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A study of epidemics of lodgepole pine dwarf mistletoe in Alberta Muir, John Alexander 1966

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A STUDY OF EPIDEMICS OF LODGEPOLE PINE DWARF MISTLETOE IN ALBERTA  by  JOHN ALEXANDER MUIR B.S.F., U n i v e r s i t y o f B r i t i s h Columbia, 1963  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF FORESTRY  i n t h e Department of Forestry  We a c c e p t t h i s t h e s i s as conforming t o t h e required standard  THE UNIVERSITY OF BRITISH COLUMBIA April,  1966  /  /  In  presenting  requirements Columbia, for  agree  reference  extensive granted It  I  is  by  and  copying the  gain  Department  thesis  in  partial  advanced  degree  at  the  that  the  Library  study.  I  of  thesis  this of  that  shall  my  for  Department  copying not  8,  of  British  Canada  shall  further  be  or  make  agree  allowed  Columbia  fulfilment  University it  that  scholarly or  by  his  publication  of  University  Vancouver  an  Head  understood  financial  The  for  this  without  of my  of  the  British  freely  available  permission purposes  of  for  may  be  representatives. this  thesis  written  for  permission  ACKNOWLEDGMENT  The d a t a o f t h i s s t u d y were c o l l e c t e d w i t h t h e a s s i s t a n c e o f Mr. E. A. Berndt w h i l e t h e w r i t e r was employed by t h e Canada Department o f F o r e s t r y R e g i o n a l L a b o r a t o r y a t Calgary, Alberta.  C o n s i d e r a b l e a s s i s t a n c e a l s o was g i v e n  by Dr. A. Kozak, xfho c a l c u l a t e d t h e r e g r e s s i o n e q u a t i o n s a t t h e Computing Centre o f t h e U n i v e r s i t y o f B r i t i s h  Columbia,  and D r s . J . E. B i e r , P. G. Haddock, and 0. S z i k l a i who reviewed the manuscript. •  ABSTRACT  The i n c r e a s e o f d i s c r e t e p o p u l a t i o n s  o f dwarf  m i s t l e t o e (Arceuthobium americanum N u t t . ) p l a n t s o r i n f e c t i o n s was s t u d i e d i n 20 y e a r o l d s t a n d s o f l o d g e p o l e c o n t o r t a Dougl.).  pine  (Pinus  M i s t l e t o e i n f e c t i o n s were s e l e c t e d from  i n f e c t e d t r e e s i n t h r e e a r e a s 100 t o 200 f t . i n d i a m e t e r . The age o f each i n f e c t i o n was d e t e r m i n e d by d i s s e c t i n g t h e i n f e c t e d h o s t wood.  I t was f o u n d t h a t t h e number o f i n f e c t i o n s  e s t a b l i s h e d a n n u a l l y had i n c r e a s e d l o g a r i t h m i c a l l y d u r i n g t h e preceding  8 t o 10 y e a r s .  Therefore  the logarithmic rates  o f i n c r e a s e i n t h e number o f i n f e c t i o n s c o u l d be c a l c u l a t e d t o d e s c r i b e t h e p a s t epidemic growth o f each m i s t l e t o e population.  The l o g a r i t h m i c r a t e s ( e q u i v a l e n t t o "compound"  i n c r e a s e o f 66 t o 96 p e r cent p e r y e a r ) demonstrated r a p i d population increase.  Although the three m i s t l e t o e  had developed i n a p p a r e n t l y  populations  d i f f e r e n t environments, the  p o p u l a t i o n r a t e s o f i n c r e a s e were not s t a t i s t i c a l l y However, f o r t h e study o f e c o l o g i c a l a s p e c t s toe e p i d e m i c s t h i s approach appears q u i t e  different.  o f dwarf m i s t l e -  promising.  - iii  -  TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  iv  LIST OF ILLUSTRATIONS  v  1  INTRODUCTION METHODS OF INVESTIGATION RESULTS OF THE INVESTIGATION  •  3 6  DISCUSSION OF RESULTS  13  LITERATURE CITED  17  -  X V  LIST OF TABLES  T a b l e 1.  Measurements o f i n f e c t e d t r e e s and dwarf m i s t l e t o e i n f e c t i o n s i n three areas  Page  6  2.  Types o f dwarf m i s t l e t o e i n f e c t i o n s c o l l e c t e d from t h r e e a r e a s o f i n f e c t e d lodgepole pine  7  3-  Ages o f dwarf m i s t l e t o e i n f e c t i o n s s e l e c t e d from t h r e e a r e a s  9  4.  