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Low temperature as it affects the selection of woody ornamentals in British Columbia Rhodes, Hubert Lloyd Joseph 1950-12-31

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LOW TEMPERATURE AS IT AFFECTS THE SELECTION OF WOODY ORNAMENTALS IN BRITISH COLUMBIA by  Hubert L l o y d Joseph Rhodes  A T h e s i s Submitted i n P a r t i a l F u l f i l m e n t of The Requirements f o r t h e Degree o f MASTER OF SCIENCE IN AGRICULTURE In the Department  of HORTICULTURE  The U n i v e r s i t y o f B r i t i s h May, 1950.  Columbia  ABSTRACT LOW TEMPERATURE AS IT AFFECTS THE SELECTION OF WOODY ORNAMENTALS IN BRITISH COLUMBIA;  by Hubert L. J . Rhodes  Low w i n t e r temperature was taken as the most important f a c t o r i n f l u e n c i n g t h e s e l e c t i o n of ornamental t r e e s and shrubs f o r d i f f e r e n t areas o f British  Columbia.  The l o c a l i t y  around a m e t e o r o l o g i c a l  s t a t i o n was made t h e u n i t o f i n v e s t i g a t i o n , with t h e m e t e o r o l o g i c a l s t a t i o n as a r e f e r e n c e p o i n t .  Average  extreme lowest temperature o f the year f o r each British  Columbia m e t e o r o l o g i c a l s t a t i o n was c a l c u l a t e d  from f i g u r e s compiled f o r the t e n y e a r p e r i o d 1940-49. # -  C e r t a i n methods were used t o i n t e r p r e t low temperature i n f o r m a t i o n i n an o r i g i n a l way: the use of the winter r a t h e r than t h e c a l e n d a r year as t h e u n i t i n c o n s i d e r i n g low temperature, the a p p l i c a t i o n of  statistical  a n a l y s i s t o express v a r i a t i o n i n low  temperature between w i n t e r s , and t h e c o n v e r s i o n o f statistical to  estimates to temperatures corresponding  a convenient p r o b a b i l i t y r a t i o e a s i l y understood by  p r a c t i c a l workers.  Average  extreme lowest temperature  of the winter based on the t e n - w i n t e r p e r i o d from 1940-41 to  1949-50, standard d e v i a t i o n , and the n i n e t y percent  p o i n t were c a l c u l a t e d f o r s e l e c t e d B. C. m e t e o r o l o g i c a l stations.  ABSTRACT - Cont The n i n e t y percent point i s t h a t  temperature  above which the extreme lowest temperature o f a s t a t i o n will fall  i n approximately nine out o f t e n w i n t e r s , and  below which the extreme lowest temperature w i l l f a l l i n approximately one out o f t e n w i n t e r s , a c c o r d i n g t o mathematical expectancy based on s t a t i s t i c a l of  analysis  temperatures observed over a p e r i o d of w i n t e r s .  This  concept combines the i n f o r m a t i o n t o be o b t a i n e d from t h e average extreme lowest temperature and the standard deviation.  The n i n e t y percent p o i n t i s found by sub-  t r a c t i n g t h e standard d e v i a t i o n m u l t i p l i e d by 1.3 the  from  average extreme lowest temperature of the w i n t e r . A survey was conducted t o o b t a i n an estimate  of  the i n j u r y t o ornamental t r e e s and shrubs i n B r i t i s h  Columbia f o l l o w i n g two severe w i n t e r s .  The i n f o r m a t i o n  was used t o t e s t the u s e f u l n e s s of low temperature data as a guide i n s e l e c t i n g woody ornamentals f o r h a r d i n e s s in  a l o c a l i t y , and t o get a c c u r a t e low temperature  l i m i t s i n the P a c i f i c c o a s t a l r e g i o n f o r a number of ornamental s p e c i e s .  