s i t y of C r o t o n t h i c k e t s from 1950 through 1982 35 F i g u r e 2 . 6 . A b s o l u t e r a t e of cover l o s s i n the C r o t o n t h i c k e t s 36 F i g u r e 2 . 7 . R e l a t i v e r a t e of cover l o s s i n the C r o t o n t h i c k e t s 37 F i g u r e 2 . 8 . Mean area of C r o t o n t h i c k e t s i n 1950 and 1982 . 38 F i g u r e 2 . 9 . Trends i n human p o p u l a t i o n d e n s i t y near the Mara Game Reserve 41 F i g u r e 3 . 1 . Monthly r a i n f a l l t o t a l s for 1982, 1983, and 1984 52 F i g u r e 3 . 2 . Mean monthly maximum and minimum temperatures . 54 F i g u r e 3 . 3 . Wet and d r y season h a b i t a t p r e f e r e n c e s from a e r i a l survey data 64 F i g u r e 3 . 4 . H a b i t a t p r e f e r e n c e s for females and males i n x i i i the dry season 65 F i g u r e 3 . 5 . H a b i t a t p r e f e r e n c e s f o r females and males i n the wet season 66 F i g u r e 4 . 1 . Seasona l d i e t c o m p o s i t i o n of females and males i n 1982, 1983, and 1984 86 F i g u r e 4 . 2 . Seasona l d i e t c o m p o s i t i o n of females and males i n 1983-84 87 F i g u r e 4 . 3 . A b s o l u t e d i e t d i v e r s i t y for females and males . 91 F i g u r e 4 . 4 . Length of o b s e r v a t i o n t ime versus number of s p e c i e s eaten by females 92 F i g u r e 4 . 5 . Length of o b s e r v a t i o n t ime v e r s u s number of s p e c i e s eaten by males 93 F i g u r e 4 . 6 . R e l a t i v e d i e t d i v e r s i t y of females and males by month 96 F i g u r e 4 . 7 . R e l a t i v e browsing d i v e r s i t y of females and males by month 98 F i g u r e 4 . 8 . Percent browse i n e l e p h a n t d i e t s v e r s u s mean monthly r a i n f a l l 104 F i g u r e 4 . 9 . S t a n d i n g c r o p biomass through the dry season . .118 F i g u r e 4 .10 . Crude p r o t e i n l e v e l s i n long gras se s through the dry season 119 F i g u r e 4 . 1 1 . Grams of crude p r o t e i n i n long g r a s s e s through the dry season and the change i n e l ephant d i e t s between g r a z i n g and browsing be fore and a f t e r the d r y season . . . 121 F i g u r e 5 . 1 . He ight d i s t r i b u t i o n s of A c a c i a g e r r a r d i i i n f i v e sample p l o t s 135 F i g u r e 5 . 2 . Percent of marked stems removed by e l e p h a n t s , x i v w i l d e b e e s t , and o ther browsers i n burned and unburned p l o t s 144 F i g u r e 5 . 3 . Percent of marked stems browsed, t r a m p l e d , and not damaged i n burned and unburned p l o t s 149 F i g u r e 5 . 4 . Frequency d i s t r i b u t i o n of r e t u r n t imes for r e s p r o u t i n g "regenerates" o r i g i n a l l y removed by e l e p h a n t s , f i r e , and w i l d e b e e s t 151 F i g u r e 5 . 5 . Change in average stem h e i g h t s in b u r n e d , unburned, and e x c l o s e d p l o t s 152 F i g u r e 5 . 6 . Change i n average stem numbers in burned , unburned, and e x c l o s e d p l o t s 155 F i g u r e 5 . 7 . S e e d l i n g s u r v i v o r s h i p i n m u l t i p l e - b u r n exper iments 1 57 F i g u r e 5 . 8 . Average number of seeds s u r v i v i n g f i v e f i r e - treatment i n t e n s i t i e s 159 F i g u r e 5 . 9 . He ight s t r u c t u r e of Acac i a woodlands i n 1974 and 1984 162 F i g u r e 5 .10 . E l e p h a n t occupancy of the Mara Game R e s e r v e , 1980 - 1983 165 F i g u r e 6 . 1 . Woodland r e c r u i t m e n t r a t e s at v a r y i n g e l ephant p o p u l a t i o n s i z e s 187 F i g u r e 6 . 2 . Woodland r e c r u i t m e n t r a t e s under v a r y i n g b u r n i n g r a t e s 188 F i g u r e 6 . 3 . Escapement r a t e s for t r e e s by h e i g h t and age c l a s s 194 F i g u r e 6 . 4 . Woodland r e c r u i t m e n t r a t e s under v a r y i n g e l ephant p o p u l a t i o n s i z e s and b u r n i n g r a t e s 200 X V ACKNOWLEDGEMENTS R e s e a r c h o f a n i n t e r n a t i o n a l n a t u r e r e q u i r e s t h e c o o p e r a t i o n a n d a s s i s t a n c e o f many p e o p l e . T h i s s t u d y was no e x c e p t i o n . I n K e n y a , my r e s e a r c h was made p o s s i b l e t h r o u g h t h e a p p r o v a l o f t h e N a t i o n a l S c i e n c e a n d R e s e a r c h C o u n c i l , t h e K e n y a R a n g e l a n d s E c o l o g i c a l M o n i t o r i n g P r o j e c t , t h e W i l d l i f e C o n s e r v a t i o n a n d M a n a g e m e n t D e p a r t m e n t a n d t h e N a r o k C o u n t y C o u n c i l . I n p a r t i c u l a r I w o u l d l i k e t o t h a n k , C . A . M w a n g o , D a v i d A n d e r e , D a v i d M b u v i , a n d S i m o n M a k a l l a h . I n t e r n a t i o n a l w o r k a l s o r e q u i r e s t h e f i n a n c i a l s u p p o r t o f many o r g a n i z a t i o n s . I am g r a t e f u l t o t h e F u l b r i g h t S c h o l a r s P r o g r a m f o r f u n d i n g t h e m a j o r p o r t i o n o f my f i e l d w o r k , a l s o S i g m a X i , New Y o r k Z o o l o g i c a l S o c i e t y , t h e E a s t A f r i c a n W i l d l i f e S o c i e t y , a n d a U n i v e r s i t y G r a d u a t e F e l l o w s h i p f o r c o v e r i n g t h e b a l a n c e o f my r e s e a r c h e x p e n s e s i n K e n y a . My y e a r o f w r i t i n g was s u p p o r t e d e n t i r e l y b y . W o r l d W i l d l i f e F u n d - U . S a n d F r i e n d s o f t h e M a s a i M a r a . F o r t h i s g e s t u r e o f f a i t h I am i n d e b t e d t o R u s s e l l E . T r a i n , J o r i e B u t l e r K e n t a n d R i c k W e y e r h a e u s e r . My s u p e r v i s o r y c o m m i t t e e m e m b e r s , A . R . E . S i n c l a i r , R o b i n L i l e y , Don L u d w i g , J u d y M y e r s , a n d Roy S t r a n g e a c h r e a d my d i s s e r t a t i o n t h o r o u g h l y a n d p r o v i d e d many u s e f u l c r i t i c i s m s a n d c o m m e n t s . A l i s t a i r B l a c h f o r d , S u s a n E r t i s , a n d S h i r l e y G r a y s t o n e h e l p e d i n a l l a s p e c t s o f my c o m p u t e r w o r k f o r w h i c h I am e s p e c i a l l y g r a t e f u l . M o n i c a T h a i n k e p t me l e g i t i m a t e w i t h t h e U n i v e r s i t y t h r o u g h o u t my e x t e n d e d s t a y i n K e n y a . L e e G a s s b u o y e d my m o r a l e on many o c c a s i o n s . My a s s i s t a n t , J o s e p h K i b r e c h , made t h e f i e l d w o r k b o t h x v i p o s s i b l e a n d e n j o y a b l e . My c o l l e a g u e s , L a u r e n c e F r a n k , R i c h a r d L a m p r e y , a n d R o b e r t S a p o l s k y p r o v i d e d c o m p a n i o n s h i p a n d i n t e l l e c t u a l s t i m u l a t i o n o v e r my y e a r s i n t h e f i e l d , w h i l e M i k e N o r t o n - G r i f f i t h s , I a i n D o u g l a s - H a m i l t o n , a n d D a v i d W e s t e r n s u p p l i e d g o o d a d v i c e f r o m N a i r o b i . I w o u l d e s p e c i a l l y l i k e t o t h a n k T e d G o s s f o r g i v i n g me t h a t f i r s t c h a n c e t o do e c o l o g i c a l r e s e a r c h i n K e n y a w h i c h h a s l a r g e l y d i r e c t e d my l i f e e v e r s i n c e a n d , p o s t h u m o u s l y , M y l e s T u r n e r who g a v e me t h e m o r a l s u p p o r t t o c a r r y on d u r i n g my m o s t d i f f i c u l t t i m e s i n t h e M a r a . My s i n c e r e t h a n k s go t o my s u p e r v i s o r , T o n y S i n c l a i r . A l t h o u g h he h a d no i d e a w h a t he was g e t t i n g i n t o when he t o o k me o n , he d e s e r v e s h i g h e s t m a r k s f o r h i s u n f a l t e r i n g s u p p o r t b o t h i n t h e f i e l d a n d on t h e h o m e f r o n t . H i s c r i t i c i s m k e p t me a s k i n g more q u e s t i o n s , h i s t r u s t k e p t me t r y i n g t o a n s w e r t h e m . My s i b l i n g s a d d e d t h e humour t o my l i f e w h i c h i s s u c h a n e c e s s a r y p a r t o f a n y m a j o r u n d e r t a k i n g . H a r v e y H i n s z g a v e me t h e m o t i v a t i o n t o t u r n my l o n g i n g s f o r t h o s e w i d e o p e n p l a i n s b a c k i n t o a r e a l i t y . W i t h o u t q u e s t i o n , I owe my d e e p e s t g r a t i t u d e t o my p a r e n t s who f i r s t t o o k me t o A f r i c a a n d r a i s e d me t o b e l i e v e t h a t wha t I c o u l d a c c o m p l i s h was o n l y l i m i t e d by t h e s c o p e o f my i m a g i n a t i o n . 1 CHAPTER 1. GENERAL INTRODUCTION The M a s a i M a r a Game R e s e r v e f o r m s t h e n o r t h e r n m o s t p o r t i o n o f t h e S e r e n g e t i - M a r a e c o s y s t e m ( F i g u r e s 1.1 a n d 1 . 2 ) . The M a r a ' s e x t e n s i v e g r a s s l a n d s h a v e e x p a n d e d s i g n i f i c a n t l y i n r e c e n t y e a r s ( G l o v e r a n d T rump 1 9 7 0 , T a i t i 1 9 7 3 , D u b l i n 1 9 8 4 , L a m p r e y 1 9 8 5 ) . T o d a y t h e y p r o v i d e t h e c r i t i c a l d r y s e a s o n r a n g e f o r a p p r o x i m a t e l y 1 .5 m i l l i o n m i g r a t o r y w i l d e b e e s t , C o n n o c h a e t e s t a u r i n u s ( S i n c l a i r e t a l . 1 9 8 5 ) . A l t h o u g h g r a s s l a n d s w e r e e x t e n s i v e i n t h e M a r a a r o u n d t h e t u r n o f t h i s c e n t u r y (Woosnam 1 9 1 3 , W h i t e 1 9 1 4 , 1 9 1 5 , B u x t o n 1 9 2 7 ) , t h e s e g r a s s l a n d s w e r e r e p l a c e d by w o o d l a n d s a n d t h i c k e t s o v e r t h e f o l l o w i n g 30 y e a r s ( L e w i s 1 9 3 5 , D a r l i n g 1 9 6 0 , S . D o w n e y , p e r s . c o m m . ) . I n t h e l a t e 1 9 5 0 s t h e s e w o o d l a n d s b e g a n a s t e a d y d e c l i n e w h i c h c o n t i n u e d t h r o u g h t h e 1 9 6 0 s a n d 1 9 7 0 s l e a v i n g few i n t a c t s t a n d s o f t r e e s w i t h i n t h e R e s e r v e b o u n d a r i e s t o d a y . The p r o g r e s s i o n o f t h e s e d e c l i n e s was n o t w e l l - d o c u m e n t e d i n t h e M a r a . W h i l e a w e a l t h o f b i o l o g i c a l i n f o r m a t i o n h a d b e e n c o l l e c t e d i n t h e S e r e n g e t i N a t i o n a l P a r k o v e r t h e t h r e e d e c a d e s o f w o o d l a n d c h a n g e , l i t t l e i n f o r m a t i o n was a v a i l a b l e f o r t h e M a r a Game R e s e r v e . I t was n o t u n t i l N o r t o n - G r i f f i t h s ( 1 9 7 9 ) q u a n t i f i e d r a p i d w o o d l a n d d e c l i n e s i n t h e n e i g h b o u r i n g n o r t h e r n S e r e n g e t i t h a t a t t e n t i o n was d r a w n t o t h e s t a t u s o f w o o d l a n d s i n t h e M a r a . L i k e many s i m i l a r d e c l i n e s i n p a r k s a n d r e s e r v e s t h r o u g h o u t e a s t , c e n t r a l , a n d s o u t h e r n A f r i c a ( L a w s 1 9 7 0 , C a u g h l e y 1 9 7 6 ) , w o o d l a n d l o s s e s i n t h e S e r e n g e t i - M a r a w e r e i n i t i a l l y v i e w e d a s " e l e p h a n t p r o b l e m s " ( D a r l i n g 1 9 6 4 , G l o v e r 1 9 6 5 , L a m p r e y e t a l . 1 9 6 7 , R u s s e l l 1 9 6 8 , G l o v e r a n d T r u m p 1 9 7 0 ) . E c o l o g i c a l d o c t r i n e F i g u r e 1 . 1 . A map of t h e S e r e n g e t i - M a r a ecosystem. F i g u r e 1.2. A map of the study a r e a , the Masai Mara Game Reserve. 4 o f t h i s p e r i o d a r g u e d t h a t e l e p h a n t ( L o x o d o n t a a f r i c a n a ) d e n s i t i e s i n p a r k s a n d r e s e r v e s , s u c h a s t h e S e r e n g e t i - M a r a , w e r e b e c o m i n g a r t i f i c i a l l y h i g h a s human s e t t l e m e n t p r e s s u r e s g rew a n d f o r c e d e l e p h a n t s i n t o p r o t e c t e d a r e a s . O n c e c o n c e n t r a t e d i n t h e s e a r e a s e l e p h a n t s e x c e e d e d t h e c a p a c i t y o f t h e l a n d s t o s u p p o r t t h e m . C o n s e q u e n t l y , e l e p h a n t s d e s t r o y e d t h e i r h a b i t a t s t h r o u g h o v e r - u t i l i z a t i o n , a n d e l e p h a n t - r e l a t e d t r e e m o r t a l i t y was e x c e e d i n g n a t u r a l r e g e n e r a t i o n . T h i s e f f e c t was d o c u m e n t e d i n t h e p a r k s o f U g a n d a ( B u e c h n e r a n d D a w k i n s 1 9 6 1 , B u s s 1 9 6 1 , L a w s 1 9 7 0 , S p e n c e a n d A n g u s 1 9 7 1 , F i e l d 1 9 7 1 , L a w s e t a_ l . 1 9 7 5 , F i e l d a n d R o s s 1 9 7 6 , M a l p a s 1 9 7 8 ) , T a n z a n i a ( L a m p r e y e t a l . 1 9 6 7 , S a v i d g e 1 9 6 8 , L a w s 1 9 7 0 , D o u g l a s - H a m i l t o n 1 9 7 2 , C r o z e 1974a & b , B a r n e s 1 9 8 2 , 1 9 8 3 ) , s o u t h e r n A f r i c a ( P i e n a a r e t a l . 1 9 6 6 , A n d e r s o n a n d W a l k e r 1 9 7 4 , C a u g h l e y a n d G o d d a r d 1 9 7 4 , Thomson 1 9 7 5 , H a n k s e t a l . 1 9 8 1 , H a l l - M a r t i n 1984) a n d o t h e r p a r k s i n K e n y a ( G l o v e r 1 9 6 3 , G l o v e r a n d S h e l d r i c k 1 9 6 4 , Agnew 1 9 6 8 , L a w s 1 9 6 9 , 1 9 7 0 ) . C o n t r o l l e d c u l l i n g o f e l e p h a n t s was i n s t i t u t e d i n t h e n a t i o n a l p a r k s o f Z imbabwe (Cumming 1 9 8 1 , 1 9 8 3 ) , M a l a w i ( B e l l 1 9 8 3 ) , S o u t h A f r i c a ( P i e n a a r 1 9 6 9 , v a n Wyk a n d F a i r a l l 1 9 6 9 , de V o s e t a l . 1 9 8 3 , O w e n - S m i t h 1 9 8 3 , P i e n a a r 1 9 8 3 ) , a n d U g a n d a ( L a w s e t a l . 1975 ) a n d r e c o m m e n d e d i n o t h e r s ( R o s s e_t a l . 1 9 7 6 , B a r n e s 1983) a s a s o l u t i o n t o t h e e l e p h a n t / w o o d l a n d d i l e m m a s . P r e s s u r e was p l a c e d on p a r k m a n a g e r s i n o t h e r a r e a s e x p e r i e n c i n g w o o d l a n d d e c l i n e s t o p u r s u e s i m i l a r o p t i o n s . L a m p r e y e t a l . ( 1 9 6 7 ) d e s c r i b e d a n i n f l u x o f e l e p h a n t s i n t o t h e S e r e n g e t i - M a r a i n t h e l a t e 1 9 5 0 s a n d e a r l y 1 9 6 0 s w h e r e t h e y h a d n o t b e e n p r e s e n t i n s i g n i f i c a n t n u m b e r s f o r a t l e a s t 5 the p r e v i o u s 40 y e a r s . D u b l i n (1984) r e v i e w e d the a n e c d o t a l h i s t o r y of t h e s e movements and the g e o g r a p h i c a l o r i g i n s of i m m i g r a t i n g e l e p h a n t s . In a r e v i e w of a l l e l e p h a n t censuses conducted i n the S e r e n g e t i - M a r a , D u b l i n and D o u g l a s - H a m i l t o n ( i n p r e s s ) document t h i s g r a d u a l r e - c o l o n i z a t i o n by e l e p h a n t s and t h e e v e n t u a l merging of t h e i r s o u t h e r n and n o r t h e r n p o p u l a t i o n s between the l a t e 1950s and the l a t e 1970s. T h i s i n c r e a s e i n e l e p h a n t numbers and d e n s i t i e s c o i n c i d e d c l o s e l y w i t h the r e p o r t e d d e c l i n e of woodlands i n the S e r e n g e t i - Mara and was c i t e d as e v i d e n c e i n support of the h y p o t h e s i s t h a t e l e p h a n t s were r e s p o n s i b l e f o r the o b s e r v e d r e v e r s i o n t o open g r a s s l a n d . In the mid-1970s, park a u t h o r i t i e s and r e s e a r c h e r s d e c i d e d t o c u l l e l e p h a n t s e x p e r i m e n t a l l y i n an attempt t o reduce t h e i r impact on l o c a l woodlands. The c u l l i n g o p e r a t i o n s met w i t h l i t t l e s u c c e s s and woodland l o s s e s c o n t i n u e d . Croze (1974a & b) c o n c l u d e d from h i s s t u d i e s , i n the c e n t r a l S e r e n g e t i woodlands around S e r o n e r a , t h a t e l e p h a n t s were not r e s p o n s i b l e f o r the o b s e r v e d woodland d e c l i n e s . H i s r e s u l t s showed t h a t t h e r e was s u f f i c i e n t r e g e n e r a t i o n t o o f f s e t the number of t r e e s k i l l e d by e l e p h a n t s . These f i n d i n g s i n s p i r e d r e s e a r c h e r s i n the S e r e n g e t i t o l o o k f u r t h e r f o r p o s s i b l e causes of woodland d e c l i n e . F i r e had l o n g been r e c o g n i z e d as a means of c o n t r o l l i n g bush encroachment and as an agent i n the r e d u c t i o n of n a t u r a l woodlands i n A f r i c a ( P h i l l i p s 1930, 1965, Buss 1961, West 1965). G l o v e r (1965, 1972) s t u d i e d i n i t i a l l y the d e t r i m e n t a l e f f e c t s of f i r e on woodland r e g e n e r a t i o n i n the S e r e n g e t i . N o r t o n - G r i f f i t h s (1979) f u r t h e r i n v e s t i g a t e d t h e s e e f f e c t s i n a d e t a i l e d study 6 c o r r e l a t i n g t h e f r e q u e n c y o f f i r e s w i t h t h e l o s s o f w o o d l a n d c a n o p y c o v e r . He f o u n d t h a t l o s s e s i n t h e S e r e n g e t i w e r e p r i m a r i l y c o r r e l a t e d w i t h t h e i n c i d e n c e o f f i r e o v e r t h e d e c a d e s t u d i e d a n d o n l y s e c o n d a r i l y w i t h t h e u s e o f t h e a r e a by e l e p h a n t s d u r i n g t h e d r y s e a s o n . A l t h o u g h h i s i n v e s t i g a t i o n d i d n o t i n c l u d e t h e M a r a , N o r t o n - G r i f f i t h s ( 1 9 7 9 ) h y p o t h e s i z e d t h a t s i m i l a r f a c t o r s w e r e o p e r a t i n g t h e r e a s w e l l . I n 1982 t h i s s t u d y was i n i t i a t e d t o i n v e s t i g a t e c h a n g e s i n t h e M a r a w o o d l a n d s o v e r t h e p a s t 30 y e a r s . V i e w i n g t h e s e c h a n g e s f r o m b o t h a n h i s t o r i c a l a n d a c o n t e m p o r a r y p e r s p e c t i v e , t h e s t u d y was a i m e d a t a d d r e s s i n g two c e n t r a l q u e s t i o n s : 1) wha t f a c t o r ( o r f a c t o r s ) w e r e r e s p o n s i b l e f o r t h e o b s e r v e d d e c l i n e o f t h e w o o d l a n d s i n t h e 1 9 6 0 s ? A n d , 2) wha t f a c t o r ( o r f a c t o r s ) a r e c u r r e n t l y r e s p o n s i b l e f o r t h e i n h i b i t i o n o f w o o d l a n d r e g e n e r a t i o n ? T h e s e q u e s t i o n s w e r e a n s w e r e d t h r o u g h e x p e r i m e n t a l a n d o b s e r v a t i o n a l f i n d i n g s . S p e c i f i c a l l y , I f o c u s e d on t h e h y p o t h e s e s t h a t i n t h e 1 9 6 0 s a n d 1 9 7 0 s : 1) e l e p h a n t - r e l a t e d m o r t a l i t y , i n a d d i t i o n t o o t h e r m o r t a l i t y f a c t o r s , was r e s p o n s i b l e f o r t h e o b s e r v e d l o s s e s i n w o o d l a n d c o v e r d e n s i t y i n t h e M a r a R e s e r v e . By k i l l i n g m a t u r e t r e e s , e l e p h a n t s i n c r e a s e d t r e e m o r t a l i t y r a t e s t o a l e v e l a b o v e r e c r u i t m e n t r a t e s , r e s u l t i n g i n a p o p u l a t i o n d e c l i n e ; a n d 2) f i r e , a l o n e , was r e s p o n s i b l e f o r t h e r a p i d d e c l i n e o f t h e w o o d l a n d s a n d t h i c k e t s . T h r o u g h a n i n c r e a s e i n f i r e f r e q u e n c y o r s e v e r i t y , f i r e s d e s t r o y e d t h e y o u n g e r , s m a l l e r s i z e c l a s s e s a n d r e d u c e d r e c r u i t m e n t r a t e s b e l o w t h e a d u l t m o r t a l i t y r a t e s e x p e r i e n c e d d u r i n g t h e t i m e o f t h e d e c l i n e s . C u r r e n t l y , t h e M a r a w o o d l a n d s do n o t a p p e a r t o be r e t u r n i n g 7 t o t h e i r f o r m e r s t a t u s . To s t u d y t h e c u r r e n t d y n a m i c s o f t h e w o o d l a n d s , I h y p o t h e s i z e d t h a t : 3) p r e s e n t d a y f i r e r e g i m e s , i n a d d i t i o n t o o t h e r f a c t o r s , p r e v e n t w o o d l a n d r e c o v e r y by c o n t i n u a l l y t o p - k i l l i n g s e e d l i n g s a n d p r e v e n t i n g t hem f r o m g r o w i n g t o more f i r e - t o l e r a n t h e i g h t c l a s s e s ; 4) e l e p h a n t s i n t h e M a r a t o d a y f e e d h e a v i l y on s e e d l i n g s a n d p r e v e n t t h e i r s u c c e s s f u l e s c a p e i n t o t h e l a r g e r h e i g h t c l a s s e s , w h e r e t h e y a r e no l o n g e r s u s c e p t i b l e t o f i r e s . F u r t h e r m o r e , e l e p h a n t s k i l l m a t u r e t r e e s w h i c h r e d u c e s t h e number o f s e e d - p r o d u c i n g i n d i v i d u a l s a n d r a i s e s t h e a d u l t m o r t a l i t y r a t e s a b o v e c u r r e n t r e c r u i t m e n t ; a n d 5) an i n c r e a s e i n t h e m i g r a t o r y w i l d e b e e s t p o p u l a t i o n i s h a v i n g a m a j o r i n h i b i t o r y e f f e c t on w o o d l a n d r e g e n e r a t i o n . By d a m a g i n g s m a l l t r e e s , w i l d e b e e s t k e e p r e c r u i t m e n t r a t e s b e l o w a d u l t m o r t a l i t y r a t e s , t h e r e b y r e d u c i n g t h e p o t e n t i a l f o r w o o d l a n d r e c o v e r y a n d f u r t h e r i n g w o o d l a n d d e c l i n e s . I b e g i n i n C h a p t e r 2 w i t h a summary o f b o t h q u a l i t a t i v e a n d q u a n t i t a t i v e d o c u m e n t a t i o n o f t h e d e c l i n e o f t h e M a r a w o o d l a n d s a n d t h i c k e t s . U s i n g t h e w r i t i n g o f e x p l o r e r s a n d h u n t e r s a n d i n t e r v i e w s w i t h l o n g - t i m e r e s i d e n t s o f t h e a r e a , I r e c o n s t r u c t t h e h i s t o r y o f t h e M a r a ' s v e g e t a t i o n o v e r t h e p a s t 100 y e a r s . The l o s s o f w o o d l a n d c o v e r , w h i c h b e g a n i n t h e 1 9 5 0 ' s , i s a n a l y z e d a n d q u a n t i f i e d f r o m a s e r i e s o f a e r i a l p h o t o g r a p h s s p a n n i n g t h e t i m e p e r i o d 1948 - 1 9 8 2 . The c h a p t e r p r o v i d e s an h i s t o r i c a l o v e r v i e w o f t h e w o o d l a n d d e c l i n e s w i t h i n t h e R e s e r v e b o u n d a r i e s a n d a l s o d i s c u s s e s w o o d l a n d c h a n g e s w h i c h h a v e b e e n d o c u m e n t e d i n t h e S e r e n g e t i N a t i o n a l P a r k . C h a p t e r 3 p r e s e n t s an a n a l y s i s o f h a b i t a t s e l e c t i o n by 8 e l e p h a n t s i n the M a r a . U s i n g both a e r i a l and ground c e n s u s i n g t e c h n i q u e s , e l e p h a n t s are p l o t t e d by h a b i t a t on monthly and s e a s o n a l bases . These d i s t r i b u t i o n s of e l e p h a n t s by h a b i t a t s are compared to the a v a i l a b i l i t y of the d i f f e r e n t h a b i t a t types over the same a r e a . By comparing e lephant s i g h t i n g s wi th the h a b i t a t a v a i l a b i l i t i e s , e l ephant h a b i t a t p r e f e r e n c e s are e s t a b l i s h e d for both the wet and dry seasons . T h i s a n a l y s i s d e s c r i b e s the d i f f e r e n t i a l use of h a b i t a t s by e l e p h a n t s i n the Reserve at d i f f e r e n t t imes of the y e a r . In Chapter 4, I examine the f o r a g i n g h a b i t s of Mara e l e p h a n t s w i t h a view towards u n d e r s t a n d i n g t h e i r i n f l u e n c e on woodland dynamics . I examine what p l a n t s p e c i e s they s e l e c t , what p a r t s of these p l a n t s are e a t e n , what growing c o n d i t i o n the p r e f e r r e d p l a n t s are i n , and at what h e i g h t s e l e p h a n t s p r e f e r to f e e d . The f e e d i n g behav iour of both a d u l t male and a d u l t female e l e p h a n t s was r e c o r d e d on a monthly b a s i s and i s summarized here on a s e a s o n a l b a s i s . The ba lance between g r a z i n g on gras se s and browsing on woody s p e c i e s i s an important a spec t of e l ephant f o r a g i n g eco logy and c r i t i c a l to management d e c i s i o n s aimed at p r e s e r v i n g s p e c i f i c h a b i t a t and p l a n t t y p e s . The f e e d i n g p a t t e r n s observed i n t h i s s tudy a r e , t h e r e f o r e , d i s c u s s e d in the c o n t e x t of c u r r e n t v e g e t a t i o n dynamics i n the Mara R e s e r v e . Chapter 5 summarizes the e x p e r i m e n t a l work i n the A c a c i a woodlands of the M a r a . T h i s c h a p t e r p r o v i d e s an overview of the f a c t o r s to which Acac i a s e e d l i n g s and t r e e s are c u r r e n t l y exposed , i n c l u d i n g : browsing by e l e p h a n t s and o t h e r browsers , t r a m p l i n g , t h r a s h i n g , and i n a d v e r t e n t h a r v e s t i n g by m i g r a t o r y w i l d e b e e s t , and i n t e r m i t t e n t b u r n i n g by w i l d f i r e s i n the 9 R e s e r v e . I d i s c u s s t h e r e s u l t s o f e x p e r i m e n t s on b o t h l a r g e - s c a l e a n d m u l t i p l e b u r n s , t h e e x c l u s i o n o f b o t h b r o w s e r s a n d b u r n i n g , a n d t h e g e r m i n a t i o n r a t e s o f s e e d s e x p o s e d t o v a r y i n g f i r e i n t e n s i t i e s . The p o t e n t i a l f o r r e c o v e r y o f w o o d l a n d s i n t h e M a r a i s t h e n d i s c u s s e d i n l i g h t o f t h e s e f i n d i n g s . R e s u l t s f r o m t h e s e e x p e r i m e n t s a n d c o n t r o l l e d s t u d i e s a r e u s e d i n C h a p t e r 6 , w h e r e I s u m m a r i z e my r e s e a r c h a n d p r e s e n t a s i m p l e m o d e l u t i l i z i n g t h e s e d a t a . The c e n t r a l q u e s t i o n s o f w h a t f a c t o r o r f a c t o r s w e r e r e s p o n s i b l e f o r t h e d r a m a t i c w o o d l a n d d e c l i n e s o b s e r v e d i n t h e 1960s a n d t h e i n h i b i t i o n o f w o o d l a n d r e c o v e r y i n t h e M a r a t o d a y a r e a d d r e s s e d i n C h a p t e r 6 . S e v e r a l h y p o t h e s e s a r e p u t f o r t h t o e x p l a i n t h e p a t t e r n s o f w o o d l a n d c h a n g e . A s i m p l e s i m u l a t i o n m o d e l w h i c h i n c o r p o r a t e s t h e i m p a c t s o f f i r e , e l e p h a n t s , w i l d e b e e s t a n d o t h e r b r o w s e r s i s c o n s t r u c t e d t o t e s t p r e d i c t i o n s u n d e r t h e c o n d i t i o n s m e a s u r e d i n t h e 1 9 6 0 s a n d t o d a y . The m o d e l i s t h e n u s e d t o g e n e r a t e s c e n a r i o s u n d e r v a r i o u s b r o w s i n g a n d b u r n i n g r e g i m e s t h a t m i g h t r e a l i s t i c a l l y o c c u r i n t h e M a r a i n t h e f u t u r e . L a s t l y , t h e f i n d i n g s o f t h i s s t u d y a r e s u m m a r i z e d a n d i m p l i c a t i o n s f o r management o f t h e R e s e r v e a r e d i s c u s s e d . 10 CHAPTER 2. THE SERENGETI-MARA WOODLANDS: AN HISTORICAL PERSPECTIVE I n t r o d u c t i o n Over the pas t 30 y e a r s , d r a m a t i c woodland d e c l i n e s have taken p l a c e i n many of the n a t i o n a l parks and r e s e r v e s of e a s t , c e n t r a l , and southern A f r i c a . The a f f e c t e d areas have e x p e r i e n c e d a r a p i d r e v e r s i o n from dense woodland to open g r a s s l a n d s (Caughley 1976). One h y p o t h e s i s to e x p l a i n these changes s t a t e s tha t e l ephant browsing has a c t i v e l y i n h i b i t e d t r e e r e g e n e r a t i o n and r e c r u i t m e n t as w e l l as i n c r e a s e d a d u l t t r e e m o r t a l i t y through f e l l i n g and b a r k - s t r i p p i n g . T h i s o v e r a l l phenomenon i s f r e q u e n t l y r e f e r r e d to as the ' e l e p h a n t prob lem' and l a r g e l y a t t r i b u t e d to the c o n c e n t r a t i o n of e l e p h a n t s i n t o p r o t e c t e d areas (Laws 1969, 1970). The r o l e of e l e p h a n t s i n woodland dynamics has been s t u d i e d i n Kenya (Glover 1963, Agnew 1968, Laws 1969, Western and van Prae t 1973, Parker 1983), Malawi (Jachmann and B e l l 1985), T a n z a n i a (Lamprey et a l . 1967, Sav idge 1968, Watson and B e l l 1969, Croze 1974 a&b, Barnes 1980, 1982, Weyerhaeuser 1982, Barnes 1983, 1985, Weyerhaeuser 1985), South A f r i c a (P i enaar et ajL. 1966, P i e n a a r 1969, Hanks et a J L 1981, H a l l - M a r t i n 1984), Uganda (Buss 1961, Buechner and Dawkins 1961, Brooks and Buss 1962, Buechner et a l . 1963, Buss and Savidge 1966, Laws and Parker 1968, Laws 1970, Wing and Buss 1970, F i e l d 1971, Laws et a l . 1975, F i e l d and Ross 1976, Smart et a l . 1985), Zambia (Caughley and Goddard 1974, Caughley 1976), and Zimbabwe (Anderson and Walker 1974, Thomson 1975, Guy 1976, 1981, Cumming 11 1 9 8 1 ) . Many o f t h e s e s t u d i e s s u p p o r t e d t h e h y p o t h e s i s t h a t e l e p h a n t f o r a g i n g was t h e m a j o r f a c t o r i n w o o d l a n d l o s s e s . N o r t o n - G r i f f i t h s ( 1 9 7 9 ) p u t f o r t h a n a l t e r n a t i v e h y p o t h e s i s t o e x p l a i n t h e l o s s o f w o o d l a n d s i n T a n z a n i a ' s n o r t h e r n S e r e n g e t i N a t i o n a l P a r k . N o r t o n - G r i f f i t h s a r g u e d t h a t t h e r i n d e r p e s t e p i d e m i c t h a t p r o f o u n d l y r e d u c e d t h e p o p u l a t i o n o f g r a z i n g u n g u l a t e s i n t h e S e r e n g e t i r e s u l t e d i n a n u n d e r u t i l i z a t i o n o f t h e h i g h l y p r o d u c t i v e g r a s s l a n d s . T h i s u n u s e d g r a s s p r o v i d e d t h e f u e l f o r w i l d f i r e s w h i c h a n n u a l l y b u r n e d t h e e n t i r e a r e a i n t h e l a t e 1 9 5 0 s a n d e a r l y 1 9 6 0 s . T r e e r e c r u i t m e n t was t h e r e f o r e i n h i b i t e d a n d some w o o d l a n d c o m m u n i t i e s w e r e e v e n t u a l l y d e s t r o y e d by f i r e . I n t h e l o n g - r u n w o o d l a n d s d e c l i n e d b e c a u s e t h e r e d u c t i o n i n r e c r u i t m e n t due t o e x t e n s i v e b u r n i n g c o u l d no l o n g e r o f f s e t t h e l o s s o f m a t u r e t r e e s t o t h e a c t i v i t i e s o f i m m i g r a t i n g e l e p h a n t s . T h e M a s a i M a r a N a t i o n a l Game R e s e r v e , w h i c h b o r d e r s t h e n o r t h e r n S e r e n g e t i , f i t s t h e g e n e r a l p a t t e r n o f w o o d l a n d l o s s e s i n A f r i c a . I n t h i s p a p e r , I e x a m i n e new l i n e s o f e v i d e n c e n o t p r e v i o u s l y a v a i l a b l e t o c o m p a r e t h e s e a l t e r n a t i v e h y p o t h e s e s a n d e v a l u a t e t h e i r r e l e v a n c e t o w o o d l a n d d y n a m i c s i n t h e M a r a . I r e v i e w b o t h q u a l i t a t i v e a n d e y e w i t n e s s a c c o u n t s o f t h e S e r e n g e t i - M a r a a r e a f r o m t h e l a t e 1 8 8 0 s t o t h e e a r l y 1 9 8 0 s . T h e s e a c c o u n t s a l l o w a s t e p - w i s e r e c o n s t r u c t i o n o f h i s t o r i c a l e v e n t s a n d p r o v i d e s t r o n g e v i d e n c e t h a t m a j o r c h a n g e s i n t h e f a u n a l a n d f l o r a l d i v e r s i t y , s t r u c t u r e , a n d e x t e n t o f w o o d l a n d s h a v e t a k e n p l a c e o v e r t h e p a s t c e n t u r y . I n a d d i t i o n , I h a v e a n a l y z e d t h e l o s s o f w o o d l a n d c a n o p y c o v e r f r o m f i v e s e t s o f a e r i a l p h o t o g r a p h s o f t h e R e s e r v e a r e a t a k e n i n 1 9 5 0 , 1 9 6 1 , 12 1967, 1974, and 1982. The q u a l i t a t i v e and q u a n t i t a t i v e ev idence taken t o g e t h e r r e v e a l s tha t the S e r e n g e t i - M a r a ecosystem has e x p e r i e n c e d a t r a n s i t i o n from open g r a s s l a n d to dense woodland and back i n l e s s than 100 y e a r s . Methods The Q u a l i t a t i v e and Eyewitness ' E v i d e n c e of V e g e t a t i o n Changes The ev idence comes from numerous s o u r c e s . I o b t a i n e d r e c o r d s for s e v e r a l decades b e f o r e and a f t e r the t u r n of the c e n t u r y from the j o u r n a l s of s l a v e t r a d e r s , r e p o r t s of e a r l y e x p l o r e r s , the d e s c r i p t i o n s of v i s i t i n g h u n t e r s , and the p e r s o n a l r e c o r d s of Narok D i s t r i c t Commiss ioners . A l l of these sources were found in the Kenya N a t i o n a l A r c h i v e s , main ly from the c o l l e c t i o n of A f r i c a n a donated by Kenya ' s f i r s t v i c e - p r e s i d e n t , Joseph Murumbi. Photographs and accounts from the time p e r i o d c o v e r i n g the 1930s through the 1950s were c o m p i l e d from s e v e r a l s o u r c e s . The M a r t i n and Osa Johnson Museum i n Chanute , Kansas , p r o v i d e d photographs taken i n the S e r e n g e t i i n the 1920s and 1930s by the Johnsons . The landscape panoramas in the photographs were r e l o c a t e d u s i n g permanent l andmarks . T h i s a l l o w e d a comparison of p r e s e n t v e g e t a t i o n wi th t h a t r e c o r d e d 50-60 y e a r s ago. M r . Syd Downey t o l d me h i s r e c o l l e c t i o n s of the S e r e n g e t i - Mara s i n c e the e a r l y 1940s. Some of h i s p h o t o g r a p h s , taken i n the Mara i n the 1940s and 1950s, were subsequent ly r e l o c a t e d . M . I . M . T u r n e r , warden of the S e r e n g e t i N a t i o n a l Park from 1956- 1972, p r o v i d e d d e t a i l e d accounts taken from h i s d a i l y d i a r i e s of 13 the p e r i o d . Rodney E l i o t t , a game warden of the Mara i n the 1950s, sent me d e s c r i p t i o n s of the area a t tha t t i m e , taken from h i s f i e l d n o t e s . The D i r e c t E v i d e n c e of V e g e t a t i o n Changes For q u a n t i t a t i v e a n a l y s i s of changes in both Acac i a woodlands and C r o t o n t h i c k e t s of the Mara Game R e s e r v e , d u r i n g the p e r i o d from 1950 to 1982, I used a s e r i e s of complete a e r i a l p h o t o g r a p h i c s u r v e y s . F i v e surveys were flown in 1950, 1961, 1967, 1974, and 1982 (Table 2 . 1 ) . V e g e t a t i o n a n a l y s i s f o l l o w e d N o r t o n - G r i f f i t h s (1979) but was m o d i f i e d to f i t the a v a i l a b l e a e r i a l c o v e r a g e . Woodland changes were e s t i m a t e d by a ' d o t - g r i d ' a n a l y s i s . The measuring g r i d s were p r e p a r e d p h o t o g r a p h i c a l l y as d e s c r i b e d by Lamprey (1985) . Dot g r i d s were made for each set of a e r i a l photography to account f o r the d i f f e r e n c e s i n p h o t o g r a p h i c s c a l e . A g r i d of 100 r e g u l a r l y - s p a c e d dot s was c o n s t r u c t e d i n a 10 x 10 p a t t e r n for the a n a l y s e s . Each dot was 0.05mm in d iameter on the 1:50,000 s c a l e p h o t o g r a p h y . S t a n d a r d i z i n g from the s m a l l e s t s c a l e photography (1974, 1:68 ,000) , the minimum d e t e c t a b l e canopy d iameter was 2.5m on the ground (Lamprey 1985). T h i s p r o v i d e d a "lowest common denominator" dot s i z e f o r use a c r o s s a l l y e a r s . The g r i d s were then a n a l y z e d under s t r o n g i l l u m i n a t i o n at 2 0 x - m a g n i f i c a t i o n . For the l a r g e r s c a l e photography , i t was neces sary to i gnore a l l t r e e s w i t h a canopy d iameter l e s s than 2.5m, i . e . those s m a l l e r than the chosen g r i d dot s i z e . Woodland canopy cover (canopy d e n s i t y ) was measured 14 T a b l e 2 . 1 . The a e r i a l p h o t o g r a p h i c s e r i e s used i n the a n a l y s e s o f woodland cover l o s s i n the Masa i Mara Game R e s e r v e . Each survey p r o v i d e d t o t a l coverage o f the s tudy a r e a . YEAR SCALE 1950 1:30,000 1961 1:50,000 1967 1:57,000 1974 1:68,000 1982 1:48,000 FLOWN BY R o y a l A i r F o r c e R o y a l A i r F o r c e R o y a l A i r F o r c e M e r i d i a n A i r w a y s Kenya Rangelands E c o l o g i c a l M o n i t o r i n g U n i t SOURCE D i r e c t o r a t e o f Overseas Survey Survey o f Kenya Survey o f Kenya Survey o f Kenya W i l d l i f e P l a n n i n g U n i t W . C . M . D . 1 5 as a p r o p o r t i o n of the number of dots t o u c h i n g t r e e s or woody v e g e t a t i o n out of the t o t a l number of do t s on the sample g r i d . T h i s pr oc edure a l l owed d i r e c t comparisons w i t h the v e g e t a t i o n t r e n d s a n a l y z e d by Lamprey (1985) i n an area immediate ly a d j a c e n t to the Reserve over the same t ime p e r i o d . When working wi th a f i n i t e dot s i z e on s m a l l s c a l e photography , one always o v e r e s t i m a t e s cover i n a way r e l a t e d to to the d o t ' s d iameter (Kershaw 1964, N o r t o n - G r i f f i t h s 1979). Lamprey (1985, Appendix F) used computer m o d e l l i n g to a n a l y z e the degree of b i a s in t h i s d o t - g r i d t e c h n i q u e . He c o n c l u d e d tha t the chosen dot s i z e , of 2.5m, would o v e r e s t i m a t e cover d e n s i t y by a f a c t o r of two or a 100% b i a s e r r o r . S i n c e the dot s i z e used was the same for a l l p h o t o g r a p h i c s e t s , t h i s b i a s was c o n s i d e r e d to be cons tant between the d i f f e r e n t s e t s and the d i r e c t i o n of changes d e t e c t e d was assumed to be u n b i a s e d . In both Acac i a and C r o t o n communit ies three measurements were c a l c u l a t e d : 1) The mean cover d e n s i t y va lue for each y e a r ' s a e r i a l photography was d e r i v e d u s i n g the above methods. 2) From these d a t a , the annua l a b s o l u t e change was c a l c u l a t e d by t a k i n g the d i f f e r e n c e in mean cover between two s u c c e s s i v e p h o t o g r a p h i c s e r i e s and d i v i d i n g t h i s by the a c t u a l number of y e a r s s e p a r a t i n g the two measurements. For example, i f mean cover was 30% in 1950 and 20% i n 1961, the annua l a b s o l u t e change would be 10% d i v i d e d by 11 y e a r s or -0.91% cover l o s s per y e a r . 3) The annual r e l a t i v e change was c a l c u l a t e d from the mean cover d e n s i t y d a t a . T h i s measure c o r r e s p o n d s to the percentage 16 of the p r e c e d i n g t ime p e r i o d ' s cover which has been l o s t by the f o l l o w i n g time p e r i o d . I f , f or example, the mean cover i n 1950 was 30% and i n 1961 20%, the annua l r e l a t i v e r a t e of change for the e n t i r e t ime p e r i o d would be -33.0% or -3.0% per y e a r . A b s o l u t e change p r o v i d e s a measure of the mean annual p e r c e n t cover l o s t each y e a r , whereas the r e l a t i v e change i s a r a t e measuring what percentage of the cover d e n s i t y i n an e a r l i e r t ime p e r i o d i s l o s t by the next p e r i o d measured. A l l s t a t i s t i c a l a n a l y s e s were performed on MINITAB (Ryan et a l . 1985). The Acac i a woodlands A l t h o u g h i n d i v i d u a l t r e e s p e c i e s cannot be i d e n t i f i e d from a e r i a l photographs at these s m a l l s c a l e s , ground r e c o r d s v e r i f y tha t the communit ies chosen for a n a l y s i s were dominated by Acac i a w i th a complex v a r i e t y of o ther s p e c i e s o c c u r r i n g to a much l e s s e r degree (Lamprey et a l . 1967, G l o v e r and Trump 1970, Trump 1972, T a i t i 1973, H e r l o c k e r 1976a & b , Lamprey 1985). S p e c i e s i d e n t i f i c a t i o n was not deemed neces sary for the a n a l y s i s , as the d e c l i n e in t o t a l woody cover d e n s i t y was the p r i m a r y f o c u s . Due to a r a i n f a l l g r a d i e n t i n the Mara R e s e r v e , r a n g i n g from 800mm per year i n the e a s t , to 1200mm per year i n the west ( N o r t o n - G r i f f i t h s et a l . 1975, Epp and A g a t s i v a 1980), the area was d i v i d e d i n t o east and west . The 1950 a e r i a l photos were used as a b a s e l i n e for a l l a n a l y s e s . They were f i r s t assembled by f l i g h t l i n e , then t r a n s e c t s were drawn down the c e n t e r of 17 each of the p a r a l l e l f l i g h t p a t h s . T h i s guarded a g a i n s t o v e r l a p of sampl ing p o i n t s on s u c c e s s i v e f l i g h t l i n e s . F i f t y p o i n t s were then randomly s e l e c t e d i n A c a c i a woodlands and cover d e n s i t y was measured. The same p o i n t s were i d e n t i f i e d on the photographs of a l l l a t e r s e r i e s and cover d e n s i t y was r e - measured. I d e n t i f i c a t i o n of p o i n t s was g r e a t l y a i d e d by use of the 1:50,000 s c a l e t o p o g r a p h i c a l map c o m p i l e d by the D i r e c t o r a t e of Overseas S u r v e y s , the Survey of Kenya , and the T a n z a n i a Survey and Mapping D i v i s i o n from these same a e r i a l p h o t o g r a p h s . F i v e r a n d o m l y - o r i e n t e d dot g r i d counts were made a t each sample p o i n t i n each s e r i e s of p h o t o g r a p h s . T h i s p r o v i d e d a mean cover e s t imate and s t a n d a r d e r r o r for each sample p o i n t . A l l sample p o i n t s were assumed to be independent of one a n o t h e r . A l l woodland cover d e n s i t y e s t i m a t e s were a r c s i n e t r a n s f o r m e d be fore s t a t i s t i c a l comparisons were performed (Zar 1984). The C r o t o n t h i c k e t s Because C r o t o n t h i c k e t s occur i n d i s c r e t e , clumped u n i t s , I measured the areas of t h i c k e t s and t h e i r changes in a d d i t i o n to changes i n cover d e n s i t y w i t h i n i n d i v i d u a l t h i c k e t s . Cover d e n s i t y was e s t i m a t e d on a l l f i v e p h o t o g r a p h i c s e r i e s . Change i n area was measured o n l y on the 1950 and 1982 photographs . These two s e t s were photographed at the l a r g e s t s c a l e and , t h e r e f o r e , t h i c k e t o u t l i n e s were c l e a r l y d e l i n e a t e d and e a s i l y compared. C r o t o n t h i c k e t s are f a r more abundant on the east s i d e . T h e r e f o r e , to s e l e c t an e q u a l number of sample p o i n t s from each 18 s i d e , sample s i z e s would have been n e c e s s a r i l y reduced by the l i m i t e d o c c u r r e n c e of t h i c k e t s on the west s i d e . By c o n s i d e r i n g eas t and west s i d e t h i c k e t s t o g e t h e r , I was a b l e to s e l e c t 50 sample p o i n t s and examine the g e n e r a l t r e n d i n C r o t o n cover l o s s a c r o s s the e n t i r e R e s e r v e . Cover was e s t i m a t e d as d e s c r i b e d above for Acac i a woodlands . Area l o s s was de termined by s e l e c t i n g 15 i n d i v i d u a l t h i c k e t s or t h i c k e t groups which were c l e a r l y photographed i n both 1950 and 1982. T r a c i n g s were made of the o u t l i n e s of these t h i c k e t s on the 1950 s e r i e s . Area was then measured, in square k i l o m e t e r s , u s i n g an area dot g r i d . Each sample t h i c k e t was r e - measured f i v e t imes to reduce the v a r i a n c e . U s i n g a Bausch and Lomb Zoom T r a n s f e r s c o p e , each of the 15 base samples were then a d j u s t e d to f i t d i r e c t l y over the 1982 p h o t o s . T h i c k e t area t h a t remained was drawn d i r e c t l y from the 1950 base t r a c i n g s and measured w i t h the area dot g r i d . As a comparat ive t e s t , t h i c k e t areas were a l s o measured u s i n g a d i g i t i z e r . Area measurements u s i n g the d i g i t i z e r became i n c r e a s i n g l y i n a c c u r a t e as t h i c k e t s became s m a l l e r and more fragmented . 