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UBC Theses and Dissertations

Water relations, survival and growth of conifer seedlings planted on a high elevation south-facing clearcut Livingston, Nigel Jonathan 1986

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WATER RELATIONS, SURVIVAL AND GROWTH OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT By NIGEL JONATHAN LIVINGSTON B . S c , U n i v e r s i t y o f N o t t i n g h a m , 1977 M . S c . , U n i v e r s i t y o f G u e l p h , 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Depar tment o f S o i l S c i e n c e 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 t h e r e q u i r e d s t a n d a r d y THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1986 ® N i g e l J o na t h an L i v i n g s t o n In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. It i s understood that copying or pu b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date //£, / 19U 1Q \ - i i ABSTRACT Equa l numbers o f D o u g l a s - f i r ( P s eudo t suga m e n z i e s i i ( M i r b . ) F r a n c o ) , w e s t e r n hemlock (Tsuga h e t e r o p h y l l a ( R a f . ) S a r g . ) , and P a c i f i c s i l v e r f i r ( A b i e s a m a b i l i s (Doug . ) F o r b e s ) s e ed l i n g s , ,we r e s p r i n g p l a n t e d , i n 1981 and 1982 , as 1-0 s t y r o p l u g s on a s o u t h - f a c i n g h i g h e l e v a t i o n c l e a r c u t l o c a t e d on Mount A r r o w s m i t h , Vancouve r I s l a n d , B r i t i s h C o l u m b i a . A number o f t r e a t m e n t s were a p p l i e d t o d e t e r m i n e whe the r m o d i f i c a t i o n o f s e e d l i n g m i c r o c l i m a t e wou ld i n c r e a s e s u r v i v a l and g r o w t h . These t r e a t m e n t s i n c l u d e d i n c l i n i n g t h e s e e d l i n g s t o t h e s o u t h w e s t , p r o v i s i o n o f shade c a r d s , i r r i g a t i o n , and i r r i g a t i o n and shade c a r d s c o m b i n e d . The h i g h e s t s u r v i v a l r a t e s , r e g a r d l e s s o f t r e a t m e n t , were e x h i b i t e d by D o u g l a s - f i r . A p p r o x i m a t e l y 72% and 82% o f u n t r e a t e d s e e d l i n g s , p l a n t e d i n 1981 and 1982 r e s p e c t i v e l y , s u r v i v e d . S u r v i v a l o f s e e d l i n g s t h a t r e c e i v e d t r e a t m e n t ranged f rom 81% t o 95%. D o u g l a s - f i r s e e d l i n g s were a b l e t o s u r v i v e and grow because t h e y were h i g h l y d rough t t o l e r a n t . U n i r r i g a t e d s e e d l i n g s l owe red t h e i r o s m o t i c p o t e n t i a l by o v e r 1.1 MPa i n t h e c o u r s e o f a g row ing season i n r e sponse t o d e c l i n i n g s o i l wa t e r p o t e n t i a l s and c o n s e q u e n t l y were a b l e t o m a i n t a i n t u r g o r . The t r a n s p i r a t i o n r a t e s o f t h e s e s e e d l i n g s were neve r l e s s t h a n 50% o f t h o s e t h a t were i r r i g a t e d . Wes te rn hem l o c k , and t o an even g r e a t e r e x t e n t , P a c i f i c s i l v e r f i r s e e d l i n g s l a c k e d s t r e s s a v o i d a n c e and t o l e r a n c e mechan i sms . C o n s e q u e n t l y t h e r e was v e r y poor s u r v i v a l o f bo th s p e c i e s . S u r v i v a l r a t e s were s i g n i f i c a n t l y i n c r e a s e d by shade c a r d s and i r r i g a t i o n but neve r exceeded 64% i n e i t h e r s p e c i e s . The e x t e n t and t y p e o f g rowth i n a l l s p e c i e s was ma r ked l y a f f e c t e d by changes i n m i c r o c l i m a t e . I r r i g a t e d s e e d l i n g s d e v e l o p e d t h e l a r g e s t s h o o t s and t h e s m a l l e s t r o o t s y s t e m s . Shaded s e e d l i n g s had l a r g e r s h o o t s , but g e n e r a l l y l e s s r o o t s , t han u n t r e a t e d s e e d l i n g s wh i ch had t h e l o w e s t shoo t t o r o o t d r y mass r a t i o s . A b o u n d a r y - l i n e a n a l y s i s model t h a t r e l a t e d s e e d l i n g s t o m a t a l c o n d u c t a n c e ( g s ) t o measurements o f h o u r l y a ve r age s o l a r i r r a d i a n c e , a i r t e m p e r a t u r e , vapour p r e s s u r e d e f i c i t and ave r age r o o t zone s o i l w a t e r p o t e n t i a l , a c c oun t ed f o r o v e r 70% o f t h e v a r i a b i l i t y i n g s . When t h e number o f hours f rom s u n r i s e was i n c l u d e d as an i n dependen t v a r i a b l e , o v e r 85% o f t h e v a r i a b i l i t y i n g s c o u l d be e x p l a i n e d . Measurements o f s e e d l i n g s e a s o n a l d r y m a t t e r a c c u m u l a t i o n were b e t t e r c o r r e l a t e d w i t h e s t i m a t e s o f s e e d l i n g g r ow i ng season t r a n s p i r a t i o n t h a n w i t h e s t i m a t e s o f ave rage g r ow ing season t o t a l s e e d l i n g g s . - i v -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v L IST OF TABLES v i i L IST OF FIGURES x i i NOTATION x v i i i ACKNOWLEDGEMENTS x x i INTRODUCTION 1 CHAPTER 1 WATER STRESS AND SURVIVAL OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT 4 I . I n t r o d u c t i o n 5 I I . Methods 6 A . S i t e D e s c r i p t i o n 6 B. E x p e r i m e n t a l D e s i g n 7 C . Measurements 9 1. Grow ing Season Weather O b s e r v a t i o n s 9 2 . Root Zone S o i l Water P o t e n t i a l 9 3 . T o t a l Twig Xy lem Water P o t e n t i a l and Osmot i c P o t e n t i a l 11 4 . S e e d l i n g T r a n s p i r a t i o n 13 5. S e e d l i n g S u r v i v a l 17 I I I . R e s u l t s and D i s c u s s i o n 17 A . Grow ing Season Weather O b s e r v a t i o n s 17 B. T o t a l Twig Xy lem P o t e n t i a l , Need le Osmot i c P o t e n t i a l and Tu rgo r P o t e n t i a l 18 C . S e e d l i n g T r a n s p i r a t i o n Ra tes 33 D. S e e d l i n g S u r v i v a l 39 1. S e e d l i n g s P l a n t e d i n 1981 39 2 . S e e d l i n g s P l a n t e d i n 1982 44 I V . C o n c l u s i o n s 48 V . R e f e r e n c e s 49 - V -Page CHAPTER 2 STOMATAL CHARACTERISTICS AND TRANSPIRATION OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT 54 I . I n t r o d u c t i o n 55 I I . Methods 57 A . S i t e and E x p e r i m e n t a l De s i g n 57 B . Measurements and Data A n a l y s i s 57 I I I . R e s u l t s and D i s c u s s i o n 59 A . Response o f g s t o Changes i n S o l a r I r r a d i a n c e 61 B . Response o f g s t o Changes i n A i r Tempe ra tu re 61 C . Response o f g s t o Changes i n Vapour P r e s s u r e D e f i c i t 67 D. Response o f g s t o Changes i n Tu rgo r P o t e n t i a l and S o i l Water P o t e n t i a l 70 E. R e l a t i o n s h i p o f g s t o t h e Time s i n c e S u n r i s e 76 F. V a r i a t i o n s o f g s w i t h Respec t t o S e e d l i n g Age and Time o f P l a n t i n g 80 G. C a l c u l a t i n g g$ and E f rom B o u n d a r y - L i n e R e l a t i o n s h i p s 81 I V . C o n c l u s i o n s 86 V . R e f e r e n c e s 90 CHAPTER 3 THE GROWTH AND WATER USE OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT 98 I . I n t r o d u c t i o n 99 I I . Methods 101 A . M i c r o m e t e o r o l o g i c a l Measurements 101 B. Growth Measurements 102 1. S e e d l i n g He i gh t 102 2 . L ea f A rea and Shoot and Root Dry M a s s . . . 102 C. C a l c u l a t i o n s 103 1. S t oma ta l Conduc tance 103 2 . T r a n s p i r a t i o n 105 - v i -Page I I I . R e s u l t s 105 A . G row ing Season Weather O b s e r v a t i o n s 105 B. Growth 106 1 . H e i g h t and L ea f A rea o f S e e d l i n g s P l a n t e d i n 1981 108 2 . H e i g h t and L e a f A rea o f S e e d l i n g s P l a n t e d i n 1982 108 3 . Shoot and Root Dry Mass and Shoot t o Root Dry Mass R a t i o I l l C . E s t i m a t e s o f T o t a l S e e d l i n g S t o m a t a l C o n d u c t a n c e , Seasona l T r a n s p i r a t i o n and Water Use E f f i c i e n c y 123 I V . D i s c u s s i o n 125 V . C o n c l u s i o n s 134 V I . R e f e r e n c e s 135 CONCLUSIONS 137 APPENDIX I - D e r i v a t i o n o f W a t e r - R e l e a s e Cu rves f o r t h e D e t e r m i n a t i o n o f C o n i f e r S e e d l i n g Osmot i c P o t e n t i a l 142 APPENDIX I I - An I n s t r u m e n t f o r M e a s u r i n g t h e Ave rage S t o m a t a l Conduc tance o f C o n i f e r S e e d l i n g s ( L i v i n g s t o n e t a l _ . , 1984 , C a n . J . F o r . R e s . 14: 512-517) 148 APPENDIX I I I - S o i l Water R e t e n t i o n Cu r ve s 155 - v i i -L IST OF TABLES T a b l e 1.1 D a i l y minimum measured v a l u e s o f t o t a l t w i g xy l em wa te r p o t e n t i a l (^Ttx) (MPa) and a ve r age r o o t zone s o i l w a t e r p o t e n t i a l (^ s ) (MPa) f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r between May and Augus t 1981. S e e d l i n g s were p l a n t e d i n 1982. S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s , T a b l e 1.2 Measured v a l u e s o f a ve r age r o o t zone s o i l w a t e r p o t e n t i a l (i|/ s) (MPa) and d a i l y minimum t o t a l t w i g xy l em p o t e n t i a l (^Ttx) ( M p a ) f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r between May and Sep tember 1983. S e e d l i n g s were p l a n t e d i n 1982. S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s T a b l e 1.3 Measured v a l u e s o f minimum o s m o t i c p o t e n t i a l i ^ ) (MPa) between May and September 1982 f o r shaded ( u s i n g shade c a r d s ) and non-shaded D o u g l a s - f i r , w e s t e r n hem l o c k , and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n 1981. S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s T a b l e 1.4 Measured v a l u e s o f minimum o s m o t i c p o t e n t i a l {%) (MPa) f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s between May and September 1983. S e e d l i n g s were p l a n t e d i n 1982. S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s T a b l e 1.5 Measured v a l u e s o f d a i l y minimum o s m o t i c p o t e n t i a l (^ir) (MPa) between May and September 1982 f o r u n t r e a t e d p l a n t e d D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n t h e p r e v i o u s y e a r (P) and p l a n t e d i n t h e c u r r e n t y e a r ( C ) . S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s , T a b l e 1.6 V a l u e s o f l i n e a r r e g r e s s i o n c o e f f i c i e n t s and r 2 f o r t h e r e l a t i o n s h i p : E = a + (i|>s - ^ T t x ) / 0 t " o r i r r i g a t e d (1) and n o n - i r r i g a t e d (NI ) D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s . The u n i t s o f a and b a r e yg cm s and MPa/(pg c m - 2 s _ 1 ) . r e s p e c t i v e l y T a b l e 1.7 D a i l y t r a n s p i r a t i o n g d a y - 1 ) o f shaded ( u s i n g shade c a r d s ) and unshaded D o u g l a s - f i r s e e d l i n g s on June 10, June 12 and June 13, 1982. The t o t a l p r o j e c t e d n e e d l e a r e a (cm ) i s g i v e n i n b r a c k e t s . The a ve r age r o o t zone s o i l wa t e r p o t e n t i a l was -0 .10 MPa on J une 12 , - v i i i Page T a b l e 1.8 P e r c e n t s u r v i v a l i n A p r i l 1982 , 1983 and 1984 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g s p l a n t e d i n A p i r l 1 9 8 1 . Numbers f o l l o w e d by t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( t = 0 .05) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range T e s t , wh i ch was a p p l i e d t o each s p e c i e s i n each y e a r . . 45 T a b l e 1.9 P e r c e n t s u r v i v a l i n A p r i l 1983 and 1984 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g s p l a n t e d i n A p r i l 1 9 8 2 . Numbers f o l l o w e d by t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( t = 0 .05 ) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range T e s t , wh i ch was a p p l i e d t o each s p e c i e s i n each y e a r . . 46 T a b l e 2.1 The maximum s t o m a t a l c onduc t an ce measured ( g s m a x ) and t h e number o f t i m e s t h i s v a l u e was o b t a i n e d (n) f o r D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s 60 T a b l e 2.2 V a l u e s o f t h e c o e f f i c i e n t a i n t h e e q u a t i o n ; 9s/9smax = 1 - e~ s d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s a ve r age s e e d l i n g s t o m a t a l c ondu c t an c e (cm s _ 1 ) » gsmax 1 S maximum g s (cm s _ 1 ) and R s i s t h e h o u r l y a ve r age g l o b a l s o l a r i r r a d i a n c e (W m - 2 ) 63 T a b l e 2.3 V a l u e s o f t h e c o e f f i c i e n t b and T m a x i n t h e e q u a t i o n ; g s / g s m a x = 1-b (T ~ ^max) d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s t h e ave r age s e e d l i n g s t oma ta l c onduc t an ce (cm s - 1 ) 9smax 1 S maximum gs ( c m s * 1 ) , T i s t h e h o u r l y a v e r age a i r t e m p e r a t u r e (°C) and T m a x i s t h e a i r t e m p e r a t u r e a t wh i ch g s = g s m a x 66 T a b l e 2.4 V a l u e s o f t h e c o e f f i c i e n t , D 0 > 5 and n, i n t h e e q u a t i o n ; g s / g S m a x = l / U + ( D / D 0 . 5 ) n ) d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s a v e r age s e e d l i n g s t o m a t a l c onduc t an ce (cm s - 1 ) » 9smax 1 S maximum g s (cm s - 1 ) » D "is t h e h o u r l y a v e r age vapour p r e s s u r e d e f i c i t (kPa) and Do.5 i s t h e vapour p r e s s u r e d e f i c i t a t wh i ch g s i s h a l f 9smax 69 - i x -Page T a b l e 2 .5 V a l u e s o f t h e c o e f f i c i e n t s , k, m and n i n t h e e q u a t i o n s gs/9smax = e (0 2. ^s 1. "0*1 and 9s/9smax • m* s - n ( * s < - 0 . 1 MPa) d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s t h e ave r age s e e d l i n g s t o m a t a l c ondu c t an c e (cm s _ 1 ) gsmax 1 S maximum g§ (cm s " 1 ) and y s i s t h e ave r age r o o t zone s o i l wa te r p o t e n t i a l ( M P a ) . . . 75 T a b l e 2.6 V a l u e s o f t h e c o e f f i c i e n t , q , r and s i n t h e e q u a t i o n ; gs/9max = P + qt + r t 2 d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s where g$ i s t h e ave r age s e e d l i n g s t o m a t a l c ondu c t an c e (cm s _ 1 ) f 9smax 1 S maximum g s (cm s~M and t i s t h e number o f hou r s f rom s u n r i s e 79 T a b l e 2.7 The p e r c e n t a g e o f t h e v a r i a n c e o f t h e ave r age s t oma t a l c ondu c t an c e o f D o u g l a s - f i r ( D F ) , Wes te rn hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) s e e d l i n g s , measured on 13 days between June and September 1982 , e x p l a i n e d by t h e b o u n d a r y - l i n e a n a l y s i s model u s i n g t h e i n d i v i d u a l v a r i a b l e s , R s ( g l o b a l s o l a r i r r a d i a n c e ) , T ( a i r t e m p e r a t u r e ) D ( vapou r p r e s s u r e d e f i c i t ) \|>s ( a v e r age r o o t zone wate r p o t e n t i a l ) and t ( t h e number o f hours f rom s u n r i s e ) , and t he v a r i a b l e s i n c o m b i n a t i o n 82 T a b l e 2.8 V a l u e s o f c o e f f i c i e n t s i n t h e l i n e a r r e g r e s s i o n e q u a t i o n ; g s c a - | e = V g s + w f o r i r r i g a t e d and n o n - i r r i g a t e d D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1 9 8 2 , f o r 13 days between June and September 1 9 8 2 , where S s c a l c i s s e e d l i n g s t o m a t a l c onduc t an ce u s i n g t he b o u n d a r y - l i n e a n a l y s i s model and g s i s measured s t o m a t a l c o n d u c t a n c e . A l s o shown a r e t h e number o f d a t a p o i n t s ( n ) , t h e c o e f f i c i e n t o f d e t e r m i n a t i o n ( r ) and t he s t a n d a r d e r r o r o f e s t i m a t e (SEE) 89 T a b l e 3 .1 Mo rpho l ogy o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g s a t t h e t i m e o f p l a n t i n g . S t anda r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s 107 T a b l e 3.2 S e e d l i n g h e i g h t (mm) i n O c t o be r 1981 , 1982 and 1983 o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g p l a n t e d i n A p r i l 1 9 8 1 . Numbers f o l l o w e d by t he same l e t t e r a re not s i g n i f i c a n t l y d i f f e r e n t ( t = 0 .05) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range Tes t wh i ch was a p p l i e d t o each s p e c i e s i n each y e a r 109 - X -Page T a b l e 3 .3 L e a f a r ea ( cm 2 ) i n O c t o be r 1982 , 1982 and 1983 o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1 9 8 1 . S t a nda r d d e v i a t i o n s were g i v e n i n b r a c k e t s 110 T a b l e 3 .4 S e e d l i n g h e i g h t (mm) i n Oc t obe r 1 9 8 2 , 1982 and 1983 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1 982 . Numbers f o l l o w e d by t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( t = 0 . 0 5 ) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range Tes t was a p p l i e d t o each s p e c i e s i n each y e a r 112 T a b l e 3 .5 L e a f a r e a ( cm 2 ) i n Oc t obe r 1982 and 1983 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1982 . Maximum s t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s 113 T a b l e 3.6 Morpho logy i n O c t o be r 1981 , 1982 and 1983 o f D o u g l a s - f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda rd d e v i a t i o n s a r e g i v e n i n b r a c k e t s 120 T a b l e 3.7 Mo rpho l ogy i n O c t o be r 1 9 8 1 , 1982 and 1983 o f we s t e r n hemlock s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s 121 T a b l e 3 .8 Morpho logy i n O c t obe r 1981 , 1982 and 1983 o f P a c i f i c s j l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1 9 8 2 . S t anda rd d e v i a t i o n s a r e g i v e n i n b r a c k e t s 122 T a b l e 3.9 Dry m a t t e r a c c u m u l a t i o n ( Y ) , s e e d l i n g t r a n s p i r a t i o n (EJOT) a n d WUF. d u r i n g t he g row ing season i n 1981 , 1982 and 1983 o f D o u g l a s - f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda rd d e v i a t i o n s o f Y a r e b r a c k e t e d . The r o o t mean squa re e r r o r s f o r EJOT were t y p i c a l l y 26%. These e r r o r s were d e t e r m i n e d by d i f f e r e n t i a t i n g e q u a t i o n (2) and assuming a 20% e r r o r f o r A, a 20% e r r o r i n D and by u s i n g t h e s t a n d a r d e r r o r o f e s t i m a t e f o r c a l c u l a t e d v e r s u s measured g s r e p o r t e d i n Chap t e r 2 127 T a b l e 3 .10 Dry m a t t e r a c c u m u l a t i o n ( Y ) , s e e d l i n g t r a n s p i r a t i o n (EJOT) a n d W I J E d u r i n g t he g row ing season i n 1982 and 1983 o f we s t e r n hemlock s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1 9 8 2 . S t anda r d d e v i a t i o n s o f Y a r e b r a c k e t e d . The r o o t mean squa re e r r o r s f o r EjOT w e r e t y p i c a l l y 28%. These e r r o r s were d e t e r m i n e d by d i f f e r e n t i a t i n g e q u a t i o n (2) and assuming a 20% e r r o r f o r A, a 10% e r r o r i n D and by u s i n g t he s t a n d a r d e r r o r o f e s t i m a t e f o r c a l c u l a t e d v e r s u s measured g s r e p o r t e d i n Chap t e r 2 128 - x i -Page T a b l e 3.11 Dry m a t t e r a c c u m u l a t i o n ( Y ) , s e e d l i n g t r a n s p i r a t i o n (EJOT) and WUE d u r i n g t h e g row ing season i n 1983 o f P a c i f i c s i l v e r - f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982. S t a n d a r d d e v i a t i o n s o f Y a r e b r a c k e t e d . The r o o t mean s qua r e e r r o r s f o r EjOT were t y p i c a l l y 30%. These e r r o r s were d e t e r m i n e d by d i f f e r e n t i a t i n g e q u a t i o n (2) and assuming a 20% e r r o r i n A, a 10% e r r o r i n D, and by u s i n g t h e s t a n d a r d e r r o r o f e s t i m a t e f o r c a l c u l a t e d v e r s u s measured g s r e p o r t e d i n C h a p t e r 2 129 T a b l e A I . l The d i f f e r e n c e between t h e o s m o t i c p o t e n t i a l a t f u l l t u r g o r (^Q) a n d o s m o t i c p o t e n t i a l a t z e r o t u r g o r (Vir) o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r - f i r s h o o t s . A l s o shown a re t h e c o r r e s p o n d i n g v a l u e s o f a p o p l a s t i c wa t e r c o n t e n t ( B ) . V a l u e s were o b t a i n e d f rom w a t e r - r e l e a s e c u r v e s . Each number i s t h e ave r age o f 10 measurements 147 - x i i -L IST OF FIGURES Page F i g u r e 1.1 Measurements o f o s m o t i c p o t e n t i a l a t f u l l t u r g o r o b t a i n e d f rom w a t e r - r e l e a s e c u r v e s ( i | % 0 ) v e r s u s t h o s e o b t a i n e d f rom p r e v i o u s l y f r o z e n sap (\|%) f o r D o u g l a s - f i r ( D F ) , we s t e r n hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) 14 F i g u r e 1.2 C o u r s e s o f a ve r age r o o t zone s o i l wa t e r p o t e n t i a l ( ^ s ) , p r e c i p i t a t i o n (P) and maximum vapour p r e s s u r e d e f i c i t (D) d u r i n g t h e 1981 g row ing season 19 F i g u r e 1.3 Cou r s e s o f a ve r age r o o t zone s o i l wa te r p o t e n t i a l (<|>s), p r e c i p i t a t i o n (P) and maximum vapour p r e s s u r e d e f i c i t (D) d u r i n g t h e 1982 g row ing season 20 F i g u r e 1.4 Cou r s e s o f a ve r age r o o t zone s o i l wa te r p o t e n t i a l ( ^ s ) , p r e c i p i t a t i o n (P) and maximum vapour p r e s s u r e d e f i c i t (D) d u r i n g t h e 1983 g row ing season 21 F i g u r e 1.5 R e l a t i o n s h i p between predawn t o t a l t w i g xy lem w a t e r p o t e n t i a l (^Ttx) a n f l a ve r age r o o t zone s o i l wa te r p o t e n t i a l (i|>s) f o r n o n - i r r i g a t e d D o u g l a s - f i r ( D F ) , w e s t e r n hemlock (WH) and P a c i f i c s i l v e r - f i r ( P S F ) . Measurements were made i n 1 9 8 1 , 1982 and 1 9 8 3 . A l s o shown i s t h e 1:1 l i n e . L i n e a r r e g r e s s i o n a n a l y s i s i n d i c a t e s predawn \pjtx (MPa) = 0 .863 ^ (MPa) - 0 .357 ( r 2 = 0 .89 ) (dashed l i n e ) 22 F i g u r e 1.6 Cou r s e s o f minimum t w i g xy lem wate r p o t e n t i a l , o s m o t i c p o t e n t i a l and minimum t u r g o r p o t e n t i a l , d u r i n g the 1982 g row ing s e a s o n , f o r i r r i g a t e d ( IRR) and n o n - i r r i g a t e d (NON-IRR) D o u g l a s - f i r s e e d l i n g s p l a n t e d i n May 1982 . V a l u e s o f minimum t u r g o r p o t e n t i a l were o b t a i n e d by s u b t r a c t i n g o s m o t i c p o t e n t i a l f rom minimum t w i g xy lem wa te r p o t e n t i a l . . . . 25 F i g u r e 1.7 Cou r s e s o f minimum t w i g xy lem wa te r p o t e n t i a l , o s m o t i c p o t e n t i a l and minimum t u r g o r p o t e n t i a l , d u r i n g t h e 1982 g row ing s e a s o n , f o r i r r i g a t e d ( IRR) and n o n - i r r i g a t e d (NON-IRR) wes t e rn hemlock s e e d l i n g s p l a n t e d i n May 1982 . V a l u e s o f minimum t u r g o r p o t e n t i a l were o b t a i n e d by s u b t r a c t i n g o s m o t i c p o t e n t i a l f rom minimum t w i g xy lem wa te r p o t e n t i a l 26 - x i i i -Page F i g u r e 1.8 F i g u r e 1.9 F i g u r e 1.10 F i g u r e 1.11 F i g u r e 1.12 F i g u r e 1.13 F i g u r e 1.14 Cou r se s o f minimum t w i g xy l em wa te r p o t e n t i a l , o s m o t i c p o t e n t i a l and minimum t u r g o r p o t e n t i a l , d u r i n g t h e 1982 g r ow ing s e a s o n , f o r i r r i g a t e d ( IRR) and n o n - i r r i g a t e d (NON-IRR) P a c i f i c s i l v e r - f i r s e e d l i n g s p l a n t e d i n May 1982. V a l u e s o f minimum t u r g o r p o t e n t i a l were o b t a i n e d by s u b t r a c t i n g o smo t i c p o t e n t i a l f rom minimum t w i g xy l em w a t e r p o t e n t i a l The r e l a t i o n s h i p between d a i l y t r a n s p i r a t i o n (E) and ave r age r o o t zone s o i l wa te r p o t e n t i a l f o r n o n - i r r i g a t e d D o u g l a s - f i r ( D F ) , w e s t e r n hemlock (WH) and P a c i f i c s i l v e r - f i r (PSF) s e e d l i n g s . Measurements were made i n 1982 on s e e d l i n g s p l a n t e d i n May o f t h a t y e a r . Each p o i n t r e p r e s e n t s t h e a ve r age E f o r t h r e e s e e d l i n g s . The c u r v e s were f i t t e d by eye , 27 The r e l a t i o n s h i p between t h e r a t i o o f d a i l y t r a n s p i r a t i o n per u n i t p r o j e c t e d l e a f a r e a o f n o n - i r r i g a t e d s e e d l i n g s t o t h a t o f i r r i g a t e d s e e d l i n g s (E^T/EJ ) and ave r age r o o t zone s o i l wa te r p o t e n t i a l (i|>s) f o r D o u g l a s - f i r ( D F ) , w e s t e r n hemlock (WH) and P a c i f i c s i l v e r - f i r (PSF) Measurements were made i n 1982 on s e e d l i n g s p l a n t e d i n May o f t h a t y e a r The d a i l y c o u r s e o f t r a n s p i r a t i o n (E) per u n i t p r o j e c t e d l e a f a r ea f o r i r r i g a t e d ( IRR) and non -i r r i g a t e d (NON-IRR) D o u g l a s - f i r s e e d l i n g s , and vapour p r e s s u r e d e f i c i t (D) f o r J u l y 24 and J u l y 27, 1982. The v a l u e s o f i|>s on J u l y 24 and J u l y 27 were -0 .5 MPa and -0 .7 MPa, r e s p e c t i v e l y , C ou r s e s o f s t o m a t a l c ondu c t an c e (gs)» t r a n s p i r a t i o n r a t e (E) and t o t a l t w i g xy lem p o t e n t i a l ( t T t x ) f ° r shaded ( c l o s e d c i r c l e s ) and unshaded (open c i r c l e s ) D o u g l a s - f i r s e e d l i n g s on June 13, 1982 Cou r se s o f t e m p e r a t u r e o f shaded (dashed l i n e ) and unshaded ( d o t t e d l i n e ) n e e d l e s o f a D o u g l a s - f i r s e e d l i n g , and a i r t e m p e r a t u r e ( s o l i d l i n e ) a t 20 cm h e i g h t nea r t h e unshaded s e e d l i n g on June 13, 1982. . C o u r s e s o f vapour p r e s s u r e d e f i c i t ( s o l i d l i n e ) , vapour p r e s s u r e d i f f e r e n c e between an unshaded D o u g l a s - f i r n e e d l e and the a i r ( b roken l i n e ) and t h e vapour p r e s s u r e d i f f e r e n c e between a shaded D o u g l a s - f i r n e e d l e and t he a i r ( d o t t e d l i n e ) on June 13, 1982 34 35 38 41 42 43 - x i v Page F i g u r e 2.1 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c o n d u c t a n c e ( g s ) t o t he maximum s t oma ta l c o n d u c t a n c e (gsmax) a n c l g l o b a l s o l a r - i r r a d i a n c e ( R s ) f o r i r r i g a t e d (•) and n o n - i r r i g a t e d (o) D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s t he ave r age o f t h r e e measu remen t s . A l s o shown i s t h e b o u n d a r y - l i n e wh i ch i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar i son o f t he b o u n d a r y - l i n e s f o r the r e l a t i o n s h i p between 9s/9smax a n <^ ^s f ° r D o u g l a s - f i r ( s o l i d l i n e ) , we s t e r n hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r - f i r ( b r o k en l i n e ) . (PPFD i n ymol m - 2 s " 1 i s a p p r o x i m a t e l y 2.04 t i m e s R s i n Wn r 2 ) 62 F i g u r e 2 .2 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t oma t a l c onduc t an ce ( g s ) t o the maximum s t oma ta l c o n d u c t a n c e (gsmax) a n d a i r t e m p e r a t u r e (T) f o r i r r i g a t e d (•) and n o n - i r r i g a t e d (o) D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s t h e ave rage o f t h r e e measu r emen t s . , A l s o shown i s t h e b o u n d a r y - l i n e wh i ch i n d i c a t e s t he upper l i m i t o f t h e o b s e r v a t i o n s . b . Compar i son o f t h e b o u n d a r y - l i n e s f o r t he r e l a t i o n s h i p between gs/9smax a n d T f o r D o u g l a s - f i r ( s o l i d l i n e ) , wes t e rn hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r - f i r ( b r o k en l i n e ) 65 F i g u r e 2 .3 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c onduc t an ce ( g s ) to the maximum s t oma ta l c o n d u c t a n c e (gsmax) a n f ' vapour p r e s s u r e d e f i c i t (D) f o r i r r i g a t e d (•) and n o n - i r r i g a t e d (o) D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s t h e a ve r age o f t h r e e measu remen t s . A l s o shown i s t he b o u n d a r y - l i n e wh i ch i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar i son o f t h e b o u n d a r y - l i n e s f o r t h e r e l a t i o n s h i p between 9s/9smax a n c l 0 f o r D o u g l a s - f i r ( s o l i d l i n e ) , w e s t e r n hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r - f i r ( b r o ken l i n e ) 68 F i g u r e 2.4 The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c ondu c t an c e ( g s ) t o t he maximum s t oma ta l c ondu c t an c e (gsmax) a n d the t u r g o r p o t e n t i a l f o r i r r i g a t e d (•) and n o n - i r r i g a t e d (o) D o u g l a s - f i r s e e d l i n g s . The s e e d l i n g s were p l a n t e d i n 1982 and t h e measurements were made on 13 days between June and September 1982 71 - XV -Page F i g u r e 2 .5 The r e l a t i o n s h i p between t h e s t oma t a l c o n d u c t a n c e o f a D o u g l a s - f i r s e e d l i n g and the h o u r l y a ve r age vapour p r e s s u r e d e f i c i t (D) ( o ) , and t u r g o r p o t e n t i a l (\|>p) (•) measured on J u l y 27 , 1982 . The " one s " mark the t i m e (06 :00 PST) when the f i r s t measurements were made. Measurements were r epea t ed e v e r y hour u n t i l 2 1 . 0 0 PST 72 F i g u r e 2.6 a . The r e l a t i o n s h i p between the r a t i o o f t h e s t o m a t a l c onduc t an ce (g$) t o t h e maximum s t oma ta l c o n d u c t a n c e (gsmax) a n d a ve rage r o o t zone s o i l wa t e r p o t e n t i a l (i|>s) f o r n o n - i r r i g a t e d D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s t h e ave rage o f t h r e e measu remen t s . A l s o shown i s t h e b o u n d a r y - l i n e wh i ch i n d i c a t e s t he upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar i son o f t h e b o u n d a r y - l i n e s f o r t he r e l a t i o n s h i p between 9s/9smax and i|) S f o r D o u g l a s - f i r ( s o l i d l i n e ) , w e s t e r n hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r - f i r ( b r o ken l i n e ) 74 F i g u r e 2.7 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c ondu c t an c e ( g s ) t o t he maximum s t oma ta l c o n d u c t a n c e (gsmax) and the t ime s i n c e s u n r i s e ( t ) f o r i r r i g a t e d (•) and n o n - i r r i g a t e d (o) D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s t h e a v e r age o f t h r e e measu remen t s . A l s o shown i s t h e b o u n d a r y - l i n e wh i ch i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar i son o f t h e b ounda r y -l i n e s f o r t he r e l a t i o n s h i p between gs/gsmax a n d t f o r D o u g l a s - f i r ( s o l i d l i n e ) , wes t e rn hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r - f i r ( b r oken l i n e ) . . . 78 F i g u r e 2 .8 The d a i l y c o u r s e s o f measured (open symbo l s ) and c a l c u l a t e d ( c l o s e d symbo l s ) s t oma ta l c onduc t ance ( g s ) T " o r i r r i g a t e d ( s o l i d l i n e s ) and n o n - i r r i g a t e d ( d o t t e d l i n e s ) D o u g l a s - f i r s e e d l i n g s on J u l y 28 , 1982 . S tomata l c onduc t an ce was c a l c u l a t e d w i t h (•) and w i t h o u t t i m e s i n c e s u n r i s e (A) as a v a r i a b l e . The ave r age r oo t zone s o i l wa te r p o t e n t i a l was - 0 . 7 3 MPa 84 F i g u r e 2.9 The d a i l y c o u r s e s o f measured (open symbo l s ) and c a l c u l a t e d ( c l o s e d symbo l s ) s t oma t a l c o n d u c t a n c e ( g s ) f o r i r r i g a t e d ( s o l i d l i n e s ) and n o n - i r r i g a t e d ( d o t t e d l i n e s ) D o u g l a s - f i r s e e d l i n g s on August 2 1 , 1982 . S tomata l c onduc t an ce was c a l c u l a t e d w i t h (•) and w i t h o u t t i m e s i n c e s u n r i s e (A) as a v a r i a b l e . The ave rage r oo t zone s o i l wa te r p o t e n t i a l was - 1 . 1 MPa 85 - x v i -F i g u r e 2 .10 F i g u r e 2 .11 F i g u r e 3.1 F i g u r e 3.2 F i g u r e 3 .3 F i g u r e 3.4 Page Compar i son o f c a l c u l a t e d s t o m a t a l c o n d u c t a n c e ( 9 s c a l c ) W l t n measured s t o m a t a l c o n d u c t a n c e ( g s ) f o r i r r i g a t e d (o) and n o n - i r r i g a t e d (o) D o u g l a s - f i r ( D F ) , w e s t e r n hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) s e e d l i n g s , p l a n t e d i n 1982 , f o r 13 days between June and Sep tember 1982 . The r e g r e s s i o n l i n e s shown ( b r oken l i n e s ) a r e f o r a l l t h e p o i n t s . The s l o p e s and i n t e r c e p t s o f t h e s e l i n e s a r e g i v e n i n T a b l e 2.8 87 Compar i son o f c a l c u l a t e d d a i l y t r a n s p i r a t i o n r a t e ( E c a i c ) u s i n g v a l u e s o f g s o b t a i n e d f rom e q u a t i o n (4) w i t h R s , D, T , i>s and t as v a r i a b l e s , w i t h d a i l y t r a n s p i r a t i o n r a t e (E) t h a t was c a l c u l a t e d u s i n g measured v a l u e s o f s t o m a t a l c o n d u c t a n c e . Bo th E and E c a i c w e r e c a l c u l a t e d as t h e sum o f t h e h o u r l y p r o d u c t s o f g s and ( D / R V T ' ) f o r i r r i g a t e d ( c l o s e d s ymbo l s ) and n o n - i r r i g a t e d (open s ymbo l s ) D o u g l a s - f i r ( o ) , we s t e r n hemlock (o) and P a c i f i c s i l v e r f i r (o ) s e e d l i n g s , p l a n t e d i n 1982 , f o r 13 days between June and Sep tember 1982 . A l s o shown i s t h e 1:1 l i n e . L i n e a r r e g r e s s i o n a n a l y s i s i n d i c a t e s E c a i c (g c m " 2 d a y 1 ) = 0 .98 E (g c m " 2 d a y - 1 ) +0.002 ( r 2 = 0 . 96 ) (dashed l i n e ) 88 Sea sona l c o u r s e o f s e e d l i n g h e i g h t i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( • ) , i r r i g a t e d (o) and i r r i g a t e d and shaded (•) D o u g l a s - f i r s e e d l i n g s p l a n t e d i n May 1982 114 Sea sona l c o u r s e o f s e e d l i n g h e i g h t i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( • ) , i r r i g a t e d (•) and i r r i g a t e d and shaded (•) we s t e r n hemlock s e e d l i n g s p l a n t e d i n May 1982 115 Sea sona l c o u r s e o f s e e d l i n g h e i g h t i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( • ) , i r r i g a t e d ( a ) and i r r i g a t e d and shaded (•) P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1982 116 Sea sona l c o u r s e o f s e e d l i n g p r o j e c t e d l e a f a r ea (A) i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( • ) , i r r i g a t e d (•) and i r r i g a t e d and shaded (•) D o u g l a s -f i r s e e d l i n g s p l a n t e d i n May 1982 . The B roken l i n e shows t h e e s t i m a t e d s e a s o n a l c o u r s e o f l e a f a r e a t h a t was used i n t h e c a l c u l a t i o n o f t h e g r ow ing season t r a n s p i r a t i o n o f i r r i g a t e d and shaded s e e d l i n g s 117 - x v i i -Page F i g u r e 3 .5 Seasona l c o u r s e o f p r o j e c t e d l e a f a r ea (A) i n J982 and 1983 o f u n t r e a t e d (o) and i r r i g a t e d (•) we s t e r n hemlock s e e d l i n g s p l a n t e d i n May 1982 118 F i g u r e 3.6 Seasona l c o u r s e o f p r o j e c t e d l e a f a r e a (A) i n 1982 and 1983 o f u n t r e a t e d (o) and i r r i g a t e d (•) P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1982 119 F i g u r e 3.7 The r e l a t i o n s h i p between g r ow ing season s e e d l i n g d r y m a t t e r a c c u m u l a t i o n (Y) and t h e a ve r age g r ow i ng s ea son s e e d l i n g canopy c o n d u c t a n c e ( g c ) f o r D o u g l a s - f i r s e e d l i n g s i n 1 9 8 1 , 1982 and 1 9 8 3 . The s l o p e o f t h e l i n e f o r c e d t h r o u g h z e r o i s 0 .231 g / ( c m 3 s " 1 ) and t h e e q u a t i o n o f t h e l i n e f i t t e d t h r o u g h t h e d a t a p o i n t s by l i n e a r r e g r e s s i o n i s Y (g) = 0 .154 g£ ( cm 3 S " 1 ) + 1.31 ( r 2 = 0 .68) 124 F i g u r e 3 .8 The r e l a t i o n s h i p between g row ing season s e e d l i n g d r y m a t t e r a c c u m u l a t i o n (Y) and g row ing season s e e d l i n g t r a n s p i r a t i o n (EJOT) f o r D o u g l a s - f i r s e e d l i n g s i n 1981 , 1982 and 1 9 8 3 . The c l o s e d c i r c l e s i n d i c a t e shaded t r e a t m e n t s . The s l o p e o f t h e l i n e f o r c e d t h r ough z e r o i s 0 .0022 g / g . The e q u a t i o n o f t h e l i n e f i t t e d t h r o u g h a l l t h e d a t a p o i n t s by l i n e a r r e g r e s s i o n i s Y (g) = 0 .0027 ET0T (9) -°.83 ( r 2 = 0 . 