E q u a t i o n c o n s t a n t s and s t a t i s t i c s f o r the l i n e a r r e l a t i o n s h i p s between t h e number o f i n f e c t i o n s e x p r e s s e d as n a t u r a l l o g a r i t h m s and i n f e c t i o n age (3 t o 10 y e a r s )  12  LIST OF ILLUSTRATIONS  Age distribution of dwarf mistletoe infections selected from three areas  - 1 -  INTRODUCTION  I n many r e g i o n s o f w e s t e r n N o r t h America, dwarf mistletoes  (Arceuthobium spp.) have been c o n s i d e r e d  i m p o r t a n t agents o f damage t o f o r e s t t r e e s ( G i l l ,  very 1935,  1957; K u i j t , 1955; L e a p h a r t , 1959, 1963; W e i r , 1916, 1918). However, c o n t r o l o f t h e m i s t l e t o e s r a r e l y has been p r a c t i s e d i n f o r e s t management. been h i n d e r e d ,  Decisions  t o implement c o n t r o l have  p a r t i c u l a r l y i n Canada, by a s c a r c i t y o f  i n f o r m a t i o n on t h e e f f e c t s o f dwarf m i s t l e t o e p a r a s i t i s m , and l i t t l e  i n v e n t o r y d a t a on t h e d i s t r i b u t i o n and i n t e n s i t y o f  dwarf m i s t l e t o e i n f e c t i o n .  A l t h o u g h t h e dwarf m i s t l e t o e s  appear q u i t e amenable t o c o n t r o l ( K u i j t , 1955. p. 599), "...few, i f any o f t h e methods o f c o n t r o l have emerged from the h y p o t h e t i c a l o r e x p e r i m e n t a l ( i b i d , pp. 596 - 601) d i s c u s s e s  stage"  ( i b i d , p. 596 ). K u i j t  some p o s s i b l e and a t t e m p t e d  methods t o c o n t r o l dwarf m i s t l e t o e s u s i n g p a r a s i t i c f u n g i , s e l e c t i v e h e r b i c i d e s , and s i l v i c u l t u r a l e r a d i c a t i o n . the use 01 a fungus p a r a s i t e (Septogloeum g i l l i i  Recently,  Ellis)  o f t h e m i s t l e t o e s h o o t s ( M i e l k e , 1959) and many h e r b i c i d e s (Quick,  1964) were f o u n d i n e f f e c t i v e .  K u i j t ( i b i d , p. 602)  also discussed the r o l e o f f o r e s t f i r e s i n l i m i t i n g the s p r e a d o f dwarf m i s t l e t o e .  - 2 -  I t appears l i k e l y t h a t c o n t r o l t r e a t m e n t s c o u l d  be  improved by more d e t a i l e d knowledge o f the b i o l o g y o f dwarf mistletoes.  Much o f the a v a i l a b l e knowledge has  ( 1 9 3 5 ) , G i l l and Hawksworth ( 1 9 6 1 ) ,  r e v i e w e d by G i l l Kuijt  (1955, I960).  be f a c i l i t a t e d  and  R e s e a r c h on s e l e c t i v e h e r b i c i d e s  by the r e c e n t  McDowell ( 1 9 6 4 ) .  r e s u l t s of p h y s i o l o g i c a l s t u d i e s  F o r some dwarf m i s t l e t o e s ,  be improved by r e c e n t o b s e r v a t i o n s  Smith, 1 9 6 5 ;  and  silvicultural on the minimum 1961;  t i m e s n e c e s s a r y t o complete the l i f e c y c l e s ( K u i j t , Scharpf, 1964;  could  Leonard ( 1 9 6 5 ) , H u l l and Leonard ( 1 9 6 4 ) ,  by Greenham and  c o n t r o l may  been  Wagener, 1962).  S i n c e t r e a t m e n t s are a p p l i e d t o c o n t r o l l a r g e populations  o f dwarf m i s t l e t o e p l a n t s o r i n f e c t i o n s , i t may  be advantageous t o s t u d y how f e c t i o n s increase  d i f f e r e n t populations  (Van der P l a n k , I 9 6 3 . p - l K  The  of i n theory  and methods t o a n a l y z e some fungus e p i d e m i c s , such as p o t a t o b l i g h t and wheat stem r u s t , have been developed r e c e n t l y Van  der P l a n k ( 1 9 6 3 , 1 9 6 5 ) .  o f i n c r e a s e o f such d i s e a s e s  He demonstrated t h a t the  by  rate  c o u l d be used t o measure the  e f f e c t i v e n e s s o f c o n t r o l t r e a t m e n t s , such as r e s i s t a n t v a r i e t i e s of p l a n t s or f u n g i c i d e s .  Such an approach, i f i t  can be a p p l i e d s u c c e s s f u l l y t o dwarf m i s t l e t o e  epidemics,  c o u l d be v e r y u s e f u l i n d e v e l o p i n g more e f f e c t i v e c o n t r o l treatments.  - 3 -  Accordingly, a study of small populations of dwarf mistletoe (Arceuthobium  americanum Nutt.) p a r a s i t i z i n g lodge-  pole pine (Pinus contorta Dougl.) i n Alberta was  undertaken.  The primary objective of the project was to determine  the  increase i n the number of infections of each population.  A  study of the spread of dwarf mistletoe from old, infected stands into adjacent 5 to 30 year-old stands ( i n Montana, Wyoming and Colorado) suggested that the establishment of dwarf mistletoe infections had occurred most frequently i n c e r t a i n years which were c a l l e d "peak periods" of i n f e c t i o n (Hawksworth and Graham, 1 9 6 3 ) •  Similar r e s u l t s have been  obtained (R. F. Scharpf, 1 9 6 5 , personal communication) i n C a l i f o r n i a i n a study of the spread of dwarf mistletoe from the infected overstorey to the healthy understorey trees i n a p a r t i a l l y logged stand.  