19 R e s u l t s V e g e t a t i o n Changes from 1880 t o 1980; the q u a l i t a t i v e e v i d e n c e The S e r e n g e t i - M a r a ecosystem l i e s w i t h i n an a r e a b r o a d l y d e s c r i b e d as M a a s a i l a n d . Of a l l the l o c a l t r i b e s , i t i s the Maasai who have had the most s i g n i f i c a n t i n f l u e n c e on t h i s system. Maasai t r i b a l l o r e r e l a t e s t h a t t h e s e nomadic p a s t o r a l i s t s f i r s t came t o the a r e a i n the mid-1700s (Mol 1980). However, d e t a i l e d r e c o r d s of Maasai h i s t o r y i n the a r e a do not a c t u a l l y b e g i n u n t i l the l a t t e r p a r t of the 19th c e n t u r y ( S a n d f o r d 1919, Fosbrooke 1948, J a c o b s 1965). I t was around t h i s time t h a t the Maasai s u f f e r e d a s e r i e s of s e t b a c k s which c o n t i n u e d w e l l i n t o the 1900s. In the e a r l y 1880s, drought s t r u c k the area and domestic s t o c k , a l r e a d y weakened by a r i d c o n d i t i o n s , succumbed t o b o v i n e pleuro-pneumonia. C o n t r o l of the d i s e a s e was n o n - e x i s t e n t and Maasai herdsmen s u f f e r e d tremendous l o s s e s of l i v e s t o c k (Thomson 1885). W i t h i n a few y e a r s , the next d i s a s t e r h i t - an e x o t i c v i r a l d i s e a s e of u n g u l a t e s - r i n d e r p e s t ( P l o w r i g h t 1963, P l o w r i g h t and M c C u l l o c h 1967, Atang and P l o w r i g h t 1969). The a c t u a l i n t r o d u c t o r y l o c u s of t h i s endemic A s i a n d i s e a s e remains u n c e r t a i n but s e v e r a l t h e o r i e s e x i s t . Some say the d i s e a s e was f i r s t i n t r o d u c e d i n t o Egypt by the N i l e e x p e d i t i o n i n 1884 and moved r a p i d l y s o u th from t h e r e . O t h e r s suggest t h a t r i n d e r p e s t was t r a n s m i t t e d by c a t t l e from the B l a c k Sea a r e a , which had been brought i n t o Khartoum. The most commonly h e l d b e l i e f i s t h a t i t e n t e r e d t h r o u g h E t h i o p i a d u r i n g the I t a l i a n i n v a s i o n of 1889 (Branagan and Hammond 1965, Mack 1970, F o r d 1971, P l o w r i g h t 20 1982). A c c o r d i n g to a l l s o u r c e s , c a t t l e s e r v e d as the i n t r o d u c t o r y h o s t s . A f r i c a n c a t t l e , c a r r y i n g no immunity to t h i s f o r e i g n d i s e a s e , d i e d r a p i d l y and in g r e a t numbers. By September 1890 i t had a r r i v e d i n the S e r e n g e t i - M a r a r e g i o n and w i t h i n a few s h o r t months over 90% of the c a t t l e were dead (Sandford 1919, M a l l e t t 1923). The ensu ing famine was i n e v i t a b l e f o r the Maasai due to t h e i r t o t a l dependence on l i v e s t o c k . The c a t a s t r o p h i c l o s s of l i v e s t o c k c r e a t e d the c o n d i t i o n s f o r d e v a s t a t i n g human e p i d e m i c s , i n c l u d i n g smal lpox (Sandford 1919, Fosbrooke 1948). The 1890s became known amongst the Maasai a s , e n k i d a a r o t o , the d e s t r u c t i o n (Baumann 1894a & b ) . Europeans t r a v e l l i n g in the a r e a at t h i s t ime d e s c r i b e d the once proud and s e l f - r e l i a n t M a a s a i , who had r e s i s t e d the i n t r u s i o n of Arab s l a v e t r a d e r s o n l y a few y e a r s e a r l i e r , as a people on the b r i n k of e x t i n c t i o n . Baumann (1894a) r e c a l l e d of h i s t r e k through M a a s a i l a n d , "The people g a t h e r e d themselves around the b a r r i e r of our camp, in the meantime u t t e r i n g c r i e s of a p i t i f u l n a t u r e , which i s now the d i s t i n g u i s h i n g c h a r a c t e r i s t i c of M a a s a i l a n d . The women had been reduced to s k e l e t o n s , from whose ho l low eyes gleamed the madness of hunger , the c h i l d r e n who were more l i k e naked f r o g s than men, " w a r r i o r s " who c o u l d s c a r c e l y c r a w l on a l l f o u r s and were d a z e d , l a n g u i s h i n g o l d men. These people a te a n y t h i n g : dead a s s e s , the h i d e , y e s , even the horns of a s l a u g h t e r e d beast they would not r e f u s e . They had f l e d from the S e r e n g e t i where hunger had d e p o p u l a t e d the e n t i r e d i s t r i c t and had become beggars to t h e i r f e l l o w countrymen who themselves had s c a r c e l y enough to e a t . " . B e r n s t e n (1979) r e c o u n t s how Maasai 21 t r i e d t o j o i n B a u m a n n ' s c a r a v a n j u s t t o s t a y a l i v e , w h i l e o t h e r s e k e d o u t a D o r o b o - l i k e ( n o m a d i c h u n t e r - g a t h e r e r ) e x i s t e n c e . Baumann ( 1 8 9 4 b ) e s t i m a t e d t h a t 75% o f t h e p e o p l e i n t h e S e r e n g e t i - M a r a r e g i o n h a d d i e d by t h e e a r l y 1 8 9 0 s . T h u s , t h e a r e a was l e f t d e v o i d o f human i n f l u e n c e by t h e t u r n o f t h e c e n t u r y a n d f o r many y e a r s t h e r e a f t e r . W i l d u n g u l a t e s o f t h e a r e a w e r e a l s o a f f e c t e d by t h e r i n d e r p e s t o u t b r e a k . A s c a t t l e n u m b e r s d w i n d l e d , t h e v i r u s p e r s i s t e d i n n u m e r o u s w i l d l i f e s p e c i e s i n c l u d i n g g i r a f f e ( G i r a f f a c a m e l o p a r d a l i s ) , w a r t h o g ( P h a c o c h o e r u s a e t h i o p i c u s ) , a n d o t h e r s . Two h e a v i l y a f f e c t e d s p e c i e s w e r e b u f f a l o ( S y n c e r u s c a f f e r ) a n d w i l d e b e e s t ( S i n c l a i r 1 9 7 7 , 1 9 7 9 ) . Due t o t h e g r e g a r i o u s , h e r d - f o r m i n g n a t u r e o f t h e s e s p e c i e s , t h e v i r a l d i s e a s e was q u i c k t o c a t c h h o l d a n d s p r e a d a m o n g s t t h e m . A l t h o u g h t h e a c t u a l n u m b e r s l o s t a r e u n k n o w n , a c c o u n t s o f b u f f a l o i n E a s t A f r i c a show t h a t t h e r e w e r e o n l y a few h e r d s l e f t by 1900 a n d s u g g e s t a l o s s o f up t o 90%. I n f a c t , W h i t e ( 1 9 1 4 ) d e s c r i b e d s h o o t i n g a b u f f a l o a s one o f t h e m a j o r h i g h l i g h t s o f h i s 1911 h u n t i n g s a f a r i t o t h e n o r t h e r n S e r e n g e t i - M a r a a r e a . V e t e r i n a r y r e c o r d s show t h a t many w i l d a n i m a l s g r a d u a l l y d e v e l o p e d i m m u n i t y t o t h e d i s e a s e . H o w e v e r , r e c r u i t m e n t o f y o u n g a n i m a l s i n t o t h e p o p u l a t i o n s m u s t h a v e b e e n v e r y l o w . The d i s e a s e t o o k i t s g r e a t e s t t o l l on c a l v e s , who l o s t t h e i r a c q u i r e d i m m u n i t y a f t e r w e a n i n g , a t a b o u t s i x m o n t h s o f a g e . H e n c e , i t became r e f e r r e d t o a s " t h e y e a r l i n g d i s e a s e " . D u r i n g t h i s same p e r i o d , t h e e l e p h a n t p o p u l a t i o n o f t h e a r e a was a l s o e x p e r i e n c i n g a r e d u c t i o n i n s i z e . H e a v y h u n t i n g p r e s s u r e was g e n e r a t e d by a l i v e l y i v o r y t r a d e , a n d t h e 22 f l o u r i s h i n g s l a v e t r a d e h e l p e d to t r a n s p o r t t h i s i v o r y , on the backs of s l a v e s , to the coas t f o r marke t ing and shipment abroad ( W a k e f i e l d 1882, 1870, F a r l e r 1882). A c c o r d i n g to the j o u r n a l s of e a r l y caravan l e a d e r s , the l o c a l Dorobo h u n t e r s r e f e r r e d to themselves as "the e l ephant people" (Fosbrooke 1968). Some of these very e l ephant h u n t e r s were the i t i n e r a n t Maasai of whom Baumann (1894, p.323) wrote , " . . . They a p p a r e n t l y t u r n e d to h u n t i n g as a means of s t a y i n g a l i v e . In a few c a s e s , men s t a t e d to me tha t they r e c e i v e d 30 c a t t l e f o r a tusk 6-7 fee t l o n g , and n ine c a t t l e f o r a tusk 2-4 feet l o n g . The a c c u r a c y of these f i g u r e s i s q u e s t i o n a b l e . What i s important i s t h a t for the f i r s t t ime many Maasai who had never been i n v o l v e d i n the i n t e r n a t i o n a l i v o r y t r a d e were now f o r c e d to do so by t h e i r sheer d e s t i t u t i o n . " . I v o r y export r e c o r d s c o m p i l e d by Spinage (1973) s u b s t a n t i a t e these r e p o r t s of widespread e l ephant s l a u g h t e r . The S e r e n g e t i - M a r a became known as an area wi thout e l e p h a n t s . Grogan and Sharp (1900) r e p o r t e d t h a t , " . . . t e n y e a r s ago e l ephant swarmed in p l a c e s l i k e t h i s , where now you w i l l not f i n d o n e . " . T h i s absence of e l e p h a n t s was i n t e r p r e t e d i n l a t e r y e a r s as t h e i r never h a v i n g o c c u r r e d i n the a r e a . Buxton (1927, p .67) wrote , " . . . e x c e p t i n g e l e p h a n t s , we c o u l d have shot n e a r l y every k i n d of game in the course of our wandering [ through the S e r e n g e t i - M a r a a r e a ] " and M e l l a n d (1938, p.176) s t a t e d , " . . . s o f a r as I know, the S e r e n g e t i does not and has never numbered e l e p h a n t s among i t s i n h a b i t a n t s . " . By the t u r n of the c e n t u r y e l ephant numbers had been g r e a t l y reduced by h u n t i n g , w i l d and domest ic u n g u l a t e s by r i n d e r p e s t / and the Maasai people by famine and d i s e a s e . 23 E x p l o r e r s and h u n t e r s of the e a r l y 1900s encountered a S e r e n g e t i - M a r a which l ooked much as i t does t o d a y . B r o a d , open expanses of g r a s s l a n d and l i g h t l y wooded savanna predominated . Buxton (1927, p.67) remarked, " . . .we came out onto u n d u l a t i n g g r a s s l a n d s , l o v e l y f e r t i l e c o u n t r y which seemed almost u n i n h a b i t e d . . . Near us was a t h i c k l y wooded range of h i l l s r u n n i n g n o r t h and south (presumably the Kuka H i l l s ) , but i n every o ther d i r e c t i o n were p l a i n s s t r e t c h i n g on and o n . " . In some a r e a s , these g r a s s l a n d s were d o t t e d w i t h A c a c i a s of a v a r i e t y of s p e c i e s . Woosnam (1913, p . 2 7 5 ) , a game warden a s s i g n e d to determine t s e t s e f l y d i s t r i b u t i o n s a l o n g the Mara R i v e r , gave s i m i l a r account s of the west s i d e of the r i v e r , i n the Mara T r i a n g l e a r e a of the p r e s e n t R e s e r v e . "It was a broad p l a i n of p a r k - l i k e c o u n t r y , f i n e g r a z i n g l a n d , s tudded w i t h the o c c a s i o n a l y e l l o w - b a r k e d A c a c i a t r e e s . " A n d , White (1915, p . 1 5 8 ) , a hunter and w r i t e r who t r a v e l l e d e x t e n s i v e l y in the n o r t h e r n S e r e n g e t i and Mara throughout the p e r i o d from 1910 to 1913, d e s c r i b e d the same area as " . . . a h i g h gras s p l a t e a u wi th a few s c a t t e r e d thorn t r e e s " and (p.162) " . . . a n open, g r a s s y r o l l i n g c o u n t r y . Here and t h e r e are low, r o c k y , c i r c u l a r o u t c r o p p i n g h i l l o c k s crowned w i t h green t h i c k e t s . . . The [ C r o t o n ] t h i c k e t s are nowhere c o n t i n u o u s , and one can always march around them." . Eastman (1927, p .57) d e s c r i b e d the area near the Sand R i v e r , i n the e a r l y 1910s where " . . . t h e r i v e r meanders through a v a s t , l e v e l , most ly smooth p l a i n , bordered w i t h low, rounded h i l l s . The p l a i n i s s p r i n k l e d w i t h t r e e s of moderate s i z e . . . We can run our c a r s anywhere at any speed up to 30 or 40 m . p . h . " . 24 By the 1930s the area had changed. The same area which 30 y e a r s e a r l i e r had been open, g r a s s y p l a i n s was d e s c r i b e d by Lewis (1935, p.445) as " . . . n u m e r o u s i n t e r s e c t i n g and narrow b e l t s of t h o r n - b r u s h [ C r o t o n ] . In order to reach the Mara R i v e r , i t was necessary to cut out a path f o r v e h i c l e s to pass through d e n s e l y - g r o w i n g Acac i a s e y a l and another s p e c i e s known [ to the Maasa i ] as ' 0 1 - j e r a i ' . " . A c c o r d i n g to H u n t i n g f o r d (1976) and Mol (1980), t h i s i s a name used f o r s e v e r a l o ther s p e c i e s of Acac i a found i n the Mara a r e a . E a r l y p h o t o g r a p h i c r e c o r d s from n a t u r a l i s t s such as M a r t i n and Osa Johnson i n the 1930s, h u n t e r s l i k e Syd Downey in the 1940s, and the f i r s t R o y a l A i r F o r c e a e r i a l photography i n 1950, showed widespread h i l l t o p t h i c k e t s and Acac i a woodlands throughout the n o r t h e r n S e r e n g e t i and M a r a . In f a c t , Syd Downey r e c a l l e d ' t a k i n g ' up to f i v e l e o p a r d s i n a day i n the dense bush of the Mara T r i a n g l e , an area which i s now known for i t s wide , open g r a s s l a n d s , an u n l i k e l y h a b i t a t f o r l e o p a r d s . C o l o n i a l a d m i n i s t r a t o r s , who r e a l i z e d the i n h e r e n t v a l u e of the r e g i o n , were q u i c k to move for p r o t e c t i o n of the a r e a . In 1937 the Tangany ika S e r e n g e t i , which compri sed the m a j o r i t y of the ecosys tem, was d e c l a r e d a game r e s e r v e . J u s t over a decade l a t e r K e n y a ' s Mara f o l l o w e d s u i t , and the S e r e n g e t i g a i n e d n a t i o n a l park s t a t u s . The g o a l was to p r e s e r v e t h i s wooded area i n what was p e r c e i v e d as i t s " p r i s t i n e " c o n d i t i o n . F e e l i n g c o n f i d e n t t h a t they had succeeded i n s e c u r i n g the area be fore any changes o c c u r r e d , Park a u t h o r i t i e s s t a t e d , i n a 1946 Roya l N a t i o n a l Parks Report ( p . 5 5 ) , t h a t , "The t s e t s e f l y s tands guard over t h i s a r e a , and even today i t i s v i r t u a l l y a g l impse i n t o 25 A f r i c a a s i t was b e f o r e t h e w h i t e man e v e r c r o s s e d i t s s h o r e s . " . T h e s e e a r l y c o n s e r v a t i o n i s t s h a d n o t r e a l i z e d t h a t l e s s t h a n 50 y e a r s e a r l i e r , t h e s e same d e n s e w o o d l a n d s h a d b e e n w i d e e x p a n s e s o f o p e n g r a s s l a n d . T h e s e t h i c k e t s a n d w o o d l a n d s w h i c h a f f o r d e d h a b i t a t s f o r a d i v e r s e a s s e m b l a g e o f v e r t e b r a t e f a u n a a l s o p r o v i d e d p r i m e s h a d e a n d r e s t i n g s i t e s f o r t s e t s e f l i e s , G l o s s i n a s w y n n e r t o n i a n d G . p a l l i d i p e s , ( L e w i s 1 9 3 5 , S y w n n e r t o n 1 9 3 6 , B e a u m o n t 1 9 4 4 , B u x t o n 1 9 5 5 , F o r d a n d C l i f f o r d 1 9 6 8 , G l o v e r a n d T rump 1 9 7 0 , L a n g r i ' d g e e_t a l . 1 9 7 0 , F o r d 1 9 7 1 ) . I n a d d i t i o n t o i n f l i c t i n g a p a i n f u l b i t e , t s e t s e f l i e s t r a n s m i t a p a r a s i t i c b l o o d d i s e a s e known a s t r y p a n o s o m i a s i s i n c a t t l e a n d " s l e e p i n g s i c k n e s s " i n m a n . B e c a u s e t h e T r y p a n a s o m a p a r a s i t e c a n be m a i n t a i n e d i n many s e c o n d a r y h o s t s , t h e v e c t o r s u r v i v e d t h e l o s s e s o f i t s h u m a n , d o m e s t i c , a n d m o s t o f i t s w i l d l i f e h o s t s i n t h e l a t e 1 8 0 0 s ( F o r d 1 9 7 1 , B o u r n 1 9 7 8 , M o l y n e u x 1 9 8 2 , R o g e r s a n d R a n d o l p h 1 9 8 5 ) . The M a a s a i w e r e k e e n l y a w a r e o f i t s p e r s i s t e n c e i n o t h e r o r g a n i s m s a n d t h e D i s t r i c t C o m m i s s i o n e r f o r N a r o k D i s t r i c t w r o t e i n a 1925 r e p o r t t h a t , " . . . t h e s t r a n g e d i s e a s e [ t r y p a n o s o m i a s i s ] was known by t h e M a a s a i t o be c a r r i e d by t o a d s ( a n d p o s s i b l y l u n g f i s h ) a n d when t r a m p l e d by c a t t l e a t w a t e r i n g h o l e s , i t w o u l d p o i s o n t h e w a t e r w i t h i t s b l o o d . " . T h r o u g h o u t t h e 1 9 5 0 ' s t h e M a a s a i u s e d t h e a r e a t h a t i s c u r r e n t l y t h e c e n t r a l a n d w e s t e r n p o r t i o n o f t h e M a r a Game R e s e r v e f o r s e a s o n a l g r a z i n g by t h e i r s h e e p a n d g o a t s . U n l i k e c a t t l e t h e s e s m a l l e r s t o c k w e r e l a r g e l y u n a f f e c t e d by t r y p a n o s o m i a s i s . A 1955 K e n y a N a t i o n a l P a r k s r e p o r t s t a t e d t h a t , " T h e w h o l e o f t h i s s e c t i o n i s d o m i n a t e d by t h e t s e t s e f l y 26 a n d p o s s i b l y f o r t h a t r e a s o n r e t a i n s i t s f u l l q u o t a o f g a m e . I t i s o f a b s o l u t e l y no u s e t o t h e M a a s a i e x c e p t f o r g r a z i n g t h e i r s m a l l s t o c k . . . " . A s l a t e a s 1 9 6 0 , t h e a r e a b e t w e e n A i t o n g ( w e l l n o r t h o f t h e M a r a Game R e s e r v e ) , t h e T a l e k R i v e r , a n d s o u t h t o t h e S e r e n g e t i r e m a i n e d u n i n h a b i t e d ( L a m p r e y 1 9 8 5 ) . W h e r e a s e a r l i e r i n t h e c e n t u r y t h e v e g e t a t i o n was i n h o s p i t a b l e t o t s e t s e o c c u p a t i o n , by t h e 1 9 3 0 s a n d 1 9 4 0 s t h e w o o d l a n d i n c r e a s e h a d a l l o w e d t h e i r p r o l i f e r a t i o n . A l s o , many r e s i d e n t w i l d u n g u l a t e s h a d , by t h i s t i m e , d e v e l o p e d i m m u n i t y t o r i n d e r p e s t ( T a y l o r a n d a n d W a t s o n 1 9 6 7 , S t e w a r t 1968) a n d now became p r i m e h o s t s f o r t h e t r y p a n o s o m i a s i s v e c t o r ( S i n c l a i r 1 9 7 9 ) . E a r l y a t t e m p t s a t m e c h a n i c a l b u s h - c l e a r i n g a n d t h e e l i m i n a t i o n o f w i l d l i f e h o s t s w e r e l a r g e l y u n s u c c e s s f u l h a v i n g l i t t l e , i f a n y , i m p a c t on t s e t s e f l y n u m b e r s ( L a n g r i d g e 1 9 6 0 ) . D e s p i t e r e p e a t e d f a i l u r e s , e f f o r t s t o e l i m i n a t e t h e f l i e s f r o m M a a s a i l a n d c o n t i n u e d f o r s e v e r a l d e c a d e s . F i n a l l y , a f t e r g r e a t e x p e n d i t u r e o f t i m e , m o n e y , a n d e f f o r t , t s e t s e e r a d i c a t i o n p r o g r a m s w e r e a b a n d o n e d i n t h e 1 9 6 0 s ( F o r d 1 9 7 1 ) . A l t h o u g h t s e t s e f l i e s b e g a n d e c l i n i n g a r o u n d t h i s same t i m e , i t was n o t b e l i e v e d t o be i n r e s p o n s e t o o f f i c i a l c o n t r o l p r o g r a m s b u t r a t h e r t o e c o l o g i c a l f a c t o r s w h i c h l e a d t o a r e d u c t i o n i n t h e i r h a b i t a t s . Two o f t h e i m p o r t a n t e c o l o g i c a l f a c t o r s w e r e t h e i n c r e a s e i n f i r e f r e q u e n c y a n d an i n c r e a s e i n e l e p h a n t d e n s i t i e s . U n u s u a l l y h i g h r a i n f a l l i n t h e e a r l y 1 9 6 0 s ( F i g u r e 2 . 1 ) r e s u l t e d i n h e a v y g r a s s p r o d u c t i o n t h r o u g h o u t t h e r e g i o n ( G l o v e r a n d Gwynne 1 9 6 1 , K e n y a Game D e p a r t m e n t A n n u a l R e p o r t s 1 9 6 1 - 1 9 6 4 , T a n z a n i a N a t i o n a l P a r k s A n n u a l R e p o r t 1 9 6 2 - 1 9 6 4 , T a l b o t a n d 1100 n 6 0 0 - —I 1 1 1 1 1 1 1920 1930 1940 1950 1960 1970 1980 Y E A R Figure 2.1. Five-year r a i n f a l l averages f o r Narok, Kenya over the p e r i o d 1914 - 1980. 28 T a l b o t 1963, G l o v e r and Trump 1970). M. Turner r e c a l l e d grass swards above the bonnet of h i s Land Rover and the f i e r c e l y hot f i r e s which p r e v a i l e d d u r i n g t h i s t i m e . The g r e a t l y reduced ungu la te p o p u l a t i o n s were unable to remove these tremendous f u e l l o a d s . L a n g r i d g e et a l . (1970, p.204 and 208) d e s c r i b e d t h i s phenomenon i n the Mara Game R e s e r v e : " . . . b e t w e e n 1961 and 1963 r a i n f a l l was very heavy throughout the d i s t r i c t and produced l u x u r i a n t g r a s s cover which a l l o w e d the b i and t r i - a n n u a l b u r n i n g . . . (meaning twice and t h r e e t imes per y e a r ) . As soon as they are dry enough, the g r a s s y p l a i n s are f i r e d by the M a a s a i . Sometimes c o n d i t i o n s are such that new growth of gras s a f t e r a f i r e i s ready for b u r n i n g w i t h i n the same season . Thus a s i n g l e a r e a may be burned twice w i t h i n a season or even three t imes d u r i n g a y e a r . . . The very f i e r c e f i r e s caused a c c e l e r a t e d d e s t r u c t i o n of the v e g e t a t i o n w i t h marked changes i n the numbers of t r e e s and s h r u b s . . . " . Between the l a t e 1950s and the e a r l y 1960s, r e s e a r c h e r s working i n the S e r e n g e t i - M a r a noted tha t e l ephant numbers were i n c r e a s i n g and subsequent browsing on woody v e g e t a t i o n was o c c u r r i n g (Lamprey e_t a l . 1967, Watson and B e l l 1969, G l o v e r and Trump 1970), I t was not a l t o g e t h e r c l e a r where these e l ephant immigrants o r i g i n a t e d . I t i s most l i k e l y tha t they came from the areas immediate ly s u r r o u n d i n g the S e r e n g e t i - M a r a ecosys tem. T h i s i n c l u d e d areas such as L o l i o n d o , the S i r i a ( a l s o O l o o l o l o or I s u r i a ) Escarpment , the Chepalunga F o r e s t and the Lambwe V a l l e y to the n o r t h and west (M. T u r n e r , p e r s o n a l c o m m u n i c a t i o n ) . These areas were e x p e r i e n c i n g r a p i d human 29 s e t t l e m e n t , i n c r e a s i n g l i v e s t o c k n u m b e r s a n d , i n some c a s e s , c u l t i v a t i o n , a n d t h e r e f o r e e l e p h a n t s w e r e b e i n g f o r c e d o u t . T h i s l e d t o a c o m p r e s s i o n o f e l e p h a n t s i n t o p r o t e c t e d a r e a s i n t h e y e a r s t h a t f o l l o w e d . The D i s t r i c t C o m m i s s i o n e r o f N a r o k ( 1 9 5 5 ) r e p o r t e d t h a t , " E l e p h a n t s c r e a t e d s e r i o u s p r o b l e m s f o r s e t t l e m e n t o f t h e s e a r e a s . T h i s n e c e s s i t a t e d t h e s h o o t i n g o f a number o f t h e s e e l e p h a n t s . The c a m p a i g n a g a i n s t shamba [ f a r m ] d a m a g i n g e l e p h a n t s i n t h e s e a r e a s h a s b e e n , on t h e w h o l e , s a t i s f a c t o r y . The r e s u l t s o f o u r p e r s i s t e n t a t t a c k h a s b e e n t o d r i v e a c e r t a i n p o r t i o n o f e l e p h a n t s b a c k t o t h e i r o l d h a u n t s . T h e s e p l a c e s a r e i n t h e M a a s a i R e s e r v e w h e r e no c u l t i v a t i o n e x i s t s " . The T a n z a n i a N a t i o n a l P a r k s A n n u a l R e p o r t ( 1 9 6 2 - 1 9 6 4 , p . 3 1 ) n o t e d t h a t " . . . V i e w i n g o f e l e p h a n t became more common i n t h e S e r e n g e t i N a t i o n a l P a r k " . W i t h e l e p h a n t d e n s i t i e s i n c r e a s i n g w i t h i n t h e p r o t e c t e d p a r k a n d r e s e r v e l a n d s ( W a t s o n a n d B e l l 1 9 6 9 , G l o v e r a n d T rump 1 9 7 0 , N o r t o n - G r i f f i t h s 1 9 7 9 , D u b l i n a n d D o u g l a s - H a m i l t o n , i n p r e s s ) , s u b s e q u e n t c h a n g e i n t h e w o o d l a n d s was i n e v i t a b l e . R i n g - b a r k i n g a n d h e a v y b r o w s i n g p r e s s u r e on a v a r i e t y o f t r e e s p e c i e s f o l l o w e d ( G l o v e r 1 9 6 5 , L a m p r e y e t a l . 1 9 6 7 , C r o z e 1974a & b ) . An a n a l y s i s o f l o n g - t e r m m o n i t o r i n g d a t a by N o r t o n - G r i f f i t h s ( 1 9 7 9 ) s h o w e d t h a t w o o d l a n d c o v e r l o s s i n t h e S e r e n g e t i c o u l d be a t t r i b u t e d p r i m a r i l y t o t h e i n c r e a s e d f r e q u e n c y a n d s e v e r i t y o f f i r e s a n d s e c o n d l y t o t h e i m p a c t s o f b r o w s i n g e l e p h a n t s . B u r n a n d b a r k - s t r i p p i n g s c a r s f o u n d i n t h e t r e e c o r e s o f two s p e c i e s i n t h e M a r a s u g g e s t e d t h a t b o t h f i r e a n d e l e p h a n t b r o w s i n g f i g u r e d p r o m i n e n t l y i n t h e i r i n d i v i d u a l h i s t o r i e s d u r i n g t h e 1 9 6 0 s ( D u b l i n , u n p u b l i s h e d d a t a ) . 30 V e g e t a t i o n C h a n g e s f r o m 1950 t o 1 9 8 2 ; t h e d i r e c t e v i d e n c e The A c a c i a w o o d l a n d s R e s u l t s o f t h e c o v e r d e n s i t y a n a l y s i s f o r t h e M a r a R e s e r v e show t h a t i n 1 9 5 0 , mean woody c o v e r was a p p r o x i m a t e l y 30% i n A c a c i a w o o d l a n d s t a n d s ( F i g u r e 2 . 2 ) . C o v e r e s t i m a t e s r a n g e d f r o m 8% t o 5 6 . 8 % i n t h e e a s t a n d 10 .7% t o 5 0 . 4 % i n t h e w e s t . F i f t y s a m p l e p o i n t s w e r e f o l l o w e d t h r o u g h t i m e on b o t h t h e e a s t a n d w e s t s i d e s . The M a r a h a s s u f f e r e d c o n t i n u a l w o o d l a n d l o s s s i n c e t h e e a r l y 1 9 5 0 s . B o t h e a s t a n d w e s t s h o w e d h i g h l y s i g n i f i c a n t c o v e r l o s s e s i n e a c h s u c c e s s i v e t i m e p e r i o d . A t w o - way ANOVA s h o w e d t h a t t h e r e was a s i g n i f i c a n t i n t e r a c t i o n b e t w e e n y e a r a n d t h e e a s t a n d w e s t s i d e s o f t h e M a r a (F = 3 . 9 1 , P < . 0 1 ) . T u k e y ' s m u l t i p l e c o m p a r i s o n t e s t s h o w e d t h a t c o v e r d e n s i t y was t h e same f o r e a s t a n d w e s t i n 1 9 5 0 , 1 9 6 1 , a n d 1967 b u t was s i g n i f i c a n t l y l o w e r i n t h e w e s t i n 1974 a n d 1982 a t t h e 1% l e v e l . T h i s i s m o s t l i k e l y t h e r e s u l t o f h i g h e r r a i n f a l l on t h e w e s t s i d e w h i c h p r o d u c e d more g r a s s f u e l f o r d r y s e a s o n f i r e s s u b s e q u e n t l y k i l l i n g more t r e e s i n t h e w e s t t h a n t h e e a s t a f t e r 1 9 6 7 . T h e h y p o t h e s e s t h a t t h e r e w e r e no d i f f e r e n c e s b e t w e e n e a s t a n d w e s t i n a b s o l u t e o r r e l a t i v e r a t e s o f c h a n g e f o r t h e d i f f e r e n t t i m e p e r i o d s w e r e a l s o t e s t e d u s i n g t w o - w a y ANOVAS ( F i g u r e s 2 . 3 a n d 2 . 4 ) . T u k e y m u l t i p l e c o m p a r i s o n t e s t s on mean r a t e s o f c h a n g e s h o w e d t h a t t h e a b s o l u t e r a t e was h i g h e r i n t h e e a s t f o r t h e p e r i o d 1950 t o 1 9 6 1 . F r o m 1967 t o 1 9 7 4 , s i g n i f i c a n t l y g r e a t e r l o s s e s o c c u r r e d i n t h e w e s t . A b s o l u t e l o s s e s w e r e n o t s i g n i f i c a n t l y d i f f e r e n t b e t w e e n e a s t a n d w e s t 31 30 -I ( H 1 1 1 ~ ~ i " 1950 1960 1970 1980 Y E A R e 2 .2 . Mean cover d e n s i t y of Acacia woodlands i n the Masai Mara Game Reserve. Percent cover d e n s i t i e s are d e r i v e d from d o t - g r i d analyses of f i v e sets of a e r i a l photographs. 32 3.0 CO CO o o % w 3 O CO PQ < 2 .0 - 1.0- 0 n.s. [] - EAST g - WEST ** 1 n.s. 1950 1961 1967 1974 to to to to 1961 1967 1974 1982 TIME PERIODS F i g u r e 2.3. Absolute r a t e (percent/year) of cover l o s s f o r Acacia woodlands i n the Mara Mara Game Reserve. The Reserve was broken i n t o east and west s i d e s f o r a n a l y s i s , (* = P<.05, ** = P<.01), 33 IS GO o o > % w 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 n.s. I 1950 1961 to to 1961 1967 *** *** i 1 1967 1974 to to 1974 1982 TIME PERIODS F i g u r e 2.4. R e l a t i v e rate (percent/year) of cover l o s s f o r Acacia woodlands i n the Mara Mara Game Reserve. The Reserve was broken i n t o east and west s i d e s f o r a n a l y s i s , (* = P<.05, *** «= P<.001). 34 for the p e r i o d s 1961 to 1967 and 1974 to 1982. A b s o l u t e r a t e s of change were h i g h e s t i n the p e r i o d 1961 to 1967. R e l a t i v e r a t e s of change f o l l o w e d a s i m i l a r t r e n d . E a s t s i d e l o s s e s were g r e a t e r than west from 1950 to 1961, r a t e s in the west exceeded those i n the east f o r the p e r i o d s 1967 to 1974 and 1974 to 1982, and eas t and west s i d e s were equa l from 1961 to 1967. L o o k i n g at r e l a t i v e r a t e s of change, a c r o s s the e n t i r e R e s e r v e , i n the p e r i o d from 1961 to 1967 a l o n e , t h e r e was a 60% to 65% d e c l i n e i n t r e e cover d e n s i t y . In the 32 y e a r s , between the f i r s t a e r i a l s e r i e s i n 1950, and the l a s t in 1982, over 95% of the Acac i a woodlands had v a n i s h e d . The C r o t o n t h i c k e t s C r o t o n t h i c k e t s have changed i n two ways over t i m e . Both a l o s s i n canopy cover w i t h i n t h i c k e t s and a l o s s of t o t a l area c o v e r e d by i n d i v i d u a l t h i c k e t s have taken p l a c e . The a n a l y s e s show t h a t both these l o s s e s have been h i g h l y s i g n i f i c a n t over the past 32 years ( F i g u r e s 2 . 5 , 2 . 6 , & 2 . 7 , a l l P - v a l u e s <.0001) . The l a r g e s t d e c l i n e s o c c u r r e d from 1961-1967 (-2.33% per year a b s o l u t e l o s s and -3.12% per year r e l a t i v e l o s s ) . The average a r e a of the 15 i n d i v i d u a l C r o t o n t h i c k e t s or t h i c k e t g r o u p i n g s , f o l l o w e d through t i m e , dropped from a mean of 4.12 km2 to 2.80 km 2 ( F i g u r e 2 . 8 ) . I t s h o u l d be mentioned tha t v a r i a b i l i t y was e s p e c i a l l y h i g h i n the C r o t o n t h i c k e t a r e a - l o s s measurements. The a c t u a l p e r i m e t e r s of some t h i c k e t s d i d not change a t a l l , though i n t e r n a l t h i n n i n g ( i . e. l o s s of cover d e n s i t y ) o c c u r r e d i n a l l 35 80 - i — I 1 : 1 1 1950 1960 1970 1980 YEAR F i g u r e 2.5. Mean cover d e n s i t y of Croton t h i c k e t s i n the Masai Mara Game Reserve. Percent cover d e n s i t i e s are d e r i v e d from d o t - g r i d analyses of f i v e s e t s of a e r i a l photographs. 1950 1961 1967 1974 to to to to 1961 1967 1974 1982 TIME PERIODS F i g u r e 2.6. Absolute r a t e (percent/year) of cover l o s s f o r Croton t h i c k e t s i n the Masai Mara Game Reserve. A l l time periods are h i g h l y s i g n i f i c a n t at the P<.0001 l e v e l . 1950 1961 1967 1974 to to to to 1961 1967 1974 1982 TIME PERIODS F i g u r e 2.7. R e l a t i v e r a t e (percent/year) of cover l o s s f o r Croton t h i c k e t s i n the Masai Mara Game Reserve. A l l time periods are h i g h l y s i g n i f i c a n t at the P<.0001 l e v e l . 38 C\} < < 4H 3 H 2 - Paired t = -5.98 p-value < 0.00001 0 1950 1982 Y E A R F i g u r e 2.8. Mean area of f i f t e e n Croton t h i c k e t s sampled i n the 1950 and 1982 a e r i a l photography (± one s.d.). 39 t h i c k e t s sampled. The reason f o r t h i s s t a b i l i t y t h r ough time i s u n c l e a r but may have t o do w i t h the o r i g i n a l shape of i n d i v i d u a l t h i c k e t s . T h i c k e t s which were r e c t a n g u l a r or c i r c u l a r i n 1950 tended t o be more r e s i s t a n t t o change. Those t h a t were l o n g and narrow or had b o t t l e n e c k s w i t h i n them were more r e a d i l y fragmented and the subsequent segments d i s a p p e a r e d e n t i r e l y , over t i m e . The a gents r e s p o n s i b l e f o r a r e a and c o v e r l o s s p r o b a b l y a c t e d b o t h t o g e t h e r and i n d i v i d u a l l y . D i s c u s s i o n A s y n t h e s i s of q u a l i t a t i v e and d i r e c t e v i d e n c e shows t h a t the S e r e n g e t i - M a r a ecosystem has e x p e r i e n c e d a change from open g r a s s l a n d t o dense woodland and back i n l e s s than a hundred y e a r s . By 1900 e l e p h a n t numbers had been g r e a t l y reduced by h u n t i n g , w i l d e b e e s t , b u f f a l o , and c a t t l e p o p u l a t i o n s were low due t o r i n d e r p e s t , and the Maasai p e o p l e had been decimated by famine and d i s e a s e . These e v e n t s l a t e i n the l a s t c e n t u r y s e t the stage f o r the e s t a b l i s h m e n t of e x t e n s i v e woodlands and t h i c k e t s i n what had f o r m e r l y been open g r a s s l a n d s . S h i e l d e d from the e f f e c t s of heavy b r o w s i n g and g r a z i n g and the a n n u a l hot f i r e s s e t by the M a a s a i , bush and woodland f o r m a t i o n p r o g r e s s e d unimpeded. By the m i d - l 9 3 0 s , the a r e a which 30 y e a r s e a r l i e r had been open g r a s s l a n d now c o m p r i s e d dense woodlands and t h i c k e t s . In 1937 the S e r e n g e t i was g a z e t t e d as a n a t i o n a l r e s e r v e . E a r l y c o n s e r v a t i o n i s t s and park a u t h o r i t i e s vowed t o m a i n t a i n t h i s d i v e r s e , woodland dominated a r e a i n what they m i s t a k e n l y viewed as i t s " p r i s t i n e " c o n d i t i o n . 40 T h e s e w o o d l a n d s a n d t h i c k e t s p e r s i s t e d f o r some t i m e b u t , d e s p i t e t h e d e s i r e t o p r e s e r v e t h e m , p r e c i p i t a t e d e c l i n e s b e g a n i n t h e l a t e 1950s a n d e a r l y 1 9 6 0 s . W i t h t h e a d v e n t o f m o d e r n m e d i c i n e s w h i c h p r o t e c t e d a n d e x t e n d e d human l i f e , c o u p l e d w i t h a d v a n c e d v e t e r i n a r y c a r e , w h i c h v a c c i n a t e d l i v e s t o c k a g a i n s t r i n d e r p e s t a n d o t h e r d i s e a s e s , u n p r e c e d e n t e d i n c r e a s e s i n human a n d c a t t l e p o p u l a t i o n s h a d o c c u r r e d i n a r e a s s u r r o u n d i n g t h e S e r e n g e t i - M a r a ( F i g u r e 2 . 9 , M o r g a n a n d S h a f f e r 1 9 6 6 , K u r j i 1 9 7 6 , L a m p r e y 1 9 8 5 ) . I t was t h e d i r e c t a n d i n d i r e c t e f f e c t s o f t h e s e i n c r e a s e s w h i c h f i n a l l y b r o u g h t a b o u t w o o d l a n d d e c l i n e s a n d a r e t u r n t o t h e o p e n g r a s s l a n d s s e e n t o d a y . Two p r i m a r y p a t h w a y s s t e m m i n g f r o m t h e i n c r e a s e i n human p o p u l a t i o n s a p p e a r t o h a v e i n i t i a t e d w o o d l a n d d e c l i n e s . The f i r s t was f i r e . U n g u l a t e p o p u l a t i o n s , s t i l l s p a r s e a s a r e s u l t o f t h e r i n d e r p e s t , w e r e u n a b l e t o r e d u c e s i g n i f i c a n t l y t h e s t a n d i n g c r o p o f d r y g r a s s r e s u l t i n g f r o m u n u s u a l l y h i g h r a i n f a l l i n t h e e a r l y 1 9 6 0 s . A s t h e d r y s e a s o n p r o g r e s s e d , f i r e s became w i d e s p r e a d . Some o f t h e s e f i r e s w e r e i n t e n t i o n a l l y s e t by t h e M a a s a i t o i m p r o v e g r a z i n g p a s t u r e s a n d t o c l e a r t s e t s e - i n f e s t e d b u s h , w h i l e o t h e r b u r n s f a c i l i t a t e d h u n t i n g by n e i g h b o u r i n g t r i b e s , some w e r e s e t by p a r k a u t h o r i t i e s u n d e r o v e r a l l f i r e management s c h e m e s , some w e r e i n a d v e r t e n t l y l i t by w a n d e r i n g h o n e y h u n t e r s a n d s t i l l o t h e r s by E u r o p e a n h u n t e r s . U n d e r c o n d i t i o n s o f n o r m a l r a i n f a l l , w o o d l a n d r e g e n e r a t i o n w o u l d h a v e b e e n h a m p e r e d by t h i s s u d d e n i n c r e a s e i n f i r e o c c u r r e n c e . U n d e r t h e h i g h r a i n f a l l c o n d i t i o n s o f t h e e a r l y 1 9 6 0 s a n d t h e s u b s e q u e n t h i g h f u e l p r o d u c t i o n t h e s e f i r e s w e r e d e v a s t a t i n g a n d s e r v e d t o c l e a r t h e a r e a o f b u s h a n d a t t r a c t game t o t h e l u s h 41 or PLH O Oh 8 - 6 - 4- 2 - — I 1 1 I 1960 1970 1980 1990 Y E A R F i g u r e 2.9. Human population d e n s i t y trends f o r the area near the Masai Mara Game Reserve. The dotted l i n e ( ) represents the t r e n d c a l c u l a t e d from settlement numbers i n the area adjacent to the Game Reserve (Lamprey 1985). The dashed l i n e ( ) represents the trend c a l c u l a t e d from n a t i o n a l census data which included the densely populated Ololunga area. (Morgan and Shaffer 1966). This area i s not adjacent to the Reserve. Graph adapted from Lamprey (1985). 42 g r a z i n g " l a w n s " c r e a t e d by f i r e s . The human i n c r e a s e a l s o o p e n e d a s e c o n d p a t h w a y t o w o o d l a n d l o s s i n p r o t e c t e d a r e a s , t h e c o m p r e s s i o n o f e l e p h a n t s . The r o l e o f e l e p h a n t s i n d r a m a t i c w o o d l a n d d e c l i n e s h a d g a i n e d much n o t o r i e t y a n d a t t e n t i o n among e c o l o g i s t s , a t t h i s same t i m e , t h r o u g h o u t A f r i c a ( B u e c h n e r a n d D a w k i n s 1 9 6 1 , B r o o k s a n d B u s s 1 9 6 2 , S i m o n 1 9 6 2 , G l o v e r 1 9 6 3 , D a r l i n g 1 9 6 4 , B u s s a n d S a v i d g e 1 9 6 6 , F i e l d 1 9 7 1 , A n d e r s o n a n d W a l k e r 1 9 7 4 , C a u g h l e y 1 9 7 6 , C r o z e e t a l . 1 9 8 1 ) . I n d i s c u s s i n g e l e p h a n t s a n d w o o d l a n d l o s s , C u r r y - L i n d a h l ( 1 9 6 8 , p . 2 6 ) s t a t e d , " . . . e x c e p t f o r man t h e r e i s no o t h e r a n i m a l i n A f r i c a t h a t i s a b l e t o a l t e r a h a b i t a t s o d r a s t i c a l l y a s d o e s t h e e l e p h a n t " . L i k e s o many o t h e r a r e a s o f A f r i c a , t h e S e r e n g e t i - M a r a w o o d l a n d s f e l t t h e e f f e c t s o f i n c r e a s e d e l e p h a n t d e n s i t i e s . The q u a n t i t a t i v e a n a l y s i s o f a e r i a l p h o t o g r a p h y , w h i c h c o v e r e d t h e m a j o r p e r i o d o f w o o d l a n d d e c l i n e , p r o v i d e d a b e t t e r u n d e r s t a n d i n g o f t h e e x a c t t i m i n g o f t h e s e l o s s e s . The h i g h e s t l o s s e s , f r o m 1961 t o 1 9 6 7 , c o r r e s p o n d e d s i g n i f i c a n t l y t o a p e r i o d o f u n u s u a l l y h i g h r a i n f a l l a n d s u b s e q u e n t f i r e s w h i c h o c c u r r e d two o r t h r e e t i m e s p e r y e a r d u r i n g t h i s t i m e ( L a n g r i d g e e t a l . 1 9 7 0 ) . W h i l e h e a l t h y t r e e s may h a v e w i t h s t o o d f i r e l o n g e r , i n t h e f a c e o f s u c h h o t f i r e s e v e n many u n b r o w s e d t r e e s d i e d . The a d d i t i o n a l h e a v y i n f l u x o f e l e p h a n t s , i n t h i s same t i m e p e r i o d , d r o v e t h e s e d e c l i n e s o f t r e e d e n s i t y e v e n f u r t h e r . E l e p h a n t i m p a c t s , s u c h a s b r a n c h b r e a k a g e a n d b a r k s t r i p p i n g , c o u l d h a v e e x a c e r b a t e d t h e e f f e c t s o f f i r e , by a d d i n g t o e x i s t i n g f u e l l o a d s o r by c a u s i n g p h y s i o l o g i c a l s t r e s s t o t h e t r e e s a n d m a k i n g t hem more v u l n e r a b l e t o f i r e . E l e p h a n t s a n d 43 f i r e s a c t e d t o g e t h e r , t h e i r r e l a t i v e c o n t r i b u t i o n s a r e n o t e a s i l y d i s t i n g u i s h e d . S e p a r a t e a n a l y s e s o f e a s t a n d w e s t s i d e s o f t h e M a r a R e s e r v e u n c o v e r e d some i n t e r e s t i n g d i f f e r e n c e s i n t h e p a t t e r n o f w o o d l a n d l o s s . A l t h o u g h t h e p e r i o d o f g r e a t e s t t r e e d e n s i t y d e c l i n e , 1 9 6 1 - 1 9 6 7 , was n o t s i g n i f i c a n t l y d i f f e r e n t b e t w e e n t h e t w o , a l l o t h e r t i m e p e r i o d s s h o w e d g r e a t e r r e l a t i v e l o s s e s on one s i d e o r t h e o t h e r . F r o m 1950 t o 1 9 6 1 , t h e e a s t e x p e r i e n c e d g r e a t e r l o s s e s o f t r e e s a n d f r o m 1967 t o 1974 a n d 1974 t o 1982 t h e r e v e r s e was t r u e . The g r e a t e r e a s t e r n l o s s e s i n t h e e a r l y t i m e p e r i o d may be a t t r i b u t e d t o a l a r g e r i n f l u x o f e l e p h a n t s t o t h a t p a r t o f t h e R e s e r v e , f o l l o w i n g t h e i r e m i g r a t i o n f r o m n e i g h b o u r i n g a r e a s ( N a r o k D i s t r i c t C o m m i s s i o n e r , A n n u a l R e p o r t , 1 9 5 5 ) . The e a s t was a l w a y s an a r e a o f g r e a t e r w o o d l a n d c o v e r d e n s i t y r e l a t i v e t o t h e w e s t , w i t h A c a c i a w o o d l a n d s , C r o t o n t h i c k e t s , a n d C o m b r e t u m w o o d l a n d s t h r o u g h o u t . E l e p h a n t s t e n d t o p r e f e r d e n s e w o o d l a n d s a n d b u s h l a n d s when t h e s e a r e a v a i l a b l e ( D a r l i n g 1 9 6 0 , G l o v e r 1 9 6 3 , Agnew 1 9 6 8 , L a w s 1 9 6 9 , 1 9 7 0 , Laws e t a l . 1 9 7 5 ) . T h e s e w o o d l a n d s w e r e a l s o d e v o i d o f humans b e c a u s e o f t h e h i g h t s e t s e f l y i n f e s t a t i o n s . The e a s t e r n w o o d l a n d s a n d t h i c k e t s , t h e r e f o r e , w o u l d h a v e b e e n c o l o n i z e d f i r s t by e l e p h a n t s a n d may h a v e e x p e r i e n c e d g r e a t e r e l e p h a n t d e p r e d a t i o n i n t h e e a r l i e r y e a r s . G r e a t e r f i r e f r e q u e n c y a n d i n t e n s i t y may e x p l a i n t h e h i g h e r r a t e o f l o s s f r o m 1967 t o 1 9 8 2 , on t h e w e s t s i d e . Due t o t h e s t r o n g e a s t - w e s t r a i n f a l l g r a d i e n t , i n n o r m a l y e a r s f i r e i m p a c t w o u l d be e x p e c t e d t o be p o s i t i v e l y c o r r e l a t e d t o t h e amoun t o f r a i n f a l l a n d t h e s u b s e q u e n t b i o m a s s p r o d u c t i o n ( N o r t o n - G r i f f i t h s 44 1979). In the p e r i o d from 1961 t o 1967, when the g r e a t e s t d e c l i n e s o c c u r r e d and the l e a s t d i f f e r e n c e s were seen between e a s t and west, u n u s u a l l y h i g h r a i n f a l l f e l l t h r oughout the a r e a . T h i s h i g h r a i n f a l l l e d t o such h i g h g r a s s p r o d u c t i o n throughout the Reserve t h a t the e f f e c t s of the normal r a i n f a l l g r a d i e n t were p r o b a b l y swamped. W i t h abundant d ry g r a s s f u e l , f i r e c o u l d have a f f e c t e d both the e a s t and west e q u a l l y . Trends i n the C r o t o n t h i c k e t s p a r a l l e l e d those of the A c a c i a woodlands, over the p a s t 30 y e a r s . A l t h o u g h some i n d i v i d u a l t h i c k e t s , i n both the e a s t and west, d i d not e x p e r i e n c e f i r e e f f e c t s t o t h e i r p e r i p h e r i e s , on average the a r e a l o s s e s have been s i g n i f i c a n t . There i s g e n e r a l l y an abrupt t r a n s i t i o n between v e g e t a t i o n t y p e s w i t h l i t t l e or no ecotone s e p a r a t i n g t h e s e t h i c k e t s from open g r a s s l a n d s . C r o t o n g e r m i n a t i o n i s most s u c c e s s f u l on the edge of t h i c k e t s and l e s s so i n l i g h t gaps w i t h i n the t h i c k e t s but r a r e l y i n the shade under o t h e r t r e e s or shrubs ( p e r s o n a l o b s e r v a t i o n ) . T h i c k e t edges, however, a r e h i g h r i s k growing s i t e s because they a r e f r e q u e n t l y s u b j e c t e d t o g r a s s f i r e s and the t r a m p l i n g and g r a z i n g e f f e c t s of h e r b i v o r e s ( N o r t o n - G r i f f i t h s 1979, D u b l i n , u n p u b l i s h e d d a t a ) . Under c o n d i t i o n s of h i g h f i r e i n c i d e n c e and h e r b i v o r e use, growth and r e g e n e r a t i o n of t h i c k e t s i s v e r y l i m i t e d and a r e a l o s s e s g e n e r a l l y r e s u l t . The s i g n i f i c a n t a r e a l o s s e s found i n the m a j o r i t y of t h i c k e t s sampled i n t h i s s tudy a r e c o n t r a r y t o the f i n d i n g s of Lamprey (1985). H i s f i n d i n g s d i d not r e f l e c t the g e n e r a l p a t t e r n of c o v e r and a r e a l o s s found i n the C r o t o n t h i c k e t s w i t h i n the Reserve b o u n d a r i e s i n t h i s s t u d y . Presumably, he 45 f o u n d no c h a n g e s i n t h e t h i c k e t s he s t u d i e d b e c a u s e o f t h e i r l o c a t i o n o u t s i d e t h e M a r a Game R e s e r v e b o u n d a r i e s . A r e a s o u t s i d e t h e R e s e r v e h a v e n o t e x p e r i e n c e d t h e same p r e s s u r e s a s a r e a s i n s i d e . F i r e a n d e l e p h a n t s may h a v e h a d l i t t l e i n f l u e n c e o u t s i d e t h e R e s e r v e , t h e f o r m e r due t o r e d u c e d f u e l l o a d s a f t e r h e a v y g r a z i n g by d o m e s t i c s t o c k a n d t h e l a t t e r due t o t h e t e n d e n c y o f e l e p h a n t s a c t i v e l y t o a v o i d human c o n t a c t . L a m p r e y u s e d a l i m i t e d number o f s a m p l i n g p o i n t s f o r h i s a n a l y s i s a n d t h i s may h a v e l i m i t e d h i s p o w e r t o d i s c r i m i n a t e s i g n i f i c a n t l o s s e s . A l l t h i c k e t s h a v e s u f f e r e d i n t e r n a l t h i n n i n g , c o n s i s t e n t w i t h t h o s e r e p o r t e d by N o r t o n - G r i f f i t h s ( 1 9 7 9 ) i n t h e n o r t h e r n S e r e n g e t i . I n t h e M a r a , t h i s l o s s c a n be a t t r i b u t e d p r i m a r i l y t o u t i l i z a t i o n by e l e p h a n t s . T h e i r m o v e m e n t s a n d b r o w s i n g w i t h i n t h i c k e t s r e s u l t s i n e x t e n s i v e s t r u c t u r a l damage t o t h e t r e e s a n d s h r u b s . W i t h t h e g e n e r a l l o s s o f o t h e r w o o d l a n d t y p e s , e l e p h a n t s now s p e n d a n i n o r d i n a t e p r o p o r t i o n o f t h e i r t i m e w i t h i n t h e s e t h i c k e t s . T h i s s e l e c t i v e h a b i t a t p r e f e r e n c e i s a c c e n t u a t e d i n t h e d r y s e a s o n when e l e p h a n t s move i n t o t h i c k e t s i n s e a r c h o f s h a d e a n d f o r a g e ( C h a p t e r 3 ) . The m a i n b o d y o f t h e C r o t o n t h i c k e t s seem r e s i s t a n t t o f i r e i n c u r s i o n , due t o h i g h s o i l m o i s t u r e a n d s p a r s e u n d e r g r o w t h ( L a n g r i d g e e_t a_ l . 