Low temperature i n f o r m a t i o n was  found u s e f u l w i t h i n l i m i t a t i o n s as an i n d i c a t i o n of t h e amount of winter i n j u r y t o woody ornamentals t o be expected i n a l o c a l i t y o f B r i t i s h Columbia a f t e r a severe w i n t e r .  ACKNOWLEDGMENTS The d i r e c t i o n o f the f o l l o w i n g prof e s s o r s i s acknowledged: P r o f e s s o r J . W. N e i l l , Department of H o r t i c u l t u r e , f o r the suggestion of the t o p i c and major d i r e c t i o n of t h e i n v e s t i g a t i o n . Dr. V. C. B r i n k , Department o f Agronomy, Dr. T. M. C. T a y l o r , Department of B i o l o g y and Botany, and P r o f e s s o r J . D. Chapman and Dr. J . R. Mackay, Department o f Geology and Geography, f o r d i r e c t i o n i n c o l l e c t i n g , a n a l y z i n g , and p r e s e n t i n g temperature i n f o r m a t i o n . Acknowledgment i s due t o Dr. A. F. Barss, Head o f t h e Department o f H o r t i c u l t u r e , f o r g e n e r a l d i r e c t i o n o f the Master's work. Mr. A. R. McCauley, D i s t r i c t M e t e o r o l o g i s t , Vancouver, gave a s s i s t a n c e by p r o v i d i n g l o c a l weather i n f o r m a t i o n . Mr. W. G. H. F i r t h , C h i e f Geographer, B. C. Department o f Lands and F o r e s t s , p r o v i d e d base maps o f B r i t i s h Columbia. Mr. W. H. Robertson, P r o v i n c i a l H o r t i c u l t u r i s t , the D i s t r i c t H o r t i c u l t u r i s t s , and a number o f nurserymen and gardeners throughout the p r o v i n c e gave a s s i s t a n c e with the w i n t e r i n j u r y survey.  TABLE OF CONTENTS Page INTRODUCTION REVIEW  OF  ANALYSIS  1  LITERATURE OF  THE  Development  .  .  SUBJECT  .  .  .  .  .  .  .  5  .  .  .  .  .  .  .  13  o f the Method  . . . . .  13  Extreme Lowest Temperature . . . . .  16  Extreme lowest temperature o f t h e year •  16  Extreme lowest temperature o f the winter . . . . . . . .  22  A n a l y s i s of extreme lowest temperature v a r i a t i o n The n i n e t y percent p o i n t  .  23  . . . . .  27  The Winter I n j u r y Survey Purpose o f t h e survey  32 . . . . . .  32  D e s c r i p t i o n o f methods  33  Results  34  Conclusion . . . . . . . . . . . .  37  DISCUSSION  . . .  SUMMARY LITERATURE CITED  39 , . . . . . . . . .  43 .  45  TABLES: Table I  Ten Year Averages of Extreme Lowest Temperature o f the Year 19 Table I I A n a l y s i s of Low Temperature Data . 30  TABLE OF CONTENTS - Cont. P  ILLUSTRATIONS  a  f i  e  ( f o l l o w i n g page)  F i g . 1 - V a r i a t i o n i n extreme lowest temperature of the w i n t e r d u r i n g the t e n winter p e r i o d from 1940-41 t o 1949-50 at f o u r B r i t i s h Columbia m e t e o r o l o g i c a l stations . . . . . . . . . . . . . . . .  24  F i g . 2 - S t a t i s t i c a l e x p r e s s i o n of extreme lowest temperature o f the w i n t e r at t e n B r i t i s h Columbia m e t e o r o l o g i c a l stations . . . . . . . . . . . . . . . •'.  26  F i g . 3 - Normal frequency d i s t r i b u t i o n curve showing approximate p r o p o r t i o n s d i v i d e d by n i n e t y percent p o i n t . . . . .  28  F i g . 4 - Approximate low temperature zones i n the s e t t l e d c o a s t a l r e g i o n . . »  38  Map - Average extreme lowest temperature f o r the t e n year p e r i o d 1940-49 . . . • Appendix APPENDIX Appendix I - Extreme Lowest Temperature of the Winter at S e l e c t e d B. C. M e t e o r o l o g i c a l S t a t i o n s f o r the Ten-Winter P e r i o d from 1940-41 to 1949-50. ... . . . . . . . . . Appendix I I - S p e c i e s of Trees and Shrubs Included i n the Winter I n j u r y Survey, 1950.  