METHODS OF INVESTIGATION  Although the Increase of dwarf mistletoe infections could be determined by observations repeated annually or less frequently, a quicker estimate of increase appeared  possible.  The age of i n d i v i d u a l , dwarf mistletoe infections can be determined by dissecting the infected host wood (Srivastava and  - 4 -  Esau, 1961;  Hawksworth and Graham, 1 9 6 3 ) .  T h e r e f o r e , by  randomly s e l e c t i n g i n f e c t i o n s and d e t e r m i n i n g t h e i r ages, one  can e s t i m a t e the r e l a t i v e number o f i n f e c t i o n s  ed p e r y e a r .  Then one  establish-  can c a l c u l a t e the r a t e o f i n c r e a s e o f  the p o p u l a t i o n o f i n f e c t i o n s (Van der P l a n k , 1963  77)  p.  which can be used t o compare p o p u l a t i o n s . Three s m a l l p o p u l a t i o n s o f dwarf m i s t l e t o e i n f e c t i o n s were s e l e c t e d i n 22 t o 25 y e a r o l d s t a n d s o f l o d g e p o l e pine.  Young s t a n d s were sampled t o reduce t h e l o s s o f  i n f e c t i o n s caused by the death o f h o s t t i s s u e . open s t a n d s were sampled t o determine  Dense and  i f mistletoe infection  had v a r i e d s i g n i f i c a n t l y w i t h d i f f e r e n c e s i n l i g h t or other f a c t o r s c o r r e l a t e d w i t h stand d e n s i t y .  exposure  The  abun-  dance o f a e r i a l shoots and seed p r o d u c t i o n o f dwarf m i s t l e t o e s g e n e r a l l y have been c o n s i d e r e d t o be d i r e c t l y r e l a t e d t o the degree o f exposure  to l i g h t  (Wagener, 1961).  One  area  (A)  o f i n f e c t e d t r e e s was found i n an open s t a n d 20 m i l e s s o u t h o f t h e Kananaskis Experiment  S t a t i o n ; the o t h e r two  (B and  C)  were l o c a t e d i n denser s t a n d s 80 m i l e s s o u t h o f the S t a t i o n and o n e - q u a r t e r m i l e a p a r t .  Each i n f e c t e d a r e a had  originated  from one o r more o l d e r , i n f e c t e d t r e e s : A and C each had t r e e (now dead); B had 6 t o 12. was  one  I n each a r e a s t a n d d e n s i t y  e s t i m a t e d by c a l c u l a t i n g average t r e e crown w i d t h  (Smith  - 5 -  and B a i l e y , 1964) a n d h e i g h t  1956).  (Smithers,  F r o m e a c h a r e a a b o u t 450 i n f e c t i o n s w e r e c o l l e c t e d using  a square g r i d o f sampling p o i n t s  Within all  a 5 f t . radius  a t 10 f t . i n t e r v a l s .  o f each sampling p o i n t  randomly  t h e i n f e c t i o n s were c o l l e c t e d e i t h e r f r o m one i n f e c t e d  tree closest t o thepoint (B a n d C ) .  ( a r e a A) o r f r o m a l l i n f e c t e d  Additional observations,  infection.  or female i n f e c t i o n s i n a m i s t l e t o e p o p u l a t i o n  information, previously Calgary,  c o l l e c t e d b y D r . J . E. N i g h s w a n d e r ,  employed  by t h e Canada Department  reduce  Unpublished  who was  of Forestry at  h a d shown t h a t t h e r a t i o o f m a l e t o f e m a l e i n f e c t i o n s  a n assumed 1:1 The  populations  frequently  deviated  a g e o f e a c h i n f e c t i o n was e s t i m a t e d  by c u t t i n g  o f t h e i n f e c t i o n and by  t h e number o f a n n u a l r i n g s i n w h i c h t h e d e e p e s t s i n k e r was embedded ( S r i v a s t a v a a n d E s a u , 1961). .The  i d e n t i f i c a t i o n o f s i n k e r s was f a c i l i t a t e d b y i m m e r s i n g cross  from  ratio.  transversely through the center  mistletoe  o f male  could  o f t h e number o f i n f e c t i o n s .  in discrete mistletoe  counting  mistletoe  I t was s u s p e c t e d t h a t a l o w p r o p o r t i o n  rate of increase  trees  s u c h a s s e x a n d number  o f b e r r i e s o n f e m a l e p l a n t s , w e r e made o n e a c h  the  selected,  s e c t i o n b r i e f l y i n methylene v i o l e t  c o r r e c t i o n was a d d e d t o t h e e s t i m a t e d between the contact  of mistletoe  and t h e i n i t i a t i o n o f m i s t l e t o e  each  (Graham, 1964). No  age f o r t h e i n t e r v a l  seeds w i t h sinkers.  thehost tissues  The i n t e r v a l  - 6 -  between i n i t i a l i n f e c t i o n and s i n k e r i n i t i a t i o n was  estimated,  i n C o l o r a d o , a t 2 y e a r s (Hawksworth and Graham, 1963).  