1 9 7 0 , D u b l i n , u n p u b l i s h e d d a t a ) . H o w e v e r , a s t h i c k e t s a r e o p e n e d , t h r o u g h t h e a c t i o n s o f e l e p h a n t s a n d o t h e r a n i m a l s , t h e y do become i n c r e a s i n g l y s u s c e p t i b l e t o t h e s p r e a d o f f i r e t h r o u g h t h e g r a s s e s g r o w i n g i n t h e s e r e c e n t l y o p e n e d g a p s ( N o r t o n - G r i f f i t h s 1 9 7 9 ) . My b u r n i n g e x p e r i m e n t s s h o w e d t h a t C r o t o n b u s h e s u n d e r 3m w e r e f r e q u e n t l y k i l l e d i n h o t f i r e s 46 a n d t h o s e o v e r 3m e x p e r i e n c e d a r e d u c t i o n i n c a n o p y a n d p r o d u c e d l i t t l e o r no s e e d c r o p i n t h e n e x t f r u i t i n g s e a s o n . E l e p h a n t a c t i v i t y a n d s u b s e q u e n t f i r e damage p r o b a b l y a c c o u n t s f o r t h e r a p i d l o s s o f s m a l l t h i c k e t p a t c h e s w h i c h h a v e become i s o l a t e d f r o m t h e m a i n b o d y o f t h e t h i c k e t s . A r e a l o s s e s h a v e b e e n s i g n i f i c a n t l y l o w e r i n t h o s e t h i c k e t s w h i c h h a v e m a i n t a i n e d t h e i r " s t r u c t u r a l i n t e g r i t y " , a s r e c t a n g u l a r o r c i r c u l a r c o n f i g u r a t i o n s . F u r t h e r s t u d i e s i n t o t h e d y n a m i c s o f t h e s e w o o d l a n d s a n d t h i c k e t s b e g a n i n 1 9 8 2 , i m m e d i a t e l y f o l l o w i n g t h e l a s t a e r i a l p h o t o g r a p h i c s u r v e y . O u t s i d e o f t h e R e s e r v e , o v e r g r a z i n g by c a t t l e i s now r e m o v i n g t h e s t a n d i n g c r o p s o l i t t l e o r no b u r n i n g i s t a k i n g p l a c e a n d woody p l a n t s a r e b e c o m i n g r e - e s t a b l i s h e d ( L a m p r e y 1 9 8 5 ) . T h i s w i d e s p r e a d " b u s h e n c r o a c h m e n t " p r o v i d e s p r i m e h a b i t a t f o r t s e t s e f l i e s , t h e i r n u m b e r s a r e i n c r e a s i n g i n a r e a s a d j a c e n t t o t h e R e s e r v e a n d a h i g h i n c i d e n c e o f t r y p a n o s o m i a s i s i s o c c u r r i n g , i n c a t t l e ( R o s s i t e r e t a l . 1 9 8 3 ) . I n s i d e t h e R e s e r v e , s i m i l a r c o n d i t i o n s p r e v a i l . W i l d e b e e s t n u m b e r s h a v e i n c r e a s e d f i v e - f o l d s i n c e t h e d i s a p p e a r a n c e o f r i n d e r p e s t i n t h e e a r l y 1 9 6 0 s ( S i n c l a i r 1 9 7 3 ) . L i k e c a t t l e , t h e m i g r a t o r y w i l d e b e e s t s i g n i f i c a n t l y r e d u c e t h e s t a n d i n g c r o p o f g r a s s e s ( M c N a u g h t o n 1976) a n d t h e f r e q u e n c y a n d s e v e r i t y o f d r y s e a s o n f i r e s a r e r e d u c e d . N o r t o n - G r i f f i t h s ( 1 9 7 9 ) p r e d i c t e d t h a t u n d e r t h e s e c o n d i t i o n s , t h e w o o d l a n d s a n d t h i c k e t s w o u l d r e - e s t a b l i s h t h e m s e l v e s a s t h e y h a v e o u t s i d e t h e R e s e r v e . C u r r e n t l y t h e r e i s no e v i d e n c e o f w o o d l a n d r e c o v e r y i n t h e M a s a i M a r a Game R e s e r v e . 47 Summary The S e r e n g e t i - M a r a ecosystem has e x p e r i e n c e d a t r a n s i t i o n from open g r a s s l a n d to dense woodland and back i n l e s s than 100 y e a r s . T h i s c h a p t e r r e c o n s t r u c t s the h i s t o r y of these changes through both q u a l i t a t i v e and q u a n t i t a t i v e e v i d e n c e . The changes i n v e g e t a t i o n p a t t e r n s are d e s c r i b e d and the b i o l o g i c a l f a c t o r s i m p l i c a t e d i n these t r a n s i t i o n s are d i s c u s s e d . At the t u r n of the c e n t u r y , the area was d e s c r i b e d by e x p l o r e r s and t r a d e r s as an open g r a s s l a n d . However, by the 1930s t h i s same area had become d e n s e l y wooded. T h i s t r a n s i t i o n i s a t t r i b u t e d to a concomitant r e d u c t i o n in man-made f i r e s . In the l a t e 1800s, w i l d l i f e and l i v e s t o c k numbers had been g r e a t l y reduced by the v i r a l d i s e a s e , r i n d e r p e s t , and humans (dependent on these an imal s ) had succumbed to s t a r v a t i o n and d i s e a s e on an epidemic s c a l e . E l e p h a n t p o p u l a t i o n s had been v i r t u a l l y e l i m i n a t e d by l o c a l hunters who s u p p l i e d a f l o u r i s h i n g i v o r y t r a d e on the c o a s t . With l a r g e h e r b i v o r e p o p u l a t i o n s at a low, c o n d i t i o n s were i d e a l f o r the e s t a b l i s h m e n t of woodlands and t h i c k e t s . The areas set a s i d e as the S e r e n g e t i N a t i o n a l Park and the Masai Mara Game Reserve were c h a r a c t e r i z e d by dense woody v e g e t a t i o n in the 1930s and 1940s. However, by the 1950s these woodlands and t h i c k e t s were a l r e a d y d e c l i n i n g . An a n a l y s i s of a e r i a l photography flown i n 1950, 1961, 1967, 1974, and 1982 showed the s teady l o s s of cover i n woodlands and t h i c k e t s . The a b s o l u t e and r e l a t i v e r a t e s of woodland cover l o s s i n the Mara Reserve were h i g h e s t from 1961 to 1967, though d e c l i n e s c o n t i n u e d i n t o the 1980s. These d e c l i n e s c o i n c i d e d w i t h an 48 i n c r e a s e i n l o c a l e l e p h a n t d e n s i t i e s a s w e l l a s an i n c r e a s e i n f i r e f r e q u e n c y a n d s e v e r i t y . D u r i n g t h i s 3 0 - y e a r p e r i o d , t h e mean c o v e r d e n s i t y o f A c a c i a w o o d l a n d s d r o p p e d s i g n i f i c a n t l y t h r o u g h o u t t h e M a r a R e s e r v e a s d i d t h e mean c o v e r d e n s i t y a n d a r e a o f C r o t o n t h i c k e t s . A l t h o u g h b u r n i n g r a t e s a r e p r e s e n t l y l o w a n d w o o d l a n d r e c o v e r y h a s b e e n p r e d i c t e d u n d e r t h e s e c o n d i t i o n s , t h e r e i s c u r r e n t l y no s i g n o f a r e t u r n t o w o o d l a n d v e g e t a t i o n i n t h e M a r a Game R e s e r v e . The r o l e o f u n p r e c e d e n t e d n u m b e r s o f r e s i d e n t e l e p h a n t s a n d m i g r a t o r y w i l d e b e e s t i n w o o d l a n d d y n a m i c s o f t h e M a r a i s s t i l l n o t f u l l y u n d e r s t o o d . 4 9 CHAPTER 3 . H A B I T A T S E L E C T I O N AND GROUP S I Z E OF ELEPHANTS I N THE MASAI MARA GAME R E S E R V E I n t r o d u c t i o n The d i f f e r e n t i a l u s e o f h a b i t a t s by e l e p h a n t s c a n s i g n i f i c a n t l y a l t e r t h e s t r u c t u r e o f a f f e c t e d p l a n t c o m m u n i t i e s ( C u r r y - L i n d a h l 1 9 6 8 , L a w s 1 9 7 0 , F i e l d 1 9 7 1 , Thomson 1 9 7 5 ) . U t i l i z a t i o n p a t t e r n s a r e i n f l u e n c e d by f o r a g e p r e f e r e n c e a n d a v a i l a b i l i t y ( L e u t h o l d a n d S a l e 1 9 7 3 , W e s t e r n a n d L i n d s a y 1985) a s w e l l a s by e x t e r n a l f a c t o r s s u c h a s e x t r e m e w e a t h e r c o n d i t i o n s ( C o r f i e l d 1 9 7 3 ) , human s e t t l e m e n t a n d c u l t i v a t i o n ( L a m p r e y e t a l . 1 9 6 7 , L a w s 1 9 7 0 , L a m p r e y 1 9 8 5 , W e s t e r n a n d L i n d s a y 1 9 8 5 ) , a n d p o a c h i n g a c t i v i t y ( D o u g l a s - H a m i l t o n 1 9 7 9 ) . O v e r t h e p a s t 25 y e a r s , t h e s e e x t e r n a l f a c t o r s h a v e l e d t o t h e c o n c e n t r a t i o n o f e l e p h a n t s i n p r o t e c t e d r e f u g e s i n many p a r t s o f t h e i r r a n g e . T o d a y m o s t o f A f r i c a ' s e l e p h a n t s s u r v i v e i n p r o t e c t e d p a r k s a n d r e s e r v e s (Cumming a n d J a c k s o n 1 9 8 4 ) . I t i s n e c e s s a r y t o know t h e p a t t e r n s o f u t i l i z a t i o n o f e l e p h a n t s i n o r d e r t o u n d e r s t a n d t h e i r i m p a c t on t h e h a b i t a t s t h e y o c c u p y i n p a r k s a n d r e s e r v e s , a n d t o make d e c i s i o n s on l o c a l m a n a g e m e n t . The M a s a i M a r a Game R e s e r v e ( t h e M a r a ) i s a s m a l l a r e a b o r d e r e d on t h r e e s i d e s by p e r m a n e n t s e t t l e m e n t s o f t h e p a s t o r a l M a a s a i p e o p l e a n d on t h e f o u r t h by t h e S e r e n g e t i N a t i o n a l P a r k o f T a n z a n i a . I n t h e l a t e 1 9 7 0 s t h e S e r e n g e t i p r o v i d e d e l e p h a n t s w i t h a s a f e r e f u g e f r o m p o a c h i n g p r e s s u r e w h i c h was h i g h a t t h a t t i m e i n s i d e a n d t o t h e n o r t h o f t h e M a r a R e s e r v e i n K e n y a ( I . D o u g l a s - H a m i l t o n , p e r s . c o m m . ) . S i n c e a b o u t 1 9 8 0 , t h e s i t u a t i o n h a s b e e n r e v e r s e d a n d p o a c h i n g p r e s s u r e h a s m o u n t e d on t h e 50 S e r e n g e t i s i d e , thus c u t t i n g o f f t h i s escape r o u t e t o the s o u t h . In the mid-1980s, d u r i n g t h i s s t u d y , e l e p h a n t s e a s o n a l movements i n and out of the Reserve were s e v e r e l y c u r t a i l e d , a p p r o x i m a t e l y 800-1100 e l e p h a n t s u t i l i z e d the Mara y e a r - r o u n d . T h i s f u l l - t i m e r e s i d e n c y produced n o t i c e a b l e b r o w s i n g e f f e c t s on the v e g e t a t i o n , s i g n i f i c a n t l y i n f l u e n c i n g the s t r u c t u r e of many p l a n t communities i n the Reserve (Chapter 5 ) . T h i s paper d e s c r i b e s the s e a s o n a l changes i n h a b i t a t s e l e c t i o n and group s i z e of e l e p h a n t s w i t h i n the Mara. H a b i t a t p r e f e r e n c e s a re d i s c u s s e d as they r e l a t e t o changes i n f e e d i n g p a t t e r n s between the seasons, w h i l e the d e t a i l s of e l e p h a n t f o r a g i n g a r e a n a l y z e d f u r t h e r i n Chapter 4. The p o s s i b l e f u n c t i o n s s e r v e d by e l e p h a n t a g g r e g a t i o n s a re examined as w e l l as the c o n s t r a i n t s p l a c e d on group s i z e by food a v a i l a b i l i t y . Study Area The Masai Mara Game Reserve (34° 45' t o 35° 30' E, 1° 15' t o 1° 45' S) l i e s on Kenya's s o u t h w e s t e r n border w i t h T a n z a n i a and forms the northernmost e x t e n s i o n of the 25,000 km 2 S e r e n g e t i - M a r a ecosystem. In 1974, 1,530 km 2 were f o r m a l l y g a z e t t e d f o r the Game Reserve b u t , f o l l o w i n g r e c e n t boundary m o d i f i c a t i o n s , o n l y 1,000 km 2 remains. The a r e a t o the n o r t h and e a s t of the Mara i s now permanently s e t t l e d by p a s t o r a l i s t s and l a r g e - s c a l e a g r i c u l t u r a l schemes (Lamprey 1985). To the west, the Mara i s b o r d e r e d by the S i r i a ( E s o i t O l o o l o l o ) Escarpment, and t o the so u t h e x t e n d s t o the S e r e n g e t i N a t i o n a l Park. 51 T h i s s m a l l , p r o t e c t e d a r e a p r e s e n t l y p r o v i d e s t h e e s s e n t i a l d r y s e a s o n ( J u n e - O c t o b e r ) r a n g e f o r many o f t h e S e r e n g e t i m i g r a n t s w h i c h i n c l u d e o v e r one m i l l i o n w i l d e b e e s t a n d o v e r o n e h u n d r e d t h o u s a n d z e b r a s ( M a d d o c k 1 9 7 9 , S i n c l a i r e t a l . 1 9 8 5 ) . T h e s e m i g r a n t s a r e j o i n e d by t h o u s a n d s o f T h o m s o n ' s g a z e l l e s a n d w i l d e b e e s t w h i c h move i n t o t h e M a r a f r o m t h e d r y , L o i t a p l a i n s t o t h e n o r t h . A t t h e s t a r t o f t h e s h o r t r a i n s , i n l a t e O c t o b e r , t h e s e m i g r a n t s l e a v e t h e M a r a . C l i m a t e R a i n f a l l i n t h e M a r a i s b i m o d a l , w i t h s h o r t r a i n s f a l l i n g i n N o v e m b e r - D e c e m b e r a n d l o n g r a i n s o c c u r r i n g i n A p r i l - M a y ( F i g u r e 3 . 1 ) . T h i s p a t t e r n i s i n f l u e n c e d by t h e I n t e r t r o p i c a l C o n v e r g e n c e Zone ( I T C Z ) w h i c h a f f e c t s t h e E a s t A f r i c a n r e g i o n f r o m Z i m b a b w e , i n t h e s o u t h , t o S u d a n , i n t h e n o r t h ( N o r t o n - G r i f f i t h s e t a_ l . 1 9 7 5 ) . T h i s b a n d o f l o w p r e s s u r e f r o n t s f o l l o w s t h e n o r t h a n d s o u t h movement o f t h e s u n w i t h a l a g o f a b o u t 5 w e e k s . D r i v e n by t r a d e w i n d s w h i c h c o n v e r g e i n t h i s a r e a f r o m b o t h h e m i s p h e r e s , t h e s y s t e m b r i n g s r a i n a n d c l o u d y w e a t h e r . The I T C Z r e a c h e s i t s n o r t h e r n l i m i t i n l a t e J u l y a n d i t s s o u t h e r n e x t r e m e i n l a t e J a n u a r y , t h u s a f f e c t i n g w e a t h e r p a t t e r n s i n t h e M a r a t w i c e e a c h y e a r . T h e M a r a a l s o h a s a p r o n o u n c e d e a s t - w e s t r a i n f a l l g r a d i e n t w i t h t h e e a s t s i d e a v e r a g i n g a p p r o x i m a t e l y 800 m m / y e a r a n d t h e w e s t s i d e a p p r o x i m a t e l y 1 200 m m / y e a r ( N o r t o n - G r i f f i t h s e_t a l . 1 9 7 5 , E p p a n d A g a t s i v a 1 9 8 0 , S t e l f o x e t a l . 1 9 8 6 ) . The w e s t 52 1 I I I I 1 1 1 1 1 1 1 J F M A M J J A S O N D MONTH F i g u r e 3.1. Monthly r a i n f a l l t o t a l s from Keekorok Lodge M e t e o r o l o g i c a l S t a t i o n l o c a t e d i n the study area. The three study years 1982, 1983, and 1984 are presented. 53 s i d e e x p e r i e n c e s much h e a v i e r r a i n f a l l because i t i s i n f l u e n c e d by the convergence of the Lake V i c t o r i a and Mau Range weather systems and l o c a l l y by the e f f e c t s of the S i r i a Escarpment . T h i s r a i n f a l l g r a d i e n t r e s u l t s in a h i g h e r grass p r o d u c t i v i t y on the west s i d e of the Mara R i v e r compared to that on the east (A. O n y e a n u s i , p e r s . comm.). Minimum and maximum d a i l y temperatures i n the Mara are c o n s t a n t throughout the year ( F i g u r e 3 . 2 ) . The average d a i l y maximum temperature f o r the years 1982-1984 was 2 8 . 1 ° C and the minimum was 1 4 . 8 ° C . P l a n t Communities In a d d i t i o n to the d i f f e r e n c e s i n annual r a i n f a l l p a t t e r n s , east and west s i d e s of the Mara are a l s o c h a r a c t e r i z e d by d i f f e r e n c e s i n p l a n t community c o m p o s i t i o n ( T a i t i 1973, Epp and A g a t s i v a 1980, Lamprey 1985). The e a s t e r n p o r t i o n of the Mara has more woody p l a n t communit ies than the west, whereas the west i s p r i m a r i l y open g r a s s l a n d wi th some woody v e g e t a t i o n a l o n g r i v e r c o u r s e s and on h i l l t o p s . A l l t r e e s and shrubs were c l a s s i f i e d a c c o r d i n g to Dale and Greenway (1961) and a l l grasses and herbs a c c o r d i n g to Edwards and Bogdan (1951). The Ngama H i l l s , to the f a r e a s t , are c o v e r e d by Combretum m o l l e - H e e r i a r e t i c u l a t a woodlands a t the h i g h e r e l e v a t i o n s , on the s t eeper s l o p e s . These woodlands merge i n t o r e l i c t or degraded t h i c k e t s ( r e f e r r e d to as Acac i a - Commiphora woodlands by Lamprey (1985)) on the r o c k y , exposed s l o p e s below. At the base of these h i l l s , i n the deeper s o i l s , Acac i a q e r r a r d i i 54 36 - i O o H W s ac E-1 O < w 30- 24- 18- • - M A X I M U M O - M I N I M U M o—cr ,o O -o- -o- -o- -O Or -O o o JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC MONTH F i g u r e 3.2. Mean monthly maximum and minimum temperatures from Keekdrok Lodge M e t e o r o l o g i c a l S t a t i o n l o c a t e d i n the study area. These maximum and minimum temperatures are averaged over the three study years 1982, 1983, and 1984. 55 woodlands form a mosaic w i t h the r e l i c t t h i c k e t communi t i e s . R e l i c t t h i c k e t s are widespread and d i v e r s e , c o n t a i n i n g s e e d l i n g s and c o p p i c i n g r o o t s t o c k s of many s p e c i e s . These i n c l u d e : Acac i a b r e v i s p i c a , A . g e r r a r d i i , A . h o c k i i , A . S e n e g a l , A l b i z i a amara, A . p e t e r s i a n a , B o s c i a a n g u s t i f o l i a , Commiphora a f r i c a n a , C . t r o t h a e , C o r d i a o v a l i s , D i c h r o s t a c h y s c i n e r e a , Grewia s p p . , L i p p i a j a v a n i c a , Ocimum americanum, Ormocarpum t r i c h o c a r p u m , and Solanum incanum. V i r t u a l l y a l l p l a n t s l i s t e d here are below 1 meter h i g h . S t a n d i n g dead t r e e s are commonly seen in t h i s community. Trump (1972) c o n s i d e r e d t h i s community to be d e r i v e d from C r o t o n t h i c k e t s , whereas Lamprey (1985) d e s c r i b e d i t as a degraded phase of areas which had been t h i c k e r Acac i a - Commiphora bushlands in the p a s t . Large areas of the n o r t h e r n S e r e n g e t i now appear to be i n an e a r l i e r phase of the d e g r a d a t i o n i n t h i s community wi th s i m i l a r s p e c i e s c o m p o s i t i o n but many more p l a n t s i n the l a r g e r h e i g h t c l a s s e s . The Acac i a g e r r a r d i i woodlands occur as h i g h l y clumped c o h o r t s tands f r e q u e n t l y found i n a s s o c i a t i o n w i t h the r e l i c t t h i c k e t s mentioned above ( H e r l o c k e r 1976a & b, Lamprey 1985). A l t h o u g h Trump (1972) d i d not d i s t i n g u i s h t h i s as a d i s t i n c t community t y p e , Lamprey (1985) documented the r a p i d i n c r e a s e of A c a c i a g e r r a r d i i woodlands i n many areas of the Mara over the pas t decade . T h i s p r o l i f e r a t i o n i s l a r g e l y a t t r i b u t e d to i t s f i r e - t o l e r a n c e (Glover and Trump 1970, Spinage and Guinness 1972, T a i t i 1973, Chapter 5 ) . I n d i v i d u a l p l a n t s p e r s i s t through t ime by s p r o u t i n g new shoots from underground r o o t s t o c k s f o l l o w i n g b u r n i n g or b r o w s i n g . A v a r i e t y of s e e d l i n g s and r o o t - c o p p i c i n g s p e c i e s are commonly found i n t h i s community. These 56 i n c l u d e : Acac i a S e n e g a l , Commiphora s p p . , D i c h r o s t a c h y s c i n e r e a , and Ormocarpum t r i c h o c a r p u m which a l l remain under one meter i n areas where b u r n i n g i s f requent or s e v e r e . The t r u e age of i n d i v i d u a l t r e e s or s e e d l i n g s i n t h i s community, l i k e those i n r e l i c t t h i c k e t s , i s d i f f i c u l t to de termine when t h e i r growth has been suppressed by b r o w s i n g , t r a m p l i n g , and f i r e s for i n d e t e r m i n a t e p e r i o d s of t i m e . Ridge t o p s , s m a l l h i l l s , and many seasona l d r a i n a g e l i n e s i n both the e a s t e r n and western p o r t i o n s of the Mara are c o v e r e d by C r o t o n dichogamus t h i c k e t s . Though Croton dominates the s p e c i e s c o m p o s i t i o n , these d i s c r e t e t h i c k e t clumps are s t i l l very d i v e r s e . Whi le most s p e c i e s f a l l below the 4 - 5 meter C r o t o n h e i g h t , s p e c i e s such as Haploce lum f o l i o l o s u m , P l e a a f r i c a n a , Tarenna g r a v e o l e n s , and T e c l e a t r i c h o c a r p a a t t a i n h e i g h t s up t o . 6 and 7 m e t e r s . In the lower l a y e r Acac i a b r e v i s p i c a , C o r d i a o v a l i s , Grewia t r i c h o c a r p a , Rhus n a t a l e n s i s , and S t r y c h n o s h e n n i n g s i i are found . T h i s community i s f r e q u e n t l y marked by one or more a d u l t G a r d e n i a j o v i s - t o n a n t i s t r e e s which occur 10 - 15 meters from the t h i c k e t edge and are never found i n s i d e the t h i c k e t s p r o p e r . T h i s community, r e f e r r e d to as " l i o n bush" by D a r l i n g (1960), i s c u r r e n t l y a p r i m a r y source of shade, dry season browse, and cover for many an imal s i n the M a r a . T h i s heavy use and repeated f i r e s have l e d to i n t e r n a l t h i n n i n g of the canopy cover and area l o s s i n recent y e a r s (Chapter 2 ) . B a l a n i t e s a e g y p t i a c a woodlands occur o n l y i n the f a r western s e c t i o n of the M a r a . T h i s community, a l s o r e f e r r e d to as B a l a n i t e s - Acac i a s e y a l woodland ( T a i t i 1973, H e r l o c k e r 57 1976b, Lamprey 1985), i s p r e v a l e n t on the open, g r a s s y , p a r k - l i k e expanses of the Mara T r i a n g l e a r e a . T a i t i (1973) r e p o r t e d a d e c l i n e in the d e n s i t y of B a l a n i t e s s tands in t h i s area which G l o v e r and Trump (1970) and Pe l l ew (1981) a t t r i b u t e d to heavy browsing by g i r a f f e , s t i l l apparent t o d a y . The m a j o r i t y of r emain ing a d u l t t r e e s are w e l l above the browsing reach of g i r a f f e s and e l e phant s and r e g e n e r a t i o n may be l i m i t e d both by seed p r e d a t o r s (Lamprey et a_l. 1974, Pe l l ew and Southgate 1 984) and browsers (Be l sky 1984, Chapter 5 ) . A l s o on the west s i d e i s a band of r i v e r i n e f o r e s t which f o l l o w s the course of the Mara R i v e r from Mara Serena n o r t h and o c c u r s i n s m a l l , d i s c r e t e pa tches to the south a l o n g the r i v e r . T h i s t h i c k and d i v e r s e f o r e s t has been a l t e r e d over the pas t 20 y e a r s . Though i t s b o r d e r s have s c a r c e l y changed, i t s f o r m e r l y c l o s e d , 1 5 - 2 0 meter canopy i s now marked wi th l a r g e l i g h t gaps c r e a t e d by the l o s s of l a r g e t r e e s . The causes for these l o s s e s are n e i t h e r we l l -documented nor u n d e r s t o o d . However, i t i s b e l i e v e d t h a t s m a l l e r t r e e s may have been removed by e l e p h a n t s , wh i l e t a l l e r t r e e s may have succumbed to d i s e a s e or merely s enesced . E l e p h a n t s have a l s o e f f e c t i v e l y t h i n n e d the u n d e r s t o r y of these f o r e s t s l e a v i n g those s p e c i e s which are not h i g h l y p r e f e r r e d as f o o d . The p r i m a r y canopy t r e e s are A l b i z i a p e t e r s i a n a , D i o s p y r o s a b y s s i n c a , E u c l e a d i v i n o r u m , and Warburgia u q a n d e n s i s . Others i n c l u d e : C a s s i n e buchanani i , E k e b e r g i a r u e p p e l i n a , Syzyqium cordatum, Pappea . c a p e n s i s , Phoenix r e c l i n a t a and the o c c a s i o n a l Podocarpus and F i c u s t r e e s . The u n d e r s t o r y has an e q u a l l y d i v e r s e shrub component i n c l u d i n g : C a r i s s a e d u l i s , Chaetacme a r i s t a t a , C r o t o n dichoqamus, Grewia 58 t r i c h o c a r p a , P h y l l a n t h u s s e p i a l i s, T e c l e a t r i c h o c a r p a , and Z i z i p h u s mucronata . The Mara i s compr i sed of a combinat ion of e d a p h i c a l l y - d e r i v e d and f i r e - i n d u c e d g r a s s l a n d s dominated by the p e r e n n i a l g r a s s , Themeda t r i a n d r a , "red oat g r a s s " . F o l l o w i n g the long r a i n s o ther t a l l g r a s s e s such as D i g i t a r i a m a c r o b l e p h a r a , H y p a r r h e n i a f i l i p e n d u l a , Pennisetum mezianum, and S e t a r i a s p h a c e l a t a a l s o f lower i n these g r a s s l a n d s . The o v e r a l l g r a s s p r o d u c t i v i t y i s h i g h , r a n g i n g from 7,000 - 8,000 k g / h a / y r ( S i n c l a i r 1975, McNaughton 1979). The m i g r a t o r y zebra and w i l d e b e e s t may remove 80 - 90 % of the s t a n d i n g c r o p biomass (McNaughton 1976, S t e l f o x et a l . 1986) be fore r e t u r n i n g south to the S e r e n g e t i . The s h o r t - c r o p p e d p l a i n s they l eave beh ind then permi t the growth and f l o w e r i n g of o t h e r , l e s s compet i tve g r a s s e s such as A r i s t i d a a d o e n s i s , E r a q r o s t i s t e n u i f o l i a , E . racemosa, Harpachne s c h i m p e r i , and Sporobo lus s t a p f i a n u s . Geology and Hydro logy The h y d r o l o g y of the Mara was d e s c r i b e d i n d e t a i l by G l o v e r (1966) . The Mara R i v e r , the l a r g e s t p e r e n n i a l r i v e r i n the S e r e n g e t i - M a r a ecosys tem, d r a i n s the n o r t h e r n S e r e n g e t i and Mara r e g i o n and f lows i n t o Lake V i c t o r i a some 100 km to the west . The Mara R i v e r o r i g i n a t e s i n the Mau Range to the n o r t h and i s fed by s e v e r a l major t r i b u t a r i e s a long i t s c o u r s e . These i n c l u d e : the T a l e k R i v e r which a r i s e s in the S i a n a h i l l s and L o i t a p l a i n s , the O l a r e Orok and J a g a r t i e k watercourses which d r a i n the Lemek v a l l e y to the n o r t h and j o i n the T a l e k R i v e r 59 c l o s e t o i t s c o n f l u e n c e w i t h t h e M a r a R i v e r , a n d t h e S a n d R i v e r w h i c h o r i g i n a t e s i n t h e L o i t a H i l l s t o t h e e a s t a n d j o i n s t h e M a r a a l o n g t h e K e n y a - T a n z a n i a b o r d e r . T h e s e r i v e r s o f t e n f l o w y e a r - r o u n d b u t i n d r y y e a r s become a s e r i e s o f s m a l l p o o l s . W i l l i a m s ( 1 9 6 4 ) h a s d e s c r i b e d t h e M a r a r e g i o n a s an e x t e n s i v e p e n e p l a i n c o m p r i s e d o f m e t a m o r p h o s e d p r e - C a m b r i a n s e d i m e n t s w h i c h h a v e b e e n m o d i f i e d o v e r t i m e by f a u l t i n g , e r o s i o n , a n d v o l c a n i c a c t i v i t y . S o i l s i n t h e a r e a a r e m a i n l y o f v o l c a n i c o r i g i n a n d r a n g e f r o m b r o w n , s a n d y l o a m s t o b l a c k s i l t s o i l s . B e l o w t h i s s h a l l o w l a y e r o f v o l c a n i c t u f f s l i e s a b a s e m e n t s y s t e m o f g n e i s s e s , s c h i s t s , a n d q u a r t z i t e s . The m o s t s i g n i f i c a n t r e l i e f i n t h e a r e a i s t h e S i r i a E s c a r p m e n t w h i c h f o r m s t h e w e s t e r n b o u n d a r y o f t h e M a r a a n d r i s e s 1 0 0 - 3 0 0 m e t e r s a b o v e t h e p l a i n s b e l o w . Mean e l e v a t i o n i n t h e M a r a i s a p p r o x i m a t e l y 1600 m e t e r s on t h e p l a i n s w i t h t h e e s c a r p m e n t r i s i n g t o 1900 m e t e r s . M e t h o d s H a b i t a t s e l e c t i o n by e l e p h a n t s was d e t e r m i n e d u s i n g two i n d e p e n d e n t t e c h n i q u e s . T h e f i r s t , t o t a l a e r i a l c o u n t s , was u s e d t o d i s t i n g u i s h s e l e c t i o n o n l y on a we t a n d d r y s e a s o n b a s i s , w h e r e a s t h e s e c o n d , m o n t h l y c e n s u s c i r c u i t s , a l l o w e d an a n a l y s i s o f h a b i t a t s e l e c t i o n b o t h by s e a s o n a n d by s e x . 60 Wet and Dry Season T o t a l Counts of E l e p h a n t s Two wet season ( l a t e A p r i l 1984 and e a r l y May 1985) and one d r y season t o t a l counts of e l e p h a n t s ( l a t e October 1984) were conducted in the n o r t h e r n S e r e n g e t i N a t i o n a l P a r k , T a n z a n i a , and the e n t i r e Masai Mara Game R e s e r v e , Kenya . Herds were counted and mapped on a l l three f l i g h t s but o c c u r r e n c e by h a b i t a t was r e c o r d e d on ly on the October 1984 and May 1985 c o u n t s . Dense ly wooded areas were searched more i n t e n s i v e l y than open areas to c o r r e c t f or the r e l a t i v e v i s i b i l i t y of e l e p h a n t s i n d i f f e r e n t h a b i t a t s . To t e s t the h y p o t h e s i s t h a t e l e p h a n t s were randomly d i s t r i b u t e d i n the a v a i l a b l e h a b i t a t s , the t o t a l number of e l e p h a n t s observed i n each h a b i t a t type was compared to an expected frequency d i s t r i b u t i o n . T h i s expected frequency d i s t r i b u t i o n was d e r i v e d from a photo mosaic produced from an a e r i a l survey of the area in e a r l y 1982 by the Kenya Rangelands E c o l o g i c a l M o n i t o r i n g U n i t . These photographs were at a s c a l e of 1:50,000, l a r g e enough to d i s t i n g u i s h h a b i t a t types on them. A l l h a b i t a t types d i s t i n g u i s h e d on the photographs were checked on the ground u s i n g a 1:50,000 t o p o g r a p h i c map of the Reserve to r e l o c a t e the a r e a s . T h i r t y l i n e t r a n s e c t s were drawn on the p h o t o g r a p h i c mosaic and a n a l y z e d f o r the p r o p o r t i o n s of d i f f e r e n t h a b i t a t s . These p r o p o r t i o n s p r o v i d e d the t h e o r e t i c a l random d i s t r i b u t i o n for e l e p h a n t s i f they showed no h a b i t a t s e l e c t i o n (Table 3 . 1 ) . For the purpose of a n a l y s i s these expec ted d i s t r i b u t i o n s were c o n v e r t e d to numbers, based on the observed sample s i z e . C h i - s q u a r e a n a l y s i s was then used to compare the observed v e r s u s the expected numbers a c r o s s a l l Table 3.1. Percent of each habitat type measured from a e r i a l photography of the Masai Mara Game Reserve flown i n 1982 and monthly census c i r c u i t s . These percentages were used to calculate the number of elephants to be expected i n each habitat type under a random d i s t r i b u t i o n . HABITAT TYPE GRASSLAND RELICT ACACIA CROTON BALANITES THICKET WOODLAND THICKET WOODLAND SWAMP OTHER Aerial Photography (%) 41 29 Monthly Circuits (%) 43 34 62 h a b i t a t t y p e s . Monthly Census C i r c u i t s A 152 km. c i r c u i t was e s t a b l i s h e d w i t h i n the R e s e r v e . I n i t i a l l y , the e n t i r e c i r c u i t was d r i v e n and the h a b i t a t types which i n t e r s e c t e d t h i s c i r c u i t were mapped to the n e a r e s t 0.1 km. (Tab le 3 . 1 ) . The c u m u l a t i v e l e n g t h of each h a b i t a t type was then expres sed as a p r o p o r t i o n of the t o t a l c i r c u i t l e n g t h . From these p r o p o r t i o n s a random frequency d i s t r i b u t i o n f o r e l e p h a n t s by h a b i t a t was p r o d u c e d . U s i n g the observed sample s i z e s of e l e p h a n t s , t h i s f requency d i s t r i b u t i o n was then c o n v e r t e d to numbers which a l l o w e d a comparison of expec ted w i t h observed numbers of males and females in each h a b i t a t type f o r each month. T h i s c i r c u i t was d r i v e n once each month from November 1983 through May 1985. T h i s p e r i o d encompassed the 1983-84 wet season and the 1984 dry season . A l l e l e p h a n t s observed from the v e h i c l e were r e c o r d e d by age, sex, and the h a b i t a t i n which they were seen . V i s i b i l i t y from the c i r c u i t was e x c e l l e n t and the s i g h t a b i l i t y of e l e p h a n t s i n the d i f f e r e n t h a b i t a t s was assumed to be e q u a l . C h i - s q u a r e a n a l y s i s was a g a i n used to compare the observed numbers of males and females by h a b i t a t type to the expected numbers for both the wet and d r y seasons and to compare the sexes w i t h i n each season . 63 R e s u l t s H a b i t a t S e l e c t i o n S e v e n h u n d r e d a n d e i g h t y - f i v e e l e p h a n t s w e r e c o u n t e d i n t h e d r y s e a s o n a n d 912 i n t h e we t s e a s o n . E l e p h a n t s s u r v e y e d d u r i n g t h e a e r i a l c o u n t s w e r e n o t d i s t r i b u t e d r a n d o m l y w i t h r e g a r d t o h a b i t a t t y p e i n e i t h e r s e a s o n ( s e a s o n a l x 2 v a l u e s : wet = 1 2 6 . 3 , d r y = 3 4 7 . 7 , d . f . = 6 , P < . 0 0 1 ) . T h e y s h o w e d d i s t i n c t h a b i t a t p r e f e r e n c e s ( F i g u r e 3 . 3 ) : i n t h e wet s e a s o n e l e p h a n t s s e l e c t e d g r a s s l a n d s , s w a m p s , a n d C r o t o n t h i c k e t s more t h a n e x p e c t e d by r a n d o m u s e . I n t h e d r y s e a s o n o n l y C r o t o n t h i c k e t s w e r e s e l e c t e d . A l l o t h e r h a b i t a t s c o n t a i n e d f e w e r e l e p h a n t s t h a n e x p e c t e d . T h e s e p a t t e r n s w e r e s i m i l a r t o t h o s e r e c o r d e d on t h e m o n t h l y c e n s u s c i r c u i t s ( F i g u r e s 3 . 4 a n d 3 . 5 ) . B o t h s e x e s s h o w e d n o n - r a n d o m u s e o f h a b i t a t s i n b o t h s e a s o n s ( x 2 v a l u e s f o r m a l e s : we t = 1 1 . 5 , number o f m a l e s (n ) = 1 1 1 , P < . 0 5 , d r y = 1 4 . 3 , n = 2 5 , P < . 0 2 5 , d . f . = 5 , x 2 v a l u e s f o r f e m a l e s : we t = 1 3 . 9 , n = 2 4 7 , P < . 0 2 5 , d r y = 3 8 . 9 , n = 1 1 6 , P < . 0 0 1 , d . f . = 5 ) . F e m a l e s s e l e c t e d g r a s s l a n d s a n d C r o t o n t h i c k e t s i n t h e we t s e a s o n w h e r e a s m a l e s s e l e c t e d g r a s s l a n d s a n d r e l i c t t h i c k e t s . I n t h e d r y s e a s o n m a l e s a n d f e m a l e s b o t h c h o s e C r o t o n t h i c k e t s a n d A c a c i a w o o d l a n d s more t h a n e x p e c t e d by r a n d o m d i s t r i b u t i o n . M a l e s a n d f e m a l e s d i d n o t d i f f e r s i g n i f i c a n t l y i n t h e i r d i s t r i b u t i o n s i n e i t h e r t h e we t ( x 2 = 8 . 0 , d . f . = 5 , n . s . ) o r d r y s e a s o n ( x 2 = 4 . 9 , d . f . = 5 , n . s . ) . S e a s o n a l d i f f e r e n c e s w e r e s i g n i f i c a n t f o r m a l e s ( x 2 = 3 3 . 2 , d . f . = 5 , P < . 0 0 1 ) a n d f e m a l e s ( x 2 = 5 8 . 7 , d . f . = 5 , P < . 0 0 1 ) . F i g u r e s 3 . 4 a n d 3 . 5 1-1 GR = grassland T l T n r r RT = relict thicket W L J AW = Acacia woodland CT = Croton thicket BW = Balanites woodland SW = swamp OT = other habitat types GR RT AW CT BW SW OT - l - - 2 J DRY GR RT AW CT BW SW OT HABITAT TYPE The h a b i t a t preferences of elephants i n the Masai Mara Game Reserve i n the wet and dry seasons. The expected values are c a l c u l a t e d from a breakdown of the Reserve by h a b i t a t type using the 1982 t o t a l a e r i a l photography. The observed numbers were taken from a e r i a l counts flown i n both seasons. Notes : 1) Values greater than zero i n d i c a t e h a b i t a t s used more than expected i f elephants were randomly d i s t r i b u t e d , while those values l e s s than zero are h a b i t a t s used l e s s than expected and 2) * = those h a b i t a t types i n which elephants were expected but were not seen. 65 GR = grassland In RT = relict thicket AW = Acacia woodland CT = Croton thicket BW = Balanites woodland OT = other habitat types FEMALES o feJU , O -1 GR RT AW CT BW OT In MALES W X O g£ W C O C D , , 0 CuD O - 1 J GR RT AW CT BW OT HABITAT TYPE F i g u r e 3.4. Dry season h a b i t a t preferences of male and female elephants i n the Masai Mara Game Reserve. The expected values were c a l c u l a t e d from a breakdown of the monthly c i r c u i t by ha b i t a t type. The observed numbers were der i v e d from censuses d r i v e n on t h i s c i r c u i t each month. Note : Values greater than zero i n d i c a t e h a b i t a t s used more than expected i f elephants were randomly d i s t r i b u t e d , while those values l e s s than zero are h a b i t a t s used l e s s than expected. 66 , v GR = grassland Q 1 -i RT = relict thicket AW = Acacia woodland CT = Croton thicket BW = Balanites woodland OT = other habitat types FEMALES o OjO 4 O -1 GR RT AW CT BW OT I n 0 MALES GR RT AW CT BW OT HABITAT TYPE Figure 3 . 5 . Wet season h a b i t a t preferences of male and female elephants i n the Masai Mara Game Reserve. The expected values were c a l c u l a t e d from a breakdown of the monthly c i r c u i t by ha b i t a t type. The observed numbers were der i v e d from censuses d r i v e n on t h i s c i r c u i t each month. Note : Values greater than zero i n d i c a t e h a b i t a t s used more than expected i f elephants were randomly d i s t r i b u t e d , while those values l e s s than zero are h a b i t a t s used l e s s than expected. 67 i l l u s t r a t e the g e n e r a l p a t t e r n of these d i f f e r e n c e s . Both males and females p r e f e r r e d g r a s s l a n d s d u r i n g the wet season and Acac i a woodlands and C r o t o n t h i c k e t s i n the dry s e a s o n . Group S i z e S e a s o n a l v a r i a t i o n i n group s i z e was c a l c u l a t e d from count d a t a . Average herd s i z e i n the wet season was 22.5 i n d i v i d u a l s / g r o u p and i n the dry season i t was 13.2 i n d i v i d u a l s / g r o u p . These averages d i f f e r e d s i g n i f i c a n t l y (t = 2 .84 , d . f . = 102, P< .01) . However, even the l a r g e r wet season herds i n the Mara never reached numbers such as the 700 r e c o r d e d i n s e a s o n a l a g g r e g a t i o n s i n Tsavo (Laws 1969) or the 400 i n Ambose l i (Western and L i n d s a y 1985) N a t i o n a l P a r k s . The l a r g e s t r e c o r d e d wet season a g g r e g a t i o n was 158 an imals and the l a r g e s t dry season group on ly 40. C o w - c a l f herds which were accompanied by a d u l t males averaged 14.8 i n d i v i d u a l s . Those herds w i t h on ly f emales , s u b a d u l t s , and c a l v e s averaged 7.5 and a l l - b u l l groups averaged 1.9 on a y e a r - r o u n d b a s i s . Mean group s i z e d i d v a r y between seasons (Tab le 3 . 2 ) . In g e n e r a l herds were l a r g e r in a l l h a b i t a t types i n the wet season , whereas l i t t l e d i f f e r e n c e o c c u r r e d between h a b i t a t s w i t h i n a season . There was no s i g n i f i c a n t c o r r e l a t i o n between average h e r d s i z e and average numbers per h a b i t a t type f o r e i t h e r the wet (r = 0 .43 , n = 8, n . s . ) or dry season (r = 0 .54, s s n = 8, n . s . ) . The l a r g e s t groups were seen i n r e l i c t t h i c k e t s , Acac i a woodlands, E u c l e a t h i c k e t s and g r a s s l a n d s i n the wet s eason . Table 3.2 Average herd sizes for each habitat type i n the wet and dry seasons. Number i n parentheses i s the number of herds observed i n each habitat type during the monthly census c i r c u i t s summed over the entire season. HABITAT TYPE GRASSLAND RELICT ACACIA CROTON SWAMP THICKET WOODLAND THICKET Wet Season 11.6 (38) 11.8 (94) 14.5 (15) 10.2 (40) 9.2 (13) Dry Season 8.9 (38) 7.4 (46) 6.0 (25) 9.6 (40) 7.8 (22) 69 D i s c u s s i o n H a b i t a t S e l e c t i o n The M a s a i M a r a Game R e s e r v e h a s e x p e r i e n c e d v e g e t a t i o n c h a n g e s i n t h e p a s t 30 y e a r s ( D u b l i n 1 9 8 4 ) . The m a j o r r e s u l t o f t h e s e c h a n g e s h a s b e e n a s i g n i f i c a n t r e d u c t i o n i n A c a c i a w o o d l a n d s a n d a t h i n n i n g o f r i v e r i n e f o r e s t s . A t t h e p r e s e n t t i m e t h e M a r a i s l a r g e l y a w i d e , o p e n g r a s s l a n d c o n t a i n i n g few s u r v i v i n g s t a n d s o f A c a c i a w o o d l a n d a n d p a t c h e s o f C r o t o n t h i c k e t a n d h i g h c a n o p y r i v e r i n e f o r e s t s a l o n g t h e M a r a R i v e r . R e s i d e n t e l e p h a n t s w h i c h h a v e b e e n l a r g e l y p r e v e n t e d f r o m u s i n g t h e i r h i s t o r i c a l s e a s o n a l m i g r a t i o n r o u t e s a r e now l i v i n g i n t h e R e s e r v e y e a r - r o u n d a n d t h e i r i m p a c t s on t h e r e m a i n i n g w o o d l a n d h a b i t a t s a r e p r o n o u n c e d ( C h a p t e r 5 ) . E l e p h a n t s i n t h e M a r a a t e woody s p e c i e s o f a l l s o r t s , a n d t h e i r u s e o f s h r u b s a n d t r e e s i n c r e a s e d s i g n i f i c a n t l y when d r y c o n d i t i o n s p r e v a i l e d ( C h a p t e r 4 ) . F a c i n g an a l r e a d y r e d u c e d a v a i l a b i l i t y o f b r o w s e f o r a g e a n d s h a d e t r e e s , e l e p h a n t s h a v e b e g u n c o n c e n t r a t i n g t h e i r t i m e w i t h i n t h e C r o t o n t h i c k e t s . T h e s e t h i c k e t s w h i c h a r e u n i q u e t o t h e n o r t h e r n S e r e n g e t i a n d M a r a r e g i o n a r e d i s c r e t e i s l a n d s o f b u s h s i t t i n g on h i l l t o p s a n d i n r i v e r d r a i n a g e s s c a t t e r e d a c r o s s t h e R e s e r v e . W i t h t h e s i g n i f i c a n t l o s s o f o t h e r w o o d l a n d h a b i t a t s i n t h e M a r a o v e r t h e p a s t t h r e e d e c a d e s , t h e s e t h i c k e t s now p r o v i d e one o f t h e l a s t w o o d e d r e f u g e s a v a i l a b l e t o e l e p h a n t s . H e r e t h e y a r e a b l e t o f i n d s h a d e , a n d a l s o t o f o r a g e on woody s p e c i e s , a n d h e r b s w h i c h t h r i v e i n t h e m o i s t , s h a d y c o n d i t i o n s w i t h i n t h e s e t h i c k e t s . C o n s e q u e n t l y , damage t o t h e i n t e r n a l s t r u c t u r e o f t h e C r o t o n 70 t h i c k e t s has become e x t e n s i v e . Many Croton bushes are shredded , t h e i r mainstems are s p l i t and b r o k e n . More p r e f e r r e d s p e c i e s w i t h i n these t h i c k e t s , such as Acac i a b r e v i s p i c a , are browsed to w i t h i n 10 cm of the ground (presumably t h i s i s the lower h e i g h t l i m i t of the e l e p h a n t s ' f o r a g i n g a b i l i t y ) . T h i s c o n s t a n t use of C r o t o n t h i c k e t s for food and shade has opened l a r g e pathways through the v e g e t a t i o n . In subsequent r a i n y seasons , these l i g h t gaps grow t h i c k swards of gras s ( N o r t o n - G r i f f i t h s 1979). Most g r a z e r s a v o i d the r i s k of h idden p r e d a t o r s i n t h i c k e t s so t h i s g r a s s i s f r e q u e n t l y l e f t to dry and form l i t t e r i n the herb l a y e r . When f i r e s occur i n the Reserve these g r a s s pathways through the t h i c k e t s burn very h o t l y and d e s t r o y the t r e e s and bushes a long t h e i r b o u n d a r i e s . As the y e a r s p r o g r e s s these t h i c k e t s become fragmented - l i k e p i e s b e i n g cu t and removed i n ever s m a l l e r p i e c e s . Acac i a woodlands have been s u b j e c t e d to s i m i l a r p r e s s u r e s , p r i m a r i l y from e l ephant b u l l s , but o c c a s i o n a l l y from c o w - c a l f groups as w e l l . Most Acac i a woodlands i n the Mara are comprised of t r e e s which are too s m a l l to be used for shade . However, in u n u s u a l l y dry seasons , b u l l s spend a l o t of t ime in these woodlands and feed h e a v i l y on the t r e e s ( L i n d s a y 1982, Western and L i n d s a y 1985, Chapter 4 and 5 ) . In the drought of 1984, a herd of a p p r o x i m a t e l y 6 b u l l e l e p h a n t s v i s i t e d a 2 s q . km. mature Acac i a s tand near E m a r t i . W i t h i n 24 hours they had l e f t 34% of the t r e e s dead or f a t a l l y damaged and another 22% w i t h many broken b r a n c h e s . Other s tands e x p e r i e n c e d s i m i l a r damage d u r i n g t h i s v e r y d r y p e r i o d . E lephant damage to r i v e r i n e f o r e s t s was s i m i l a r , a l l l ow-growing v e g e t a t i o n was removed. 