7 8 ) , and t h e e q u a t i o n o f t h e l i n e , a l s o f i t t e d by l i n e a r r e g r e s s i o n , t h r o u g h t h e p o i n t s e x c l u d i n g shade t r e a t m e n t s i s Y (g ) = 0 .0036 E TQT (g ) - 2 . 0 ( r 2 = 0 .88 ) 126 F i g u r e A I . l The r e l a t i o n s h i p between s e e d l i n g shoo t mass and shoo t t o t a l xy l em p o t e n t i a l ( s hoo t T|») f o r a D o u g l a s - f i r s e e d l i n g . The mass o f t h e s hoo t when shoo t t i s z e r o (Mg) was d e t e r m i n e d f rom t h e l e a s t s q u a r e s o f r e g r e s s i o n o f t h e l i n e a r p o r t i o n o f t h e l i n e 145 F i g u r e A I . 2 The r e l a t i o n s h i p between s e e d l i n g shoo t r e l a t i v e w a t e r c o n t e n t ( shoo t RwC) and t h e i n v e r s e o f shoo t t o t a l xy l em p o t e n t i a l ( ( s h o o t ^ ) - 1 ) . The a p o p l a s t i c w a t e r c o n t e n t ( B ) , o s m o t i c p o t e n t i a l a t f u l l t u r g o r (<|%o) and^osmot i c p o t e n t i a l a t z e r o t u r g o r ( K ) a r e i n d i c a t e d ' 146 F i g u r e A I I I . l S o i l wa t e r r e t e n t i o n c u r v e s f o r 0-5 cm ( • ) , 5-10 (o ) and 15-25 cm (•) dep th s 157 - x v i i i -NOTATION A s e e d l i n g l e a f a r ea on a p r o j e c t e d a r e a b a s i s (cm s e e d l i n g - 1 ) g S e e d l i n g canopy c ondu c t an c e d e f i n e d as t h e p r o d u c t o f t h e s e e d l i n g p r o j e c t e d l e a f a r e a and t h e ave r age s e e d l i n g s t o m a t a l c o n d u c t a n c e (cm s ) g"c a v e r age g r ow ing season s e e d l i n g canopy c o n d u c t a n c e ( cm 3 s _ 1 ) B t i s s u e a p o p l a s t i c w a t e r f r a c t i o n ( d i m e n s i o n l e s s ) C i i n t e r n a l C 0 2 c o n c e n t r a t i o n (L L ' 1 o r cm 3 m - 3 ) D vapour p r e s s u r e d e f i c i t ( kPa ) D Q 5 vapour p r e s s u r e d e f i c i t , d e t e r m i n e d by b o u n d a r y - l i n e a n a l y s i s , a t wh i ch s e e d l i n g s t o m a t a l c o n d u c t a n c e i s h a l f i t s maximum v a l u e (kPa) E s e e d l i n g t r a n s p i r a t i o n r a t e per u n i t p r o j e c t e d l e a f a r ea (g c m - 2 d a y - 1 ) E j t r a n s p i r a t i o n r a t e pe r u n i t p r o j e c t e d l e a f a r ea o f i r r i g a t e d s e e d l i n g s (g cm~ 2 d a y - 1 ) E N I t r a n s p i r a t i o n r a t e per u n i t p r o j e c t e d l e a f a r ea o f n o n - i r r i g a t e d , unshaded s e e d l i n g s (g c m - 2 d a y - 1 ) ^TOT t o t a l amount o f wa t e r t r a n s p i r e d by a s e e d l i n g d u r i n g a g r ow i ng season (g) M shoo t mass a t a g i v e n shoo t w a t e r p o t e n t i a l (g) M D shoo t d r y mass (g) M Q shoo t d r y mass a t f u l l t u r g o r (g) P r a i n f a l l r a t e (mm d a y - 1 ) R g l o b a l s o l a r i r r a d i a n c e ( i . e . , s o l a r i r r a d i a n c e on a h o r i z o n t a l s u r f a c e ) (W m - 2 ) R y t h e gas c o n s t a n t f o r w a t e r vapour ( 0 . 4 6 2 m 3 kPa k g - 1 K _ 1 ) - x i x T a i r t e m p e r a t u r e (°C) T ' a b s o l u t e a i r t e m p e r a t u r e (K) T a i r t e m p e r a t u r e d e t e r m i n e d by boundary l i n e a n a l y s i s a t wh i ch m a x s e e d l i n g s t o m a t a l c ondu c t an c e i s a t i t s maximum (°C) T n t e m p e r a t u r e o f unshaded n e e d l e (°C) 1"nsh t e m p e r a t u r e o f shaded n e e d l e (°C) d n e e d l e d i a m e t e r (m) n e , vapou r p r e s s u r e o f t h e a i r (kPa) a e vapou r p r e s s u r e o f t h e s t o m a t a l c a v i t i e s assumed t o be t h e s a t u r a t e d vapou r p r e s s u r e a t n e e d l e t e m p e r a t u r e ( kPa ) e vapour p r e s s u r e o f t h e s t o m a t a l c a v i t i e s o f shaded s e e d l i n g s n assumed t o be t h e s a t u r a t e d vapou r p r e s s u r e a t n e e d l e t e m p e r a t u r e (kPa) e*(T) s a t u r a t i o n vapour p r e s s u r e a t t e m p e r a t u r e T (kPa) g^ boundary l a y e r c onduc t an ce on one s i d e o f n eed l e (cm s - 1 ) g a v e r age s e e d l i n g s t o m a t a l c onduc t an ce ( i . e . , t h e t r a n s p i r a t i o n r a t e pe r u n i t n e ed l e p r o j e c t e d a r e a per u n i t d i f f e r e n c e i n v apou r p r e s s u r e between s t o m a t a l and a i r c a v i t i e s ) (cm s _ 1 ) g . m , u maximum s t o m a t a l c ondu c t an c e (cm s - 1 ) smax r 2 c o e f f i c i e n t o f d e t e r m i n a t i o n i n a l i n e a r r e g r e s s i o n a n a l y s i s ( d i m e n s i o n l e s s ) t t i m e s i n c e s u n r i s e (h) u w ind speed (m s _ 1 ) t u r g o r p o t e n t i a l c a l c u l a t e d by s u b t r a c t i n g n e e d l e o s m o t i c p o t e n t i a l f r om t o t a l x y l em p o t e n t i a l (MPa) ip s a v e r age s o i l w a t e r p o t e n t i a l measured o v e r t h e v e r t i c a l e x t e n t o f t h e s e e d l i n g r o o t zone a p p r o x i m a t e l y 0 .5 m f rom t h e s e e d l i n g ( c a l c u l a t e d as t h e a r i t h m e t i c a ve r age o f t h e s o i l w a t e r p o t e n t i a l a t t h e 5 0 , 100 , 200 and 300 mm d e p t h s ) (MPa) - XX -t o t a l n e e d l e xy l em p o t e n t i a l (MPa) *T tx t o t a l t w i g xy l em p o t e n t i a l (MPa) i|> n eed l e o s m o t i c p o t e n t i a l (MPa) i|> n e e d l e o s m o t i c p o t e n t i a l a t f u l l t u r g o r (MPa) V n e e d l e o s m o t i c p o t e n t i a l a t z e r o t u r g o r (MPa) - x x i -ACKNOWLEDGEMENTS I t i s i m p o s s i b l e t o a d e q u a t e l y e x p r e s s t h e e x t e n t o f my g r a t i t u d e t o my w i f e , E l e a n o r , who m a i n t a i n e d a s e e m i n g l y i n e x a u s t i b l e r e s e r v o i r o f p a t i e n c e f o r t h e d u r a t i o n o f my s t u d i e s a t U . B . C . I t hank her f o r h e r encouragement and f o r her s u p p o r t , bo th f i n a n c i a l and e m o t i o n a l , w i t h o u t wh i ch I c o u l d not have comp l e t ed my t h e s i s . I t i s a p l e a s u r e a l s o t o r e c o r d my t h a n k s t o D r . T . A . B l a c k , my academic s u p e r v i s o r , f o r h i s g u i d a n c e , a s s i d u i t y and f r i e n d s h i p . I t hank t h e o t h e r members o f my s u p e r v i s o r y c omm i t t e e : D r . M.D. Novak, D r . T .M . B a l l a r d , and D r . L . F . E b e l l f o r t h e i r a d v i c e and a s s i s t a n c e d u r i n g my P h . D . p r o g r a m . I am g r e a t l y i n d e b t e d t o Doug Beames who not o n l y p r o v i d e d i n v a l u a b l e h e l p and e x p e r i e n c e i n v i r t u a l l y e v e r y a s p e c t o f t h e d e s i g n and c o n s t r u c t i o n o f t h e po romete r but was a l s o a good f r i e n d . I t hank M r . J . Ba ranowsk i f o r m a c h i n i n g t h e po romete r chamber and Bob S t a t h e r s f o r h i s c o l l a b o r a t i o n d u r i n g my r e s e a r c h , and a l s o D r . D .L . S p i t t l e h o u s e f o r h i s s u p p o r t and i n t e r e s t i n my wo rk . I have g r e a t l y en j oyed my s t a y i n t h e Depar tment o f S o i l S c i e n c e not l e a s t because o f t h e f r i e n d l y and s t i m u l a t i n g a tmosphere c r e a t e d by my c o l l e a g u e s whom I t h a n k . I s h a l l m i s s our l u n c h - t i m e d i s c u s s i o n s . I am v e r y g r a t e f u l t o M a c M i l l a n - B l o e d e l L t d . , who p r o v i d e d t h e o p p o r t u n i t y f o r me t o conduc t t h i s r e s e a r c h , and i n p a r t i c u l a r t o M r . G. Dunsworth who i n i t i a t e d t h e r e s e a r c h p r o j e c t wh i ch was m a i n l y s u p p o r t e d by S e c t i o n 88 f unds f rom t he B .C . M i n i s t r y o f F o r e s t s . A d d i t i o n a l f unds were p r o v i d e d by c o n t r a c t s f rom t he B .C . S c i e n c e C o u n c i l and a g r a n t f rom the N a t u r a l S c i e n c e and E n g i n e e r i n g Resea r ch C o u n c i l . - 1 -INTRODUCTION I t i s now g e n e r a l l y r e c o g n i z e d t h a t t he s u p p l y o f t i m b e r i n t he P a c i f i c N o r t h w e s t , once c o n s i d e r e d i n e x h a u s t i b l e , i s f a r f rom l i m i t l e s s and t h a t o n l y i n t e n s i v e r e f o r e s t a t i o n o p e r a t i o n s w i l l e n su r e t h a t y i e l d s can be s u s t a i n e d . P u b l i c c on ce rn has been somewhat assuaged w i t h t h e p a s s i n g o f a c t s such as t h e F o r e s t P r a c t i c e s A c t , i n Oregon i n 1972 , and the F o r e s t Act i n B r i t i s h Co l umb ia i n 1978 , wh i ch makes i t a l e g a l o b l i g a t i o n f o r t e n u r e h o l d e r s t o s u c c e s s f u l l y r e f o r e s t c u t o v e r l a n d s . R e f o r e s t a t i o n s u c c e s s on Vancouver I s l a n d , B .C . has been l i m i t e d by w a t e r s t r e s s wh i ch i s c o n s i d e r e d to be the s i n g l e most i m p o r t a n t cause o f c o n i f e r s e e d l i n g m o r t a l i t y i n t he f i r s t f i v e y e a r s a f t e r p l a n t i n g ( A r n o t t 1 9 7 5 ) . S e e d l i n g e s t a b l i s h m e n t i s p a r t i c u l a r l y d i f f i c u l t on exposed s o u t h - f a c i n g s l o p e s . T h i s p rob lem l e d t o a t h r e e y e a r s t u d y , s u p p o r t e d by B .C . M i n i s t r y o f F o r e s t s S e c t i o n 88 f u n d s , o f t h e wa te r r e l a t i o n s , s u r v i v a l and g rowth o f c o n i f e r s e e d l i n g s p l a n t e d on a c l e a r c u t l o c a t e d on Mount A r r o w s m i t h , Vancouver I s l a n d . The s i t e was s e l e c t e d because i t had a h i s t o r y o f p l a n t i n g f a i l u r e s , none o f wh i ch c o u l d be s a t i s f a c t o r i l y e x p l a i n e d . As p a r t o f t h e s t udy S t a t h e r s (1983) c o n c l u d e d t h a t h i gh s u r f a c e t e m p e r a t u r e s were l i k e l y a ma jo r c ause o f s e e d l i n g m o r t a l i t y . The s t u dy began i n A p r i l 1981 when n e a r l y 3,000 s e e d l i n g s were p l a n t e d a t the s i t e . These c o n s i s t e d o f equa l number o f D o u g l a s - f i r , wes t e rn hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s . The s e e d l i n g s were l a i d out i n a randomized c o m p l e t e - b l o c k d e s i g n t o t e s t whether t r e a t m e n t s such as t he p r o v i s i o n o f shade c a r d s o r i n c l i n i n g t h e - 2 -s e e d l i n g s t o t h e sou thwes t wou ld i n c r e a s e s u r v i v a l even i n t h o s e s p e c i e s , such as P a c i f i c s i l v e r f i r , wh i ch n o r m a l l y canno t t o l e r a t e such s i t e s . In May 1982 a p p r o x i m a t e l y 1,000 a d d i t i o n a l s e e d l i n g s were p l a n t e d u s i n g t h e same s p e c i e s , p r ovenance and s t o c k t y p e as i n t h e p r e v i o u s y e a r . F ou r t r e a t m e n t s were t e s t e d : shade ( p r o v i d e d by shade c a r d s ) , i r r i g a t i o n ( w a t e r was p r o v i d e d by a t r i c k l e i r r i g a t i o n sys tem) shade and i r r i g a t i o n , and no shade and no i r r i g a t i o n . I r r i g a t i o n was used w i t h t h e r a t i o n a l e t h a t i t m igh t be p o s s i b l e t o s e p a r a t e t h e e f f e c t s o f h i g h s o i l s u r f a c e t e m p e r a t u r e , h i g h e v a p o r a t i v e demand and low s o i l w a t e r p o t e n t i a l on s e e d l i n g s u r v i v a l . The r e s u l t s o f t h i s s t u d y fo rm t h e b a s i s o f t h e t h r e e c h a p t e r s c o m p r i s i n g t h i s t h e s i s , wh i ch has been w r i t t e n i n paper f o r m a t . In C h a p t e r 1, t h e s e a sona l and d i u r n a l c o u r s e o f t w i g xy l em p o t e n t i a l , t u r g o r p o t e n t i a l and o s m o t i c p o t e n t i a l and t h e r e l a t i o n s h i p between s e e d l i n g t r a n s p i r a t i o n and s o i l wa t e r p o t e n t i a l f o r t h e t h r e e s p e c i e s a r e p r e s e n t e d , as a r e t h e e f f e c t s o f s h a d i n g and t r i c k l e i r r i g a t i o n on bo th s e e d l i n g wa t e r use and s e e d l i n g s u r v i v a l . F i n a l l y s e e d l i n g s u r v i v a l i s d i s c u s s e d i n r e l a t i o n t o d r ough t t o l e r a n c e mechan i sms . In C h a p t e r 2 , t h e s t o m a t a l r e s pon s e s o f each o f t h e t h r e e s p e c i e s , t o e n v i r o n m e n t a l and p h y s i o l o g i c a l v a r i a b l e s a r e d e s c r i b e d . Changes i n t h e s e r e s p o n s e s o v e r two y e a r s and d i f f e r e n c e s i n r e s p o n s e s between one and two y e a r o l d s e e d l i n g s o f t h e same s p e c i e s a r e a l s o d i s c u s s e d . F i n a l l y , a b o u n d a r y - l i n e a n a l y s i s model o f s t o m a t a l b e h a v i o u r , based on measured s t o m a t a l r e s p o n s e s , i s d e v e l o p e d . V a l u e s o f s t o m a t a l c o n d u c t a n c e , g e n e r a t e d by t h i s model a r e combined w i t h measured h o u r l y - 3 -a v e r a g e s o f vapour p r e s s u r e d e f i c i t , and l e a f a r ea to e s t i m a t e d a i l y s e e d l i n g wa te r u s e . In Chap t e r 3 , t h e e f f e c t s o f i r r i g a t i o n , shade and a c o m b i n a t i o n o f t h e s e t r e a t m e n t s on t h e mon th l y shoo t h e i g h t and l e a f a r e a , and s ea sona l r o o t and shoo t d r y m a t t e r a c c u m u l a t i o n o f each o f t h e s p e c i e s i s r e p o r t e d . The s ea sona l wa te r use and ave rage s ea sona l s t o m a t a l c o n d u c t a n c e o f s e e d l i n g s a r e c a l c u l a t e d u s i n g the model d eve l oped i n C h a p t e r 1, and a r e r e l a t e d t o d r y m a t t e r p r o d u c t i o n ove r t h e same p e r i o d . The wa te r use e f f i c i e n c y o f each s p e c i e s i s t hen e s t i m a t e d . Append i x I d e s c r i b e s t he t e c h n i q u e used t o g e n e r a t e p r e s s u r e - v o l u m e c u r v e s f o r t he d e t e r m i n a t i o n o f s e e d l i n g o smo t i c p o t e n t i a l . Append i x I I i s a p r e v i o u s l y p u b l i s h e d paper t h a t d e s c r i b e s t h e d e s i g n and t e s t i n g o f t h e s e e d l i n g po romete r used i n t h i s s t u d y . REFERENCES A r n o t t , J . T . 1975 . F i e l d pe r f o rmance o f c o n t a i n e r - g r o w n and b a r e r o o t t r e e s i n C o a s t a l B r i t i s h C o l u m b i a . Can . J . F o r . Re s . 5: 1 8 6 - 1 9 5 . S t a t h e r s , R . J . 1983 . A s t u dy o f s o i l t e m p e r a t u r e and s e e d l i n g s u r v i v a l i n a f o r e s t c l e a r c u t . M .Sc . T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , V an c ouve r , B . C . , Canada . - 4 -CHAPTER 1 WATER STRESS AND SURVIVAL OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT - 5 -WATER STRESS AND SURVIVAL OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT I . INTRODUCTION Wate r s t r e s s r e s u l t i n g f rom d r o u g h t i s c o n s i d e r e d t o be one o f the ma jo r f a c t o r s l i m i t i n g c o n i f e r s e e d l i n g r e g e n e r a t i o n i n t h e P a c i f i c N o r t h w e s t ( A r n o t t 1 9 7 5 ) . S t r e s s a r i s e s t h r ough a p l a n t ' s i n a b i l i t y t o m a i n t a i n adequa te c e l l t u r g o r i n c o n d i t i o n s o f h i g h a t m o s p h e r i c e v a p o r a t i v e demand o r low s o i l w a t e r p o t e n t i a l . P r o l o n g e d s t r e s s can have ma j o r e f f e c t s on p l a n t deve l opmen t and morpho logy (Wa l t on 1980; Wa t t s et a]_. 1 9 8 1 ) . Even low l e v e l s o f s t r e s s can a d v e r s e l y a f f e c t g rowth ( H s a i o e t j i l _ . 1 9 7 6 ) . J o n e s (1983) has d e f i n e d the a b i l i t y o f p l a n t s t o s u r v i v e d r ough t as d r ough t t o l e r a n c e . Mechan isms t h a t c o n t r i b u t e t o d r o u g h t t o l e r a n c e can be s e p a r a t e d i n t o two g r oups : ( i ) s t r e s s a v o i d a n c e mechanisms t h a t m i n i m i z e t he o c c u r r e n c e o f damaging wa t e r d e f i c i t s , and ( i i ) s t r e s s t o l e r a n c e mechanisms t h a t m a i n t a i n p h y s i o l o g i c a l a c t i v i t y as p l a n t water-d e f i c i t s i n c r e a s e . One e x t r e m e l y i m p o r t a n t s t r e s s t o l e r a n c e mechanism i s o smo t i c a d j u s t m e n t whereby c e l l t u r g o r i s m a i n t a i n e d by means o f i n c r e a s e s i n c e l l s o l u t e c o n c e n t r a t i o n ( B e r n s t e i n 1961 ; Osmond 1963; H s a i o j i t ^ ] _ . 1 9 7 6 ) . F u l l t u r g o r ma i n t enan ce o c c u r s when t he c e l l o s m o t i c p o t e n t i a l d e c r e a s e s a t t he same r a t e as t he t o t a l p o t e n -t i a l o f t he c e l l {yj) w h i l e p a r t i a l t u r g o r ma i n t enance o c c u r s when the d e c r e a s e i n i s l e s s than t h a t i n ¥j. O smo t i c a d j u s t m e n t has been o b s e r v e d i n many wood p l a n t s ( Ty ree et a l_. 1978; P a r k e r £ t _aU 1982; R i t c h i e and S h u l a 1984) . - 6 -T r e a t m e n t s t h a t mod i f y s e e d l i n g m i c r o c l i m a t e can a f f e c t bo th t he d u r a t i o n and l e v e l o f w a t e r s t r e s s . Shade c a r d s , f o r e xamp l e , were e f f e c t i v e i n i n c r e a s i n g s e e d l i n g s u r v i v a l on s i t e s i n Oregon (Hobbs e t al_. 1 9 8 0 ) . D r i p i r r i g a t i o n o f s e e d l i n g s was e f f e c t i v e i n bo th r a i s i n g s o i l w a t e r p o t e n t i a l and d e c r e a s i n g s o i l t e m p e r a t u r e ( S t a t h e r s 1 9 8 3 ) . The o b j e c t i v e o f t h i s c h a p t e r i s t o d e s c r i b e t he s e a s ona l and d i u r n a l c o u r s e s o f s e e d l i n g t w i g xy l em w a t e r p o t e n t i a l , t u r g o r p o t e n t i a l , o s m o t i c p o t e n t i a l , t h e r e l a t i o n s h i p between s e e d l i n g t r a n s p i r a t i o n and s o i l w a t e r p o t e n t i a l , and t h e s u r v i v a l o f t h r e e s p e c i e s o f c o n i f e r s p l a n t e d on a s o u t h - f a c i n g h i g h e l e v a t i o n c l e a r - c u t . The e f f e c t s o f s h a d i n g and t r i c k l e i r r i g a t i o n on bo th s e e d l i n g water-r e l a t i o n s and s e e d l i n g s u r v i v a l w i l l be r e p o r t e d . F i n a l l y s e e d l i n g s u r v i v a l w i l l be d i s c u s s e d i n r e l a t i o n t o d r ough t t o l e r a n c e mechan i sms . I I . METHODS A . S i t e D e s c r i p t i o n The e x p e r i m e n t a l s i t e i s l o c a t e d a t an e l e v a t i o n o f 1150 m on a 30° s o u t h - f a c i n g s l o p e on M t . A r r o w s m i t h , V an c ouve r I s l a n d , B r i t i s h Co l umb i a (49° 13 ' N, 124° 3 6 ' W ) . T h i s a r e a i s c h a r a c t e r i z e d by e x t e n d e d p e r i o d s o f summer- d r ough t and v e r y h i g h s u r f a c e s o i l t emper -a t u r e s ( S t a t h e r s 1 9 8 3 ) . The s o i l , an O r t h i c H u m o - F e r r i c P o d z o l , i s a g r a v e l l y sandy loam o f v a r i a b l e dep th ( 0 . 4 - 1.2 m) and v o l u m e t r i c c o a r s e f r a gmen t s ( 0 . 15 - 0.65 g r e a t e r t h a n 2 mm) o v e r compact g l a c i a l t i l l . The s i t e was h a r v e s t e d i n 1974 ( J . D r i b u r g , M a c M i l l a n B l o e d e l L t d . , p e r s o n a l c ommun i c a t i on ) and i s c o v e r e d by a canopy o f f i r e w e e d - 7 -( E p i l o b i u m a n g u s t i f o l i u m L . ) . L u p i n e ( L u p i n u s l a t i f o l i u s A g a r d b . ) and s a l a l ( G a u l t h e r i a s h a l l o p P u r s h . ) . The a d j a c e n t n a t u r a l f o r e s t c o n s i s t s o f a p r e d o m i n a n t l y D o u g l a s - f i r ( P s eudo t s uga m e n z i e s i i ( M i r b . ) F r a n c o ) o v e r s t o r y and w e s t e r n hemlock (Tsuga h e t e r o p h y l l a ( R a f . S a r g . ) u n d e r s t o r y . B. E x p e r i m e n t a l D e s i g n D u r i n g the f i r s t two weeks o f A p r i l 1 9 8 1 , 2 ,880 s e e d l i n g s were p l a n t e d on t he s i t e , 1.5 m a p a r t . T he r e were equa l numbers o f h i g h -e l e v a t i o n p r o venan ce s o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r ( A b i e s a m a b i l i s ( D o u g l . ) F o r b e s ) 1-0 c o n t a i n e r - g r o w n s t y r o -p l u g s . The s e e d l i n g s were k e p t i n c o l d s t o r a g e f o r f o u r months p r i o r t o p l a n t i n g . They were p l a n t e d i n m i n e r a l s o i l wh i c h r e q u i r e d the remova l o f t h e s u r f a c e o r g a n i c l a y e r wh i ch ranged be tween 0 .00 and 0 .05 m i n t h i c k n e s s . The s e e d l i n g s were l a i d ou t i n a r andom i zed c o m p l e t e - b l o c k d e s i g n t o t e s t t h r e e t r e a t m e n t s f o r each o f t h e t h r e e s p e c i e s . The n i n e s p e c i e s - t r e a t m e n t c o m b i n a t i o n s were r e p l i c a t e d i n 32 b l o c k s ( e i g h t o f t h e s e b l o c k s were s u b s e q u e n t l y used f o r d e s t r u c t i v e s a m p l i n g and were no t i n c l u d e d i n any s t a t i s t i c a l a n a l y s i s o f g rowth and s u r v i v a l ) . Shade was p r o v i d e d i n two o f t h e t r e a t m e n t s . In one ( h e r e a f t e r -r e f e r r e d to as t h e s e l f - s h a d i n g t r e a t m e n t ) t he s e e d l i n g s were p l a n t e d i n c l i n e d t o t h e s ou t hwes t so t h a t r o o t c o l l a r wou l d be shaded by the f o l i a g e d u r i n g the m i d d l e o f t h e d a y . In t h e o t h e r shade t r e a t m e n t ( h e r e a f t e r r e f e r r e d t o as t he shade c a r d t r e a t m e n t ) shade was p r o v i d e d by a 0 .2 m h i g h x 0 .3 m w i de waxed c a r d b o a r d shade c a r d ( m a n u f a c t u r e d by - 8 -I n t e r n a t i o n a l F o r e s t S u p p l i e s , Eugene , O r egon , U . S . A . ) w h i c h was p l a c e d abou t 0.05 m to t he s ou t hwes t o f t h e s t e m . The shade c a r d was s l o p e d abou t 10 - 20° back o v e r t he s e e d l i n g t o e n su r e t h a t shade wou l d be p r o v i d e d a t sma l l s o l a r z e n i t h a n g l e s . In t h e t h i r d t r e a t m e n t ( c o n t r o l ) s e e d l i n g s were p l a n t e d v e r t i c a l l y and w i t h o u t shade c a r d s . D u r i n g the f i r s t two weeks o f May 1982, a n o t h e r 1,080 s e e d l i n g s were p l a n t e d . Seven hundred and twen ty o f t h e s e were used t o c r e a t e e i g h t a d d i t i o n a l b l o c k s ( t h e r e m a i n i n g 360 s e e d l i n g s were used f o r d e s t r u c t i v e s a m p l i n g ) . The same t h r e e s p e c i e s , p r o v e n a n c e , s t o c k t y p e and p l a n t i n g t e c h n i q u e were used as i n t he p r e v i o u s y e a r . The r e were f o u r t r e a t m e n t s : shade ( p r o v i d e d by shade c a r d s o f t h e same s i z e and p l a c e d i n t he same p o s i t i o n as i n t h e p r e v i o u s y e a r ) , i r r i g a t i o n , shade and i r r i g a t i o n and no shade and no i r r i g a t i o n ( c o n t r o l ) . I r r i g a t i o n was chosen as a t r e a t m e n t i n o r d e r t o ( i ) s e p a r a t e t h e e f f e c t s o f s o i l s u r f a c e t e m p e r a t u r e ( S t a t h e r s 1983), s o i l w a t e r s u p p l y , and e v a p o r a t i v e demand on s e e d l i n g w a t e r s t r e s s and s t o m a t a l c ondu c t an c e and ( i i ) t o d e t e r m i n e the e f f e c t o f s u s t a i n e d h i g h s o i l w a t e r p o t e n t i a l on s e e d l i n g s u r v i v a l and d e ve l o pmen t . A t r i c k l e i r r i g a t i o n sys tem (components m a n u f a c t u r e d by D r i p - E z e S y s t e m s , El C a j o n , C a l i f o r n i a , U . S .A . ) was i n s t a l l e d t o s upp l y w a t e r t o t h e i r r i g a t e d s e e d l i n g s . Water was s i p h o n e d f rom a 3,500-L c a p a c i t y f i r e t r u c k t o a g a s o l i n e - p o w e r e d pump t h a t d e l i v e r e d w a t e r t h r ough d r i p e m i t t e r s t o i n d i v i d u a l s e e d l i n g s . D u r i n g i r r i g a t i o n each s e e d l i n g r e c e i v e d a p p r o x i m a t e l y n i n e l i t r e s o f w a t e r p e r hour f o r t h r e e t o four-h o u r s . Water was a p p l i e d when t e n s i o m e t e r s on t he s i t e i n d i c a t e d t h a t t he s o i l w a t e r p o t e n t i a l ( Y S ) was l e s s t h an -0.04 MPa. - 9 -C . Measurements 1. G r ow i ng Season Wea the r O b s e r v a t i o n s In 1 9 8 1 , 1982 and 1983 s t a n d a r d f o r e s t m i c r o c l i m a t e measurements were made f rom May u n t i l O c t o b e r . G l o b a l s o l a r i r r a d i a n c e was measured w i t h a h o r i z o n t a l l y p o s i t i o n e d p y r anome t e r (Model L i - 2 0 0 S , L i - c o r I n c . , L i n c o l n , N e b r a s k a , U . S . A . ) wh i ch was c a l i b r a t e d w i t h a l a b o r a t o r y s t a n d a r d p y r anome t e r (K i pp and Z o n e n , D e l f t , H o l l a n d ) a t t h e b e g i n n i n g and end o f each s e a s o n . R a i n f a l l was measu red w i t h a t i p p i n g b u c k e t r a i n gauge (Model RG2501, S i e r r a M i s c o , I n c . , B e r k e l e y , C a l i f o r n i a , U . S . A . ) wh i ch had a r e s o l u t i o n o f 1 mm. R e l a t i v e h u m i d i t y and a i r -t e m p e r a t u r e a t the 1 m h e i g h t was measured w i t h a s u l p h o n a t e d p o l y s t y r e n e s e n s o r (Model 2 0 1 , P h y s - C h e m i c a l R e s e a r c h C o r p . , New Y o r k , N . Y . , U . S . A . ) and t h e r m i s t o r (Model UUT -51 J1 , Fenwal E l e c t r o n i c s C o r p o r a t i o n , F ramingham, M a s s . , U . S . A . ) , r e s p e c t i v e l y . The c a l i b r a t i o n o f t he r e l a t i v e h u m i d i t y s e n s o r wh i ch was f r e q u e n t l y che cked i n t he f i e l d u s i n g an Assmann p s y c h r o m e t e r , d i d no t change s i g n i f i c a n t l y d u r i n g t h e g r ow i ng s e a s o n . Wind speed was measured a t t he 0 .4 m h e i g h t w i t h a cup anemometer (Model 014A Met-One, S u n n e y v a l e , C a l i f o r n i a , U . S . A . ) w h i c h had a s t a l l i n g speed o f 0.5 m s " 1 . Da ta was r e c o r d e d as one hour-a ve r age s o r t o t a l s u s i n g a Model CR-21 da t a l o g g e r (Campbe l l S c i e n t i f i c , L o g a n , U t a h , U . S . A . ) , s t o r e d on a u d i o c a s s e t t e t a p e and l a t e r -t r a n s f e r r e d t o a m i c r o c o m p u t e r f o r p r o c e s s i n g . 2 . Roo t Zone S o i l Wa te r P o t e n t i a l S o i l w a t e r p o t e n t i a l s g r e a t e r than - 0 . 1 MPa were measured u s i n g t e n s i o m e t e r s i n s t a l l e d on two p l o t s . The t e n s i o m e t e r s , s i m i l a r t o - 10 -t h o s e d e s c r i b e d by Van Bave l e t ( 1 9 6 8 ) , had po rous c e r a m i c cups ( S o i l M o i s t u r e Equ ipment C o r p . , S a n t a B a r b a r a , C a l i f o r n i a , U . S . A . ) w i t h an a i r - e n t r y v a l u e o f 0 .1 MPa. A c c e s s h o l e s were made by d r i v i n g a 12 mm d i a m e t e r s t e e l r od v e r t i c a l l y i n t o t h e s o i l t o t h e d e s i r e d d e p t h . Abou t 1 cm 3 o f m o i s t sand was pou red i n t o an a c c e s s h o l e b e f o r e a t e n s i o m e t e r was i n s e r t e d . P a i r s o f t e n s i o m e t e r s 300 mm a p a r t were i n s t a l l e d a t t he 5 0 , 100 , 150 , 200 , 300 and 500 mm d e p t h s . S o i l w a t e r p o t e n t i a l s l e s s t h a n - 0 . 1 MPa were measured u s i n g Model PCT-55 t h e r m o c o u p l e p s y c h r o m e t e r s (Wescor I n c . , L ogan , U t a h , U . S . A . ) w i t h a Model HR-33T dew p o i n t m i c r o v o l t m e t e r (Wescor I n c . ) on p s y c h r o -m e t r i c and dew p o i n t modes. P a i r s o f t h e rmocoup l e p s y c h r o m e t e r s , 300 mm a p a r t , were i n s t a l l e d i n t h e same p l o t s and a t t h e same dep th s as t h e t e n s i o m e t e r s . A 150-mrn by 300-mrn h o l e was e x c a v a t e d t o bed rock abou t 500 mm f r om a s e e d l i n g on each o f t h e p l o t s . Two a c c e s s h o l e s a t each o f t he above dep ths were made by d r i v i n g a 9-mm d i a m e t e r s t e e l rod about 100 mm i n t o t h e s i d e o f t h e h o l e n e a r e s t t h e s e e d l i n g . S t o n e - f r e e s o i l was l i g h t l y packed a round the t h e rmocoup l e p s y c h r o m e t e r a f t e r i t had been pushed t o t h e end o f t h e a c c e s s h o l e . Most o f t h e t h e r m o c o u p l e p s y c h r o m e t e r w i r e was t hen b u r i e d i n t h e l a r g e h o l e wh i ch was r e f i l l e d a f t e r a l l t h e t h e rmocoup l e p s y c h r o m e t e r s had been i n s t a l l e d . Measurements o f fs were t a k e n e ve r y two t o s i x days f rom mid-May u n t i l t h e end o f September i n each y e a r . The ave r age r o o t zone v a l u e o f ¥ s was c a l c u l a t e d as the a r i t h m e t i c a ve r age o f a l l t h e t e n s i o m e t e r o r t h e r m o c o u p l e p s y c h r o m e t e r measurements t o a dep th o f 300 mm. - 11 -3 . T o t a l Tw i g Xy l em Wate r P o t e n t i a l and Osmo t i c P o t e n t i a l T o t a l t w i g xy l em w a t e r p o t e n t i a l ( T j t x ) w a s measured w i t h a p r e s s u r e chamber (PMS I n c . , C o r v a l l i s , O r egon , U . S . A . ) . The g r a v i t a -t i o n a l component , wh i ch i s ve ry s m a l l f o r s e e d l i n g s (Kaufmann 1 9 7 7 ) , was n e g l e c t e d . Tw igs r a n g i n g f rom 30 t o 60 mm i n l e n g t h were removed f rom s e e d l i n g s w i t h s u r g i c a l s c i s s o r s , s e a l e d i n Z i p l o c bags (Dow Chem i c a l C o r p . , I n d i a n a p o l i s , I n d . , U . S . A . ) c o n t a i n i n g damp t i s s u e , and t r a n s -p o r t e d t o t h e p r e s s u r e chamber where measurements o f y y t x w e r e o b t a i n e d w i t h i n 2 - 4 m i nu t e s o f e x c i s i o n . No more t han 2 t w i g s were removed f r om any s e e d l i n g . H o u r l y measurements o f Y j t x w e r e m a c ' e o n a l l t h r e e s p e c i e s on s e l e c t e d days d u r i n g t he t h r e e y e a r s o f f i e l d o b s e r v a t i o n s . Measurements o f ^ were o b t a i n e d u s i n g Model C-52 t h e r m o c o u p l e p s y c h r o m e t e r chambers (Wescor I n c . ) w i t h an HR-33T dew p o i n t m i c r o -v o l t m e t e r . Between May 1982 and March 1983 , and May and O c t o b e r 1983 , measurements o f ^ were made e v e r y t h r e e t o f o u r w e e k s . A t p redawn, between 10 - 15 n e e d l e s were removed f rom a s e l e c t e d s e e d l i n g and t h e i r sap e x t r a c t e d w i t h m o d i f i e d v i c e - g r i p s t h a t squashed them between two 6 .3 mm d i a m e t e r d i s c s o f f i l t e r p a p e r . The use o f v i c e - g r i p s e n su r ed t h a t t h e same p r e s s u r e wou l d be e x e r t e d on d i f f e r e n t s a m p l e s . The s a t u r a t e d d i s c s were i m m e d i a t e l y wrapped i n p a r a f i l m and p l a c e d i n a i r -t i g h t v i a l s , whose open i ng s were c o v e r e d w i t h p a r a f i l m and c a p p e d . The v i a l s were t hen p l a c e d i n a thermos f l a s k c o n t a i n i n g a s o l u t i o n o f d ry i c e and a c e t one t o p r e v e n t any c h e m i c a l t r a n s f o r m a t i o n o c c u r r i n g i n t h e sap d u r i n g s t o r a g e . Sap was e x t r a c t e d f r om the n e e d l e s b e f o r e f r e e z i n g b e c a u s e , d u r i n g t h e f r e e z i n g and t h a w i n g o f p l a n t t i s s u e , c e l l membranes - 12 -a r e r u p t u r e d and a p o p l a s t i c w a t e r d i l u t e s sap f rom t he s y m p l a s t ( M a r k h a r t e t al_. 1981; Campbe l l e t a]_. 1979; T y r e e 1 9 7 6 ) . Samples c o l -l e c t e d i n t h e f i e l d were a lways a n a l y s e d w i t h i n 48 h o u r s . Samples were thawed w i t h i n f i v e m i nu t e s o f t h e i r remova l f r om the v i a l s . T h i s m i n i -m i z e d p o s s i b l e e n z y m a t i c h y d r o l y s i s o f s t a r c h and s uga r s wh i c h l o w e r s t h e o s m o t i c p o t e n t i a l o f t h e sap ( Tu rne r e t 1979; Brown and Tanne r 1 9 8 3 ) . Each thawed d i s c was p l a c e d i n a t h e r m o c o u p l e p s y c h r o m e t e r sample chamber wh i ch had been c a l i b r a t e d u s i n g KC1 s a l t s o l u t i o n s o f known o s m o t i c p o t e n t i a l . The sample chamber was k e p t i n a s t y r o f o a m box f o r a minimum o f 15 m i nu t e s t o a l l o w t he rma l g r a d i e n t s t o d i s s i p a t e b e f o r e measurement . The sample ^ was o b t a i n e d u s i n g t he dew p o i n t mode a f t e r t he t h e rmocoup l e c o o l i n g c o e f f i c i e n t had been a d j u s t e d f o r t h e t e m p e r a t u r e . Th ree r e p l i c a t e measurements were made f o r each sample u s i n g t h r e e s e p a r a t e C-52 chambe r s . The t u r g o r p o t e n t i a l ( ?p ) was c a l c u l a t e d by s u b t r a c t i n g yn f r om Ty t x* T h i s method was v a l i d a t e d by c ompa r i ng measurements o f w% w i t h d e t e r m i n a t i o n s o f ln a t f u l l t u r g o r ( i . e . Y ^ ) o b t a i n e d u s i n g w a t e r -r e l e a s e c u r v e s as d e s c r i b e d by S c h o l a n d e r e t al_. (1965) and Brown and Tanne r ( 1 9 8 3 ) . The two measurements a r e e x p e c t e d t o show good ag reement because d a t a f rom w a t e r - r e l e a s e c u r v e s i n d i c a t e d t h a t d i f f e r e n c e s between ^ n a t f u l l t u r g o r and z e r o t u r g o r d i d no t e x ceed 0 .3 MPa (Append i x 1 ) . W a t e r - r e l e a s e c u r v e s were g e n e r a t e d f o r t e n s e e d l i n g s o f each s p e c i e s . B e f o r e e x c i s i o n o f t h e s e e d l i n g s a t predawn t he two h a l v e s o f a p o l y s t y r e n e cup wh i ch had been c u t a l o n g i t s l o n g i t u d i n a l a x i s were g l u e d t o g e t h e r a round t h e base o f t h e s e e d l i n g s t e m . The cup was f i l l e d w i t h w a t e r and t he immersed stem e x c i s e d abou t 5 cm f rom the - 13 -b a s e . The s h o o t was l e f t t o r e h y d r a t e i n t h e dark f o r a minimum o f 12 hours b e f o r e a w a t e r - r e l e a s e c u r v e was g e n e r a t e d . A t t h i s t i m e n e e d l e s were removed f r om the shoo t f o r t h e d e t e r m i n a t i o n o f yv u s i n g t he f r o z e n sap me thod . F i g u r e 1.1 shows t he r e s u l t s o f 30 c o m p a r i s o n s o f t h e two me thods . W h i l e t h e r e was e x c e l l e n t ag r eemen t , vv o f t he f r o z e n sap was g e n e r -a l l y s l i g h t l y h i g h e r t han o b t a i n e d f r om t h e r e l e a s e c u r v e s . T h i s m i g h t have been t he r e s u l t o f damage t o c e l l membranes and sub sequen t d i l u t i o n o f t h e sap w i t h a p o p l a s t i c w a t e r d u r i n g t he e x t r a c t i o n p r o c e s s u s i n g t he v i c e - g r i p s . 4 . S e e d l i n g T r a n s p i r a t i o n The t r a n s p i r a t i o n r a t e o f shaded s e e d l i n g s was e s t i m a t e d u s i n g E = ( e n - e a ) / ^ - 1 + g b ^ H R v T ' ) (1 ) where R v i s t h e gas c o n s t a n t f o r w a t e r v a p o u r , T ' i s t he a b s o l u t e a i r t e m p e r a t u r e , e n i s t he s a t u r a t e d vapour p r e s s u r e o f t he s t o m a t a l c a v i -t i e s (assumed t o equa l t h e s a t u r a t e d vapou r p r e s s u r e a t n eed l e t e m p e r a -t u r e ) , e a i s t h e vapour p r e s s u r e o f t h e a i r , g s i s t he ave r age hypo -s t o m a t a l c o n d u c t a n c e o f t h e s e e d l i n g , and i s t he ave r age boundary l a y e r c o n d u c t a n c e . The boundary l a y e r c o n d u c t a n c e (cm s _ 1 ) o f t h e n e e d l e s on s e e d l i n g s b e h i n d shade c a r d s was e s t i m a t e d u s i n g ^ = ( l / 1 . 