RESULTS OF THE  INVESTIGATION  O b s e r v a t i o n s made i n the t h r e e a r e a s sampled (Table 1) and d e t a i l e d o b s e r v a t i o n s on the m i s t l e t o e i n f e c t i o n s (Table 2) i n d i c a t e d t h a t t h e m i s t l e t o e was  growing  vigorously. TABLE I .  Measurements o f i n f e c t e d t r e e s and dwarf m i s t l e t o e i n f e c t i o n s i n t h r e e a r e a s . Area A  Tree age  ( y r s . ) 1. average 2. range  (av.)  av. crown w i d t h ( f t . ) av. h e i g h t (ft.) No.  t r e e s (and s a m p l i n g p o i n t s )  I n f e c t i o n s p e r t r e e 1. av. 2. range Av.  s i z e of I n f e c t i o n ( l e s s than 8 y r s . old) (sq. i n . )  There was  B  C  21.6 18-26  22.0 14-24  24-8 23-26  5.0 18.0  2.5 12.1  2.9 10.6  33(33)  202(9).  55(3)  14-3 1-118  2.2 1-12  8.7 1-83  1.21  0.57  0.54  l i t t l e e v i d e n c e o f o t h e r f a c t o r s which might have  i n f l u e n c e d m i s t l e t o e r e p r o d u c t i o n such as r o d e n t damage t o  - 7 -  m i s t l e t o e - i n f e c t e d bark, fungus d i s e a s e o f m i s t l e t o e shoots o t h e r s e r i o u s d i s e a s e of the host t r e e s . dead, m i s t l e t o e i n f e c t i o n s were observed  A l s o , very  or  few  on dead t r e e s or  on dead branches of l i v i n g t r e e s (Table 2 ) .  These o b s e r v a t i o n s  i n d i c a t e d t h a t the number o f m i s t l e t o e i n f e c t i o n s had not been reduced  s e r i o u s l y by the death o f host  Table 2.  tissue.  Types of dwarf m i s t l e t o e i n f e c t i o n s  collected  from three areas of i n f e c t e d lodgepole pine.-  Area  A Type o f i n f e c t i o n  Number of  C  infections  10  14  11  Male Female w i t h b e r r i e s with flowers only Sex i n d e t e r m i n a b l e  246 110 100 5  183 173 8512  174 42 117 148  Total  471  453  478  July 4 to  Aug. 10 to  Dead Living  B  Sampling  1  May 26 to June 25  date  An a n a l y s i s of t r e e crown widths and each area  (Table 1)  confirmed  21  11  h e i g h t s from  the s u b j e c t i v e choice of areas  - 8 -  B and C as h a v i n g s i g n i f i c a n t l y g r e a t e r s t a n d d e n s i t i e s t h a n A.  Area A a l s o had a l a r g e r number o f dwarf m i s t l e t o e i n -  f e c t i o n s p e r t r e e and a s i g n i f i c a n t l y l a r g e r average s i z e of i n f e c t i o n .  These d i f f e r e n c e s i n m i s t l e t o e i n c i d e n c e and  growth might be r e l a t e d t o t h e f a s t e r t r e e growth (Hawksworth, I 9 6 0 ) o r presumably b e t t e r l i g h t c o n d i t i o n s i n a r e a A.  (Baranyay, 1 9 6 2 )  However, one s p e c i e s o f dwarf m i s t l e t o e i n  C a l i f o r n i a has been r e p o r t e d t o grow b e t t e r under shaded conditions  (Wagener,  1961).  Other d i f f e r e n c e s between a r e a s were o b s e r v e d i n the number o f i n f e c t i o n s o f v a r i o u s t y p e s (Table 2 ) . number o f male and female i n f e c t i o n s i n each a r e a  The  deviated  s i g n i f i c a n t l y from an assumed 1 : 1 r a t i o o n l y i n a r e a B which had  s i g n i f i c a n t l y more female i n f e c t i o n s .  The r a t i o o f  female i n f e c t i o n s w i t h b e r r i e s t o female i n f e c t i o n s w i t h o u t . b e r r i e s , however, was v e r y d i f f e r e n t i n each a r e a 1 : 1 ; i n B, 2 : 1 ; and C, 1 : 3 •  : i n A,  Such d i f f e r e n c e s may i n d i c a t e  d i f f e r e n c e s i n t h e epidemic b e h a v i o r o f t h e m i s t l e t o e o r , more l i k e l y , may r e f l e c t d i f f e r e n c e s i n t h e date o f s a m p l i n g (Table 2 ) .  By August 1 0 , when a r e a C was sampled, more  young i n f e c t i o n s may have become v i s i b l e (as i n d i c a t e d by the l a r g e r number o f " s e x i n d e t e r m i n a b l e " C, Table 2) o r seed d i s c h a r g e  i n f e c t i o n s i n area  and t h e r e s u l t i n g d i s a p p e a r a n c e  - 9 -  o f b e r r i e s may  have been i n i t i a t e d a l r e a d y , t h u s r e s u l t i n g  i n the l a r g e r number o f f e m a l s i n f e c t i o n s w i t h o u t b e r r i e s  in  a r e a C. A t o t a l o f 1440  dwarf m i s t l e t o e  c o l l e c t e d i n the t h r e e a r e a s , and were d e t e r m i n e d . i n f e c t i o n age TABLE 3  The  i n f e c t i o n s were  the ages o f 1402  numbers o f m i s t l e t o e  infections  Ages o f dwarf m i s t l e t o e from t h r e e a r e a s .  