71 Now these f o r e s t s are compr i sed p r i m a r i l y of t a l l canopy t r e e s whose l e a v e s are w e l l out of the reach of e l e p h a n t s . Many t r e e s are b e g i n n i n g to d i e . A l t h o u g h the cause of these l o s s e s i s not c e r t a i n they are most l i k e l y due to d i s e a s e or o l d age . But the e f f e c t s of t r a m p l i n g by l a r g e mammals may a l s o be i m p l i c a t e d in the compact ion of s o i l and the d e s t r u c t i o n of f i n e s u r f a c e r o o t s . Newly-formed l i g h t gaps l e f t by f a l l e n canopy t r e e s would p r o v i d e a good o p p o r t u n i t y for f o r e s t r e g e n e r a t i o n but w i l l p r o b a b l y s u f f e r heavy p r e s s u r e from e lephant b r o w s i n g . E l e p h a n t s do u t i l i z e the g r a s s l a n d s i n the R e s e r v e . T h e i r p r e f e r r e d s p e c i e s i s Cynodon d a c t y l o n , a gras s which grows in l o w - l y i n g a r e a s , o f t en inundated by s u r f a c e water . The Mara g r a s s l a n d s , however, are p r i m a r i l y composed of Themeda t r i a n d r a . The Cynodon areas are l i m i t e d i n ex tent and are a l s o used by the m i g r a t o r y w i l d e b e e s t and zebra a f t e r the i n i t i a l s t a n d i n g c r o p of Themeda has been removed. The sheer number of w i l d e b e e s t presen t d u r i n g the dry season p r o b a b l y d i s p l a c e s e l e p h a n t s from Cynodon a r e a s . Dry c o n d i t i o n s a lone can l e a d to e x t e n s i v e use of woodland areas by e l e p h a n t s and subsequent e x t e n s i v e damage. The a d d i t i o n a l f a c t o r of the compet ing m i g r a t o r y w i l d e b e e s t d u r i n g the d r y season exacerbate s the s i t u a t i o n (Chapter 4 ) . Mara e l e p h a n t s may s e l e c t h a b i t a t s based on the a v a i l a b i l i t y of p r e f e r r e d forage t y p e s . T h e i r f o r a g i n g h a b i t s , as de termined through d i r e c t o b s e r v a t i o n , i n d i c a t e t h a t they feed on g r a s s e s and herbs immediate ly f o l l o w i n g the r a i n s and s w i t c h to a browse d i e t i n the dry season when a d e c l i n e i n the q u a l i t y and q u a n t i t y of herbaceous s p e c i e s o c c u r s . The d i s t r i b u t i o n of these forage types i n d i f f e r e n t h a b i t a t s 72 p r o b a b l y d i c t a t e s t h e p a t t e r n s o f h a b i t a t s e l e c t i o n b e t w e e n s e a s o n s . T h i s i s c o n s i s t e n t w i t h t h e f i n d i n g s o f L e u t h o l d a n d S a l e ( 1 9 7 3 ) , L e u t h o l d ( 1 9 7 7 a ) , a n d W e s t e r n a n d L i n d s a y ( 1 9 8 5 ) who f o u n d t h a t s e a s o n a l m o v e m e n t s w e r e l a r g e l y d e t e r m i n e d by t h e d i s t r i b u t i o n o f f o r a g e q u a l i t y a n d q u a n t i t y f o r e l e p h a n t s i n T s a v o a n d A m b o s e l i N a t i o n a l P a r k s i n K e n y a . What i s n o t q u a n t i t a t i v e l y e s t a b l i s h e d f o r M a r a e l e p h a n t s i s w h e t h e r t h e i r c h o i c e o f h a b i t a t s i s m o s t s i g n i f i c a n t l y c o r r e l a t e d w i t h f o r a g e q u a n t i t y , f o r a g e q u a l i t y , some c o m b i n a t i o n o f t h e two f a c t o r s , o r o t h e r f a c t o r s s u c h a s d i s t u r b a n c e . D u r i n g t h e r a i n s when f o r a g e o f a l l t y p e s was a b u n d a n t , M a r a e l e p h a n t s w e r e p r i m a r i l y g r a z e r s , l i k e t h o s e i n o t h e r p o p u l a t i o n s ( F i e l d 1 9 7 1 , F i e l d a n d R o s s 1 9 7 6 , Guy 1 9 7 6 , B a r n e s 1 9 8 2 , W e s t e r n a n d L i n d s a y 1 9 8 5 ) . M a r a e l e p h a n t s s e l e c t e d o p e n g r a s s l a n d s , s w a m p s , a n d C r o t o n t h i c k e t s d u r i n g t h e we t s e a s o n . T h i s i s c o n s i s t e n t w i t h t h e i d e a t h a t f o r a g e q u a l i t y i s t h e d e t e r m i n i n g f a c t o r i n h a b i t a t c h o i c e b e c a u s e t h e new g r a s s e s a n d s p r o u t i n g s e e d l i n g s g r o w i n g i n t h e s e a r e a s a r e h i g h l y n u t r i t i o u s . A l t h o u g h new b r o w s e l e a v e s may h a v e h i g h e r a b s o l u t e c r u d e p r o t e i n l e v e l s t h a n new g r a s s e s (We inmann 1 9 5 9 , D o u g a l l 1 9 6 3 , D o u g a l l a n d G l o v e r 1 9 6 4 , D o u g a l l e t a l . 1 9 6 4 , F i e l d a n d R o s s 1 9 7 6 , M c N a u g h t o n e t a_ l . 1 9 8 5 ) , t h e y may a l s o c o n t a i n h i g h l e v e l s o f s e c o n d a r y c o m p o u n d s s u c h a s t a n n i n s w h i c h may i n t e r f e r e w i t h f e e d i n g ( C o l e y 1 9 8 3 , S u k u m a r 1 9 8 5 ) . F o r t h e m o s t p a r t , t h e h a b i t a t s s e l e c t e d d u r i n g t h e we t s e a s o n w e r e d o m i n a t e d by g r a s s e s . U n l i k e A m b o s e l i e l e p h a n t s ( L i n d s a y 1 9 8 2 , P o o l e 1 9 8 2 ) , M a r a e l e p h a n t s f o l l o w e d a d r y s e a s o n f o r a g i n g p a t t e r n more l i k e t h a t 73 r e p o r t e d f o r e l e p h a n t s i n o ther s easona l areas such as Queen E l i z a b e t h and Kidepo V a l l e y N a t i o n a l P a r k s , Uganda ( F i e l d 1971, F i e l d and Ross 1976), Sengwa W i l d l i f e Research A r e a , Zimbabwe (Guy 1976), and Ruaha N a t i o n a l P a r k , T a n z a n i a (Barnes 1982). They swi tched to a p r e d o m i n a n t l y browse d i e t i n the dry season . D o u g a l l et a l . (1964), F i e l d (1971) and Barnes (1982) p o i n t e d out t h a t woody s p e c i e s m a i n t a i n e d h i g h e r crude p r o t e i n l e v e l s r e l a t i v e to gras se s d u r i n g w a t e r - l i m i t e d t i m e s . The n u t r i t i o n a l q u a l i t y of gras se s d e c l i n e s r a p i d l y as they beg in to age in the dry s eason . H a b i t a t c h o i c e s i n the dry season may r e f l e c t these forage p r e f e r e n c e s . E l e p h a n t s of both sexes were observed u t i l i z i n g C r o t o n t h i c k e t s and Acac i a woodlands . L e u t h o l d and Sa le (1973) suggested tha t e l ephant h a b i t a t s e l e c t i o n i n Tsavo N a t i o n a l Park was most ly l i m i t e d by the q u a n t i t y of food a v a i l a b l e and may be c o n s t r a i n e d f u r t h e r by the d i s t r i b u t i o n of permanent water sources which are c r i t i c a l to t h e i r s u r v i v a l , p a r t i c u l a r l y d u r i n g the dry season ( C o r f i e l d 1973). The f i n d i n g s of Western and L i n d s a y (1985) i n Ambosel i p a r t i a l l y supported t h i s i d e a . In the d r y season , Ambosel i e l e p h a n t s u t i l i z e d the swamps most h e a v i l y . These swamps were the lowest i n crude p r o t e i n ( q u a l i t y ) but the h i g h e s t i n forage biomass ( q u a n t i t y ) . However, e l e p h a n t s used the bushed- g r a s s l a n d h a b i t a t to a s i m i l a r extent i n the dry s eason . T h i s b u s h e d - g r a s s l a n d h a b i t a t was lowest i n a v a i l a b l e forage biomass but s i g n i f i c a n t l y h i g h e r than swamps i n a v a i l a b l e crude p r o t e i n . From t h i s ev idence and my f i n d i n g s i n the M a r a , i t seems l i k e l y tha t e l e p h a n t s may s e l e c t p r i m a r i l y on the b a s i s of forage q u a l i t y but may be l i m i t e d i n t h e i r c h o i c e by the amount of food 74 a v a i l a b l e w i t h i n t h e i r r a n g e o f m o v e m e n t . The r e l a t i v e i m p o r t a n c e o f q u a l i t y v e r s u s q u a n t i t y may be m e d i a t e d by l o c a l e l e p h a n t d e n s i t i e s . I n a r e a s o f h i g h d e n s i t y , e l e p h a n t s may be more r e s t r i c t e d by t h e a b s o l u t e q u a n t i t y o f a v a i l a b l e f o o d , r e g a r d l e s s o f t h e n u t r i t i o n a l v a l u e o f t h e t y p e o f f o r a g e e a t e n o r h a b i t a t i n w h i c h i t i s f o u n d . I n t h e M a r a , w h e r e e l e p h a n t d e n s i t i e s a r e n o t c o n s i d e r e d t o be h i g h , t h e i r c h o i c e o f h a b i t a t s may be i n f l u e n c e d t o a g r e a t e r e x t e n t by f o r a g e q u a l i t y t h a n q u a n t i t y a s t h e y a p p e a r t o be i n A m b o s e l i , w h e r e l o c a l d e n s i t i e s a r e much h i g h e r . G r o u p S i z e I t i s p o s s i b l e t h a t e l e p h a n t s f o r m a g g r e g a t i o n s a s a d i r e c t c o n s e q u e n c e o f t h e n u m b e r s i n a h a b i t a t ( i . e . p r e f e r r e d h a b i t a t s s u p p o r t h i g h e r n u m b e r s a n d d e n s i t i e s a n d , t h e r e f o r e , l a r g e r h e r d s i z e s a r e f o u n d ) . H o w e v e r , t h e d a t a do n o t s u p p o r t t h i s h y p o t h e s i s . I n f a c t , t h e r e was no c o r r e l a t i o n b e t w e e n e l e p h a n t n u m b e r s i n s p e c i f i c h a b i t a t s , a n d a v e r a g e g r o u p s i z e i n t h e s e same h a b i t a t s . G r o u p s i z e a p p e a r e d t o be d e t e r m i n e d by f a c t o r s o t h e r t h a n r a n d o m a g g r e g a t i o n s b a s e d on h a b i t a t p r e f e r e n c e . V a r i a t i o n i n mean h e r d s i z e h a s b e e n r e p o r t e d i n o t h e r s t u d i e s ( T a b l e 3 . 3 ) , b u t t h e a c t u a l d e t e r m i n a n t s o f g r o u p s i z e a r e n o t f u l l y u n d e r s t o o d . I n some a r e a s , p o a c h i n g a c t i v i t y h a s l e d t o l a r g e a g g r e g a t i o n s w h i c h d i d n o t show s e a s o n a l c h a n g e s ( L a w s e t a l . 1 9 7 5 , D o u g l a s - H a m i l t o n a n d H i l l m a n 1 9 8 1 ) . B u t , i n g e n e r a l , a v e r a g e h e r d s i z e d o e s seem t o be c o r r e l a t e d w i t h s e a s o n , l a r g e r h e r d s f o r m i n t h e we t s e a s o n when a v a i l a b i l i t y o f Table 3.3. Average herd sizes reported for a variety of African elephant populations. Table adapted from Laws (1969). LOCATION Tsavo National Park, Kenya Amboseli National Park, Kenya Murchison F a l l s National Park, Uganda Queen Elizabeth National Park, Uganda Luangwa Valley, Zambia Serengeti National Park, Tanzania (north) Serengeti National Park, Tanzania (south) Masai Mara Game Reserve, Kenya (wet season) Masai Mara Game Reserve, Kenya (dry season) AVERAGE GROUP SIZE SOURCE 13.5 Glover (1963) 13.0 Watson and B e l l (1969) 25.0 Western and Lindsay (1985 12.1 Buechner et a l . (1963) 12.0 Laws et a l . (1975) 5.9 Laws and Parker (1968) 3.9 Laws and Parker (1968) 52.0 Watson and B e l l (1969) 54.5 Dublin (unpubl. data) 19.0 Watson and B e l l (1969) 22.5 Dublin (unpubl. data) 13.2 Dublin (unpubl. data) 76 p r e f e r r e d f o r a g e i s g r e a t e r . The v a r i a t i o n i n a v e r a g e h e r d s i z e s r e c o r d e d f o r d i f f e r e n t e l e p h a n t p o p u l a t i o n s c o u l d , t h e r e f o r e , be t h e r e s u l t o f c o u n t s d o n e i n d i f f e r e n t s e a s o n s o r on p o p u l a t i o n s o f e l e p h a n t s e x p e r i e n c i n g d i f f e r e n t l e v e l s o f h u n t i n g p r e s s u r e . S e a s o n a l v a r i a t i o n i n h e r d s i z e h a s a l s o b e e n a t t r i b u t e d t o t h e s e a s o n a l i t y o f m a t i n g a n d b i r t h p e a k s . . E s t r u s a n d , h e n c e , m a t i n g o c c u r s d u r i n g o r s l i g h t l y a f t e r t h e p e a k o f t h e l o n g r a i n s ( H a n k s 1 9 6 9 , D u b l i n 1 9 8 3 , M o s s 1 9 8 3 , W e s t e r n a n d L i n d s a y 1 9 8 5 ) . A t t h i s t i m e m a l e s t e m p o r a r i l y j o i n c o w - c a l f h e r d s t o g a i n a c c e s s t o e s t r o u s f e m a l e s . B i r t h s t h e n f o l l o w a 2 2 - m o n t h g e s t a t i o n a n d o c c u r j u s t b e f o r e o r d u r i n g t h e r a i n s ( H a n k s 1 9 6 9 , W e y e r h a e u s e r 1 9 8 2 ) . M a r a e l e p h a n t h e r d s may show a s i m i l a r p a t t e r n ; t h e a v e r a g e s i z e o f h e r d s c o n t a i n i n g a d u l t m a l e s was c o n s i d e r a b l y l a r g e r t h a n e x c l u s i v e l y c o w - c a l f g r o u p s , a n d t h e a v e r a g e g r o u p s i z e o v e r a l l , was h i g h e r i n t h e wet s e a s o n . D o u g l a s - H a m i l t o n ( 1 9 7 2 ) , M o s s ( 1 9 8 1 ) , M o s s a n d P o o l e ( 1 9 8 3 ) , a n d W e s t e r n a n d L i n d s a y ( 1 9 8 5 ) h a v e a l l s u g g e s t e d t h a t s o c i a l b e n e f i t s may p r o v i d e a s t r o n g b a s i s f o r h e r d f o r m a t i o n . F o r e x a m p l e , e l e p h a n t s may a g g r e g a t e on a p e r i o d i c b a s i s a s a means o f m a i n t a i n i n g a n d s t r e n g t h e n i n g b o n d s o r e s t a b l i s h i n g d o m i n a n c e h i e r a r c h i e s w i t h i n k i n g r o u p s o r m e r e l y among i n d i v i d u a l s who may i n t e r a c t t h r o u g h o u t t h e i r l o n g l i v e s (Moss 1 9 8 1 , S . A n d e l m a n , p e r s . c o m m . ) . R e c e n t f i n d i n g s by K . P a y n e ( u n p u b l . d a t a ) s u g g e s t t h a t t h e l o w f r e q u e n c y s o u n d s a s s o c i a t e d w i t h c e r t a i n b e h a v i o r a l p a t t e r n s among e l e p h a n t s may a c t u a l l y be e x c h a n g e s o f i n f o r m a t i o n on l e v e l s p r e v i o u s l y u n r e c o g n i z e d . P e r i o d i c a g g r e g a t i o n s w o u l d p r o v i d e a n o p p o r t u n i t y f o r s u c h 77 e x c h a n g e s b e t w e e n i n d i v i d u a l s a n d h e r d s . L a w s e t a l . ( 1 9 7 5 ) c i t e d p r e d a t i o n on e l e p h a n t s a s a b a s i s f o r a g g r e g a t i o n . W e s t e r n a n d L i n d s a y ( 1 9 8 5 ) d i s c u s s e d t h e p o s s i b l e f o r a g i n g b e n e f i t s w h i c h l a r g e r g r o u p s may a c c r u e t h r o u g h t h e e x c h a n g e o f i n f o r m a t i o n o r t h r o u g h f a c i l i t a t i o n b u t e m p h a s i z e d t h a t t h e r e i s c u r r e n t l y no h a r d e v i d e n c e t o s u p p o r t t h e s e i d e a s . U n t a n g l i n g t h e r e l a t i v e c o n t r i b u t i o n s o f v a r i o u s f a c t o r s t o g r o u p f o r m a t i o n a n d t e n u r e i s a d i f f i c u l t t a s k . L a r g e r h e r d s seem t o be d e s i r a b l e f o r a v a r i e t y o f r e a s o n s b u t a r e p o s s i b l e o n l y when l o c a l f o o d s u p p l i e s a r e n o t l i m i t e d . I n an a n i m a l t h e s i z e o f a n e l e p h a n t , t h i s c o n d i t i o n c o u l d r e s t r i c t t h e f o r m a t i o n o f l a r g e g r o u p s t o t h e r a i n y s e a s o n o n l y . Summary I n s u m m a r y , M a r a e l e p h a n t s f i t t h e g e n e r a l p a t t e r n o f h a b i t a t s e l e c t i o n a n d g r o u p f o r m a t i o n o b s e r v e d i n o t h e r A f r i c a n e l e p h a n t p o p u l a t i o n s . B o t h s e x e s c h o s e h a b i t a t t y p e s w h i c h p r o d u c e d l a r g e q u a n t i t i e s o f n u t r i t i o u s g r a s s e s d u r i n g t h e we t s e a s o n , a n d b o t h s w i t c h e d t o o t h e r h a b i t a t s w h i c h p r o v i d e d b r o w s e v e g e t a t i o n i n t h e d r y s e a s o n . I n a d d i t i o n , a v e r a g e g r o u p s i z e was l a r g e r , i n v i r t u a l l y a l l h a b i t a t s , i n t h e wet s e a s o n t h a n i n t h e d r y . S e a s o n a l d i f f e r e n c e s i n h e r d s i z e w e r e n o t t h e r e s u l t o f r a n d o m a g g r e g a t i o n s f o r m i n g i n p r e f e r r e d h a b i t a t s , b u t w e r e m o r e l i k e l y an i n d i r e c t r e s u l t o f b u l l s j o i n i n g c o w - c a l f h e r d s t o b r e e d d u r i n g t h e r a i n s a n d h e r d s c o n g r e g a t i n g , when f o o d was n o t l i m i t e d , t o i n t e r a c t , t o d e t e r m i n e d o m i n a n c e h i e r a r c h i e s , a n d t o r e - e s t a b l i s h b o n d s . B e f o r e a n y p r o g r e s s c a n be made on a s i t e - s p e c i f i c c o u r s e 78 o f m a n a g e m e n t , i t i s e s s e n t i a l t h a t t h e l o c a l p a t t e r n s o f e l e p h a n t h a b i t a t u t i l i z a t i o n a n d t h e p o t e n t i a l i m p a c t s o f e l e p h a n t s on t h e s e h a b i t a t s be f u l l y u n d e r s t o o d . The a c t u a l m a g n i t u d e o f t h e i r e f f e c t s may be m o d i f i e d by l o c a l c o n d i t i o n s s u c h a s w e a t h e r , p o a c h i n g a c t i v i t y , o r t h e a c c e s s i b i l i t y o f s e a s o n a l m i g r a t o r y r o u t e s t o a l l o w d i s p e r s a l a n d a v o i d o v e r u t i l i z a t i o n o f h a b i t a t s . I n f u t u r e , t h e s e a n d o t h e r f a c t o r s mus t be t a k e n i n t o a c c o u n t when f o r m u l a t i n g p l a n s f o r t h e management o f e l e p h a n t p o p u l a t i o n s a n d p l a n t c o m m u n i t i e s i n p r o t e c t e d a r e a s . 79 CHAPTER 4. FEEDING ECOLOGY OF ELEPHANTS IN THE MASAI MARA GAME RESERVE I n t r o d u c t i o n The past 30 y e a r s have been a time of major change i n the woodland h a b i t a t s of e a s t , c e n t r a l , and southern A f r i c a . In many parks and r e s e r v e s , woodlands have d e c l i n e d . T h e o r e t i c a l e x p l a n a t i o n s for these changes have l e d to a grea t d e a l of c o n t r o v e r s y and much s p e c u l a t i o n (P ienaar 1969, Laws 1970, Caughley 1976). However, many r e s e a r c h e r s agree tha t the e x p o n e n t i a l growth of human p o p u l a t i o n s d u r i n g t h i s c e n t u r y i s l i n k e d to woodland l o s s . The subsequent expans ion of c u l t i v a t i o n and s e t t l ement has r e s u l t e d i n both c o n c e n t r a t i o n of e l e p h a n t s i n t o p r o t e c t e d a r e a s , and an i n c r e a s e in frequency of human-induced f i r e s . Both f i r e and e l e p h a n t s have p l a y e d r o l e s i n the documented woodland l o s s e s , though t h e i r r e l a t i v e c o n t r i b u t i o n i s in debate . Buss (1961), Lawton and Gough (1970), and N o r t o n - G r i f f i t h s (1979) have suppor ted the idea tha t f i r e p l a y e d the p r i m a r y r o l e in woodland l o s s , but most r e s e a r c h suppor t s the c o n v e r s e . E l e p h a n t s a r e w i d e l y thought to be the p r i m a r y i n i t i a t o r s of woodland change, w i t h f i r e s a c t i n g to m a i n t a i n the v e g e t a t i o n i n a g r a s s l a n d phase t h e r e a f t e r ( E g g e l i n g 1947, Buechner and Dawkins 1961, Brooks and Buss 1962, Lamprey et a l . 1967, Laws 1969, Wing and Buss 1970, F i e l d 1971, Spence and Angus 1971, H a r r i n g t o n and Ross 1974, Laws et a l . 1975, Thomson 1975, Guy 1976, F i e l d and Ross 1976, Barnes 1982, Smart et a l . 1985). The p o t e n t i a l s y n e r g i s t i c e f f e c t s of f i r e and e l e p h a n t s 80 have not yet been a n a l y s e d . Over the past 30 y e a r s , woodlands and t h i c k e t s i n the S e r e n g e t i - M a r a have been d i s a p p e a r i n g . S i m i l a r events have taken p l a c e over e a s t e r n , s o u t h e r n , and c e n t r a l A f r i c a , f o r example i n Tsavo N a t i o n a l P a r k , Kenya (Laws 1969, P a r k e r 1983), Ruaha (Savidge 1968, Barnes 1982, 1983) and Lake Manyara (Weyerhaeuser 1982) N a t i o n a l P a r k s , T a n z a n i a , Queen E l i z a b e t h and M u r c h i s o n F a l l s N a t i o n a l P a r k s , Uganda (Buss 1961, Buechner and Dawkins 1961, Brooks and Buss 1962, Buechner et a l . 1963, Buss and Savidge 1966, Laws and Parker 1968, F i e l d and Laws 1970, F i e l d 1971, Laws et a l . 1975, F i e l d and Ross 1976) and the Sengwa Research A r e a , Zimbabwe (Anderson and Walker 1974, Guy 1976, 1981). These changes have c o i n c i d e d w i t h i n t e n s i v e human se t t l ement on park boundar i e s and subsequent c o n c e n t r a t i o n of e l e p h a n t s from p e r i p h e r a l areas i n t o h a b i t a t s unable to support t h e i r numbers (Anderson 1973, Guy 1976, D u b l i n and D o u g l a s - H a m i l t o n , i n p r e s s ) . At the same t i m e , f i r e frequency has i n c r e a s e d due to both human a c t i v i t y and c l i m a t i c f a c t o r s ( L a n g r i d g e et a l . 1970, K u r j i 1976, N o r t o n - G r i f f i t h s 1979). The s e p a r a t e and s y n e r g i s t i c e f f e c t s of man- induced f i r e and e l e p h a n t s have been i m p l i c a t e d i n these h a b i t a t changes , b u t , u n t i l r e c e n t l y , l a c k of data has p r e v e n t e d an a c c u r a t e assessment of t h e i r r e l a t i v e i m p o r t a n c e . In t h i s s t u d y , e l ephant f e e d i n g behav iour was observed i n c o n j u n c t i o n wi th c o n t r o l l e d exper iments u s i n g browsing e x c l o s u r e s and v a r y i n g f i r e reg imes . I c o n s i d e r the e f f e c t s of these e x p e r i m e n t a l f i r e s and mammalian h e r b i v o r e s i n the s t r u c t u r i n g of woodland communit ies (Chapter 5 ) . D i r e c t 81 o b s e r v a t i o n of f r e e - r a n g i n g e l e p h a n t s c o v e r e d two and a h a l f y e a r s (1982-1985) i n the Masa i Mara Game Reserve where e l e p h a n t s were accustomed to humans and v e h i c l e s . I c o l l e c t e d data on male and female e l e p h a n t s wi thout d i s t u r b i n g t h e i r normal a c t i v i t i e s . T h i s s tudy i n v e s t i g a t e d how r e c e n t i n c r e a s e s i n the r e s i d e n t e l e phant p o p u l a t i o n may be i m p a c t i n g v e g e t a t i o n i n the Reserve and , whether c u r r e n t e l ephant f e e d i n g p a t t e r n s are p l a y i n g a r o l e in the i n h i b i t i o n of woodland r e g e n e r a t i o n . T h i s c h a p t e r d e s c r i b e s : a) s e a s o n a l and s e x u a l d i f f e r e n c e s i n d i e t c o m p o s i t i o n ; b) a b s o l u t e and r e l a t i v e d i e t d i v e r s i t y ; c) average l e n g t h of f o r a g i n g bout s ; and d) the c h a r a c t e r i s t i c s of p l a n t s i n the d i e t . Methods O b s e r v a t i o n s c o v e r e d t h r e e d r y seasons (June - October 1982, 1983, and 1984) and two wet seasons (November - May 1982- 83 and 1983-84) . Data f o r the wet season 1983-84 and the 1984 dry season are more complete than the p r e v i o u s seasons due to the l o s s of some o r i g i n a l d a t a . More than 500 o b s e r v a t i o n p e r i o d s of b u l l s and more than 1,000 of females were r e c o r d e d d u r i n g the s tudy (Table 4 . 1 ) . Each o b s e r v a t i o n p e r i o d c o n s i s t e d of an u n i n t e r r u p t e d b l o c k of 1 5 - 3 0 minutes w i t h each f o c a l a n i m a l . By c h o o s i n g a d i f f e r e n t i n d i v i d u a l f o r each o b s e r v a t i o n p e r i o d r a t h e r than f o l l o w i n g one i n d i v i d u a l a l l day , I a v o i d e d the p o t e n t i a l problem of i d i o s y n c r a t i c e l ephant f e e d i n g p a t t e r n s . S h o r t o b s e r v a t i o n p e r i o d s a l s o a l l o w e d more d i f f e r e n t i n d i v i d u a l s to be observed i n any g i v e n month. 82 Table 4.1. Study p e r i o d s , number of f o c a l animals, seasonal and mean monthly r a i n f a l l . SEASON FOCAL ANIMALS TOTAL RAINFALL MEAN MONTHLY M F (mm) (mm) Dry 1982 75 156 196.6 39.4 Dry 1983 104 221 378.1 75.6 Dry 1984 82 175 221.3 44.3 Wet 1982-83 152 289 775.7 110.8 Wet 1983-84 127 230 540.9 77.3 83 F o c a l e l e p h a n t s were observed from a d i s t a n c e not exceeding 25 m e t e r s . When neces sary 10' x 40' L e i t z b i n o c u l a r s were used f o r forage s p e c i e s i d e n t i f i c a t i o n . I observed e l e p h a n t s from a v e h i c l e i n open, exposed a r e a s , but I observed on foot when e l e p h a n t s were i n t h i c k bush or woodland a r e a s . F o c a l i n d i v i d u a l s were chosen on a d a i l y b a s i s from herds that were l o c a t e d from h i g h vantage p o i n t s or a l o n g random t r a n s e c t s d r i v e n through the Reserve in the e a r l y morning . No i n d i v i d u a l s were sampled more than once per month though many r e s i d e n t i n d i v i d u a l s were observed r e p e a t e d l y throughout the y e a r . B u l l s were more mobi le than c o w - c a l f herds and some i n d i v i d u a l s d i s a p p e a r e d e n t i r e l y for months a t a t ime , w h i l e o t h e r s remained i n the Reserve y e a r - r o u n d . Each month I at tempted to sample e q u a l numbers of both sexes , however, t h i s was not always p o s s i b l e because the a d u l t sex r a t i o was h i g h l y skewed towards females throughout the y e a r . The p e r i o d from November through May i s r e f e r r e d to as the wet season , wh i l e June through October c o n s t i t u t e s the d r y season . T h i s i s c o n s i s t e n t w i t h o ther a n a l y s e s for the S e r e n g e t i - M a r a system ( S i n c l a i r and N o r t o n - G r i f f i t h s 1979). D i e t c h o i c e was examined for d i f f e r e n c e s between sexes w i t h i n each season , between seasons w i t h i n each sex and o v e r a l l d i f f e r e n c e s throughout the y e a r . The f o l l o w i n g components of f o r a g i n g were a n a l y z e d : d i e t c o m p o s i t i o n , a b s o l u t e d i e t d i v e r s i t y , r e l a t i v e d i e t d i v e r s i t y or d i e t evenness , average d u r a t i o n of f o r a g i n g b o u t s , and the c h a r a c t e r i s t i c s of p l a n t s i n the d i e t . A r c s i n e t r a n s f o r m a t i o n s were performed on percentage data where n e c e s s a r y . A l l 84 s t a t i s t i c a l a n a l y s e s were performed u s i n g t e c h n i q u e s d e s c r i b e d by Zar (1984). A b s o l u t e d i e t a r y d i v e r s i t y i s the t o t a l number of p l a n t s p e c i e s i n c l u d e d i n the o b s e r v e d d i e t s i n a g i v e n month or season. R e l a t i v e d i v e r s i t y of d i e t or d i e t "evenness", J , e x p r e s s e s the observed d i v e r s i t y as a p r o p o r t i o n of the maximum p o s s i b l e d i v e r s i t y i n a g i v e n d a t a s e t , p t i s the p r o p o r t i o n of the d i e t d e v o t e d t o each f o r a g e s p e c i e s u t i l i z e d , k i s the number of d i s t i n g u i s h a b l e f o r a g e s p e c i e s consumed. T h i s index i s a v a r i a t i o n on the Shannon-Wiener d i v e r s i t y index (Zar 1984) and i s r e f e r r e d t o as r e l a t i v e d i v e r s i t y or evenness by P i e l o u (1966). T h i s r e l a t i v e d i v e r s i t y index was used by Barnes (1982) i n a s i m i l a r way f o r a n a l y z i n g e l e p h a n t d i e t s . In t h i s s t u d y I have used the same f o r m u l a which i s d e f i n e d by Zar (1984) a s : J = - | p i * l o g ( p t ) / l o g ( k ) H i g h e r v a l u e s of J i n d i c a t e more even f o r a g i n g among the s e l e c t e d p l a n t s p e c i e s . Because k i s g e n e r a l l y an u n d e r e s t i m a t e of the a c t u a l number of s p e c i e s i n the d i e t , J w i l l o v e r e s t i m a t e d i e t "evenness". However, i t i s a u s e f u l index f o r comparing g e n e r a l f o r a g i n g p a t t e r n s of males and females i n the two seasons. The l e n g t h of a f e e d i n g bout was the amount of time a f o c a l a n i m a l a t e a g i v e n f o r a g e type b e f o r e s w i t c h i n g t o a n o t h e r . I t was assumed t h a t the l e n g t h of a f e e d i n g bout was p o s i t i v e l y c o r r e l a t e d t o the t o t a l amount of f o r a g e consumed i n a g i v e n bout. Average f e e d i n g bouts were c a l c u l a t e d f o r males and 85 females i n each month and each season . Then average f e e d i n g bouts were summed f o r each forage type and d i v i d e d by the number of i n d i v i d u a l bouts o b s e r v e d . Forage use , w i t h r e g a r d to the food p l a n t ' s p h e n o l o g i c a l c o n d i t i o n , p l a n t p a r t e a t e n , and the h e i g h t at which f o r a g i n g took p l a c e were r e c o r d e d . P l a n t p h e n o l o g i c a l c o n d i t i o n s i n c l u d e d : l e a f l e s s , dry l e a v e s , green l e a v e s , b u d d i n g , l e a v e s w i t h f l o w e r s , and l e a v e s wi th f r u i t s . P l a n t p a r t s were broken i n t o the c a t e g o r i e s : r o o t s , l e a v e s and r o o t s , l e a v e s and s h o o t s , branches and t w i g s , l eaves on ly and bark o n l y . F o r a g i n g h e i g h t s were r e c o r d e d as : 0 - 1m, 1 - 2m, 2 - 3m, and above 3m. R e s u l t s F e e d i n g d i f f e r e n c e s between males and females D i e t c o m p o s i t i o n by forage type Seasonal d i e t c o m p o s i t i o n d i f f e r e d between males and f emales . The frequency d i s t r i b u t i o n s of b u l l and cow d i e t s over the f i v e forage types ( g r a s s e s , h e r b s , s h r u b s , t r e e s , and t r e e s e e d l i n g s ) v a r i e d i n a l l dry and wet seasons sampled ( F i g u r e s 4.1 and 4 . 2 ) . The sources of these s e a s o n a l d i e t d i f f e r e n c e s became apparent when s e a s o n a l means f o r each forage type ( F i g u r e 4.2) were compared f o r the 1983-84 da ta (Table 4 . 2 ) . In the wet s eason , females devoted s i g n i f i c a n t l y more t ime to f o r a g i n g on s h r u b s , wh i l e males a te more t r e e s e e d l i n g s and t r e e s . Males 86 DRY males females WET males i females 1982 1 9 8 2 - 8 3 1983 1 9 8 3 - 8 4 1984 S H R U B S ^ ^ T R E E S ^ X ^ - S E E D L I N G S - ^ 7 \ ^ G R A S S E S H E R B S Figure 4.1. Mean percentage d i e t composition by forage type f o r females and males. The data covers three dry seasons (1982, 1983, 1984) and two wet seasons (1982-83 and 1983-84). The s t a r s compare feeding p a t t e r n s both between sexes and seasons. 87 50-| O 40- E-1 30 H X + O • o • + - DRY SEASON, FEMALES O - WET SEASON, FEMALES X - DRY SEASON, MALES • - WET SEASON, MALES 20 H o O + X + o • + X X o SHRUB GRASS SEEDL HERBS TREES FORAGE TYPE Figure 4.2. Mean percentage d i e t composition by forage type f o r females and males i n the 1983-84 wet season and the 1984 dry season. 88 Table 4.2. Mean d i e t composition comparisons between sexes for a l l forage types. Tukey's multiple comparison tests (with unequal sample sizes) were performed. Significance l e v e l s are presented. (Dry season f o c a l "n" = 257; wet season = 357). FORAGE SEASON MEAN % MEAN % SIGNIFICANCE TYPE FEMALES MALES LEVEL GRASSES dry 22 15 n.s. wet 33 28 n.s. HERBS dry 12 7 0.01 wet 15 15 n.s. SHRUBS dry 45 47 n.s. wet 38 30 0.01 TREES dry 4 9 0.05 wet 1 5 0.05 SEEDLINGS dry 17 22 0.05 wet 13 22 0.01 89 and females d i d not feed s i g n i f i c a n t l y d i f f e r e n t l y on gras se s in the wet season , the dry season as a whole , or the l a t e dry season from August through O c t o b e r . At the h e i g h t of the long r a i n s , A p r i l and May, new gras se s were h i g h l y p r e f e r r e d by both sexes . However, i n the e a r l y dry season , June and J u l y , females spent a s i g n i f i c a n t l y g r e a t e r p r o p o r t i o n of t h e i r t ime f e e d i n g on g r a s s e s than d i d males (t = 2 .37 , d . f . = 99, P< .02) . Females a l s o spent more t ime f e e d i n g on herbs i n the dry season whi l e males devoted more time to e a t i n g t r e e s e e d l i n g s and t r e e s . In g e n e r a l , o v e r a l l male d i e t s were s i g n i f i c a n t l y h i g h e r in browse components ( s h r u b s , t r e e s e e d l i n g s , and t r e e s ) than o v e r a l l female d i e t s (t = 2 .45 , d . f . = 612, P<.025) , t h i s d i f f e r e n c e was seen i n both the wet (t = 2 . 0 9 , d . f . = 355, P<.05) and dry (t = 2 .67 , d . f . = 255, P<.01) seasons . C o n v e r s e l y , females u t i l i z e d the herbaceous s p e c i e s (grasses and herbs) s i g n i f i c a n t l y more throughout the year (t = 2 .35 , d . f . 612, P<.02) and p a r t i c u l a r l y d u r i n g the dry season (t = 3 .03 , d . f . = 255, P< .01) . G r a s s e s i n the d i e t c o n t r i b u t e d more to t h i s observed d i f f e r e n c e than h e r b s . Among the g r a s s e s , Cynodon d a c t y l o n was the most important s p e c i e s i n the d i e t throughout the y e a r . Themeda t r i a n d r a was chosen i n a h i g h l y s e a s o n a l manner - d u r i n g and immediate ly f o l l o w i n g the r a i n s . Themeda was eaten more f r e q u e n t l y when w i l d e b e e s t were not p r e s e n t i n the R e s e r v e , t h a t i s d u r i n g the s h o r t r a i n s of November and December and d u r i n g the long r a i n s of A p r i l and May, j u s t b e f o r e the m i g r a n t s a r r i v e d . Beeiurn sp . was the p r e f e r r e d herb but more than a dozen o ther s p e c i e s were 90 eaten d u r i n g t h e i r s h o r t p e r i o d s of a v a i l a b i l i t y . Among the shrub s p e c i e s p r e f e r r e d were Acac i a b r e v i s p i c a , C r o t o n d ichogamus, E u c l e a d ivornum, and Solanum incanum. T r e e s and s e e d l i n g s of Acac i a g e r r a r d i i , D i c h r o s t a c h y s c i n e r e a , and Ormocarpum t r i c h o c a r p u m were important i n e l ephant d i e t s throughout the y e a r . D i e t d i v e r s i t y The a b s o l u t e d i v e r s i t y of p l a n t s p e c i e s c o n t r i b u t i n g to e l ephant d i e t s changed throughout the y e a r . I d e n t i f i c a t i o n of s h r u b s , t r e e s , and t r e e s e e d l i n g s to s p e c i e s was p o s s i b l e in a l l seasons but gras se s c o u l d o n l y be i d e n t i f i e d to genera d u r i n g the dry season . F i g u r e 4.3 p r e s e n t s the a b s o l u t e number of p l a n t s p e c i e s in the d i e t s , a c r o s s a l l forage t y p e s . A l t h o u g h t h i s i s an underes t imate of d i e t a r y components , s i g n i f i c a n t d i f f e r e n c e s i n e l ephant food c h o i c e s were s t i l l d e t e c t a b l e . To t e s t i f d i e t d i v e r s i t y was independent of o b s e r v a t i o n time the number of p l a n t s p e c i e s r e c o r d e d i n the d i e t s was compared w i t h the t o t a l o b s e r v a t i o n time for each month. No s i g n i f i c a n t c o r r e l a t i o n was found between o b s e r v a t i o n time and the number of s p e c i e s eaten for females ( F i g u r e 4 . 4 , Spearman rank c o r r e l a t i o n , r g = 0 .22 , n = 12, n . s . ) or males ( F i g u r e 4 . 5 , r g = 0 .07 , n = 12, n . s . ) . From t h i s , I assumed t h a t a b s o l u t e d i e t d i v e r s i t y was an independent measure of d i e t p r e f e r e n c e and not a f u n c t i o n of the amount of t ime the e l e p h a n t s were observed i n a g i v e n month. Females m a i n t a i n e d a s i g n i f i c a n t l y broader d i e t than males a c r o s s the year and in both the dry and wet seasons (Table 4 . 3 ) . t—>i Q W E - i—i CO w I—I o w CO o w m S 35 n 30 H 25 20 H 15 H > - females I o - males \ o • o—o 10 H — i — i — i — i — i — i — i — i — i — i — i — | — N D J F M A M J J A S 0 MONTH F i g u r e 4.3. Absolute d i e t d i v e r s i t y (number of species i n the d i e t each month) f o r females and males i n 1983-84. 92 o w CO o W PQ 35 -i 30 H 25 H 20 H 15 FEMALES r s = 0.22, n.s. — i 1 r — i i i 300 400 500 600 700 800 900 TOTAL FEEDING TIME (min) Figure 4 . 4 . The number of species eaten versus the t o t a l feeding time observed i n each month fo r female elephants. 93 CO W r—I o w PU CO O w PQ S & 28 2 6 - 2 4 - 22 2 0 - 1 8 - 1 6 - 14 MALES r c = 0.07, n.s. i | i i - i • i 1 I 150 200 250 300 350 400 TOTAL FEEDING TIME (min) F i g u r e 4 . 5 . The number of species eaten versus the t o t a l feeding time observed i n each month f o r male elephants. Table 4.3. Absolute d i e t d i v e r s i t y comparison between males and females by season. d.f. FEMALES MALES t-value p-value Annual mean 22 25.17 19.75 3.75 0.01 Dry season 8 28.20 20.60 3.43 0.01 Wet season 12 23.00 19.14 2.59 0.05 95 R e l a t i v e d i e t d i v e r s i t y o r " e v e n n e s s " r e l a t e s t h e d i s t r i b u t i o n o f d i e t c h o i c e s t o t h e n u m b e r s o f d i f f e r e n t c h o i c e s a v a i l a b l e ( F i g u r e 4 . 6 ) . No s i g n i f i c a n t d i f f e r e n c e s w e r e f o u n d b e t w e e n m a l e s a n d f e m a l e s a c r o s s t h e y e a r o r i n t h e we t a n d d r y s e a s o n s ( T a b l e 4 . 4 ) . On a v e r a g e f e m a l e s a n d m a l e s d i s t r i b u t e d t h e i r t i m e e v e n l y among a l l s p e c i e s i n a l l f o r a g e t y p e s . H o w e v e r , i n t h e m o n t h s o f N o v e m b e r a n d A p r i l r e l a t i v e d i e t d i v e r s i t y f e l l b e l o w . 6 5 f o r m a l e s a n d . 5 0 - f o r f e m a l e s . T h e s e m o n t h s came a t t h e e n d o f l o n g d r y s p e l l s when f o r a g e q u a l i t y a n d q u a n t i t y was l o w a n d f o r a g e c h o i c e was r e d u c e d . The l o w d i e t " e v e n n e s s " i n d i c a t e s t h a t e l e p h a n t s f e d d i s p r o p o r t i o n a t e l y on a few p r e f e r r e d s p e c i e s i n t h o s e two m o n t h s . When r e l a t i v e d i e t a r y d i v e r s i t y was a n a l y z e d f o r b r o w s e s p e c i e s a l o n e t h e r e w e r e s i g n i f i c a n t d i f f e r e n c e s b e t w e e n m a l e s a n d f e m a l e s ( F i g u r e 4 . 7 ) . A v e r a g e d a c r o s s t h e y e a r , r e l a t i v e b r o w s e d i e t s o f m a l e s w e r e d i s t r i b u t e d more e v e n l y t h a n t h o s e o f f e m a l e s ( t = 2 . 5 5 , d . f . = 2 2 , P < . 0 2 ) . T h i s d i f f e r e n c e o c c u r r e d i n t h e we t s e a s o n when m a l e s c h o s e a s i g n i f i c a n t l y more e v e n d i e t t h a n f e m a l e s ( t = 3 . 5 1 , d . f . = 1 2 , P < . 0 1 ) . I n t h e d r y s e a s o n , m a l e s a n d f e m a l e s h a d s i m i l a r b r o w s i n g p a t t e r n s ( t = 0 . 1 2 , d . f . = 8 , n . s . ) . The l o w e r r e l a t i v e d i v e r s i t y o f b r o w s e s p e c i e s t h r o u g h o u t t h e y e a r i n t h e d i e t s o f f e m a l e s i n d i c a t e d t h a t t h e y c o n t i n u a l l y s p e n t a d i s p r o p o r t i o n a t e amoun t o f t h e i r b r o w s i n g t i m e on a s m a l l number o f h i g h l y p r e f e r r e d s p e c i e s . M a l e s , h o w e v e r , d e m o n s t r a t e d s e a s o n a l c h a n g e s i n t h e " e v e n n e s s " o f t h e i r b r o w s i n g . I n t h e d r y s e a s o n , t h e y a l s o s e l e c t e d a few p r e f e r r e d s p e c i e s t o b r o w s e . H o w e v e r , i n t h e we t s e a s o n , when Figure 4.6. R e l a t i v e d i e t d i v e r s i t y or d i e t "evenness" for female and male elephants i n 1983-84. Table 4 . 4 . Seasonal comparison of r e l a t i v e d i e t d i v e r s i t y between the sexes. d.f. FEMALES MALES Annual mean 22 .73 .80 Dry season 8 .70 .79 Wet season 12 .75 .80 t-value p-value 1.20 n.s. 0.57 n.s. 1.73 n.s. 98 E - t — I CO DH W > i — i Q O CO o DH PQ > i — i DH 1.0 n 0.9 H 0.8 H 0.7 H 0.6 H 0.5 • - f e m a l e s O - m a l e s "1 I l I l I I — l — I — i — i — i — i N D J F M A M J J A S 0 MONTH F i g u r e 4.7. R e l a t i v e browsing d i v e r s i t y or "evenness" f o r female and male elephants i n 1983-84. 99 t h e i r d i e t w a s l a r g e l y c o m p r i s e d o f h e r b a c e o u s s p e c i e s , m a l e s a p p a r e n t l y s a m p l e d s m a l l a m o u n t s o f a w i d e v a r i e t y o f a v a i l a b l e s p e c i e s . L e n g t h s o f f e e d i n g b o u t s o n f o r a g e t y p e s M a l e s a n d f e m a l e s s p e n t s i m i l a r a m o u n t s o f t i m e f e e d i n g o n o n e f o r a g e t y p e b e f o r e s w i t c h i n g t o a n o t h e r ( f o r a g i n g b o u t s ) . T h i s a p p l i e d b e t w e e n s e a s o n s a n d a c r o s s t h e e n t i r e y e a r ( T a b l e 4.5a & b ) . I n a n a n a l y s i s a c r o s s a l l f o r a g e t y p e s , t h e r e w e r e n o s i g n i f i c a n t d i f f e r e n c e s i n a v e r a g e l e n g t h o f f o r a g i n g b o u t s b e t w e e n t h e s e x e s a c r o s s t h e y e a r o r w i t h i n e i t h e r s e a s o n . C h a r a c t e r i s t i c s o f p l a n t s i n t h e d i e t T o s e e w h e t h e r t h e s e x e s c h o s e t h e i r f o o d u s i n g t h e s a m e c r i t e r i a , u t i l i z a t i o n w a s e x a m i n e d i n t e r m s o f t h e c o n d i t i o n o f t h e c h o s e n p l a n t , t h e s p e c i f i c p l a n t p a r t s e a t e n , a n d t h e h e i g h t a t w h i c h f e e d i n g t o o k p l a c e . N o s i g n i f i c a n t d i f f e r e n c e s w e r e f o u n d b e t w e e n m a l e s a n d f e m a l e s f o r a n y o f t h e s e c o n d i t i o n a l p r o p e r t i e s , f o r a n y f o r a g e t y p e , i n a n y s e a s o n . A l t h o u g h n o s i g n i f i c a n t d i f f e r e n c e s i n t h e p l a n t p a r t s u s e d w e r e f o u n d , I c o u l d n o t r u l e o u t t h e p o s s i b i l i t y t h a t m o r e s u b t l e c h o i c e s w e r e b e i n g m a d e w h i c h I w a s u n a b l e t o d e t e c t . E l e p h a n t s u t i l i z e d f o r a g e i n t h e g r e e n l e a f s t a g e m o r e t h a n a l l o t h e r c a t e g o r i e s o f p l a n t p h e n o l o g y ( s e e M e t h o d s ) , w h e n a v a i l a b l e . F o r h e r b s , s h r u b s , t r e e s , a n d s e e d l i n g s , t h e g r e e n l e a f s t a g e w a s u s e d e x c l u s i v e l y . F o r g r a s s e s , l e a f c o n d i t i o n w a s s e l e c t e d a c c o r d i n g t o a v a i l a b i l i t y . S o , m o r e d r y l e a v e s Table 4.5. Average length of foraging bouts across a l l forage types for males and females throughout 1983-84 (a); and between sex comparisons (b). (a) Average length of foraging bouts i n minutes N D J F M A M J J A S O Females 5.0 3.6 2.5 2.8 3.7 3.0 3.5 7.7 6.8 3.9 5.7 3.4 Males 3.7 4.4 2.4 2.9 3.8 3.0 4.5 6.4 6.0 4.1 5.0 4.2 (b) Between sex comparisons of mean length of foraging bouts i n each season. d.f. Annual mean 22 Wet season Dry season 12 Females 4.3 3.4 5.5 Males 4.2 3.5 5.1 t-value p-value 0.17 0.22 0.39 n.s. n.s. n.s. 101 were consumed d u r i n g the dry season and more green l e a v e s i n the wet s e a s o n . Males consumed s i g n i f i c a n t l y more g r a s s i n the dry l e a f c o n d i t i o n than females in both the dry (x2 = 8 . 