8 4 ) ( u / d n ) 1 / 2 (2 ) - 14 -Release Curve l|>no (MPa) Figure 1.1 Measurements of osmotic potent ia l at f u l l turgor obtained from water-re lease curves (^Q) versus those obtained from prev ious ly frozen sap for Doug las - f i r (DF), western hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) . - 15 -where d n i s t he n eed l e d i a m e t e r i n m and u i s t he w i nd speed i n m s~l ( S p i t t l e h o u s e and B l a c k 1 9 8 2 ) . T h i s assumes a s h e l t e r f a c t o r o f 1, g i v e n the r e l a t i v e l y low d e n s i t y and open s t r u c t u r e o f t h e s e e d l i n g f o l -i a g e ( L and sbe r g e t a]_. 1 9 7 1 ) . T h i s a s s u m p t i o n i s s u p p o r t e d by r e s u l t s f r o m G r a n t (1983) who s u g g e s t s t h a t f o r low w i nd speed s (< 1.5 m s _ 1 ) m i c r o s c a l e t u r b u l e n c e i s such t h a t t h e f l o w ' s e e s ' the s h o o t as a h i g h l y po rous t w i g c y l i n d e r w i t h a l e n g t h s c a l e r e l a t e d t o n eed l e l e n g t h . A e r odynam i c t h e o r y , u s i n g v a l u e s o f s u r f a c e roughness d e t e r m i n e d by S t a t h e r s e t a l_. (1985) f o r the Mount A r r o w s m i t h s i t e , i n d i c a t e d t h a t w i n d speed s a t s e e d l i n g h e i g h t ( e . g . 0 .15 m) a r e a minimum o f 50% o f t h o s e a t 0 .4 m h e i g h t . F u r t h e r m o r e , measurements o f w i nd speed b e h i n d a shade c a r d u s i n g a hot w i r e anemometer i n d i c a t e d t h a t t y p i c a l l y w i nd speeds a r e n eve r l e s s t h an 10% o f t h o s e a t the same h e i g h t i n t h e open . C o n s e q u e n t l y u b e h i n d the shade c a r d was assumed t o be 5% o f u a t t h e 0 .4 m h e i g h t . In w inds r a n g i n g f r om 0 .5 - 1.0 m s ~ l ( a t 0 .4 m h e i g h t ) t h e c o r r e s p o n d i n g minimum g^, f o r a shaded n eed l e 0 .001 m i n d i a m e t e r , wou l d range f r om 2.3 t o 3.9 cm s _ 1 . The s m a l l e s t o f t h e s e v a l u e s i s a l m o s t s i x t i m e s g r e a t e r t han maximum measured g s f o r D o u g l a s - f i r s e e d l i n g s . The t r a n s p i r a t i o n r a t e o f unshaded s e e d l i n g s was e s t i m a t e d u s i n g a s i m p l i f i e d v e r s i o n o f (1) wh i c h assumes gb i s l a r g e enough t h a t ( e n - e a ) « D, t h e vapour p r e s s u r e d e f i c i t o f t he a i r , and t h a t g D _ 1 i s n e g l i g i b l e compared w i t h g s " 1 . T h i s can be w r i t t e n as (Tan e t a l . 1978; R i h a and Campbe l l 1985) E = D g s / ( R v T ' ) (3) - 16 -E q u a t i o n (3) was used because gb o f unshaded s e e d l i n g s was e s t i m a t e d t o be a t l e a s t 10 t i m e s g s . Tan e t a]_. (1978) s u g g e s t e d t h a t n e g l e c t i n g boundary l a y e r c onduc t an ce compensa tes somewhat f o r t h e u n d e r e s t i m a t e o f E t h a t r e s u l t s f r om u s i n g D as an e s t i m a t e o f t h e vapou r p r e s s u r e d i f f e r e n c e between n eed l e s t o m a t a l c a v i t i e s and t he a i r . V a l u e s o f D a t s c r e e n h e i g h t were u sed s i n c e t h e s e v a l u e s were o n l y 4 - 8 % l e s s t h an t h o s e t h a t had been measured a t s e e d l i n g h e i g h t w i t h t he r e l a t i v e h u m i d i t y and t e m p e r a t u r e s e n s o r s i n t h e CS-102 p o r o -m e t e r . Measurements o f g s were made w i t h a CS-102 t r a n s i e n t t y p e p o r o -me te r (M i c r ome t Sys tems I n c . , V a n c o u v e r , C a n a d a ) . A l l t he s e e d l i n g ' s f o l i a g e i s e n c l o s e d by a s t a i n l e s s s t e e l chamber f o r l e s s t h an one m i nu t e d u r i n g t h i s measurement ( L i v i n g s t o n e t al_. 1984) (Append i x I I ) . H o u r l y measurements o f g s were made on a l l t h r e e s p e c i e s on 16 days between June 10 and September 9 , 1982 , 10 o f wh i c h were sunny a l l day , and on 5 days between J une 6 and Augus t 14 , 1983 . F ou r o f t h e s e days were sunny a l l day . T o t a l p r o j e c t e d l e a f a r e a was d e t e r m i n e d w i t h i n t h r e e weeks o f t he g s measurements e i t h e r d i r e c t l y u s i n g a l e a f a r ea me te r (Model L i - 3 0 0 0 , L i - C o r I n c . , L i n c o l n , N e b r a s k a , U . S . A . ) , o r by u s i n g r e g r e s s i o n e q u a t i o n s t h a t r e l a t e p r o j e c t e d n e e d l e a r e a t o t h e mass o f n e e d l e s d r i e d t o 65°C f o r one day ( L i v i n g s t o n e t al_. 1 9 8 4 ) . S e e d l i n g n eed l e t e m p e r a t u r e was measured w i t h a f i n e w i r e ( 0 . 075 mm) c o p p e r -c o n s t a n t a n t h e r m o c o u p l e . Abou t 40 mm o f t h i s w i r e was wound a round a n eed l e w i t h t h e t h e rmocoup l e j u n c t i o n a t t a c h e d t o t h e n e e d l e ' s u n d e r -s i d e w i t h a drop o f c y a n o a c r y l a t e g l u e . A n o t h e r f i n e w i r e t h e rmocoup l e made f r om t h i s w i r e was p l a c e d a p p r o x i m a t e l y 50 mm b e h i n d a shade c a r d - 17 -and 200 mm above the s o i l s u r f a c e . A r a d i a t i v e s h i e l d was p r o v i d e d by s a n d w i c h i n g t he t h e r m o c o u p l e between two p l a s t i c s p oon s , t h e o u t s i d e s u r f a c e s o f wh i ch were c o a t e d w i t h a l u m i n i z e d m y l a r t a p e . Bo th t he rmo-c o u p l e s were r e f e r e n c e d t o a t h e r m i s t o r the rmomete r l o c a t e d 0 .5 m benea th t h e s o i l s u r f a c e . 5 . S e e d l i n g S u r v i v a l S e e d l i n g s u r v i v a l was a s s e s s e d mon th l y f r om May u n t i l O c t o b e r i n 1 9 8 1 , 1982 and 1983 ( s e e d l i n g h e i g h t , d i s c u s s e d i n C h a p t e r 3 , was measured c o n c u r r e n t l y ) . A v i s u a l r a n k i n g s y s t em was u s e d . In t h i s s y s t em a ' 3 ' was a s s i g n e d t o s e e d l i n g s w i t h no v i s i b l e s i g n s o f c h l o r o s i s o r n e c r o s i s , a ' 2 ' was a s s i g n e d t o s e e d l i n g s w i t h no more t h a n 50% o f t h e i r n e e d l e a r e a a f f e c t e d , a ' 1 ' was a s s i g n e d t o s e e d l i n g s w i t h l e s s t h an 100% but more t h a n 50% o f t h e i r n e e d l e a r e a a f f e c t e d . S e e d -l i n g s whose e n t i r e need l e a r ea was n e c r o t i c were c o n s i d e r e d t o be dead . I I I . RESULTS AND DISCUSSION A . G row ing Season Weather O b s e r v a t i o n s The 1981 g r ow i ng season was c h a r a c t e r i z e d by c o o l and wet wea t h e r f r om t he t i m e the s e e d l i n g s were p l a n t e d u n t i l m i d - J u l y . An e x t e n d e d d r y p e r i o d o c c u r r e d between J u l y 10 and Augus t 26 d u r i n g wh i ch l e s s than 10 mm o f r a i n f e l l . E x t r e m e l y h i g h a i r t e m p e r a t u r e s (maxima ranged f rom 25 - 37°C) and low r e l a t i v e h u m i d i t i e s r e s u l t e d i n vapour p r e s s u r e d e f i c i t s t h a t a t t i m e s exceeded 4 . 5 kPa ( F i g u r e 1 . 2 ) . Roo t zone <ys d e c r e a s e d f r om m i d - J u l y u n t i l t h e end o f Augus t r e a c h i n g a minimum o f - 1 . 7 MPa on Augus t 2 5 , r e f l e c t i n g t h e c o a r s e n a t u r e o f t h e s o i l . A - 18 -v e g e t a t i o n remova l e x p e r i m e n t c o n d u c t e d i n 1983 i n 4 m x 4 m p l o t s , i n wh i ch s o i l w a t e r c o n t e n t was measured w i t h a n e u t r o n p r o b e , i n d i c a t e d t h a t , a t t h e 0 .3 m d e p t h , c ompe t i n g v e g e t a t i o n , such as f i r e w e e d , a c c o u n t s f o r much o f t h e s o i l w a t e r d e p l e t i o n . The g r ow i ng season i n 1982 was c h a r a c t e r i z e d by a wet s p r i n g and a ho t and dry summer. The summer d r o u g h t was b r oken by a s h o r t p e r i o d o f r a i n f a l l i n e a r l y Augus t wh i c h was s u f f i c i e n t t o s i g n i f i c a n t l y r a i s e y s ( F i g u r e 1 . 3 ) . By c o n t r a s t t h e summer o f 1983 was e x c e p t i o n a l l y wet and c o o l . T o t a l r a i n f a l l f r om May t h r o u g h Sep tember was 399 mm. C l o udy and o v e r -c a s t days were f r e q u e n t . The l o n g e s t p e r i o d w i t h o u t a p p r e c i a b l e r a i n -f a l l o c c u r r e d d u r i n g t h e 44 days between J u l y 14 and Augu s t 28 ( F i g . 1 . 4 ) . On t h e b a s i s o f w e a t h e r r e c o r d s f r om P o r t A l b e r n i ( l o c a t e d a p p r o x i m a t e l y 15 km t o t h e s o u t h e a s t o f t h e s i t e ) f o r t h e p r e v i o u s t e n y e a r s , t he w e a t h e r d u r i n g t h e e a r l y p a r t o f t h e g r ow i ng season o f t he d r i e s t o f t h e t h r e e y e a r s ( i . e 1982) was s i m i l a r t o t h e 1 0 - y e a r a v e r a g e f o r t h a t p a r t o f t h e y e a r . B. T o t a l Tw i g Xy l em P o t e n t i a l , N eed l e O smo t i c P o t e n t i a l and T u r g o r  P o t e n t i a l s Predawn v a l u e s o f y j t x f ° r t h e t h r e e s p e c i e s were s i g n i f i c a n t l y l o w e r t h a n Ys when f s > - 0 . 5 MPa ( F i g u r e 1 . 5 ) . F o r Ys < - 0 . 5 MPa v a l u e s o f predawn f T / tx w e r e g e n e r a l l y c l o s e r t o <p s . These r e s u l t s a r e s i m i l a r t o t h o s e f ound by o t h e r w o r k e r s ( C l e a r y 1971 ; H a l l g r e n 1978; K e l l i h e r e t a l_. 1 9 8 4 ) . A l l s p e c i e s e x h i b i t e d a p r o g r e s s i v e d e c r e a s e i n d a i l y minimum r r t x between May and Augus t o f 1981 . T h i s c o r r e s p o n d e d t o a s i m i l a r - 19 -1981 MAY J U N JUL A U G SEP Figure 1.2 Courses of average root zone so i l water potent ia l (i|< s), p r e c i p i t a t i o n (P) and maximum vapour pressure d e f i c i t (D) during the 1981 growing season. - 20 -1982 MAY J U N JUL A U G SEP Figure 1.3 Courses of average root zone s o i l water potent ia l ( * s ) , p r e c i p i t a t i o n (P) and maximum vapour pressure d e f i c i t (D) during the 1982 growing season. F i g u r e 1.4 C o u r s e s o f a v e r a g e r o o t zone s o i l wa t e r p o t e n t i a l (i|>s)» p r e c i p i t a t i o n (P) and maximum vapour p r e s s u r e d e f i c i t (D) d u r i n g t h e 1983 g r ow ing s e a s o n . - 22 -F i g u r e 1.5 R e l a t i o n s h i p between predawn t o t a l t w i g xy l em wa t e r p o t e n t i a l (^Ttx) a n d a v e r age r o o t zone s o i l wa t e r p o t e n t i a l (ii»s) f o r n o n - i r r i g a t e d D o u g l a s - f i r ( D F ) , w e s t e r n hemlock (WH) and P a c i f i c s i l v e r f i r ( P S F ) . Measurements were made i n 1981, 1982 and 1983. A l s o shown i s t h e 1:1 l i n e . L i n e a r r e g r e s s i o n a n a l y s i s i n d i c a t e s predawn ntx fMPa) = 0.863 )s (MPa) - 0.357 ( r 2 = 0.89) (dashed l i n e ) . - 23 -d e c l i n e i n a ve r age r o o t zone v$ ( T ab l e 1 . 1 ) . The d e c r e a s e i n d a i l y minimum ^ j t x was most p ronounced i n D o u g l a s - f i r , f o l l o w e d by w e s t e r n hemlock and t hen P a c i f i c s i l v e r f i r . T h i s was a l s o o b s e r v e d i n 1982 ( F i g u r e s 1 . 6 , 1.7 and 1 . 8 ) . In 1983 r e l a t i v e l y h i g h v a l u e s o f y s and d a i l y minimum YJ^X ( T ab l e 1 .2) p e r s i s t e d a l l summer e x c e p t f o r a s h o r t p e r i o d between J u l y and A u g u s t . Measurements o f were no t made i n 1 9 8 1 . In 1982 b o t h t he i r r i -g a t e d and n o n - i r r i g a t e d t r e a t m e n t s i n a l l s p e c i e s e x h i b i t e d a a p r o g r e s -s i v e d e c r e a s e i n vv d u r i n g the summer ( F i g u r e s 1.6 - 1 . 8 ) . V a l u e s o f "TTT o f n o n - i r r i g a t e d t r e a t m e n t s were a lway s l o w e r t h an t h o s e o f i r r i g -a t e d t r e a t m e n t s , t he d i f f e r e n c e s b e i n g most p ronounced i n D o u g l a s - f i r e s p e c i a l l y i n t he l a t t e r p a r t o f t h e f i e l d s e a s o n . In t he n o n - i r r i g a t e d t r e a t m e n t s t h e g r e a t e s t d e c r e a s e i n ^ o c c u r r e d between J une and J u l y ( c o i n c i d i n g w i t h a r e d u c t i o n i n stem e l o n g a t i o n ) w i t h minimum v a l u e s o c c u r r i n g a t t he end o f t he f i e l d s e a s o n . The o s m o t i c a d j u s t m e n t t h a t o c c u r r e d between May and the f i r s t p e r i o d o f heavy r a i n i n Sep tember was l i k e l y due t o s o l u t e a c c u m u l a t i o n r a t h e r t han c e l l d e h y d r a t i o n because Y,, i n a l l s p e c i e s and t r e a t m e n t s d i d not i n c r e a s e u n t i l March 1 9 8 3 . The low v a l u e s o f measured a t t he end o f t h e summer and t h r o u g h o u t t h e w i n t e r , a r e c o n s i s t e n t w i t h t he w e l l documented phenomenon o f h i g h f o l i a r s u ga r c o n c e n t r a t i o n s o c c u r r i n g i n many woody p l a n t s p e c i e s t h a t i s a s s o c i a t e d w i t h c o l d h a r d i n e s s ( L e v i t t 1 9 8 0 ) . V a l u e s o f ^ i n shaded s e e d l i n g s were no t s i g n i f i c a n t l y d i f f e r e n t t o t h o s e i n unshaded s e e d l i n g s ( T ab l e 1 . 3 ) . Obse r ved v a l u e s o f ^ f o r t h e i r r i g a t e d D o u g l a s - f i r and w e s t e r n hemlock s e e d l i n g s a r e s i m i l a r t o o t h e r p u b l i s h e d v a l u e s f o r t h e s e s p e c i e s ( R i t c h i e and S h u l a 1984; K a n d i k o e t al_. 1 9 8 0 ) . - 24 -T a b l e 1 . 1 . D a i l y minimum measured v a l u e s o f t o t a l t w i g x y l em w a t e r p o t e n t i a l (vjtx) (MPa) and a v e r a g e r o o t zone s o i l w a t e r p o t e n t i a l ( ¥ 5 ) (MPa) f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s between May and Augu s t 1981 . S e e d l i n g s were p l a n t e d i n A p r i l 1 9 8 1 . S t a n d a r d d e v i a t i o n s o f vjtx a r e g i v e n i n b r a c k e t s . *s D o u g l a s - f i r Wes t e rn hemlock P a c i f i c s i l v e r May 30 - 0 . 0 9 - 1 . 8 ( 0 . 1 ) - 1 . 3 ( 0 . 1 ) — — June 15 - 0 . 1 5 - 1 . 9 ( 0 . 2 ) - 1 . 4 ( 0 . 1 ) - 1 . 1 ( 0 . 1 ) J u l y 27 - 0 . 3 2 - 1 . 9 ( 0 . 1 ) - 1 . 6 ( 0 . 1 ) - 1 . 2 ( 0 . 2 ) Augu s t 25 - 1 . 7 0 - 3 . 2 ( 0 . 2 ) - 1 . 9 ( 0 . 2 ) - 1 . 6 ( 0 . 2 ) - 25 -MAY JUN JUL AUG SEP -0.4 F i g u r e 1.6 C o u r s e s o f minimum t w i g xy lem wa te r p o t e n t i a l , o s m o t i c p o t e n t i a l and minimum t u r g o r p o t e n t i a l , d u r i n g t h e 1982 g r ow i ng s e a s o n , f o r i r r i g a t e d ( IRR) and (NON-IRR) D o u g l a s - f i r s e e d l i n g s p l a n t e d V a l u e s o f minimum t u r g o r p o t e n t i a l were s u b t r a c t i n g p o t e n t i a l n o n - i r r i g a t e d i n May 1 9 8 2 . o b t a i n e d by o s m o t i c p o t e n t i a l f rom minimum t w i g xy l em wa t e r - 26 -MAY JUN JUL AUG SEP co 2 < i X C D a. i 5 to o -3 -1 -3 F i g u r e 1.7 Cou r s e s o f minimum t w i g xy l em wa te r p o t e n t i a l , o s m o t i c p o t e n t i a l and minimum t u r g o r p o t e n t i a l , d u r i n g t h e 1982 g r ow i ng s e a s o n , f o r i r r i g a t e d ( IRR) and n o n - i r r i g a t e d (NON-IRR) we s t e r n hemlock s e e d l i n g s p l a n t e d i n May 1 9 8 2 . V a l u e s o f minimum t u r g o r p o t e n t i a l were o b t a i n e d by s u b t r a c t i n g o s m o t i c p o t e n t i a l f rom minimum t w i g xy l em wa t e r p o t e n t i a l . - 27 -MAY JUN JUL AUG SEP -1 9 - 2 >-x -3 0 1 o -2 • PR o NON-IRR F i g u r e 1.8 Cou r s e s o f minimum t w i g xy lem wa te r p o t e n t i a l , o s m o t i c p o t e n t i a l and minimum t u r g o r p o t e n t i a l , d u r i n g t h e 1982 g r ow i ng s e a s o n , f o r i r r i g a t e d ( IRR) and n o n - i r r i g a t e d (NON-IRR) P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1 9 8 2 . V a l u e s o f minimum t u r g o r p o t e n t i a l were o b t a i n e d by s u b t r a c t i n g o s m o t i c p o t e n t i a l f rom minimum t w i g xy l em wa te r p o t e n t i a l . - 28 -T a b l e 1 . 2 . Measu red v a l u e s o f a v e r age r o o t zone s o i l w a t e r p o t e n t i a l ( Y s ) ( M P a ) and d a i l y minimum t o t a l t w i g xy l em p o t e n t i a l ( 4 ' T t x ) ( M P a ) f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s between May and Sep tember 1983 . S e e d l i n g s were p l a n t e d i n A p r i l 1 9 8 1 . S t a n d a r d d e v i a t i o n s o f y y t x a r e g i v e n i n b r a c k e t s . *s D o u g l a s - f i r Wes t e r n hemlock P a c i f i c s i l v e r May 20 - 0 . 0 6 - 1 . 6 ( 0 . 2 ) - 1 . 2 ( 0 . 1 ) - 0 . 9 ( 0 . 1 ) June 13 - 0 . 0 5 - 1 . 7 ( 0 . 1 ) -1.4 ( 0 . 2 ) - 1 . 1 ( 0 . 2 ) J u l y 27 - 0 . 1 8 - 2 . 2 ( 0 . 3 ) - 1 . 6 ( 0 . 1 ) - 1 . 1 ( 0 . 1 ) Augus t 1 - 0 . 9 1 -2.4 ( 0 . 2 ) - 1 . 6 ( 0 . 2 ) - 1 . 0 ( 0 . 1 ) Sep tember 8 - 0 . 0 5 - 1 . 8 ( 0 . 1 ) - 1 . 3 ( 0 . 1 ) - 0 . 9 ( 0 . 2 ) - 29 -T a b l e 1 . 3 . Measu red v a l u e s o f minimum o s m o t i c p o t e n t i a l (4^ ) (MPa) be tween May and Sep tember 1982 f o r shaded ( u s i n g shade c a r d s ) and non- shaded D o u g l a s - f i r , w e s t e r n hem lock , and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n 1 9 8 1 . S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s . D o u g l a s - f i r Wes t e rn hemlock P a c i f i c s i l v e r f i r May 4 shade - 1 . 8 ( 0 . 2 ) - 1 . 0 ( 0 . 2 ) - 0 . 8 ( 0 . 2 ) no shade - 1 . 9 ( 0 . 2 ) - 1 . 2 ( 0 . 2 ) - 0 . 9 ( 0 . 1 ) J une 16 shade - 1 . 8 ( 0 . 1 ) - 1 . 0 ( 0 . 1 ) - 0 . 9 ( 0 . 1 ) no shade - 2 . 1 ( 0 . 3 ) - 1 . 2 ( 0 . 2 ) - 0 . 9 ( 0 . 2 ) J u l y 27 shade - 2 . 4 ( 0 . 1 ) - 1 . 8 ( 0 . 1 ) - 1 . 3 ( 0 . 1 ) no shade - 2 . 6 ( 0 . 3 ) - 1 . 7 ( 0 . 2 ) - 1 . 2 ( 0 . 2 ) Augu s t 26 shade - 2 . 9 ( 0 . 2 ) - 1 . 7 ( 0 . 2 ) - 1 . 5 ( 0 . 2 ) no shade - 2 . 9 ( 0 . 2 ) - 1 . 9 ( 0 . 2 ) - 1 . 3 ( 0 . 1 ) Sep tember 9 shade - 3 . 0 ( 0 . 3 ) - 1 . 8 ( 0 . 2 ) _ _ no shade - 2 . 9 ( 0 . 2 ) - 2 . 0 ( 0 . 1 ) - 1 . 4 ( 0 . 2 ) - 30 -In 1983 s m a l l e r changes i n o s m o t i c p o t e n t i a l were o b s e r v e d i n a l l t h e s p e c i e s ( T a b l e 1 . 4 ) . The f a c t t h a t l e s s a d j u s t m e n t o c c u r r e d i n t h e e x c e p t i o n a l l y wet summer, and t h a t i n t h e p r e v i o u s y e a r much g rea te r -o s m o t i c a d j u s t m e n t was o b s e r v e d i n t h e n o n - i r r i g a t e d t h a n i n t h e i r r i -g a t e d t r e a t m e n t s s u g g e s t s t h a t o s m o t i c a d j u s t m e n t i s not a s e a s ona l r e s pon se bu t r a t h e r a r e s p o n s e t o e n v i r o n m e n t a l s t r e s s . T a b l e 1.5 shows t h a t i n 1982 t h e r e was v i r t u a l l y no d i f f e r e n c e i n d a i l y minimum yn o f s e e d l i n g s p l a n t e d i n 1981 and 1982 . I t i s l i k e l y t h a t c o n s i d e r a b l e o s m o t i c a d j u s t m e n t o c c u r r e d i n t h e v e r y d ry summer of 1981 c o r r e s p o n d i n g t o t h e p r o g r e s s i v e d e c l i n e i n y s and minimum d a i l y ¥rtx ( T a b l e 1 . 1 ) . I n 1982 o s m o t i c a d j u s t m e n t e n a b l e d t h e D o u g l a s - f i r s e e d l i n g s t o c o n s i s t e n t l y m a i n t a i n t u r g o r d u r i n g t h e summer ( F i g 1 . 6 ) . In c o n t r a s t , t h e P a c i f i c s i l v e r - f i r a nd , t o a l e s s e r - e x t e n t , t he w e s t e r n hemlock s e e d l i n g s were unab l e t o m a i n t a i n t u r g o r t h r o u g h o u t t h e same p e r i o d ( F i g . 1.7 and 1 . 8 ) . The re a r e t h r e e 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 e n e g a t i v e v a l u e s o f Yp computed f o r a l l t h e s p e c i e s : ( i ) t h e r e was some d i l u t i o n o f t he sap by a p o p l a s t i c w a t e r d u r i n g t h e e x t r a c t i o n p r o c e s s wh i ch l e d t o an o v e r e s t i m a t e o f vn a nd , t h e r e f o r e , an u n d e r e s t i m a t e o f ¥p, ( i i ) yu was o v e r e s t i m a t e d because sap samp les were t a k e n a t predawn r a t h e r than a t t h e t ime o f minimum t o t a l xy l em w a t e r p o t e n t i a l ; howeve r , measu re -ments o f ¥ j t x a n d wh i c h were made e v e r y two hou r s on two days i n J u l y 1982 d i d no t r e v e a l s i g n i f i c a n t d i u r n a l changes i n y%\ and ( i i i ) v a l u e s o f Yp were u n d e r e s t i m a t e d be cause t h ey were computed by sub -t r a c t i n g n e e d l e o s m o t i c p o t e n t i a l f r om t o t a l t w i g xy l em w a t e r p o t e n t i a l ra ther- t h an n e e d l e o s m o t i c p o t e n t i a l f r om t o t a l n e e d l e xy l em w a t e r - 31 -T a b l e 1 . 4 . Measu red v a l u e s o f minimum o s m o t i c p o t e n t i a l ( v v ) (MPa) f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s between May and Sep tember 1983 . S e e d l i n g s were p l a n t e d i n May 1 9 8 1 . S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s . D o u g l a s - f i r Wes t e rn hemlock P a c i f i c s i l v e r f i r May 20 - 2 . 1 ( 0 . 2 ) - 1 . 3 ( 0 . 1 ) - 0 . 9 ( 0 . 1 ) J une 13 - 2 . 0 ( 0 . 2 ) - 1 . 5 ( 0 . 2 ) - 1 . 0 ( 0 . 2 ) J u l y 27 - 2 . 3 ( 0 . 1 ) - 1 . 4 ( 0 . 1 ) - 1 . 0 ( 0 . 1 ) Augu s t 21 - 2 . 7 ( 0 . 3 ) - 1 . 7 ( 0 . 2 ) - 0 . 9 ( 0 . 1 ) Sep tember 8 - 2 . 7 ( 0 . 2 ) - 1 . 3 ( 0 . 1 ) - 1 . 1 ( 0 . 2 ) - 32 -T a b l e 1 . 5 . Measu red v a l u e s o f d a i l y minimum o s m o t i c p o t e n t i a l (<?„) (MPa) between May and Sep tember 1982 f o r u n t r e a t e d D o u g l a s - f i r , w e s t e r n hem l o c k , and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n t h e p r e v i o u s y e a r (P) and p l a n t e d i n t h e c u r r e n t y e a r ( C ) . S t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s . Doug l a s - f i r Wes t e r n hemlock P a c i f i c s i l v e r May 4 P - 1 . 9 ( 0 . 2 ) - 1 . 2 ( 0 . 1 ) - 0 . 9 ( 0 . 1 ) C - 1 . 8 ( 0 . 2 ) - 1 . 4 ( 0 . 2 ) - 0 . 7 ( 0 . 2 ) J une 16 P - 2 . 1 ( 0 . 2 ) - 1 . 2 ( 0 . 2 ) - 0 . 9 ( 0 . 1 ) C - 2 . 0 ( 0 . 3 ) - - 1 . 2 ( 0 . 1 ) J u l y 27 P - 2 . 6 ( 0 . 3 ) - 1 . 7 ( 0 . 1 ) - 1 . 2 ( 0 . 2 ) C - 2 . 5 ( 0 . 2 ) - 1 . 8 ( 0 . 1 ) - 1 . 0 ( 0 . 1 ) A u g u s t 26 P - 2 . 9 ( 0 . 1 ) - 1 . 9 ( 0 . 2 ) - 1 . 3 ( 0 . 2 ) C - 2 . 9 ( 0 . 2 ) - 1 . 6 ( 0 . 2 ) - 1 . 1 ( 0 . 1 ) Sep tember 9 P - 2 . 9 ( 0 . 1 ) - 2 . 0 ( 0 . 1 ) - 1 . 4 ( 0 . 1 ) C - 2 . 7 ( 0 . 2 ) - 2 . 2 ( 0 . 3 ) - -- 33 -p o t e n t i a l ( ? j n x ) . R i t c h i e and H i n k l e y ( 1 9 7 1 ) , i n a growth chamber s t u d y o f t w o - y e a r - o l d D o u g l a s - f i r s e e d l i n g s , f ound t h a t p r e s s u r e chamber measurements o f y j t x w e r e a l w a y s l e s s t h an ^rnx* They h y p o t h e s i z e d t h a t t h e p i t h o f a D o u g l a s - f i r t w i g a c t e d as a w a t e r s i n k so t h a t f i l l i n g o f t h e p i t h w i t h sap d u r i n g p r e s s u r i z a t i o n wou l d l e a d t o an u n d e r e s t i m a t i o n o f Y j t x * * n c o n t r a s t K e l l i h e r e t JJ1_. 1984 w o r k i n g w i t h young D o u g l a s - f i r t r e e s f ound no s i g n i f i c a n t d i f f e r e n c e between *T t x a " d Y rnx -C. S e e d l i n g T r a n s p i r a t i o n Ra t e s The maximum d a i l y t r a n s p i r a t i o n r a t e s on a p r o j e c t e d l e a f a r ea b a s i s (E) o f w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s were a p p r o x i m a t e l y 60% and 43%, r e s p e c t i v e l y , o f t h o s e o f D o u g l a s - f i r s e e d -l i n g s . D a i l y t r a n s p i r a t i o n r a t e s o f n o n - i r r i g a t e d D o u g l a s - f i r s e e d l i n g s d i d no t d e c r e a s e w i t h d e c r e a s i n g <ps as much as t h o s e o f t he non -i r r i g a t e d w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s ( F i g . 1 . 9 ) . F i g u r e 1.10 shows t he r a t i o o f d a i l y t r a n s p i r a t i o n o f n on -i r r i g a t e d s e e d l i n g s (ENJ .) t o t h a t o f i r r i g a t e d s e e d l i n g s ( E j ) as a f u n c t i o n o f <F s. A t v s o f - 1 . 2 MPa the d a i l y t r a n s p i r a t i o n o f non-i r r i g a t e d D o u g l a s - f i r s e e d l i n g s was o v e r 50% o f t h a t o f i r r i g a t e d s e e d -l i n g s . T h i s compares w i t h 40% and 25% f o r w e s t e r n hemlock and P a c i f i c s i l v e r - f i r , r e s p e c t i v e l y , and i n d i c a t e s t he g r e a t e r degree o f s t r e s s t o l e r a n c e e x h i b i t e d by D o u g l a s - f i r s e e d l i n g s . The ma i n t enance o f t u r g o r c o r r e s p o n d e d t o t he a b i l i t y o f t he n o n - i r r i g a t e d D o u g l a s - f i r s e e d l i n g s t o m a i n t a i n r e l a t i v e l y h i g h v a l u e s o f g s as ¥ s d e c r e a s e d . - 34 -Figure 1.9 The r e l a t i o n s h i p between d a i l y t r a n s p i r a t i o n (E) and average root zone s o i l water potent ia l (ij/ s) for n o n - i r r i g a t e d Doug las - f i r (DF) , western hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) seed l i ngs . Measurements were made in 1982 on seedl ings planted in May of that yea r . Each point represents the average E for three seed l ings . The curves were f i t t e d by eye. - 35 -—1 « -• 1982 i > — i i — i — • T " 1 • • • DF • • • _ • • WH * * • * * _i " — * i i i 1 * * PSF < 1 0 - 0 5 0-5 Ew/ Ei 0 5 -12 -1-0 -08 -0-6 -04 -02 Vs (MPa) Figure 1.10 The r e l a t i o n s h i p between the r a t i o of d a i l y t r a n s p i r a t i o n per unit projected l e a f area of non-Irr igated seedl ings to that of I r r i g a t e d seedl ings ( E N I / E J ) and average root zone s o i l water potent ia l (* s ) for Doug las - f i r (DF) , western hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) . Measurements were made in 1982 on seedl ings planted in May of that y e a r . - 36 -A l l t h r e e s p e c i e s showed a l i n e a r r e l a t i o n s h i p between the w a t e r p o t e n t i a l d rop i n t h e s o i l - p l a n t s y s t em and t r a n s p i r a t i o n r a t e w i t h a n o n - z e r o i n t e r c e p t ( T ab l e 1 . 6 ) . T h i s i s not u nexpe c t e d i n v i ew o f the r e s u l t s i n F i g . 1.5 and i s a s i m i l a r r e s u l t t o t h a t r e p o r t e d by K e l l i h e r e t al_. ( 1 9 8 4 ) . However , i n c o n t r a s t t o t h e i r f i n d i n g s t h a t , as ys d e c r e a s e d f r om - 0 . 0 1 t o - 1 . 1 MPa, t he v a l u e o f b i n c r e a s e d by a f a c t o r o f t h r e e , t h e v a l u e o f b f o r t h e u n t r e a t e d s e e d l i n g s was o n l y 22 - 28% g r e a t e r t han t h a t f o r t h e i r r i g a t e d s e e d l i n g s . T r a n s p i r a t i o n r a t e s o f t h e c o n i f e r s e e d l i n g s were g r e a t l y r e d u c e d on days w i t h h i g h vapou r p r e s s u r e d e f i c i t s because o f a l m o s t c omp l e t e s t o m a t a l c l o s u r e ( T h i s i s d i s c u s s e d i n t h e c o n t e x t o f s t o m a t a l c o n d u c -t a n c e c h a r a c t e r i s t i c s o f t he s p e c i e s , a t g r e a t e r l e n g t h i n C h a p t e r 2 ) . On such days d i f f e r e n c e s between t he t r a n s p i r a t i o n r a t e s o f i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s d e c r e a s e d . T h i s a c c o u n t s f o r some o f t he s c a t t e r i n F i g . 1 . 10 . The e f f e c t i s i l l u s t r a t e d i n F i g . 1.11 i n wh i ch t h e h o u r l y t r a n s p i r a t i o n r a t e s o f i r r i g a t e d and n o n - i r r i g a t e d D o u g l a s - f i r s e e d l i n g s a r e compared on a day w i t h m o d e r a t e l y h i g h D ( J u l y 2 4 , 1982) and a day w i t h ve r y h i g h D ( J u l y 27, 1 9 8 2 ) . The e f f e c t on t r a n s p i r a t i o n o f t he i n c r e a s e d D f r om J u l y 24 t o J u l y 27 was more p ronounced on t he i r r i g a t e d s e e d l i n g s t han on t he n o n - i r r i g a t e d s e e d -l i n g s whose t r a n s p i r a t i o n r a t e s were a l r e a d y l i m i t e d by low ¥ s . T h i s r e s u l t e d i n a l o w e r r a t i o o f d a i l y t r a n s p i r a t i o n o f n o n - i r r i g a t e d t o i r r i g a t e d s e e d l i n g s on J u l y 24 ( 0 . 6 8 ) t h an on J u l y 27 ( 0 . 8 3 ) d e s p i t e b e i n g 0 .25 MPa l o w e r on the l a t t e r day . D a i l y t r a n s p i r a t i o n r a t e s o f s e e d l i n g s b e h i n d shade c a r d s were s i m i l a r t o t h o s e o f unshaded s e e d l i n g s on t he t h r e e days i n June 1982 - 37 -T a b l e 1 . 6 . V a l u e s o f l i n e a r r e g r e s s i o n c o e f f i c i e n t s and r 2 f o r t h e r e l a t i o n s h i p : E = a + (Y s - ¥ T t x ) / b f ° r i r r i g a t e d ( I ) and n o n - i r r i g a t e d (NI ) D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s . The u n i t s o f a and b a r e pg c m - 2 s " 1 and MPa / ( yg c m - 2 s - 1 ) , r e s p e c t i v e l y . S p e c i e s T r e a t m e n t a b r 2 D o u g l a s - f i r I - 1 . 7 2 0 .36 0 . 8 8 NI - 1 . 4 5 0 .44 0 . 7 9 Wes t e r n hemlock I - 0 . 8 3 0 .43 0 . 86 NI - 0 . 2 9 0 .55 0 .81 P a c i f i c s i l v e r f i r I NI - 0 . 6 5 0 .47 0 . 92 - 0 . 1 9 0 .59 0 . 83 - 38 -Time (PST) F i g u r e 1.11 The d a i l y c o u r s e o f t r a n s p i r a t i o n (E) per u n i t p r o j e c t e d l e a f a r ea f o r i r r i g a t e d ( IRR) and n o n - i r r i g a t e d (NON-IRR) D o u g l a s - f i r s e e d l i n g s , and vapour p r e s s u r e d e f i c i t (D) f o r J u l y 24 and J u l y 2 7 , 1982 . The v a l u e s o f * s on J u l y 24 and J u l y 27 were - 0 . 5 MPa and - 0 . 7 MPa, r e s p e c t i v e l y . - 39 -when measurements were t a k e n ( T a b l e 1 . 7 ) . On a l l t h r e e days unshaded s e e d l i n g s had h i g h e r t r a n s p i r a t i o n r a t e s i n t h e mo rn i ng w h i c h c o r r e s -ponded w i t h l o w e r d a i l y minimum T j t x ( F i g . 1 . 1 2 ) . These d i f f e r e n c e s were t h e r e s u l t o f t he s l i g h t l y l o w e r day t ime need l e t e m p e r a t u r e s ( F i g . 1 .13) a nd , c o n s e q u e n t l y , l o w e r ( e n - e a ) b e h i n d t he shade c a r d s ( F i g . 1 . 1 4 ) . Kaufmann (1979) a l s o f ound t he t r a n s p i r a t i o n r a t e s o f shaded Enge lmann s p r u c e s e e d l i n g s were d e c r e a s e d as a r e s u l t o f l o w e r e d n eed l e t e m p e r a t u r e s . The l o w e r boundary l a y e r c o n d u c t a n c e o f t he shaded s e e d l i n g s a l s o c o n t r i b u t e d t o t h e i r l o w e r t r a n s p i r a t i o n r a t e s . The e f f e c t w i l l be most p ronounced i n t he e a r l y mo rn i ng when g s i s r e l a t i v e l y h i g h (Sm i th 1 9 8 0 ) . B e f o r e 11:00 h PST unshaded s e e d l i n g s and shaded s e e d l i n g s t y p i c a l l y had s i m i l a r v a l u e s o f g s ( F i g . 1 . 1 2 ) ; however , unshaded s e e d l i n g s had h i g h e r ( e n - e a ) and , c o n s e q u e n t l y , h i g h e r t r a n s p i r a t i o n r a t e s . A f t e r 11:00 h PST as ( e n - e a ) i n c r e a s e d , g s o f unshaded s e e d l i n g s d e c r e a s e d more r a p i d l y t han t h a t o f shaded s e e d l i n g s , c a u s i n g t r a n s p i r a t i o n r a t e s o f t h e f o r m e r t o d e c r e a s e more r a p i d l y t han t he l a t t e r . D. S e e d l i n g S u r v i v a l In a l l s p e c i e s and t r e a t m e n t s t h e r e were h i g h e r r a t e s o f m o r t a l i t y o f s e e d l i n g s p l a n t e d i n 1981 t han o f t h o s e p l a n t e d i n 1982 . T h i s r e f l e c t s t he much s e v e r e r c o n d i t i o n s t h a t were p r e v a l e n t i n t he e a r l i e r y e a r . S i m i l a r l y t he low m o r t a l i t y d u r i n g t h e summer o f 1983 r e f l e c t s t h e r e l a t i v e l y m i l d c o n d i t i o n s o f t h a t y e a r . - 40 -T a b l e 1 . 7 . D a i l y t r a n s p i r a t i o n (g d a y 1 ) o f shaded ( u s i n g shade c a r d s ) and unshaded D o u g l a s - f i r s e e d l i n g s on J une 10 , J une 12 and June 1 3 , 1982 . The t o t a l p r o j e c t e d n e e d l e a r e a ( c m 2 ) i s g i v e n i n b r a c k e t s . The a v e r age r o o t zone s o i l w a t e r p o t e n t i a l was - 0 . 1 0 MPa on J une 1 2 . Shade No shade J u n e 10 6 . 5 6 . 4 ( 1 2 4 . 3 ) ( 1 3 4 . 5 ) J u n e 12 9 .2 7 .6 ( 1 4 1 . 0 ) ( 1 2 8 . 8 ) J une 13 8 . 1 7 .8 ( 1 2 4 . 3 ) ( 1 3 4 . 5 ) - 41 -6 9 12 15 Time (PST) F i g u r e 1.12 Cou r s e s o f s t o m a t a l c ondu c t an c e ( g s ) , t r a n s p i r a t i o n r a t e (E) and t o t a l t w i g xy l em p o t e n t i a l ( i J r t x ) f ° r shaded ( c l o s e d c i r c l e s ) and unshaded (open c i r c l e s ) D o u g l a s - f i r s e e d l i n g s on June 1 3 , 1982 . - 42 -3 5 10 1 1 " 1 " 1 1 0 4 8 12 16 20 24 Time (PST) F i g u r e 1.13 Cou r s e s o f t e m p e r a t u r e o f shaded (dashed l i n e ) and unshaded ( d o t t e d l i n e ) n e e d l e s o f a D o u g l a s - f i r s e e d l i n g , and a i r t e m p e r a t u r e ( s o l i d l i n e ) a t 2f) cm h e i g h t nea r t h e unshaded s e e d l i n g on June 1 3 , 1982 . - 43 -F i g u r e 1.14 Cou r s e s o f vapour p r e s s u r e d e f i c i t ( s o l i d l i n e ) , vapour p r e s s u r e d i f f e r e n c e between an unshaded D o u g l a s - f i r n e e d l e and t h e a i r ( b r o ken l i n e ) and t h e vapour p r e s s u r e d i f f e r e n c e between a shaded D o u g l a s - f i r n e e d l e and t h e a i r ( d o t t e d l i n e ) on June 13 , 1982 . - 44 -1. S e e d l i n g s p l a n t e d i n 1981 The s u r v i v a l o f s e e d l i n g s p l a n t e d i n 1981 i s summar i zed i n T a b l e 1.8 f o r each o f t he n i n e s p e c i e s and t r e a t m e n t c o m b i n a t i o n s . S u r v i v a l f i g u r e s a r e g i v e n f o r A p r i l r a t h e r t h an t he p r e v i o u s O c t o b e r (as r e p o r t e d by S t a t h e r s (1983) ) because o v e r 90% of t he s e e d l i n g s wh i ch had s u f f e r e d s e v e r e damage d u r i n g t h e summer and wh i ch had been d e s i g n a t e d a " 3 " i n O c t o b e r 1981 (and hence had been c l a s s i f i e d as a l i v e ) , were dead by the f o l l o w i n g A p r i l . T h i s , t o g e t h e r w i t h t h e f a c t t h a t w i n t e r s i n t h e Mount A r r o w s m i t h r e g i o n a r e r e l a t i v e l y m i l d s u g g e s t s t h a t l i t t l e o f t h e s e e d l i n g m o r t a l i t y c o u l d be a t t r i b u t e d t o w i n t e r c o n d i t i o n s . A t the end o f t h r e e y e a r s t h e r e was s i g n i f i c a n t l y g r e a t e r s u r v i v a l i n u n t r e a t e d D o u g l a s - f i r (72%) t han i n t he u n t r e a t e d w e s t e r n hemlock (7%) and P a c i f i c s i l v e r - f i r (4%). Shade c a r d s , w h i l s t f a r f r om e l i m i n -a t i n g s e e d l i n g m o r t a l i t y , s i g n i f i c a n t l y i n c r e a s e d s u r v i v a l i n a l l s p e c i e s . The e f f e c t was not as p ronounced i n D o u g l a s - f i r because o f t he a l r e a d y h i g h s u r v i v a l r a t e s i n t h e u n t r e a t e d s e e d l i n g s . I n c l i n i n g t h e s e e d l i n g s i n c r e a s e d the s u r v i v a l o f o n l y D o u g l a s - f i r s e e d l i n g s , and by t h e second y e a r s e e d l i n g s o f a l l t h e s p e c i e s had r e sponded g e o t r o p i c a l l y so t h a t f rom then on t h e r e was no o b s e r v a b l e d i f f e r e n c e between i n c l i n e d s e e d l i n g s and t he c o n t r o l . Mos t o f t h e s e e d l i n g m o r t a l i t y o c c u r r e d i n t he f i r s t y e a r when c o n d i t i o n s were most s e v e r e . Seve r e n e c r o s i s and c h l o r o s i s were f i r s t o b s e r v e d i n m i d - A u g u s t 1 9 8 1 , and by September o f t h a t y e a r s i g n i f i c a n t m o r t a l i t y was o b s e r v e d . - 45 -T a b l e 1 . 8 . P e r c e n t s u r v i v a l i n A p r i l 1982 , 1983 and 1984 o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1 9 8 1 . Numbers f o l l o w e d by the same l e t t e r a 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 ( t = 0 . 