infections  A.  2 3 4 5 6 7 8  9 10 11 12 13 14 15 16 17 18 Totals  per  c l a s s f o r each a r e a are summarized i n T a b l e 3*  Area  Infection Age  infections  B  C  Number o f  122 171 77 45 30 14 8 3  1  infections  92 161 109 48 14 4 5 4 2 3 2 2 2 3 1  173 130 69 47 22 17 14 3 3  1 471  453  478  selected  -10-  In g e n e r a l , the numbers o f i n f e c t i o n s were l a r g e s t young age groups and decreased r a p i d l y w i t h i n f e c t i o n age  i n the  increasing  (Figure 1 ) . ieo  +  160  AREA A  140  120  100  80  B  x +  C  o  X +  O  +  X  O  z  60  Z 40 X 20  O +  o  9 +  $ + + * + + + 10  INFECTION  F i g . 1.  18  AGE  yrs.  Age d i s t r i b u t i o n of dwarf m i s t l e t o e i n f e c t i o n s i n three areas o f i n f e c t e d t r e e s .  The s m a l l e r number o f 2 year as compared w i t h 3 year o l d i n f e c t i o n s i n two  areas, and the absence o f 1 year  infections,  were assumed to have been caused by the i n t e r v a l between the f a l l of m i s t l e t o e seed onto the host and the development of  - 11  -  symptoms o f t h e i n f e c t i o n ; ; W i t h t h e e x c e p t i o n o f one i n f e c t i o n , no i n f e c t i o n s o l d e r t h a n 10 y e a r s were i n c l u d e d a r e a s A and C. per  i n t h e random samples f r o m  I n a r e a B, however, 1 t o 3 i n f e c t i o n s  i n f e c t i o n age 10 t o 16 y e a r s were found i n t h e sample.  T h i s may i n d i c a t e t h a t t h e m i s t l e t o e  p o p u l a t i o n i n a r e a 3 had  expanded q u i t e s t e a d i l y f o r a w h i l e o r t h a t a l a r g e r number o f o l d e r i n f e c t e d t r e e s i n B had produced a w i d e r d i s t r i b u t i o n o f o l d e r i n f e c t i o n s which i n c r e a s e d  t h e i r p r o b a b i l i t y of being  selected. When t h e number o f i n f e c t i o n s were p l o t t e d i n f e c t i o n age ( F i g . 1 ) ,  a logarithmic  r e l a t i o n s h i p between  the two v a r i a b l e s was apparent ( F r e e s e , 1964, Therefore the l o g a r i t h m i c to s t r a i g h t l i n e logarithm  126).  p.  r e l a t i o n s h i p s c o u l d be t r a n s f o r m e d  ( l i n e a r ) r e l a t i o n s h i p s by p l o t t i n g t h e  o f t h e number o f i n f e c t i o n s .  The s l o p e s o f t h e  s t r a i g h t l i n e s are estimates of the l o g a r i t h m i c increase  against  f o r the m i s t l e t o e  populations.  rates of  The s l o p e s we're"  c a l c u l a t e d u s i n g s t a t i s t i c a l methods ( S t e e l and T o r r i e , I 9 6 0 , pp. 161-169) t o e v a l u a t e how w e l l t h e t r a n s f o r m e d d a t a was d e s c r i b e d u s i n g s t r a i g h t l i n e s .  The l i n e a r e q u a t i o n s  were c a l c u l a t e d o n l y f o r i n f e c t i o n ages 3 t o 10 y e a r s s i n c e t h e number o f i n f e c t i o n s l e s s t h a n 3 and o l d e r t h a n 10 y e a r s p r o b a b l y were a f f e c t e d by t h e m i s t l e t o e the death o f i n f e c t e d h o s t t i s s u e .  incubation  period  and  - 12 -  The c a l c u l a t i o n s , summarized i n Table 4 , TABLE 4  E q u a t i o n c o n s t a n t s and s t a t i s t i c s f o r t h e l i n e a r r e l a t i o n s h i p s between t h e number o f i n f e c t i o n s e x p r e s s e d as n a t u r a l l o g a r i t h m s and i n f e c t i o n age ( 3 t o 1 0 y e a r s ).  Area Equation constants Intercept slope  B 7.255 -0.673  6 . 7 4 1 - 0 . 6 0 4  0.986  0.956  Combined 6.349 - 0 . 5 0 6  6 . 7 8 1 - 0 . 5 9 4  0.982  O.965  Statistics l i n e a r c o r r e l a t i o n coefficient F-test of significance of i n d i v i d u a l slopes F-test of significance o f d i f f e r e n c e s between a l l slopes  208. 9S5*"'  63.795* 1 6 4 . 6 3 2 * * 3 0 2 . 0 7 4 * 2.242  "  ns  P r o b a b i l i t y o f t h e s e F v a l u e s o c c u r r i n g by chance i s l e s s t h a n 0.01 ns  P r o b a b i l i t y o f t h i s F v a l u e o c c u r r i n g by chance i s g r e a t e r t h a n 0.05  demonstrated w i t h a h i g h degree o f c o n f i d e n c e t h a t t h e number o f m i s t l e t o e i n f e c t i o n s had i n c r e a s e d l o g a r i t h m i c a l l y .  