59 , d . f . 1, P<.005) and wet season (x2 = 46 .64 , d . f . = 1, P< .001) . T h i s d i f f e r e n c e support s the idea t h a t males , w i th t h e i r g r e a t e r i n t a k e of bu lk and lower r e l a t i v e energy demands ( S i k e s 1971), are b e t t e r a b l e to u t i l i z e poor q u a l i t y , dry g r a s s e s . These d i f f e r e n c e s are a n a l y z e d more f u l l y below. Male and female e l ep h an t s fed almost e x c l u s i v e l y on the l e a v e s and shoots of a l l forage types w i th o n l y o c c a s i o n a l use of r o o t s . Root f e e d i n g was not s i g n i f i c a n t i n any season , but b u l l s and cows f o l l o w e d the same g e n e r a l p a t t e r n of u s e . Shrub and t r e e bark was a l s o consumed by both sexes i n s m a l l amounts, p r i m a r i l y i n the dry season . F e e d i n g h e i g h t p a t t e r n s a p p l y o n l y to the t r e e s and s h r u b s . Throughout the y e a r , e l e p h a n t s spent the m a j o r i t y of t h e i r f e e d i n g t ime on shrubs (males = 80%, females = 79%) i n the 0 - 1m h e i g h t c l a s s and on t r e e s (males = 63%, females = 60%) i n the 1 - 2m c l a s s . T h e i r a c t i v i t y of s e l e c t i v e l y removing s e e d l i n g s wh i l e f o r a g i n g was termed "weeding". In a s i n g l e f o r a g i n g bout , i n d i v i d u a l male and female e l e p h a n t s removed as many as 35 s e e d l i n g s (below 1m) i n f i v e m i n u t e s , a r a t e of over 400 per h o u r . Both sexes foraged at h i g h e r and h i g h e r l e v e l s as the dry season p r o g r e s s e d . Seasona l d i f f e r e n c e s w i t h i n sexes are p r e s e n t e d in the f o l l o w i n g s e c t i o n s . 102 Female f e e d i n g p a t t e r n s D i e t c o m p o s i t i o n by forage type Females changed t h e i r d i e t w i th season ( F i g u r e 4 . 2 ) . A two-way a n a l y s i s of v a r i a n c e between season and forage type showed tha t the d i e t s of females d i f f e r e d s i g n i f i c a n t l y w i t h both season (F = 5 .59 , P<.025) and forage types (F = 3 .44 , P< .01) . There was a l s o a s i g n i f i c a n t i n t e r a c t i o n between season and forage type (F = 2 . 4 1 , P< .05) . T h i s i n t e r a c t i o n i s due to the i n f l u e n c e of season on r e l a t i v e q u a l i t y between forage t y p e s . Dry season d i e t c o m p o s i t i o n showed a s i m i l a r p a t t e r n between 1982 and 1984 but d i f f e r e d i n 1983 ( F i g u r e 4 . 1 ) . The decrease i n browsing ( t r e e s , s h r u b s , and s e e d l i n g s ) and the i n c r e a s e i n g r a z i n g (grasses and herbs) i n 1983 may have been due to unseasonably h i g h r a i n f a l l (378.1mm) d u r i n g tha t p e r i o d . Wet season d i e t s a l s o v a r i e d between the two seasons sampled. T h i s d i f f e r e n c e was a t t r i b u t e d to the s i g n i f i c a n t l y h i g h e r r a i n f a l l i n the 1982-83 wet season (775.7mm) v e r s u s the 1983-84 wet season (540.9mm) when the r a i n s l a r g e l y f a i l e d and dry c o n d i t i o n s p r e v a i l e d . The main d i f f e r e n c e s appeared to be i n the herb and shrub forage t y p e s . In the wet season of 1982-83 herbs were p r o b a b l y more abundant due to h i g h e r r a i n f a l l and , t h e r e f o r e , c o n s t i t u t e d a l a r g e r p r o p o r t i o n of the d i e t . From the 1983-84 d a t a , i t was apparent t h a t females found new herbs h i g h l y d e s i r a b l e . On the o t h e r hand, f e e d i n g on shrubs was h i g h e r i n the 1983-84 wet season when females were under more p r e s s u r e to browse due to a shortage of g r e e n , herbaceous 103 f o r a g e . Comparison of the 1983-84 wet season to the 1984 dry season shows a g e n e r a l tendency for a more herbaceous d i e t i n t imes of h i g h e r r a i n f a l l and i n c r e a s e d browse i n the d i e t d u r i n g the dry s eason , p a r t i c u l a r l y from shrubs ( F i g u r e s 4.2 and 4 . 8 , T a b l e 4 . 6 a ) . The c o n t r i b u t i o n of g r a s s e s to d i e t s a l s o d i f f e r e d between dry and wet seasons . To f u r t h e r a n a l y z e , the p r o p o r t i o n of g r a s s e s i n the d i e t was d i v i d e d i n t o the e a r l y (June and J u l y ) and l a t e (August through October ) dry s eason . In the l a t e dry season d i e t s , the gras s c o m p o s i t i o n (3.7%) was s i g n i f i c a n t l y l e s s than i n the wet season of (32.9% (t = 3 .39 , d . f . = 335, P<.001)) and in the e a r l y dry season (50.8% (t = 2 .83 , d . f . 173, P < . 0 1 ) ) . Herbs were more important i n the wet season d i e t s , and t r e e s and t r e e s e e d l i n g s c o n t r i b u t e d more to dry season d i e t s , but not to a s i g n i f i c a n t degree . D i e t d i v e r s i t y The d i e t s of females expanded i n a b s o l u t e d i v e r s i t y in the dry season and narrowed in the wet season (Table 4.3 and F i g u r e 4 . 3 , t = 3 . 0 5 , d . f . = 10, P< .02) . The r e l a t i v e d i v e r s i t y of d i e t s of females d i d not v a r y by season e i t h e r a c r o s s a l l forage types (t = 1.14, d . f . = 10, n . s . ) or for browse s p e c i e s a lone (t = 0 .47 , d . f . = 10, n . s . ) . Cows showed t h e i r lowest r e l a t i v e d i e t d i v e r s i t y for browse s p e c i e s i n March and November. Each of these months r e p r e s e n t e d the end of l ong dry s p e l l s when h i g h q u a l i t y forage was s c a r c e and browsing a c t i v i t y was h i g h . Females t r a v e l l e d to permanent water sources where they fed on shrubs and t r e e s by the w a t e r ' s edge. The low d i e t "evenness" 104 CO E- 1 CO o PS PQ E-< W O PS W 90 n 80 70 60 50- 40- 30 O O r s = -0.96 p < .001 • - females O - males O O — I — i — | — i — | 100 120 140 20 40 60 80 MEAN MONTHLY RAINFALL (mm) Figure 4.8. The re l a t i o n s h i p of percent browse in the diet to the mean monthly r a i n f a l l for female and male elephants. Note : * = both males and females showed equal percentages of browse in the diets when mean monthly r a i n f a l l was 75.6mm. 105 Table 4.6. Between season comparison of diets by forage type within females and males. Tukey's multiple comparion tests (with unequal sample sizes) were performed. Significance l e v e l s are presented. (a) FEMALES (dry season = 175; FORAGE DRY TYPE GRASSES 22 HERBS 12 SHRUBS 45 TREES 4 SEEDLINGS 17 wet season = 230) WET SIGNIFICANCE LEVEL 33 0.01 15 n.s. 38 0.05 1 n.s. 13 n.s. (b) MALES (dry season = 82; wet season = 175) FORAGE TYPE GRASSES HERBS SHRUBS TREES SEEDLINGS DRY 15 7 47 9 22 WET 28 15 30 5 22 SIGNIFICANCE LEVEL 0.001 0.01 0.01 n.s. n.s. 106 i n d i c a t e s t h a t females chose a few, favoured browse s p e c i e s and fed d i s p r o p o r t i o n a t e l y on them. Lengths of f e e d i n g bouts on forage types Females d i d not m a i n t a i n a c o n s t a n t bout d u r a t i o n on p a r t i c u l a r forage types i n d i f f e r e n t seasons . In f a c t , f o r a g i n g bouts of cows were s i g n i f i c a n t l y l onger i n the dry season (Table 4 .7a). V a r i a t i o n s in f e e d i n g p a t t e r n s on s e v e r a l , but not a l l , forage types accounted for these s i g n i f i c a n t s e a s o n a l d i f f e r e n c e s . F o r a g i n g bouts on h e r b s , t r e e s and s e e d l i n g s were s i g n i f i c a n t l y l onger i n the dry season . A l t h o u g h f e e d i n g bouts on g r a s s e s d i d not d i f f e r s i g n i f i c a n t l y between the wet and dry seasons , a c l o s e r examinat ion showed important d i f f e r e n c e s between f e e d i n g p a t t e r n s in the wet and e a r l y dry seasons . In the e a r l y dry season cows averaged 10.2 minutes per f o r a g i n g bout on g r a s s e s , wh i l e i n the wet season , they averaged o n l y 4.34 minutes per bout , a s i g n i f i c a n t d i f f e r e n c e (t = 6.33, d . f . = 7, P<.001). E a r l y d r y season g r a s s e s were a major component of the d i e t d u r i n g t h i s p e r i o d . However, by the l a t e dry season f e e d i n g bouts were s i m i l a r i n l e n g t h to those in the wet season (t = 0.42, d . f . = 8, n . s . ) . C h a r a c t e r i s t i c s of p l a n t s in the d i e t A l l forage t y p e s , w i t h the e x c e p t i o n of g r a s s e s , were eaten o n l y when i n green l e a f . The c o n d i t i o n of grasses eaten d i f f e r e d between seasons (x2 = 835.6, d . f . = 1, P<.001) and c h o i c e was de termined by what was a v a i l a b l e . When green gras s 107 Table 4.7. Between season comparisons of the length of foraging bouts on d i f f e r e n t forage types within females and males. Tukey's multiple comparison tests were performed. Significance l e v e l s are presented. Mean lengths are measured i n minutes. (a) FEMALES FORAGE DRY WET SIGNIFICANCE TYPE LEVEL GRASSES 6.3 4.3 n.s. HERBS 2.9 2.0 0.01 SHRUBS 4.6 3.7 n.s. TREES 4.5 1.6 0.01 SEEDLINGS 3.5 2.1 0.05 OVERALL 5.5 3.4 0.05 (b) MALES FORAGE DRY TYPE GRASSES 6.9 HERBS 2.0 SHRUBS 4.6 TREES 6.9 SEEDLINGS 3.7 OVERALL 5.1 WET SIGNIFICANCE LEVEL 3.4 n.s. 2.8 n.s. 2.6 0.01 3.6 0.02 3.3 n.s. 3.5 0.01 108 l e a v e s were u b i q u i t o u s , over 80% of the g r a s s e s chosen were i n green l e a f . However, i n the d r y season , dry l e a v e s and stems made up 87% of the g r a s s e s e a t e n . Even in the most severe dry weather , females m a i n t a i n e d over 10% of the gras s component i n the d i e t as green l e a f , by moving to areas of p e r e n n i a l water where some green g r a s s e s c o u l d be found year r o u n d . Females d i d not eat a l l p l a n t p a r t s e q u a l l y . Leaves and new stems of a l l forage types predominated in the d i e t throughout the y e a r . R o o t s , bark and woody branches were used i n s m a l l amounts, p r i m a r i l y i n the d r y season . There were s u f f i c i e n t data on shrubs to t e s t whether females p r e f e r r e d to feed at p a r t i c u l a r h e i g h t s in d i f f e r e n t seasons (Table 4 . 8 a ) . In the wet season, female e l e p h a n t s p r e f e r r e d new shoots and l eaves which f r e q u e n t l y s p r o u t e d from shrubs below the 1m l e v e l . In the dry season , cows expanded t h e i r f o r a g i n g to i n c l u d e g r e a t e r p r o p o r t i o n s of o ther h e i g h t c l a s s e s and , t h e r e f o r e , l e s s p r e f e r r e d l e a v e s . T h i s change i n the dry season was p r o b a b l y a d i r e c t consequence of the reduced a v a i l a b i l i t y of newer shoots nearer the ground . Male f e e d i n g p a t t e r n s D i e t c o m p o s i t i o n by forage type A two-way a n a l y s i s of v a r i a n c e of d i e t c o m p o s i t i o n showed t h a t the d i e t s of b u l l s were s i g n i f i c a n t l y d i f f e r e n t both between seasons (F = 15.72, P<.0005) and between forage types (F 3 . 5 2 , P< .01) . The frequency d i s t r i b u t i o n of forage types in Table 4.8. Feeding height preferences on shrubs and a test of the d i s t r i b u t i o n of foraging heights between seasons for females and males. (a) FEMALES HEIGHT CLASSES 0-lm l-2m 2m+ TOTAL MINUTES Dry season 855 Wet season 1142 249 188 83 13 1187 1343 (b) MALES X* = 91.53 d.f. = 2 p < .001 HEIGHT CLASSES 0-lm l-2m 2m+ TOTAL MINUTES Dry season 387 115 8 546 Wet season 538 55 611 X2 = 53.25 d.f. = 2 p < .001 110 t h e d i e t v a r i e d w i t h i n e a c h s e a s o n b e t w e e n t h e y e a r s s a m p l e d ( F i g u r e 4 . 1 ) . The l o w e r s e e d l i n g a n d t r e e u s e i n t h e d r y s e a s o n o f 1983 may h a v e b e e n d u e t o g r e a t e r r a i n f a l l d u r i n g t h a t p e r i o d t h a n i n e i t h e r t h e 1982 o r 1984 d r y s e a s o n s ( T a b l e 4 . 1 ) . T h i s h i g h e r r a i n f a l l l e d t o l o c a l f o r a g e c o n d i t i o n s w h i c h w e r e more s i m i l a r t o r a i n y s e a s o n c o n d i t i o n s t h a n t o d r y s e a s o n c o n d i t i o n s . The o b s e r v e d d e c r e a s e i n b r o w s i n g a c t i v i t y a n d t h e i n c r e a s e i n g r a s s a n d h e r b u s e m e r e l y r e f l e c t e d t h e r e l a t i v e c h a n g e i n q u a l i t y b e t w e e n t h e s e f o r a g e t y p e s . The f a i l e d r a i n s o f t h e 1 9 8 3 - 8 4 we t s e a s o n l e d t o a g e n e r a l p a t t e r n o f i n c r e a s e d b r o w s i n g a n d r e d u c e d g r a z i n g ( F i g u r e 4 . 1 ) . The t i m e s p e n t e a t i n g g r a s s was a n a l y z e d i n more d e p t h . M a l e s f o l l o w e d a s i m i l a r p a t t e r n t o t h a t s e e n i n f e m a l e s . I n t h e l a t e d r y s e a s o n , g r a s s e s a c c o u n t e d f o r o n l y 4 . 4% o f m a l e d i e t s w h i c h was s i g n i f i c a n t l y l e s s t h a n 3 2 . 7 % i n t h e e a r l y d r y s e a s o n ( t = 3 . 4 4 , d . f . = 8 0 , P < . 0 0 1 ) a n d 2 7 . 8 % i n t h e we t s e a s o n ( t = 2 . 5 2 , d . f . = 1 7 4 , P < . 0 2 ) . The s i g n i f i c a n t d e c l i n e i n g r a s s e a t e n i n t h e l a t e d r y s e a s o n was b o t h a p r o d u c t o f i t s r e d u c e d a v a i l a b i l i t y f o l l o w i n g t h e a r r i v a l o f t h e w i l d e b e e s t a n d p e r h a p s i t s r e d u c e d p a l a t a b i l i t y due t o p h e n o l o g i c a l c h a n g e s . I n t h e d r y s e a s o n , s h r u b s made up a s i g n i f i c a n t l y h i g h e r p r o p o r t i o n o f t h e d i e t t h a n i n t h e we t s e a s o n ( F i g u r e 4 . 2 a n d T a b l e 4 . 6 b ) . T r e e s w e r e a l s o u t i l i z e d more i n t h e d r y s e a s o n b u t n o t s i g n i f i c a n t l y s o . T h e r e was no s e a s o n a l c h a n g e i n s e e d l i n g u s e among m a l e s . H o w e v e r , i t i s i m p o r t a n t t o n o t e t h a t s e e d l i n g s c o m p r i s e d a l m o s t a q u a r t e r o f t h e i r o v e r a l l d i e t s , t h r o u g h o u t t h e y e a r , a n d m a l e s f r e q u e n t l y c o n s u m e d up t o 400 s e e d l i n g s i n o n e h o u r o f f e e d i n g . 111 D i e t d i v e r s i t y Among b u l l s , t h e r e was no s i g n i f i c a n t change in a b s o l u t e d i e t d i v e r s i t y between the wet and d r y seasons (Table 4.3 and F i g u r e 4 . 3 , t = 0 .76 , d . f . = 10, n . s . ) . Males u t i l i z e d over 50 p l a n t s p e c i e s d u r i n g the y e a r , though these p r e f e r e n c e s swi tched between i n d i v i d u a l s p e c i e s s e a s o n a l l y . B u l l s d i d not show any s e a s o n a l change in r e l a t i v e d i e t d i v e r s i t y or "evenness" when a n a l y z e d a c r o s s a l l forage types (Tab le 4.4 and F i g u r e 4 . 6 , t = 0 .21 , d . f . = 10, n . s . ) . Males spent more t ime browsing d u r i n g the d r y season and l e s s t ime g r a z i n g ( F i g u r e 4 . 8 ) . However, f or the browse c a t e g o r i e s of s h r u b s , t r e e s , and s e e d l i n g s combined, b u l l s had s i g n i f i c a n t l y h i g h e r J - v a l u e s i n the wet season than i n the dry season ( F i g u r e 4 . 7 , t = 2 .44 , d . f . = 10, P< .05) . T h i s i n d i c a t e s tha t b u l l s foraged more even ly on browse s p e c i e s d u r i n g tha t t i m e . T h i s h i g h e r "evenness" suggests tha t b u l l s used a g r e a t e r number of browse s p e c i e s but i n s m a l l e r i n d i v i d u a l amounts. In the dry season , when browse compri sed over 75% of the d i e t , males a p p a r e n t l y devoted more time to a few p r e f e r r e d s p e c i e s , j u s t as females d i d when b r o w s i n g . Lengths of f e e d i n g bouts on forage types The average l e n g t h s of f o r a g i n g bouts a c r o s s a l l forage types were h i g h e r i n the dry season (Table 7 b ) . T h i s s easona l d i f f e r e n c e was e x p l a i n e d by the s i g n i f i c a n t l y h i g h e r average f o r a g i n g bouts on t r e e s and shrubs i n the dry season . L i k e f ema le s , males showed d i s t i n c t l y d i f f e r e n t f e e d i n g p a t t e r n s on 1 12 the g r a s s component of t h e d i e t , when broken i n t o e a r l y and l a t e d r y season and wet season. F o r a g i n g bouts were s i g n i f i c a n t l y l o n g e r ( t = 3.00, d . f . = 7, P<.02) i n the e a r l y d r y season (mean = 7.87 min u t e s / b o u t ) than i n the wet season (mean = 3.43 m i n u t e s / b o u t ) . The l e n g t h of f o r a g i n g bouts d i d not d i f f e r s i g n i f i c a n t l y between the wet and l a t e d r y seasons ( t = 0.95, d . f . = 8 , n . s . ) . C h a r a c t e r i s t i c s of p l a n t s i n the d i e t L i k e f e m a l e s , males used s i g n i f i c a n t l y more green g r a s s l e a v e s i n the wet season than i n the d r y season ( x 2 = 256.6, d . f . = 1, P<.001). In the wet season, 70% of the g r a s s l e a v e s eaten by b u l l s were g r e e n , whereas i n the d r y season t h i s f i g u r e dropped t o 6%. Green g r a s s l e a v e s were always p r e f e r r e d over d r y when a v a i l a b l e . I n a l l o t h e r f o r a g e t y p e s o n l y green l e a v e s were u t i l i z e d . Male e l e p h a n t s f e d p r i m a r i l y on the l e a v e s and shoots of a l l f o r a g e t y p e s . Roots of some s h r u b s , s e e d l i n g s , h e r b s , and g r a s s e s a l l o c c u r r e d i n the d i e t s i n s m a l l amounts. Bark and branches were seen i n the dry season d i e t s but not t o a s i g n i f i c a n t degree. Males browsed a t d i f f e r e n t h e i g h t s i n d i f f e r e n t seasons. For s h r u b s , these p r e f e r e n c e s changed i n a manner s i m i l a r t o t h a t seen f o r females ( T a b l e 8 b ) . Whereas, i n the wet season, males p r e d o m i n a n t l y f e d on the 0 - 1m h e i g h t c l a s s , i n the d r y season, f o r a g i n g a t o t h e r h e i g h t s i n c r e a s e d . T h i s change i n the d i s t r i b u t i o n of f e e d i n g h e i g h t s r e f l e c t e d a p r e f e r e n c e f o r . t h e 0 - 1m c l a s s d u r i n g p e r i o d s when new growth was s t i m u l a t e d by 1 13 r a i n f a l l . Many shrubs sent out e x t e n s i v e , c o p p i c i n g shoots a t the onset of the r a i n s . T h i s was p a r t i c u l a r l y apparent f o l l o w i n g hot f i r e s or damage to mainstems by e l e p h a n t s , w i l d e b e e s t and o t h e r s . D u r i n g the d r y season , when s p r o u t s were no longer a v a i l a b l e , e l e p h a n t s expanded t h e i r f o r a g i n g to i n c l u d e h i g h e r l e v e l s . For t r e e s , the data were not e x t e n s i v e enough to e s t a b l i s h h e i g h t p r e f e r e n c e s i n each season , however, the g e n e r a l p a t t e r n was s i m i l a r to tha t found f o r shrub use . A l t h o u g h males can feed more e a s i l y at g r e a t e r h e i g h t s than females , the d i s t r i b u t i o n of t h e i r f e e d i n g h e i g h t s , i n the M a r a , was the same. T h i s was p r o b a b l y due to a s c a r c i t y of p r e f e r r e d forage s p e c i e s i n the c l a s s e s above 2m, yet s t i l l w i t h i n t h e i r r e a c h . Males d i d u t i l i z e forage at g r e a t e r h e i g h t s than females when i t was a v a i l a b l e and o c c a s i o n a l l y pushed t r e e s over to get at l eaves i n the t r e e crowns . F a l l e n t r e e s w i t h i n the r i v e r i n e f o r e s t s and i n the open, Acac i a woodlands demonstrated the extent of t h i s b e h a v i o u r . P i s c u s s i o n Mara e l e p h a n t s f o l l o w e d the same g e n e r a l f o r a g i n g p a t t e r n s observed i n many A f r i c a n e l ep h an t p o p u l a t i o n s ( N i c h o l s o n 1954, Buss and Wing 1970, N a p i e r - B a x and S h e l d r i c k 1963, Laws and Parker 1968, F i e l d 1971, L e u t h o l d and S a l e 1973, Wyatt and E l t r i n g h a m 1974, Laws et a l . 1975, Thomson 1975, Guy 1976, F i e l d and Ross 1976, L e u t h o l d 1977a & b , T i e s z e n et a l . 1979, Barnes 1982, Weyerhaeuser 1982, Hansen et a l . 1985). Males and females showed s i m i l a r s e a s o n a l d i e t changes . Both sexes 1 14 c o n c e n t r a t e d on g r a s s e s and herbs i n the r a i n y season and browse s p e c i e s i n the dry season . Males browsed more than females , w h i l e female d i e t s c o n t a i n e d more herbaceous matter than males throughout the y e a r . These s e a s o n a l changes i n e l ep h an t d i e t s are most l i k e l y a d i r e c t r e f l e c t i o n of both the r e l a t i v e q u a n t i t i e s of p r e f e r r e d forage and the a b i l i t y of e l e p h a n t s to t r a c k crude p r o t e i n l e v e l s . E f f e c t s of food q u a l i t y Shrubs were used throughout the year by both sexes but compri sed a h i g h e r p r o p o r t i o n of d i e t s of females i n the wet season . There was no ev idence to support Barnes ' (1982) f i n d i n g tha t females a te s i g n i f i c a n t l y more woody components ( twigs and branches) than l e a f y ones ( l eaves and shoots ) in the dry season . However, woody forage d i d not compri se a l a r g e component of e l ephant d i e t s in any season i n the M a r a . T h i s may have been a r e f l e c t i o n of the l o c a l s c a r c i t y of p r e f e r r e d woody f o r a g e . In accordance w i t h recent o p t i m a l f o r a g i n g t h e o r y , e l e p h a n t s , as g e n e r a l i s t h e r b i v o r e s , s h o u l d s e l e c t forage i n a manner which maximizes t h e i r net energy i n t a k e (Be lovsky 1986). The a d d i t i o n a l c o s t s of a c q u i s i t i o n and a s s i m i l a t i o n of c e r t a i n forage c o n t a i n i n g d e b i l i t a t i n g t o x i n loads must be worked i n t o t h i s o v e r a l l e q u a t i o n (Rhoades 1979, 1983). O l i v i e r (1978) and Barnes (1982) s p e c u l a t e d that s e a s o n a l changes in e l ephant d i e t s may be both c o n t r o l l e d and c o n s t r a i n e d by secondary compound l e v e l s i n the a v a i l a b l e f o r a g e . W h i l e g r a s s e s may have s t r u c t u r a l d e f e n s e s , such as s i l i c a , which c r e a t e d i g e s t i o n problems f o r some g r a z e r s ( O l i v i e r 1978, McNaughton et a l . 1 15 1 9 8 5 ) , t h e y p r e s e n t no p r o b l e m f o r e l e p h a n t s . F u r t h e r m o r e , t o x i n l e v e l s i n g r a s s e s a r e n e g l i g i b l e a n d n o t g e n e r a l l y c o n s i d e r e d a c o n s t r a i n t on e l e p h a n t d i e t c h o i c e ( O l i v i e r 1 9 7 8 , B a r n e s 1 9 8 2 ) . H o w e v e r , M b i ( 1 9 7 8 ) , M i l t o n ( 1 9 7 9 ) , C o l e y ( 1 9 8 0 ) , O a t e s e t a l . ( 1 9 8 0 ) , M a c a u l e y a n d F o x ( 1 9 8 0 ) a n d B r y a n t e t a l . ( 1 9 8 5 ) f o u n d t h a t t h e v u l n e r a b l e p l a n t p a r t s o f a v a r i e t y o f t r e e s a n d s h r u b s s p e c i e s , s u c h a s y o u n g s h o o t s , s t e m s , a n d l e a v e s ( w h i c h s e a s o n a l l y c o m p r i s e a l a r g e p o r t i o n o f e l e p h a n t d i e t s ) c o n t a i n h i g h e r a m o u n t s o f t e r p e n o i d s a n d t o t a l p h e n o l s ( q u a n t i t a t i v e t o x i n s ) , t h a n o l d e r l e a v e s a n d woody m a t e r i a l s . T h e s e f i n d i n g s c o n t r a d i c t t h o s e o f F e e n y ( 1 9 7 0 , 1 9 7 6 ) , M c K e y ( 1 9 7 4 , 1 9 7 9 ) , a n d R h o a d e s a n d C a t e s ( 1 9 7 6 ) who f o u n d t h a t o l d e r , more m a t u r e f o l i a g e o f p e r e n n i a l t r e e s a n d s h r u b s c o n t a i n e d g r e a t e r q u a n t i t a t i v e c h e m i c a l l o a d s t h a n new g r o w t h . T h e s e same i n v e s t i g a t o r s d i d s p e c u l a t e , h o w e v e r , t h a t y o u n g l e a v e s may c o n t a i n h i g h e r c o n c e n t r a t i o n s o f q u a l i t a t i v e t o x i n s , s u c h a s a l k a l o i d s a n d c y a n o g e n i c g l y c o s i d e s a n d t h e r e f o r e s t i l l be w e l l - d e f e n d e d f r o m h e r b i v o r y . I f we a s s u m e t h a t t h e f o r m e r f i n d i n g s a p p l y i n e l e p h a n t f o r a g e s p e c i e s , t h e n t h e o b s e r v a t i o n s t h a t e l e p h a n t s a t e l e s s b r o w s e a n d h a d s h o r t e n e d f e e d i n g b o u t s on b r o w s e s p e c i e s i n t h e wet s e a s o n , when new g r o w t h was a b u n d a n t , l e n d s s u p p o r t t o t h e h y p o t h e s i s t h a t e l e p h a n t s f o r a g e i n a m a n n e r a i m e d a t m i n i m i z i n g t h e i r t o x i c i n t a k e . H o w e v e r , i f we a s s u m e t h e l a t t e r f i n d i n g s t o be t r u e i n t h i s c a s e , t h e n we m u s t l o o k f o r o t h e r e x p l a n a t i o n s f o r t h e o b s e r v e d d i e t c h o i c e s . B u t C o l e y ( 1 9 8 0 ) p o i n t e d o u t t h a t t h e l a t t e r , m o r e c l a s s i c a l v i e w s o f p l a n t d e f e n s e s t r a t e g i e s , w e r e l a r g e l y d e v e l o p e d f o r 116 temperate systems and needed to be re - examined , p a r t i c u l a r l y i n t r o p i c a l systems, where o p p o s i t e p a t t e r n s have tended to be the c a s e . As most work on p l a n t - h e r b i v o r e c o e v o l u t i o n has been conducted in the n e o t r o p i c s and the temperate zones , more work i s r e q u i r e d on p a t t e r n s of p l a n t defense among A f r i c a n s p e c i e s , which have evo lved w i t h a broad range of h e r b i v o r e s for m i l l i o n s of y e a r s . O l i v i e r (1978) argued t h a t the d i g e s t i v e system of e l e p h a n t s renders them more s e n s i t i v e to p l a n t t o x i n s than s y m p a t r i c ruminants and that t h i s i n f l u e n c e s t h e i r d i e t c h o i c e . Whi le i t may be t r u e tha t e l e p h a n t s are s e n s i t i v e to p l a n t t o x i n s , i t i s a l s o the case t h a t they have v e r y h i g h a b s o l u t e d a i l y energy requ irements (S ikes 1971, Laws e_t a_l. 1 975) . In order to meet these needs d u r i n g t imes of food s h o r t a g e , e l ephant d i e t s may be chosen p r i m a r i l y to maximize energy i n t a k e and s e c o n d a r i l y to min imize t o x i n i n g e s t i o n . To a c h i e v e t h i s , e l e p h a n t s may d i v e r s i f y t h e i r d i e t s and , t h u s , a v o i d a b u i l d u p of t o x i n s from defended p l a n t s w h i l e s t i l l meet ing t h e i r energy needs . A l t h o u g h t o x i n s may ac t s e c o n d a r i l y to i n t e r f e r e w i t h d i g e s t i v e p r o c e s s e s and energy a s s i m i l a t i o n , i t i s u n l i k e l y t h a t e l e p h a n t s are s e r i o u s l y a f f e c t e d by t o x i c i t y l e v e l s i n the d i e t . E l e p h a n t s a r e , however, a f f e c t e d by d e c l i n i n g food q u a l i t y and q u a n t i t y . When the a v a i l a b i l i t y of s u i t a b l e forage f a l l s below s u b s i s t e n c e l e v e l s , e l e p h a n t s i n i t i a l l y show a d e c l i n e i n o v e r a l l body c o n d i t i o n ( A l b l 1971, Guy 1976, Barnes 1982), i n acute c a s e s , they may even s t a r v e to death ( C o r f i e l d 1973), w h i l e i n c h r o n i c s i t u a t i o n s they may show d e c l i n i n g r e p r o d u c t i v e r a t e s , d e f e r r e d s e x u a l m a t u r i t y , l engthened i n t e r b i r t h 1 1 7 i n t e r v a l s , and i n c r e a s e d c a l f m o r t a l i t y (Laws et a l . 1975, Laws 1981b, Weyerhaeuser 1982). Masai Mara e l e p h a n t s tended to p i c k the most n u t r i t i o u s s p e c i e s f i r s t (grasses f o l l o w i n g the r a i n s and browse s p e c i e s i n the dry s e a s o n ) , and r e s o r t e d to p o o r e r q u a l i t y forage o n l y as the former became u n a v a i l a b l e . In g e n e r a l , e l ephant f o r a g i n g p a t t e r n s appeared to be aimed more at max imiz ing energy i n t a k e than m i n i m i z i n g t o x i n l o a d s . E f f e c t s of the w i l d e b e e s t m i g r a t i o n The Masai Mara Game Reserve i s the northernmost e x t e n s i o n of the S e r e n g e t i - M a r a ecosystem where, every dry season, over a m i l l i o n m i g r a t o r y w i l d e b e e s t take up r e s i d e n c e . These m i g r a n t s remove over 90% of the s t a n d i n g c r o p d u r i n g t h e i r s tay ( F i g u r e 4 . 9 ) . Immediately f o l l o w i n g c e s s a t i o n of the r a i n s and p r i o r to the a r r i v a l of the w i l d e b e e s t , both sexes of e l ep h an t s showed an obv ious p r e f e r e n c e f o r g r a s s e s . At t h i s t ime , the newly germinated g r a s s e s were very abundant and at the peak of t h e i r d i g e s t i b l e p r o t e i n l e v e l s ( F i g u r e 4 . 1 0 ) . However, upon the a r r i v a l of the w i l d e b e e s t , a d i s t i n c t change in d i e t c h o i c e o c c u r r e d . E l e p h a n t s immediate ly d e c r e a s e d t h e i r f e e d i n g on g r a s s and they s topped f e e d i n g on g r a s s a l t o g e t h e r in the l a t t e r s tages of the w i l d e b e e s t occupancy , d e s p i t e the p r o d u c t i o n of new gras s f o l l o w i n g i n t e r m i t t e n t l o c a l s torms . W i l d e b e e s t kept the g r a s s e s grazed down to lawn h e i g h t (McNaughton 1984). At t h i s h e i g h t g r a s s e s may have become d i f f i c u l t f or e l e p h a n t s to e a t . T h i s change in f e e d i n g p a t t e r n s p r o b a b l y r e f l e c t e d a 118 0 0 s co < o I — I m o DS o I — I Q CO 350 300 250- 200- 150 100 50 M J J A S 0 MONTH Figure 4.9. Standing crop biomass through the dry season (during the time the migratory wildebeest are present in the study area). 119 12-i 11- ^ 10-» — i W EH O DH DH W Q P DH O w U DH w DU 9 H 8- 7- 6- 5- 4- 3 2 H n 1 1 1 i i M J J A S 0 MONTH Figure 4.10. Percent crude protein of long grasses over the course of the dry season (redrawn from S i n c l a i r 1975). 1 20 d e c l i n e i n both g r a s s q u a n t i t y and q u a l i t y . Woody s p e c i e s remain r e l a t i v e l y h i g h e r i n crude p r o t e i n than herbaceous s p e c i e s as the dry season p r o g r e s s e s . Pe l lew (1981) r e p o r t e d t h a t some p r e f e r r e d browse s p e c i e s , such as Acac i a g e r r a r d i i , A . S e n e g a l , and Commiphora t r o t h a e , m a i n t a i n e d crude p r o t e i n l e v e l s above 13% even i n o l d e r l e a v e s . D o u g a l l (1963) and D o u g a l l et a l . (1964) found even h i g h e r v a l u e s f o r the mature l e a v e s of A c a c i a b r e v i s p i c a (17%), B o s c i a a n g u s t i f o l i a (33%), and Solanum incanum (30%) which were a l s o used by Mara e l e p h a n t s i n the dry season . The g r a s s e s eaten by e l e p h a n t s , such as Themeda t r i a n d r a and Cynodon d a c t y l o n drop as low as 5% and 8% crude p r o t e i n d u r i n g the dry season (Douga l l 1963, D o u g a l l and G l o v e r 1964, F i e l d 1971, S i n c l a i r 1975). By the h e i g h t of the d r y season , e l e p h a n t s spent the m a j o r i t y of t h e i r f e e d i n g t ime on the a v a i l a b l e browse s p e c i e s ( F i g u r e 4 . 1 1 ) . Throughout A f r i c a e l e p h a n t s are c o n s i d e r e d the pr imary agents of h a b i t a t change (Laws 1970, Thomson 1975). A l t h o u g h F i e l d (1971) suggested tha t g i r a f f e may compete w i t h e l ephant under c e r t a i n c i r c u m s t a n c e s , no o t h e r s p e c i e s i s known to a l t e r h a b i t a t s as s i g n i f i c a n t l y , or to compete w i t h e l e p h a n t s f o r g r a z i n g r e s o u r c e s . The ev idence p r o v i d e d above , however, sugges ts t h a t the sheer numbers of m i g r a t o r y w i l d e b e e s t , coming i n t o the Mara each y e a r , so a l t e r the h a b i t a t d u r i n g t h e i r a n n u a l s tay that they come i n t o d i r e c t c o m p e t i t i o n w i t h e l e p h a n t s l a t e in the dry season . A l though e l ep h an t browsing a c t i v i t y i n c r e a s e s s i g n i f i c a n t l y d u r i n g any p e r i o d of low r a i n f a l l ( F i g u r e 4 . 8 ) , c o m p e t i t i o n wi th the w i l d e b e e s t may e x a c e r b a t e t h i s p a t t e r n and r e s u l t in e l e p h a n t s p l a c i n g even 1 2 1 Figure 4 . 1 1 . Grams crude protein per m 2 of long grasses during the dry season ( l e f t a x i s , l i n e graph) and a percentage breakdown of elephant d i e t s between grazing (G) and browsing (B) in the wet and dry seasons (right a x i s , bar graphs). 1 22 g r e a t e r p r e s s u r e on a v a i l a b l e b r o w s e s p e c i e s i n t h e d r y s e a s o n . C r o z e ( 1 9 7 4 a ) s t u d i e d t h e f e e d i n g b e h a v i o u r o f b u l l e l e p h a n t s i n a n a r e a o f t h e c e n t r a l S e r e n g e t i w h e r e w i l d e b e e s t w e r e n o t p r e s e n t i n t h e d r y s e a s o n . He f o u n d t h a t b u l l s s p e n t a p p r o x i m a t e l y 70% o f t h e i r t i m e i n t h e A c a c i a w o o d l a n d s a n d 30% o f t h e i r t i m e i n v e g e t a t i o n a l o n g p e r m a n e n t w a t e r s o u r c e s . B e t w e e n t h e two h a b i t a t s , b r o w s i n g t o o k u p 34% o f t h e e l e p h a n t s ' f e e d i n g t i m e . T h i s i s i n c o n t r a s t t o e l e p h a n t s i n t h e M a r a who s p e n t 70% o f t h e i r f o r a g i n g t i m e on b r o w s e d u r i n g t h e d r y s e a s o n . E f f e c t s o f s e a s o n a l c h a n g e F e m a l e e l e p h a n t s s e e m e d t o be more s e n s i t i v e t o e n v i r o n m e n t a l c h a n g e s t h a n t h e i r m a l e c o u n t e r p a r t s . Cow e l e p h a n t s a r e e i t h e r p r e g n a n t o r l a c t a t i n g t h r o u g h o u t m o s t o f t h e i r a d u l t l i v e s a n d , t h e r e f o r e , t h e i r e n e r g y demands a r e h i g h r e l a t i v e t o m a l e s . F e m a l e f o r a g i n g p a t t e r n s d i f f e r e d f r o m m a l e s i n w a y s w h i c h may r e f l e c t t h e s e e n e r g e t i c d i f f e r e n c e s . T h r o u g h o u t t h e y e a r , f e m a l e s m a i n t a i n e d a h i g h e r a b s o l u t e d i e t d i v e r s i t y t h a n m a l e s a n d t h i s d i f f e r e n c e became e v e n g r e a t e r i n t h e d r y s e a s o n . T h i s e x p a n s i o n i n f e m a l e d i e t c h o i c e was c o n s i s t e n t w i t h t h e p r e d i c t i o n f r o m o p t i m a l f o r a g i n g t h e o r y t h a t f o r a g e r s s h o u l d e x p a n d t h e i r d i e t s t o i n c l u d e l e s s - p r e f e r r e d i t e m s when more d e s i r a b l e i t e m s become l e s s a v a i l a b l e ( S c h o e n e r 1 9 7 1 , P y k e 1 9 8 4 ) . M a l e s s h o w e d no p a r a l l e l s e a s o n a l c h a n g e i n d i e t d i v e r s i t y . W i t h l o w e r r e l a t i v e e n e r g e t i c r e q u i r e m e n t s m a l e s may h a v e b e e n a b l e t o mee t t h e i r n e e d s by i n c r e a s i n g t h e i r b u l k i n t a k e r a t e on a few s p e c i e s d u r i n g e n e r g y - l i m i t e d t i m e s , 1 23 r a t h e r than by d i v e r s i f y i n g t h e i r d i e t s . O l i v i e r (as c i t e d by Barnes 1982) s p e c u l a t e d t h a t due to t h e i r s m a l l e r body s i z e females must be even more c a u t i o u s of t o x i n c o n t e n t than b u l l s . T h i s proposed d i f f e r e n c e i n s e n s i t i v i t y to t o x i n s c o u l d p a r t i a l l y e x p l a i n why females e l e p h a n t s d i v e r s i f i e d t h e i r d i e t s and reduced the r i s k of dangerous t o x i n l e v e l s i n any s i n g l e s p e c i e s . R e l a t i v e d i e t d i v e r s i t y or d i e t a r y "evenness" d i d not change s e a s o n a l l y i n b u l l s or cows when a l l forage types were compared. E l e p h a n t f o r a g i n g t ime was d i s t r i b u t e d s i m i l a r l y among a l l s p e c i e s of g r a s s e s , h e r b s , s h r u b s , t r e e s , and s e e d l i n g s throughout the y e a r . However, an a n a l y s i s of browse s p e c i e s o n l y showed s i g n i f i c a n t d i f f e r e n c e s between sexes and between seasons . Males fed more e v e n l y than females i n the wet season whereas females showed no s easona l change. These f i n d i n g s suggest tha t males d i s t r i b u t e d t h e i r t ime more e v e n l y among more browse s p e c i e s d u r i n g the wet season . G r e a t e r d i e t "evenness" i n the wet season may have been l a r g e l y due to the s imul taneous s p r o u t i n g peak of a v a r i e t y of s e e d l i n g s f o l l o w i n g the onset of the r a i n s . T h i s f l u s h of new growth a l l o w e d b u l l s to d i s t r i b u t e t h e i r f o r a g i n g time among a broad range of n u t r i t i o u s browse i t e m s . Barnes (1982) r e p o r t e d these same s e a s o n a l p a t t e r n s of d i e t evenness for b u l l e l e p h a n t s but had no comparable data for cows. I t was assumed tha t the l e n g t h of f o r a g i n g bouts was p o s i t i v e l y c o r r e l a t e d to the a b s o l u t e amount of forage consumed, though the q u a n t i t a t i v e e x p r e s s i o n of t h i s r e l a t i o n s h i p i s c u r r e n t l y b e i n g i n v e s t i g a t e d by L i n d s a y ( i n p r e p . ) . B u l l s and 124 cows d i d not d i f f e r s i g n i f i c a n t l y from one another i n the l e n g t h of t h e i r f o r a g i n g bouts throughout the y e a r . In the d r y season, both sexes had s i g n i f i c a n t l y l onger bouts when a n a l y z e d a c r o s s a l l forage t y p e s . Presumably , once a good forage type was found, e l e p h a n t s fed f o r a l onger t ime b e f o r e s w i t c h i n g to a new t y p e . These longer f o r a g i n g bouts i n the dry season were accounted for by d i f f e r e n c e s i n the use of i n d i v i d u a l forage types by b u l l s and cows. Females spent s i g n i f i c a n t l y longer bouts on h e r b s , t r e e s and s e e d l i n g s , w h i l e males i n c r e a s e d the l e n g t h of f o r a g i n g bouts on shrubs and t r e e s . T h i s i s s i m i l a r to Barnes ' (1982) o b s e r v a t i o n s on the browsing p a t t e r n s of b u l l s season i n Ruaha N a t i o n a l P a r k , T a n z a n i a . Both sexes had s i g n i f i c a n t l y longer f e e d i n g bouts on gras se s i n the e a r l y dry season than in the l a t e dry season or wet seasons . T h i s s easona l d i f f e r e n c e i n f o r a g i n g bouts on g r a s s e s has been i n t e r p r e t e d as a r e f l e c t i o n of the e l e p h a n t s ' p r e f e r e n c e for h i g h g r a s s q u a l i t y and q u a n t i t y immediate ly f o l l o w i n g the r a i n s , j u s t p r i o r to the a r r i v a l of the w i l d e b e e s t m i g r a t i o n (see a b o v e ) . The c h a r a c t e r i s t i c s of food p l a n t s used by e l e p h a n t s remained c o n s i s t e n t throughout the y e a r . Cows and b u l l s a te a l l forage types i n t h e i r green l e a f c o n d i t i o n , when a v a i l a b l e . Leaves and shoots were always eaten more than o ther p l a n t p a r t s , such as t w i g s , b a r k , or b r a n c h e s . Some use of r o o t s and bark o c c u r r e d i n the dry season . T h i s same p a t t e r n was seen by F i e l d (1971) , F i e l d and Ross (1976), Guy (1976), O l i v i e r (1978), Barnes (1982) , and Ishwaran (1983) i n e l e p h a n t s from d i f f e r e n t l o c a l i t i e s . F i e l d (1971) e x p l a i n s t h i s as the r e s u l t of 1 25 e l e p h a n t s c o n s t a n t l y s eek ing the h i g h e s t a v a i l a b l e crude p r o t e i n l e v e l s i n t h e i r f o r a g e . E f f e c t s of woodland d i s a p p e a r a n c e E l e p h a n t s fed p r i m a r i l y i n the 0 - 1m h e i g h t range . A l t h o u g h e l e p h a n t s expanded t h e i r d i e t s to i n c l u d e o ther h e i g h t c l a s s e s d u r i n g the dry season , t h e i r f e e d i n g below one meter accounted f o r an annual mean of 80% of the browse d i e t s . Because s e e d l i n g s were o f t e n consumed at a r a t e of over 400 per h o u r , the e f f e c t s were n o t i c e a b l e when e n t i r e herds began "weeding" out s e e d l i n g s in open g r a s s l a n d s . In a l l o ther forage t y p e s , f e e d i n g took p l a c e e x c l u s i v e l y in the 0 - 1m h e i g h t range . These f i n d i n g s are c o n s i s t e n t w i t h those of Brooks (1957) , Buss (1961), Wing and Buss (1970), F i e l d and Ross (1976), Guy (1976) , and Weyerhaeuser (1985) but c o n t r a r y to those of Croze (1974b) for e l e p h a n t s of the c e n t r a l S e r e n g e t i woodlands i n the e a r l y 1970's . Croze found t h a t e l e p h a n t s fed l a r g e l y i n p r o p o r t i o n to a v a i l a b i l i t y for a l l s i z e c l a s s e s except those under one meter , which were r a r e l y e a t e n . E i t h e r e l ephant food p r e f e r e n c e s have changed for reasons which are not c l e a r or t h i s h i g h use of forage under one meter i s a d i r e c t r e s u l t of the change i n r e l a t i v e a v a i l a b i l i t y of forage i n o t h e r , p o s s i b l y more p r e f e r r e d , h e i g h t c l a s s e s . E i t h e r way, t h i s d i f f e r e n t i a l use of s e e d l i n g s may account f o r a s i g n i f i c a n t p r o p o r t i o n of the l o s t r e c r u i t m e n t p o t e n t i a l i n l o c a l t r e e p o p u l a t i o n s t o d a y . We know tha t major changes i n woodland communit ies have taken p l a c e over the past 25 y e a r s . These i n c l u d e a l o s s of 126 t r e e cover i n the l a r g e r h e i g h t c l a s s e s throughout the Mara Game R e s e r v e . Some areas have e x p e r i e n c e d as much as a 95% r e l a t i v e l o s s s i n c e 1950 (Chapter 2 ) . T h i s d e c l i n e was l a r g e l y the r e s u l t of f i r e and e l ephant impacts on the t r e e s in the p a s t , and t h e i r c o n t i n u e d n e g a t i v e i n f l u e n c e on s e e d l i n g r e g e n e r a t i o n , today (Chapter 5 ) . These impacts were exacerbated by o ther f a c t o r s , such as w i l d e b e e s t and s m a l l , mammalian browsers (Be l sky 1984). W h i l e e l e phant s are c e r t a i n l y one of the p r i m a r y b i o l o g i c a l f a c t o r s i n woodland changes , Mara e l ephant d e n s i t i e s ( a p p r o x i m a t e l y 0.75 - 1 .00/km 2 ) are low r e l a t i v e to o ther parks and r e s e r v e s i n A f r i c a . T a n z a n i a ' s Lake Manyara N a t i o n a l Park s u p p o r t s d e n s i t i e s up to 6 . 