0 5 ) a c c o r d i n g t o D u n c a n ' s New M u l t i p l e Range T e s t , w h i c h was a p p l i e d t o each s p e c i e s i n each y e a r . A p r i l 1982 T r e a tmen t D o u g l a s - f i r Wes t e rn hemlock P a c i f i c s i l v e r f i r C o n t r o l 88 (a ) 25 (a ) 11 (a ) S e l f shade 91 (a ) 25 (a ) 13 (a ) Shade c a r d s 98 (a ) 63 (b) 38 (b) A p r i l 1983 T r e a t m e n t D o u g l a s - f i r Wes t e rn hemlock P a c i f i c s i l v e r f i r C o n t r o l 74 (a ) 14 (a) 8 ( a ) S e l f shade 86 (b) 19 (a) 9 ( a ) Shade c a r d s 97 (b) 48 (b) 34 (b) A p r i l 1984 T r e a t m e n t D o u g l a s - f i r Wes t e r n hemlock P a c i f i c s i l v e r f i r C o n t r o l 72 (a ) 7 ( a ) 4 (a ) S e l f shade 81 (a) 13 (a ) 7 (a ) Shade c a r d s 95 (b) 42 (b) 31 (b) - 46 -T a b l e 1 . 9 . P e r c e n t s u r v i v a l i n A p r i l 1983 and 1984 o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1982 . Numbers f o l l o w e d by t he same l e t t e r a r e no t s i g n i f i c a n t l y d i f f e r e n t ( t = 0 . 05 ) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range T e s t , wh i c h was a p p l i e d t o each s p e c i e s i n each y e a r . A p r i l 1983 T r e a t m e n t D o u g l a s - f i r We s t e r n hemlock P a c i f i c s i l v e r f i r C o n t r o l 88 (a ) 40 (a ) 30 (a ) Shade c a r d s 93 (a) 71 (b) 57 (b) I r r i g a t i o n 91 (a ) 60 (b) 59 (b) I r r i g a t i o n and 90 (a ) 74 (b) 60 (b) shade c a r d s A p r i l 1984 T r e a tmen t D o u g l a s - f i r Wes t e r n hemlock P a c i f i c s i l v e r f i r C o n t r o l 82 (a ) 34 (a ) 19 (a ) Shade c a r d s 89 (a) 63 (b) 45 (b) I r r i g a t i o n 87 (a ) 57 (b) 43 (b) I r r i g a t i o n and 83 (a) 64 (b) 53 (b) shade c a r d s - 47 -2 . S e e d l i n g s p l a n t e d i n 1982 As i n t h e c a s e o f 1981 p l a n t e d s e e d l i n g s t h e r e was s i g n i f i c a n t l y g r e a t e r s u r v i v a l i n u n t r e a t e d D o u g l a s - f i r t han i n t h e u n t r e a t e d w e s t e r n hemlock and P a c i f i c s i l v e r - f i r ( T a b l e 1 . 9 ) . T h i s c o r r e s p o n d s t o t h e o b s e r v a t i o n t h a t o n l y t he D o u g l a s - f i r s e e d l i n g s were a b l e t o m a i n t a i n t u r g o r t h r o u g h o u t t h e s eason ( F i g s . 1.6 - 1 . 8 ) . In c o n t r a s t , t h e r e were c o n s i d e r a b l e p e r i o d s o f t u r g o r l o s s i n t h e P a c i f i c s i l v e r f i r s e e d l i n g s and , t o a l e s s e r e x t e n t , i n t he we s t e r n hemlock s e e d l i n g s . T h i s wou l d a l s o e x p l a i n t h e d i f f e r e n c e s i n t h e 1981 and 1982 s u r v i v a l r a t e s o f t he s e e d l i n g s p l a n t e d i n 1 9 8 1 . I r r i g a t i o n d i d no t p r e v e n t h i g h r a t e s o f m o r t a l i t y i n w e s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g s a l t h o u g h s u r v i v a l i n t h e s e t r e a t m e n t s was a p p r o x i m a t e l y t w i c e t h a t o f n o n - i r r i g a t e d s e e d l i n g s . F i g u r e s 1.7 and 1.8 show t h a t d e s p i t e i r r i g a t i o n bo th w e s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g s were no t a b l e to m a i n t a i n t u r g o r t h r o u g h o u t t h e s e a s o n , a l t h o u g h f r om m i d - J u l y onwards t u r g o r was h i g h e r i n i r r i g a t e d than i n n o n - i r r i g a t e d s e e d l i n g s . S u r v i v a l r a t e s f o r n o n - i r r i g a t e d , shaded w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s i n A p r i l 1984 were 63% and 45%, r e s p e c t i v e -l y , and were s i m i l a r to s u r v i v a l r a t e s f o r t h e i r r i g a t e d t r e a t m e n t s bu t s i g n i f i c a n t l y h i g h e r t han the c o n t r o l t r e a t m e n t s . The l i m i t e d s u c c e s s o f shade c a r d s i n r e d u c i n g m o r t a l i t y c o u l d be due , i n p a r t , t o t h e i r e f f e c t on s e e d l i n g t u r g o r . U n t i l t h e end o f June 1982 , when the t o t a l n e e d l e a r e a o f shaded s e e d l i n g s began t o exceed t h a t o f non-shaded s e e d -l i n g s ( d i s c u s s e d i n C h a p t e r 3 ) , shaded s e e d l i n g s had h i g h e r minimum Y j t x t h a n unshaded s e e d l i n g s ( F i g . 1 .12) w h i l e h a v i n g s i m i l a r ^ - 48 -( T a b l e 1 . 3 ) . C o n s e q u e n t l y , shaded s e e d l i n g s m a i n t a i n e d h i g h e r l e v e l s o f t u r g o r t h an unshaded s e e d l i n g s d u r i n g t h e p e r i o d o f w a t e r s t r e s s t h a t o c c u r r e d between p l a n t i n g and t he b e g i n n i n g o f J u l y . The r e was no t a s i g n i f i c a n t i n t e r a c t i o n between shade and i r r i g a t i o n t r e a t m e n t s e x c e p t w i t h P a c i f i c s i l v e r - f i r i n 1984 ( T a b l e 1 . 9 ) . S t a t h e r s (1983) a r gued t h a t t he rma l s t r e s s was l i k e l y t h e major-c au se o f s e e d l i n g m o r t a l i t y and t h a t h i g h e r m o r t a l i t y o c c u r r e d i n 1981 t han i n 1982 because t h e magn i t ude and d u r a t i o n o f h i g h s u r f a c e t e m p e r a -t u r e s were g r e a t e r i n 1 9 8 1 . In a d d i t i o n , he a rgued t h a t t he s i g n i f i c a n t d i f f e r e n c e i n s u r v i v a l between n o n - i r r i g a t e d s haded , and c o n t r o l t r e a t -ments c o u l d be a t t r i b u t e d t o t he d i r e c t e f f e c t o f shade c a r d s on r e d u c -i n g s u r f a c e s o i l t e m p e r a t u r e s a nd , h en c e , t h e rma l s t r e s s . T h i s a rgument d i d no t cons i de r - t h e e f f e c t o f shade c a r d s on s e e d l i n g t u r g o r no r d i d i t e x p l a i n why s h a d i n g (and i r r i g a t i o n ) , w h i l e d e c r e a s i n g s o i l s u r f a c e t e m p e r a t u r e s f rom 60 - 70°C to 30 - 35°C, o n l y had l i m i t e d s u c c e s s i n i n c r e a s i n g s e e d l i n g s u r v i v a l . F u r t h e r m o r e i t d i d no t e x p l a i n why t h e s u r v i v a l o f D o u g l a s - f i r s e e d l i n g s was so much g r e a t e r than t h a t o f the o t h e r s p e c i e s . I V . CONCLUSIONS D o u g l a s - f i r s e e d l i n g s , p l a n t e d i n t he s p r i n g as 1-0 s t y r o p l u g s a t a h i g h e l e v a t i o n s o u t h - f a c i n g s i t e , e x h i b i t e d a h i g h deg ree o f d r o u g h t t o l e r a n c e . The mechanism appea red t o be s t r e s s t o l e r a n c e r e s u l t i n g f rom c o n s i d e r a b l e o s m o t i c a d j u s t m e n t wh i ch e n a b l e d t he s e e d l i n g s t o m a i n t a i n t u r g o r t h r o u g h o u t t h e g r ow ing s e a s o n . C o n s e q u e n t l y t h e D o u g l a s - f i r s e e d l i n g s no t o n l y s u r v i v e d s e v e r e d r o u g h t b u t were a b l e t o m a i n t a i n - 49 -d a i l y t r a n s p i r a t i o n r a t e s t h a t were neve r l e s s than 50% o f t h o s e a c h i e v e d under opt imum s o i l m o i s t u r e c o n d i t i o n s . T r a n s p i r a t i o n r a t e s w e r e , however , ma r ked l y l i m i t e d unde r a l l s o i l m o i s t u r e c o n d i t i o n s by h i g h v apou r p r e s s u r e d e f i c i t s t h a t c o n s i d e r a b l y r e d u c e d s t o m a t a l c o n d u c t a n c e . Wes te rn hem lo ck , and t o an even g r e a t e r e x t e n t , P a c i f i c s i l v e r f i r s e e d l i n g s , e x h i b i t e d a f a i l u r e to cope w i t h d r ough t because o f t he l a c k o f bo th s t r e s s a v o i d a n c e and t o l e r a n c e mechan isms and c o n s e q u e n t l y s u f f e r e d e x t r e m e l y h i g h m o r t a l i t y . Shade c a r d s i n c r e a s e d t he s u r v i v a l o f D o u g l a s - f i r s e e d l i n g s p l a n t e d i n 1981 , b u t no t t h o s e p l a n t e d i n 1982; i r r i g a t i o n had no s i g n i f i c a n t e f f e c t on the s u r v i v a l o f D o u g l a s - f i r s e e d l i n g s wh i ch was g e n e r a l l y h i g h r e g a r d l e s s o f t he t r e a t m e n t . The use o f shade c a r d s , i r r i g a t i o n and bo th shade c a r d s and i r r i g a t i o n d i d i n c r e a s e s u r v i v a l i n both w e s t e r n hemlock and P a c i f i c s i l v e r - f i r bu t n o t t o an a c c e p t a b l e l e v e l . These r e s u l t s i n d i c a t e t h a t even d r a m a t i c m o d i f i c a t i o n o f a s e e d l i n g ' s m i c r o -c l i m a t e does no t e n su r e i t s s u r v i v a l . The h i g h e r s u r v i v a l o f shaded s e e d l i n g s c o u l d be e x p l a i n e d by t he e f f e c t o f shade c a r d s i n r e d u c i n g s e e d l i n g t r a n s p i r a t i o n r a t e s and d u r i n g t he mo rn i ng t h e r e b y i n c r e a s i n g t he d a i l y minimum v a l u e o f Y j t x ' I n c l i n i n g s e e d l i n g s had o n l y a sma l l e f f e c t on s u r v i v a l . V . REFERENCES A r n o t t , J . T . 1 9 7 5 . F i e l d p e r f o rmance o f c o n t a i n e r - g r o w n and b a r e r o o t t r e e s i n C o a s t a l B r i t i s h C o l u m b i a . C a n . J . F o r . R e s . 5 : 1 8 6 - 1 9 5 . B e r n s t e i n , L. 1 9 6 1 . Osmot i c a d j u s t m e n t o f p l a n t s t o s a l i n e m e d i a . I . S t eady S t a t e . Am. J . B o t . 4 8 : 9 0 9 - 9 1 7 . - 50 -B rown , P.W. and C . B . T a n n e r . 1 9 8 3 . A l f a l f a o s m o t i c p o t e n t i a l : A c ompa r i s o n o f t h e w a t e r - r e l e a s e c u r v e and f r o z e n - t i s s u e me thods . A g r o n . J . 7 5 : 9 1 - 9 3 . C a m p b e l l , G . S . , R . I . P a p e n d i c k , E. R ab i e and A . J . S h a y a - N g o w i . A c o m p a r i s o n o f o s m o t i c p o t e n t i a l e l a s t i c modu lus and a p o p l a s i t c w a t e r i n l e a v e s o f d r y l a n d w i n t e r whea t . A g r o n . J . 7 1 : 3 1 - 3 6 . C l e a r y , B .D . 1 9 7 1 . The e f f e c t o f p l a n t m o i s t u r e s t r e s s on the p h y s i o l -ogy and e s t a b l i s h m e n t o f p l a n t e d D o u g l a s - f i r and Ponde ro sa p i n e s e e d l i n g s . P h . D . t h e s i s , Oregon S t a t e U n i v e r s i t y , C o r v a l l i s , O r egon , U . S . A . G r a n t , H.R. 1 9 8 3 . The s c a l i n g o f f l o w i n v e g e t a t i v e s t r u c t u r e s . B o u n d a r y - L a y e r M e t e o r o l . 2 7 : 1 7 1 - 1 8 4 . H a l l g r e n , S.W. 1978 . P l a n t - w a t e r r e l a t i o n s i n D o u g l a s - f i r s e e d l i n g s and s c r e e n i n g s e l e c t e d f a m i l i e s f o r d r o u g h t r e s i s t a n c e . M.S . t h e s i s , Oregon S t a t e U n i v e r s i t y , C o r v a l l i s , O r e g o n , U . S . A . H i n c k l e y , T .M . and G.A . R i t c h i e . 1973 . A t h e o r e t i c a l model f o r c a l c u l a t i o n o f xy lem sap p r e s s u r e f r om c l i m a t o l o g i c a l d a t a . Am. M i d i . N a t . 9 0 : 5 6 - 6 9 . Hobbs , S . D . , R .H . B y a r s , D.C. Henneman and C .R . F r o s t . 1980 . F i r s t y e a r p e r f o rmance i n 1-0 c o n t a i n e r i z e d D o u g l a s - f i r s e e d l i n g s on d r o u g h t y s i t e s i n Sou thwes t O r egon . F o r e s t Re sea r ch L a b o r a t o r y , R e s ea r c h Note 6 9 . Oregon S t a t e U n i v e r s i t y , C o r v a l l i s , O r egon . H s a i o , T . C . , E. A cevedo , E. F e r e r e s and D.W. H e n d e r s o n . 1976 . Water-s t r e s s , g rowth and o s m o t i c a d j u s t m e n t . P h i l . T r a n s . R. S o c . L ondon . B 2 7 3 : 4 7 9 - 5 0 0 . - 51 -J o n e s , H.G. 1 9 8 3 . P l a n t s and m i c r o c l i m a t e . Cambr idge U n i v e r s i t y P r e s s . C amb r i d ge , U.K. K a n d i k o , P . A . , R. T imm i s , and J . W o r r a i l . 1 980 . P r e s s u r e vo lume c u r v e s o f s h o t s and r o o t s o f normal and d r o u g h t c o n d i t i o n e d w e s t e r n hemlock s e e d l i n g s . C a n . J . F o r . R e s . 1 0 : 1 0 - 1 6 . Kau fmann , M.R. 1979 . S t oma t a l c o n t r o l and t he deve l opmen t o f water-d e f i c i t i n Enge lmann s p r u c e s e e d l i n g s d u r i n g d r o u g h t . C a n . J . F o r . R e s . 9 : 2 9 8 - 3 0 4 . Kau fmann , M.R. 1976 . S t oma t a l r e s p o n s e o f Enge lmann s p r u c e t o h u m i d i t y , l i g h t and w a t e r s t r e s s . P l a n t P h y s i o l . 5 7 : 8 9 8 - 9 0 1 . K e l l i h e r , F . M . , T . A . B l a c k and A . G . B a r r . 1984 . E s t i m a t i o n o f t w i g xy l em w a t e r p o t e n t i a l i n young D o u g l a s - f i r t r e e s . Can . J . F o r . R e s . 1 4 : 4 8 1 - 4 8 7 . L a n d s b e r g , J . J . and A . S . Thorn. 1 9 7 1 . Ae rodynam i c p r o p e r t i e s o f a p l a n t o f complex s t r u c t u r e . Q u a r t . J . Roy . M e t e o r o l . S o c . 9 7 : 5 6 5 - 5 7 0 . L e v i t t , J . 1980 . Responses o f P l a n t s t o E n v i r o n m e n t a l S t r e s s e s . V o l . 1. C h i l l i n g , F r e e z i n g , and H i gh Tempe ra tu r e S t r e s s e s . Academic P r e s s , New Y o r k . 497 pp . L i v i n g s t o n , N . J . , T . A . B l a c k , D. Beames and B .G . D u n s w o r t h . 1984 . An i n s t r u m e n t for- mea su r i n g t he a ve r age s t o m a t a l c ondu c t an c e o f c o n i f e r - s e e d l i n g s . C a n . J . F o r . R e s . 1 4 : 5 1 2 - 5 1 7 . M a r k h a r t , A . H . , I I I , N. S i o n i t and J . H . S i e dow . 1 9 8 1 . C e l l water-d i l u t i o n : An e x p l a n a t i o n o f a p p a r e n t n e g a t i v e turgor- p o t e n t i a l s . C a n . J . B o t . 5 9 : 1 7 2 2 - 1 7 2 5 . Osmond, B. 1963 . O x a l a t e s and i o n i c e q u i l i b r i u m i n A u s t r a l i a n s a l t bushes ( A t r i p l e x ) . N a t u r e 1 9 8 : 5 0 3 - 5 0 4 . - 52 -P a r k e r , C .W. , S . G . P a l l a r d y , T . M . H i n c k l e y and R.O. T e s k e y . 1982 . Sea sona l changes i n t i s s u e wa te r r e l a t i o n s o f t h r e e woody s p e c i e s o f the Q u e r c u s - c a r y a f o r e s t t y p e . E c o l o g y 6 3 : 1 2 5 9 - 1 2 6 7 . R i h a , S . J . and G . S . C a m p b e l l . 1 9 8 5 . E s t i m a t i n g w a t e r f l u x e s i n D o u g l a s - f i r p l a n t a t i o n s . C a n . J . F o r . R e s . 1 5 : 7 0 1 - 7 0 7 . R i t c h i e , G.A. and R .G. S h u l a . 1984 . Sea sona l changes o f t i s s u e - w a t e r r e l a t i o n s i n s hoo t s and r o o t s y s t ems o f D o u g l a s - f i r s e e d l i n g s . F o r . S c i . 3 0 : 5 3 8 - 5 4 8 . S c h o l a n d e r , P . F . , H.T. Hammel, E .D . B r a d s t r e e t and E .A . Hemmingsen. 1965 . Sap p r e s s u r e i n v a s c u l a r p l a n t s . S c i e n c e 1 4 8 : 3 3 9 - 3 4 5 . S m i t h , W.K. 1 9 8 0 . Impo r t ance o f a e r odynam i c r e s i s t a n c e t o w a t e r use e f f i c i e n c y i n t h r e e c o n i f e r s unde r f i e l d c o n d i t i o n s . P l a n t P h y s i o l . 6 5 : 1 3 2 - 1 3 5 . S p i t t l e h o u s e , D .L . and T . A . B l a c k . 1982 . A g r ow i ng season water-b a l a n c e model used t o p a r t i t i o n w a t e r use between t r e e s and u n d e r -s t o r y . pp . 1 9 5 - 2 1 4 . I n : P r o c . Can . H y d r o l . Symp. 8 2 , H y d r o l . P r o c e s s e s I n f o r . A r e a s . June 1 4 - 1 5 , 1982 , F r e d e r i c t o n , N .B . S t a t h e r s , R . J . 1 9 8 3 . A s t udy o f s o i l t e m p e r a t u r e and s e e d l i n g s u r v i v a l i n a f o r e s t c l e a r c u t . M .Sc . t h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r , B . C . , Canada . S t a t h e r s , R . J . , T . A . B l a c k , and M.D. Novak . 1 985 . M o d e l l i n g s o i l t e m p e r a t u r e i n f o r e s t c l e a r - c u t s u s i n g C l i m a t e S t a t i o n d a t a . A g r i . F o r . Me t . 3 6 : 1 5 3 - 1 6 4 . T a n , C . S . , T . A . B l a c k , and J . Y . Nnyamah. 1978 . A s i m p l e d i f f u s i o n model o f t r a n s p i r a t i o n a p p l i e d t o a t h i n n e d D o u g l a s - f i r s t a n d . E c o l o g y 5 9 : 1 2 2 1 - 1 2 2 9 . - 53 -T u r n e r , N . C . , J . E . Begg and M.L. T o n n e t . 1978 . O smo t i c a d j u s tmen t o f sorghum and s u n f l o w e r c r o p s i n r e s p o n s e t o w a t e r d e f i c i t s and i t s i n f l u e n c e on the w a t e r p o t e n t i a l a t wh i ch s t oma ta c l o s e . A u s t . J . P l a n t P h y s i o l . 5 : 597 -608 . T y r e e , M.T. 1976 . N e g a t i v e t u r g o r p r e s s u r e i n p l a n t c e l l s : f a c t o r f a l l a c y ? C a n . J . B o t . 5 4 : 2 7 3 8 - 2 7 4 6 . T y r e e , M.T . , Y . N . S . Cheung , M.E. MacGregor and T . A . T a l b o t . 1978 . The c h a r a c t e r i s t i c s o f s e a s o n a l and o n t o g e n e t i c changes i n t h e t i s s u e - w a t e r r e l a t i o n s o f A c e r , P o p u l u s , Tsuga and P i c e a . C a n . J . B o t . 5 6 : 6 3 5 - 6 4 7 . Van B a v e l , C . H . M . , G . B . S t i r k , and K . J . B r u s t . 1968 . H y d r a u l i c p r o p e r t i e s o f a c l a y loam s o i l and t he f i e l d measurements o f water-u p t a k e by r o o t s . I . I n t e r p r e t a t i o n o f w a t e r c o n t e n t and p r e s s u r e p r o f i l e s . S o i l S c i . S o c . Am. P r o c . 3 2 : 3 1 0 - 3 1 7 . W a l t o n , D .C . 1980 . B i o c h e m i s t r y and p h y s i o l o g y o f a b s c i s i c a c i d . Annua l Rev i ews of P l a n t P h y s i o l o g y . 3 1 : 4 5 3 - 4 8 9 . W a t t s , S . , J . L . R o d r i g u e z , S . E . E v a n s , and W . J . D a v i e s . 1 9 8 1 . Root and s hoo t g rowth o f p l a n t s t r e a t e d w i t h a b s c i s i c a c i d . Anna l o f Bo tany 4 7 : 5 9 5 - 6 0 2 . - 54 -CHAPTER 2 STOMATAL CHARACTERISTICS AND TRANSPIRATION OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT - 55 -STOMATAL CHARACTERISTICS AND TRANSPIRATION OF THREE SPECIES OF CONIFER SEEDLINGS PLANTED ON A SOUTH-FACING HIGH ELEVATION CLEARCUT I . INTRODUCTION A t ho r ough u n d e r s t a n d i n g o f s e e d l i n g w a t e r r e l a t i o n s i s r e q u i r e d b e f o r e t r e e b r e e d e r s and s i l v i c u l t u r a l i s t s can e s t a b l i s h t h e most r e a l i s t i c c r i t e r i a f o r t he s e l e c t i o n o f s p e c i e s , p r o v e n a n c e , s t o c k t y pe and o p e r a t i o n a l t r e a t m e n t s t h a t w i l l o p t i m i z e r e g e n e r a t i o n . In t h i s r e g a r d much i n t e r e s t has been f o c u s e d on the r o l e o f s t oma ta i n t h e r e g u l a t i o n o f t r a n s p i r a t i o n and p h o t o s y n t h e s i s . M e a s u r e -ments o f t he s t o m a t a l r e s pon s e s o f s e e d l i n g s t o e n v i r o n m e n t a l c o n d i t i o n s have been l i m i t e d by i n a d e q u a t e i n s t r u m e n t a t i o n ( L i v i n g s t o n e t al_. 1984; Kaufmann 1 9 8 1 ) , and t o da te few i n t e n s i v e f i e l d s t u d i e s o f such r e s p o n s e s have been r e p o r t e d ( G r o s s n i k l e and B l a k e 1985; Hobbs 1 9 8 4 ) . The deve l opmen t o f a s a t i s f a c t o r y model t o e x p l a i n t he e f f e c t s o f v a r i o u s e n v i r o n m e n t a l v a r i a b l e s upon s t o m a t a l c o n d u c t a n c e depends o f adequa t e know ledge o f s t o m a t a l a c t i o n a t t he c e l l u l a r l e v e l . U n f o r t u n -a t e l y a t p r e s e n t t h e r e i s c o n s i d e r a b l y more know ledge o f t h e e f f e c t s o f t h e s e v a r i a b l e s on s t o m a t a l a p e r t u r e r a t h e r t han t h e i r mode o f a c t i o n o r c o n t r o l ( L a s s o i e 1982; J a r v i s e t j i K 1 9 8 1 ) . A l t h o u g h t h i s p r e c l u d e s t h e c o n s t r u c t i o n o f a m e c h a n i s t i c model o f s t o m a t a l a c t i o n , i t i s p o s s i b l e t o p roduce what J a r v i s (1976) c a l l s a " p henomeno l o g i c a l m o d e l " . Tha t i s a model t h a t p r e d i c t s s t o m a t a l c o n d u c t a n c e u s i n g e x p e r i m e n t a l l y d e t e r -mined r e l a t i o n s between s t o m a t a l c o n d u c t a n c e and v a r i o u s e n v i r o m e n t a l v a r i a b l e s . - 56 -A commonly used app roach i n phenomeno l o g i c a l t y p e m o d e l i n g i s b o u n d a r y - l i n e a n a l y s i s , whereby a c u r v e i s drawn t h r ough t he upper-most p o i n t s i n a p l o t o f g s a g a i n s t a s i n g l e i n d ependen t v a r i a b l e . I t i s assumed t h a t p o i n t s on t h i s l i n e r e p r e s e n t t h e maximum p o s s i b l e c o n d u c t -ance f o r a g i v e n v a l u e o f t h e i n d e p e n d e n t v a r i a b l e w h i l s t p o i n t s be low t h i s l i n e r e p r e s e n t c o n d u c t a n c e s l i m i t e d by o t h e r v a r i a b l e s , f o r wh i ch b o u n d a r y - l i n e c u r v e s a r e a l s o d e t e r m i n e d (Webb 1972; J a r v i s 1 9 7 6 ) . In t h e s i m p l e s t c a se i t i s assumed t h a t t h e l i m i t i n g f a c t o r s a r e m u l t i p l i -c a t i v e and t h a t s t o m a t a l c ondu c t an c e r e sponds t o t he v a r i a b l e s i n d e p e n d -e n t l y . However t h e r e have been some r e p o r t s t h a t i n t e r a c t i o n s do o c c u r such as t h a t between vapou r p r e s s u r e d e f i c i t and a i r t e m p e r a t u r e (Ng and J a r v i s 1980; L e v e r e n z 1 9 8 1 ) . A l a r g e number o f p o i n t s a r e r e q u i r e d t o g e n e r a t e b o u n d a r y - l i n e c u r v e s t h a t w i l l be bo th r e g u l a r and c o n t i n u o u s . F o r t h i s r e a son i n d i v -i d u a l f u n c t i o n s a r e o f t e n o b t a i n e d f r om c o n t r o l l e d e n v i r o n m e n t s t u d i e s ( J one s 1983) w i t h t he a s s u m p t i o n t h a t r e s p o n s e f u n c t i o n s measured i n t he l a b o r a t o r y a r e t h e same as t h o s e t h a t o c c u r i n t h e f i e l d . However , d i f f e r e n c e s between such measured r e s p o n s e s have been r e p o r t e d (Kanemasu and Tanne r 1 9 6 7 ) . T h i s c h a p t e r ( i ) d e s c r i b e s t he s t o m a t a l r e s p o n s e s t o e n v i r o n m e n t a l and p h y s i o l o g i c a l v a r i a b l e s ( g l o b a l s o l a r i r r a d i a n c e ( R s ) , a i r t empe r -a t u r e ( T ) , a v e r age r o o t zone s o i l w a t e r p o t e n t i a l ( ? s ) , vapou r p r e s -s u r e d e f i c i t ( D ) , and n eed l e t u r g o r p o t e n t i a l ( Y p ) ) o f t h r e e s p e c i e s o f c o n i f e r s e e d l i n g s g row ing on a s o u t h - f a c i n g , h i g h e l e v a t i o n c l e a r c u t , ( i i ) examines how t h e s e r e s p o n s e s change o v e r two y e a r s and compares t h e r e s p o n s e s o f one and two y e a r o l d s e e d l i n g s o f the same s p e c i e s , ( i i i ) - 57 -d e s c r i b e s and t e s t s a b o u n d a r y - l i n e a n a l y s i s model o f s t o m a t a l b e h a v i o u r wh i c h was d e v e l o p e d f o r t h e e s t i m a t i o n o f d a i l y s e e d l i n g t r a n s p i r a t i o n . I I . METHODS A . S i t e and E x p e r i m e n t a l D e s i g n The s i t e and e x p e r i m e n t a l d e s i g n a r e d e s c r i b e d i n d e t a i l i n C h a p t e r 1 . B r i e f l y , t he e x p e r i m e n t a l s i t e i s l o c a t e d a t an e l e v a t i o n o f 1150 m on a 30° s o u t h - f a c i n g s l o p e . The s o i l i s a g r a v e l l y sandy loam o v e r compact g l a c i a l t i l l . In A p r i l 1981 equa l numbers o f D o u g l a s - f i r ( P s eudo t s uga m e n z i e s i i ( M i r b . ) F r a n c o ) , w e s t e r n hemlock (Tsuga h e t e r o p h y l l a ( R a f . S a r g . ) and P a c i f i c s i l v e r f i r ( A b i e s a m a b i l i s ( D o u g l . ) F o r b e s ) 1-0 c o n t a i n e r grown s t y r o p l u g s were l a i d ou t i n a r andom i zed c o m p l e t e - b l o c k d e s i g n . T he r e were 32 b l o c k s w i t h 90 s e e d -l i n g s pe r b l o c k . The re were t h r e e t r e a t m e n t s : shade p r o v i d e d by 0.2 m h i g h by 0 .3 m w ide shade c a r d s , s e l f shade p r o v i d e d by p l a n t i n g t h e s e e d l i n g s i n c l i n e d t o t h e s o u t h w e s t , and a c o n t r o l . In May 1982 e i g h t a d d i t i o n a l b l o c k s were l a i d ou t u s i n g the same t h r e e s p e c i e s , p r o v e n -an ce , s t o c k t y p e and p l a n t i n g t e c h n i q u e as i n t h e p r e v i o u s y e a r . Four-t r e a t m e n t s were t e s t e d : i r r i g a t i o n (wa te r was p r o v i d e d by a t r i c k l e i r r i g a t i o n s y s t e m ) , shade and i r r i g a t i o n , and no shade and no i r r i g a t i o n ( c o n t r o l ) . Wate r was a p p l i e d when t e n s i o m e t e r s on t he s i t e i n d i c a t e d t h a t ¥ s was l e s s t han - 0 . 0 4 MPa. B. Measurements and Da t a A n a l y s i s S t a n d a r d h o u r l y a ve r age m i c r o m e t e o r o l o g i c a l measurements o f R s , T and D a t t he 1 m h e i g h t , w i nd speed (u) a t t h e 0 . 4 m h e i g h t and - 58 -p r e c i p i t a t i o n , and measurements o f r o o t zone vs w i t h t e n s i o m e t e r s and t h e r m o c o u p l e p s y c h r o m e t e r s a r e d e s c r i b e d i n C h a p t e r 1. S t o m a t a l c o n d u c t a n c e was measu red u s i n g a t r a n s i e n t t y p e po r ome t e r ( L i v i n g s t o n ^ t a]_. 1984) ( Append i x I I ) a l s o d e s c r i b e d i n C h a p t e r 1. H o u r l y measurements o f s e e d l i n g g s were made on the t h r e e s p e c i e s on 13 d a y s , n i n e o f wh i ch were sunny a l l day , between J une 10 and September 9 , 1982 and on f i v e d a y s , f o u r o f wh i c h were sunny a l l day , between J une 6 and Augus t 14 , 1983 . Measurements were made on s e e d l i n g s p l a n t e d i n 1981 and 1982 bu t were c o n f i n e d t o s e e d l i n g s i n t h e i r r i g a t e d and n o n - i r r i g a t e d t r e a t m e n t s w i t h no s hade . A p p r o x i m a t e l y 400 h o u r l y v a l u e s o f ave rage s e e d l i n g g s , each c a l c u l a t e d by a v e r a g i n g 2 t o 3 mea su r e -m e n t s , were made on each s p e c i e s i n 1982 , w h i l e 160 were made i n 1 9 8 3 . The p r o j e c t e d n e e d l e a r e a ( A ) , r e q u i r e d i n t h e measurement o f g s , was d e t e r m i n e d w i t h i n t h r e e weeks o f t h e g s measurements e i t h e r d i r e c t l y u s i n g a l e a f a r e a mete r (Model L i - 3 0 0 0 , L i - C o r I n c . , L i n c o l n , N e b r a s k a , U . S . A . ) , o r by u s i n g r e g r e s s i o n e q u a t i o n s t h a t r e l a t e p r o j e c t e d n e e d l e a r e a t o t he mass o f n e ed l e s d r i e d t o 65°C f o r one day ( L i v i n g s t o n e t a]_. 1 9 8 4 ) . H o u r l y measurements o f vjtx were a l s o made on d i f f e r e n t , bu t s i m i l a r l y s i z e d , s e e d l i n g s w i t h a p r e s s u r e chamber (PMS I n c . , C o r v a l l i s , O r egon , U . S . A . ) . No more t han two t w i g s were removed f r om any s e e d -l i n g . A p p r o x i m a t e l y e ve r y 3 t o 4 weeks d u r i n g t h e g r ow i ng seasons i n 1982 and 1983 measurements o f ^ were o b t a i n e d w i t h t h e r m o c o u p l e p s y c h r o m e t e r chambers u s i n g t h e t e c h n i q u e d e s c r i b e d i n C h a p t e r 1 and c a l c u l a t e d by s u b t r a c t i n g ^ t x f r om - 59 -B o u n d a r y - l i n e a n a l y s i s was p e r f o rmed t o d e t e r m i n e t he r e l a t i o n s h i p between g s and R s , T, D, Y s and Y P , and t he number o f hours s i n c e s u n r i s e ( t ) . A l l v a r i a b l e s were c o n s i d e r e d t o a c t i n d e p e n d e n t l y b u t m u l t i p l i c a t i v e l y . I t was h y p o t h e s i z e d i n i t i a l l y t h a t g s was a f u n c t i o n o f R s , T , D and ¥p, i . e . 9 s = 9smax f<M 9(T) h(D) j ( y p ) (1) where gsmax i s t h e maximum c o n d u c t a n c e and f , g , h and j a r e t h e f u n c -t i o n s t h a t d e s c r i b e t he b o u n d a r y - l i n e c u r v e s f o r t he r e l a t i o n between g s and t he h o u r l y ave rage v a l u e o f each v a r i a b l e . D a i l y s e e d l i n g t r a n s p i r a t i o n r a t e on a p r o j e c t e d l e a f a r e a b a s i s was c a l c u l a t e d as t h e sum o f t h e h o u r l y p r o d u c t s o f a ve r age v a l u e s o f g s and ave rage v a l u e o f D / (R V T ' ) a t the 1 m h e i g h t . As d i s c u s s e d i n t h e p r e v i o u s c h a p t e r , t h i s makes t h e r e a s o n a b l e a s s u m p t i o n f o r n e e d l e s t h a t gb i s l a r g e enough t h a t e n - e a i s w e l l a p p r o x i m a t e d by D and t h a t t he boundary l a y e r r e s i s t a n c e ( g b - 1 ) i s n e g l i g i b l e compared t o the s t o m a t a l r e s i s t a n c e ( g s - 1 ) . I I I . RESULTS AND DISCUSSION The maximum v a l u e s o f g s measured f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r were 0 . 4 4 , 0.31 and 0 .24 cm s " 1 , r e s p e c t -i v e l y ( T a b l e 2 . 1 ) . These v a l u e s were o b s e r v e d i n i r r i g a t e d s e e d l i n g s b e f o r e s o l a r noon and o n l y when D < 1.0 k P a . Murphy and F e r r e l l (1982) r e p o r t e d g S max o f ° « 5 9 s _ 1 1 n D o u g l a s - f i r s a p l i n g s , w h i l e H a l l g r e n - 60 -T a b l e 2.1 The maximum s t o m a t a l c ondu c t an c e measured ( g s r T i a x ) and t h e number o f t i m e s t h i s v a l u e was o b t a i n e d (n) f o r D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s . S p e c i e s g s m a x (cm s - 1 ) D o u g l a s - f i r Wes te rn hemlock P a c i f i c s i 1 ve r f i r 0 .44 0 .31 0 .24 6 2 3 - 61 -(1978) w o r k i n g w i t h D o u g l a s - f i r s e e d l i n g s measured g S max o f ° » 4 3 cm s - 1 . Runn i ng (1976) r e p o r t e d a gsmax ° f 0*23 cm s " 1 f o r 1 - 3 m t a l l w e s t e r n hemlock w h i l e Teskey e t al_. (1984) o b s e r v e d g s o f 0 . 35 cm s " 1 i n P a c i f i c s i l v e r f i r s e e d l i n g s . A . Response o f g s t o Changes i n G l o b a l S o l a r I r r a d i a n c e F i g u r e 2 . 1a shows the r e l a t i o n s h i p o b t a i n e d when gs/gsmax f ° r D o u g l a s - f i r i s p l o t t e d a g a i n s t R s and i n d i c a t e s t h a t o t h e r v a r i a b l e s b e s i d e s R s l i m i t g s . B o u n d a r y - l i n e a n a l y s i s p r oduced r e s p o n s e c u r v e s f o r t he t h r e e s p e c i e s ( F i g u r e 2 . 1 b ) wh i c h can be d e s c r i b e d by -aR 9s/9smax = 1 - e s (2 ) where a i s a c o n s t a n t . V a l u e s o f t h e c o n s t a n t i n (2) f o r t h e t h r e e s p e c i e s a r e g i v e n i n T a b l e 2 . 2 . Response c u r v e s f o r t he r e l a t i o n between gs/gsmax a n d p h o t o s y n t h e t i c pho ton f l u x d e n s i t y i n ymol n r 2 s " 1 can be g e n e r a t e d by m u l t i p l y i n g R s i n W n r 2 by 2 .04 (Meek e t a l . 1 9 8 4 ) . In g ene r a l D o u g l a s - f i r s t oma ta opened more r a p i d l y w i t h i n c r e a s i n g l i g h t t h an t h o s e o f w e s t e r n hemlock and P a c i f i c s i l v e r f i r ( F i g u r e 2 . 1 b ) . The r e s p o n s e o f g s t o l i g h t f o r t h e s e s p e c i e s was t y p i c a l o f t h a t f ound i n o t h e r s t u d i e s on c o n i f e r s ( L e v e r e n z 1974; Tan e t al_. 1977; H i n c k l e y e t al_. 1 9 7 8 ) . B. Response o f g s t o changes i n A i r Tempe ra tu r e The o b v i o u s d i f f i c u l t y i n s e p a r a t i n g t h e e f f e c t s o f t e m p e r a t u r e and vapour p r e s s u r e d e f i c i t s on gs has l e d t o c o n t r a d i c t o r y r e s u l t s - 52 -F igure 2.1 a . The r e l a t i o n s h i p between the r a t i o of the stomatal conductance ( g s ) to the maximum stomatal conductance (Ssnax) a n f 1 g lobal sol a r - i r r a d i a n c e (R s ) for i r r i g a t eH (•) and non - i r r i g a t ed (o) Doug l a s - f i r s e ed l i n g s . Each point i s the average of three measurements. Also shown i s the boundary- l ine which i n d i c a t e s the upper l i m i t of the obse rva t i ons , b. Comparison of the boundary- l ines for the r e l a t i o n s h i p between gs/gsmax a n n l R s for Doug l a s - f i r ( s o l i d l i n e ) , western hemlock (dotted l i n e ) and P a c i f i c s i l v e r f i r (broken l i n e ) . (PPFD in ymol n r 2 s - 1 i s approx imate ly 2.04 t imes R s in Wm - 2 ) . - 63 -T a b l e 2.2 -aR V a l u e s o f t h e c o e f f i c i e n t a i n t h e e q u a t i o n ; g s / g s n i a x = 1 - e s d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s t h e ave r age s e e d l i n g s t o m a t a l c ondu c t an c e (cm s - 1 ) gsmax i s maximum g s (cm s _ 1 ) » and R s i s t h e h o u r l y a ve r age g l o b a l s o l a r i r r a d i a n c e (W m ) . Yea r o f Yea r o f Wes te rn P a c i f i c P l a n t i n g Measurement D o u g l a s - f i r hemlock s i l v e r f i r 1981 1982 0 .018 0 .013 0 .010 1981 1983 0 .019 0 .012 1982 1982 0 .018 0 .012 0.011 - 64 -( J one s 1 9 8 3 ) . However e v i d e n c e t h a t t h e opt imum t e m p e r a t u r e f o r g s i s r e l a t e d t o t h e t e m p e r a t u r e c h a r a c t e r i s t i c s o f t h e enzymes i n v o l v e d i n s t o m a t a l a c t i o n (Rogers e t j i l _ . 1979; Ou t l aw e t ail_. 1979) s u p p o r t s t h e c o n t e n t i o n t h a t T i s an i n d e p e n d e n t v a r i a b l e . The r e l a t i o n s h i p between gs/9smax a n d T f ° r D o u g l a s - f i r i s shown i n F i g u r e 2 . 2 a . Maximum g s o c c u r r e d a t abou t 18°C. In w e s t e r n hemlock and P a c i f i c s i l v e r - f i r b o u n d a r y - l i n e a n a l y s i s r e v e a l e d s i m i l a r -r e l a t i o n s h i p s w i t h a p ronounced d e c l i n e i n g s above and be low 17.5°C and 17.0°C, r e s p e c t i v e l y ( F i g u r e 2 . 2 b ) . A l l t he b o u n d a r y - l i n e a n a l y s i s c u r v e s can be d e s c r i b e d by 9s/9smax * 1 - b(T - T m a x ) 2 (3) where b i s a c o n s t a n t and T m a x i s t h e a i r t e m p e r a t u r e a t wh i c h maximum g s o c c u r s . V a l u e s o f t h e c o n s t a n t s i n (3) a r e g i v e n i n T a b l e 2 . 3 . A s i m i l a r r e s p o n s e o f g s t o t e m p e r a t u r e has been r e p o r t e d by L e v e r e n z ( 1 9 7 4 ) , J a r v i s (1975) and by Ng (1978) who f ound t h a t g s i n S c o t s p i n e ( P i n u s s y l v e s t r i s L . ) , a t c o n s t a n t D, d e c r e a s e d above and be low 20°C. In c o n t r a s t W a r r i t e t a]_. (1980) f ound t h a t t e m p e r a t u r e had no e f f e c t o v e r a 13°C t o 29°C range on g s o f a p p l e t r e e s a t c o n s t a n t D. Kaufmann (1976) and Runn i ng (1976) c o n c l u d e d t h a t t empe r -a t u r e was no t a s i g n i f i c a n t v a r i a b l e c o n t r o l l i n g g s i n c o n i f e r s unde r f i e l d c o n d i t i o n s p r o v i d e d D was t a k e n i n t o a c c o u n t . - 65 -F i g u r e 2.2 The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c o n d u c t a n c e (g$) t o t h e maximum s t o m a t a l c o n d u c t a n c e ( g s m a x ) and a i r t e m p e r a t u r e (T ) f o r i r r i g a t e d ( • ) and n o n - i r r i g a t e d (o ) D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s the average o f t h r e e measuremen ts . A l so shown i s t h e b o u n d a r y - l i n e wh ich i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar ison o f t h e b o u n d a r y - l i n e s f o r t h e r e l a t i o n s h i p between gs/gsmax a r , d T f o r D o u g l a s - f i r ( s o l i d l i n e ) , w e s t e r n hemlock H o t t e d l i n e ) and P a c i f i c s i l v e r f i r (broken l i n e ) . - 66 -T a b l e 2 .3 V a l u e s o f t h e c o e f f i c i e n t b and T m a x i n t he e q u a t i o n ; gs/gsmax = 1 - b (T - T m a x ) d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s t h e a v e r age s e e d l i n g s t oma t a l c ondu c t an c e (cm s ) g Smax i s maximum g s (cm s - 1 ) » T i s t h e h o u r l y a ve r age a i r t e m p e r a t u r e (°C) and T m a x i s t h e a i r t e m p e r a t u r e a t wh i ch g s = gsmax • Year o f Year o f D o u g l a s - f i r Western P a c i f i c P l a n t i n g Measurement hemlock s i l v e r f i r D T m a x b T m a x b T m a x 1981 1982 0 .0053 18 .0 0 .0054 18 .0 0 .0102 17 . 0 1981 1983 0 .0061 18 .0 0 .0053 17 .5 1982 1982 0 .0058 18 .0 0 .0066 17 . 5 0 .0097 1 7 . 