Further-  -  13  -  more, a s t a t i s t i c a l t e s t ( F r e e s e , 1 9 6 4 . pp.  84-85)  of  the  l o g a r i t h m i c r a t e s i n d i c a t e d t h a t the d i f f e r e n c e s between r a t e s were not s i g n i f i c a n t l y g r e a t e r t h a n t h o s e which be expected by chance v a r i a t i o n . t h a t the r a t e o f i n c r e a s e was  T h e r e f o r e i t was  concluded  the same i n a l l a r e a s  despite  d i f f e r e n c e s between a r e a s such as g e o g r a p h i c l o c a t i o n stand density.  The  could  and  r a t e s o f i n c r e a s e were 0 . 5 1 t o 0 . 6 7  p e r y e a r f o r l o g a r i t h m i c i n c r e a s e o r 6 6 t o 9 6 per cent p e r y e a r f o r "compound i n t e r e s t "  increase.  DISCUSSION OF RESULTS  I t was fidence  demonstrated w i t h a h i g h degree o f con-  ( w i t h the s i g n i f i c a n t "F" v a l u e s  and l i n e a r  cor-  r e l a t i o n c o e f f i c i e n t s , Table 4 ) t h a t the number o f dwarf m i s t l e t o e i n f e c t i o n s e s t a b l i s h e d per y e a r had l o g a r i t h m i c a l l y i n the t h r e e p o p u l a t i o n s sampled.  of  increased  mistletoe  These r e s u l t s s u g g e s t e d t h a t s m a l l d i s c r e t e p o p u l a -  t i o n s o f dwarf m i s t l e t o e do not always i n c r e a s e as suggested by Hawksworth and Graham ( 1 9 6 3 ) .  irregularly In  contrast  t o t h e i r r e p o r t of more i n f e c t i o n s e s t a b l i s h e d i n c e r t a i n y e a r s ("peak p e r i o d s " ) for  w i t h presumably b e t t e r  i n f e c t i o n , t h i s s t u d y has  conditions  demonstrated a l o g a r i t h m i c  i n c r e a s e o f i n f e c t i o n s w h i c h i m p l i e s many s u c c e s s i v e w i t h good c o n d i t i o n s f o r i n f e c t i o n .  years  - 14 -  "Peak p e r i o d s " o f i n f e c t i o n have been f o u n d , however, d u r i n g t h e i n i t i a l i n f e c t i o n o f young s t a n d s (Hawksworth and Graham, 1963).  These p e r i o d s may be caused, I b e l i e v e ,  by i r r e g u l a r o r i n f r e q u e n t p r o d u c t i o n the o l d , i n f e c t e d t r e e s .  o f m i s t l e t o e seed on  T h i s may e x p l a i n why m i s t l e t o e  i n f e c t i o n s r a r e l y have been f o u n d i n s t a n d s 20 t o 25 y e a r s o l d , adjacent t o o l d e r , i n f e c t e d stands,  i n central Alberta  (Dowding, 1929, p. 98) and i n t h e Highwood R i v e r v a l l e y (Near a r e a s B and C) i n t h i s s t u d y .  The d a t a f o r a r e a B  (p. 11) a l s o s u g g e s t e d t h a t m i s t l e t o e p o p u l a t i o n s  may  i n c r e a s e i r r e g u l a r l y a t an e a r l y s t a g e o f t h e growth o f t h e populations.  S h o r t l y t h e r e a f t e r , however, m i s t l e t o e p o p u l a -  t i o n s may b e g i n t o i n c r e a s e r a p i d l y . The s c a r c i t y o f i n f e c t i o n s on young t r e e s a d j a c e n t t o o l d , i n f e c t e d s t a n d s was o f c o n s i d e r a b l e  i n t e r e s t because  at a d i s t a n c e o f 100 f t . o r more away from t h e a p p a r e n t l y n o n - i n f e c t i v e s t a n d s i n t h e Highwood v a l l e y , many a r e a s o f young i n f e c t e d t r e e s were found.  extensive  These i n f e c t e d  t r e e s were u s u a l l y found around one o r more o l d t r e e s which were i n f e c t e d remnants o f t h e p r e v i o u s and K u i j t  stand.  (1955, P« 602) have s p e c u l a t e d  W e i r (1916)  that the i s o l a t e d ,  i n f e c t e d t r e e s may be more a c t i v e s o u r c e s o f new i n f e c t i o n s because o f g r e a t e r exposure t o l i g h t .  I t appears t h a t t h e  - 15 -  d e s t r u c t i o n of i s o l a t e d , i n f e c t e d t r e e s should receive priority recently  i n applying m i s t l e t o e c o n t r o l treatments, burned o r l o g g e d  high  especially i n  areas.  The most s i g n i f i c a n t r e s u l t o f t h i s s t u d y was t h e s u c c e s s f u l use o f a m a t h e m a t i c a l model t o d e s c r i b e t h e p r o g r e s s o f t h r e e dwarf m i s t l e t o e e p i d e m i c s .  This  objective  approach s h o u l d f a c i l i t a t e s t u d i e s o f t h e i n f l u e n c e o f e n v i r o n m e n t a l f a c t o r s on m i s t l e t o e e p i d e m i c s .  