0 0 / k m 2 (Weyerhaeuser 1982), w h i l e Kenya ' s Ambose l i N a t i o n a l Park has l o c a l d e n s i t i e s up to 10 .00 /km 2 (Western and L i n d s a y 1985). Few obv ious s i g n s of e l ephant a c t i v i t y meet the eyes of c a s u a l o b s e r v e r s i n t o d a y ' s Masai Mara Game R e s e r v e . S t a n d i n g t r e e s are not u n i f o r m l y b a r k - s t r i p p e d or t o p p l e d , e l e p h a n t s are e x e r t i n g a more s u b t l e i n f l u e n c e . The p r e s e n t day r o l e of Masai Mara e l e p h a n t s i n woodland dynamics i s not so much one of d e s t r o y e r as one of i n h i b i t o r (Chapter 5 ) . The r e l a t i v e c o n t r i b u t i o n of e l e p h a n t s to the l o s s of a d u l t t r e e s or the i n h i b i t i o n of woodland r e g e n e r a t i o n may be h i g h l y dependent on l o c a l weather c o n d i t i o n s . Dry y e a r s , l i k e 1984, l e a d to i n c r e a s e d brows ing on woody p l a n t s p e c i e s because of the e l e p h a n t s ' dependence on browse d u r i n g dry p e r i o d s . The innate a b i l i t y of e l e p h a n t s to sw i t ch to g r a s s e s when browse s p e c i e s have been v i r t u a l l y e l i m i n a t e d , makes them a u n i q u e , and 127 p o t e n t i a l l y more d e t r i m e n t a l h e r b i v o r e than those s t r i c t browsers , l i k e g i r a f f e s , whose p o p u l a t i o n dynamics are more c l o s e l y l i n k e d to browse a v a i l a b i l i t y ( F i e l d 1971, N o r t o n - G r i f f i t h s 1979, Pe l lew 1983). A l t h o u g h e l ephant p o p u l a t i o n s might e v e n t u a l l y respond to woodland h a b i t a t l o s s through d e c r e a s e d r e p r o d u c t i v e r a t e s as suggested by Laws et a l . (1975) i t may be too l a t e to save a f f e c t e d t r e e p o p u l a t i o n s . And , even i f the woodlands c o u l d s u r v i v e u n t i l a d e c l i n e i n e l ephant numbers o c c u r s , o ther b r o w s e r s , f i r e s , and the m i g r a t o r y w i l d e b e e s t , might e f f e c t i v e l y i n h i b i t woodland r e g e n e r a t i o n . Summary The f e e d i n g eco logy of f r e e - r a n g i n g e l e p h a n t s i n the Masai Mara Game Reserve was s t u d i e d over a two and a h a l f year p e r i o d by d i r e c t o b s e r v a t i o n . The s tudy i n v e s t i g a t e d the s easona l use of g r a s s e s , s h r u b s , h e r b s , s e e d l i n g s , and a d u l t t r e e s by both male and female e l e p h a n t s , w i t h an emphasis on the o v e r a l l impacts of e l e p h a n t s on the remain ing woodlands and t h i c k e t s . Both male and female e l e p h a n t s c o n c e n t r a t e d on g r a s s e s and herbs i n the wet season and woody s p e c i e s i n the d r y . Males c o n s i s t e n t l y browsed more than females , whi l e females used more herbaceous f o r a g e . E l e p h a n t d i e t s changed upon the a r r i v a l of the m i g r a t o r y w i l d e b e e s t h e r d s , s w i t c h i n g from g r a z i n g to browsing as the s t a n d i n g c r o p of g r a s s was r a p i d l y reduced by the m i g r a n t s . Females m a i n t a i n e d a h i g h e r a b s o l u t e d i e t d i v e r s i t y than males throughout the y e a r . T h i s d i f f e r e n c e was most pronounced i n the dry season . Males d i s t r i b u t e d t h e i r • f o r a g i n g t ime more even ly among the a v a i l a b l e browse s p e c i e s 128 d u r i n g the wet season than d u r i n g the d r y , whereas females showed no s easona l change . However, at the h e i g h t of the dry season , a few favoured browse s p e c i e s were fed upon d i s p r o p o r t i o n a t e l y by both sexes . Both sexes had longer f o r a g i n g bouts i n the dry season i n d i c a t i n g t h a t once a good forage type was found, e l ephant fed longer b e f o r e s w i t c h i n g to a new t y p e . E l e p h a n t s c o n c e n t r a t e d t h e i r f e e d i n g a c t i v i t y i n the 0 - 1m h e i g h t c l a s s and almost e x c l u s i v e l y a te the green l eaves and shoots of a l l forage t y p e s . E l e p h a n t impacts on woody v e g e t a t i o n in the Mara i n c r e a s e d in the dry season . These impacts were f u r t h e r e x a c e r b a t e d by the a r r i v a l of the m i g r a t o r y w i l d e b e e s t who removed almost a l l a v a i l a b l e gras s l e a v i n g no a l t e r n a t i v e forage f o r the e l e p h a n t s . As w e l l , the e l e p h a n t s c u r r e n t l y have r e s t r i c t e d a c c e s s to t h e i r former dry season d i s p e r s a l areas which are now e x p e r i e n c i n g a g r i c u l t u r a l development , i n t e n s i v e l i v e s t o c k g r a z i n g , and severe poach ing a c t i v i t y . As a r e s u l t , e l e p h a n t s are c u r r e n t l y a p r i m a r y f a c t o r i n the i n h i b i t i o n of woodland r e g e n e r a t i o n in the Mara Game R e s e r v e . 129 CHAPTER 5. THE EFFECTS OF ELEPHANTS, F I R E , WILDEBEEST AND BROWSERS ON THE ACACIA WOODLANDS I n t r o d u c t ion The l o s s of woodlands i n the Masai Mara Game Reserve of Kenya over the past 30 y e a r s has l e f t the area an open g r a s s l a n d . These woodlands f o r m e r l y p r o v i d e d both food and p r o t e c t i o n for many s p e c i e s of w i l d l i f e . Today , there i s l i t t l e woody m a t e r i a l a v a i l a b l e to browsing s p e c i e s and much of the cover a f f o r d e d o ther s p e c i e s has dwindled away (Glover and Trump 1970, D u b l i n 1984, Lamprey 1985). The p o t e n t i a l f o r r e g e n e r a t i o n of these woodlands i s of i n t e r e s t from both an e c o l o g i c a l and a management p e r s p e c t i v e . R e g e n e r a t i o n seems to be l i m i t e d by e x i s t i n g b i o l o g i c a l c o n d i t i o n s i n the R e s e r v e . The r e c o v e r y of these woodlands i s now dependent on the a b i l i t y of s e e d l i n g s to e s t a b l i s h themselves and grow to m a t u r i t y . I t has been h y p o t h e s i z e d tha t t h i s p r o c e s s i s c u r r e n t l y be ing i n h i b i t e d by a combinat ion of s e v e r a l b i o l o g i c a l f a c t o r s ; each one a f f e c t i n g the woodlands i n d i f f e r e n t ways at d i f f e r e n t t i m e s . Based on past work, B e l s k y (1984) summarized these agents of m o r t a l i t y and i n h i b i t i o n as f i r e , e l e p h a n t s , and g i r a f f e . She added the e f f e c t s of s m a l l browsing mammals and w i l d e b e e s t to t h i s l i s t but d i d not q u a n t i f y t h e i r r e l a t i v e impacts on woodlands. A l t h o u g h r e s e a r c h has been done on the e f f e c t s of these f a c t o r s on mature t r e e s and t h e i r i n f l u e n c e on woodland dynamics i n l o c a l areas of the S e r e n g e t i N a t i o n a l Park ( G l o v e r 1965, Lamprey et a l . 1967, Croze 1974a & b, N o r t o n - G r i f f i t h s 1979, Pe l l ew 1983), no q u a n t i t a t i v e i n f o r m a t i o n was 130 a v a i l a b l e on the p r o c e s s of s e e d l i n g e s t a b l i s h m e n t and i t s r o l e i n woodland r e g e n e r a t i o n in the Mara t o d a y . The exper iments i n t h i s s tudy were des igned to s eparate and a n a l y z e the r e l a t i v e e f f e c t s of f i r e , e l e p h a n t s , and w i l d e b e e s t on s e e d l i n g p o p u l a t i o n s . U s i n g e x p e r i m e n t a l e v i d e n c e , t h i s c h a p t e r examines the hypotheses t h a t these f a c t o r s , a c t i n g a lone or i n c o m b i n a t i o n , are e f f e c t i v e l y i n h i b i t i n g s e e d l i n g e s t a b l i s h m e n t and the r e c o v e r y of Acac i a woodlands i n the Masai Mara Game R e s e r v e . Background I n f o r m a t i o n A s t r o n g c o r r e l a t i o n has been e s t a b l i s h e d between f i r e and woodland l o s s i n the S e r e n g e t i - M a r a ecosystem ( N o r t o n - G r i f f i t h s 1979, Lamprey 1985, D u b l i n , Chapter 2 ) . Throughout A f r i c a f i r e has l o n g been r e c o g n i z e d as a p r i m a r y f a c t o r i n t r e e m o r t a l i t y and the i n h i b i t i o n of s e e d l i n g growth ( C h a r t e r and Keay 1960, Buechner and Dawkins 1961, G l o v e r 1965, 1968, S e i f E l Din and Obe id 1971, Spinage and Guinness 1972, H a r r i n g t o n and Ross 1974, Thomson 1975, Brookman-Amissah et a l . 1980, T r o l l o p e 1982a, S a b i i t i 1986). For these r e a s o n s , f i r e has been w i d e l y used as a t o o l to combat bush encroachment and p r o t e c t domest ic g r a z i n g l ands (West 1958, Thomas and P r a t t 1967, P r a t t and K n i g h t 1971, S t r a n g 1973, 1974, T r o l l o p e 1972, 1982b). However, i n n a t u r a l ecosys tems , l i k e the S e r e n g e t i - M a r a , e c o l o g i s t s and managers have l ooked f o r ways to min imize the d e t r i m e n t a l e f f e c t s of f i r e on woodlands and g r a s s l a n d s . N o r t o n - G r i f f i t h s (1979) e s t i m a t e d that over a t e n - y e a r 131 p e r i o d (1962-1972) the canopy cover of woodlands in the n o r t h e r n S e r e n g e t i had d e c l i n e d by 26% on average and up to 50% i n the northernmost a r e a s . He a t t r i b u t e d these l o s s e s p r i m a r i l y to the e f f e c t s of i n c r e a s e s i n the f requency and s e v e r i t y of f i r e s . However, he d i d not c onc l ude that f i r e a lone was r e s p o n s i b l e for the l o s s of canopy c o v e r . In o ther areas w i t h i n the system, he r e p o r t e d an o v e r a l l woodland l o s s of 7% over t h i s same time p e r i o d . These l o s s e s were a t t r i b u t e d to an i n c r e a s e i n l o c a l e l ephant d e n s i t i e s and the subsequent impact of t h e i r browsing a c t i v i t i e s on i n d i v i d u a l woodland s t a n d s . Croze (1974a & b) d e s c r i b e d i n g r e a t e r d e t a i l the r o l e of e l e p h a n t s i n the dynamics of the c e n t r a l S e r e n g e t i woodlands . He e s t i m a t e d the l o s s of mature t r e e s to e l e p h a n t s at a r a t e of 2.5% per year on a v e r a g e , w i t h l o c a l l o s s e s as h i g h as 6.0% per y e a r . Based upon the age s t r u c t u r e of t r e e s i n h i s s tudy a r e a , he c o n c l u d e d t h a t under these c o n d i t i o n s , e l e p h a n t s d i d not pose a severe t h r e a t to the f u t u r e of woodlands . G l o v e r (1965) , Lamprey et a l . (1967), and H e r l o c k e r (1976a) d i s a g r e e d , a r g u i n g t h a t e l ephant r e l a t e d damage was more e x t e n s i v e and woodland r e - e s t a b l i s h m e n t more l i m i t e d . These s t u d i e s c o n c e n t r a t e d p r i m a r i l y on the impact of e l e p h a n t s on mature t r e e s i n a r e s t r i c t e d a r e a of the system and l e s s on the e f f e c t of e l e p h a n t s on s e e d l i n g s u r v i v o r s h i p i n g e n e r a l . Over the pas t 20 y e a r s , the S e r e n g e t i ' s m i g r a t o r y w i l d e b e e s t p o p u l a t i o n has i n c r e a s e d by a f a c t o r of f i v e ( S i n c l a i r and N o r t o n - G r i f f i t h s 1979). N o r t o n - G r i f f i t h s (1979) s p e c u l a t e d t h a t the i n c r e a s e of these g e n e r a l i z e d g r a z e r s would reduce the s t a n d i n g c r o p of gras s thereby r e d u c i n g f i r e s e v e r i t y 1 32 and enhancing s e e d l i n g s u r v i v o r s h i p . However, w i l d e b e e s t have o t h e r d i r e c t l y d e t r i m e n t a l e f f e c t s on the woody v e g e t a t i o n . W i l d e b e e s t damage s e e d l i n g s in s i g n i f i c a n t numbers through t h e i r t r a m p l i n g , i n a d v e r t e n t b r o w s i n g , and s p a r r i n g a c t i v i t i e s d u r i n g the r u t . These e f f e c t s are p r e d i c t e d to be most pronounced i n the n o r t h e r n S e r e n g e t i and Mara woodlands where the w i l d e b e e s t have the most extended c o n t a c t w i t h woody s p e c i e s d u r i n g t h e i r annua l dry season m i g r a t i o n . Pe l l ew (1981, 1983), working i n the c e n t r a l S e r e n g e t i woodlands , i n v e s t i g a t e d the r o l e which g i r a f f e s p l a y e d in l o c a l woodland dynamics . He c o n c l u d e d that the r a t e of growth of t r e e s from one s i z e - c l a s s i n t o the next was h e a v i l y dependent on the extent of browsing by g i r a f f e . T h i s browsing r e t a r d e d the growth of t r e e s and p r o l o n g e d t h e i r p e r i o d of f i r e - s u s c e p t i b i l i t y . The o v e r a l l e f f e c t merely compounded the impacts of f i r e and e l e p h a n t s on woodland r e g e n e r a t i o n . In the Masai Mara Game R e s e r v e , the e f f e c t s of g i r a f f e are m i n i m a l . The e x i s t i n g woodland communit ies are not f a v o u r a b l e f o r g i r a f f e s due to the l o s s of t r e e s i n the h e i g h t c l a s s e s they p r e f e r . These l o s s e s exceed those found by N o r t o n - G r i f f i t h s (1979) in the n o r t h e r n S e r e n g e t i ( D u b l i n , Chapter 2 ) . C o n s e q u e n t l y , many g i r a f f e s have emigrated to o ther areas and t h e r e has been a consequent decrease in t h e i r p o p u l a t i o n numbers w i t h i n the Reserve (Lamprey 1985, K . R . E . M . U . u n p u b l . d a t a ) . Woodland r e g e n e r a t i o n in the Mara i s , n o n e t h e l e s s , i n s e r i o u s j e o p a r d y . E l e p h a n t s c u r r e n t l y r e s i d e y e a r - r o u n d in unprecedented numbers, f i r e s c o n t i n u e to b u r n , and there are the added t r a m p l i n g , t h r a s h i n g , and browsing e f f e c t s of an i n c r e a s e d 133 w i l d e b e e s t p o p u l a t i o n which v i s i t s the a r e a f o r t h r e e to four months each y e a r . Methods F i v e s tudy s i t e s were e s t a b l i s h e d w i t h i n the Acac i a g e r r a r d i i woodland communi t i e s . S i t e s were s e l e c t e d for homogeneity of c o m p o s i t i o n , h e i g h t d i s t r i b u t i o n s and d e n s i t y of s e e d l i n g s between s i t e s . One-way ANOVAS were conducted on t r a n s f o r m e d (see below) h e i g h t s and stem numbers of each of the f i v e s i t e s when the s tudy began. There was no s i g n i f i c a n t d i f f e r e n c e amongst any of the f i v e s i t e s on e i t h e r h e i g h t or number of stems ( h e i g h t s : F = 2 .04 , n . s . ; stems: F = 1.86, n . s . ) . A l s o , s i t e s were d e s c r i b e d i n terms of the d e n s i t i e s and frequency d i s t r i b u t i o n s of A c a c i a s i n the d i f f e r e n t h e i g h t c l a s s e s measured (Table 5 . 1 , F i g u r e 5 . 1 ) . These d i s t r i b u t i o n s show a s i z e s t r u c t u r e which i s h e a v i l y b i a s e d towards the under 1m h e i g h t c l a s s , w i t h o ther h e i g h t c l a s s e s c o m p r i s i n g o n l y a s m a l l p r o p o r t i o n of a l l t r e e s and o c c u r r i n g i n very low numbers. Each s i t e was d i v i d e d i n t o t h r e e s epara te treatment p l o t s : (a) burned and browsed, (b) browsed o n l y and (c) n e i t h e r burned nor browsed. Treatments (a) and (b) were conducted i n 25 x 100m p l o t s . Treatment (c) p l o t s were 15 x 15m fenced e x c l o s u r e s . The l a t t e r e xc l ude d a l l l a r g e browsing mammals. G r a z e r s had f r e e a c c e s s to t rea tments (a) and (b) but not ( c ) . Each treatment p l o t was surrounded by a 10m f i r e b r e a k to guard a g a i n s t i n v a s i o n by w i l d f i r e s . 134 Table 5.1. Seedling densities per hectare by height c l a s s . Mean densities (± one s.d.) are also presented. HEIGHT CLASS (m) SITE NO. 0-1 1 850 1-2 2-3 3+ 25 38 36 982 1105 720 19 17 20 32 < 0 29 24 0 32 51 37 5 595 0 Mean Density: 850 ± 202 12 ± 1 1 29 ± 17 32 ± 5 135 SITE 1 SITE 2 100- B 80 < - d 2 60H 40- £ 20H CL 0-1 1-2 2-3 HEIGHT (m) 3+ lOO-i CO AS  80- CL 2 60- NT  40- CE ER 20-a. 1 -JZ3- 0-1 1-2 2-3 3+ HE1GHT (m) SITE 3 SITE 4 c_> u u lOO-i 80- 60- 40 20 H 0 0-1 1-2 2-3 HEIGHT (m) 3+ e w lOO-i 80- 60- 40- 20- 0 1 0-1 1-2 2-3 3+ HEIGHT (m) SITE 5 8 o 2 lOO-i 80- 80- 40- 20 0 I — i - r <=P- -1 1-2 2-3 3+ HEIGHT (m) Figur e 5.1. Height d i s t r i b u t i o n s of Acacia g e r r a r d i i i n f i v e sample s i t e s . 1 36 M e a s u r i n g the E f f e c t s of Browsing The term " s e e d l i n g " i s used throughout the t e x t for a l l Acac i a s l e s s than 1m, as i t was i m p o s s i b l e to d i s t i n g u i s h wi thout d e s t r u c t i v e sampl ing those which were growing from seed v e r s u s those s p r o u t i n g from r o o t s t o c k s . However, e x c a v a t i o n s of many such s e e d l i n g s , i n a d j a c e n t a r e a s , r e v e a l e d tha t most were c o p p i c i n g s h o o t s . Due to t h i s p r o c e s s of c o p p i c i n g , s t u d i e s of the p o p u l a t i o n dynamics of A f r i c a n t r e e s i n many f i r e - d e r i v e d savanna systems have been based on h e i g h t c l a s s e s r a t h e r than age d i s t r i b u t i o n s (Glover 1965, V e s e y - F i t z g e r a l d 1973, Spinage and Guinness 1972, L e u t h o l d 1977b, B e l s k y 1984, Lamprey 1985, S a b i i t i 1986, Jachmann and B e l l 1985). A l l p l o t s were e s t a b l i s h e d i n June of 1982 and measured every s i x months u n t i l May of 1985. W i t h i n each p l o t a l l s e e d l i n g s and t r e e s were i n d i v i d u a l l y tagged and a c c u r a t e l y mapped to i n s u r e f i n d i n g them a g a i n f o l l o w i n g t r e a t m e n t s . Sampl ing p e r i o d s f o r both the b u r n i n g and browsing t rea tments were as f o l l o w s : May-June ( p r e - w i l d e b e e s t ) and November-December ( p o s t - w i l d e b e e s t ) . A year i n t o the s t u d y , the treatment (c) e x c l o s u r e p l o t s were d i v i d e d i n h a l f , w i t h the g r a s s c l i p p e d every three months on one s i d e and l e f t u n d i p p e d on the o t h e r . The c l i p p i n g treatment most c l o s e l y s i m u l a t e d the g r a z i n g e f f e c t s e x p e r i e n c e d by p l a n t s in the burned and browsed (a) and browsed o n l y (b) treatment p l o t s a n d , t h e r e f o r e , was the most r e a l i s t i c c o n t r o l . T h i s m a n i p u l a t i o n was a l s o performed to i n v e s t i g a t e the p o s s i b l e c o m p e t i t i v e i n h i b i t i o n of s e e d l i n g growth by n e i g h b o u r i n g g r a s s e s . I t s h ou l d be noted that t h i s m a n i p u l a t i o n o n l y a d d r e s s e d the p o t e n t i a l f o r above ground 137 c o m p e t i t i o n . The s tudy of c o m p e t i t i o n between p l a n t s below ground f o r water or o t h e r r e s o u r c e s was not w i t h i n the scope of t h i s r e s e a r c h . I n i t i a l l y , the l o n g e s t stem of each p l a n t was measured and t a g g e d . In each f o l l o w i n g sample p e r i o d the h e i g h t of the marked stem, t o t a l number of stems, and c o n d i t i o n of every p l a n t were measured. C o n d i t i o n r e f e r r e d to any s i g n s of browsing by e l e p h a n t s and other s p e c i e s p l u s the e f f e c t s of t r a m p l i n g and t h r a s h i n g by m i g r a t o r y w i l d e b e e s t on l eaves and stems of marked p l a n t s . In the m a j o r i t y of c a s e s , the f a c t o r r e s p o n s i b l e for stem removal or damage c o u l d be r e a d i l y d i s t i n g u i s h e d . When a marked stem had d i e d but the i n d i v i d u a l s e e d l i n g was s t i l l a l i v e , the cause of stem death was r e c o r d e d and the l o n g e s t remain ing l i v e stem was then tagged w i t h the o r i g i n a l i d e n t i f i c a t i o n number. Those p l a n t s m i s s i n g a l t o g e t h e r were i n i t i a l l y noted as "miss ing" in tha t sampl ing p e r i o d and l a t e r c l a s s i f i e d as "dead" i f they d i d not reappear by the end of the s t u d y . The fa t e of each "miss ing" i n d i v i d u a l was de termined by i n s p e c t i o n when p o s s i b l e . P l a n t s which r e s p r o u t e d i n subsequent sampl ing p e r i o d s , r e f e r r e d to as "regenerates" , were re tagged wi th t h e i r o r i g i n a l i d e n t i f i c a t i o n numbers. A l l i n d i v i d u a l s were f o l l o w e d over a minimum of s i x months and a maximum of t h r e e y e a r s . New s e e d l i n g s were tagged as they were found . Measur ing the E f f e c t s of B u r n i n g In the f i r s t y e a r , b u r n i n g exper iments were conducted i n O c t o b e r , a t the end of the dry season . The m i g r a t o r y w i l d e b e e s t a r r i v e d i n the s tudy a r e a each year i n l a t e June or e a r l y J u l y 138 and i n some a r e a s removed up to 95% of the s t a n d i n g c r o p of gras s b e f o r e l e a v i n g i n e a r l y O c t o b e r . T h e r e f o r e b u r n i n g i n October proved d i f f i c u l t because of the l a c k of gras s f u e l and a l l subsequent burns were conducted i n the s h o r t dry season (February and M a r c h ) . At t h i s t ime w i l d e b e e s t were not p r e s e n t , and there was s u f f i c i e n t f u e l f o r b u r n i n g (see Chapter 4 ) . For each burn treatment the p r e v a i l i n g wind speed, r e l a t i v e h u m i d i t y , a i r t empera ture , s u r f a c e and b e l o w - s u r f a c e temperatures d u r i n g b u r n s , f u e l m o i s t u r e , r a t e of spread and flame h e i g h t s were r e c o r d e d . As heavy, wood f u e l s were uncommon i n the p l o t s and c o n t r i b u t e d an i n s i g n i f i c a n t amount to a c t u a l f u e l l o a d i n g s , the e x p e r i m e n t a l burns were e x c l u s i v e l y g r a s s f i r e s . The dominant g r a s s e s p r e s e n t were Themeda t r i a n d r a and Pennisetum mezianum. Based on Rothermel (1972) and Sneeuwjagt and Frandsen (1977) , these gras s f u e l s were assumed to produce a heat y i e l d of a p p r o x i m a t e l y 18,000 k j per kg . F u e l l o a d i n g s were e s t i m a t e d u s i n g a p o i n t - f r a m e a n a l y s i s c a l i b r a t e d from o v e n - d r i e d g r a s s c l i p p i n g s (McNaughton 1979). F i r e i n t e n s i t i e s were c a l c u l a t e d from Byram's (1959) f o r m u l a : I = Hwr where I = f i r e i n t e n s i t y (kW/m), H = heat y i e l d ( k J / k g ) , w = dry f u e l consumed ( k g / m 2 ) , and r = r a t e - o f - s p r e a d (m/ sec ) . Rothermel and Deeming (1980) recommended the use of t h i s e q u a t i o n in e x p e r i m e n t a l b u r n i n g s i t u a t i o n s s i m i l a r to those a p p l i e d in t h i s s t u d y . F i r e s were set between 1200 and 1500 hours and were very c o n s i s t e n t i n c h a r a c t e r both between s i t e s 139 and b u r n i n g seasons (Tab le 5 . 2 ) . A l l f i r e s were measured in the 1000 - 2000 kW/m or k j / m / s e c range and c l a s s i f i e d as "moderately hot" f o l l o w i n g McArthur and Cheney (1966) and T r o l l o p e (1982b). In a d d i t i o n to these l a r g e - s c a l e b u r n i n g e x p e r i m e n t s , m u l t i p l e - b u r n exper iments were conducted on three groups of 100 w i l d s e e d l i n g s . T h i s experiment was des igned to s i m u l a t e the e f f e c t s of r epea ted f i r e s on the root r e s e r v e s of e s t a b l i s h e d s e e d l i n g s . Three d i f f e r e n t f u e l l o a d i n g s which had been r e c o r d e d under n a t u r a l c o n d i t i o n s were used i n these e x p e r i m e n t s : 150g/m 2 , 300g /m 2 , and 600g /m 2 . These p l a n t s were watered and r e - b u r n e d once they reached t h e i r o r i g i n a l h e i g h t s . A l l p l a n t s were burned ten t i m e s . Seed g e r m i n a t i o n exper iments were conducted under d i f f e r e n t b u r n i n g c o n d i t i o n s to s i m u l a t e the e f f e c t s of w i l d f i r e s on seeds in the s u r f a c e l a y e r of the s o i l (0 - 2cm). Acac i a g e r r a r d i i seeds were c o l l e c t e d from mature t r e e s i n the Mara and s o r t e d to remove any damaged or i n s e c t - i n f e s t e d spec imens . From these seeds , f i v e s e t s of ten groups (wi th 200 seeds i n each) were randomly s e l e c t e d and s u b j e c t e d to one of f i v e d i f f e r e n t f u e l l o a d i n g s : 200 g / m 2 , 400 g / m 2 , 600 g / m 2 , 800 g / m 2 , and 1000 g / m 2 . T h i s d i s t r i b u t i o n of f u e l l o a d i n g s was c o n s i d e r e d to be r e p r e s e n t a t i v e of the e n t i r e range of f i e l d c o n d i t i o n s found i n the M a r a . Seeds were sown i n t o the top 2cm of s o i l on c l e a r e d , one square metre p l o t s . F u e l l o a d i n g s on these p l o t s were then set at one of the f i v e e x p e r i m e n t a l l o a d i n g s . A c o n t r o l group of seeds not exposed to b u r n i n g and the f i v e d i f f e r e n t treatment groups were then put i n p e t r i d i s h e s and kept m o i s t . G e r m i n a t i o n r a t e s were r e c o r d e d on a d a i l y b a s i s . A one-way 140 Table 5.2. Ch a r a c t e r i s t i c s of large-scale experimental burns. Fuel loads Fuel moisture A i r temperature Relative humidity Wind speed F i r e i n t e n s i t y = 200 - 400 g/m2 < 35% = 27°C - 30°C < 30% < 10 km/hr = 1000 - 2000 kW/m 141 ANOVA was performed on these data to measure the e f f e c t s of f u e l l o a d i n g s on seed g e r m i n a t i o n . Data A n a l y s i s Square r o o t s of a l l p l a n t h e i g h t s , l o g a r i t h m i c t r a n s f o r m a t i o n s of a l l stem numbers, and a r c s i n e t r a n s f o r m a t i o n s of a l l percentage da ta ( i . e. percent of stems removed) were performed to a l l o w the use of p a r a m e t r i c s t a t i s t i c a l a n a l y s e s (Zar 1984). The problem of " p s e u d o r e p l i c a t i o n " i n data a n a l y s i s ( H u r l b e r t 1984) was a d d r e s s e d . I c o n c l u d e d that i n d i v i d u a l marked s e e d l i n g s w i t h i n burned and browsed (a) and browsed o n l y (b) t reatment p l o t s c o u l d not be c o n s i d e r e d independent o b s e r v a t i o n s because of the nature of the f e e d i n g and movement p a t t e r n s of e l e p h a n t , w i l d e b e e s t , and o ther b r o w s e r s . I f an an imal e n t e r e d an e x p e r i m e n t a l p l o t and a te or damaged one s e e d l i n g , the p r o b a b i l i t y of a n e i g h b o u r i n g s e e d l i n g b e i n g s i m i l a r l y a f f e c t e d would i n c r e a s e . For t h i s r e a s o n , a l l measurements were averaged w i t h i n each of the p l o t s i n the f i v e s i t e s and a l l ANOVAS on s e e d l i n g measurements from l a r g e - s c a l e treatment p l o t s were weighted by sample s i z e . ANOVAS were performed on MINITAB (Ryan et a l . 1985) f o r s m a l l , b a l a n c e d data s e t s and BMDP (Dixon 1985) for we ighted , mixed e f f e c t s mode l s . 142 R e s u l t s L a r g e - s c a l e F i e l d Exper iments M o r t a l i t y of Trees and S e e d l i n g s For the purpose of c a l c u l a t i n g mature t r e e m o r t a l i t y r a t e s , t h r e e hundred t r e e s g r e a t e r than 3m h i g h were randomly s e l e c t e d throughout the R e s e r v e , marked and t h e i r f a t e s f o l l o w e d throughout the s t u d y . Mature t r e e s s u f f e r e d m o r t a l i t y r a t e s of 7% (n = 300, s . e .= 1.5%) per year due to e l ephant damage and another 1% (n = 300, s . e .= 0.6%) from o ther n a t u r a l c a u s e s . However, under extreme c o n d i t i o n s , l i k e the drought of 1984, the m o r t a l i t y r a t e s of t r e e s were much h i g h e r i n l o c a l i z e d a r e a s . For example, in October of 1984, a herd of a p p r o x i m a t e l y 6 b u l l e l e p h a n t s v i s i t e d a 2 s q . km. of 753 mature Acac i a s t a n d . W i t h i n 24 hours they had k i l l e d or f a t a l l y damaged 256 (34%) of the t r e e s and another 166 (22%) of the t r e e s had many broken b r a n c h e s . Other s tands e x p e r i e n c e d s i m i l a r damage d u r i n g t h i s very dry p e r i o d . M o r t a l i t y r a t e s of s e e d l i n g s were c a l c u l a t e d for each of the f i v e s tudy s i t e s . E s t i m a t e s of the p e r c e n t of s e e d l i n g s k i l l e d were based on the averages and s t a n d a r d d e v i a t i o n s amongst the f i v e s i t e s . W i t h i n these e x p e r i m e n t a l s i t e s , 4% ( s . e . = 0.5%) of the 6000 s e e d l i n g s marked i n i t i a l l y i n treatment p l o t s (a) and (b) were k i l l e d by e l e p h a n t s , 1% ( s . e . = 0.6%) by w i l d e b e e s t t r a m p l i n g and t h r a s h i n g , and another 1% ( s . e . = 0.3%) through o ther n a t u r a l c a u s e s . In the burned and browsed treatment p l o t s ( a ) , f i r e k i l l e d an a d d i t i o n a l 4% ( s . e . 143 = 0.8%) of a l l marked s e e d l i n g s each y e a r . T o t a l s e e d l i n g m o r t a l i t y r a t e s averaged 10% ( s . e . = 1.2%) per y e a r . T h i s annua l m o r t a l i t y g r e a t l y exceeded the e s t i m a t e d r a t e of s e e d l i n g replacement of 2% ( s . e . = 0.6%) per annum (approx . 17 new s e e d l i n g s per h a / y r ) a c r o s s the f i v e e x p e r i m e n t a l s i t e s . S e e d l i n g I n h i b i t i o n : the e f f e c t s of f i r e and an imal s The g r e a t e s t e f f e c t of f i r e , e l e p h a n t s , o ther browsers , and w i l d e b e e s t t r a m p l i n g was the i n h i b i t i o n of growth in s e e d l i n g s under 1m i n h e i g h t ( F i g u r e 5 . 2 ) . In each sampl ing p e r i o d , 30% - 60% of a l l stems marked i n the p r e v i o u s p e r i o d were removed i n unburned p l o t s and in burned p l o t s 90 - 100% of marked stems were removed by a c o m b i n a t i o n of f i r e , e l e p h a n t s , w i l d e b e e s t and o ther browsers between sampl ing p e r i o d s . A l t h o u g h i n d i v i d u a l s e e d l i n g s were not k i l l e d , t h e i r growth was s e v e r e l y i n h i b i t e d by t h i s e x t e n s i v e u t i l i z a t i o n and they were e f f e c t i v e l y h e l d below 1m through the combined e f f e c t s of f i r e , w i l d e b e e s t , e l e p h a n t s and o ther b r o w s e r s . The f r a c t i o n of stems removed by e l e p h a n t s , w i l d e b e e s t , and o ther browsers combined was a n a l y z e d a c r o s s the f i v e s tudy s i t e s f o r the wet and dry season i n burned and browsed, browsed o n l y , and n e i t h e r burned nor browsed treatment p l o t s u s i n g a we ighted , three -way , mixed e f f e c t s ANOVA. Season, s i t e , and treatment e f f e c t s were a l l s i g n i f i c a n t (Tab le 5 . 3 ) . Stem l o s s was s i g n i f i c a n t l y g r e a t e r i n the dry season than the wet, and was g r e a t e r on burned than unburned p l o t s (Tukey ' s m u l t i p l e comparison a t the 5% s i g n i f i c a n c e l e v e l ) . Two of the f i v e s i t e s showed s i g n i f i c a n t l y g r e a t e r l o s s e s than the o ther t h r e e . 144 ELEPHANTS WILDEBEEST OTHER BROWSERS o -j S CJ E-1 CO O E- o 40 30 H 80 10 H • — burned o - unburned DRY WET DRY SEASONS DRY WET Figure 5.2. Percent of marked stems removed in each season by elephants, wildebeest, and other browsers (± one s.e. showing the v a r i a b i l i t y between s i t e s ) . 145 T a b l e 5 . 3 . ANOVA r e s u l t s f o r the f r a c t i o n o f stems removed b y : (a) a l l causes o f m o r t a l i t y combined; (b) e l e p h a n t - r e l a t e d m o r t a l i t y o n l y ; and (c) w i l d e b e e s t - r e l a t e d m o r t a l i t y o n l y a c r o s s s easons , s i t e s , and t r e a t m e n t s . A we ighted three-way mixed e f f e c t s ANOVA model was used ( s i t e was c o n s i d e r e d a random e f f e c t and the o t h e r s were f i x e d ) . F - r a t i o s a r e r e p o r t e d below, * * = P<.01 , * * * = P<.001. EFFECT D . F . ALL CAUSES ELEPHANT WILDEBEEST COMBINED ONLY ONLY SEASON 1 74.30*** 63.60*** SITE 4 4.76** n . s . 138.61*** TREATMENT 2 118.41*** 965.58*** n . s . REMAINDER 22 146 A weighted two-way ANOVA was performed s e p a r a t e l y on w i l d e b e e s t - r e l a t e d stem l o s s (Tab le 5 . 3 ) . Only dry season data were a n a l y z e d because the w i l d e b e e s t are not p r e s e n t i n the wet s eason . M i g r a t o r y w i l d e b e e s t removed on average 29% of a l l marked stems, in a l l p l o t s combined, d u r i n g t h e i r annua l three to four month d r y - s e a s o n r e s i d e n c y in the t h r e e s tudy y e a r s . These stems were p r i m a r i l y k i l l e d by u n i n t e n t i o n a l brows ing , t h r a s h i n g by r u t t i n g males and t r a m p l i n g by c o n c e n t r a t e d herds of m i g r a n t s . The range of stem removal by w i l d e b e e s t was 10 85% over three y e a r s on the f i v e treatment s i t e s . Stem l o s s e s were not s i g n i f i c a n t l y h i g h e r i n burned than unburned p l o t s but there was a s i g n i f i c a n t s i t e e f f e c t owing to the h i g h l y l o c a l i z e d nature of damage by w i l d e b e e s t . Whereas s e e d l i n g s i n some l o c a t i o n s were o n l y l i g h t l y damaged, s e e d l i n g s in o ther areas were v i r t u a l l y a l l damaged. These d i f f e r e n c e s may be accounted for by the movement p a t t e r n s of m i g r a t o r y w i l d e b e e s t . In the dry season, w i l d e b e e s t f o l l o w l o c a l thunders torms and then c o n c e n t r a t e i n areas of r ecen t r a i n f a l l f o r t h r e e to four d a y s . The p e r c e n t of stems removed by e l e p h a n t s a lone was a n a l y z e d a c r o s s seasons , s i t e s , and treatments w i t h a weighted three-way ANOVA (Table 5 . 3 ) . E l e p h a n t s showed two important p a t t e r n s of stem use . F i r s t , they removed a s i g n i f i c a n t l y h i g h e r p r o p o r t i o n of r e s p r o u t i n g stems on burned p l o t s than unburned p l o t s (Tukey ' s m u l t i p l e comparison a t the 5% s i g n i f i c a n c e l e v e l ) . E l e p h a n t s removed an average of 33% of a l l marked stems every s i x months i n burned p l o t s and 20% i n unburned p l o t s ( F i g u r e 5 . 2 ) . S e c o n d l y , they removed 147 s i g n i f i c a n t l y more stems i n the dry season than i n the wet season (Tab le 5 . 3 , season e f f e c t , P<.001) . No s i g n i f i c a n t s i t e e f f e c t was found . Other b r o w s e r s , such as impala (Aepyceros melampus), G r a n t ' s ( G a z e l l a g r a n t i ) and Thomson's ( G a z e l l a thomsoni) g a z e l l e s , d i k d i k (Madoqua k i r k i i ) , g i r a f f e ( G i r a f f a c a m e l o p a r d a l i s ) , and r h i n o c e r o s ( D i c e r o s b i c o r n i s ) removed an average of 14% burned p l o t s and 5% unburned p l o t s between seasons . E l e p h a n t s removed more stems than other browsers on both burned and unburned p l o t s d u r i n g both the wet and dry season . A weighted two-way ANOVA was performed on the f r a c t i o n of stems browsed, t r a m p l e d , or not damaged i n burned and unburned p l o t s a c r o s s each of the 5 s tudy s i t e s (Tab le 5 . 4 ) . Both s i t e and treatment e f f e c t s were s i g n i f i c a n t . O v e r a l l , 38% of s e e d l i n g s i n unburned p l o t s had no v i s i b l e browsing damage v e r s u s 16% i n burned p l o t s ( F i g u r e 5 . 3 ) . A second a n a l y s i s on browse damage, o n l y , showed no s i g n i f i c a n t s i t e d i f f e r e n c e s but h i g h l y s i g n i f i c a n t d i f f e r e n c e s between burned and unburned p l o t s . Browsing was s i g n i f i c a n t l y h i g h e r on burned p l o t s than unburned p l o t s (at the 5% s i g n i f i c a n c e l e v e l ) . Whi le o n l y 57% of the unburned s e e d l i n g s were browsed, 78% of those in burned p l o t s had been browsed to some e x t e n t . T h i s p r e f e r e n c e was p r o b a b l y due to a q u a l i t a t i v e d i f f e r e n c e between r e s p r o u t i n g , burned s e e d l i n g s and unburned s e e d l i n g s . Of those s e e d l i n g s which had been browsed the m a j o r i t y had damage to both the l e a v e s and stems. A t h i r d a n a l y s i s f or t r a m p l i n g damage, a l o n e , showed no s i g n i f i c a n t d i f f e r e n c e between t rea tments in the p e r c e n t of 14U T a b l e 5 . 4 . ANOVA r e s u l t s f o r the f r a c t i o n o f stems damaged b y : (a) a l l causes combined; (b) brows ing damage o n l y ; and (c) t r a m p l i n g damage o n l y a c r o s s s i t e s and t r e a t m e n t s . A we ighted two-way mixed e f f e c t s ANOVA model was used ( s i t e was c o n s i d e r e d a random e f f e c t and t r e a t m e n t f i x e d ) . F - r a t i o s are r e p o r t e d below, * * = P<.005 / * * * = P<.001. EFFECT D . F . A L L CAUSES COMBINED BROWSING ONLY TRAMPLING ONLY SITE 33.08** n . s . 54.62*** TREATMENT 13615.13*** 9459.93*** n . s . REMAINDER 4 149 O PS OH 100 90 80 70 60 50 40 30 20 10 0 4> • - BURNED O - UNBURNED 4 4 • BROWSED NOT DAMAGED TRAMPLED Figure 5.3. Percent of marked stems browsed," not damaged and trampled over the enti r e study period (± one s.e. showing the v a r i a b i l i t y between s i t e s ) . 150 i n d i v i d u a l s t r a m p l e d (5% on unburned p l o t s and 6% on burned p l o t s ) . There was, however, a s i g i f i c a n t s i t e e f f e c t . A m u l t i p l e comparison t e s t showed tha t two out of the f i v e s i t e s had a s i g n i f i c a n t l y h i g h e r percentage of stems t rampled than the o t h e r three (at the 5% s i g n i f i c a n c e l e v e l ) . T h i s i s p r o b a b l y e x p l a i n e d by the h i g h l y l o c a l i z e d p a t t e r n s of w i l d e b e e s t impacts d e s c r i b e d above . A l t h o u g h r e l a t i v e l y few s e e d l i n g s were a c t u a l l y k i l l e d each y e a r , many were r e p e a t e d l y browsed to ground l e v e l , r e s p r o u t i n g at a l a t e r d a t e . T h i s p r o c e s s was termed " r e v e r s a l " and these s e e d l i n g s were c a l l e d "regenerates" . The cause of t h e i r d i s a p p e a r a n c e was r e c o r d e d whenever p o s s i b l e . Removals by e l e p h a n t , f i r e , and w i l d e b e e s t were e a s i l y d i s t i n g u i s h e d from one a n o t h e r . The most i n t e r e s t i n g d e t a i l of these removals was the p e r i o d of t ime r e q u i r e d for r e s p r o u t i n g ( F i g u r e 5 . 4 ) . The m a j o r i t y (over 90%) of the p l a n t s removed by w i l d e b e e s t or f i r e , tha t d i d r e s p r o u t , r e t u r n e d w i t h i n s i x months. Those removed by e l e p h a n t s , however, e x p e r i e n c e d much g r e a t e r d e l a y s i n r e c o v e r y . Only 31% r e s p r o u t e d w i t h i n 6 months, another 54% took a y e a r , 9% took 18 months, and the remain ing 7% r e q u i r e d over 2 y e a r s to regrow. T h e r e f o r e , not on ly d i d e l e p h a n t s remove the g r e a t e s t p r o p o r t i o n of s e e d l i n g s at ground l e v e l but these s e e d l i n g s took much longer to r e c o v e r . S e e d l i n g Growth: stem numbers and h e i g h t s F i g u r e 5.5 shows the change i n stem h e i g h t s over the e n t i r e s tudy p e r i o d averaged over a l l s i t e s f o r each t r e a t m e n t . A weighted two-way ANOVA model was used to examine stem h e i g h t s 151 FIRE 100 - i 80- CY  2 E 60- or w 40- E 20- 0- 100 60 g 6 0 D Sf 40 20 0 35 WILDEBEEST 100 80 Z 60 40 20 0 ELEPHANT 35 rV\l 0-6 6-12 1 2-18 18-24 24+ NUMBER OF MONTHS UNTIL RESPROUTING Figure 5.4. Frequency distribution, of return times for resprouting "regenerates" o r i g i n a l l y removed by elephants, wildebeest, and f i r e . 152 60 -I • 50- 40- 30- 20- 10- 0 a "Q • - o - CLIPPED EXCLOSURE UNCLIPPED EXCLOSURE BROWSED ONLY BROWSED AND BURNED \ O J i 1982 1983 1984 1985 TIME OF YEAR Figure 5 . 5 . Change in the average heights of marked stems over the study period. Arrows indicate experimental burns. 153 amongst s i t e s and t rea tments a t the b e g i n n i n g of the s t u d y . No s i g n i f i c a n t d i f f e r e n c e s were found i n stem h e i g h t s between s i t e s (F = 1.96, n . s . ) or treatment p l o t s (F = 3 .01 , n . s . ) . A weighted two-way ANOVA was performed to examine the o v e r a l l d i f f e r e n c e s i n changes i n stem h e i g h t s between burned and browsed p l o t s ( a ) , browsed o n l y p l o t s ( b ) , and an average of the c l i p p e d and u n d i p p e d h a l v e s of e x c l o s u r e p l o t s (c) at the end of the s t u d y . No s i g n i f i c a n t d i f f e r e n c e s were found between s i t e s (F = 1.66, n . s . ) , however, s i g n i f i c a n t d i f f e r e n c e s in the change i n stem h e i g h t s were found between t rea tments (F = 588.59, P<.001) . T u k e y ' s m u l t i p l e comparison t e s t s showed that the s e e d l i n g s which were n e i t h e r burned nor browsed grew s i g n i f i c a n t l y more than those which were browsed o n l y and"those which were browsed and burned (at the 5% s i g n i f i c a n c e l e v e l ) . In both the burned and browsed (a) and browsed o n l y (b) treatment p l o t s stem h e i g h t s d e c l i n e d throughout the s t u d y . However, stem h e i g h t s i n the browsed on ly treatment p l o t s d i d not d e c l i n e as much as those in the browsed and burned treatment p l o t s (at the 5% s i g n i f i c a n c e l e v e l ) . Stems which were browsed on ly d e c l i n e d from 38cm, on a v e r a g e , to 26cm, whereas those which were burned and browsed dropped from 37.5cm to 16cm over three y e a r s . In c o n t r a s t , s e e d l i n g s i n e x c l o s u r e s grew between 10cm and 15cm per y e a r . The graph of mean stem h e i g h t s over time ( F i g u r e 5.5) sugges ted t h a t w i t h i n the n e i t h e r burned nor browsed treatment (c) those s e e d l i n g s i n the c l i p p e d h a l f grew even more than those i n the u n d i p p e d h a l f . So , i n a f u r t h e r a n a l y s i s I d i v i d e d treatment (c) i n t o two s e p a r a t e treatments - c l i p p e d and 154 u n d i p p e d . I then performed a weighted two-way ANOVA on the change in stem h e i g h t s between s tudy s i t e s i n four treatment p l o t s : burned and browsed, browsed o n l y , c l i p p e d w i t h no b u r n i n g or browsing and u n d i p p e d wi th no b u r n i n g or b r o w s i n g . A l t h o u g h no d i f f e r e n c e s were found between s i t e s (F = 1.89, n . s . ) , t h e r e was s t i l l a s i g n i f i c a n t treatment e f f e c t (F = 39 .61 , P<.01) even wi th the reduced sample s i z e r e s u l t i n g from the s e p a r a t i o n of c l i p p e d and u n d i p p e d t r e a t m e n t s . The change i n stem h e i g h t s was s i g n i f i c a n t l y g r e a t e r in c l i p p e d than u n d i p p e d p l o t s and each of these t rea tments showed s i g n i f i c a n t l y more growth than the o ther two treatments which both showed stem h e i g h t d e c l i n e s (Tukey ' s m u l t i p l e comparison t e s t s at the 5% s i g n i f i c a n c e l e v e l ) . A l t h o u g h both the c l i p p e d and u n d i p p e d p l o t s s t a r t e d from an average h e i g h t of 36cm, the c l i p p e d h a l f grew to 55cm on a v e r a g e , wh i l e the u n d i p p e d h a l f grew to o n l y 47cm by the end of the s t u d y . The removal of g r a s s appears to enhance s e e d l i n g growth , but the n e g a t i v e e f f e c t s of b u r n i n g and browsing appear to swamp t h i s e f f e c t i n u n p r o t e c t e d p l o t s . No s i g n i f i c a n t d i f f e r e n c e s in the average number of stems per p l a n t were found amongst s i t e s (F = 3 . 