5 - 67 -C . Responses o f g s t o Changes i n Vapour P r e s s u r e D e f i c i t A l t h o u g h the e x a c t mechan ism by w h i c h g s r e sponds t o D i s no t known, i t i s g e n e r a l l y a c c e p t e d t h a t t h e s t oma ta r e spond t o i n c r e a s e d D d i r e c t l y r a t h e r t han t o t h e r e du ced b u l k l e a f w a t e r p o t e n t i a l t h a t r e s u l t s f r om i n c r e a s e d t r a n s p i r a t i o n r a t e s ( S h e r i f f and Kay 1977; Ty r ee and Y a n o u l i s 1980; J a r v i s and M o r r i s o n 1981; S h e r i f f 1 9 8 4 ) . F o r e x a m p l e , i n c a se s when g s i s so r e du ced t h a t t r a n s p i r a t i o n d e c l i n e s (as r e p o r t e d i n C h a p t e r 1) and the w a t e r p o t e n t i a l o f t h e l e a f as a who le i n c r e a s e s (Tan e t al_. 1 9 7 7 ) , t h e s t o m a t a l r eponse must be c a u s e d by a change i n w a t e r r e l a t i o n s o f e i t h e r t h e who le e p i d e r m i s ( F a r q u h a r 1978) o r t he c e l l s a d j a c e n t t o each s t oma te ( M a i e r - M a e r c k e r 1983) i n d e -penden t o f t h e w a t e r r e l a t i o n s o f t h e b u l k o f t he l e a f ( S h e r i f f 1 9 8 4 ) . We l l d e f i n e d and c o n t i n u o u s b o u n d a r y - l i n e c u r v e s were o b t a i n e d f r om p l o t s o f gs/gmax v e r s u s D ( F i g u r e 2 . 3 a ) . The boundary a n a l y s i s c u r v e s shown i n F i g u r e 2 .3a and b can a l l be d e s c r i b e d by V^smax " "C1 + W o e s ) " ) (4 ) where n i s a c o n s t a n t and D 0 . 5 i s t he v a l u e o f D when g s i s h a l f t he maximum. A l l s p e c i e s showed a marked d e c l i n e i n g s as D exceeded 1 k P a . T h i s e f f e c t was most p ronounced i n P a c i f i c s i l v e r f i r f o l l o w e d by w e s t e r n hemlock and D o u g l a s - f i r . The c o r r e s p o n d i n g v a l u e s o f t h e c o n s t a n t s i n (4) f o r t h e t h r e e s p e c i e s a r e p r e s e n t e d i n T a b l e 2 . 4 . A s i m i l a r t y p e o f c u r v i l i n e a r r e s p o n s e o f g s t o i n c r e a s i n g D has been o b s e r v e d i n o t h e r s t u d i e s on c o n i f e r s ( L e v e r e n z 1974; Tan e t a l . - 68 -F i g u r e 2 .3 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c o n d u c t a n c e ( g s ) t o t h e maximum s t o m a t a l c o n d u c t a n c e (9smax) a n c 1 vapour p r e s s u r e d e f i c i t (D) f o r i r r i g a t e d ( • ) and n o n - i r r i g a t e d (o ) D o u g l a s - f i r s e e d l i n g s . Fach p o i n t i s t h e average o f t h r e e m e a s u r e m e n t s . A l so shown i s t h e b o u n d a r y - 1 i n p wh ich i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar ison o f t h e b o u n d a r y - l i n e s f o r t h e r e l a t i o n s h i p between gs/gsmax a n d n f o r D o u g l a s - f i r ( s o l i d l i n e ) , w e s t e r n hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r f i r ( b r o k e n l i n e ) . - 69 -T a b l e 2.4 V a l u e s o f t h e c o e f f i c i e n t , D 0.5 and n, i n t he e q u a t i o n ; gs/gsmax = 1(1 + ( D / D 0 . 5 ) n ) d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g where g s i s t h e a v e r age s e e d l i n g s t oma t a l c ondu c t an c e (cm s ) , gsmax 1 S maximum g s (cm s ) , D i s t h e h o u r l y a ve r age vapour p r e s s u r e d e f i c i t (kPa) and D o .5 "is t h e vapour p r e s s u r e d e f i c i t a t wh i ch g s i s h a l f gsmax* Year o f Year o f D o u g l a s - f i r Western P a c i f i c P l a n t i n g Measurement hemlock s i l v e r f i r Do.5 n Do.5 n Do.5 1981 1982 2.42 4 .71 2 .23 5.50 1.80 1981 1983 2.39 4 .74 2.10 5.51 -1982 1982 2.31 4 . 85 2.16 5.64 1.91 - 70 -1977; Ng 1978; Wat t s and N e i l s o n 1978; J ohnson and F e r r e l l 1983; K e l l i h e r 1985; G r o s s n i c k l e and B l a k e 1 9 8 6 ) . However , Runn i ng (1980 and 1984) i n r e v i e w i n g o t h e r work s u g g e s t s t h a t a l i n e a r f u n c t i o n can be u sed t o r e l a t e g s t o D. D. Response o f g s t o Changes i n T u r g o r P o t e n t i a l and S o i l Water P o t e n t i a l The s c a t t e r p l o t and b o u n d a r y - l i n e c u r v e f o r gs/gsmax v e r s u s f o r D o u g l a s - f i r ( F i g u r e 2 . 4 ) wh i c h i s t y p i c a l o f t h o s e p l o t t e d f o r t h e o t h e r two s p e c i e s , shows t h a t when no o t h e r f a c t o r s a r e l i m i t i n g , 9s/9smax d e c r e a s e s w i t h i n c r e a s i n g >pp. T h i s i n d i c a t e s t h a t Vp, w h i c h i s an e s t i m a t e o f bu l k t u r g o r p r e s s u r e r a t h e r t h an t he t u r g o r p r e s s u r e o f gua rd c e l l s and a s s o c i a t e d e p i d e r m a l c e l l s , i s a f f e c t e d by g s and no t v i c e v e r s a . S i n c e ¥p d e c r e a s e s as a r e s u l t o f t he i n c r e a s e d e v a p o r a t i o n r a t e as s t oma ta open , i t i s l i k e l y t h a t a t some p o i n t t he l o w e r e d ^p has a n e g a t i v e f eedback e f f e c t on g s . Some o f t he s c a t t e r i n F i g u r e 2 .4 i s t h e r e s u l t o f the s t r o n g h y s t e r e s i s i n t h e r e l a t i o n between g s and *p . F i g u r e 2 . 5 shows t h a t even though t u r g o r p o t e n t i a l i n c r e a s e d a f t e r r e a c h i n g a minimum a t m i d -m o r n i n g , t h e r e was no t a c o r r e s p o n d i n g i n c r e a s e i n g s and t h a t some o t h e r f a c t o r was l i m i t i n g g s . T he r e was no c l e a r i n d i c a t i o n i n any o f t he s p e c i e s , o f a c r i t i c a l t h r e s h o l d f p o r y j t x be low wh i ch s t oma ta r a p i d l y c l o s e as has been r e p o r t e d i n o t h e r s t u d i e s on gymnosperms (War ing and Runn i ng 1978; Drew and F e r r e l l 1979; Te skey e t a l . 1984; G r o s s n i c k l e and B l a k e 1 9 8 5 ) . - 71 -F i g u r e 2 .4 The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c o n d u c t a n c e ( g s ) t o t he maximum s t oma t a l c onduc t an ce (Qsmax) and t he t u r g o r p o t e n t i a l f o r i r r i g a t e d (•) and n o n - i r r i g a t e d (o) D o u g l a s - f i r s e e d l i n g s . The s e e d l i n g s were p l a n t e d i n 1982 and t h e measurements were made on 13 days between June and September 1 9 8 2 . - 72 -% (MPa) 0 0.5 1 1.5 2 0.4 i 1 1 1 1 D (kPa) F i g u r e 2 .5 The r e l a t i o n s h i p between t he s t o m a t a l c ondu c t an c e o f a D o u g l a s - f i r s e e d l i n g and t h e h o u r l y ave rage vapou r p r e s s u r e d e f i c i t (D) ( o ) , and t u r g o r p o t e n t i a l [%) (•) measured on J u l y 2 7 , 1982 . The " o n e s " mark t h e t i m e (06 :00 PST) when t h e f i r s t measurements were made. Measurements were r e p e a t e d e v e r y hour u n t i l 2 1 . 0 0 PST. - 73 -The s c a t t e r p l o t shown i n F i g u r e 2 .6a i l l u s t r a t e s t h a t t h e r e i s a s i g n i f i c a n t i n f l u e n c e o f v s on g s . T h i s wou l d s u g g e s t t h a t g s i s i n p a r t c o n t r o l l e d by a base (predawn) y j t x ' W n e n *s 1 S l ° w » a n d c o n s e q u e n t l y base y j t x 1 S l ° w » 9s 1 S l i m i t e d a l l day by h y d r a u l i c f a c t o r s wh i ch a l m o s t c o m p l e t e l y o v e r r i d e t h e o t h e r r e s p o n s e s . C u r v e s d e r i v e d f r om b o u n d a r y - l i n e a n a l y s i s o f 9s/9smax v e r s u s vs p l o t s f o r t h e t h r e e s p e c i e s ( F i g u r e 2 . 6 b ) a r e d e s c r i b e d by t h e f o l l o w i n g 9s /9smax = e k Y s (0 > * s > - 0 . 1 MPa) (5 ) and 9s/9smax = nvps - n < - 0 . 1 MPa) (6) where k, m and n a r e c o n s t a n t s . The v a l u e s o f t h e s e c o n s t a n t s a r e g i v e n i n T a b l e 2 . 5 . The b o u n d a r y - l i n e c u r v e s i n d i c a t e , i n a l l s p e c i e s , t h a t when no o t h e r f a c t o r s a r e l i m i t i n g , t he l a r g e s t r a t e o f d e c r e a s e i n g s , w i t h d e c r e a s i n g ¥ 5 , o c c u r s between 0 and - 0 . 1 MPa. A t <rs o f - 1 . 5 MPa, g s o f D o u g l a s - f i r s e e d l i n g s i s a p p r o x i m a t e l y 50% of 9smax- T h i s compares t o 30% and 18% f o r w e s t e r n hemlock and P a c i f i c s i l v e r f i r , r e s p e c t i v e l y . These f i g u r e s c o r r e s p o n d t o t h e r e d u c t i o n i n s e e d l i n g t r a n s p i r a t i o n r a t e s t h a t were o b s e r v e d i n 1982 ( C h a p t e r 1 ) . F u r t h e r m o r e , t h e d i f f e r e n c e s i n r e s p o n s e t o r e du ced 4> s between s p e c i e s c o r r e s p o n d t o d i f f e r e n c e s i n t h e amount o f o s m o t i c a d j u s t m e n t e x h i b i t e d by each s p e c i e s ( d i s c u s s e d i n C h a p t e r 1) w h i c h , f o r e xamp l e , e n a b l e d D o u g l a s - f i r s e e d l i n g s t o m a i n t a i n r e l a t i v e l y h i g h e r l e v e l s o f t u r g o r a t low Y s t han w e s t e r n hemlock o r P a c i f i c s i l v e r f i r s e e d l i n g s . - 74 -F i g u r e 2 .6 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c o n d u c t a n c e ( g s ) t o t h e maximum s t o m a t a l c o n d u c t a n c e (9smax) a n d average r o o t zone s o i l wa te r p o t e n t i a l ( ^ s ) f o r n o n - i r r i g a t e d D o u g l a s - f i r s e e d l i n g s . Each p o i n t i s t h e average o f t h r e e measuremen ts . A l so shown i s t h e b o u n d a r y - l i n e wh ich i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , b . Compar ison o f t h e b o u n d a r y - l i n e s f o r t h e r e l a t i o n s h i p between g s / g s m a x a n f l ^s f o r D o u g l a s - f i r ( s o l i d l i n e ) , w e s t e r n hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r f i r ( b r o k e n l i n e ) . Tab l e 2.5 V a l u e s o f t h e c o e f f i c i e n t , k, m and p i n t h e e q u a t i o n s gs /gsnax = e ( 0 2. ^s i i M P a ) a n c ' g s / g s r n a x = m <)Js + n (^ s < - 0 . 1 MPa) d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g where g s i s t h e ave rage s e e d l i n g s t o m a t a l c ondu c t an c e (cm s _ 1 ) » 9smax i s t h e maximum g s (cm s " ) and ip s i s t he ave rage r oo t zone s o i l wa te r p o t e n t i a l ( M P a ) . Year o f Year o f D o u g l a s - f i r Western hemlock P a c i f i c s i l v e r - f i r P l a n t i n g Measurement k m n k m n k m n 1981 1982 1.74 0.21 0.86 1.76 0 .37 0 . 88 3.01 0 .26 0.77 1981 1983 1.51 0 .24 0.88 1.73 0 .32 0.87 3.01 - -1982 1982 1.63 0 .26 0 .88 1.86 0 .38 0 .87 3.34 0 .39 0 .75 <J1 - 76 -A s i m i l a r r e s pon se o f g s t o ns as t h a t t o predawn ¥rt. x has been r e p o r t e d i n o t h e r s t u d i e s (Runn ing 1976 and 1980; K e l l i h e r e t a l . 1985; K e l l i h e r 1 9 8 5 ) . However , Runn i ng (1984) i m p l i e s t h a t f o r Y S l o w e r than - 1 . 5 MPa, gs/9smax 1 S c l o s e t o z e r o . E . R e l a t i o n s h i p between g s and t h e Time s i n c e S u n r i s e On a l l d a y s , i n c l u d i n g t h o s e t h a t were o v e r c a s t a l l day , when measurements were t a k e n , t h e h i g h e s t s t o m a t a l c o n d u c t a n c e s were measured d u r i n g t he m i d d l e o f t h e mo rn i n g a f t e r wh i ch t h e r e was p ronounced s t oma-t a l c l o s u r e . D e s p i t e a marked d e c r e a s e i n D and i n c r e a s e i n i n t he l a t e a f t e r n o o n t h e r e was not a c o r r e s p o n d i n g i n c r e a s e i n g s ( F i g u r e 2 . 5 ) . L i g h t l e v e l s were not l i m i t i n g a t t h i s t ime because the s e e d -l i n g s , b e i n g l o c a t e d on a s ou t hwes t f a c i n g s l o p e , were s t i l l e xposed t o d i r e c t s o l a r i r r a d i a n c e even a t low sun a n g l e s . O t h e r r e s e a r c h e r s have r e p o r t e d s i m i l a r d i u r n a l c o u r s e s o f g s ; Murphy and F e r r e l l (1982) i n D o u g l a s - f i r s a p l i n g s i n f i v e h a b i t a t t y p e s , Duryea and L a vende r (1982) i n D o u g l a s - f i r s e e d l i n g s , Kaufmann (1976) i n Eng lemann s p r u c e ( P i c e a e n g e l m a n n i i P a r r y ) , and M i l n e j^t j* l_ . (1985) i n S i t k a s p r u c e ( P i c e a s i t c h e n s i s (Bong . ) C a r r ) . L e v e r e n z e t al_. (1982) r e p o r t ( t h e i r F i g u r e s 2, 3 and 4) t h a t t he ave r age g s o f S i t k a s p r u c e s h o o t s was h i g h e s t i n t he e a r l y morn i ng and t hen p r o g r e s s i v e l y d e c l i n e d t h r o u g h o u t t h e day . In some c a s e s t h i s d e c l i n e was i n t e r r u p t e d a t noon when t h e r e was a s l i g h t r e c o v e r y i n ave rage g s . Towards the end o f t h e day , even though l i g h t l e v e l s were s i m i l a r t o t h o s e i n t he e a r l y mo rn i n g when t he maximum ave rage g s was measu r ed , t h e s t oma ta were a l m o s t c l o s e d . - 77 -F i g u r e 2 .7 shows the s c a t t e r p l o t o f gs/Ssmax v e r s u s t h e number o f hou r s f rom s u n r i s e ( t ) f o r D o u g l a s - f i r and the b o u n d a r y - l i n e c u r v e s d e r i v e d f o r t h e t h r e e s p e c i e s . The b o u n d a r y - l i n e c u r v e s can a l l be d e s c r i b e d by the second o r d e r p o l y n o m i a l 9s/9smax = P + q t + r t 2 (7) where t he v a l u e s o f t h e c o n s t a n t s p, q and r a r e g i v e n i n T a b l e 2 . 6 . The b o u n d a r y - l i n e c u r v e s ( F i g u r e 2 . 7b ) i n d i c a t e t h a t , w i t h no other-f a c t o r s l i m i t i n g , g s w i l l r a p i d l y d e c l i n e a f t e r m i d -mo rn i n g w i t h no r e c o v e r y i n t h e l a t t e r p a r t o f t he d a y . I t i s p o s s i b l e t h a t t h i s d i u r n a l p a t t e r n o f g s i s r e l a t e d t o a b s c i s i c a c i d (ABA) c o n c e n t r a t i o n a t t h e gua rd c e l l s s i n c e ABA i s known t o p l a y a key r o l e i n r e g u l a t i n g gua rd c e l l i o n t r a n s p o r t ( H s i a o 1 9 7 6 ) . The l e n g t h o f t ime t h a t t h e s t oma t a r ema in c l o s e d o r p a r t i a l l y c l o s e m i gh t w e l l depend on how q u i c k l y ABA i s f u l l y m e t a b o l i s e d o r moves t o o t h e r s i t e s . W r i g h t and H i r o n ( 1 9 6 9 ) , W r i g h t ( 1 9 7 7 ) , S i v a kuma ran e t a]_. (1980) and o t h e r s have d e m o n s t r a t e d t h a t c o n c e n t r a t i o n s o f endogenous ABA i n c r e a s e m a r k e d l y i n w a t e r - s t r e s s e d p l a n t s . ABA i s s y n t h e s i z e d i n l e a f c h l o r o p l a s t s ( M i l b o r r o w 1 9 7 4 ) , t h e l e a f c y t o p l a s m (Ha r t ung e t 1981) and t h e r o o t s (Wa l t on e t aj_. 1 9 7 6 ) . The e x a c t mechanism by wh i ch ABA p r o d u c t i o n i s t r i g g e r e d i s no t known; however , P i e r c e and Ras chke (1980) s p e c u l a t e t h a t ABA p r o d u c t i o n i s t r i g g e r e d when Yp o f t he bu l k l e a f f a l l s t o n e a r z e r o . - 78 -1.0 x CD E CO , r j ) CO 0.5 0.0 1.0 0.5 0.0 • • • * • • • • • • • • • • • • e • • • c m O O O o o O O O o o O O O O O O O 0 . O O O O 0 • o O ^^•'•^  • • O O «w O O O^S. o o V . • \. O O O o x . O O O \ o \ O O O • \ O O O o \ • * o • \ o o o o \ o O O O o o o o 0 o o o o O O O (a) • o o O 0 o o o 0 0 o o o o o 0o 0 o o o o o o O O Oo o o O O O o o o o o O O O o 0 o o o • 0 o o o o o o o o o o o O O O • t • o o \ o \ o \ o X • • \ o \ • \ • \ o o \ o o o o \ o o o \ o o o o \ O O O O > O O O O — , . . 3 6 9 12 Time from sunrise (h) 15 F i g u r e 2 .7 a . The r e l a t i o n s h i p between t h e r a t i o o f t h e s t o m a t a l c o n d u c t a n c e ( g s ) t o t h e maximum s t o m a t a l c o n d u c t a n c e ( g s n a x ) and t h e t i m e s i n c e s u n r i s e ( t ) f o r i r r i g a t e d ( • ) and n o n - i r r i g a t e d (o ) D o u g l a s - f i r s e e d l i n g s . Fach p o i n t i s t h e average o f t h r e e m e a s u r e m e n t s . A l s o shown i s t h e b o u n d a r y - l i n e wh ich i n d i c a t e s t h e upper l i m i t o f t h e o b s e r v a t i o n s , h . Compar ison o f t h e b o u n d a r y - l i n e s f o r t h e r e l a t i o n s h i p between g s / g s m a x a n r t t f o r D o u g l a s - f i r ( s o l i d l i n e ) , w e s t e r n hemlock ( d o t t e d l i n e ) and P a c i f i c s i l v e r f i r ( b r o k e n l i n e ) . Tab l e 2.6 V a l u e s o f t h e c o e f f i c i e n t , q , r and s i n the e q u a t i o n ; g s /gsmax = p + qt + r t 2 d e r i v e d by b o u n d a r y - l i n e a n a l y s i s f o r D o u g l a s - f i r , wes te rn hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s where g s i s t h e a ve r age s e e d l i n g s t oma t a l conduc tance (cm s - 1 ) » Qsmax 1 S t he maximum g s (cm s " 1 ) and t i s t h e number o f hours f rom s u n r i s e . Yea r o f Year o f D o u g l a s - f i r Wes te rn hemlock P a c i f i c s i l v e r f i r P l a n t i n g Measurement P q r P q r P q r 1981 1982 0.66 0.09 - 0 . 0 0 8 0.44 0 .14 - 0 . 0 0 7 0 .71 0 .08 - 0 . 0 0 6 1981 1983 0.70 0 .08 - 0 . 007 0.46 0.12 - 0 . 0 0 7 - - -1982 1982 0.67 0 .08 - 0 . 0 0 5 0 .45 0 .13 - 0 . 0 0 7 0 .71 0 .08 - 0 . 0 0 6 - 80 -E. V a r i a t i o n o f g s w i t h r e s p e c t t o s e e d l i n g age and p l a n t i n g t i m e . The v a l u e s o f t he c o e f f i c i e n t s o b t a i n e d by b o u n d a r y - l i n e a n a l y s i s o f measurements made i n 1982 were no d i f f e r e n t f o r s e e d l i n g s p l a n t e d i n t h a t y e a r o r i n 1 9 8 1 . S i m i l a r l y s t o m a t a l c o n d u c t a n c e c h a r a c t e r i s t i c s o f s e e d l i n g s ( p l a n t e d i n 1981) measured i n 1983 were no t s i g n i f i c a n t l y d i f f e r e n t f rom c h a r a c t e r i s t i c s measured i n 1982 ( T a b l e s 2.2 - 2 . 6 ) . S i n c e a l l o f a s e e d l i n g ' s f o l i a g e was e n c l o s e d i n t h e p o r ome t e r chamber used i n t h i s s t udy a n d , t h e r e f o r e , t h e a v e r age g s o f t he e n t i r e s e e d l i n g o b t a i n e d , i t was no t p o s s i b l e t o d i r e c t l y compare the s t o m a t a l r e s p o n s e s o f new and o l d n e e d l e s . However , by t h e end o f J u l y new need l e s t y p i c a l l y c o n s t i t u t e d abou t 30% ( F i g u r e s 3.4 - 3 .6 i n C h a p t e r 3) o f t h e t o t a l n e e d l e a r e a , so t h a t , had t h e r e been s i g n i f i c a n t d i f f e r e n c e s i n s t o m a t a l b e h a v i o u r between new and o l d n e e d l e s , marked changes i n t h e o v e r a l l s e e d l i n g r e s p o n s e wou ld have been o b s e r v e d d u r i n g t h e g r ow i ng s e a s o n . These f i n d i n g s a r e no t c o n s i s t e n t w i t h t h o s e o f o t h e r r e s e a r c h e r s . Fo r examp le , L e v e r e n z et a l_. (1982) found t h a t , f o r t h e same c o n d i t i o n s , g s o f one y e a r - o l d S i t k a s p r u c e f o l i a g e was o v e r t w i c e t h a t o f t he two y e a r - o l d f o l i a g e . G r o s s n i c k l e and B l a k e (1985) f ound t h a t w h i t e s p r u c e ( P i c e a g l a u c a (Moench) V o s s . ) s t oma ta i n new n e e d l e s showed l e s s s e n s i t i v i t y t o i n c r e a s e s i n D, a t low v a l u e s o f D, t h an s t oma ta i n o l d e r n e e d l e s ; however , a t h i g h e r v a l u e s o f D, t hey were more s e n s i t i v e t o i n c r e a s e s i n D. In c o n t r a s t , j a c k p i n e ( P i n u s  b a n k s i a n a Lamb.) s t oma ta i n o l d n e e d l e s , a t a l l l e v e l s of D, were more s e n s i t i v e t o i n c r e a s e s i n D than s t oma ta i n new n e e d l e s . Wa t t s e t a l . (1976) o b s e r v e d t h a t s t oma ta i n newly emerged S i t k a s p r u c e n e e d l e s were - 81 -more s e n s i t i v e t o D t han s t omata i n o l d e r n e e d l e s , but t h a t t h e s e d i f f e r e n c e s i n r e sponse were no t o b s e r v e d when s hoo t e x p a n s i o n was n e a r l y c omp l e t e i n l a t e J u l y . Waggoner and T u r n e r (1971) f ound t he o p p o s i t e r e s pon se i n r e d p i n e ( P i n u s r e s i n o s a A i t . ) , where f o r t h e same v a l u e o f D, g s was h i g h e r i n newly emerged n e e d l e s t han i n one y e a r - o l d n e e d l e s . F. C a l c u l a t i n g g s and E f rom B o u n d a r y - L i n e R e l a t i o n s h i p s S t o m a t a l c o n d u c t a n c e c a l c u l a t e d f r om t he r e l a t i o n s h i p s d e r i v e d f r om b o u n d a r y - l i n e a n a l y s i s o f d a t a , c o l l e c t e d i n 1982 on s e e d l i n g s p l a n t e d i n t h a t y e a r , were compared w i t h measured v a l u e s o f g s o f i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s o b t a i n e d i n 1982 and 1983 ( Tab l e 2 . 7 ) . S t oma t a l c o n d u c t a n c e s were c a l c u l a t e d u s i n g 9s = 9smax f ( R s > 9 (T ) h(D) j ( y s ) k ( t ) (8) w i t h o n l y one i n d ependen t v a r i a b l e o r c o m b i n a t i o n s o f i n d ependen t v a r i a b l e s . No s i n g l e e n v i r o n m e n t a l v a r i a b l e c o u l d a c c o u n t f o r more t han 30% o f t h e v a r i a t i o n i n g s i n any o f t h e s p e c i e s . The use o f two v a r i a b l e s , R s and D, c o u l d a c c o u n t f o r 60%, 58% and 61% o f t he v a r i a t i o n i n g s f o r D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r , r e s p e c t i v e l y . No more t han 70% o f t h e v a r i a t i o n i n D o u g l a s - f i r g s c o u l d be a c c o u n t e d f o r by c o m b i n i n g a l l t h e v a r i a b l e s e x c e p t f o r t , compared t o 67% and 64% T a b l e 2.7 The p e r c e n t a g e o f the v a r i a n c e o f t h e ave rage s t oma ta l c onduc t ance o f D o u g l a s - f i r ( D F ) , w e s t e r n hemlock (WH) and P a c i f i c s i l v e r f i r (PSF) s e e d l i n g s , measured on 13 days between June and September 1982 , e x p l a i n e d by t he b o u n d a r y - l i n e a n a l y s i s model u s i n g t he i n d i v i d u a l v a r i a b l e s , R s ( g l o b a l s o l a r i r r a d i a n c e ) , T ( a i r t empe r a t u r e ) D (vapour p r e s s u r e d e f i c i t ) i|>s ( a v e r age r o o t zone wa te r p o t e n t i a l ) and t ( t h e number o f hours from s u n r i s e ) , and the v a r i a b l e s i n c o m b i n a t i o n . % V a r i a n c e E x p l a i n e d % V a r i a n c e E x p l a i n e d V a r i a b l e DF WH PSF Comb i na t i o n DF WH PSF o f V a r i a b l e s Rs 27 30 24 R S ,D 60 58 61 T 15 18 17 Rs . n .^s 67 63 65 D 19 21 16 R s , n , * s , T 70 67 69 •s 5 8 9 R s , D , T , t 78 72 77 t 41 37 39 89 87 85 - 83 -f o r w e s t e r n hemlock and P a c i f i c s i l v e r f i r , r e s p e c t i v e l y . W h i l s t y s a l o n e a c c o u n t e d f o r l e s s t han 10% of t he v a r i a t i o n i n g s i n a l l s p e c i e s , i t d i d a c c o u n t , when combined w i t h t he o t h e r v a r i a b l e s , f o r t he d i f f e r e n c e i n g s between i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s ( F i g u r e s 2 .8 and 2 . 9 ) . S i m i l a r r e s u l t s have been r e p o r t e d by J a r v i s e t ^1_. (1981) who, i n f i t t i n g t h e same t ype o f model t o measurements o f s t o m a t a l c ondu c t an c e o f S c o t s p i n e , c o u l d a c c oun t f o r 70% o f t h e v a r i a t i o n i n g s by changes i n p h o t o s y n t h e t i c pho ton f l u x d e n s i t y and vapou r p r e s s u r e d e f i -c i t . They f ound t h a t o n l y i n t he l a t t e r p a r t o f t he summer when Y $ were l o w , d i d t h e i n c l u s i o n o f F f t x s i g n i f i c a n t l y i n c r e a s e the e x p l a i n e d v a r i a t i o n . However , t he i n c l u s i o n o f t e m p e r a t u r e d i d no t a t any t ime have a s i g n i f i c a n t e f f e c t . S i m i l a r l y W a r r i t e t aj_. (1980) f ound t h a t most o f t he v a r i a t i o n i n g s o f a pp l e l e a v e s c o u l d be a c c o u n t e d f o r by p h o t o s y n t h e t i c pho ton f l u x d e n s i t y and vapou r p r e s s u r e d e f i c i t , and t h a t t he i n c l u s i o n o f o t h e r v a r i a b l e s such as T and Y[t% d i d no t i n c r e a s e t he amount o f e x p l a i n e d v a r i a b i l i t y . F i g u r e s 2.8 and 2.9 show t h a t i t i s t h e i n c l u s i o n o f t as an i n d e p e n d e n t v a r i a b l e t h a t l i m i t s t he a f t e r n o o n v a l u e s o f c a l c u l a t e d g s so t h a t they do no t g r e a t l y exceed t h e measured v a l u e s . T h i s e f f e c t i s most p ronounced on days w i t h low D. However , on some days ( F i g . 2 .8 ) i t was no t p o s s i b l e t o e x p l a i n t he v e r y low measured g s i n t he m o r n i n g . The i n c l u s i o n o f t as an i n dependen t v a r i a b l e i n c r e a s e d t he amount o f e x p l a i n e d v a r i a b i l i t y i n t h e s t o m a t a l c o n d u c t a n c e to 89% i n D o u g l a s - f i r and 87% and 85% i n w e s t e r n hemlock and P a c i f i c s i l v e r f i r , r e s p e c t i v e l y ( T a b l e 2 . 7 ) . T h i s r e s u l t i s no t u n i q u e , s i n c e J o ne s ( 1 9 8 3 ) , i n - 84 -0.5 6 9 12 15 18 21 T i m e (PST) F i g u r e 2 .8 The d a i l y c o u r s e s o f measured (open s ymbo l s ) and c a l c u l a t e d ( c l o s e d s ymbo l s ) s t o m a t a l c o n d u c t a n c e ( g s ) f o r i r r i g a t e d ( s o l i d l i n e s ) and n o n - i r r i g a t e d ( d o t t e d l i n e s ) D o u g l a s - f i r s e e d l i n g s on J u l y 2 8 , 1982 . S t oma ta l c onduc t an ce was c a l c u l a t e d w i t h (•) and w i t h o u t t i m e s i n c e s u n r i s e ( A ) as a v a r i a b l e . The ave r age r o o t zone s o i l wa t e r p o t e n t i a l was - 0 . 7 3 MPa. - 85 -0.5 T i m e (PST) F i g u r e 2.9 The d a i l y c o u r s e s o f measured (open symbo l s ) and c a l c u l a t e d ( c l o s e d symbo l s ) s t o m a t a l c o n d u c t a n c e ( g s ) f o r i r r i g a t e d ( s o l i d l i n e s ) and n o n - i r r i g a t e d ( d o t t e d l i n e s ) D o u g l a s - f i r s e e d l i n g s on Augus t 2 1 , 1982 . S t oma ta l c o n d u c t a n c e was c a l c u l a t e d w i t h (•) and w i t h o u t t i m e s i n c e s u n r i s e (A) as a v a r i a b l e . The a ve r age r o o t zone s o i l wa t e r p o t e n t i a l was - 1 . 1 MPa. - 86 -r e v i e w i n g m u l t i p l e r e g r e s s i o n mode ls used t o d e t e r m i n e s t o m a t a l r e s p o n s e , f ound t h a t f r e q u e n t l y i t had been n e c e s s a r y t o i n c l u d e t ime as an i n d ependen t v a r i a b l e . F i g u r e 2 .10 compares measured g s o f i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s w i t h g s c a l c u l a t e d u s i n g t h e b o u n d a r y - l i n e e q u a t i o n w i t h R s , D, T , <F s and t . The s l o p e s and i n t e r c e p t s o f r e g r e s s i o n s o f c a l c u l a t e d v e r s u s measured g s f o r i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s were not s i g n i f i c a n t l y d i f f e r e n t so t h a t i r r i g a t e d and non-i r r i g a t e d s e e d l i n g s c o u l d be c o n s i d e r e d t o b e l o n g t o t h e same p o p u l a t i o n ( T a b l e 2 . 8 ) . The s l o p e s and i n t e r c e p t s o f r e g r e s s i o n e q u a t i o n s f o r t he comb ined d a t a , f o r each s p e c i e s , wh i ch T t e s t s r e v e a l e d d i d no t s i g n i -f i c a n t l y d i f f e r f r om one and z e r o , r e s p e c t i v e l y , a r e p r e s e n t e d i n T a b l e 2 .8 F i g u r e 2 .11 shows the e x c e l l e n t agreement between measured and mode led d a i l y t r a n s p i r a t i o n r a t e s f o r the t h r e e s p e c i e s . T r a n s p i r a t i o n r a t e s were b e t t e r e s t i m a t e d on a d a i l y b a s i s , r a t h e r t h an an h o u r l y b a s i s , because i n g e n e r a l g s was s l i g h t l y o v e r e s t i m a t e d i n the mo rn i ng and u n d e r e s t i m a t e d i n t he a f t e r n o o n ( F i g u r e s 2 .8 and 2 . 9 ) . I V . CONCLUSIONS B o u n d a r y - l i n e a n a l y s i s o f f i e l d g s d a t a p r oduced f u n c t i o n s t h a t s u c c e s s f u l l y a c c o u n t e d f o r t he s t o m a t a l b e h a v i o u r o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s . However , on an h o u r l y b a s i s g s was s l i g h t l y o v e r e s t i m a t e d i n t he mo rn i ng and u n d e r e s t i m a t e d i n t he a f t e r n o o n . B e s t r e s u l t s were a c h i e v e d by i n c l u d i n g t h e number o f hou r s f rom s u n r i s e as an i n d ependen t v a r i a b l e . - 87 -F i g u r e 2 .10 Compar i son o f c a l c u l a t e d s t oma t a l c onduc t an ce ( g s c a l c ) w i t h measured s t oma t a l c onduc t an ce ( g s ) f o r i r r i g a t e d (o) and n o n - i r r i g a t e d (o) D o u g l a s - f i r ( D F ) , we s t e r n hemlock (WH) and P a c i f i c s i l v e r - f i r (PSF) s e e d l i n g s , p l a n t e d i n 1982 , f o r 13 days between June and September 1 9 8 2 . The r e g r e s s i o n l i n e s shown ( b r oken l i n e s ) a re f o r a l l t h e p o i n t s . The s l o p e s and i n t e r c e p t s o f t h e s e l i n e s a re g i v e n i n T a b l e 2 . 8 . - 88 -F i g u r e 2 .11 Compa r i s on o f c a l c u l a t e d d i a l y t r a n s p i r a t i o n r a t e ( E c a - | C ) u s i n g v a l u e s o f g s o b t a i n e d f r om e q u a t i o n (8) w i t h R s , D, T, ¥ s and t as v a r i a b l e s , w i t h d a i l y t r a n s p i r a t i o n r a t e (E) t h a t was c a l c u l a t e d u s i n g measured v a l u e s o f s t o m a t a l c o n d u c t a n c e . Bo th E and E c a i c were c a l c u l a t e d as t h e sum o f t he h o u r l y p r o d u c t o f g s and (D/R V T ' ) f o r i r r i g a t e d ( c l o s e d symbo l s ) and n o n - i r r i g a t e d (open symbo l s ) D o u g l a s - f i r (o), w e s t e r n hemlock (•) and P a c i f i c s i l v e r f i r (O) s e e d l i n g s , p l a n t e d i n 1 9 8 2 , f o r 13 days between June and September 1 9 8 2 . A l s o shown i s t h e 1:1 l i n e . L inear-r e g r e s s i o n a n a l y s i s i n d i c a t e s E c a i c (g c m - 2 d a y " 1 ) = 0 .98 E (g c m - 2 d a y " 1 ) + 0 .002 ( r 2 = 0 . 9 8 ) (dashed l i n e ) . - 89 -T a b l e 2.8 V a l u e s o f c o e f f i c i e n t s i n t h e l i n e a r r e g r e s s i o n e q u a t i o n ; g s c a l c = V g + w f o r i r r i g a t e d and n o n - i r r i g a t e d D o u g l a s - f i r , w e s t e r n hemlock ana P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1982 , f o r 13 days between June and September 1 9 8 2 , where g s c a l c i s s e e d l i n g s t o m a t a l c o n d u c t a n c e u s i n g t h e b o u n d a r y - l i n e a n a l y s i s model and g s i s measured s t o m a t a l c o n d u c t a n c e . A l s o shown a r e t h e number o f d a t a p o i n t s ( n ) , t h e c o e f f i c i e n t o f d e t e r m i n a t i o n ( r 2 ) and t h e s t a n d a r d e r r o r o f e s t i m a t e ( S E E ) . S p e c i e s v w n r 2 SEE D o u g l a s - f i r I r r i g a t e d 1.06 - 0 . 0 1 6 203 0.87 0 .07 N o n - I r r i g a t e d 1.02 - 0 . 0 0 6 203 0 .90 0 .06 Combined Data 1.05 - 0 . 0 1 2 406 0 .89 0 .07 Wes te rn hemlock I r r i g a t e d 1.10 0 .015 197 0 .86 0 .05 N o n - I r r i g a t e d 0 .96 - 0 . 0 0 3 204 0 .89 0 .06 Combined Data 1.08 0 .008 401 0 .87 0 .05 P a c i f i c s i l v e r f i r I r r i g a t e d 1.09 0 .020 150 0 .84 0 .04 N o n - I r r i g a t e d 1.06 - 0 . 0 0 6 120 0 .89 0 .03 Combined Da ta 1.07 0 .004 370 0 .86 0 .03 - 90 -The r e was no e v i d e n c e t o s u g g e s t t h a t t h e r e was c r i t i c a l t h r e s h o l d t u r g o r p o t e n t i a l be low wh i ch s t oma ta c l o s e d a l t h o u g h a d e c r e a s e i n ? s c au s ed a c o r r e s p o n d i n g d e c r e a s e i n g s . I n c r e a s i n g g s appea red t o c a u s e t u r g o r p o t e n t i a l t o d e c r e a s e as a r e s u l t o f t h e i n c r e a s e d t r a n s p i r a t i o n r a t e . The s t o m a t a l r e s p o n s e s o f a l l t h r e e s p e c i e s t o changes i n e n v i r o n -menta l v a r i a b l e s and t ime d i d no t d i f f e r o v e r two y e a r s , no r were t h e r e d i f f e r e n c e s i n r e s pon se between s e e d l i n g s p l a n t e d i n 1981 and 1982 . D a i l y s e e d l i n g t r a n s p i r a t i o n r a t e s on a p r o j e c t e d l e a f a r e a b a s i s were s u c c e s s f u l l y e s t i m a t e d by summing t he p r o d u c t o f t he c a l c u l a t e d h o u r l y a ve r age g s and t he measured h o u r l y ave rage v a l u e s o f D / (R V T ' ) . REFERENCES Cowan, I . R . and G.D. F a r q u h a r . 1977 . S t o m a t a l f u n c t i o n i n r e l a t i o n t o l e a f m e t a b o l i s m and e n v i r o n m e n t . Ir^ The I n t e g r a t i o n o f A c t i v i t y i n t he H i g h e r P l a n t . S o c i e t y f o r E x p e r i m e n t a l B i o l o g y Symposium 3 1 : 4 7 1 - 5 0 5 . Drew, A . P . and W.K. F e r r e l l . 1979 . Sea sona l changes i n t h e water-b a l a n c e o f D o u g l a s - f i r ( P s eudo t s uga m e n z i e s i i ) s e e d l i n g s grown unde r d i f f e r e n t l i g h t i n t e n s i t i e s . C a n . J . B o t . 5 7 : 6 6 6 - 6 7 4 . D u r y e a , M.L. and D.P . L a v e n d e r . 1 9 8 2 . Water r e l a t i o n s , g rowth and s u r v i v a l o f r o o t - w r e n c h e d D o u g l a s - f i r s e e d l i n g s . C a n . J . F o r . R e s . 1 2 : 5 4 5 - 5 5 5 . F a r q u h a r , G .D . 1 978 . F e e d f o r w a r d r e s p o n s e s o f s t oma ta t o h u m i d i t y . A u s t . J . P l a n t P h y s i o l . 5 : 7 8 7 - 8 0 0 . - 91 -F a r q u h a r , G . D . , D.R. Dubbe, and K. R a s c h k e . 1978 . G a i n o f t he f eedback l o o p i n v o l v i n g c a r bon d i o x i d e and s t o m a t a : t h e o r y and measurement . P l a n t P h y s i o l . 6 2 : 4 0 6 - 4 1 2 . G r o s s n i c k l e , S . C . and T . J . B l a k e . 1 986 . E n v i r o n m e n t a l and p h y s i o l o g i c -a l c o n t r o l o f n eed l e c ondu c t an c e f o r b a r e - r o o t b l a c k s p r u c e , w h i t e s p r u c e and j a c k - p i n e s e e d l i n g s on b o r e a l c u t - o v e r s i t e s . C a n . J . B o t . 64 ( i n p r e s s ) . H a l l g r e n , S.W. 1978 . P l a n t w a t e r r e l a t i o n s i n D o u g l a s - f i r s e e d l i n g s and s c r e e n i n g s e l e c t e d f a m i l i e s f o r d r ough t r e s i s t a n c e . M.S . t h e s i s , Oregon S t a t e U n i v e r s i t y , C o r v a l l i s , O r e g o n , U . S . A . H a r t u n g , W., B. H e i l m a n n , and H. G i m m l e r . 1 9 8 1 . Do c h l o r o p l a s t s p l a y a r o l e i n a b s c i s i c a c i d s y n t h e s i s ? P l a n t S c i e n c e L e t t e r s 2 2 : 2 3 5 - 2 4 2 . H i n c k l e y , T . M . , J . P . L a s s o i e , and S.W. R u n n i n g . 1 978 . Tempora l and s p a t i a l v a r i a t i o n s i n t h e w a t e r s t a t u s o f f o r e s t t r e e s . F o r e s t S c i e n c e Monograph No. 2 0 , 72 pp . Hobbs , S . D . 1984 . The i n f l u e n c e o f s p e c i e s and s t o c k t y p e s e l e c t i o n on s t a n d e s t a b l i s h m e n t , an e c o p h y s i o l o g i c a l p e r s p e c t i v e . In S eed -l i n g P h y s i o l o g y and R e f o r e s t a t i o n S u c c e s s . E d i t e d by M.L . Duryea and G . N . B rown . M a r t i n u s N i j h o f f / D r . W. Junk P u b l i s h e r s , B o s t o n , pp . 1 7 9 - 2 2 4 . H s i a o , T . C . 1976 . S t oma t a l i o n t r a n s p o r t . J_n E n c y c l o p e d i a o f P l a n t P h y s i o l o g y , New S e r i e s , V o l . 2 . T r a n s p o r t i n P l a n t s I I . P a r t B . T i s s u e s and O r g a n s . S p r i n g e r - V e r l a g , New Y o r k , p p . 1 9 5 - 2 2 1 . J a r v i s , P .G . 1975 . Water t r a n s f e r i n p l a n t s . j_n Heat and Mass T r a n s -f e r i n t h e B i o s p h e r e . P a r t . I . T r a n s f e r p r o c e s s e s i n t h e p l a n t e n v i r o n m e n t . E d i t e d by D.A. de V r i e s and N.H. A f g a n . S c r i p t a Book Company, W a s h i n g t o n , D . C . , U . S . A . , pp . 3 6 9 - 3 9 4 . - 92 -J a r v i s , P .G . 1976 . The i n t e r p r e t a t i o n o f t h e v a r i a t i o n s i n l e a f w a t e r - p o t e n t i a l amd s t o m a t a l c o n d u c t a n c e f ound i n c a n o p i e s i n t h e f i e l d . P h i l . T r a n s . R. S o c , London , S e r . B. 2 7 3 : 5 9 3 - 6 1 0 . J a r v i s , P .G . and J . I . L M o r r i s o n . 