Multiple  r e g r e s s i o n s a m p l i n g c o u l d be used t o i n v e s t i g a t e t h e e f f e c t of e n v i r o n m e n t a l f a c t o r s on t h e l o g a r i t h m i c r a t e o f i n c r e a s e . Some e n v i r o n m e n t a l f a c t o r s , such as s t a n d  density,  were measured i n t h e p r e s e n t s t u d y , but t h e i r e f f e c t s were not s t u d i e d w i t h m u l t i p l e r e g r e s s i o n a n a l y s i s s i n c e three populations  were sampled.  Nevertheless,  only  the observed  e n v i r o n m e n t a l d i f f e r e n c e s appeared u n i m p o r t a n t s i n c e t h e r a t e s o f i n c r e a s e were not s t a t i s t i c a l l y d i f f e r e n t (Table 4 ) . T h i s appears r e a s o n a b l e s i n c e a p p r o x i m a t e l y  equal-sized  areas o f i n f e c t e d t r e e s were s e l e c t e d t o be sampled.  It  i s u n l i k e l y t h a t a c t u a l d i f f e r e n c e s i n r a t e s o f i n c r e a s e were c o n c e a l e d by c o l l e c t i n g an i n s u f f i c i e n t number o f i n f e c t i o n s s i n c e v e r y h i g h c o r r e l a t i o n c o e f f i c i e n t s (0.96 t o 0.99) were found.  The t h r e e s i m i l a r r a t e s o f i n c r e a s e and t h e d i f f e r e n t  numbers o f i s o l a t e d , i n f e c t e d t r e e s (6 t o 12 i n B; 0 i n A and  - 16 -  C) suggested t h a t the o l d , i n f e c t e d t r e e s had  contributed  i n s i g n i f i c a n t l y - at l e a s t i n the r e c e n t p a s t - t o the o f the m i s t l e t o e p o p u l a t i o n s .  increase  I t i s emphasized, however,  t h a t a l a r g e number o f o l d , i n f e c t e d t r e e s may  result in a  l a r g e r number o f d i s c r e t e e p i d e m i c s o r p o p u l a t i o n s  o f dwarf  mistletoe. S i n c e some dwarf m i s t l e t o e e p i d e m i c s can be desc r i b e d by l o g a r i t h m i c c u r v e s , the e p i d e m i c s c o u l d be u s i n g Van  der P l a n k * s  i n the b a s i c e q u a t i o n s necessary,  (1963, 1965)  approach.  studied  Many changes  and many y e a r s o f o b s e r v a t i o n would be  however, t o a p p l y h i s comprehensive, m a t h e m a t i c a l  models f o r p l a n t d i s e a s e s , such as wheat stem r u s t , t o dwarf m i s t l e t o e e p i d e m i c s .  The m u l t i p l e r e g r e s s i o n approach  suggested i n t h i s study may  provide  i n f o r m a t i o n of  value  i n p r e d i c t i n g the development o f dwarf m i s t l e t o e e p i d e m i c s and the r e s u l t i n g damage t o i n f e c t e d s t a n d s .  - 17  -  LITERATURE CITED  Baranyay, J.A.  1962.  Phenological observations hemlock dwarf m i s t l e t o e  on w e s t e r n (Arceuthobium  campylopodum G i l l forma t s u g e n s i s ) . Canada Department o f F o r e s t r y B i Monthly Progress Dowding, E.S.  1929.  The  Report 18(4):3-4.  vegetation of A l b e r t a . I l l  The  s a n d h i l l areas of c e n t r a l A l b e r t a with p a r t i c u l a r r e f e r e n c e t o the  ecology  o f Arceuthobium americanum N u t t . J o u r n a l o f E c o l o g y 17:82-105. Freese,  Gill,  1964.  F.  1935.  L.S.  L i n e a r r e g r e s s i o n models f o r f o r e s t r e s e a r c h . U.S.  Forest S e r v i c e Research  Paper FPL 17.  Madison, W i s c o n s i n .  Arceuthobium i n the U n i t e d Connecticut  .  1957-  States.  Academy o f A r t s and  Transactions. Dwarfmistletoe  136pp.  Sciences  32:111-245. of lodgepole  pine.  U.S.  F o r e s t S e r v i c e . F o r e s t Pest L e a f l e t 18.  7pp.  and F. G. Hawksworth. 1961. a l i t e r a t u r e review.  The  U. S.  mistletoes: Forest  S e r v i c e T e c h n i c a l B u l l e t i n 1242.  87pp.  - 18  1964.  Graham, S.O.  -  D i f f e r e n t i a l s t a i n i n g o f Arceuthobium t i s s u e s i n the h o s t .  (Abstr.)  Phyto-  p a t h o l o g y 54:1433. Greenham, C.G.  and O.A.  Leonard. 1965.  The  amino a c i d s  some m i s t l e t o e s and t h e i r  of  hosts.  American J o u r n a l o f Botany 52:41-47Hawksworth, F.G.  I960. Growth r a t e o f dwarf m i s t l e t o e i n f e c t i o n s i n r e l a t i o n to the c l a s s o f the h o s t . U.S.  crown  Forest  Service,  Rocky M o u n t a i n F o r e s t and Range Experiment S t a t i o n . and D. P. Graham 1963-  .  R e s e a r c h note Spread and  41*  inten-  s i f i c a t i o n o f dwarf m i s t l e t o e i n lodgepole  pine reproduction.  