1 1 , n . s . ) or t rea tments (F = 2 .49 , n . s l ) at the b e g i n n i n g of t h i s s tudy ( F i g u r e 5 . 6 ) . A weighted two-way ANOVA on changes in stem numbers over the e n t i r e study s t i l l showed no s i g n i f i c a n t s i t e e f f e c t (F = 3 .93 , n . s . ) . However, changes i n the average number of stems per p l a n t d i d v a r y by treatment (F = 410 .85 , P<.001) . In e x c l o s u r e p l o t s , there was no apparent change i n the average number of stems per p l a n t in e i t h e r the c l i p p e d or u n d i p p e d 155 w CO o b 7 - 1 E - < CO 4 - 3 - 2 - 1- 0 . • - o - CLIPPED EXCLOSURE UNCLIPPED EXCLOSURE BROWSED ONLY BROWSED AND BURNED i J 1 1982 1983 1984 1985 TIME OF YEAR Figure 5.6. Change in the average number of stems per marked seedling over the study period. Arrows indicate experimental burns. 156 s i d e s . Those p l o t s which were browsed but not burned showed a s teady d e c l i n e i n average stem numbers per i n d i v i d u a l from 3.6 to 1 .7 . T u k e y ' s m u l t i p l e comparison t e s t s r e v e a l e d t h a t t h i s l o s s of stems on browsed p l o t s was s i g n i f i c a n t l y g r e a t e r than e i t h e r e x c l o s u r e s or burned and browsed p l o t s (at the 5% s i g n i f i c a n c e l e v e l ) . By the end of the s t u d y , the average number of stems per p l a n t was s i g n i f i c a n t l y g r e a t e r i n burned and browsed p l o t s (5 .5 s t e m s / p l a n t ) than i n e x c l o s u r e p l o t s (3 .5 s t e m s / p l a n t ) which were n e i t h e r burned nor browsed (at the 5% s i g n i f i c a n c e l e v e l ) . Whi l e b u r n i n g exper iments a p p a r e n t l y s t i m u l a t e d an immediate i n c r e a s e i n stem numbers, stem numbers d e c l i n e d r a p i d l y due to browsing i n the t ime p e r i o d s between burns but rose a g a i n f o l l o w i n g each subsequent burn ( F i g u r e 5.6) . M u l t i p l e - b u r n Exper iments F i g u r e 5.7 shows the p a t t e r n of s e e d l i n g m o r t a l i t y i n the m u l t i p l e - b u r n e x p e r i m e n t s . The p e r c e n t of p l a n t s s u r v i v i n g are p l o t t e d a g a i n s t the number of b u r n i n g t r i a l s f or each treatment g r o u p . P l a n t s i n the l i g h t e s t b u r n i n g treatment ( I50g/m 2 ) showed v e r y h i g h s u r v i v o r s h i p w i t h o n l y e i g h t p l a n t s be ing l o s t over the e n t i r e p e r i o d . Those i n the second b u r n i n g treatment (300g/m 2 ) had over 80% s u r v i v o r s h i p u n t i l the seventh f i r e when s u r v i v o r s h i p dropped r a p i d l y , l e a v i n g o n l y 10% of the p l a n t s by the end of the s t u d y . The most severe treatment (600g/m 2 ) showed a s i m i l a r p a t t e r n of s u r v i v o r s h i p , but heavy l o s s e s o c c u r r e d e a r l i e r i n the sequence of t r e a t m e n t s : by the f i f t h burn s u r v i v o r s h i p had f a l l e n below 60% and by the f i n a l burn 157 OH co DH o > > CO EH iz ; w o DH W DH 100 - i 90 80 70 60 50 40 30 20 10 0 A V O - - 150 g/m 2 - 300 g/m 2 - 600 g/m 2 O 200 - 400 g/iri \ -9 0 1 2 3 4 5 6 7 8 9 10 BURN NUMBER Figure 5.7. Seedling s u r v i v o r s h i p f o r m u l t i p l e - b u r n experiments under three burning treatments. Note : * = s e e d l i n g s u r v i v o r s h i p f o r three, s e q u e n t i a l , l a r g e - s c a l e experimental burns where f u e l loadings were 200 - 400 g/m2. 1 58 there were no s u r v i v o r s at a l l . F i g u r e 5.7 a l s o shows s u r v i v o r s h i p from the l a r g e - s c a l e burn exper iments which had f u e l l o a d s between the f i r s t and second treatment l e v e l s . The s u r v i v o r s h i p p a t t e r n s were i n l i n e w i t h those produced by the f i r s t t h r e e t r i a l s of the m u l t i p l e - b u r n e x p e r i m e n t s . Seed G e r m i n a t i o n Exper iments The f i r e - t r e a t e d seed exper iments demonstrated a h i g h l y s i g n i f i c a n t e f f e c t of f u e l l o a d i n g s on g e r m i n a t i o n r a t e s ( F i g u r e 5 .8 , F = 1175.5 , P<.001) . G e r m i n a t i o n r a t e s were h i g h e r (mean = 64%) i n those seeds exposed to 400 g /m 2 than i n those exposed to the c o o l e r temperatures e x p e r i e n c e d at 200 g /m 2 (mean = 29%), or the h o t t e r temperatures at 600 g /m 2 (mean = 40%). A l l three of these t rea tment s produced h i g h e r g e r m i n a t i o n r a t e s than those of c o n t r o l seeds (mean = 18%). The r a t e of s u c c e s s f u l g e r m i n a t i o n d e c l i n e d as f u e l l o a d i n g s rose to 800 and 1000 g / m 2 . D i s c u s s i o n I f woodland r e g e n e r a t i o n were s t r i c t l y dependent on e x i s t i n g s e e d l i n g d e n s i t i e s , the r e c o v e r y of Mara woodlands would be a s s u r e d . S e e d l i n g d e n s i t i e s throughout the Reserve are s t i l l h i g h but may be s t e a d i l y d e c l i n i n g under c o n t i n u e d p r e s s u r e from t r a m p l i n g by w i l d e b e e s t , browsing by e l e p h a n t s and o t h e r s , and w i l d f i r e s . Whi l e Croze (1974b) c o n c l u d e d tha t Acac i a woodlands i n the S e r e n g e t i c o u l d w i t h s t a n d e l ep h ant p r e d a t i o n , and N o r t o n - G r i f f i t h s (1979) p r e d i c t e d tha t the 159 O O C\2 OS OH Q s OS o co Q CO d 125- 100- 75- 50- 25- 0 CON 200 400 600 800 1000 F U E L LOADINGS (g /m 2 ) Figure 5.8. The average number of seeds germinating i n ten sets (200 seeds each) under each of f i v e d i f f e r e n t f u e l l oading treatments (± one s.d.). F u e l loadings of 200, 400, and 600 g/m2 a l l s t i m u l a t e d germination beyond c o n t r o l l e v e l s . 160 i n c r e a s e which has o c c u r r e d i n w i l d e b e e s t numbers would l e a d to a r e d u c t i o n i n f i r e s and a g r e a t e r chance of woodland r e c o v e r y , t h i s r e c o v e r y has not o c c u r r e d yet i n the M a r a . Woodland r e g e n e r a t i o n i s s e v e r e l y i n h i b i t e d by the combined e f f e c t s of e l e p h a n t s , f i r e , and w i l d e b e e s t (Chapter 6 ) . E l e p h a n t s Under good growing c o n d i t i o n s , t r e e s i n the Mara may r e q u i r e 1 5 - 2 0 y e a r s to reach 3m, a t which they are no l onger v u l n e r a b l e to a l l but the most severe f i r e s . U n t i l they reach t h i s h e i g h t they e x p e r i e n c e damage from b r o w s i n g , t r a m p l i n g and f i r e and even above t h i s h e i g h t they are s t i l l i n f l u e n c e d by e l e p h a n t s and g i r a f f e (Croze 1974a & b , Pe l l ew 1983). Based on work by Croze (1974b) and Pe l lew (1983) , N o r t o n - G r i f f i t h s (1979) and B e l s k y (1984) assumed that e l e p h a n t s " l a r g e l y i gnored" t r e e s under 1m and, t h e r e f o r e , had l i t t l e a f f e c t on s e e d l i n g s u r v i v o r s h i p in the S e r e n g e t i . In c o n t r a s t , r e s u l t s from t h i s s tudy demonstrate t h a t e l ephant browsing i s c u r r e n t l y a p r i m a r y f a c t o r i n s e e d l i n g m o r t a l i t y and the i n h i b i t i o n of s e e d l i n g growth i n the M a r a . There are s e v e r a l p o s s i b l e e x p l a n a t i o n s f o r t h i s d i f f e r e n c e i n f i n d i n g s . F i r s t , Croze (1974a & b) c o n c l u d e d t h a t S e r e n g e t i e l e p h a n t s i n the l a t e 1960s and e a r l y 1970s browsed t r e e s i n approximate p r o p o r t i o n to t h e i r h e i g h t a v a i l a b i l i t i e s , but a v o i d e d t r e e s under 1m. T r e e s above 1m were abundant , c o m p r i s i n g up to 60% of the t o t a l p o p u l a t i o n i n the Acac i a woodlands s t u d i e d (Lamprey et a l . 1967, G l o v e r 1968, Croze 161 1974b, and N o r t o n - G r i f f i t h s 1979). In the Mara there has been a major change i n the h e i g h t d i s t r i b u t i o n of t r e e s f o l l o w i n g a p r o g r e s s i v e l o s s of the t a l l e r c l a s s e s ( D u b l i n 1984, Chapter 2 ) . U n l i k e the h e i g h t d i s t r i b u t i o n of t r e e s i n the 1960s, the c u r r e n t h e i g h t s t r u c t u r e of the Mara woodlands i s h e a v i l y b i a s e d towards the 0 - 1m h e i g h t c l a s s ( F i g u r e 5 . 9 ) . D u b l i n (Chapter 4) showed t h a t over 80% of the browse d i e t s of e l e p h a n t s i n the Mara came from t r e e s l e s s than 1m, which i s i n p r o p o r t i o n to the c u r r e n t frequency d i s t r i b u t i o n of t r e e h e i g h t s in Acac i a woodland s t a n d s . T h e r e f o r e , the observed d i f f e r e n c e i n the f e e d i n g behav iour of Mara e l e p h a n t s may have r e s u l t e d from t h i s change i n the p o p u l a t i o n s t r u c t u r e of t r e e s . S e c o n d l y , e l e p h a n t s browsing on s e e d l i n g s may m i s t a k e n l y appear to be f e e d i n g on nearby g r a s s e s . S e e d l i n g s occur in t h e i r h i g h e s t d e n s i t i e s i n open g r a s s l a n d a r e a s of the M a r a . From a d i s t a n c e , i t i s p o s s i b l e to mis take t h e i r f e e d i n g on s e e d l i n g s f o r g r a z i n g on g r a s s e s . I de termined forage s e l e c t i o n by e l e p h a n t s in the Mara through d i r e c t , c l o s e - u p o b s e r v a t i o n s of i n d i v i d u a l an imals ( D u b l i n , Chapter 4 ) , whereas e a r l i e r s t u d i e s o f t e n determined the forage p r e f e r e n c e s of e l e p h a n t s through t h e i r impact on v e g e t a t i o n and t h e i r d i s t r i b u t i o n among h a b i t a t s . These l a t t e r , i n d i r e c t methods can be m i s l e a d i n g . When e l e p h a n t s forage on s e e d l i n g s , t h e r e i s no obv ious s i g n l e f t a f t e r the s e e d l i n g i s c o m p l e t e l y removed. The p a t t e r n s of e l ephant f o r a g i n g r e c o r d e d i n the Mara are c o n s i s t e n t wi th f i n d i n g s from o ther e l ephant p o p u l a t i o n s . S t u d i e s by Brooks (1957) , Buss (1961), F i e l d and Ross (1976), Guy (1976) , Jachmann and B e l l (1985) , Okula and S i s e (1986) , and Weyerhaeuser (1985) 162 > 3 8 2 - 3 l - J o £ 1-2 o w < 1 s CROZE 1974 s j DUBLIN 1984 ii§i l l l l l l l l 1 1 1 • i ' . I I I I 90 60 30 0 30 PERCENT 60 90 F i g u r e 5.9. D i s t r i b u t i o n by height c l a s s f o r Acacias i n the Seronera woodlands (Croze 1974b) and i n the Mara woodlands (Dublin 1984). 163 a l l r e p o r t e d tha t e l e p h a n t s u t i l i z e d r e g e n e r a t i n g s e e d l i n g s where they were a v a i l a b l e . I t i s , t h e r e f o r e , p o s s i b l e tha t e a r l i e r s t u d i e s of e l ephant f e e d i n g i n the S e r e n g e t i s imply f a i l e d to n o t i c e the extent to which e l e p h a n t s u t i l i z e d s e e d l i n g s . E l e p h a n t s were the most important cause i n r e d u c i n g s e e d l i n g h e i g h t back to ground l e v e l each y e a r . T h i s e f f e c t was c o n s i s t e n t l y h i g h e r i n the burned p l o t s . A l t h o u g h a l a r g e p r o p o r t i o n of these s e e d l i n g s d i d e v e n t u a l l y r e s p r o u t , those taken by e l e p h a n t s took much longer to come back than those removed by f i r e or w i l d e b e e s t . T h i s suggests tha t e l e p h a n t s d i d more e x t e n s i v e damage to the p l a n t s than d i d f i r e or t r a m p l i n g e f f e c t s (and hence the p l a n t s r e q u i r e d a l onger r e c o v e r y p e r i o d ) . D u r i n g t h i s p e r i o d of r e c o v e r y from e l ephant b r o w s i n g , s e e d l i n g s were exposed for a l o n g e r time to o ther f a c t o r s a f f e c t i n g s u r v i v o r s h i p and e s t a b l i s h m e n t . The impact of e l e p h a n t s on the r e g e n e r a t i o n of woodlands i n the Mara i s f u r t h e r e x a c e r b a t e d by the c u r r e n t d i s t r i b u t i o n of l o c a l e l ephant p o p u l a t i o n s . The n o r t h e r n S e r e n g e t i , j u s t to the south of the M a r a , i s an e x t e n s i v e area of prime e l ephant h a b i t a t . In the 1960s and 1970s t h i s area s u p p o r t e d a l a r g e number of e l e p h a n t s which s e a s o n a l l y t r a v e l l e d n o r t h to the Mara (Watson and B e l l 1969, Watson et a l . 1969, D u b l i n and D o u g l a s - H a m i l t o n , i n p r e s s ) but were not r e s i d e n t a l l y e a r . Today, e l e p h a n t s are be ing d r i v e n out of the n o r t h e r n S e r e n g e t i by i n t e n s i v e poach ing p r e s s u r e . Because of t h i s i n f l u x from the south and i n c r e a s i n g human s e t t l e m e n t on the Reserve b o u n d a r i e s , the s e a s o n a l m i g r a t i o n of e l e p h a n t s out of the Mara has been cut 164 o f f a lmost e n t i r e l y . C u r r e n t l y , e l e p h a n t s are h e a v i l y c o n c e n t r a t e d w i t h i n the Reserve ( F i g u r e 5.10) and over 1000 e l e p h a n t s are i n r e s i d e n c e y e a r - r o u n d . I f poach ing i n the n o r t h e r n S e r e n g e t i c o u l d be c u r b e d , e l e p h a n t s might move back i n t o t h a t a r e a , thereby t e m p o r a r i l y e a s i n g the browsing p r e s s u r e on woodlands i n the M a r a . F i r e F i r e has p l a y e d an important r o l e i n the d e c l i n e of woodlands and the i n h i b i t i o n of r e g e n e r a t i o n in the S e r e n g e t i - Mara ( D u b l i n 1984, Chapter 2) and i n many o ther areas of A f r i c a (Buechner and Dawkins 1961, Thomas and P r a t t 1967, G l o v e r 1968, Pe l lew 1983, T r o l l o p e 1982a, 1984). But the impact of f i r e has changed i n the Mara over the past 5 - 1 0 y e a r s . S i n c e the m i d - 1970s a g r e a t e r number of the m i g r a t o r y w i l d e b e e s t (whose p o p u l a t i o n numbers c l o s e to 1.5 m i l l i o n ) have been spending the dry season in the M a r a . Over the course of t h e i r 3 - 4 month r e s i d e n c e , the w i l d e b e e s t remove a s i g n i f i c a n t p r o p o r t i o n of the s t a n d i n g c r o p of dry g r a s s ( D u b l i n Chapter 4 ) . Whereas, i n the p a s t , hot d r y season f i r e s burned a n n u a l l y , d e s t r o y i n g woody v e g e t a t i o n , today they are not as damaging when they do o c c u r . Most f i r e s i n the Mara now take p l a c e d u r i n g the s h o r t d r y season i n F e b r u a r y and M a r c h . At t h i s time of the year the w i l d e b e e s t are not p r e s e n t and re s ident , h e r b i v o r e s are not abundant enough to remove a s i g n i f i c a n t p o r t i o n of the g r a s s f u e l s . However, the s h o r t r a i n s of November-December do not produce the same h i g h g r a s s biomass as the long r a i n s a n d , 165 Figure 5.10. Elephant occupance w i t h i n the Mara Game Reserve from 12 a e r i a l surveys flown by the Kenya Rangelands E c o l o g i c a l M o nitoring U n i t (K.R.E.M.U.) between 1980 and 1983. The blocks represent the number of f l i g h t s i n which elephants were seen i n each of the 10km x 10km g r i d squares. Note : The surveys were flown over a much l a r g e r area (approx. 6,400 sq.km.), however, the only elephants seen were i n or cl o s e to the Reserve, as shown. 166 t h e r e f o r e , s h o r t dry season f i r e s are not as damaging as f i r e s i n the l a t e dry season . The l a r g e - s c a l e e x p e r i m e n t a l burns mimicked the c h a r a c t e r i s t i c s of these w i l d f i r e s w e l l . A l t h o u g h these "moderately hot" gras s f i r e s r e s u l t e d in almost 100% t o p k i l l of Acac i a g e r r a r d i i s e e d l i n g s , t o t a l s e e d l i n g m o r t a l i t y was o n l y 3 5%. The p a t t e r n s of f i r e impact d i s c u s s e d here a p p l y to a wide v a r i e t y of l e s s abundant t r e e s p e c i e s i n the M a r a . P r e s e n t l y , s u c c e s s f u l r e g e n e r a t i o n i n the Mara seems l i m i t e d to f i r e - r e s i s t a n t s p e c i e s such as Acac i a g e r r a r d i i (Glover and Trump 1970, P r a t t and K n i g h t 1971, Spinage and Guinness 1972, H e r l o c k e r 1976a & b ) . Acac i a g e r r a r d i i s e e d l i n g s i n the Mara showed a h i s t o r y of r epea ted b u r n i n g s as i n d i c a t e d by t h e i r l a r g e r o o t s t o c k s . F i r e , i n f a c t , s t i m u l a t e d the regrowth of m u l t i p l e new stems which were then g r a d u a l l y reduced by browsers and repeated b u r n s . R e s p r o u t i n g seemed to be l i m i t e d p r i m a r i l y by water and the m a j o r i t y of s e e d l i n g s reappeared s h o r t l y a f t e r the next r a i n s . C o p p i c i n g i s , i n f a c t , the most commonly r e p o r t e d response to b u r n i n g of woody s p e c i e s i n A f r i c a (P i enaar 1959, Kennan 1971, P r a t t and K n i g h t 1971, T r o l l o p e 1982a, S a b i i t i 1986). S t r a n g (1974) r e p o r t e d tha t e l even y e a r s of r e g u l a r hot f i r e s had not reduced the number of woody p l a n t s but mere ly l e d to c o p p i c i n g and d e l a y e d woodland development . B u t , can t h i s p a t t e r n of b u r n i n g and r e s p r o u t i n g go on i n d e f i n i t e l y ? To answer t h i s q u e s t i o n , the m u l t i p l e - b u r n exper iments were d e s i g n e d to s i m u l a t e the e f f e c t s of r epea ted burns on s e e d l i n g s . The p r o c e s s of s e e d l i n g r e c o v e r y was sped up in these exper iments through a r t i f i c i a l w a t e r i n g a n d , t h e r e f o r e , the 167 r e s u l t s may have exaggerated the r a t e s of m o r t a l i t y caused by annua l w i l d f i r e s . However, even from a c o n s e r v a t i v e p e r s p e c t i v e , the r e s u l t s suggest t h a t root r e s e r v e s are f i n i t e and t h a t repeated burns would r e s u l t in an e v e n t u a l d i s a p p e a r a n c e of t r e e s under 3m. I f w i l d e b e e s t p o p u l a t i o n s d e c l i n e d to t h e i r former low numbers ( S i n c l a i r 1979) and they no l onger m i g r a t e d to the Mara to remove the dry g r a s s s t a n d i n g c r o p (Maddock 1979), hot dry season w i l d f i r e s c o u l d a g a i n become a common o c c u r r e n c e - once or even twice each s e a s o n . T h i s would presumably a c c e l e r a t e the p r o c e s s of woodland d e c l i n e which i s a l r e a d y t a k i n g p l a c e ( N o r t o n - G r i f f i t h s 1979, D u b l i n , Chapter 2 ) . The e f f e c t s of w i l d f i r e s on seeds i n the s o i l bed may a l s o reduce the p o t e n t i a l f o r woodland r e c o v e r y . S t o r y (1952), Harker (1959) , S a b i i t i (1986), and S a b i i t i and Wein ( i n p r e s s ) r e p o r t e d t h a t exposure to f i r e s s t i m u l a t e d the g e r m i n a t i o n of some s p e c i e s of Acac i a seeds . However, T r o l l o p e ( 1982a) argued tha t t h i s was not n e c e s s a r i l y so and that s t i m u l a t i o n of g e r m i n a t i o n may o n l y be t rue when burns are f o l l o w e d by f a v o u r a b l e m o i s t u r e c o n d i t i o n s . E x p e r i m e n t a l f i n d i n g s in the Mara suggest tha t g e r m i n a t i o n r a t e s may be a f u n c t i o n of the a c t u a l i n t e n s i t y of the f i r e to which seeds are exposed . At t emperatures r e c o r d e d on the s o i l s u r f a c e d u r i n g average burns (400 g / m 2 ) , seeds were s t i m u l a t e d to germinate w e l l beyond c o n t r o l l e v e l s . The g e r m i n a t i o n r a t e s of those seeds exposed to somewhat c o o l e r burns (200 g /m 2 ) a l s o exceeded c o n t r o l s . However, h o t t e r burns s i g n i f i c a n t l y r e t a r d e d the g e r m i n a t i o n r a t e s of A c a c i a g e r r a r d i i seeds compared to the c o n t r o l s . Such 168 f u e l l o a d i n g s and f i r e i n t e n s i t i e s are found under n a t u r a l c o n d i t i o n s i n the M a r a . The Mara woodlands c u r r e n t l y c o n t a i n a very s m a l l p r o p o r t i o n of mature , s e e d - p r o d u c i n g t r e e s . A l t h o u g h the l e n g t h of l i f e f or seeds a l r e a d y w i t h i n the s o i l i s unknown, i t i s p r o b a b l y not i n d e f i n i t e . The o n l y o ther seeds a v a i l a b l e are those c a r r i e d by t r a n s i e n t h e r b i v o r e s , l i k e e l e p h a n t s , from o u t s i d e the Reserve and d e p o s i t e d w i t h i n . Under c u r r e n t c o n d i t i o n s , t h i s r e q u i r e s not o n l y l o n g - d i s t a n c e movements by c a r r i e r s but a l s o t r a v e l to areas i n h a b i t e d by l o c a l p a s t o r a l i s t s or p o a c h e r s . The l i m i t e d seed source in the Mara may e v e n t u a l l y l i m i t the r e g e n e r a t i o n p o t e n t i a l of e x i s t i n g woodlands; the r o l e of hot f i r e s i n r e d u c i n g g e r m i n a t i o n r a t e s of seeds in the s o i l f u r t h e r e x a c e r b a t e s t h i s p r o b l e m . In the B r a c h y s t e g i a woodlands of M a l a w i , B e l l and Jachmann (1984) found tha t e l e p h a n t s a c t u a l l y a v o i d e d burned a r e a s . From t h i s they c o n c l u d e d tha t f i r e c o u l d be an e f f e c t i v e t o o l i n m a n i p u l a t i n g e l ephant d i s t r i b u t i o n s and r e d u c i n g the impact of t h e i r browsing on woodlands. However, in t h i s s t u d y , e l e p h a n t s browsed even more i n t e n s i v e l y on burned p l o t s . T h i s was most l i k e l y because newly r e s p r o u t i n g s e e d l i n g s were h i g h in p r o t e i n ( D o u g a l l et a l . 1964, Pe l lew 1981) and browse of a l l k inds was i n s h o r t supp ly i n the M a r a . The r e s u l t s from my c o n t r o l l e d , m u l t i p l e - b u r n exper iments ( F i g u r e 5.7) suggest tha t even under c u r r e n t b u r n i n g c o n d i t i o n s ( f u e l l o a d i n g of 200 - 4 0 0 g / m 2 ) , root r e s e r v e s are p r o b a b l y b e i n g d e p l e t e d by s h o r t dry season f i r e s . T h i s , c o u p l e d w i t h c o n t i n u e d browsing by e l e p h a n t s , d i m i n i s h e s the l i k e l i h o o d of 169 woodland r e c o v e r y . A change in both b u r n i n g and browsing regimes w i l l be neces sary i f the c u r r e n t t r e n d towards open g r a s s l a n d s i s to be s lowed or h a l t e d (see Chapter 6 ) . W i l d e b e e s t Though the combinat ion of e l e p h a n t s and f i r e appears to be e f f e c t i v e l y i n h i b i t i n g the r e c o v e r y of Acac i a woodlands i n the M a r a , t h e r e i s a t h i r d important f a c t o r . The r o l e of w i l d e b e e s t i n removing the s t a n d i n g c r o p and thus l i m i t i n g the i n t e n s i t y of f i r e s has been d i s c u s s e d above . W i l d e b e e s t , however, have a second, l e s s obv ious r o l e in woodland dynamics . Under presen t day c o n d i t i o n s , the sheer numbers of w i l d e b e e s t i n h a b i t i n g the Mara Reserve d u r i n g the dry season are hav ing a s i g n i f i c a n t impact on the woody v e g e t a t i o n through t r a m p l i n g and f e e d i n g . When the w i l d e b e e s t f i r s t en ter the M a r a , j u s t f o l l o w i n g the c e s s a t i o n of the long r a i n s , the g r a s s e s are t a l l and g r e e n . The w i l d e b e e s t move through these a r e a s , g r a z i n g as they go. I n a d v e r t e n t l y , they b i t e o f f many stems of r e g e n e r a t i n g s e e d l i n g s which are h idden i n the t a l l g r a s s , and they trample o t h e r s . When they f i n a l l y l eave the Mara t h e i r g r a z i n g grounds are t r a n s f o r m e d i n t o a dry w a s t e l a n d , w i th l i t t l e s i g n of l i v e s e e d l i n g s . In a d d i t i o n to these t r a m p l i n g and a c c i d e n t a l browsing e f f e c t s , male w i l d e b e e s t have a f u r t h e r impact on the woody v e g e t a t i o n . The S e r e n g e t i w i l d e b e e s t are at the end of t h e i r r u t t i n g p e r i o d when they f i r s t a r r i v e i n the M a r a , and r e s i d e n t w i l d e b e e s t (from the Mara Reserve and L o i t a P l a i n s area) are 170 s t i l l i n the peak of t h e i r b r e e d i n g season . L i k e many o ther r u t t i n g u n g u l a t e s , male w i l d e b e e s t spar w i t h s e e d l i n g s and s m a l l t r e e s i n a d d i t i o n to o ther males . Though t h i s damage i s most p r e v a l e n t i n the 1-2m h e i g h t c l a s s (which i s u n d e r r e p r e s e n t e d i n the Mara) i t i s obv ious i n t r e e s under 1m, as w e l l . B e l s k y (1984) r e p o r t e d that young b u l l w i l d e b e e s t broke tops and branches of A c a c i a s i n the range of 30-150cm. Such t h r a s h i n g of s e e d l i n g s may reduce the v i g o u r of the p l a n t s but i s not as s i g n i f i c a n t a m o r t a l i t y f a c t o r as t r a m p l i n g and browsing which k i l l l a r g e numbers of stems i n the Mara each y e a r . Other Browsers In a d d i t i o n to e l e p h a n t s , the Mara s t i l l p r o v i d e s s u f f i c i e n t h a b i t a t f or a r i c h d i v e r s i t y of o ther browsing mammals. Among these are i m p a l a , d i k d i k , some g i r a f f e , a few r h i n o c e r o s e s and s e a s o n a l l y even the Thomson's and G r a n t ' s g a z e l l e s have been shown to feed on woody s p e c i e s ( T i e s z e n e_t a l . 1979, p e r s . comm.). As B e l s k y (1984) sugges ted , these s p e c i e s p r o b a b l y were not major agents of m o r t a l i t y , but they d i d have a measureable impact on s e e d l i n g s . As t h i s s tudy has shown, each year the m a j o r i t y of s e e d l i n g s were reduced to ground l e v e l by s e v e r a l browsing s p e c i e s . T h i s i n h i b i t i o n of growth by browsing i s a s i g n i f i c a n t f a c t o r i n the f a i l u r e of s e e d l i n g s i n the Mara to ever reach 1m l e t a lone grow beyond i t . 171 Summary The number of mature t r e e s i n the Mara has been reduced over the past 30 y e a r s . The remain ing mature t r e e s are now b e i n g l o s t at a r a t e of over 8% per y e a r . The f u t u r e of these d i s a p p e a r i n g woodlands i s dependent on the p o t e n t i a l f or replacement from r e g e n e r a t i n g s e e d l i n g s . In the M a r a , the growth p o t e n t i a l of s e e d l i n g s and c o p p i c i n g r o o t s t o c k s i s be ing s e v e r e l y i n h i b i t e d . In t h i s s t u d y , 4% of a l l s e e d l i n g s were k i l l e d a n n u a l l y by e l e p h a n t s , 4% by f i r e , 1% by w i l d e b e e s t t r a m p l i n g and t h r a s h i n g and another 1% through o ther n a t u r a l c a u s e s . S e e d l i n g s e x p e r i e n c e d the g r e a t e s t impacts from e l e p h a n t s and o ther browsers i n the dry season . W i l d e b e e s t , e l e p h a n t s , and o ther browsers removed up to 60% of a l l s u r v i v i n g stems in unburned p l o t s and an even g r e a t e r p r o p o r t i o n i n burned p l o t s . Whi l e w i l d e b e e s t impacts were s i m i l a r under both t r e a t m e n t s , e l e p h a n t s and o ther browsers showed a d i s t i n c t p r e f e r e n c e for s e e d l i n g s i n burned p l o t s . Browsing e f f e c t s on s e e d l i n g s v a r i e d a c c o r d i n g l y and were s i g n i f i c a n t l y h i g h e r i n burned p l o t s than i n unburned p l o t s . The m a j o r i t y of s e e d l i n g s removed at ground l e v e l by w i l d e b e e s t or f i r e r e s p r o u t e d w i t h i n s i x months. Those taken by e l e p h a n t s , however, e x p e r i e n c e d much g r e a t e r d e l a y s i n r e c o v e r y . T h i s suggests tha t e l e p h a n t s d i d more severe damage to the p l a n t s than d i d f i r e or w i l d e b e e s t . S e e d l i n g s exposed to browsing an imal s showed s i g n i f i c a n t d e c r e a s e s in h e i g h t over the s tudy but were s i g n i f i c a n t l y t a l l e r than those s e e d l i n g s which had been burned and browsed. Those s e e d l i n g s which were browsed but not burned showed a steady 172 d e c l i n e i n stem numbers. However, b u r n i n g , c o u p l e d w i t h b r o w s i n g , s t i m u l a t e d an i n c r e a s e i n the stem numbers of marked s e e d l i n g s . In e x c l o s u r e p l o t s , where s e e d l i n g s were n e i t h e r burned nor browsed, they grew a maximum of 10 - 15cm per year w h i l e the average number of stems remained more or l e s s the same. M u l t i p l e - b u r n exper iments demonstrated tha t s e e d l i n g s u r v i v o r s h i p was i n v e r s e l y r e l a t e d to the l e v e l of f i r e i n t e n s i t y . S e e d l i n g s u r v i v o r s h i p remained h i g h a f t e r repea ted c o o l burns ( f u e l l oads up to 150g/m 2 ) but dropped s i g n i f i c a n t l y a f t e r repea ted hot burns ( f u e l l o a d s > 3 0 0 g / m 2 ) . Seed g e r m i n a t i o n r a t e s were s t i m u l a t e d beyond c o n t r o l l e v e l s by f i r e s of 200 - 600g/m 2 but d e c l i n e d at h i g h e r f u e l l o a d i n g s . Under c u r r e n t c o n d i t i o n s , i t i s u n l i k e l y tha t mature t r e e s w i l l e v e n t u a l l y be r e p l a c e d and tha t woodlands i n the Mara w i l l expand or even p e r s i s t . A s i g n i f i c a n t change i n one or more of the p r e v a i l i n g i n h i b i t o r y f a c t o r s must take p l a c e for woodlands w i t h i n the Reserve to s u c c e s s f u l l y r e g e n e r a t e . 173 CHAPTER 6. DYNAMICS OF THE MARA WOODLANDS: PAST, PRESENT, AND FUTURE I n t r o d u c t i o n The r o l e of e l e p h a n t s i n woodland d e c l i n e s has s t i m u l a t e d much c o n t r o v e r s y among e c o l o g i s t s and managers over the y e a r s . In the m a j o r i t y of cases e l e p h a n t s have been c i t e d as the p r i m a r y cause of woodland l o s s e s i n parks and r e s e r v e s throughout A f r i c a ( E g g e l i n g 1947, Buechner and Dawkins 1961, Brooks and Buss 1962, P i e n a a r et a l . 1966, Wing and Buss 1970, Laws 1970, F i e l d 1971, Spence and Angus 1971, H a r r i n g t o n and Ross 1974, Laws et a l . 1975, Thomson 1975, Guy 1976, Barnes 1982, Weyerhaeuser 1985). The S e r e n g e t i - M a r a woodlands p r e s e n t e d no e x c e p t i o n to t h i s case (Glover 1965, 1968, Lamprey et a l . 1967, R u s s e l l 1968, G l o v e r and Trump 1970). By the 1960s, r e s e a r c h e r s and Park managers in the S e r e n g e t i were a l r e a d y deep ly i n v o l v e d in the c o n t r o v e r s y . Tsavo N a t i o n a l P a r k , i n n e i g h b o u r i n g Kenya , had become a f o c a l p o i n t f o r the s tudy of "elephant problems" (Glover and S h e l d r i c k 1964, Laws 1969, 1970, Myers 1973, Parker 1983) and the q u e s t i o n of c o n t r o l l e d c r o p p i n g of e l ephant p o p u l a t i o n s was much in the f o r e f r o n t . Throughout southern A f r i c a , park managers and e c o l o g i s t s had a l r e a d y begun c r o p p i n g e l e p h a n t s i n an attempt to h a l t woodland l o s s e s (P ienaar e_t a l . 1966, van Wyk and F a i r a l l 1969, P i e n a a r 1969). And , today , c u l l i n g i s s t i l l advocated and p r a c t i c e d i n a number of c o u n t r i e s ( B e l l 1983, Cumming 1983, de Vos et a l . 1983, Owen-Smith 1983, P i e n a a r 1983). In few of these c a s e s , i f any , has i t ever been f u l l y e s t a b l i s h e d t h a t 174 e l e p h a n t s a r e , i n f a c t , the p r i m a r y agent d r i v i n g the observed t r e n d s from dense woodland to open g r a s s l a n d s . My study of the d e c l i n e and dynamics of the Masai Mara woodlands p r o v i d e d an o p p o r t u n i t y to address t h i s i s s u e i n a d e d u c t i v e manner. Two q u e s t i o n s were c e n t r a l to t h i s s t u d y . F i r s t , what f a c t o r ( s ) were r e s p o n s i b l e for the woodland d e c l i n e s over the pas t 30 y e a r s ? And , second , what f a c t o r ( s ) are c u r r e n t l y p r e v e n t i n g any s i g n i f i c a n t r e c o v e r y of woodlands in the Reserve? Under the f i r s t q u e s t i o n , the "1960s e l ephant" h y p o t h e s i s suggests tha t e l e p h a n t s , a l o n e , were r e s p o n s i b l e f o r the observed d e c l i n e s through t h e i r impacts on mature t r e e s . T h i s h y p o t h e s i s p r e d i c t s t h a t the r a t e s of e l ephant damage measured i n the e a r l y 1960s, d u r i n g the p e r i o d of the most extreme d e c l i n e s (Lamprey et a l . 1967, Croze 1974a & b ) , had been s u f f i c i e n t to account f o r the observed l o s s e s . A l t e r n a t i v e l y , the "1960s f i r e " h y p o t h e s i s s t a t e s t h a t f i r e , a l o n e , through i t s e f f e c t on t r e e s and s e e d l i n g s under 3m, reduced r e c r u i t m e n t r a t e s to the p o i n t where they c o u l d not o f f s e t a d u l t t r e e m o r t a l i t y r a t e s . The f i r e h y p o t h e s i s p r e d i c t s tha t b u r n i n g r a t e s measured i n the e a r l y 1960s ( S i n c l a i r 1975, N o r t o n - G r i f f i t h s 1979), had been c a p a b l e of c a u s i n g the documented l o s s of woodlands i n the n o r t h e r n S e r e n g e t i and M a r a . In answer to the second q u e s t i o n , the "1980s f i r e " h y p o t h e s i s s t a t e s that f i r e , a l o n e , through i t s r e p e a t e d e f f e c t on s e e d l i n g s and s m a l l t r e e s i s capab le of i n h i b i t i n g woodland r e g e n e r a t i o n . The h y p o t h e s i s p r e d i c t s tha t the presen t day r a t e s of b u r n i n g , w i t h i n the Reserve b o u n d a r i e s , c o u l d h a l t the 175 r e c o v e r y of the Mara woodlands and produce the p a t t e r n s seen t o d a y . U s i n g the r a t e s of browsing by e l ephants tha t I r e c o r d e d i n the Mara over the past f o u r y e a r s , the "1980s e l ephant" h y p o t h e s i s argues tha t e l e p h a n t s a l o n e , through t h e i r e f f e c t s on both s e e d l i n g s and f u l l y mature t r e e s , are p r e v e n t i n g the r e g e n e r a t i o n of the Mara woodlands . From recent census work, I e s t a b l i s h e d t h a t e l ephant numbers were at unprecedented h i g h s i n the M a r a , due to p o a c h i n g in o ther areas of t h e i r range , and t h a t the Mara i s now e x p e r i e n c i n g heavy browsing by e l e p h a n t s on a y e a r - r o u n d b a s i s . I p r e d i c t e d t h a t , t a k i n g i n t o c o n s i d e r a t i o n the observed e f f e c t of e l e p h a n t s both on the s e e d l i n g c l a s s ( t r e e s under 1m) and those which have escaped the e f f e c t s of f i r e (over 3m), the woodlands w i l l not be a b l e to recover w i t h the c u r r e n t numbers of r e s i d e n t e l e p h a n t s . In a d d i t i o n to these four p r i m a r y hypotheses , I a l s o i n v e s t i g a t e d the i n d i v i d u a l and s y n e r g i s t i c e f f e c t s of w i l d e b e e s t and browsers (o ther than e l e p h a n t s ) at t h e i r e s t i m a t e d l e v e l s i n each time s c e n a r i o . To i n v e s t i g a t e the p l a u s i b i l i t y of these d i f f e r e n t h y p o t h e s e s , I have deve loped a model which i n c o r p o r a t e s a number of measureable f a c t o r s i n v o l v e d i n both pas t and p r e s e n t woodland dynamics . The model i s de s igned to examine the above hypotheses under a v a r i e t y of c o n d i t i o n s . Combinat ions of b u r n i n g r a t e s , e l e p h a n t browsing r a t e s , w i l d e b e e s t t r a m p l i n g and t h r a s h i n g e f f e c t s , and the impact of r e s i d e n t browsers , as de termined from a c t u a l measurements i n the f i e l d , are used i n the model and r e s u l t s are then compared wi th p r e d i c t i o n s . 176 The Model 1. The Assumptions T h i s model i s a f i r s t attempt at s i m u l a t i n g a c o m p l i c a t e d and dynamic n a t u r a l system in which many f a c t o r s operate s i m u l t a n e o u s l y . For t h i s r e a s o n , t h i s i n i t i a l e f f o r t i s n e c e s s a r i l y s i m p l i s t i c b u t , n o n e t h e l e s s , i n f o r m a t i v e i n i t s l i m i t e d way. In d e s i g n i n g a q u a l i t a t i v e model of t h i s type i t i s n e c e s s a r y to make a number of assumptions about the c o n d i t i o n s under which the model can be expected to be a c c u r a t e . The s t a t e d assumptions s h o u l d be both b i o l o g i c a l l y r e a l i s t i c and c o n s e r v a t i v e . The f a c t o r s a f f e c t i n g woodland dynamics i n the Mara and i n c l u d e d w i t h i n the model are the annua l r a t e s o f : a) e l ephant impact on s e e d l i n g s and mature , a d u l t t r e e s , b) b u r n i n g , c) the damage due to the t r a m p l i n g , t h r a s h i n g and i n a d v e r t e n t browsing by the m i g r a t o r y w i l d e b e e s t , and d) browsing by r e s i d e n t browsers o t h e r than e l e p h a n t s . A . E l e p h a n t s E l e p h a n t s a f f e c t t r e e s of a l l h e i g h t s found i n the Acac i a woodlands of the M a r a . The r a t e s of browsing by e l e p h a n t s are t r e a t e d as p r o p o r t i o n a l to e l ephant p o p u l a t i o n s i z e s (as de termined from a e r i a l t o t a l c o u n t s ) . In answering the i n i t i a l q u e s t i o n about the causes of woodland d e c l i n e s in the 1960s and 1970s, I have assumed tha t e l e p h a n t s fed a c c o r d i n g to the 1 77 p a t t e r n s s t a t e d by Croze (1974a & b) and t h a t they l a r g e l y i g n o r e d s e e d l i n g s under 1m d u r i n g the t ime when l a r g e r t r e e s were more abundant . In answering the second q u e s t i o n about c u r r e n t woodland dynamics , I have de termined browsing r a t e s from d i r e c t o b s e r v a t i o n s of e l ephant f e e d i n g behav iour and from the measured e f f e c t s e l e p h a n t s have had on marked t r e e s of a l l h e i g h t c l a s s e s . B . F i r e F i r e a f f e c t s a l l t r e e s l e s s than 3m h i g h . The b u r n i n g r a t e used i n the presen t c a l c u l a t i o n s i s de termined by the percentage of a r e a burned over t ime ( N o r t o n - G r i f f i t h s 1979), which i s assumed to be e q u i v a l e n t to the percentage of t r e e s burned (when t r e e s are u n i f o r m l y d i s t r i b u t e d ) . I t i s a l s o assumed tha t b u r n i n g r a t e s are c o r r e l a t e d not on ly w i t h f u e l l o a d i n g s but a l s o w i t h the number of people r e s i d e n t n e a r b y . T h i s assumption i s made because most f i r e s in t h i s p a r t of A f r i c a are b e l i e v e d to be l i t by humans and not s t a r t e d by l i g h t n i n g . I assumed, t h e r e f o r e , tha t a t the t u r n of the c e n t u r y , a l t h o u g h there were few w i l d e b e e s t and there were p r o b a b l y s u f f i c i e n t f u e l l o a d i n g s to support severe f i r e s , r e l a t i v e l y few f i r e s o c c u r r e d because human p o p u l a t i o n s i n the area were very s m a l l . 1 78 C . W i l d e b e e s t In the M a r a , w i l d e b e e s t s i g n i f i c a n t l y a f f e c t o n l y those t r e e s under 1m. The r a t e s of m o r t a l i t y and stem l o s s on s e e d l i n g s due to w i l d e b e e s t were c o n s i d e r e d to be n e g l i g i b l e d u r i n g the p e r i o d of r a p i d woodland l o s s i n the 1960s. D u r i n g t h i s p e r i o d , w i l d e b e e s t numbers were s t i l l low f o l l o w i n g t h e i r r e c o v e r y from r i n d e r p e s t , and t h e i r annua l m i g r a t o r y movements d i d not take them to the Mara in s i g n i f i c a n t numbers (Pennycuick 1975, Maddock 1979). W i l d e b e e s t were assumed to have a measureable impact on woodland dynamics on ly when they had reached t h e i r c u r r e n t p o p u l a t i o n s i z e of around 1.5 m i l l i o n a n i m a l s . The m a j o r i t y of these a n i m a l s v i s i t the Mara d u r i n g the dry season each y e a r . D. R e s i d e n t Browsers (other than e l e p h a n t s ) L i k e w i l d e b e e s t , browsers i n the Mara are assumed to a f f e c t o n l y those t r e e s under 1m. G i r a f f e numbers are r e l a t i v e l y low i n the M a r a , p r o b a b l y due to a shor tage of d e s i r a b l e f o r a g e . So, t h i s means tha t the s m a l l e r s p e c i e s , such as i m p a l a , d i k d i k , and G r a n t ' s g a z e l l e s , a t some t imes of the y e a r , are the pr imary browsers i n v o l v e d in the woodland dynamics . Recent a e r i a l censuses ( S i n c l a i r and D u b l i n , u n p u b l i s h e d data) as compared w i t h e a r l i e r census work ( S i n c l a i r and N o r t o n - G r i f f i t h s 1979) i n d i c a t e t h a t r e s i d e n t browser p o p u l a t i o n s i z e s have not changed s i g n i f i c a n t l y over the past 15 - 20 y e a r s . T h e r e f o r e , I have assumed t h a t browsing r a t e s by an imal s o ther than e l e p h a n t s were 179 the same i n the 1960s as my measurements have shown them to be i n the Mara t o d a y . Only f i r e and e l e p h a n t s are c o n s i d e r e d to be agents of bo th m o r t a l i t y and r e v e r s i o n of t r e e s i n t o s m a l l e r h e i g h t c l a s s e s , whereas , w i l d e b e e s t ac t as r e v e r s i o n and i n h i b i t i o n agents ( N o r t o n - G r i f f i t h s 1979, Pe l l ew 1983), and browsers ac t on ly as i n h i b i t i o n agents (see Appendix A ) . 2. C o n s t a n t s and V a r i a b l e s The t r e e p o p u l a t i o n used i n the model i s d e s c r i b e d by s e v e r a l c o n s t a n t s . These c o n s t a n t s (Table 6.1) are d e r i v e d from the r e s u l t s of Lamprey et a l . (1967) , G l o v e r (1968) , Croze (1974a & b ) , H e r l o c k e r (1976a), N o r t o n - G r i f f i t h s (1979), and Pe l l ew (1981, 1983), i n a d d i t i o n to my own d a t a . Tree d e n s i t i e s we're c o n v e r t e d to a 10 h e c t a r e b a s i s f o r the purpose of a n a l y s i s . Seven v a r i a b l e s are b u i l t i n t o the model (Tab le 6 . 