1 9 8 1 . The c o n t r o l o f t r a n s p i r a t i o n and p h o t o s y n t h e s i s by t he s t o m a t a . 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S t o m a t a l d i f f u s i o n r e s i s t a n c e o f snap b e a n s . I . I n f l u e n c e o f l e a f - w a t e r p o t e n t i a l . P l a n t P h y s i o l . 4 4 : 1 5 4 7 - 1 5 5 2 . Kau fmann, M.R. 1976 . S t o m a t a l r e s p o n s e o f Engelmann s p r u c e t o h u m i d i t y , l i g h t , and w a t e r s t r e s s . P l a n t P h y s i o l . 5 7 : 8 9 8 - 9 0 1 . Kau fmann, M.R. 1981 . A u t o m a t i c d e t e r m i n a t i o n o f c o n d u c t a n c e , t r a n s p i r a t i o n , and e n v i r o n m e n t a l c o n d i t i o n s i n f o r e s t t r e s s . F o r e s t S c i . 4 : 8 1 7 - 8 2 7 . K e l l i h e r , F . M . , T . A . B l a c k and A . G . B a r r . 1984 . E s t i m a t i o n o f t w i g xy l em p o t e n t i a l i n young D o u g l a s - f i r t r e e s . C a n . J . F o r . R e s . - 93 -K e l l i n e r , F .M . 1985 . S a l a l u n d e r s t o r y remova l e f f e c t s on t he s o i l w a t e r r eg ime and t r e e t r a n s p i r a t i o n r a t e s i n a D o u g l a s - f i r f o r e s t . P h . D . T h e s i s , Depa r tmen t o f S o i l s c i e n c e , U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r , B .C . L a s s o i e , J . P . 1982 . P h y s i o l o g i c a l a c t i v i t y i n D o u g l a s - f i r . Jji^ A n a l y s i s o f C o n i f e r o u s F o r e s t E co sy s t ems i n t h e Western U n i t e d S t a t e s . US/ IPB S y n t h e s i s S e r i e s No. 14 . E d . R .L . Edmonds. H u t c h i n s o n Ross P u b l . C o . , S t r o u d s b u r g , PA, USA, p p . 1 2 6 - 1 8 5 . L e v e r e n z , J .W. 1974 . Net p h o t o s y n t h e s i s as r e l a t e d t o s hoo t h i e r a r c h y i n a l a r g e dominant D o u g l a s - f i r t r e e . M .Sc . t h e s i s , U n i v e r s i t y o f W a s h i n g t o n , S e a t t l e , WA, USA. 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E n v i r o n m e n t a l and p h y s i o l o g i c a l c o n t r o l o f w a t e r f l u x t h r ough P i n u s c o n t o r t a . C a n . J . F o r . R e s . 1 0 : 8 2 - 9 1 . R u n n i n g , S.W. 1984 . Do cumen t a t i o n and p r e l i m i n a r y v a l i d a t i o n o f H 2 0 T rans and D a y t r a n s , two mode l s o f p r e d i c t i n g t r a n s p i r a t i o n and w a t e r s t r e s s i n w e s t e r n c o n i f e r o u s f o r e s t s . USDA F o r e s t S e r v i c e Re s ea r c h P a p e r . RM-252. Rocky Moun t a i n F o r e s t and Range E x p e r i m e n t S t a t i o n , F o r t C o l l i n s , C o l o . S h e r i f f , D.W. 1984 . E p i d e r m a l t r a n s p i r a t i o n and s t o m a t a l r e s p o n s e s t o h u m i d i t y : some hypo t he s e s e x p l o r e d . P l a n t , C e l l and E n v i r o n m e n t 7 : 6 6 9 - 6 7 7 . S h e r i f f , D.W. and P . E . K a y e . 1977 . The r e s p o n s e o f d i f f u s i v e c o n d u c t a n c e i n w i l t e d and u n w i l t e d A t r i p ! e x H a s t a t a L. l e a v e s t o h u m i d i t y . Z e i t s c h r i f t F u r P f l a n z e n p h y s i o l o g i e 8 3 : 4 6 3 - 4 6 6 . S i v a k u m a r a n , S . , R. Mo rgan , J . H e a l d and M.A. H a l l . 1980 . E f f e c t o f w a t e r s t r e s s o f m e t a b o l i s m o f a b s c i s i c a c i d i n P o p u l u s r o b u s t a X S c h n i e d and E u p h o r b i a l a t h y r u s L. P l a n t , C e l l and E n v i r o n m e n t 3 : 1 6 3 - 1 7 3 . T an , C . S . and T . A . B l a c k . 1976 . F a c t o r s a f f e c t i n g t h e canopy r e s i s t -ance o f a D o u g l a s - f i r f o r e s t . B o u n d a r y - L a y e r Me t . 1 0 : 4 7 5 - 4 8 8 . T a n , C . S . , T . A . B l a c k and J . U . Nnyamah. 1977 . C h a r a c t e r i s t i c s o f s t o m a t a l d i f f u s i o n r e s i s t a n c e i n a D o u g l a s - f i r f o r e s t exposed t o s o i l w a t e r d e f i c i t s . C a n . J . F o r . R e s . 7 : 595 -604 . - 96 -T e s k e y , R .O . , C . C . G r i e r and T . M . H i n c k l e y . 1984 . Change i n p h o t o s y n t h e s i s and w a t e r r e l a t i o n s w i t h age and s ea son i n A b i e s  a m a b i l i s . Can J . F o r . R e s . 1 4 : 7 7 - 8 4 . T y r e e , M.T. and P. Y i a n o u l i s . 1 9 8 0 . The s i t e o f t h e water-e v a p o r a t i o n f rom s u b - s t o m a t a l c a v i t i e s , l i q u i d pa th r e s i s t a n c e s and h y d r o a c t i v e s t o m a t a l c l o s u r e . A n n a l s o f Bo tany 4 6 : 1 7 5 - 1 9 3 . Waggoner , P . E . and N.C. T u r n e r . 1 9 7 1 . T r a n s p i r a t i o n and i t s c o n t r o l by s t oma ta i n a p i n e f o r e s t . Conn . A g r i c . E x p . S t n . B u l l . 7 2 6 , 87 p p . W a l t o n , D . C . , M.A. H a r r i s o n and P. Co t e \ 1976 . The e f f e c t s o f water-s t r e s s on a b s c i s i c a c i d l e v e l s and m e t a b o l i s m i n r o o t s o f P h a s e o l u s v u l g a r i s . P l a n t a . 1 2 0 : 6 3 - 6 9 . W a r i n g , R .H . and S.W. Runn ing 1978 . Sapwood w a t e r s t o r a g e : i t s c o n t r i b u t i o n t o t r a n s p i r a t i o n and e f f e c t upon w a t e r c o n d u c t a n c e t h r o u g h the stems o f o l d growth D o u g l a s - f i r . P l a n t , C e l l , E n v i r o n . 1 :131 -140 . W a r r i t , B . , J . J . L a nd sbe r g and M.R. T h o r p e . 1980 . Responses o f a p p l e l e a f s t oma ta t o e n v i r o n m e n t a l f a c t o r s . P l a n t , C e l l , E n v i r o n . 3 : 1 3 - 2 2 . W a t t s , W.R. and R .E . N e i l s o n . 1978 . P h o t o s y n t h e s i s i n S i t k a s p r u c e ( P i c e a s i t c h e n s i s (Bong . ) C a r r . ) V I I I . Measurements o f s t o m a t a l c o n d u c t a n c e and  lkC02 u p t a k e i n c o n t r o l l e d e n v i r o n m e n t s . J . A p p l . E c o l . 1 5 : 2 4 5 - 2 5 5 . Webb, R.A. 1 9 7 2 . Use o f t h e boundary l i n e i n t h e a n a l y s i s o f b i o l o g i c a l d a t a . J . H o r t i c . S c i . 4 7 : 3 0 9 - 3 1 9 . - 97 -W r i g h t , S . T . C . 1977 . The r e l a t i o n s h i p between l e a f w a t e r p o t e n t i a l ( ¥ l e a f ) and t he l e v e l s o f a b s c i s i c a c i d and e t h y l e n e i n e x c i s e d whea t l e a v e s . P l a n t a 1 3 4 : 1 8 3 - 1 8 9 . W r i g h t , S . T . C . and R.W.P. H i r o n . 1969 . (+) - a b s c i s i c a c i d , t h e growth i n h i b i t o r i n d e t a ched wheat l e a v e s f o l l o w i n g a p e r i o d o f w i l t i n g . N a t u r e 2 2 4 : 7 1 9 - 7 2 0 . - 98 -CHAPTER 3 THE GROWTH AND WATER USE OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT - 99 -CHAPTER 3 THE GROWTH AND WATER USE OF CONIFER SEEDLINGS PLANTED ON A HIGH ELEVATION SOUTH-FACING CLEARCUT I . INTRODUCTION S i l v i c u l t u r i s t s w i l l o b t a i n t h e most s u c c e s s f u l r e g e n e r a t i o n on d r y s i t e s by p l a n t i n g s e e d l i n g s t h a t not o n l y s u r v i v e d r ough t but have t h e h i g h e s t g rowth r a t e s . S t r e s s - t o l e r a n t s e e d l i n g s t h a t can m a i n t a i n p h y s i o l o g i c a l a c t i v i t y as w a t e r d e f i c i t s i n c r e a s e ( J ones 1983) w i l l grow more t h a n s e e d l i n g s t h a t a v o i d s t r e s s by c l o s i n g t h e i r s t o m a t a . F u r t h e r m o r e , d u r i n g a p e r i o d o f d r o u g h t , o n l y s t r e s s t o l e r a n t s e e d l n g s w i l l be a b l e t o d e v e l o p an e x t e n s i v e r oo t sys tem and t h e r e b y i n c r e a s e w a t e r u p t a k e . The shoo t t o r o o t r a t i o a t p l a n t i n g , and t h e s e e d l i n g ' s a b i l i t y t o change t h i s r a t i o , can have s i g n i f i c a n t e f f e c t s on s u r v i v a l and growth ( K o z l o w s k i 1982; L o p u s h i n s k y and Beebe 1 9 7 6 ) . F o r example a s e e d l i n g w i t h a h i g h shoo t t o r o o t r a t i o w i l l be more s u s c e p t i b l e t o d e s i c c a t i o n t h a n a s e e d l i n g w i t h a l o w e r r a t i o (Drew and F e r e l l 1 9 7 9 ) . The s h o o t s and r o o t s o f p l a n t i n g s t o c k can be m a n i p u l a t e d t o p r o v i d e t h e most a p p r o p r i a t e r a t i o o f t r a n s p i r i n g l e a f s u r f a c e a r e a t o w a t e r a b s o r b i n g r o o t s u r f a c e , e i t h e r by n u r s e r y p r a c t i c e s such as w r e n c h i n g o r p r u n i n g (Du ryea and L a v e n d e r 1982; E i s and Long 1 9 7 3 ) , o r by m o d i f y i n g a s e e d l i n g ' s m i c r o c l i m a t e , f o r e x amp l e , by p r o v i d i n g shade (Drew 1 9 8 3 ) . - 100 -A number o f s t u d i e s have shown t h a t g rowth i s w e l l c o r r e l a t e d t o t r a n s p i r a t i o n ( G i l e s e t al_. 1984; W a l l i s e t a l_. 1983; Boye r 1 9 7 6 ) . However , Tanner and S i n c l a i r (1983) a rgue t h a t growth i s l i k e l y b e t t e r r e l a t e d t o s t o m a t a l c ondu c t an c e ( g s ) because t he ne t C 0 2 f l u x i n t o a l e a f i s p r o p o r t i o n a l t o g s . C e n t r a l t o t h i s argument i s t h e a s s u m p t i o n t h a t t h e i n t e r n a l C 0 2 c o n c e n t r a t i o n o f t h e l e a f (C-j) i s c o n s t a n t . Wong e t al_. (1979) have shown t h i s t o be t r u e f o r a number o f s p e c i e s ; howeve r , o t h e r wo r ke r s have shown t h a t C-j i n c o n i f e r s v a r i e s bo th d i u r n a l l y and d u r i n g a d r y i n g p e r i o d ( P r i c e e t al_. 1986; L e v e r e n z 1 9 8 1 ) . On o v e r c a s t d a y s , when t h e vapour p r e s s u r e d e f i c i t (D) i s l ow and g s h i g h , p h o t o s y n t h e s i s c o u l d be l i m i t e d by low p h o t o s y n t h e t i c pho ton f l u x d e n s i t y (PPFD) and not by g s . The s t r o n g c o r r e l a t i o n o f g rowth w i t h t r a n s p i r a t i o n i n t r e e s appea r s t o be due t o ( i ) t r a n s p i r a t i o n b e i n g p r o p o r t i o n a l t o D ( f o r low t o modera te D ) , wh i ch i s w e l l c o r r e l a t e d t o PPFD, and ( i i ) bo th t r a n s p i r a t i o n and p h o t o s y n t h e s i s b e i n g d e c r e a s e d by low s o i l wa t e r p o t e n t i a l s and h i g h D. The o b j e c t i v e o f t h i s c h a p t e r i s (1) t o d e s c r i b e t h e e f f e c t s o f i r r i g a t i o n , shade and a c o m b i n a t i o n o f t h e s e t r e a t m e n t s on t h e m o n t h l y s h oo t g r o w t h , and t o t a l r o o t and shoo t g rowth d u r i n g t h e g row ing season o f t h r e e s p e c i e s o f c o n i f e r s e e d l i n g s g row ing on a s o u t h - f a c i n g h i g h e l e v a t i o n c l e a r c u t and (2) t o d e t e r m i n e whe the r t o t a l g r ow ing season d r y m a t t e r p r o d u c t i o n i s b e t t e r r e l a t e d t o v a l u e s o f t o t a l g r ow ing season t r a n s p i r a t i o n o r a ve r age g row ing season s t o m a t a l c o n d u c t a n c e c a l c u l a t e d u s i n g t h e s t o m a t a l c onduc t an ce b o u n d a r y - l i n e r e l a t i o n s h i p d e s c r i b e d i n C h a p t e r 2 . - 101 -I I . METHODS The e x p e r i m e n t a l s i t e and d e s i g n a r e d e s c r i b e d i n d e t a i l i n C h a p t e r 1 . B r i e f l y , i n A p r i l 1981 equa l numbers o f D o u g l a s - f i r ( P s e u d o t s u g a  m e n z i e s i i ( M i r b . ) F r a n c o ) , w e s t e r n hemlock (Tsuga h e t e r o p h y l l a ( R a f . S a r g . ) and P a c i f i c s i l v e r f i r ( A b i e s a m a b i l i s ( D o u g l . ) F o r b e s ) 1-0 c o n t a i n e r - g r o w n s t y r o p l u g s were l a i d ou t i n a r andomi zed c o m p l e t e b l o c k d e s i g n . The re were 32 b l o c k s w i t h 90 s e e d l i n g s pe r b l o c k . There were t h r e e t r e a t m e n t s : shade p r o v i d e d by 0.2 m h i g h by 0 .3 m w ide s h a d e c a r d s , s e l f shade p r o v i d e d by p l a n t i n g t h e s e e d l i n g s i n c l i n e d t o t h e s o u t h w e s t , and a c o n t r o l . In 1982 e i g h t a d d i t i o n a l b l o c k s were l a i d out u s i n g t h e same t h r e e s p e c i e s , p r o v e n a n c e , s t o c k t y p e and p l a n t i n g t e c h n i q u e as i n t h e p r e v i o u s y e a r . Fou r t r e a t m e n t s were t e s t e d : shade ( p r o v i d e d by shade c a r d s ) , i r r i g a t i o n (wa t e r was p r o v i d e d by a t r i c k l e i r r i g a t i o n s y s t e m ) , shade and i r r i g a t i o n , and no shade and no i r r i g a t i o n . Water was a p p l i e d when t e n s i o m e t e r s on t h e s i t e i n d i c a t e d t h a t t h e s o i l wa t e r p o t e n t i a l (ip s) was l e s s t han - 0 . 0 4 MPa. A . M i c r o m e t e o r o l o g i c a l Measurements As d e s c r i b e d i n C h a p t e r 1 c o n t i n u o u s h o u r l y a ve r age measurements o f g l o b a l s o l a r i r r a d i a n c e ( R s ) , w ind speed (u) a t t h e 0 .4 m h e i g h t , p r e c i p i t a t i o n and a i r t e m p e r a t u r e (T) and r e l a t i v e h u m i d i t y at t h e 1 m h e i g h t were r e c o r d e d w i t h a d a t a l o g g e r (CR21 , Campbe l l S c i e n t i f i c I n c . , L o g a n , U t a h , U . S . A . ) a t t h e e x p e r i m e n t a l s i t e d u r i n g t h e g row ing season i n 1981 , 1982 and 1983 . - 102 -S o i l wa t e r p o t e n t i a l s g r e a t e r t han - 0 . 1 MPa were measured u s i n g t e n s i o m e t e r s i n s t a l l e d a t t h e 5 0 , 100 , 150 , 2 0 0 , 300 and 500 mm d e p t h . S o i l wa t e r p o t e n t i a l s l e s s t han - 0 . 1 MPa were measured u s i n g t h e r m o c o u p l e p s y c h r o m e t e r s i n s t a l l e d at t h e same dep th s as t h e t e n s i o m e t e r s . Measurements o f i|>s were t a k e n e v e r y two t o s i x days t h r o u g h o u t t h e g row ing season i n each y e a r . The ave r age r oo t zone v a l u e o f \|>s was c a l c u l a t e d as t h e a r i t h m e t i c ave rage o f a l l t h e t e n s i o m e t e r o r p s y c h r o m e t e r measurements t o a dep th o f 300 mm. B. Growth Measurements 1 . S e e d l i n g H e i g h t The h e i g h t , d e f i n e d as t he d i s t a n c e f rom the t i p o f t h e l e a d e r t o t h e s o i l s u r f a c e , o f a l l l i v i n g s e e d l i n g s was measured w i t h a met re s t i c k each mon th , f rom May t o O c t o b e r , i n 1 9 8 1 , 1982 , and 1 9 8 3 . A l a r g e number o f s e e d l i n g s , many o f wh i ch e x h i b i t e d some g r o w t h , d i e d b e f o r e t h e end o f t h e s t u dy (as r e p o r t e d i n C h a p t e r 1) and were not i n c l u d e d i n t h e a n a l y s i s o f h e i g h t d a t a . Data a n a l y s i s was pe r f o rmed on o n l y t h o s e s e e d l i n g s t h a t were a l i v e i n O c t o be r 1 9 8 3 . 2 . L e a f A r e a and Shoot and Root Dry Mass The t o t a l p r o j e c t e d need l e a rea o f s e e d l i n g s was d e t e r m i n e d e i t h e r d i r e c t l y , u s i n g an a r ea mete r (Model L i - 3 0 0 0 , L i - C o r I n c . , L i n c o l n , N e b r a s k a , U . S . A . ) , o r by u s i n g r e g r e s s i o n e q u a t i o n s t h a t r e l a t e d p r o j e c t e d n eed l e a rea t o t h e mass o f n e ed l e s d r i e d t o 65°C f o r one d a y . - 103 -On l y a l i m i t e d number o f s e e d l i n g s were s e l e c t e d f o r l e a f a r ea measurement because o f t h e d e s t r u c t i v e n a t u r e o f t h e measurement and because o f t h e poor s u r v i v a l o f s e e d l i n g s i n p a r t i c u l a r t r e a t m e n t s . Wh i l e i t was r e c o g n i s e d t h a t t h e sma l l sample s i z e would make any s t a t i s t i c a l a n a l y s i s d i f f i c u l t , i t was f e l t t h a t as l a r g e a number o f s e e d l i n g s as p o s s i b l e s hou l d be l e f t i n t h e ground so t h a t t h e s t u d y c o u l d be c o n t i n u e d beyond 1 9 8 3 . A c c o r d i n g l y d u r i n g a g row ing season o n l y t h o s e s e e d l i n g s t h a t had been s e l e c t e d f o r s t o m a t a l c o n d u c t a n c e measurements ( d e s c r i b e d i n t h e p r e c e e d i n g c h a p t e r s ) were h a r v e s t e d f o r l e a f a r ea d e t e r m i n a t i o n . The m a j o r i t y o f s e e d l i n g s were h a r v e s t e d i n 1982 when i n t e n s i v e measurements o f g s were made on i r r i g a t e d un shaded , and n o n - i r r i g a t e d unshaded s e e d l i n g s o f a l l t h e s p e c i e s , and on shaded D o u g l a s - f i r s e e d l i n g s . Between 3 and 4 s e e d l i n g s o f a p a r t i c u l a r t r e a t m e n t and s p e c i e s were sampled e v e r y t i m e a l e a f a r ea d e t e r m i n a t i o n was made. In a d d i t i o n , at t h e b e g i n n i n g and end o f t h e g r ow i ng season o f each o f t h e 3 y e a r s o f t he s t u d y , between 3 and 10 s e e d l i n g s were h a r v e s t e d i n t h o s e t r e a t m e n t s where t h e r e were enough s u r v i v i n g s e e d l i n g s . These s e e d l i n g s were washed o f s o i l and p l a c e d i n a d r y i n g oven a t 65°C f o r 48 h o u r s . B e f o r e d r y i n g t h e t o t a l p r o j e c t e d l e a f a r ea o f each s e e d l i n g was mea su r ed . C . C a l c u l a t i o n s 1. S t o m a t a l Conduc tance H o u r l y v a l u e s o f ave rage s e e d l i n g s t oma t a l c onduc t an ce between s u n r i s e and s un se t were e s t i m a t e d f o r e v e r y day o f t h e g row ing season i n - 104 -1 9 8 1 , 1982 and 1983 u s i n g t h e b o u n d a r y - l i n e a n a l y s i s model d e s c r i b e d i n C h a p t e r 2 where 9 S = g smax f ( R s ) g ( T ) h ( D ) J<*s> k ( t ) ( 1 ) and 9smax i s t h e maximum s t o m a t a l c o n d u c t a n c e , t i s t h e number o f h ou r s f rom s u n r i s e and f , g , h, j and k a r e t h e f u n c t i o n s t h a t d e s c r i b e t h e b o u n d a r y - l i n e c u r v e s f o r t h e r e l a t i o n between g s and t h e h o u r l y a ve r age o f each v a r i a b l e . I t was assumed t h a t d u r i n g t h e day i|>s d i d no t c h a n g e . F o r days when measurements o f i|>s were not made, was e s t i m a t e d by i n t e r p o l a t i n g between measurements made on p r e c e d i n g and s u c c e e d i n g d a y s . The c o n s t a n t s used i n t h e f u n c t i o n s were t h o s e r e p o r t e d i n C h a p t e r 2 t h a t had been d e t e r m i n e d f rom measurements made on 13 days i n 1982 on s e e d l i n g s p l a n t e d i n A p r i l o f t h a t y e a r . S e e d l i n g canopy c o n d u c t a n c e ( g c ) , wh i ch can be c o n s i d e r e d t o be t h e s t o m a t a l c o n d u c t a n c e on a s e e d l i n g b a s i s , was c a l c u l a t e d as t h e p r o d u c t o f t h e t o t a l p r o j e c t e d n e e d l e a r e a (A) o f t h e s e e d l i n g and t h e a v e r a g e d a i l y s e e d l i n g s t o m a t a l c ondu c t an c e ( g s ) . T h i s c a l c u l a t i o n e n a b l e s a c ompa r i s on o f t h e g rowth and s t o m a t a l c onduc t ance o f d i f f e r e n t l y s i z e d s e e d l i n g s . Fo r days when measurements o f A were not made, A was e s t i m a t e d by i n t e r p o l a t i n g between measurements made on o t h e r d a y s . T h i s i n t e r p o l a t i o n was based on t h e ob se r ved s e a s o n a l c o u r s e o f s e e d l i n g h e i g h t and l e a f a r e a ( d i s c u s s e d b e l o w ) . A g row ing s ea son v a l u e o f s e e d l i n g canopy c ondu c t an c e (g£) was e s t i m a t e d by a v e r a g i n g v a l u e s o f g c wh i ch were computed f o r e v e r y day o f t h e g r ow i ng s e a s o n . - 105 -2. T r a n s p i r a t i o n H o u r l y v a l u e s o f t r a n s p i r a t i o n , on a s e e d l i n g b a s i s , between s u n r i s e and s u n s e t , were e s t i m a t e d f o r e v e r y day o f t he g row ing season i n 1981, 1982 and 1983. H o u r l y t r a n s p i r a t i o n r a t e s o f shaded and unshaded s e e d l i n g s were computed f rom E = A D g s / ( R v T ' ) (2) where R v i s t h e gas c o n s t a n t f o r wa te r v a p o u r , T' i s t h e a b s o l u t e a i r t e m p e r a t u r e and t he a s sump t i o n s a r e made (as d i s c u s s e d i n Chap t e r 1) t h a t D a p p r o x i m a t e s t h e vapour p r e s s u r e d i f f e r e n c e between t h e s t o m a t a l c a v i t i e s and t h a t t h e n eed l e boundary l a y e r r e s i s t a n c e (gb~M i s n e g l i g i b l e compared t o s t o m a t a l r e s i s t a n c e ( g s - 1 ) « A l t h o u g h i n C h a p t e r 2 c a l c u l a t i o n s o f t r a n s p i r a t i o n r a t e s o f t h e shaded D o u g l a s - f i r s e e d l i n g s were made w i t h o u t mak ing t h e s e a s s u m p t i o n s , i t was found t h a t c a l c u l a t i o n s u s i n g (2) r e s u l t e d i n a c c e p t a b l y sma l l e r r o r s i n t h e t r a n s p i r a t i o n r a t e s o f t h e s e s e e d l i n g s . The t o t a l amount o f wa t e r t r a n s p i r e d by a s e e d l i n g i n a g row ing season (EJQT) was c a l c u l a t e d by summing t h e h o u r l y e s t i m a t e s o f E f o r e v e r y day o f t h a t g row ing s e a s o n . I I I . RESULTS A . Grow ing Season Weather O b s e r v a t i o n s The wea the r o b s e r v a t i o n s made i n 1981, 1982 and 1983 a r e d e s c r i b e d i n d e t a i l i n Chap t e r 1. B r i e f l y , t he 1981 g r ow ing season was - 106 -c h a r a c t e r i z e d by coo l and wet wea the r f rom t h e t ime t h e s e e d l i n g s were p l a n t e d u n t i l m i d - J u l y . An ex t ended d r y p e r i o d o c c u r r e d between J u l y 10 and Augus t 26 d u r i n g wh i ch l e s s t h an 10 mm o f r a i n f e l l . E x t r e m e l y h i g h a i r t e m p e r a t u r e s (maxima ranged f rom 25°C t o 37°C) and low a b s o l u t e h u m i d i t i e s r e s u l t e d i n vapour p r e s s u r e d e f i c i t s t h a t a t t i m e s exceeded 4 . 5 k P a . Root zone s d e c r e a s e d f rom m i d - J u l y u n t i l t h e end o f Augus t r e a c h i n g a minimum o f - 1 . 7 MPa on Augus t 2 5 . The g r ow ing season i n 1982 was c h a r a c t e r i z e d by a wet s p r i n g and a hot and d r y summer. The summer d r ough t was b roken by a s h o r t p e r i o d o f r a i n f a l l i n e a r l y A u g u s t . B e f o r e t h i s r a i n f a l l , r o o t zone i|>s had d e c r e a s e d t o - 0 . 7 5 MPa. Root zone \|>s d e c r e a s e d f rom e a r l y Augus t u n t i l t h e b e g i n n i n g o f September r e a c h i n g a minimum o f - 1 . 2 MPa. By c o n t r a s t t h e summer o f 1983 was e x c e p t i o n a l l y wet and c o o l . T o t a l r a i n f a l l f r om May t o t h e end o f September was 399 mm. A minimum r oo t zone i|>s o f - 0 . 5 MPa was reached i n m i d - A u g u s t . B. Growth The m o r p h o l o g i c a l c h a r a c t e r i s t i c s o f t h e s e e d l i n g s b e f o r e t h e y were p l a n t e d i n 1981 and 1982 a r e summar ized i n T a b l e 3 . 1 . The re were not l a r g e o v e r a l l d i f f e r e n c e s between s e e d l i n g s o f t h e same s p e c i e s , a l t h o u g h t h e r o o t s o f t h e 1982 D o u g l a s - f i r s e e d l i n g s were s l i g h t l y s m a l l e r t h a n t h o s e o f s e e d l i n g s p l a n t e d i n t h e p r e v i o u s y e a r . C o n v e r s e l y w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n 1982 had s l i g h t l y l a r g e r r o o t s y s t ems t han t h o s e o f s e e d l i n g s p l a n t e d i n 1 9 8 1 . - 107 -T a b l e 3 .1 Mo rpho l ogy o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s a t t h e t ime o f p l a n t i n g . S t anda rd d e v i a t i o n s a r e g i v e n i n b r a c k e t s . S p e c i e s Year He i gh t Shoot t o Dry We ight (mm) Root R a t i o (g) Doug l a s -• f i r 1981 144 (9) 2.4 ( 0 . 2 ) 3.7 ( 0 . 4 ) 1982 152 (12) 2.6 ( 0 . 2 ) 3 .4 ( 0 . 2 ) Wes te rn hemlock 1981 116 (13) 3.1 ( 0 . 2 ) 1.1 ( 0 . 2 ) 1982 109 (6) 2.8 ( 0 . 2 ) 1.3 ( 0 . 2 ) P a c i f i c s i l v e r f i r 1981 91 (7) 2.8 ( 0 . 1 ) 1.2 ( 0 . 2 ) 1982 82 (8) 2 .6 ( 0 . 2 ) 1.4 ( 0 . 3 ) - 108 -1 . H e i g h t and L e a f A r ea o f S e e d l i n g s P l a n t e d i n 1981 A summary o f t h e h e i g h t measurements made on s e e d l i n g s p l a n t e d i n 1981 i s p r e s e n t e d i n T ab l e 3 . 2 . In a l l t he s p e c i e s t h e p r o v i s i o n o f shade c a r d s was t h e most e f f e c t i v e t r e a t m e n t i n p r omo t i n g h e i g h t g r o w t h . I n c l i n i n g s e e d l i n g s had no s i g n i f i c a n t e f f e c t on h e i g h t . Shaded P a c i f i c s i l v e r f i r s e e d l i n g s e x h i b i t e d t h e l a r g e s t r e l a t i v e i n c r e a s e i n h e i g h t o ve r t h e 3 y e a r s (300%) f o l l o w e d by shaded D o u g l a s - f i r and wes t e rn hemlock s e e d l i n g s (260% and 150% r e s p e c t i v e l y ) . In a l l s p e c i e s shaded s e e d l i n g s were a p p r o x i m a t e l y 18% t a l l e r t han unshaded s e e d l i n g s . In a l l t r e a t m e n t s and s p e c i e s ove r 70% o f t h e h e i g h t g rowth t h a t t ook p l a c e o ve r 3 y e a r s was a c c o m p l i s h e d i n t h e f i r s t g r ow ing s e a s o n . T a b l e 3 .3 shows t he t o t a l p r o j e c t e d l e a f a r ea o f s e e d l i n g s h a r v e s t e d a t t h e end o f each g row ing season between A p r i l 1981 and O c t o be r 1 9 8 3 . By t he end o f t h e f i r s t g row ing season t he l e a f a r ea s o f shaded D o u g l a s - f i r wes t e rn hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s exceeded t h o s e o f unshaded s e e d l i n g s by a p p r o x i m a t e l y 20%, 25% and 28% r e s p e c t i v e l y . These d i f f e r e n c e s i n l e a f a r ea between t r e a t m e n t s became more p ronounced ove r t he nex t two y e a r s . As was t h e ca se w i t h s e e d l i n g h e i g h t , most o f t h e i n c r e a s e i n l e a f a r ea o c c u r r e d i n t h e f i r s t g r ow i ng season f o l l o w e d by a pronounced d e c l i n e i n g rowth r a t e s i n subsequen t y e a r s . 2 . H e i g h t and L e a f A r ea o f S e e d l i n g s P l a n t e d i n 1982 Shaded , n o n - i r r i g a t e d s e e d l i n g s p l a n t e d i n 1982 , l i k e t h o s e p l a n t e d i n 1 9 8 1 , were s i g n i f i c a n t l y t a l l e r ( w i t h t h e e x c e p t i o n o f we s t e r n - 109 -T a b l e 3.2 S e e d l i n g h e i g h t (mm) i n Oc t obe r 1 9 8 1 , 1982 and 1983 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g p l a n t e d i n A p r i l 1 9 8 1 . Numbers f o l l o w e d by t he same l e t t e r a re not s i g n i f i c a n t l y d i f f e r e n t ( t = 0 .05) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range Te s t wh ich was a p p l i e d t o each s p e c i e s i n each y e a r . T rea tmen t D o u g l a s - f i r Western hem!ock P a c i f i c s i l v e r f i r O c t o b e r 1981 C o n t r o l 283 (a ) 150 (a ) 116 (a ) S e l f Shade 288 (a) 141 (a) 122 (a) Shade Ca rds 331 (b) 164 (b) 140 (b) O c t o b e r 1982 C o n t r o l 310 (a) 173 (a) 141 (a) Shade Ca rds 360 (b) 192 (a ) 162 (b) O c t o b e r 1983 C o n t r o l 348 (a) 201 (a) 161 (a) Shade Ca rds 410 (b) 237 (b) 187 (b) - 110 -T a b l e 3 .3 L e a f a r e a ( cm 2 ) i n Oc t obe r 1 9 8 2 , 1982 and 1983 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1 9 8 1 . S t a nda r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s . T r ea tmen t D o u g l a s - f i r Western hemlock P a c i f i c s i l v e r f i r O c t o b e r 1981 C o n t r o l 120 (26) 50 (8) 54 (12) Shade Ca rds 144 (30) 62 (14) 69 (14) O c t o b e r 1982 C o n t r o l 133 (18) 68 (16) 63 (16) Shade Ca rds 172 (24) 88 (12) - — O c t o b e r 1983 C o n t r o l 158 (18) 83 (14) 91 (14) Shade Ca rds 217 (21) 121 (19) 128 (22) - I l l -h e m l o c k ) , and had l a r g e r l e a f a r e a s than s e e d l i n g s t h a t were u n t r e a t e d ( T a b l e s 3 .4 and 3 . 5 ) . In g e n e r a l s h a d e d , n o n - i r r i g a t e d s e e d l i n g s were t h e same h e i g h t as unshaded , i r r i g a t e d s e e d l i n g s but had a s m a l l e r l e a f a r e a . In a l l t h e s p e c i e s t h e b i g g e s t i n c r e a s e i n h e i g h t and l e a f a r e a was e x h i b i t e d by t h o s e s e e d l i n g s t h a t were bo th i r r i g a t e d and s h a d e d . By the end o f O c t o b e r 1983 t h e l e a f a r ea s o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s t h a t r e c e i v e d t h i s t r e a t m e n t exceeded t h o s e o f u n t r e a t e d s e e d l i n g s by a p p r o x i m a t e l y 70%, 65% and 50% r e s p e c t i v e l y . The c o r r e s p o n d i n g d i f f e r e n c e s i n h e i g h t were 40%, 30% and 50% r e s p e c t i v e l y . The s ea sona l c o u r s e s o f s e e d l i n g h e i g h t i n 1982 and 1983 f o r t h e 3 s p e c i e s a r e p r e s e n t e d i n F i g u r e s 3.1 t o 3 . 3 . As was t he case w i t h s e e d l i n g s p l a n t e d i n 1981 , most o f t h e h e i g h t i n c r e a s e o c c u r r e d between t h e b e g i n n i n g o f May and t he end o f June o f t h e f i r s t g row ing s e a s o n . D i f f e r e n c e s i n h e i g h t between t r e a t m e n t s d i d not become more pronounced i n t h e f o l l o w i n g y e a r . S e e d l i n g l e a f a r ea deve lopment 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 o f s e e d l i n g h e i g h t ( F i g u r e s 3.4 t o 3 . 6 ) i n t h a t most g rowth o c c u r r e d i n t h e f i r s t two months a f t e r t h e s e e d l i n g s were p l a n t e d . However d i f f e r e n c e s between t r e a t m e n t s became more pronounced i n subsequen t g row ing s e a s o n s . 3 . Shoo t and Root Dry Mass and Shoot t o Root Dry Mass R a t i o S h o o t , r o o t and t o t a l d r y mas se s , and shoo t t o r o o t d r y mass r a t i o s o f s e e d l i n g s p l a n t e d i n 1981 and 1982 a r e p r e s e n t e d i n T a b l e s 3.6 t o 3 . 8 . G e n e r a l l y s e e d l i n g s t h a t were bo th i r r i g a t e d and shaded had the - 112 -T a b l e 3 .4 S e e d l i n g h e i g h t (mm) i n O c t obe r 1 9 8 2 , 1982 and 1983 o f D o u g l a s - f i r , we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1 9 8 2 . Numbers f o l l o w e d by t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( t = 0 . 0 5 ) a c c o r d i n g t o Duncan ' s New M u l t i p l e Range Tes t was a p p l i e d t o each s p e c i e s i n each y e a r . T r ea tmen t D o u g l a s - f i r Wes te rn hemlock P a c i f i c s i l v e r f i r O c t o b e r 1982 C o n t r o l 296 (a) 168 (a) 127 (a) Shade Ca rd s 345 (b) 178 (a ) 153 (b) I r r i g a t i o n 337 (b) 181 (a) 159 (b) I r r i g a t i o n and 368 (b) 212 (b) 182 ( c ) Shade Ca rds O c t o b e r 1983 C o n t r o l 333 (a ) 204 (a ) 157 ( a ) Shade Ca rds 391 (b) 210 (a) 191 (b) I r r i g a t i o n 421 ( c ) 241 (a ) 214 (b) I r r i g a t i o n and 461 ( c ) 265 (b) 239 ( c ) Shade Ca rds - 113 -T a b l e 3 .5 L e a f a r e a ( cm 2 ) i n Oc tobe r 1982 and 1983 o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1982 . S t a nda r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s . T r ea tmen t D o u g l a s - f i r Wes te rn hemlock P a c i f i c s i l v e r f i r O c t o b e r 1982 C o n t r o l 135 (18) 57 ( I D 63 (12) Shade Ca rds 155 (24) - - - -I r r i g a t i o n 161 (24) 70 (14) 83 (16) I r r i g a t i o n and 171 (21) 78 (12) -Shade Cards O c t o b e r 1983 C o n t r o l 141 (22) 68 (6) 78 (10) Shade Ca rds 170 (27) 80 (ID - -I r r i g a t i o n 190 (24) 94 (17) 106 (13) I r r i g a t i o n and 234 (30) 112 (12) 118 (15) Shade Ca rds F i g u r e 3 .1 Sea sona l c o u r s e o f s e e d l i n g h e i g h t i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( t ) , i r r i g a t e d (Q) and i r r i g a t e d and shaded (•) D o u g l a s - f i r s e e d l i n g s p l a n t e d i n May 1982 . - 115 -F i g u r e 3 .2 Sea sona l c o u r s e o f s e e d l i n g h e i g h t i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( • ) , i r r i g a t e d (•) and i r r i g a t e d and shaded (•) w e s t e r n hemlock s e e d l i n g s p l a n t e d i n May 1982 . - 116 -F i g u r e 3 . 3 Sea sona l c o u r s e o f s e e d l i n g h e i g h t i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( • ) , i r r i g a t e d (•) and i r r i g a t e d and shaded (•) P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1 9 8 2 . - 117 -E o 240 200 -160 -120 80 MAY JUN JUL AUG SEP MAY JUN JUL AUG SEP 1982 1983 F i g u r e 3 .4 Seasona l c o u r s e o f s e e d l i n g p r o j e c t e d l e a f a r e a (A) i n 1982 and 1983 o f u n t r e a t e d ( o ) , shaded ( t ) , i r r i g a t e d (o) and i r r i g a t e d and shaded (•) D o u g l a s - f i r s e e d l i n g s p l a n t e d i n May 1982 . The Broken l i n e shows t h e e s t i m a t e d s e a s ona l c o u r s e o f l e a f a r e a t h a t was used i n t h e c a l c u l a t i o n o f t h e g r ow i ng season t r a n s p i r a t i o n o f i r r i g a t e d and shaded s e e d l i n g s . - 118 -110 3 0 I 1 1 . »- 1 1 1 1 1 1  MAY JUN JUL AUG SEP MAY JUN JUL AUG SEP 1982 1983 F i g u r e 3 .5 Seasona l c o u r s e o f p r o j e c t e d l e a f a r e a (A) i n 1982 and 1983 o f u n t r e a t e d (o) and i r r i g a t e d (•) we s t e r n hemlock s e e d l i n g s p l a n t e d i n May 1 9 8 2 . - 119 -30 MAY JUN JUL AUG SEP MAY JUN JUL AUG SEP 1982 1983 F i g u r e 3.6 Seasona l c o u r s e o f p r o j e c t e d l e a f a r e a (A) i n 1982 and 1983 o f u n t r e a t e d (o) and i r r i g a t e d (•) P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n May 1 9 8 2 . Tab l e 3.6 Mo rpho l ogy i n Oc tobe r 1981 , 1982 and 1983 o f D o u g l a s - f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda rd d e v i a t i o n s are g i v en i n b r a c k e t s . Year Year Shoot Dry Root Dry T o t a l Dry Shoot t o Root P l a n t e d Measured Mass (g) Mass (g) Mass (g) Dry Mass R a t i o C o n t r o l 1981 1981 4 .1 ( 0 . 6 ) 1.3 ( 0 . 3 ) 5.4 ( 0 . 7 ) 3 .2 ( 0 . 3 ) II 1981 1982 6.3 ( 0 . 9 ) 2.8 ( 0 . 4 ) 9 .1 ( 1 . 2 ) 2.2 ( 0 . 3 ) 1981 1983 9 .5 (l.D 4 . 2 ( 0 . 6 ) 13 .7 ( 1 . 4 ) 2 .2 ( 0 . 2 ) 1982 1982 4.6 ( 0 . 5 ) 1.5 ( 0 . 4 ) 6.1 ( 0 . 8 ) 3.0 ( 0 . 3 ) II 1982 1983 7.2 ( 0 . 9 ) 2 .6 ( 0 . 5 ) 9 . 8 ( 1 . 3 ) 2.7 ( 0 . 2 ) I r r i g a t i o n 1982 1982 5.8 ( 1 . 0 ) 1.6 ( 0 . 2 ) 7.4 (l.D 3.6 ( 0 . 2 ) 1982 1983 9 .5 ( 1 . 3 ) 2.4 ( 0 . 4 ) 11 .9 ( 1 . 5 ) 4 .1 ( 0 . 2 ) Shade Card 1981 1982 8.2 ( 1 . 5 ) 2.5 ( 0 . 5 ) 10.7 ( 1 . 8 ) 3.4 ( 0 . 2 ) 1981 1983 12 .6 ( 2 . 8 ) 4 . 2 ( 0 . 7 ) 16 .8 ( 3 . 1 ) 3 .0 ( 0 . 1 ) I r r i g a t i o n and 1982 1983 10 .2 ( 1 . 6 ) 2 .4 ( 0 . 4 ) 12 .6 ( 1 . 9 ) 4 . 3 ( 0 . 2 ) Shade Card T a b l e 3.7 Mo rpho l ogy i n Oc tobe r 1 9 8 1 , 1982 and 1983 o f wes t e rn hemlock s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda r d d e v i a t i o n s a re g i v en i n b r a c k e t s . Year Year Shoot Dry Root Dry T o t a l Dry Shoot t o Root P l a n t e d Measured Mass (g) Mass (g) Mass (g) Dry Mass R a t i o C o n t r o l 1981 1982 1.4 ( 0 . 3 ) 0 .7 ( 0 . 1 ) 2.1 ( 0 . 4 ) 2 .2 ( 0 . 4 ) II 1982 1983 1.8 ( 0 . 3 ) 0 .8 ( 0 . 2 ) 2.6 ( 0 . 4 ) 2.1 ( 0 . 2 ) I r r i g a t i o n 1982 1983 2.3 ( 0 . 4 ) 0 .9 ( 0 . 2 ) 3.2 ( 0 . 6 ) 2.6 ( 0 . 1 ) .Shade Card 1982 1983 2.1 ( 0 . 5 ) 0 .9 ( 0 . 3 ) 3.0 ( 0 . 7 ) 2.4 ( 0 . 2 ) I r r i g a t i o n and 1982 1983 2.6 ( 0 . 4 ) 0 .9 ( 0 . 2 ) 3.5 ( 0 . 5 ) 2 .8 ( 0 . 1 ) Shade Card Tab l e 3 .8 Mo rpho l ogy i n Oc tobe r 1981 , 1982 and 1983 o f P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda rd d e v i a t i o n s are g i v e n i n b r a c k e t s . Year Year Shoot Dry Root Dry T o t a l Dry Shoot t o Root P l a n t e d Measured Mass (g) Mass (g) Mass (g) Dry Mass R a t i o C o n t r o l 1981 1983 2.2 ( 0 . 4 ) 0 .7 ( 0 . 2 ) 2 .9 ( 0 . 6 ) 3.1 ( 0 . 4 ) II 1982 1983 1.6 ( 0 . 3 ) 0.6 ( 0 . 2 ) 2.2 ( 0 . 4 ) 2.5 ( 0 . 8 ) I r r i g a t i o n 1982 1983 2.3 ( 0 . 5 ) 0 .6 ( 0 . 3 ) 2.9 ( 0 . 8 ) 4 .0 (l.D I r r i g a t i o n and 1982 1983 2.4 ( 0 . 3 ) 0.7 ( 0 . 2 ) 3.1 ( 0 . 5 ) 3.3 ( 0 . 