Journal  o f F o r e s t r y 61:587-591H u l l , R.J.  and O.A.  Leonard. 1964 mistletoes dron).  K u i j t , J . 1955-  P h y s i o l o g i c a l aspects of (Arceuthobium and  Plant Physiology  Phoraden-  39:996-1017.  Dwarf m i s t l e t o e s . B o t a n i c a l Review 21:569-627-  .I960.  Morphological  aspects of p a r a s i t i s m i n  t h e dwarf m i s t l e t o e s  (Arceuthobium ).  U n i v e r s i t y of C a l i f o r n i a i n Botany 3 0 : 3 3 7 - 4 3 6 .  Publications  - 19 -  .  1961.  Observations  on t h e l i f e  cycles  i n Arceuthobium campylopodum. L e a f l e t s o f Western Botany 9:133-134Leaphart, CD.1959.  This m i s t l e t o e gives the k i s s o f death to trees.  Western  Conservation  Journal l 6 ( l ) : 4 4 - 4 7 . . 1963.  Dwarf m i s t l e t o e s : a s i l v i c u l t u r a l / challenge.  J o u r n a l o f F o r e s t r y 61:  40-46. McDowell, L.L. 1964.  P h y s i o l o g i c a l r e l a t i o n s h i p s between dwarf m i s t l e t o e and ponderosa p i n e . Ph.D.  T h e s i s Oregon S t a t e U n i v e r s i t y -  University Microfilms. Michigan. M i e l k e , J . L . 1959.  Ann A r b o r ,  ( D i s s e r t a t i o n A b s t r a c t s 25:53)  I n f e c t i o n experiment w i t h gillii,  Septogloeum  a fungus p a r a s i t i c on dwarf  mistletoe.  J o u r n a l o f F o r e s t r y 57:  925-926. P a r k e r , H.A. 1942.  Control of Mistletoe.  Canada Department  o f Mines and R e s o u r c e s . Land, P a r k s and F o r e s t Branch.  Silviculture  L e a f l e t 15• 2pp. Quick, C R . 1964.  Experimental  h e r b i c i d a l control of  - 20 -  dwarf m i s t l e t o e s on some C a l i f o r n i a conifers.  U. S. F o r e s t S e r v i c e .  P a c i f i c Southwest F o r e s t and Range Experiment  Station.  Research  note 47 •  9pp. S c h a r p f , R.F. 1964.  E p i d e m i o l o g y and p a r a s i t i s m o f t h e dwarf m i s t l e t o e Arceuthobium  cam-  pylopodum Engelm. i n C a l i f o r n i a . Ph.D. Thesis.-  University of California.  U n i v e r s i t y M i c r o f i l m s . Ann A r b o r , Michigan.  (Dissertation Abstracts  24:3922) Smith, J.H.G. and G.R. B a i l e y . 1964.  Influence of stocking  and s t a n d d e n s i t y on crown w i d t h s o f Douglas f i r and l o d g e p o l e p i n e . Commonwealth F o r e s t r y Review 43-' 243-246 Smith, R.B. 1965-  Some r e s u l t s o f a r t i f i c i a l  inoculation  w i t h w e s t e r n hemlock dwarf m i s t l e t o e seeds.  Canada Department o f F o r e s t r y ,  Bi-Monthly Progress Report. S m i t h e r s , L.A. 1956.  21(6):3-4«  Assessment o f s i t e p r o d u c t i v i t y i n dense l o d g e p o l e p i n e s t a n d s .  Canada  Department o f N o r t h e r n A f f a i r s and N a t i o n a l Resources.  Forest  Research  - 21 -  Division.  T e c h n i c a l note no. 30- - 20pp.  S r i v a s t a v a , L.M. and K. Esau. 1961.  R e l a t i o n o f dwarf  m i s t l e t o e (Arceuthobium) t o t h e xylem t i s s u e o f c o n i f e r s . I .  Anatomy  o f p a r a s i t e s i n k e r s and t h e i r w i t h h o s t xylem. Botany  American J o u r n a l o f  48:159-167-  S t e e l , R.G.D. and J.H. T o r r i e . I960.  P r i n c i p l e s and p r o -  cedures o f s t a t i s t i c s . Company, I n c . Van d e r P l a n k ,  J.E. 1963.  connection  M c G r a w - H i l l Book  T o r o n t o , O n t a r i o . 481pp.  P l a n t d i s e a s e s : e p i d e m i c s and  control.  Academic P r e s s , I n c . New  Y o r k , New York. 349 'pp. . 1965.  Dynamics o f e p i d e m i c s o f p l a n t Science  Wagener, W.W.  1961.  disease.  147:120-124-  The i n f l u e n c e o f l i g h t on t h e e s t a b l i s h ment and growth o f dwarf m i s t l e t o e on ponderosa and J e f f r e y p i n e s . Forest Service.  Pacific  U. S.  Southwest  F o r e s t and Range Experiment S t a t i o n . R e s e a r c h note 81. 5PP. 1962  Dwarf m i s t l e t o e i n c u b a t i o n p e r i o d on ponderosa and J e f f r e y p i n e s i n C a l i f o r n i a . Forest Science  8:16-20.  - 22 -  Weir, J.R. 1916. .  Mistletoe  i n j u r y to c o n i f e r s i n the  northwest. Agriculture. .1918.  U. S. Department o f B u l l e t i n 360.  E f f e c t s of mistletoe Journal  36 pp.  on young c o n i f e r s .  of A g r i c u l t u r a l Research  12:715-718.  

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