2 ) . S i x of these v a r i a b l e s are expres sed as " m o r t a l i t y " , " r e v e r s i o n " , or " i n h i b i t i o n " r a t e s . M o r t a l i t y r a t e s r e f e r to the percentage of s e e d l i n g s or mature , a d u l t t r e e s which are k i l l e d a n n u a l l y by a g i v e n f a c t o r . " R e v e r s a l " r a t e s r e f e r to the p r o p o r t i o n of s e e d l i n g s which are browsed or t rampled back to ground l e v e l but l a t e r r e s p r o u t and " i n h i b i t i o n " r a t e s p e r t a i n to the percentage of s e e d l i n g s which r e p e a t e d l y have stems removed though s t i l l m a i n t a i n some stems above ground l e v e l . The seventh v a r i a b l e , b u r n i n g r a t e , i s d e r i v e d from the p r o p o r t i o n of woodland a r e a burned each year and assumed to be equa l to the p e r c e n t of t r e e s 180 Table 6.1. Constants which are b u i l t into the model. FOR ALL PLANTS; 1) Seedling d e n s i t i e s : 850/ha 2) Adult tree (>3m) den s i t i e s : 32/ha 3) New seedlings: 17/ha/year 4) Growth of seedlings: 15cm/year 5) F i r e escapement height: 3m 6) Natural mortality rate of adult trees and seedlings: 1%/year FOR BURNED PLANTS: 1) Number of plants under lm which are k i l l e d by f i r e : 5% 2) Number of plants i n the 0-lm class which revert to the 0-lm c l a s s : 95% 3) Number of plants i n the l-2m class which revert to the 0-lm c l a s s : 90% 4) Number of plants i n the 2-3m class which revert to the 0-lm c l a s s : 5% 5) Number of plants i n which revert to the the 2-3m class l-2m c l a s s : 29% 181 Table 6.2. The parameters varied i n the model. 1) Burning rate 2) Elephant mortality rate on seedlings 3) Elephant reversal rate on seedlings 4) Wildebeest i n h i b i t i o n rate on seedlings 5) Wildebeest reversal rate on seedlings 6) Browser i n h i b i t i o n rate on seedlings 7) Mortality rate of mature, adult trees 182 exposed to f i r e s a n n u a l l y . In examining the four working h y p o t h e s e s , the input v a l u e s of these seven v a r i a b l e s are set at a c t u a l v a l u e s r e p o r t e d from f i e l d s t u d i e s i n the S e r e n g e t i woodlands d u r i n g the 1960s or from my own s t u d i e s i n the Mara in the 1980s. P r e d i c t i o n s are made from each h y p o t h e s i s f o r each t ime s c e n a r i o ( i . e. the 1960s and the 1980s) and then c o n s i d e r e d u s i n g the p e r t i n e n t v a l u e of each v a r i a b l e for the a p p r o p r i a t e time p e r i o d . 3. T e s t C o n d i t i o n s For the purpose of answering my two c e n t r a l q u e s t i o n s , I e s t a b l i s h e d two da ta s e t s , one f o r the 1960s and one for the 1980s (Table 6 . 3 ) . P r e d i c t i o n s were generated from the "elephant and " f i r e " hypotheses put f o r t h to e x p l a i n the woodland l o s s e s in the 1960s and the c u r r e n t i n h i b i t i o n of woodland r e c o v e r y . To i s o l a t e the i n d i v i d u a l e f f e c t s of f i r e , e l e p h a n t s , and o ther f a c t o r s , a l l o ther r a t e s were h e l d c o n s t a n t , whi l e the f a c t o r of i n t e r e s t was v a r i e d w i t h i n r e a l i s t i c ranges . To determine the s y n e r g i s t i c e f f e c t s of these f a c t o r s on woodland dynamics , the e f f e c t s of o ther browsers and w i l d e b e e s t were added to those of e l e p h a n t s and f i r e . Recru i tment r a t e (R) i s the r a t i o of t r e e s e n t e r i n g the h e i g h t c l a s s t a l l e r than 3m to mature t r e e s d y i n g . I f R i s g r e a t e r than u n i t y then the t r e e p o p u l a t i o n i s growing . For the f i g u r e s , the n a t u r a l l o g of R i s used so t h a t the t h r e s h o l d v a l u e i s z e r o . When l n ( R ) i s g r e a t e r than 0, a d u l t r e c r u i t m e n t i s exceed ing a d u l t m o r t a l i t y and the t r e e p o p u l a t i o n i s growing , Table 6.3. The te s t conditions for the 1960s and 198 which were used i n the simulation model. THE 1960s 450 approximate elephant population size 62.0% burning rate 2.5% o v e r a l l elephant-related adult tree mortality 6.0% l o c a l i z e d elephant-related adult tree mortality 1.0% other natural mortality of adult trees 26.0% browser i n h i b i t i o n rate on seedlings THE 1980s 1100 approximate elephant population size 5.0% burning rate 7.0% elephant-related adult tree mortality 4.0% elephant mortality rate on seedlings 1.0% other natural mortality of adult trees 8.0% elephant reversal rate on seedlings 1.0% wildebeest reversal rate on seedlings 29.0% wildebeest i n h i b i t i o n rate on seedlings 26.0% browser i n h i b i t i o n rate on seedlings 184 and v i c e v e r s a . R e s u l t s Woodland D e c l i n e s i n the 1960s The v a l u e s of v a r i a b l e s i n the 1960s s c e n a r i o were set u s i n g da ta c o l l e c t e d i n the S e r e n g e t i N a t i o n a l Park d u r i n g t h a t t i m e . I t was assumed t h a t d u r i n g t h i s p e r i o d e l e p h a n t s l a r g e l y i g n o r e d s e e d l i n g s under 1m. However, two l e v e l s of a d u l t t r e e m o r t a l i t y by e l e p h a n t s were used i n these c a l c u l a t i o n s . F i r s t , I used the m o r t a l i t y r a t e s r e p o r t e d by Lamprey et a l . (1967) and Croze (1974b), f or s e v e r e l y a f f e c t e d l o c a l areas of the c e n t r a l S e r e n g e t i woodlands, (approx . 6%). Second, C r o z e ' s more c o n s e r v a t i v e e s t i m a t e s for the o v e r a l l r a t e of e l e p h a n t - r e l a t e d t r e e m o r t a l i t y of 2.5% were run through the model . B u r n i n g r a t e s were a l s o set a c c o r d i n g to those measured at the t i m e . A l t h o u g h N o r t o n - G r i f f i t h s (1979) r e p o r t e d a 75 - 100% b u r n i n g r a t e in the a r e a b o r d e r i n g the Mara d u r i n g t h i s p e r i o d , the more c o n s e r v a t i v e average of 62% b u r n i n g throughout the t a l l g r a s s l a n d s was used ( S i n c l a i r 1975). Browsing r a t e s , by s p e c i e s o ther than e l e p h a n t s , were set at 26% per year and w i l d e b e e s t were c o n s i d e r e d to have no impact at t h i s t i m e . I f e l e p h a n t s , a l o n e , were r e s p o n s i b l e for the d e c l i n e i n the woodlands ("1960s e l ephant" h y p o t h e s i s ) , and i f a l l o ther f a c t o r s were set at z e r o , then an o v e r a l l r e c r u i t m e n t v a l u e l n ( R ) of l e s s than 0 s h o u l d o c c u r . T a b l e 6.4 shows t h a t at a d u l t m o r t a l i t y r a t e s of 3.5% per year (2.5% due to e l e p h a n t s , Table 6.4. The In(Recruitment rates) for f i r e , elephants, and browsers acting alone i n the 1960s scenario. Those values less than zero indicate woodland los s , whereas those values greater than zero indicate woodland increase. FACTOR In(Recruitment rate) F i r e -2.91 Elephants (at 2.5% elephant-related adult tree mortality) 2.74 Elephants (at 6.0% elephant-related adult tree mortality) 2.05 Browsers 2.46 186 p l u s , 1.0% due to n a t u r a l c a u s e s ) , the ln (R) v a l u e e q u a l s 2 .74 . At the h i g h e s t r e p o r t e d a d u l t m o r t a l i t y r a t e s of 7.0% (6.0% due to e l e p h a n t s , p l u s , 1.0% due to o t h e r n a t u r a l causes ) the l n ( R ) v a l u e was s t i l l g r e a t e r than 0, a t 2 .05 , c o n t r a r y to tha t p r e d i c t e d by the e l ephant h y p o t h e s i s . I f f i r e , a l o n e , caused the woodland d e c l i n e s of the 1960s ("1960s f i r e " h y p o t h e s i s ) , and i f a l l o ther f a c t o r s were h e l d a t z e r o , then the r e c r u i t m e n t v a l u e ( l n ( R ) ) s h o u l d be l e s s than 0. T a b l e 6.4 shows the ln (R) v a l u e to be -2 .91 under these c o n d i t i o n s , i n agreement wi th the f i r e h y p o t h e s i s . Browsers , a l o n e , were unable to reduce the l n ( R ) v a l u e below z e r o (Table 6 . 4 ) . F i g u r e 6.1 shows the l n ( R ) v a l u e s for d i f f e r e n t p o p u l a t i o n s i z e s of e l e p h a n t s (as a percentage of c u r r e n t e l ephant numbers in the Mara) wi thout o ther browsers or w i l d e b e e s t , w i th o ther browsers but no w i l d e b e e s t , and c o u p l e d w i t h o ther browsers and w i l d e b e e s t . At C r o z e ' s (1974b) e s t imate for o v e r a l l e l e p h a n t - r e l a t e d t r e e m o r t a l i t y (2.5%/year) i n a d d i t i o n to o ther n a t u r a l m o r t a l i t y (1.0%/year) and o ther b r o w s e r s , ln (R) was 1.16 ( F i g u r e 6 . 1 ) . Even when e l e p h a n t - r e l a t e d t r e e m o r t a l i t y r a t e s were set at t h e i r h i g h e s t r e p o r t e d l e v e l s (6 .0%/year) , l n ( R ) was s t i l l above zero ( 0 . 4 7 ) . The a d d i t i o n of browsing e f f e c t s to those of f i r e , a l o n e , o n l y made the ln (R) v a l u e more n e g a t i v e ( F i g u r e 6 . 2 ) . When f i r e , e l e p h a n t s , and browsers are a l l a c t i n g t o g e t h e r and a d u l t m o r t a l i t y r a t e s are set at 7.0%/year (6.0% due to e l e p h a n t s , p l u s 1.0% due to o t h e r n a t u r a l c a u s e s ) , the l n ( R ) v a l u e was - 8 . 2 3 . When a d u l t t r e e m o r t a l i t y r a t e s were set a t 3.5%/year (2.5% due to e l e p h a n t s , p l u s 1.0% due to o ther n a t u r a l c a u s e s ) , 187 —6.0 ' — • — i — | — i — i — i — j — i — i — i — | — i — i — i — | — i — i — i — j — i 0 20 40 60 80 100 % OF CURRENT E L E P H A N T POPULATION Figure 6.1. The n a t u r a l log of recruitment r a t e s (R) f o r v a r y i n g elephant p o p u l a t i o n s : a) without wildebeest or browsers; b) with browsers but no wildebeest; and c) w i t h both wildebeest and browsers. Those values l e s s than zero i n d i c a t e woodland l o s s , while those values greater than zero i n d i c a t e woodland i n c r e a s e s . Note : The dotted l i n e at 40% represents elephant population s i z e s of the 1960s. The dotted l i n e at 100% represents the c u r r e n t elephant population s i z e i n the Mara. Burning r a t e s are held at zero. 188 0 20 40 60 80 100 BURNING RATE (%) Figure 6.2. The n a t u r a l l o g of recruitment r a t e s (R) f o r va r y i n g burning r a t e s : a) without wildebeest or browsers; b) w i t h browsers but no wildebeest; and c) with both wildebeest and browsers. Those values l e s s than zero i n d i c a t e woodland l o s s , w hile those values greater than zero i n d i c a t e woodland i n c r e a s e s . Note : The dotted l i n e at 62% represents the burning r a t e s of the 1960s. The dotted l i n e at 5% represents the current burning r a t e s i n the Mara. Elephant impacts are h e l d at zero. 189 the l n ( R ) was - 7 . 9 5 . T h i s l a t t e r case most a c c u r a t e l y d e s c r i b e s the a c t u a l 1960s s c e n a r i o when s i g n i f i c a n t woodland l o s s e s o c c u r r e d (Chapter 2 ) . Woodland Dynamics i n the 1980s A l l v a r i a b l e v a l u e s under the 1980s s c e n a r i o were set from those r e c o r d e d in the course of t h i s s t u d y . B u r n i n g r a t e s have been v e r y much reduced in recent y e a r s , s i n c e the w i l d e b e e s t have moved to the Mara i n l a r g e numbers d u r i n g the dry season . For the purposes of t h i s m o d e l l i n g e x e r c i s e , I have set c u r r e n t day b u r n i n g r a t e s at 5% per y e a r . E l e p h a n t s are at t h e i r h i g h e s t r e c o r d e d p o p u l a t i o n numbers, over 2.4 t imes those counted i n the l a t e 1960s and e a r l y 1970s f o r the Mara (Stewart and T a l b o t 1962, T a l b o t and Stewart 1964, D u b l i n and D o u g l a s - H a m i l t o n , i n p r e s s ) . A d u l t t r e e m o r t a l i t y r a t e s were set at 8.0% (7.0% due to e l e p h a n t s and 1.0% due to n a t u r a l c a u s e s ) . Browsing r a t e s were the same as those used i n the 1960s s c e n a r i o as recent census data and t h a t of T a l b o t and Stewart (1964) and S t e l f o x et a l . (1986) shows l i t t l e change in the p o p u l a t i o n s i z e s of these s p e c i e s . The most important a d d i t i o n a l f a c t o r in the c u r r e n t day s i t u a t i o n i s t h a t of the m i g r a t o r y w i l d e b e e s t . T h e i r impacts have been i n c o r p o r a t e d i n t h i s mode l . The "1980s f i r e " h y p o t h e s i s s t a t e s t h a t f i r e , a l o n e , i s r e s p o n s i b l e f o r the i n h i b i t i o n of woodland r e c o v e r y . I f f i r e i s r e s p o n s i b l e , then at t o d a y ' s b u r n i n g r a t e s , w i t h a l l o ther f a c t o r s b e i n g h e l d at z e r o , the l n ( R ) v a l u e s h o u l d be l e s s than 0. T a b l e 6.5 and F i g u r e 6.2 show t h a t the c u r r e n t l n ( R ) va lue for f i r e , a c t i n g a l o n e , i s 4 .66 , a number c o n s i d e r a b l y g r e a t e r Table 6.5. The In(Recruitment rates) for f i r e , elephants, browsers, and wildebeest acting alone i n the 1980s scenario. Those values less than zero indicate woodland l o s s , whereas those value greater than zero indicate woodland increase. FACTOR In(Recruitment rate) F i r e 4.66 Elephants (at 7.0% elephant-related adult tree mortality) •0.14 Browsers Wildebeest 2.46 2.58 191 than z e r o . F i r e , t h e r e f o r e , i s not the main i n h i b i t o r of s e e d l i n g r e g e n e r a t i o n . The "1980s e l ephant" h y p o t h e s i s s t a t e s t h a t e l e p h a n t s , in the absence of any o ther f a c t o r s , can prevent the expans ion of the Mara woodlands . In t h i s c a s e , e l ephant impact , a l o n e , s h o u l d r e s u l t i n a l n ( R ) v a l u e of l e s s than 0. Under these c o n d i t i o n s , the l n ( R ) v a l u e was, i n f a c t , - 0 .14 (Table 6.5 and F i g u r e 6 . 1 ) . T h e r e f o r e , e l e p h a n t s are c a p a b l e of p r e v e n t i n g s e e d l i n g r e g e n e r a t i o n under c u r r e n t c o n d i t i o n s but not to a grea t degree . N e i t h e r browsers nor w i l d e b e e s t , when c o n s i d e r e d i n the absence of a l l o ther f a c t o r s , reduced the l n ( R ) to a n e g a t i v e v a l u e (Table 6 . 5 ) . Even when w i l d e b e e s t and browsers are added to the c u r r e n t b u r n i n g e f f e c t s , ln (R) v a l u e s s t i l l remain p o s i t i v e ( F i g u r e 6 . 2 ) . O b v i o u s l y , the a d d i t i o n of w i l d e b e e s t and o ther browsers to the e f f e c t s of e l e p h a n t s d r i v e s l n ( R ) v a l u e s even f u r t h e r below zero ( F i g u r e 6 . 1 ) . Under c u r r e n t c o n d i t i o n s f o r e l e p h a n t s , f i r e , w i l d e b e e s t , and o ther browsers , combined, the l n ( R ) v a l u e e q u a l s - 5 . 6 4 , i n d i c a t i n g tha t the woodlands are s t i l l d e c l i n i n g . Woodland Dynamics i n the 1890s To c h a l l e n g e the model under a v a r i e t y of p l a u s i b l e c o n d i t i o n s , I went back and r e c o n s t r u c t e d the c o n d i t i o n s of the l a t e 1890s and e a r l y 1900s to see what p a t t e r n of woodland growth would be g e n e r a t e d , assuming tha t woodland dynamics were o p e r a t i n g i n s i m i l a r ways then as they are t o d a y . I t i s 1 92 important to note tha t t h e r e are l i m i t a t i o n s which accompany t h i s a s s u m p t i o n . Tes t c o n d i t i o n s were set as a c c u r a t e l y as p o s s i b l e from my h i s t o r i c a l r e c o n s t r u c t i o n of the p e r i o d (Chapter 2 ) , however, t h e r e were no a c t u a l r e c o r d s a v a i l a b l e for r a i n f a l l , b u r n i n g r a t e s , or an imal numbers. F o l l o w i n g the grea t r i n d e r p e s t e p i d e m i c , w i l d e b e e s t and human numbers had been reduced to n e g l i g i b l e amounts. L i k e w i s e , poach ing had g r e a t l y reduced the e l ephant p o p u l a t i o n to the p o i n t where no e l e p h a n t s were r e p o r t e d by hunters f o r s e v e r a l decades f o l l o w i n g the t u r n of the c e n t u r y . F i r e s were presumed to be min imal due to the low human p o p u l a t i o n s i n a r e a s nearby . And , I assumed that the browsing impact was not s i g n i f i c a n t l y d i f f e r e n t from t h a t of today (though t h i s c o u l d be an o v e r e s t i m a t i o n of t h e i r impact i f r i n d e r p e s t had a l s o reduced t h e i r numbers) . I f r i n d e r p e s t d i d a f f e c t browsers and reduce t h e i r numbers, then my c a l c u l a t i o n may o v e r e s t i m a t e the combined e f f e c t s of a l l four f a c t o r s d u r i n g t h i s p e r i o d and , t h e r e f o r e , underes t imate t r e e r e c r u i t m e n t r a t e s . N a t u r a l m o r t a l i t y of a d u l t t r e e s was c o n s i d e r e d to be 1.0%. To examine t h i s s c e n a r i o , the b u r n i n g r a t e was set at 5%/year, e l ephant and w i l d e b e e s t e f f e c t s were set at z e r o , and the impacts of o ther browsers set at the c u r r e n t r a t e of 26% per y e a r . Under t u r n of the c e n t u r y c o n d i t i o n s , the l n ( R ) v a l u e was w e l l above zero ( 3 . 0 8 ) , i n d i c a t i n g an i n c r e a s e i n woodland p o p u l a t i o n s . T h i s i s c o n s i s t e n t w i t h the p a t t e r n of woodland expans ion which took p l a c e between the l a t e 1890s and the 1940s. 193 Escapement Rates of T r e e s under D i f f e r e n t S c e n a r i o s In a d d i t i o n to l o o k i n g at r e c r u i t m e n t r a t e s i n t o the a d u l t h e i g h t c l a s s , I a l s o l ooked at the r a t e s of r e c r u i t m e n t i n t o a v a r i e t y of h e i g h t c l a s s e s p r i o r to r e a c h i n g the 3m c l a s s . I r e f e r to these as escapement r a t e s and they are p r e s e n t e d i n F i g u r e 6.3 as l o g l O of the number e s c a p i n g from each h e i g h t c l a s s r e l a t i v e to 100,000 s t a r t i n g at the zero h e i g h t c l a s s . To make these r a t e s comparable to s u r v i v a l r a t e s by age, I have assumed tha t p l a n t s reach the 15cm c l a s s in a p p r o x i m a t e l y one y e a r , the 1m h e i g h t c l a s s i n 6 y e a r s , the 2m c l a s s i n 11 y e a r s , and the 3m c l a s s i n 15 y e a r s . I have c o n s i d e r e d t h r e e d i f f e r e n t s c e n a r i o s i n the c a l c u l a t i o n s p r e s e n t e d i n F i g u r e 6 .3 : 1) the c o n d i t i o n s a t the t u r n of the c e n t u r y , 2) the c o n d i t i o n s of the 1960s, and 3) those c o n d i t i o n s e x i s t i n g in the Mara t o d a y . The t u r n of the c e n t u r y p e r i o d showed the g r e a t e s t escapement r a t e s i n t o a l l h e i g h t c l a s s e s , whereas the c o n d i t i o n s of the 1960s (except for escapement i n t o the 15cm and 1m c l a s s e s ) were the l o w e s t . T h i s i s c o n s i s t e n t w i t h the p a t t e r n s of woodland growth and d e c l i n e r e p o r t e d f o r these two t ime p e r i o d s . 194 Figure 6.3. Escapement values f o r Acacia q e r r a r d i i to 0.15m, 1.0m, 2.0m, and 3.0m height c l a s s e s p l o t t e d as the log(a cohort of 100,000 i n d i v i d u a l s i n the s t a r t i n g p o p u l a t i o n ) . I assume that 0.15m i s achieved at 1 year, 1.0m at 6 years, 2.0m at 11 years, and 3.0m at approximately 15 years. Three d i f f e r e n t time scenarios are presented. 195 D i s c u s s i o n The 1960s and 1970s The h y p o t h e s i s t h a t e l e p h a n t s , a l o n e , were r e s p o n s i b l e for the observed woodland l o s s e s i n the 1960s and 1970s seems u n l i k e l y . Even under the most extreme c o n d i t i o n s of e l e p h a n t - r e l a t e d t r e e m o r t a l i t y , e l e p h a n t s were not a b l e to reduce r e c r u i t m e n t r a t e s below m o r t a l i t y r a t e s (Tab le 6 . 4 ) . However, f i r e a lone was e a s i l y a b l e to h o l d r e c r u i t m e n t r a t e s w e l l below m o r t a l i t y r a t e s even at b u r n i n g r a t e s which were c o n s e r v a t i v e (62% per year ) for t h a t p e r i o d of time ( N o r t o n - G r i f f i t h s 1979). T h e r e f o r e , I c o u l d not r e j e c t the e x p l a n a t i o n that f i r e was r e s p o n s i b l e for the woodland d e c l i n e s . Browsers s erved o n l y to lower r e c r u i t m e n t r a t e s but were not capab le of r e d u c i n g woodlands on t h e i r own. These f i n d i n g s support the c o n t e n t i o n of Croze (1974b) , N o r t o n - G r i f f i t h s (1979) and o t h e r s tha t e l e p h a n t s were not r e s p o n s i b l e for the l o s s of woodland canopy cover i n the n o r t h e r n S e r e n g e t i and Mara r e g i o n . D e s p i t e t h e i r sometimes s i g n i f i c a n t e f f e c t s on l o c a l t r e e s t a n d s , e l e p h a n t s were not c a p a b l e of moving the woodlands i n t o a phase of d e c l i n e on t h e i r own. A l t h o u g h e l ephant p o p u l a t i o n s were i n c r e a s i n g w i t h i n the S e r e n g e t i and Mara boundar i e s d u r i n g t h i s p e r i o d (Stewart and T a l b o t 1962, T a l b o t and Stewart 1964, Watson and B e l l 1969, D u b l i n and D o u g l a s - H a m i l t o n , in p r e s s ) , they cannot f a i r l y be blamed f o r the l o s s . These r e s u l t s support the argument tha t under the p r e v a i l i n g b u r n i n g c o n d i t i o n s of the t i m e , f i r e , a l o n e , was a b l e 196 to h a l t the s u c c e s s i o n of woodlands and produce the observed t r e n d towards open g r a s s l a n d s . R a i n f a l l d u r i n g t h i s p e r i o d was uncommonly h i g h , promot ing u n u s u a l l y h i g h g r a s s p r o d u c t i v i t y throughout the a r e a . In a d d i t i o n , w i l d e b e e s t p o p u l a t i o n s were s t i l l be ing h e l d below c a r r y i n g c a p a c i t y by the v i r a l d i s e a s e , r i n d e r p e s t , and , t h e r e f o r e , they d i d not reduce the grass f u e l s s i g n i f i c a n t l y each dry season ( S i n c l a i r 1979). C o n s e q u e n t l y , the e a r l y 1960s was a p e r i o d of f requent and severe f i r e s i n the n o r t h e r n S e r e n g e t i and Mara (Langr idge et a_l. 1970, D u b l i n , Chapter 2 ) . C u r r e n t Dynamics Though c o n d i t i o n s i n the Mara are c u r r e n t l y very d i f f e r e n t from those r e c o r d e d 20 y e a r s ago, the woodlands c o n t i n u e to d e c l i n e ( D u b l i n Chapter 2 ) , and at presen t t h e r e i s no s i g n of r e c o v e r y . In answer to the q u e s t i o n of what f a c t o r ( s ) are p r e v e n t i n g woodland r e g e n e r a t i o n , the h y p o t h e s i s tha t f i r e , a l o n e , i s i n h i b i t i n g woodland r e c o v e r y seems i m p l a u s i b l e (Tab le 6 . 5 ) . Recru i tment r a t e s under c u r r e n t b u r n i n g r a t e s exceed a d u l t m o r t a l i t y r a t e s . However, the same cannot be s a i d f o r the e f f e c t s of e l e p h a n t s in the M a r a . Given the r a t e s of e l ephant impact measured in the Mara d u r i n g the e a r l y 1980s, the h y p o t h e s i s tha t e l e p h a n t s , a l o n e , are p r e v e n t i n g woodland r e c o v e r y seems l i k e l y . E l e p h a n t s are h o l d i n g r e c r u i t m e n t r a t e s below those neces sary to b a l a n c e a d u l t m o r t a l i t y r a t e s (Tab le 6 . 5 ) . With the a d d i t i o n of browsers and the m i g r a t o r y w i l d e b e e s t , woodlands are d e c r e a s i n g at an even more r a p i d r a t e 197 ( F i g u r e 6 . 1 ) . W i l d e b e e s t and o ther browsers t o g e t h e r , or c o u p l e d w i t h c u r r e n t b u r n i n g r a t e s ( F i g u r e 6 . 2 ) , s t i l l cannot d r i v e r e c r u i t m e n t r a t e s below m o r t a l i t y in the absence of e l e p h a n t s . Due to the presen t h i g h r a t e of gras s o f f t a k e by the m i g r a t o r y w i l d e b e e s t (Chapter 4 ) , f u e l l o a d i n g s i n the Mara are no l o n g e r s u f f i c i e n t to support hot burns by the end of the dry season . Today b u r n i n g i s l a r g e l y r e s t r i c t e d to the s h o r t dry season , when f u e l l o a d s are lower , m o i s t u r e content i s h i g h e r , and f i r e s are l e s s damaging when they do o c c u r . I f these c o n d i t i o n s p e r s i s t , then f i r e cannot be c o n s i d e r e d a major concern i n the i n h i b i t i o n of woodland r e c o v e r y . However, i f there were a s i g n i f i c a n t change i n w i l d e b e e s t numbers, f i r e c o u l d once a g a i n become a major element i n the c o n t r o l of woody r e g e n e r a t i o n . E l e p h a n t s , a l o n e , now appear to be a b l e to h o l d down woodland p o p u l a t i o n s i n the M a r a . Poaching a c t i v i t y i n the S e r e n g e t i and the s e t t l e m e n t of most l a n d s u r r o u n d i n g the Reserve have l e d to a change i n the p a t t e r n s of e l ephant d i s t r i b u t i o n and numbers in the pas t few y e a r s ( D u b l i n and D o u g l a s - H a m i l t o n , i n p r e s s ) . Today the Mara i s u t i l i z e d a l l y e a r - r o u n d by a p p r o x i m a t e l y 1,000 e l e p h a n t s , over twice the numbers r e c o r d e d in the 1960s. These e l e p h a n t s r e l y h e a v i l y on the a v a i l a b l e browse m a t e r i a l , p a r t i c u l a r l y d u r i n g the dry season (Chapters 3 & 4 ) . Because t h e r e i s a s c a r c i t y of t r e e s i n the l a r g e r h e i g h t c l a s s e s , e l e p h a n t s now c o n c e n t r a t e t h e i r browsing e f f o r t s on the "weeding" out of s e e d l i n g s (Chapter 4 & 5 ) . Croze (1974b) r e p o r t e d tha t i n the 1960s and e a r l y 1970s 198 e l e p h a n t s i n the S e r e n g e t i l a r g e l y i g n o r e d these s e e d l i n g s but today t r e e s under 1m comprise a s i g n i f i c a n t p r o p o r t i o n of e l ephant d i e t s . A l t h o u g h t h i s change may be a r e f l e c t i o n of a v a i l a b i l i t y r a t h e r than p r e f e r e n c e , i t has important r e p e r c u s s i o n s for woodland dynamics . As N o r t o n - G r i f f i t h s (1979) c o n c l u d e d , the S e r e n g e t i - M a r a woodlands seem to be f a r more s e n s i t i v e to impacts on r e g e n e r a t i n g s e e d l i n g s than to those on mature t r e e s . F u r t h e r m o r e , C a u g h l e y ' s (1976) "s tab le l i m i t c y c l e " h y p o t h e s i s of woodland r e c o v e r y cannot work u n l e s s s e e d l i n g s have a sa fe refuge from e lephant b r o w s i n g . S e e d l i n g s i n the Mara today have no such immunity. In the case of the Mara woodlands, e l e p h a n t s were not capab le of i n i t i a t i n g the woodland d e c l i n e s r e p o r t e d two decades ago. However, once the a d u l t t r e e d e n s i t i e s had been reduced by the p r e v i o u s p e r t u r b a t i o n ( i . e. i n c r e a s e d b u r n i n g r a t e s f o l l o w i n g a r e d u c t i o n i n w i l d e b e e s t numbers and the i n c r e a s e d frequency of man-made f i r e s ) e l e p h a n t s d i d a c c e l e r a t e the r a t e of d e c l i n e . Today , e l e p h a n t s are h o l d i n g the Mara ecosystem i n a g r a s s l a n d phase . T h i s p a t t e r n suggests t h a t the Mara has two l o c a l l y s t a b l e s t a t e s ( i n the sense of H o l l i n g (1973) ) , p r e d o m i n a n t l y woodland or g r a s s l a n d , and t h a t an e x t e r n a l f a c t o r such as f i r e i s neces sary to move the system between these two s t a t e s . E l e p h a n t s a p p a r e n t l y cannot move the system from one s t a t e to a n o t h e r , but once i t i s i n the g r a s s l a n d phase , e l e p h a n t s can h o l d i t t h e r e . 199 The F u t u r e These f i n d i n g s s t i m u l a t e some i n t e r e s t i n g q u e s t i o n s about the f u t u r e of the Mara woodlands: 1) Would the woodlands s t a b i l i z e i f e l ephant numbers d e c l i n e d due to poach ing or o ther f a c t o r s ? A s imple graph of the i n t e r a c t i o n of f i r e and e l ep h an t s h e l p s to answer t h i s q u e s t i o n ( F i g u r e 6 . 4 ) . The s c e n a r i o s r e p r e s e n t e d by t h i s graph i n c l u d e browsing at c u r r e n t l e v e l s but have not i n c l u d e d the impacts of w i l d e b e e s t . Even i f we p o s t u l a t e d a t o t a l d e c l i n e of e l e p h a n t s , woodland r e c o v e r y r a t e s w i l l be h i g h l y dependent on the r a t e of b u r n i n g each y e a r . G i v e n p r e s e n t b u r n i n g r a t e s of 5% per y e a r , the e l ephant p o p u l a t i o n i n the Mara would have to be 50% lower than t h e i r c u r r e n t numbers to a c h i e v e a b a l a n c e of t r e e r e c r u i t m e n t and m o r t a l i t y . To a t t a i n an i n c r e a s e i n woodlands would r e q u i r e a f u r t h e r r e d u c t i o n in e l ephant numbers even i f b u r n i n g r a t e s remained low. R e a l i s t i c a l l y , dry season b u r n i n g r a t e s w i l l not i n c r e a s e i f w i l d e b e e s t numbers remain h i g h . 2) What would happen i f a v i r u l e n t s t r a i n of r i n d e r p e s t r e t u r n e d to the system and reduced w i l d e b e e s t numbers to pre-1960s l e v e l s ? At the t u r n of the c e n t u r y c o n d i t i o n s were, i n f a c t , s i m i l a r to t h i s s c e n a r i o ; w i l d e b e e s t and e l ephant numbers were low and woodlands i n c r e a s e d . However, there was one n o t a b l e d i f f e r e n c e , f i r e p r o b a b l y had a l i m i t e d r o l e i n the e a r l y 1900s because human p o p u l a t i o n s i n the area had a l s o been reduced . 200 % OF CURRENT POPULATION Figure 6.4. The natural log of recruitment rates (R) for both varying elephant population sizes and burning rates. In a l l cases, the impacts of wildebeest are held at zero and those of other browsers are held at t h e i r current rate. Burning rates are indicated on the rig h t , v e r t i c a l a x i s . Those values less than zero indicate woodland loss, while those values greater than zero indicate woodland increases. 201 Today, the a r e a a d j a c e n t to the Mara i s d e n s e l y p o p u l a t e d on a y e a r - r o u n d b a s i s (Lamprey 1985). These p a s t o r a l i s t peop le s have always used f i r e as a t o o l i n the c u l t i v a t i o n of p a s t u r e l a n d for t h e i r l i v e s t o c k . The main f a c t o r l i m i t i n g the spread of f i r e s set by man today i s the amount of f u e l a v a i l a b l e to b u r n . T h e r e f o r e , i f w i l d e b e e s t numbers were reduced today b u r n i n g r a t e s might w e l l r e t u r n to those of the 1960s (above 60% per year ) and f i r e would, once a g a i n , become an important f a c t o r in woodland dynamics . I t would then become important to ask: 3) At what b u r n i n g r a t e would we a c h i e v e a ba lance between r e c r u i t m e n t and m o r t a l i t y r a t e s i f e l e p h a n t s and w i l d e b e e s t were reduced? F i g u r e 6.4 a l l o w s us to answer t h i s q u e s t i o n by l o o k i n g at the combined e f f e c t s of v a r y i n g l e v e l s of f i r e and e l ephant i m p a c t s . Even i f e l e p h a n t s were t o t a l l y e l i m i n a t e d from the Reserve , the woodlands would not beg in r e c o v e r y u n l e s s b u r n i n g r a t e s were h e l d at l e s s than 40% per y e a r . T h i s seems an u n l i k e l y p o s s i b i l i t y . G i v e n the amount of g r a s s produced i n a normal year i n the Mara (Chapter 4) b u r n i n g r a t e s of over 75% ( N o r t o n - G r i f f i t h s 1979) would be expected i n the absence of s i g n i f i c a n t w i l d e b e e s t o f f t a k e . I f e l ephant numbers in the Mara r e t u r n e d to t h e i r 1960s l e v e l s (approx . 40% of the c u r r e n t p o p u l a t i o n s i z e ) , woodlands c o u l d o n l y be s u s t a i n e d under a 10% annual b u r n i n g r a t e , an even l e s s l i k e l y p o s s i b i l i t y . For t r e e r e c r u i t m e n t to exceed m o r t a l i t y when w i l d e b e e s t are h e l d a t t h e i r c u r r e n t l e v e l s , s i m u l a t i o n s r e v e a l e d tha t e l ephant numbers had to be reduced by 40% or more, even wi th 202 b u r n i n g r a t e s h e l d a t z e r o . Not on ly i s i t unreasonable to assume that f i r e c o u l d be t o t a l l y e l i m i n a t e d from t h i s ecosystem b u t , g i v e n the p r e c a r i o u s s t a t u s of e l e p h a n t s i n many p a r t s of A f r i c a today ( D o u g l a s - H a m i l t o n 1979), p o p u l a t i o n r e d u c t i o n s of t h i s magnitude are not a d e s i r a b l e a l t e r n a t i v e . Management I m p l i c a t i o n s Under presen t day c o n d i t i o n s , the Mara seems to be l o c k e d i n t o a g r a s s l a n d phase . Noth ing s h o r t of d r a m a t i c r e d u c t i o n s i n e l ephant numbers combined wi th the c o n t r o l of b u r n i n g seem a b l e to r e v e r s e t h i s t r e n d . F i r e may be m a i n t a i n e d at low l e v e l s i f w i l d e b e e s t numbers remain h i g h but how can we a l l e v i a t e the impacts of e l e p h a n t s wi thout h a v i n g p h y s i c a l l y to remove them? C u r r e n t l y , the n o r t h e r n S e r e n g e t i , which b o r d e r s the Mara R e s e r v e , i s v i r t u a l l y d e v o i d of e l e p h a n t s , a l t h o u g h areas of s u i t a b l e h a b i t a t e x i s t . I t i s p o a c h i n g , a l o n e , which keeps the e l e p h a n t s from f r e e l y u t i l i z i n g t h i s area which has h i s t o r i c a l l y h e l d l a r g e numbers (Watson and B e l l 1969, Watson et §_1. 1969). The r e s u l t i n g c o n c e n t r a t i o n of e l e p h a n t s i n t o the Mara i s not d e s i r a b l e but c o u l d be r e l i e v e d i f S e r e n g e t i Park a u t h o r i t i e s c o u l d be h e l p e d to s t o p the poach ing e f f o r t s which plague the n o r t h . In t h i s age of e x t e n s i v e e l ephant p o a c h i n g throughout A f r i c a ( D o u g l a s - H a m i l t o n 1983), c r o p p i n g e l e p h a n t s f o r unnecessary reasons i s u n a c c e p t a b l e . When t h e r e i s h a b i t a t a v a i l a b l e for them to roam f r e e l y , i s i t not our r e s p o n s i b i l i t y to s ecure i t f o r them? H i s t o r y has r e p e a t e d l y shown t h a t the S e r e n g e t i - M a r a i s by 203 no means a s t a b l e system. P e r t u r b a t i o n s , both n a t u r a l and man- made, p l a y a major r o l e i n the dynamics of t h i s area ( S i n c l a i r & N o r t o n - G r i f f i t h s 1979). For t h i s r e a s o n , i t i s e s s e n t i a l tha t t r e n d s i n v e g e t a t i o n and an imal p o p u l a t i o n s i n the Mara be c l o s e l y m o n i t o r e d over t ime so t h a t changes can be documented as they o c c u r . From a management p e r s p e c t i v e , i t i s f a r b e t t e r to t r a c k changes as they take p l a c e r a t h e r than c o n f r o n t the outcome when changes go u n n o t i c e d . Managers s h ou l d always view change as i n t e g r a l and , t h u s , an e s s e n t i a l c o n s i d e r a t i o n i n p l a n n i n g f o r the f u t u r e . Whether the Mara s h ou l d remain an open g r a s s l a n d , whether i t s h o u l d be c o n s c i o u s l y managed to a l l o w woodland r e c o v e r y or whether i t s h ou l d be a l l o w e d to proceed a l o n g i t s own course wi thout i n t e r v e n t i o n i s a d e c i s i o n for l o c a l a u t h o r i t i e s . P o l i t i c a l p r e s s u r e s and economic r e a l i t i e s w i l l be c e n t r a l to the f u t u r e of the M a r a . C o n s e r v a t i o n g o a l s for the Reserve now r e s t w i t h the Kenyan government. I t w i l l be t h e i r r e s p o n s i b i l i t y to formula te management p l a n s which w i l l address the needs of both the l o c a l peop le s and the w i l d l i f e . To h e l p them w i t h t h i s t a s k , s c i e n t i s t s must p r o v i d e the necessary i n f o r m a t i o n on which they can base t h e i r d e c i s i o n s . The f i n d i n g s p r e s e n t e d here may have important i m p l i c a t i o n s for management of the Mara i n f u t u r e . 204 LITERATURE CITED Agnew, A . D . Q . 1968. O b s e r v a t i o n s on the changing v e g e t a t i o n i n Tsavo N a t i o n a l Park ( E a s t ) . E . A f r . W i l d . J . 6:75-80. A l b l , P . 1971. 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L i n d s a y . 1984. Seasona l herd dynamics of a savanna e l ephant p o p u l a t i o n . A f r . J . E c o l . 22:229- 244. Weyerhaeuser , F . J . 1982. On the eco logy of the Lake Manyara e l e p h a n t s . M . S c . t h e s i s , Y a l e U n i v . Weyerhaeuser , F . J . 1985. Survey of e l ephant damage to baobabs i n T a n z a n i a ' s Lake Manyara N a t i o n a l P a r k . A f r . J . E c o l . 23:235-243. W h i t e , S . E . 1914. A f r i c a n Camp F i r e s . Thomas Ne l son & Sons, London. 415pp. W h i t e , S . E . 1915. The R e d i s c o v e r e d C o u n t r y . Hodden & S t o t t e n , London. 358pp. W i l l i a m s , L . A . J . 1964. Geology of the Mara R i v e r - S iana a r e a . Report No. 66, G e o l o g i c a l Survey of Kenya , M i n i s t r y of N a t u r a l R e s o u r c e s , N a i r o b i . Wing, L . and I . O . B u s s . 1970. E l e p h a n t s and f o r e s t s . W i l d . Monogr. No. 19. The W i l d l i f e S o c i e t y . 223 Woosnam, R . B . 1913. Report on a s e a r c h for G l o s s i n a on the Amala (Engabei) R i v e r , southern Masai R e s e r v e , E a s t A f r i c a p r o t e c t o r a t e . B u l l . E n t . Res . 4:271-278. Wyat t , J . R . and S . K . E l t r i n g h a m . 1974. The d a i l y a c t i v i t y of the e l ephant i n the Rwenzori N a t i o n a l P a r k , Uganda. E . A f r . W i l d . J . 12:273-290. Z a r , J . H . 1984. B i o s t a t i s t i c a l A n a l y s i s , 2nd E d i t i o n . P r e n t i c e - H a l l , Engelwood C l i f f s , N . J . 224 APPENDIX A . THE WOODLAND DYNAMICS MODEL T h i s appendix p r o v i d e s the parameter d e f i n i t i o n s and mathemat i ca l e x p r e s s i o n s i n c o r p o r a t e d in the woodland dynamics model of Chapter 6. Each e q u a t i o n expresses a p a r t i c u l a r p r o p o r t i o n or number which i s used i n f u r t h e r c a l c u l a t i o n s . T h e r e f o r e , i t i s important to d e f i n e the t e r m i n o l o g y used i n the word d e s c r i p t i o n s of each mathemat ica l e x p r e s s i o n i n o r d e r to f o l l o w the l o g i c of the model . The program was w r i t t e n i n "awk" and run on a Vax 11/750 computer . Animals and f i r e have three d i f f e r e n t e f f e c t s on s e e d l i n g s : " k i l l i n g " , " r e v e r s i n g " , and " i n h i b i t i n g " . " K i l l e d " r e f e r s to s e e d l i n g s or t r e e s which are removed and do not r e t u r n . "Reversed" r e f e r s to those s e e d l i n g s t o t a l l y reduced to ground l e v e l but r e s p r o u t i n g at some l a t e r d a t e . " I n h i b i t e d " d e s c r i b e s those s e e d l i n g s which l o s e some but not a l l stems and are e f f e c t i v e l y kept i n the h e i g h t c l a s s below 1m. Only e l e p h a n t s and f i r e ac t as m o r t a l i t y a g e n t s . F i r e , w i l d e b e e s t , e l e p h a n t s and o ther browsers can a l l a c t as r e v e r s i o n a g e n t s , whereas, o n l y w i l d e b e e s t and browsers (which may i n c l u d e e l e p h a n t s under some s c e n a r i o s ) a c t as agents of i n h i b i t i o n . Recru i tment r a t e (R) i s the p r o p o r t i o n of t r e e s e n t e r i n g the a d u l t h e i g h t c l a s s (3m) to the number of a d u l t t r e e s d y i n g each y e a r . The da ta are p r e s e n t e d as the n a t u r a l l o g (In) of R- v a l u e s . D e f i n i t i o n s of the parameters e n t e r e d i n t o the model : $1 = p r o p o r t i o n of s e e d l i n g s and t r e e s burned $2 = p r o p o r t i o n of s e e d l i n g s "reversed" by 225 w i l d e b e e s t $3 = p r o p o r t i o n of s e e d l i n g s " k i l l e d " by e l e p h a n t s $4 = p r o p o r t i o n of s e e d l i n g s "reversed" by e l e p h a n t s $5 = p r o p o r t i o n of s e e d l i n g s " i n h i b i t e d " by e l e p h a n t s p l u s o ther browsers $6 = no. of a d u l t t r e e s " k i l l e d " by e l e p h a n t s and o ther n a t u r a l causes $7 = p r o p o r t i o n of s e e d l i n g s " i n h i b i t e d " by w i l d e b e e s t Word d e s c r i p t i o n s of e q u a t i o n s i n the mode l : q5 = no. of s e e d l i n g e n t e r i n g the p o p u l a t i o n a n n u a l l y q6 = no. of s e e d l i n g s r e g e n e r a t i n g a f t e r " r e v e r s a l " by f i r e q7 = p r o p o r t i o n of s e e d l i n g s r e g e n e r a t i n g a f t e r " r e v e r s a l " by w i l d e b e e s t q 7 l = no. of s e e d l i n g s r e g e n e r a t i n g a f t e r " r e v e r s a l " by w i l d e b e e s t q8 = no. of s e e d l i n g s r e g e n e r a t i n g a f t e r " r e v e r s a l " by e l e p h a n t s q9 = s t a r t i n g number of r e g e n e r a t i n g s e e d l i n g s q 9 l = no. s u r v i v i n g f i r e , e l e p h a n t , and w i l d e b e e s t e f f e c t s qlO = no. of s e e d l i n g s " i n h i b i t e d " by browsers q101 = no. of s e e d l i n g s " i n h i b i t e d " by w i l d e b e e s t 226 q11 = no. of r e c r u i t s i n f i r s t h e i g h t c l a s s (<l5cm) q12 = no. e s c a p i n g f i r e (F) q13 = no. e s c a p i n g (F) and w i l d e b e e s t " r e v e r s a l " (W) q14 = no. e s c a p i n g F , W, and e l ephant " k i l l i n g " and " r e v e r s a l " (E) q15 = no. e s c a p i n g F , W, E , and o ther browsers (B) q151 = no. e s c a p i n g F , W, E , and B = no . e s c a p i n g at year 1 q16 = p r o p o r t i o n e s c a p i n g a f t e r year 1 q l 7 = no. e s c a p i n g at year 6 q l 8 = no. e s c a p i n g at year 7 q l 9 = p r o p o r t i o n e s c a p i n g at year 7 q20 = no. e s c a p i n g at year 11 q21 = no. e s c a p i n g at year 12 q22 = p r o p o r t i o n e s c a p i n g at year 12 q23 = no. e s c a p i n g at year 15 q24 = r e c r u i t m e n t r a t e (R) q25 = n a t u r a l l o g of R M a t h e m a t i c a l e x p r e s s i o n s i n c o r p o r a t e d in the model : q5 = 170. q6 = 0.95*$1*8500 q7 = $2*(1-$1) q71 = q7*8500 q8 = $4*8500 q9 = (q5+q6+q71+q8) q9l = q9*(1 -$1)* (1 -$3-$4)* (1 -q7) 227 q10 q91*$5 q l O l = q9l* (1 -$5)*$7 q11 = q9+q10+101 q1 2 = (q11*(1-$1))+(0.05*$1*q11) q1 3 = ( l -q7)*q12 q1 4 = ( 1-$3-$4)*q13 q15 = (1-$5)*q14 q1 51 = (1-$7)*q15 q16 = q151/q11 q36 = Iog10(l00000*q16) q17 = q151*(exp(5* log(q16) ) ) q37 = Iog l0 ( l00000*(q17 /q11) ) q l 8 = (q17*(1-$1)) + (q17*$1*0. 1 ) q1 9 = q18/q17 q20 = q l 8 * ( e x p ( 4 * l o g ( q 1 9 ) ) ) q47 = l o g 1 0 ( 1 0 0 0 0 0 * ( q 2 0 / q 1 1 ) ) q21 = ( q 2 0 * (1-$1 ) ) + ( q 2 0 * $ 1 * 0 . 6 6 ) q22 = q21/q20 q23 = q21*(exp(3* log (q22) ) ) q57 = Iog l0 ( l00000* (q23 /q11 ) ) q24 q23/$6 q25 = ln (q24)

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