4 ) Shade Card - 123 -l a r g e s t shoo t and t o t a l d r y masses f o l l o w e d by unshaded i r r i g a t e d s e e d l i n g s . The t o t a l d r y masses o f unshaded i r r i g a t e d D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s a f t e r one g row ing season t y p i c a l l y exceeded t h o s e o f u n t r e a t e d s e e d l i n g s by 20%, 60% and 90% r e s p e c t i v e l y . U n t r e a t e d s e e d l i n g s had t h e l o w e s t shoo t and t o t a l d r y masses bu t c o n v e r s e l y had s i m i l a r o r even g r e a t e r r o o t d r y masses t h a n any o f t h e o t h e r t r e a t m e n t s . C o n s e q u e n t l y u n t r e a t e d s e e d l i n g s t y p i c a l l y had t h e l o w e s t shoo t t o r o o t d r y mass r a t i o s o f a l l t h e s e e d l i n g s . W i t h t h e e x c e p t i o n o f we s t e r n hemlock s e e d l i n g s , t h i s r a t i o d e c r e a s e d i n s u c c e s s i v e g row ing s e a s o n s . A l l t h e o t h e r t r e a t m e n t s i n c r e a s e d shoo t t o r o o t d r y mass r a t i o s w i t h t h e l a r g e s t i n c r e a s e o c c u r r i n g i n shaded i r r i g a t e d s e e d l i n g s . In g e n e r a l , unshaded i r r i g a t e d s e e d l i n g s had h i g h e r shoo t t o r o o t d r y mass r a t i o s t h a n shaded n o n - i r r i g a t e d s e e d l i n g s . C . E s t i m a t e s o f T o t a l S e e d l i n g S t o m a t a l C o n d u c t a n c e , Sea sona l  T r a n s p i r a t i o n and Water Use E f f i c i e n c y The r e l a t i o n s h i p between t h e t o t a l s eason d r y m a t t e r a c c u m u l a t i o n (Y) i n 1982 and 1983 and e s t i m a t e s o f a ve r age g row ing season canopy c o n d u c t a n c e Cgc) f o r D o u g l a s - f i r s e e d l i n g s p l a n t e d i n 1981 and 1982 i s p r e s e n t e d i n F i g u r e 3 . 7 . V a l u e s o f Y were o b t a i n e d by s u b t r a c t i n g t h e t o t a l d r y we i gh t o f s e e d l i n g s h a r v e s t e d a t t h e b e g i n n i n g o f t h e g r ow i ng season f rom t h a t o f s e e d l i n g s , i n t h e same t r e a t m e n t , h a r v e s t e d a t t h e end o f t h e g row ing s e a s o n . A p p r o x i m a t e l y 65% o f t h e v a r i a t i o n i n Y c o u l d be a c c oun t ed f o r by " g c . A h i g h e r f r a c t i o n o f t h e v a r i a t i o n - 124 -F i g u r e 3.7 The r e l a t i o n s h i p between g row ing season s e e d l i n g d r y m a t t e r a c c u m u l a t i o n (Y) and t h e a v e r age g r ow ing season t o t a l s e e d l i n g s t o m a t a l c onduc t an ce Cgc) f o r D o u g l a s - f i r s e e d l i n g s i n 1 9 8 1 , 1982 and 1 9 8 3 . The s l o p e o f t h e l i n e f o r c e d t h r o u g h z e r o i s 0 .231 g / ( c m 3 s ) and t h e e q u a t i o n o f t h e l i n e f i t t e d t h r o u g h t he d a t a p o i n t s by l i n e a r r e g r e s s i o n i s Y (g) = 0 .154 " g c ( c m 3 s - 1 ) + 1.31 ( r z = 0 . 6 8 ) . - 125 -i n Y was a c coun t ed f o r by r e l a t i n g Y t o e s t i m a t e d t o t a l g r ow ing season s e e d l i n g t r a n s p i r a t i o n ( F i g u r e 3 . 8 ) . The b e s t l i n e a r r e g r e s s i o n f i t was o b t a i n e d ( r = 0 .88) when shaded s e e d l i n g s were e x c l u d e d f rom t he a n a l y s i s s i n c e t h e r e s u l t s i n d i c a t e d t h a t t h e t o t a l d r y m a t t e r p r o d u c t i o n o f t h e s e s e e d l i n g s was s i g n i f i c a n t l y l owe r than t h a t o f unshaded s e e d l i n g s even though t h e y used a p p r o x i m a t e l y t h e same amount o f wa te r per u n i t l e a f a r e a . The s l o p e o f t h e r e g r e s s i o n l i n e f o r c e d t h r o u g h z e r o ( w i t h shaded s e e d l i n g s i n c l u d e d ) i s 0 .0022 wh i ch i s t h e w a t e r use e f f i c i e n c y (WUE) o f t h e D o u g l a s - f i r s e e d l i n g s . The i n v e r s e o f t h e s l o p e g i v e s t h e amount o f wa t e r (450 g) expended d u r i n g t h e p r o d u c t i o n o f 1 g o f d r y m a t t e r . The g r o w t h , wa te r u s e d , and WUE o f s e e d l i n g s r e c e i v i n g d i f f e r e n t t r e a t m e n t s f o r t he t h r e e s p e c i e s a r e g i v e n i n T a b l e s 3.9 t o 3 . 1 1 . In D o u g l a s - f i r , v a l u e s o f WUE ranged f rom 0 .0017 t o 0 .0029 ( T a b l e 3 . 9 ) . Wes te rn hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s had l owe r WUE wh i ch ranged f rom 0.0011 t o 0 . 0 0 1 5 . I V . DISCUSSION The r e s u l t s o f t h i s s t udy i n d i c a t e t h a t m o d i f i c a t i o n o f a s e e d l i n g ' s m i c r o c l i m a t e , whe the r by p r o v i d i n g shade o r w a t e r , o r a c o m b i n a t i o n o f t h e s e t r e a t m e n t s , can have a p ronounced e f f e c t on bo t h t h e e x t e n t and t y p e o f s e e d l i n g g r o w t h . I t i s i m p o r t a n t t o r e c o g n i s e , p a r t i c u l a r l y i n t h e ca se o f we s t e r n hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s , t h a t c o n s i d e r a b l e b i a s was i n t r o d u c e d i n t o t h e r e s u l t s - 126 -F i g u r e 3 .8 The r e l a t i o n s h i p between g row ing season s e e d l i n g d r y m a t t e r a c c u m u l a t i o n (Y) and g row ing season s e e d l i n g t r a n s p i r a t i o n ( E J O T ) f o r D o u g l a s - f i r s e e d l i n g s i n 1 9 8 1 , 1982 and 1 9 8 3 . The c l o s e d c i r c l e s i n d i c a t e shaded t r e a t m e n t s . The s l o p e o f t h e l i n e f o r c e d t h r o u g h z e r o i s 0 .0022 g / g . The e q u a t i o n o f t h e l i n e f i t t e d t h r o u g h a l l t he d a t a p o i n t s by l i n e a r r e g r e s s i o n i s Y(g) • 0 .0027 EJOT (9) -0*83 ( r 2 = 0 . 7 8 ) , and t he e q u a t i o n o f t h e l i n e , a l s o f i t t e d by l i n e a r r e g r e s s i o n , t h r o u g h t h e p o i n t s e x c l u d i n g shade t r e a t m e n t s i s Y(g) = 0 .0036 EjQT (9) - 2 . 0 ( r 2 = 0 . 8 8 ) . Tab l e 3.9 Dry m a t t e r a c c u m u l a t i o n ( Y ) , s e e d l i n g t r a n s p i r a t i o n (ETQJ) and WUE d u r i n g t h e g row ing season i n 1981 , 1982 and 1983 o f D o u g l a s - f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda r d d e v i a t i o n s o f Y a r e b r a c k e t e d . The r oo t mean squa re e r r o r s f o r ETQJ were t y p i c a l l y 26%. These e r r o r s were d e t e r m i n e d by d i f f e r e n t i a t i n g e q u a t i o n (2) and assuming a 20% e r r o r f o r A, a 10% e r r o r i n D and by u s i n g the s t a n d a r d e r r o r o f e s t i m a t e f o r c a l c u l a t e d v e r s u s measured g s r e p o r t e d i n Chap t e r 2 . Yea r P l a n t e d Year Measured Y (g) E T 0 T (g) WUE (g g - 1 ) C o n t r o l 1981 1981 1.9 ( 0 . 4 ) 1100 0 .0017 II 1981 1982 3.6 ( 0 . 7 ) 1500 0 .0024 I I 1981 1983 5.2 ( 1 . 2 ) 1800 0 .0029 II 1982 1982 2.6 ( 0 . 7 ) 1300 0 .0020 II 1982 1983 3.4 ( 0 . 8 ) 1600 0 .0021 I r r i g a t i o n 1982 1982 3.6 ( 0 . 9 ) 1700 0 .0021 n 1982 1983 4.2 ( 1 . 0 ) 1800 0 .0023 Shade Card 1981 1982 3.5 ( 1 . 0 ) 1800 0 .0019 1981 1983 5.1 ( 1 . 2 ) 2100 0 .0024 I r r i g a t i o n and 1982 1983 4 .0 ( 0 . 8 ) 2000 0 .0020 Shade Card T a b l e 3 .10 Dry m a t t e r a c c u m u l a t i o n ( Y ) , s e e d l i n g t r a n s p i r a t i o n (EJOT) a n d W u"E d u r i n g t h e g row ing season i n 1982 and 1983 o f we s t e r n hemlock s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t a nda r d d e v i a t i o n s o f Y a r e b r a c k e t e d . The r oo t mean square e r r o r s f o r EjOT were t y p i c a l l y 28%. These e r r o r s were d e t e r m i n e d by d i f f e r e n t i a t i n g e q u a t i o n (2) and assuming a 20% e r r o r f o r A, a 10% e r r o r i n D and by u s i n g the s t a n d a r d e r r o r o f e s t i m a t e f o r c a l c u l a t e d v e r s u s measured g s r e p o r t e d i n Chap t e r 2 . Yea r Year Y (g) E T 0 T (g) WUE P l a n t e d Measured (g g " ) C o n t r o l 1981 1982 0.6 ( 0 . 3 ) 500 0 .0012 1982 1983 0 .6 ( 0 . 2 ) 400 0 . 0015 I r r i g a t i o n 1982 1983 0 .9 ( 0 . 3 ) 700 0 .0013 Shade Card 1981 1983 0.7 ( 0 . 3 ) 800 o.oong I r r i g a t i o n and 1982 1983 1.1 ( 0 . 3 ) 800 0 .0014 Shade Card T a b l e 3.11 Dry m a t t e r a c c u m u l a t i o n ( Y ) , s e e d l i n g t r a n s p i r a t i o n (ETQJ) and WUE d u r i n g t h e g row ing season i n 1983 o f P a c i f i c s i l v e r f i r s e e d l i n g s p l a n t e d i n A p r i l 1981 and May 1982 . S t anda r d d e v i a t i o n s o f Y a re b r a c k e t e d . The r o o t mean square e r r o r s f o r ETQJ were t y p i c a l l y 30%. These e r r o r s were d e t e r m i n e d by d i f f e r e n t i a t i n g e q u a t i o n (2) and assuming a 20% e r r o r i n A, a 10% e r r o r i n D, and by u s i n g the s t a n d a r d e r r o r o f e s t i m a t e f o r c a l c u l a t e d v e r s u s measured g s r e p o r t e d i n Chap te r 2 . Yea r Year Y (g) E T 0 T (g) WUE P l a n t e d Measured (g g _ 1 ) C o n t r o l 1981 1983 0.7 ( 0 . 3 ) 600 0 .0012 1982 1983 0 .6 ( 0 . 3 ) 500 0 .0012 I r r i g a t i o n 1982 1983 0 .8 ( 0 . 2 ) 700 0 .0010 I r r i g a t i o n and 1982 1983 0 .9 ( 0 . 3 ) 800 0 .0011 Shade Card - 130 -because o n l y t h e r e l a t i v e l y few s e e d l i n g s t h a t s u r v i v e d u n t i l t h e end o f t h e s t u dy ( s ee T a b l e s 1.8 and 1.9 i n C h a p t e r 1) were i n c l u d e d i n t h e g rowth a n a l y s i s . D o u g l a s - f i r and P a c i f i c s i l v e r f i r a r e d e t e r m i n a t e s p e c i e s so t h a t t h e i r w i n t e r buds c o n t a i n p r i m o r d i a o f a l l t he l e a v e s t h a t w i l l expand d u r i n g t h e f i r s t t h r e e months o f t h e f o l l o w i n g g row ing season (Kramer and K o z l o w s k i 1 9 7 9 ) . The 1-0 s e e d l i n g s o f t h e s e s p e c i e s , used i n t h i s s t u d y , were n u r s e r y r a i s e d as c o n t a i n e r grown s t y r o p l u g s , d i d not have a wa t e r s t r e s s h i s t o r y , and would have had a l a r g e number o f l e a f p r i m o r d i a when t hey were p l a n t e d a t t h e e x p e r i m e n t a l s i t e . Such s e e d l i n g s would have been e xpe c t ed t o e x h i b i t good g rowth between t he b e g i n n i n g o f May and t h e end o f June i f t h e e n v i r o n m e n t a l c o n d i t i o n s d i d not become t o o s e v e r e . The f a c t t h a t u n t r e a t e d P a c i f i c s i l v e r f i r s e e d l i n g s , wh i ch a r e not s t r e s s t o l e r a n t ( C h a p t e r 1 ) , e x h i b i t e d s i g n i f i c a n t g rowth even when c o n d i t i o n s were s e v e r e enough t o cause v e r y h i g h r a t e s o f m o r t a l i t y would i n d i c a t e t h a t t h i s s p e c i e s d i s p l a y s , what J one s (1983) d e s c r i b e s as o p t i m i s t i c but n o n - r e s p o n s i v e b e h a v i o u r . The s e e d l i n g s o f t h i s s p e c i e s , used more wa te r t han j u s t i f i e d i n o r d e r t o a c h i e v e g rowth and c o n s e q u e n t l y became h i g h l y s t r e s s e d when wa te r was l i m i t e d . Even t h o s e s e e d l i n g s t h a t were i r r i g a t e d d i d not d i s p l a y enough s t o m a t a l c o n t r o l t o p r e v en t d e s i c c a t i o n i n t h e f a c e o f h i g h e v a p o r a t i v e demand. C o n v e r s e l y D o u g l a s - f i r s e e d l i n g s , wh i ch a r e s t r e s s t o l e r a n t , a c h i e v e d good g rowth w i t h o u t e x p o s i n g t h e m s e l v e s t o t h e r i s k o f s e v e r e d e s i c c a t i o n and hence m o r t a l i t y . In bo th s p e c i e s t h e l i m i t e d shoo t g rowth i n subsequen t g row ing seasons i s l i k e l y due , i n p a r t , t o t h e d r ough t c o n d i t i o n s , t h a t o c c u r r e d - 131 -i n J u l y and Augus t i n bo th 1981 and 1 9 8 2 , l i m i t i n g t h e deve l opment o f new l e a f p r i m o r d i a . The f a c t t h a t d i f f e r e n c e s i n l e a f a r e a between t r e a t m e n t s became more p ronounced i n s u c c e s s i v e g rowth seasons s u g g e s t s t h a t a t r e a t m e n t such as i r r i g a t i o n not o n l y e f f e c t s c u r r e n t g rowth but t h e nex t y e a r s g rowth t h r o u g h i t s e f f e c t on l e a f p r i m o r d i a d e v e l o p m e n t . U n l i k e D o u g l a s - f i r and P a c i f i c s i l v e r f i r , w e s t e r n hemlock i s an i n d e t e r m i n a t e s p e c i e s . The m a j o r i t y o f l e a f and shoo t p r i m o r d i a a r e bo th p roduced and expanded i n t h e same g row ing season and a r e not s i g n i f i c a n t l y e f f e c t e d by t h e p r e v i o u s y e a r s g row ing c o n d i t i o n s . T h e r e f o r e i t i s somewhat s u r p r i s i n g t h a t t h e growth i n t h e f i r s t y e a r a f t e r p l a n t i n g was g r e a t e r t h an t h a t e x h i b i t e d i n t h e f o l l o w i n g y e a r s wh i ch had l e s s s e v e r e wea the r c o n d i t i o n s . One e x p l a n a t i o n f o r t h e r e d u c t i o n i n t h e r a t e o f shoo t g rowth i n subsequen t g r ow i ng s e a s o n s , wh i ch a l s o a p p l i e s t o t h e o t h e r s p e c i e s , i s t h a t t h e e xpo su r e o f s e e d l i n g s t o w a t e r - s t r e s s i n t h e i r f i r s t y e a r o f g r o w t h , c auses s i g n i f i c a n t changes i n t h e i r deve lopment and m o r p h o l o g y , p a r t i c u l a r l y i n t h e a l l o c a t i o n o f c a r b o h y d r a t e s t o t h e r o o t s o r s h o o t s . I n c r e a s e d r o o t g r o w t h , t o e x p l o i t a l a r g e r s o i l v o l ume , and d e c r e a s e d s hoo t g r o w t h , t o l i m i t t r a n s p i r a t i o n a l a r e a , a r e bo th i m p o r t a n t a d a p t a t i o n s t o d r ough t ( H s i a o and Acevedo 1 9 7 4 ) . Such m o r p h o l o g i c a l changes a r e t h o u g h t t o be r e l a t e d t o a b s c i s i c A c i d (ABA) c o n c e n t r a t i o n s , wh i ch i n c r e a s e i n w a t e r - s t r e s s e d p l a n t s (W r i gh t and H i r o n 1969; S i v a kuma ran e t a l _ . , 1 9 8 0 ) , t o c y t o k i n i n (CK) c o n c e n t r a t i o n s wh i ch d e c r e a s e i n w a t e r - s t r e s s e d t i s s u e ( V a a d i a 1 9 7 6 ) , o r t o ABA t o CK r a t i o s ( Ta l and Imber , 1 9 7 1 ) . - 132 -I t i s s i g n i f i c a n t t h a t i n a l l t h e s p e c i e s , t h e s e e d l i n g s show ing t h e l a r g e s t amount o f r o o t deve l opment were t h o s e t h a t were exposed t o t h e l a r g e s t and most p r o l o n g e d wa t e r d e f i c i t s ( a f t e r 3 y e a r s some o f t h e u n t r e a t e d D o u g l a s - f i r s e e d l i n g s had d e v e l o p e d r o o t s t h a t were o v e r 1 m l o n g ) . I t i s l i k e l y t h a t t h e i r r i g a t e d s e e d l i n g s , wh i ch d e v e l o p e d v e r y few r o o t s and had t h e h i g h e s t shoo t t o r o o t d r y mass r a t i o s , wou ld be v e r y u n l i k e l y t o s u r v i v e a summer d r ough t i f i r r i g a t i o n was no l o n g e r a v a i l a b l e . T h i s d e m o n s t r a t e s t h a t when a s s e s s i n g t h e o v e r a l l b e n e f i t s o f a p a r t i c u l a r t r e a t m e n t , l o n g - t e r m e f f e c t s must be c o n s i d e r e d . The e f f e c t s o f shade c a r d s on s e e d l i n g g r o w t h , and i n p a r t i c u l a r on s hoo t t o r o o t d r y mass r a t i o s a r e s i m i l a r t o t h o s e r e p o r t e d by Drew and F e r r e l l (1977) and Drew (1983) f o r D o u g l a s - f i r s e e d l i n g s . One e x p l a n a t i o n f o r t h e g r e a t e r shoo t g rowth e x h i b i t e d by t h e shaded s e e d l i n g s i s t h a t t h e s e s e e d l i n g s were a b l e t o compensate f o r t h e l ow l i g h t l e v e l s by a l l o c a t i n g more d r y m a t t e r t o t h e s h o o t s t h e r e b y i n c r e a s i n g t h e p h o t o s y n t h e t i c s u r f a c e a r e a . The r e s u l t s p r e s e n t e d i n F i g u r e 2 .8 i n d i c a t e t h a t shaded D o u g l a s - f i r s e e d l i n g s , wh i ch had l a r g e r l e a f a r e a s but s i m i l a r s t o m a t a l c o n d u c t a n c e s t o unshaded s e e d l i n g s o f t h e same s p e c i e s , and t h e r e f o r e wou l d have used s i m i l a r amounts o f w a t e r pe r u n i t l e a f a r e a , must have had t h e i r g rowth l i m i t e d by a r e d u c t i o n i n p h o t o s y n t h e s i s . T h i s r e d u c t i o n i n p h o t o s y n t h e s i s was l i k e l y due t o t h e l o w e r l i g h t l e v e l s b e h i n d shade c a r d s . T h i s r e s u l t , t o g e t h e r w i t h t h e f a c t t h a t g row ing season d r y m a t t e r p r o d u c t i o n was b e t t e r r e l a t e d t o e s t i m a t e s o f g r ow i ng season t r a n s p i r a t i o n t han t o e s t i m a t e s o f g r ow ing season t o t a l s t o m a t a l - 133 -c o n d u c t a n c e would s u p p o r t t h e c o n t e n t i o n , p r e s e n t e d by P r i c e e t a l . (1986) t h a t D o u g l a s - f i r , wh i ch e x h i b i t s l i t t l e dependence o f s t o m a t a l c o n d u c t a n c e on C-j i s a c a rbon d i o x i d e i n s e n s i t i v e s p e c i e s , and t h a t p h o t o s y n t h e s i s r a t e s and t h e r e f o r e growth r a t e s , a r e g e n e r a l l y not l i m i t e d by s t o m a t a l c onduc t an ce u n l e s s D i s h i g h and l i g h t i s s a t u r a t i n g . The sma l l d i f f e r e n c e s i n d r y m a t t e r p r o d u c t i o n between i r r i g a t e d and n o n - i r r i g a t e d D o u g l a s - f i r s e e d l i n g s m igh t be due t o t h e f a c t t h a t s e e d l i n g t r a n s p i r a t i o n , and t h e r e f o r e g r o w t h , i s l i m i t e d , under a l l m o i s t u r e c o n d i t i o n s , by h i g h D t h r o u g h i t s e f f e c t on s t oma t a l c ondu c t an c e as d e s c r i b e d i n Chap t e r 2 . The f a c t t h a t d i f f e r e n c e s i n d r y m a t t e r a c c u m u l a t i o n between i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s i n a l l s p e c i e s were s i m i l a r t o d i f f e r e n c e s i n t h e e s t i m a t e s o f g r ow ing season wa t e r use f o r t h e same t r e a t m e n t s and s p e c i e s shows t h a t t h e t r a n s p i r a t i o n model u s e d , c o u l d be u s e f u l not o n l y i n p r e d i c t i n g s e e d l i n g g r o w t h , but i n p r e d i c t i n g t h e e f f e c t s o f p a r t i c u l a r t r e a t m e n t s on s e e d l i n g g r o w t h . The e s t i m a t e s o f s e a sona l WUE f o r t h e t h r e e s p e c i e s a r e s i m i l a r t o t o s e a s ona l v a l u e s f o r C 3 a g r i c u l t u r a l c r o p s r e v i ewed by J ones ( 1 9 8 3 ) ; howeve r , P r i c e e t a}_. (1986) r e p o r t much h i g h e r d a i l y v a l u e s o f WUE f o r D o u g l a s - f i r t r e e s but show t h a t WUE changed s u b s t a n t i a l l y f rom day t o day as ^ s d e c l i n e d and d i f f e r e d between i r r i g a t e d and n o n - i r r i g a t e d t r e e s . S e i l e r and J ohnson (1985) r e p o r t h i g h e r d a i l y v a l u e s o f WUE f o r l o b l o l l y p i n e ( P i n u s t a eda L.) s e e d l i n g s wh i ch i n c r e a s e d i n s e e d i n g s t h a t were g i v e n m o i s t u r e s t r e s s c o n d i t i o n i n g t r e a t m e n t s . - 134 -V . CONCLUSIONS Shade , i r r i g a t i o n o r a c o m b i n a t i o n o f t h e s e t r e a t m e n t s had a d i s t i n c t e f f e c t on t he growth o f c o n i f e r s e e d i n g s p l a n t e d on a s o u t h - f a c i n g h i g h e l e v a t i o n c l e a r c u t . A l l s e e d l i n g s r e g a r d l e s s o f t h e t r e a t m e n t , showed a p ronounced d e c l i n e i n s e a s o n a l shoo t g rowth one y e a r a f t e r p l a n t i n g . T h i s d e c l i n e was l e s s p ronounced i n s e e d l i n g s t h a t r e c e i v e d s hade , i r r i g a t i o n , o r shade and i r r i g a t i o n . In t h o s e s e e d l i n g s where t r e a t m e n t was w i t h h e l d , t h e r e was a marked i n c r e a s e i n r o o t g r o w t h , c o n s e q u e n t l y t h e s e s e e d l i n g s had t h e l o w e s t shoo t t o r oo t d r y mass r a t i o s . D o u g l a s - f i r s e e d l i n g s e x h i b i t e d a h i g h degree o f d r ough t t o l e r a n c e so t h a t even i n t h e d r i e s t y e a r t h e r e was o n l y a 20% d i f f e r e n c e i n d r y m a t t e r a c c u m u l a t i o n between i r r i g a t e d and n o n - i r r i g a t e d s e e d l i n g s . Wes te rn hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s , d e s p i t e not b e i n g d r ough t t o l e r a n t , expended v a l u a b l e wa t e r t o a c h i e v e g rowth and t h e r e b y exposed t h e m s e l v e s t o d e s i c c a t i o n and many s u b s e q u e n t l y d i e d . Even i n s u r v i v i n g s e e d l i n g s t h i s b e h a v i o u r c o u l d not be d e s c r i b e d as d r ough t a v o i d a n c e because much o f t h e g r o w t h , e s p e c i a l l y i n t h e f i r s t y e a r a f t e r p l a n t i n g , was i n t h e s h o o t s . G row ing season s e e d l i n g d r y m a t t e r p r o d u c t i o n was w e l l r e l a t e d t o e s t i m a t e s o f g r ow i ng season s e e d l i n g t r a n s p i r a t i o n t h a t were d e r i v e d by summing t h e p r o d u c t o f v a l u e s o f s e e d l i n g l e a f a r e a , g s , o b t a i n e d f rom t h e b o u n d a r y - l i n e a n a l y s i s model d e s c r i b e d i n C h a p t e r 2 , and h o u r l y D / ( R V T ' ) . L e s s s u c c e s s was a c h i e v e d i n r e l a t i n g d r y m a t t e r p r o d u c t i o n - 135 -t o e s t i m a t e s o f g row ing season t o t a l s e e d l i n g s t oma t a l c o n d u c t a n c e . T h i s i s c o n s i s t e n t w i t h t h e r e s u l t s o f L e v e r e n z (1981) and P r i c e e t a l . (1986) wh i ch i n d i c a t e t h a t , w i t h d e c r e a s i n g l i g h t l e v e l s , t h e r e d u c t i o n i n p h o t o s y n t h e s i s i s g r e a t e r t han t h a t i n s t oma t a l c o n d u c t a n c e . V I . REFERENCES B o y e r , J . D . 1976 . Water d e f i c i t s and p h o t o s y n t h e s i s . In wa te r d e f i c i t s and p l a n t g r o w t h . V o l . 4 , E d i t e d by T . T . K o z l o w s k i . Academic P r e s s , New Y o r k , p p . 1 5 3 - 1 9 0 . Drew, A . P . 1983 . O p t i m i z i n g g rowth and deve lopment o f 2-0 D o u g l a s - f i r s e e d l i n g s by a l t e r i n g l i g h t i n t e n s i t y . Can . J . F o r . R e s . 13 : 4 2 5 - 4 2 8 . Drew, A . P . , and W.K. F e r r e l l . 1979 . Seasona l changes i n t h e wa te r b a l a n c e o f D o u g l a s - f i r ( P s eudo t suga m e n z i e s i i ) s e e d l i n g s grown under d i f f e r e n t l i g h t i n t e n s i t i e s . C a n . J . B o t . 57: 6 6 6 - 6 7 4 . D u r y e a , M . L . , and D.P . L a v e n d e r . 1982 . Water r e l a t i o n s , g r o w t h , and s u r v i v a l o f r o o t -w r en ched D o u g l a s - f i r s e e d l i n g s . Can . J . F o r . R e s . 12: 5 4 5 - 5 5 5 . E i s , S . , and J . R . L o n g . 1 9 7 3 . Root p r u n i n g i n t h e n u r s e r y . U .S . F o r . S e r v . T ree P l a n t . N o t e s , 2 4 ( 1 ) : 2 0 - 2 2 . G i l e s , D .G . , T . A . B l a c k , and D.L . S p i t t l e h o u s e . 1 985 . D e t e r m i n a t i o n o f g r ow i ng season s o i l wa te r d e f i c i t s on a f o r e s t e d s l o p e u s i n g wa te r b a l a n c e a n a l y s i s . C an . J . F o r . Re s . 15: 1 0 7 - 1 1 4 . H s i a o , T . C . , and E. A c evedo . 1974 . P l a n t r e s pon se s t o wa te r d e f i c i t s , w a t e r use e f f i c i e n c y and d rough t r e s i s t a n c e . A g r i c . Me t eo r o l . 14: 5 9 - 8 4 . J o n e s , H.G. 1 9 8 3 . P l a n t s and m i c r o c l i m a t e : a q u a n t i t a t i v e app roach t o e n v i r o n m e n t a l p l a n t p h y s i o l o g y . Cambr idge U n i v e r s i t y P r e s s , C amb r i d ge , U.K. K o z l o w s k i , T . T . 1982 . Water s u p p l y and t r e e g r o w t h . P a r t 1 . Water d e f i c i t s . F o r e s t r y A b s t r a c t s , 43: 5 7 - 9 5 . K r ame r , P . J . , and T . T . K o z l o w s k i . 1979 . P h y s i o l o g y o f woody p l a n t s . Academic P r e s s , New Y o r k . - 136 -L e v e r e n z , J .W. 1 9 8 1 . P h o t o s y n t h e s i s and t r a n s p i r a t i o n i n l a r g e f o r e s t - g r o w n D o u g l a s - f i r : d i u r n a l v a r i a t i o n . C a n . J . B o t . 59 : 3 4 9 - 3 5 6 . L o p u s h i n s k y , W., and T . Beebe . 1976 . R e l a t i o n s h i p o f s h o o t - r o o t r a t i o t o s u r v i v a l and growth o f o u t p l a n t e d D o u g l a s - f i r and Ponde ro sa p i n e s e e d l i n g s . U . S . Dep. A g r i c . F o r . S e r v . R e s . Note PNW-274. P r i c e , D .T . , T . A . B l a c k , and F .M . K e l l i h e r . 1986 . E f f e c t s o f s a l a l u n d e r s t o r y remova l on p h o t o s y n t h e t i c r a t e and s t o m a t a l c onduc t an ce o f young D o u g l a s - f i r t r e e s . C a n . J . F o r . R e s . In p r e s s . S e i l e r , J . R . and J . D . J o h n s o n . 1 9 8 5 . P h o t o s y n t h e s i s and t r a n s p i r a t i o n o f L o b l o l l y p i n e s e e d l i n g s as i n f l u e n c e d by m o i s t u r e - s t r e s s c o n d i t i o n i n g . F o r e s t S c i . 3: 7 4 2 - 7 4 9 . S i v a k u m a r a n , S . , R. Ho r gan , J . H e a l d , and M.A. H a l l . 1 980 . E f f e c t o f w a t e r s t r e s s on m e t a b o l i s m o f a b s c i s i c a c i d i n P opu l u s r o b u s t a x s c h n i e d and E u p h o r b i a l a t h y r u s L. P l a n t , C e l l and E n v i r o n m e n t , 3: 1 6 3 - 1 7 3 . T a l , M. , and D. Imber . 1 9 7 1 . Abnormal s t o m a t a l b e h a v i o u r and hormonal i n b a l a n c e i n f l a c c a , a w i l t y mutant o f t o m a t o . I I I . Hormonal e f f e c t s on t he wa te r s t a t u s i n t h e p l a n t . P l a n t P h y s i o l . 4 7 : 8 4 9 - 9 5 0 . T a n n e r , C . B . , and T . R . S i n c l a i r . 1 9 8 3 . E f f i c i e n t wa t e r use i n c r op p r o d u c t i o n : r e s e a r c h o r r e - s e a r c h ? _In_ L i m i t a t i o n s t o e f f i c i e n t w a t e r use i n c r o p p r o d u c t i o n . E d i t e d by H.M. T a y l o r , W.R. J o r d a n and T . R . S i n c l a i r . M a d i s o n , W i s . The Amer i c an S o c i e t y o f Agronomy. V a a d i a , Y . 1 976 . P l a n t hormones and wa t e r s t r e s s . P h i l . T r a n s . R . S o c . London , S e r . B. 273: 5 1 3 - 5 2 2 . Wong, S . C . , I . R . Cowan, and G .D . F a r q u h a r . 1979 . S t oma ta l c o n d u c t a n c e c o r r e l a t e s w i t h p h o t o s y n t h e t i c c a p a c i t y . Na t u r e ( L o n d o n ) , 282: 4 2 4 - 4 2 6 . W r i g h t , S . T . C , and R.W.P. H e r o n . 1969 . (+) - a b s c i s i c a c i d , t h e g rowth i n h i b i t o r i n d e t a ched wheat l e a v e s f o l l o w i n g a p e r i o d o f w i l t i n g . N a t u r e , 224: 7 1 9 - 7 2 0 . W a l l i s , C . H . , T . A . B l a c k , 0 . He r t zman , and V . J . W a l t o n . 1 9 8 3 . A p p l i c a t i o n o f a wa t e r b a l a n c e model t o e s t i m a t i n g hay growth i n t h e Peace R i v e r r e g i o n . A t m o s p h e r e - o c e a n , 2 1 : 3 2 6 - 3 4 3 . - 137 -CONCLUSIONS D o u g l a s - f i r s e e d l i n g s , p l a n t e d i n t h e s p r i n g as 1-0 s t r y r o p l u g s , were s u c c e s s f u l l y e s t a b l i s h e d on a s o u t h - f a c i n g h i g h e l e v a t i o n c l e a r c u t . The s e e d l i n g s e x h i b i t e d a h i g h deg ree o f d r ough t t o l e r a n c e wh i ch e n a b l e d them t o s u r v i v e and grow i n c o n d i t i o n s o f h i g h a t m o s p h e r i c demand and l ow s o i l wa t e r p o t e n t i a l s . D o u g l a s - f i r s e e d l i n g s were a b l e t o m a i n t a i n d a i l y t r a n s p i r a t i o n r a t e s t h a t were neve r l e s s t h an 50% o f t h o s e a c h i e v e d under opt imum s o i l m o i s t u r e c o n d i t i o n s . D rough t t o l e r a n c e was a c h i e v e d because s e e d l i n g s were a b l e t o l o w e r t h e i r o s m o t i c p o t e n t i a l , wh i ch appeared t o be due t o a c c u m u l a t i o n o f s o l u t e s i n l e a f c e l l s , and t h e r e b y m a i n t a i n t u r g o r t h r o u g h o u t t h e g r ow i ng s e a s o n . T h i s mechanism i s an example o f s t r e s s t o l e r a n c e ( J ones 1 9 8 3 ) . The f a c t t h a t l i t t l e o s m o t i c a d j u s tmen t o c c u r r e d i n a wet summer and when s e e d l i n g s were i r r i g a t e d s u g g e s t s t h a t t h e o s m o t i c a d j u s tmen t was a r e s p o n s e t o e n v i r o n m e n t a l s t r e s s r a t h e r t h an b e i n g a s e a sona l r e s p o n s e . Wes te rn hem lo ck , and t o an e v e r g r e a t e r e x t e n t , P a c i f i c s i l v e r f i r s e e d l i n g s , wh i ch were a l s o p l a n t e d as 1-0 s t y r o p l u g s a t t h e same s i t e , were not s u c c e s s f u l l y e s t a b l i s h e d . Bo th s p e c i e s were unab l e t o s u r v i v e d r o u g h t because t h e y l a c k e d s t r e s s a v o i d a n c e and t o l e r a n c e mechan i sms . M a j o r m o d i f i c a t i o n o f t h e s e e d l i n g s ' m i c r o c l i m a t e , whe the r t h r o u g h t he p r o v i s i o n o f shade o r t h e a p p l i c a t i o n o f wa t e r o r a c o m b i n a t i o n o f t h e s e t r e a t m e n t s , s i g n i f i c a n t l y i n c r e a s e d s e e d l i n g s u r v i v a l i n bo th s p e c i e s . However , a f t e r 3 y e a r s , s u r v i v a l o f t h e s e e d l i n g s r e c e i v i n g t h e s e t r e a t m e n t s n e v e r exceeded 65% and was l o w e r t h a n t h a t a c h i e v e d by - 138 -D o u g l a s - f i r s e e d l i n g s t h a t had r e c e i v e d no t r e a t m e n t . Wes te rn hemlock and P a c i f i c s i l v e r f i r s e e d l i n g s , d e s p i t e not b e i n g d r ough t t o l e r a n t , expended v a l u a b l e wa te r i n a c h i e v i n g shoo t g rowth a f t e r p l a n t i n g , and t h e r e b y exposed t h e m s e l v e s t o d e s s i c a t i o n . C o n s e q u e n t l y many s e e d l i n g s d i e d . There was e v i d e n c e f rom e x p e r i m e n t s c onduc t ed on D o u g l a s - f i r s e e d i n g s t h a t shade c a r d s , a p a r t f rom r e d u c i n g s o i l s u r f a c e t e m p e r a t u r e , reduced s e e d l i n g t r a n s p i r a t i o n r a t e s ( i . e . , g s - 1 ) i n t h e mo rn i ng as a r e s u l t o f a d e c r e a s e i n n e e d l e t e m p e r a t u r e and hence t he vapour p r e s s u r e d i f f e r e n c e between n eed l e s t oma t a l c a v i t i e s and t h e a i r . Because ( i ) t h i s r e d u c t i o n i n t r a n s p i r a t i o n r a t e r e s u l t e d i n an i n c r e a s e i n t h e minimum t o t a l t w i g xy l em p o t e n t i a l and ( i i ) t h e r e was no s i g n i f i c a n t d i f f e r e n c e between t he o s m o t i c p o t e n t i a l o f shaded and unshaded s e e d l i n g s , t h e shaded s e e d l i n g s had h i g h e r t u r g o r p o t e n t i a l s t h a n s i m i l a r l y s i z e d unshaded s e e d l i n g s . The e x t e n t and t y p e o f g rowth i n a l l s p e c i e s was m a r k e d l y a f f e c t e d by changes i n m i c r o c l i m a t e . A l l s e e d l i n g s , r e g a r d l e s s o f t h e t r e a t m e n t , showed a d e c l i n e i n shoo t g rowth and an i n c r e a s e i n r oo t g rowth i n t h e i r second and t h i r d g row ing s e a s o n s . T h i s was l i k e l y i n r e sponse t o t h e d r ough t c o n d i t i o n s t h a t o c c u r r e d i n t h e i r f i r s t y e a r o f g r o w t h . T h i s phenomenon was l e a s t p ronounced i n i r r i g a t e d s e e d l i n g s wh i ch d e v e l o p e d t h e l a r g e s t s hoo t s and had t h e s m a l l e s t r o o t s y s t e m s . Shaded s e e d l i n g s l i k e l y i n c r e a s e d shoo t g rowth t o compensate f o r t h e l owe r l i g h t l e v e l s b eh i n d shade c a r d s . U n t r e a t e d s e e d l i n g s d e v e l o p e d t h e l a r g e s t r o o t s y s t ems and c o n s e q u e n t l y had t he l o w e s t shoo t t o r o o t d r y mass r a t i o s . - 139 -The s t o m a t a l c o ndu c t an c e s o f a l l s e e d l i n g s , whether i n wet o r d r y s o i l , were m a r k e d l y reduced by h i g h vapour p r e s s u r e d e f i c i t s . T h i s r e s p o n s e , and a l s o t h e r e sponse o f s t o m a t a l c ondu c t an c e t o changes i n o t h e r e n v i r o n m e n t a l v a r i a b l e s , such as g l o b a l s o l a r i r r a d i a n c e , a i r t e m p e r a t u r e and ave rage r o o t zone s o i l wa t e r p o t e n t i a l , d i d not d i f f e r o ve r two g row ing seasons nor were t h e r e d i f f e r e n c e s i n r e s pon se between s e e d l i n g s p l a n t e d i n two s u c c e s s i v e y e a r s . B o u n d a r y - l i n e a n a l y s i s ( J a r v i s 1976) o f f i e l d g s d a t a , w i t h t h e a s s u m p t i o n t h a t a l l v a r i a b l e s a c t i n d e p e n d e n t l y but m u l t i p i i c a t i v e l y , p roduced f u n c t i o n s t h a t , i n a l l s p e c i e s , whether i r r i g a t e d o r n o n - i r r i g a t e d , a c coun ted f o r o ve r 85% o f t h e v a r i a b i l i t y i n g s . T h i s l e v e l o f s u c c e s s c o u l d o n l y be a c h i e v e d by i n c l u d i n g the number o f hours f rom s u n r i s e as an i n dependen t v a r i a b l e . W i thou t t h e i n c l u s i o n o f t h i s v a r i a b l e o n l y 70% o f t h e v a r i a b i l i t y i n g s c o u l d be e x p l a i n e d . There was no e v i d e n c e o f a c r i t i c a l t h r e s h o l d t u r g o r p o t e n t i a l be low wh i ch s tomata c l o s e d . D a i l y s e e d l i n g t r a n s p i r a t i o n r a t e s were s u c c e s s f u l l y e s t i m a t e d by summing the p r o d u c t o f h o u r l y a ve r age g s , o b t a i n e d f rom t he b o u n d a r y - l i n e a n a l y s i s m o d e l , measured h o u r l y a ve r age D / ( R V T ' ) and s e e d l i n g p r o j e c t e d l e a f a r e a . E s t i m a t e s o f g r ow ing season s e e d l i n g t r a n s p i r a t i o n were b e t t e r c o r r e l a t e d w i t h g row ing season s e e d l i n g d r y m a t t e r a c c u m u l a t i o n t han e s t i m a t e s o f a ve r age g row ing season t o t a l s e e d l i n g s t o m a t a l c o n d u c t a n c e . The b e t t e r c o r r e l a t i o n between s e e d l i n g t r a n s p i r a t i o n and g rowth can be e x p l a i n e d as f o l l o w s . T r a n s p i r a t i o n r a t e s and p h o t o s y n t h e s i s r a t e s a r e l ow when ( i ) D i s l ow (on such days PPFD i s u s u a l l y low) ( i i ) D i s h i g h enough so t h a t t h e r e i s s t oma ta l - 140 -c l o s u r e and ( i i i ) t h e s o i l w a t e r p o t e n t i a l i s l o w . However bo th r a t e s a r e h i g h when PPFD i s h i g h , s o i l w a t e r p o t e n t i a l i s h i g h and D i s not h i g h enough t o cause s t o m a t a l c l o s u r e . The p o o r e r c o r r e l a t i o n between c o n d u c t a n c e and growth i s not s u p r i s i n g i n v i ew o f t h e work o f L e v e r e n z (1981) and P r i c e e t a ] _ . (1986) who showed t h a t i n c o n i f e r s p h o t o s y n t h e s i s , and hence g r o w t h , a t l ow PPFD, i s o f t e n l i m i t e d by PPFD and no t by s t o m a t a l c o n d u c t a n c e . T h i s s t u dy has shown t h a t s u c c e s s f u l s e e d l i n g e s t a b l i s h m e n t i s p o s s i b l e on s i t e s t h a t had p r e v i o u s l y been c o n s i d e r e d d i f f i c u l t t o r e p l a n t due t o d r o u g h t , and t h a t s e e d l i n g s can be e s t a b l i s h e d , a t a c c e p t a b l y h i g h l e v e l s , even w i t h o u t ma jo r m o d i f i c a t i o n o f t h e s e e d l i n g s ' m i c r o c l i m a t e , p r o v i d e d t h e c o r r e c t s p e c i e s i s p l a n t e d . D o u g l a s - f i r s e e d l i n g s , even when i r r i g a t e d , o n l y t r a n s p i r e d a maximum o f 2 .5 L o f w a t e r d u r i n g a g r ow i ng season and had w a t e r use e f f i c i e n c i e s ( 0 . 0022 g g - 1 ) t h a t were s i m i l a r t o t h o s e o f C 3 a g r i c u l t u r a l c r o p s . P r o v i d e d D o u g l a s - f i r s e e d l i n g s can q u i c k l y e s t a b l i s h r o o t s , g rowth w i l l not be g r e a t l y reduced by low s o i l wa t e r p o t e n t i a l s . T h i s i s shown by t h e f a c t t h a t d r y m a t t e r a c c u m u l a t i o n i n n o n - i r r i g a t e d s e e d l i n g s was o n l y 20% l e s s t han t h a t o f i r r i g a t e d s e e d l i n g s , even i n a g r ow i ng season when s o i l wa t e r p o t e n t i a l s r ea ched - 1 . 2 MPa. A f t e r 3 y e a r s n o n - i r r i g a t e d s e e d l i n g s had d eve l o ped r o o t s t h a t e x p l o i t e d a s o i l vo lume a p p r o x i m a t e l y 1 m deep and w i t h a r a d i u s o f 0 . 15 m. D u r i n g a g r ow i ng season such s e e d l i n g s would o n l y d e p l e t e t h e v o l u m e t r i c s o i l wa t e r c o n t e n t by a maximum o f 4% even assuming t h a t t h e y wou ld use as much wa te r as i r r i g a t e d s e e d l i n g s . - 141 -REFERENCES J a r v i s , P .G . 1976 . The i n t e r p r e t a t i o n and t h e v a r i a t i o n s i n l e a f w a t e r - p o t e n t i a l and s t o m a t a l c o n d u c t a n c e found i n c a n o p i e s i n t h e f i e l d . P h i l . T r a n s . R. S o c , L ondon , Se r B. 273: 5 9 3 - 6 1 0 . J o n e s , H .G. 1 9 8 3 . P l a n t s and M i c r o c l i m a t e . Cambr idge U n i v e r s i t y P r e s s . C amb r i d ge , U .K . L e v e r e n z , J .W . 1 9 8 1 . P h o t o s y n t h e s i s and t r a n s p i r a t i o n i n l a r g e f o r e s t - g r o w n D o u g l a s - f i r t r e e s . C a n . J . F o r . R e s . 14: 4 8 1 - 4 8 7 . P r i c e , D .T . , T . A . B l a c k and F .M . K e l l i h e r . 1 9 8 6 . E f f e c t s o f s a l a l u n d e r s t o r y removal on p h o t o s y n t h e t i c r a t e and s t o m a t a l c ondu c t an c e o f young D o u g l a s - f i r t r e e s . C a n . J . F o r . R e s . 16 ( i n p r e s s ) . - 142 -APPENDIX I DERIVATION OF WATER-RELEASE CURVES FOR THE DETERMINATION OF CONIFER SEEDLING OSMOTIC POTENTIAL - 143 -APPENDIX I DERIVATION OF WATER-RELEASE CURVES FOR THE DETERMINATION OF CONIFER SEEDLING OSMOTIC POTENTIAL Measurements o f t h e o s m o t i c p o t e n t i a l a t f u l l t u r g o r (%o) and z e r o t u r g o r ( ^ ) o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r - f i r s e e d l i n g s were o b t a i n e d f rom w a t e r - r e l e a s e c u r v e s t h a t were g ene r a t e d u s i n g t h e method d e s c r i b e d by S c h o l a n d e r e t ail_. ( 1965 ) . Cu rves were g e n e r a t e d f o r t en s e e d l i n g s o f each s p e c i e s . A shoo t was cu t f rom a r e h y d r a t e d s e e d l i n g and s e a l e d i n a sma l l z i p l o c bag (Dow Chemica l C o r p . , I n d i a n a p o l i s , I n d . ) and w e i g h e d . F o l l o w i n g we i gh i n g a sma l l s e c t i o n was t hen c u t f rom t h e bag t o a l l o w t he shoot stem t o e x t end o u t s i d e t h e s e a l . The bagged shoo t was t hen s e a l e d i n a p r e s s u r e chamber w i t h t h e c u t end o f t h e stem e x p o s e d . The chamber was p r e s s u r i z e d w i t h a i r a t a r a t e o f a p p r o x i m a t e l y 6 kPa s _ 1 . P r e s s u r i z a t i o n was c o n t i n u e d u n t i l sap appeared on t h e c u t s u r f a c e . A t t h e e n d p o i n t , t h e p r e s s u r e was r e c o r d e d and then s l o w l y r e l e a s e d . The shoo t was removed and w e i g h e d . The shoo t xy lem p o t e n t i a l (i{i) o b t a i n e d f rom t h i s measurement and t he shoo t mass p r o v i d e d one d a t a p o i n t . O the r d a t a p o i n t s were o b t a i n e d by p r e s s u r i z i n g t h e chamber 0.2 - 0 .3 MPa beyond t he l a s t e n d p o i n t and a b s o r b i n g t he emerg ing sap w i t h a t i s s u e . A f t e r a p p r o x i m a t e l y 15 m i n u t e s t h e p r e s s u r e was r e l e a s e d and t he shoot r e w e i g h e d . V a l u e s o f shoo t mass and were o b t a i n e d u n t i l shoo t <J> was -4 .5 t o -5 .0 MPa, -4 .0 t o -4 .5 MPa, and -3 .0 t o -3 .5 f o r D o u g l a s - f i r , - 144 -w e s t e r n hemlock and P a c i f i c s i l v e r - f i r r e s p e c t i v e l y . A f t e r t h e f i n a l p r e s s u r e was r e c o r d e d , t h e shoot was we ighed and t h en d r i e d t o 100°C f o r 48 hours t o o b t a i n shoot d r y mass (M^) . F i g u r e A I . l shows a t y p i c a l p l o t o f s hoo t ij> v e r s u s shoo t mass f o r a D o u g l a s - f i r s e e d l i n g . The i n t e r c e p t ( s h oo t mass a t <|> = 0) o f t h e l e a s t s q u a r e s r e g r e s s i o n l i n e f o r t he l i n e a r p o r t i o n o f F i g u r e A I . l was t a k e n as t h e shoo t mass a t f u l l t u r g o r ( M 0 ) . The shoot r e l a t i v e wa te r c o n t e n t (RWC) was t hen c a l c u a t e d as RWC = (M - M d ) / ( M Q - M r f) ( A I . l ) where M i s t h e shoo t mass a t a g i v e n shoo t Tp. To o b t a i n i|4 and shoo t RWC was p l o t t e d a g a i n s t 1/shoot ij> ( F i g u r e A I . 2 ) . An a s sump t i on i s made t h a t t h e a p o p l a s t i c wa te r f r a c t i o n (B) i s c o n s t a n t ( Ty r ee 1976) so t h a t i|% i n t h e sympl a s t a t a g i v e n s hoo t RWC i s g i v e n by so t h a t 1 / ^ = (RWC - B ) / ( « i r ( j (1 - B ) ) ( A I . 3 ) Be low t h e t u r g o r l o s s p o i n t , shoo t ^ = ^ wh i ch r e s u l t s i n a l i n e a r r e l a t i o n s h i p between 1/shoot i|> and shoo t RWC w i t h an RWC i n t e r c e p t equa l t o B and a s l o p e o f l/(<Wro ( 1 - B ) ) . The i n t e r c e p t o f t h i s l i n e at RWC = 1 g i v e s an e s t i m a t e o f ^ 0 i n t h e sympl a s t . T a b l e A I . l shows t he d i f f e r e n c e s between i | % 0 and ^ a t a l l t he T u r g o r l o s s p o i n t f o r a l l t h e s p e c i e s . T h i s d i f f e r e n c e neve r exceeded 0 .3 MPa. - 145 -Shoot Mass (9) l i r e A I . l The r e l a t i o n s h i p between s e e d l i n g shoo t mass and shoo t t o t a l xy l em p o t e n t i a l ( s hoo t f o r a D o u g l a s - f i r s e e d l i n g . The mass o f t h e shoo t when shoo t i|> i s z e r o ( M 0 ) was d e t e r m i n e d f rom t he l e a s t s q u a r e s r e g r e s s i o n o f t h e l i n e a r p o r t i o n o f t h e l i n e . - 146 -Shoot RWC -10 F i g u r e A I . 2 The r e l a t i o n s h i p between s e e d l i n g shoot r e l a t i v e wa te r c o n t e n t ( s hoo t RWC) and t he i n v e r s e o f shoo t t o t a l x y l em p o t e n t i a l ( ( s h o o t 'J>)"1)« The a p o p l a s t i c wa te r c o n t e n t ( B ) , o s m o t i c p o t e n t i a l a t f u l l t u r g o r (^0) and o s m o t i c p o t e n t i a l a t z e r o t u r g o r (i)4) a r e i n d i c a t e d . - 147 -T a b l e A I . l The d i f f e r e n c e between t h e o s m o t i c p o t e n t i a l a t f u l l t u r g o r (%o) and o s m o t i c p o t e n t i a l a t z e r o t u r g o r (Vir) o f D o u g l a s - f i r , w e s t e r n hemlock and P a c i f i c s i l v e r - f i r s h o o t s . A l s o shown a r e t h e c o r r e s p o n d v a l u e s o f a p o p l a s t i c wa t e r c o n t e n t ( B ) . V a l u e s were o b t a i n e d f rom w a t e r - r e l e a s e c u r v e s . Each number i s t h e ave r age o f 10 measu remen t s . S p e c i e s • - (MPa) B Doug l a s -• f i r 0 .28 0 .28 Wes te rn hemlock 0 .23 0 .29 P a c i f i c s i l v e r - f i r 0 .21 0 .23 - 148 -APPENDIX I I AN INSTRUMENT FOR MEASURING THE AVERAGE STOMATAL CONDUCTANCE OF CONIFER SEEDLINGS. ( L i v i n g s t o n e t a l . , 1984 , C a n . J . F o r . S c i . 14: 512-517) - 149 -An instrument for measuring the average stomatal conductance of conifer seedlings N. J. LIVINGSTON, T . A . BLACK, AND D. BEAMES Deportment of Soil Science. University of British Columbia. Vancouver. B.C.. Canada V6T 2A2 AND B. G. DltNSWORTH Woodlands Services. MacMillan Bloedel Co. Ltd.. Nanaimo. B.C.. Canada V9R 5H9 Received August 26. 1983' Accepted March IS. 1984 LIVINGSTON. N. J . , T. A. BLACK. D. BEAMES. and B G. DUNSWORTH. 1984. An instrument for measuring the average stomata! conductance of conifer seedlings Can. J. For. Res. 14: 512—517. A ventilated, transient-type porometer was designed to oondestructively measure the average stomatal conductance of conifer seedlings. The porometer consists of a low-power microprocessor unit and a stainless steel chamber which encloses the seedling. Conductance is calculated from the measured rate of increase in chamber relative humidity above the ambient level. Consequently, chamber air does not have to be dried prior to measurement. Direct readout of stomatal conductance is provided by means of a liquid crystal display and a serial (RS232) port. Porometer calibration over a range of humidities showed that the effective chamber volume was consistently 259 larger than the actual chamber volume. Stomatal conductance measurements made on Douglas-fir (Pseudotsuga menziesii (Mirb. I Franco) seedlings using the porometer agreed well with average values obtained with a ventilated diffusion porometer using four needle samples. The porometer proved to be very convenient to use in a forest clearcut environment, with the measurement procedure taking about I min. Measurements can be made on a seedling over the growing season because the use of the instrument causes no injury to stem, branches, and needles. LIVINGSTON. N. J . T. A. BLACK. D. BEAMES et B. G. DUNSWORTH. 1984. An instrument for measuring the average stomatal conductance of conifer seedlings. Can J. For. Res. 14: 512-517. Un porometre ventite du type a transit a iii mis au point pour mesurer de facon non-destructive la conductance stomatique moyenne. Le porometre compone un microprocesseur de faible puissance et unc chambre en acier inoxydable qui enferme le semis. La conductance est calculee a partir de ia mesure du taux d augmentation d'humiditc relative au-dessus du niveau ambiant Consequemment lair de la chambre n'a pas a itre deshumidifie' avant la prise de donnees. La lecture directe de la conductance stomatique est rendue possible par un affichage a crista! liquide et par une interface a port serie (RS 232). La calibrage du porometre sur une gam me d'humidiles a montrt que le volume efficace euil de facon consistante 259 plus grande comparativement au volume des chambres utilisees actuellement. Des mesures de la conductance stomatique effectuees sur de* semis de sapinde Douglas {Pseudotsuga menziesii (Mirb.) Franco) avec le porometre son; en accord avec les valeurs moyennes obtenues avec un porometre de diffusion ventile' utilisant des echantillons a 4 aiguilles. Le porometre s'est avert efficace dans le contexle forestier dune coupe d'eclaircie. la prise de mesure ne neeessitant approximativement que I min. Des mesures peuvenl etre prises sur un semis pendant la saison de croissancc car ('utilisation de I'instrument ne cause aucune blessure a la tige. aux rameaux et aux aiguilles [Traduit par Ic journal) I n t r o d u c t i o n The most promising approach to quantitative measurements of stomatal conductance is provided by water vapour diffusion porometers. These can be categorized into two classes, those that take measurements under steady state conditions (e.g. , Beardsell et al. 1972) and those thai measure rales of change of relative humidity (e.g.. Kanemasu et al. 1969). While a number of systems have been devised to meet specialized needs (e.g.. Bingham and Coyne 1977; Kohsiek 1981: Kaufmann 1981), porometer methods published to date are often inade-quate for use in certain applications. For example, our studies of water stress in conifer seedlings required a rugged and por-table instrument that would nondestructively measure the average stomatal conductance of seedlings of various species growing in high elevation clearcuts and allow measurements to be made on the same seedling over the growing season. This paper describes the design, calibration, and tests of an instrument that satisfies these requirements. The instrument is microprocessor based and gives a direct readout of stomatal conductance and transpiration rate obtained from transient 'Revised manuscript received February 6. 1984. measurements of relative humidity in a chamber placed over a seedling. Porometer design The flux of water vapour from a seedling (F. milligrams per second) in a well-stirred porometer chamber is given by [ I ] F = <Ap,/Ar)V where Ap, is the change in water vapour density, p. (milligrams per cubic centimetre) over the time period A i (seconds), and V is the volume of the chamber (cubic centimetres). The aver-age stomatal conductance of the seedling (#.. centimetres per second) is given by [2] *. = F/(A(p.»(D - P >» where A is the projected area of the evaporating leaf or needle surface (square centimetres). p,*(7") is the saturation water vapour density (milligrams per cubic centimetre) at air tem-perature (T). It is assumed that the air in the stomatal cavities is saturated and that the boundary layer resistance is negligibly small so that the needle is at the same temperature as the air in the chamber. In this transient system, values of g. can be - 150 -LIVINGSTON ET AL. S U I T f S T T O H P L A T E F)G. 1. Diagram of the stainless steel porometer chamber showing the removable top plate with fan and sensors, and the split bottom plate. The parts arc as follows: (I) hinge for bottom plate: (2) tight-ening clamp for bottom plate; (3) hinge for clamping rod; (4) alumi-num clamping rod; (5) soft rubber gasket: (6) foam rubber gasket; (7) hole for seedling stem; (8) teflon gasket; (9) DC fan; (10) electrical connector; (II) humidity and temperature sensing unit: (12) clamping rod slot; (13) wing nut. obtained over a wide range of ambient vapour densities, but measurements must be completed before the decrease in water vapour density deficit is large enough to affect the stomatal conductance. Because the conductance is measured at ambient vapour density, the chamber air does not require drying before each measurement. The porometer system has two subunits: (/) a porometer chamber containing a humidity sensor, a temperature sensor, and a DC-powered fan, and ( « ) a low power microprocessor unit and liquid crystal display housed in a snail carrying case. The case also contains the system's power supplies, four 6 V 2.6 A h solid-gel rechargeable batteries (Elpower Corp. , Santa Ana, C A , U . S . A . ) . A 1.5-m electrical cable with con-nectors at both ends links the porometer chamber to the microprocessor unit. Porometer d u m b e r The chamber, designed to accommodate conifer seedlings up to 30 cm in height, consists of three pans: a thin-walled stain-less steel cylinder, a removable top plate, and a split bottom plate, both of which are machined from stainless steel (316) (Fig. 1). This material was chosen to minimize tarnishing and water adsorption by the chamber walls (Dixon and Grace 1982). Because the cylinder is open at both ends, chamber vapour density equilibrates quickly to that of the surrounding air before each measurement. The bottom plate is hinged U I M U mnzir ', FIG. 2. Circuit used to generate frequencies from the Vaisala relative humidity- and thermistor sensors. and has a 1 5-cm diameter hole at its centre. This enables it to be opened and clamped around the base of a seedling. A pliable rubber gasket lining the hole and the inner edges of the plate ensures an air-tight seal around the stem of the seedling. The inside surfaces of the top and bottom plates each have a teflon gasket seated in a milled groove that runs on the inside of a lip at the edge of each plate. An effective seal is thereby established when the cylinder is placed between the plates. Separate relative humidity and temperature sensing units, described in a later section, are mounted on a circuit board measuring 2.4 cm wide by 4.4 cm long, which is attached to the underside of the top plate. The circuit board is pro-tected by a stainless steel cover with the sensing elements exposed to the chamber. A 6-V DC fan (R. Marx-Luder, 1721 Gemmrigheim/Neckar, Germany) is mounted on the top plate. Power for the fan (300 mA) is provided by two of the 6 V •olid-gel batteries connected in parallel, that are housed with the microprocessor unit. We have found that this fan could be replaced with two 30 mA 12 V D C Micronel fans. Electronics Humidity and temperature tensing The relative humidity sensing element is a thin film capacitor with an organic polymer dielectric (Humicap mode) 6064. Vaisala Company, Finland). The capacitance of the sensor depends on water adsorption in the organic polymer layer. The capacitance ranges from approximately 44 pF at 0% rela-tive humidity (RH) to 57 pF at 100% R H . Because of the sensor's small capacitance, the length of its leads are min-imized to reduce stray capacitance. An integrated circuit function generator (XR-2206, Exar Integrated Systems Inc.. Sunnyvale, C A , U . S . A . ) chosen for its excellent frequency •ability (20 ppm °C~') is used to produce a square wave signal, the frequency (fm) of which is inversely proportional to the product of die sensor capacitance and a fixed value resistor (Fig. 2). Two of the 6-V batteries are connected in series, and the output is regulated down to 10 V for the XR-2206 circuitry. The output of the generator is linearly related to R H (±0.1 % RH) between IS and 8 5 % , which is the normal operating range of the porometer and which corresponds to a frequency range of 7 5 - 6 5 kHz. The humidity tensor was calibrated by means of a constant temperature water bath and a dewpoint hygrom-eter. Saturated air was passed through the water bath and then the dewpoint hygrometer to measure the dewpoint temperature. It was men passed over the humidity sensor and the resulting relative humidity reading recorded. A i r temperature (D is tensed with a precision thermistor (FenwaU U U A 35JI). A n additional XR-2206 is employed to - 151 -C A N . J . FOR RES. V O L . 14. 1984 M SOCt* T WOJOH FAN OP 1S02 mc«op«oc£ssc* —{ *S-ZSZ-c""] 1 VOLTAGE •EtUUTWS MM cnton I KCHAWEABU M T T H I E S FIG. 3. Schematic of the seedling porometer electronics. generate a square wave signal, the frequency </T) of which is inversely proportional to the product of the thermistor resis-tance and a fixed capacitor. The output frequency of the oscillator ranges between 20 and 200 kHz, which corresponds to a temperature range of 0 - 5 O ° C . Microprocessor unit The square wave outputs from the humidity and temperature sensors in the porometer chamber are carried via the connector cable to the microprocessor unit (Fig. 3) and are sampled every 2 s. A timer which measures the length of one period of a square wave is used to determine the signal frequency to an accuracy equivalent to ± 0 . 0 3 % R H and ± 0 . 0 7 ° C from 0 to 7 0 ° C . The microprocessor C P U (RCA 1802) is programmed to compute the values of relative humidity and temperature from the respective frequencies. The calibrations of the sensor units are entered and stored in the microprocessor by means of a 16-key keyboard. Four quadratic equations which are monotonic and contin-uous, arc used to compute saturated vapour density over the range 0 - S O ° C Values of saturated vapour density are accurate to within 0.1 % of the Smithsonian Meteorological Table values (List 1951) over this range. The water vapour flux is calculated using [ I ] after applying the least squares method of smoothing over four points so that four measurements are taken before the first value is computed, g, is then calculated using [2] with the average values of the four p, and T measurements. After this, the computation is updated every 2 s and relayed to the liquid crystal display. Three C M O S erasable programmable read-only memory (EPROM) chips (27CI6), which provide a total of 6 K bytes of storage space, hold the various computational routines. Approximately 0.25 K bytes of C M O S random access mem-ory (RAM) is used to store the constants used in the com-putations. The values of these constants, which include the chamber volume and leaf area, are entered directly from the keyboard. A continuous memory is provided by a 3.6-V nickel-cadmium battery backup system which enables con-stants to be stored for periods of many months. This battery system is trickle charged by the solid-gel batteries. The same 12-V power supply used for the XR-2206 circuitry is regulated down to 5 V to power the microprocessor system which draws approximately 10 mA. After the porometer chamber is placed over a conifer seed-ling one of seven variables (flH, fx, R H . T, p., F, and g,) can be monitored on the display by pressing the appropriate func-tion key on the keyboard. This immediately activates the fan in the porometer chamber. After a 2-s delay, to ensure that com-plete mixing of the air has taken place, the selected quantity is sampled, displayed, and then updated every 2 s. When stomatal conductance or vapour flux is monitored, the first reading is not displayed until 8 s have elapsed because of the curve smoothing routine described earlier. The fan is automatically shut off after 40 s to conserve battery power. Teats and calibration Chamber ventilation It is important that air in the seedling chamber is well mixed to ensure that the humidity sensor measures the true average chamber humidity and that a high boundary layer conductance results in needle temperature being maintained close to air temperature. To determine the extent of mixing throughout the chamber, air speeds were measured systematically using a hot-wire anemometer. No stagnation spots were found when a Douglas-fir (Pseudotsugo memiesii (Mir.) Franco) seedling with a projected needle area of approximately 370 crrr was placed in the chamber. Typically, air speeds ranged from 80 to 180 cm s~' which correspond to boundary layer conductances ranging from 7 to 9 cm s~' , respectively (Landsberg and Thorn 1971). The lowest air speed of 35 cm s"' was measured in a small region near the bottom of the chamber. This corresponds to a boundary layer conductance of 5 cm $"' . Fine wire (0.075 mm) copper-con stantan thermocouples were used to measure differences between needle and air temperatures in laboratory and greenhouse experiments con-ducted on Douglas-fir seedlings. At low stomatal conductances (0.05 cm s"1) needle temperature was approximately 0.08°C lower than air temperature, while at intermediate conductances (0.20 cm s~') needle temperature was approximately 0.15°C lower than air temperature. These measurements confirmed calculations, based on energy balance and exchange theory applied to a leaf (Campbell 1977), in which net longwave radiation exchange between seedling and the chamber was approximated using the Christiansen equation (Jacob 1957). Calculations using our lowest estimate of boundary layer conductance showed that even at extremely high stomatal conductance (0.7 cm s~') needle temperature would only be 0.9°C lower than air temperature. However, when chamber temperature exceeds air temperature by S°C. at this stomatal conductance, needle temperature would only be 0.5°C lower than air temperature. Water vapour adsorption There are numerous surfaces within the porometer chamber that can adsorb water vapour (Gandar and Tanner 1976). These include the chamber walls and fan blades. Unless the adsorp-tion or de sorption of this water vapour is very small compared with the increase in water vapour density in the chamber, resulting from seedling transpiration, significant errors can arise when measuring transpiration rate and stomatal conduc-tance. A calibration procedure is therefore necessary to quan-tify and correct for water vapour sorption effects. For this purpose, an artificial seedling consisting of an aluminum stem and four stainless steel leaves was constructed. Saturated filter paper of known surface area was attached to the leaves to provide an evaporating surface. The base of the seedling rested on the pan of a balance with a resolution of I mg beneath the porometer chamber, so that the seedling stem entered the cham-ber through the hole in the base plate exposing the leaves to the inside of the chamber. Evaporation rate was determined by measuring the loss of water every 5 s. Vapour fluxes ranged from 0 to 1.4 mg s"' which were similar in magnitude to vapour - 152 -LIVINGSTON ET AL. 0-2 0-4 0-6 0-8 t O Actual flux (mg f ) FIG 4. Apparent water vapour flux (App) measured by the seed-ling porometer versus actual flux (Act) measured by weight loss of an artificial seedling. See text for the results of comparison using satur-ated filter paper discs. fluxes measured in the field, the maximum of which seldom exceeded 0.7 mg s"'. Following the method of Kaufmann (1981), the gravi-metrically determined vapour flux was regressed against that calculated from measured changes of relative humidity in the chamber (Fig. 4). The slope of the regression line is 0.8, which indicates that 25% of the water vapour added to the chamber is adsorbed by internal surfaces. The calibration factor, 1.25, is entered into the microprocessor memory and can be changed at any time using the keyboard. This implies that the effective volume of the porometer chamber is 25% greater than the actual chamber volume (Turner and Parlange 1970). The test was repeated using 1 cm 3 saturated filter paper discs and a 0.01 mg resolution balance. The slope and the intercept of the regression line were 0.83 and 0.00, respectively (r 2 = 0.96), for fluxes ranging from 0 to 0.15 mg s " ' , while the smallest de-tectable flux was 0.01 mg s"'. Because the vapour fluxes were measured over a wide range of relative humidities and over time periods ranging from 5 to 30 s, it appears that the ad-sorption of water vapour is proportional to the rate of change of absolute humidity in the chamber. This is in contrast with Kaufmann (1981) who found that in a teflon-lined chamber there was an inexplicably sharp onset of adsorption at high fluxes of water vapour. Leaf area determinations The total needle area of a seedling must be known to obtain an absolute measurement of stomatal conductance (see [2]). Accordingly, a method was devised that enables a quick and nondestructive estimate of projected needle area. Eighty one seedlings were sampled, consisting of equal numbers of Douglas-fir. western hemlock (Tsuga heterophylla (Raf.) Sarg.). and Pacific silver fir (Abies amabilis (Doug.) Forbes) seedlings. The height (/V), crown length, root collar diameter (X>), and number of branches (£) were measured on each and their projected area measured with an area meter (model Li-3000, Licor Inc.. Lincoln, N E , U . S . A . ) . The resulting TIME It) FIG. 5. A typical time course of average seedling stomatal conduc-tance during the period of measurement. TABLE 1. The mean ratio of stomatal conductance measurements made on 22 Douglas-fir seedlings after 20 s to those made 10. 30. 40. 60. and 120 s after the porometer was placed around each seedling Time interval (s) 10 20 30 40 60 120 Ratio 1.1 1 0 1.0 1.1 14 16 Standard deviation 0.2 0 0.1 0.2 0.3 0.4 equations which best estimated projected needle area in square centimetres are as follows: Douglas-fir, A = 18.3 D B + 30.58 <r' = 0.92); western hemlock, A = 10.4 DB + 2.50 (r 2 = 0.82); Pacific silver fir, A = 18.0 D H + 6.70 (r 3 = 0.86) where D and W are in centimetres. These equations were only used when individual seedlings could not be destructively sam-pled to determine their projected needle area. Time course of measurements on conifer seedlings Experiments were carried out to determine (i) the time required to obtain steady stomatal conductance readings and (ii) the effect of depriving the seeding of light during the mea-surement period. Measurements were made outdoors over a 2-min period on 22 1 -and 2-year-old Douglas-fir seedlings on the University of British Columbia campus and on planted seedlings at a high elevation research site in the Cameron Valley, Vancouver Island. Figure 5 shows a typical time course of stomatal conductance obtained using the porometer on an individual seedling. The results snow that a steady reading of stomatal conductance can be obtained within 20 s of the cham-ber being placed around the seedling and that slow response to light deprivation is apparent after about 40 s. This is further illustrated in Table I which shows the ratio of stomatal conduc-tance measurements made after 20 s to those made after •elected time intervals for the 22 seedlings. The time taken to reach a steady reading of stomatal conductance was indepen-dent of the water vapour flux or the stomatal conductance being measured. The maximum increase in the relative humidity in the chamber over the first 20 s was 5 % . Field measurements The porometer was used on a regular basis from June to September 1982. Measurements of stomatal conductance and - 153 -CAN. I. FOR. S E E D L I N G POROMETER 0 . ( c m f ) FIG 6 Comparison of the average needle conductance of Douglas-fir seedlings measured using a ventilated diffusion porometer that uses four-needle samples with the average needle conductance measured using the seedling porometer. Linear regression analysis indicates needle porometer g. « 0.81 seedling porometer g, + 0.005 (r s = 0.97). transpiration rate were made on Douglas-fir, western hemlock, and Pacific silver fir seedlings that were growing on a high elevation, south-facing clearcut slope in the Cameron Valley. It took about 1 min to make a complete measurement. This included the time required to position the baseplate (approxi-mately 20 s), make the measurement (20 s), and remove the entire porometer. The porometer proved to be convenient to use in a forest clearcut environment. After the 4 months of field1 use, the calibration of the sensors had not changed significantly. The calibrations of the humidity and temperature sensors were checked against an Assmann psychrometer at the begin-ning of each day. Care was taken to ensure the porometer chamber was kept in the shade when it was not in use. Radi-ative heating of the stainless steel walls of the porometer cham-ber sometimes resulted in the air temperature in the sunlit chamber being raised as much as 3°C above that of the external air. This effect can be reduced by painting the outside surfaces white or covering them with aluminized mylar. Measurements of stomatal conductance made on Douglas-fir seedlings were compared with those made with a ventilated diffusion porometer described by Tan and Black (1978). The Utter measurement used samples of four needles which were removed from the same seedlings. Figure 6 shows the results of this comparison for August 24, 1982. Seven seedlings were used in the study and measurements were made at hourly inter-vals throughout the day. At the end of the experiment the needle area of each seedling was determined using a leaf area meter. In general, conductance measurements made on individ-ual needles were 19% lower than those made on whole seedlings. This difference might have resulted because of the approximately 3 min it took to remove the needles from the seedlings, transport them in a sealed plastic bag to the needle VOL. 14. I W 4 3-0 2 2-0 o to > Q| . 1 1 L I I I I T I M E (h) FIG 7. Comparison of the daytime course of average stomatal con-ductance of irrigated Douglas-fir. western hemlock, and Pacific silver fir seedlings growing in a nigh elevation forest clearcut in the Cameron Valley. Also shown is the course of the water vapour pressure defi-cit (VPD). DF, Douglas-fir. WH. western hemlock; PSF. Pacific silver fir. porometer, and make the measurement. During this time some stomatal closure might have occurred. Evaporation from the bark of the snoots and stem had virtually no effect on the whole seedling conductance measurements. Tests in a greenhouse showed that this evaporative flux accounted for less than 0 . 5 % of the total water loss from a Douglas-fir seedling with an average stomatal conductance of 0.28 cm s ' 1 . Figure 7 shows the diurnal courses of stomatal conductance of irrigated Douglas-fir, western hemlock, and Pacific silver fir seedlings growing in the high elevation clearcut, measured using the seedling porometer throughout August 7, 1982, which was a clear day. Leaf area was calculated using the regression equations given previously. A l l species showed a marked reduction in stomatal conductance during the afternoon when vapour pressure deficit was high. Summary A transient-type porometer was developed that nondestruc-tively measures the stomatal conductance of conifer seedlings. The instrument was used successfully in a high elevation forest clearcut over a summer to determine the stomatal character-istics of Douglas-fir, western hemlock, and Pacific silver fir seedlings. There was good agreement between measurements made with the porometer on Intact seedlings and those made on •elected needles by a ventilated diffusion porometer. Acknowledgnnents We thank Mr. J. Baranowski for valuable assistance in the design and machining of the porometer chamber, and Mr. F. KelUher for making the ventilated porometer measurements of - 154 -LIVINGSTON ET AX needle conductance in the field. This research was supported by a British Columbia Ministry of Forests contract, and grants from the British Columbia Science Council and the Natural Sciences and Engineering Research Council of Canada. BEARDSELL. M. F . P. C. JARVIS. and B. DAVIDSON. 1972. A null balance diffusion porometer suitable for use with leaves of many shapes. J. Appl. Ecol. 9: 677 -690. BINGHAM. C. E.. and P. I. COYNE. 1977. A portable, temperature-controlled steady-state porometer for field measurements of transpi-ration and photosynthesis. Photosynthetic .^ II: 148-160. CAMPBELL. C. C. 1977. An introduction loenvironmental biophysics. Springer-Verlag. New York. DIXON. W.. and J. GRACE. 1982. Water uptake by some chamber materials. Plant Cell Environ. 5: 323-327. GANDAR. P. W . and C. B. TANNER. 1976 Water vapour sorption by the walls and sensors of stomatal diffusion porometers. Agron. J. 68: 245 - 249. JACOB. M. 1957. Heat transfer. Vol II. John Wiley. Nev. York. KANEMASI'. E. T.. G. W. THI'RTELL. and C. B. TANNER 1969 Design, calibration and field use of a stomatal diffusion porometer Plant Physiol. 44: 881-885. KAUFMANN. M. R 1981. Automatic determination of conductance. transpiration and environmental conditions in forest trees. For Sci 27: 817-827. KOHS1EK. W 1981. A rapid-circulation evaporation chamber for mea-suring bulk stomatal resistance. J. Appl. Meteorol. 20: 42-5?. LANDSBERG. J. J., and A. S. T/HOM 1971. Aerodynamic properties of a plant of complex structure. Q. J. R. Meteorol Soc. 97:565 - 570 LIST. R. J. 1951. Smithsonian meteorological tables Vol. 114 Smithsonian Institution Press. Washington. DC. TAN . C. S.. and T. A. BLACK. 1978 Evaluation of a ventilated diffusion porometer for the measurement of stomatal diffusion resistance of Douglas-fir needles Arch Meteorol Geophv* Bioklimatol Ser B. 26: 257-273 TURNER. N. C . and J Y. PARLANCE. 1970. Analysis of operation and calibration of ventilated diffusion porometer. Plant Phvsiol 46: 175-177. - 155 -APPENDIX I I I SOIL WATER RETENTION CURVES - 156 -APPENDIX I I I SOIL WATER RETENTION CURVES The pu rpose o f t h i s append i x i s t o g i v e t h e l a b o r a t o r y - d e t e r m i n e d w a t e r r e t e n t i o n c u r v e s ( s o i l wa t e r m a t r i x p o t e n t i a l ( i | > s ) (MPa) Vs v o l u m e t r i c wa te r c o n t e n t ( 9 ) (m 3 H 2 0 M - 3 ) ) a t t h r e e d ep t h s (0 -5 cm, 5-10 cm, and 15-25 cm) f o r t h e g r a v e l l y sandy loam a t t h e mount A r r o w s m i t h e x p e r i m e n t a l s i t e . The measurements were made on u n d i s t u r b e d c o r e s ( 5 . 3 6 cm d i a m e t e r x 3 .93 cm l o n g ) u s i n g S o i l M o i s t u r e I n c . p r e s s u r e p l a t e s . The r e t e n t i o n c u r v e s have been c o r r e c t e d f o r s t o ne c o n t e n t (64% a t 0-5 cm, 68% a t 5-10 cm and 67% a t 15-25 c m ) . - 157 -F i g u r e A I I I . l S o i l wa t e r r e t e n t i o n c u r v e s f o r 0-5 cm ( • ) , 5-10 (o) and 15-25 cm ('•) dep th s 

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