LOW TEMPERATURE AS IT AFFECTS THE SELECTION OF • WOODY ORNAMENTALS IN BRITISH COLUMBIA INTRODUCTION One o f the important  steps i n the development  of h o r t i c u l t u r e i n any r e g i o n i s the o b t a i n i n g o f i n f o r mation on s u i t a b l e ornamental p l a n t s f o r d i f f e r e n t p a r t s o f the country.  The accumulation  o f such i n f o r -  mation i s u s u a l l y the r e s u l t o f c o n s i d e r a b l e  experience  I n v o l v i n g a l a r g e amount o f t r i a l and e r r o r with a range o f p l a n t m a t e r i a l s . In the o l d e r p a r t s o f the world  the behaviour  of ornamental p l a n t s and t h e i r s u i t a b i l i t y f o r d i f f e r e n t areas  i s w e l l known.  As l i t t l e known o r  newly d i s c o v e r e d p l a n t s a r e i n t r o d u c e d t o gardens their suitability for particular districts  i s deter-  mined with the h e l p o f i n f o r m a t i o n about p l a n t s which have been long i n c u l t i v a t i o n i n these Great  districts.  B r i t a i n i s an example o f a country which has a  w e l l developed h o r t i c u l t u r e i n connection long period of c i v i l i z a t i o n .  with i t s  D e t a i l e d i n f o r m a t i o n on  s u i t a b l e ornamentals i s g e n e r a l l y a v a i l a b l e f o r a l l the d i f f e r e n t l o c a l i t i e s from the southwestern coast to t h e n o r t h e r n i s l a n d s . In the settlement  o f the new world  immigrants  c u s t o m a r i l y brought with them t h e p l a n t s with which  they had been f a m i l i a r i n t h e i r o l d surroundings. soon found  which of these would s u r v i v e i n the  l a n d where they happened t o s e t t l e . to  They  new  People have tended  r e l y on those i n t r o d u c e d t r e e s and  have proved s u c c e s s f u l , r a t h e r than  shrubs which  explore the p o s s i -  b i l i t i e s of n a t i v e s p e c i e s or other p l a n t s which they had not known i n t h e i r o l d surroundings.  Nurseries  have made a p r a c t i c e of growing o n l y the p l a n t s f o r which t h e r e i s c o n s i d e r a b l e demand.  Consequently  there has been a c o n s e r v a t i v e t r e n d i n the p l a n t i n g of  ornamentals. There are u s u a l l y a few  s p e c i e s of good  ornamental p l a n t s which are p a r t i c u l a r l y w e l l s u i t e d to  the c l i m a t e of an a r e a .  overlooked conducted.  These s p e c i e s may  be  u n l e s s a w e l l o r g a n i z e d scheme of t r i a l s i s Before our surroundings  f a c t o r i l y landscaped,  can be  satis-  a thorough knowledge of the  best e x i s t i n g p l a n t m a t e r i a l s must be a t t a i n e d . In B r i t i s h Columbia t h e r e i s a d e f i n i t e need f o r b e t t e r organized and more r e a d i l y a v a i l a b l e i n f o r m a t i o n as to which p l a n t s may different l o c a l i t i e s .  be grown i n  Even i n the w e l l s e t t l e d  d i s t r i c t s around Vancouver t h e r e are few  gardens  where p o s s i b i l i t i e s i n p l a n t m a t e r i a l s are e x p l o i t e d . Most gardeners have t o make a choice of p l a n t s w i t h -  out any r e a l knowledge of t h e wide a r r a y ornamentals which might be used*  o f good  Some p l a n t s  are p a r t i c u l a r l y adapted t o l o c a l c o n d i t i o n s r e a d i l y a v a i l a b l e a t the l o c a l n u r s e r i e s , sequently they a r e not w i d e l y grown.  which a r e not  and con-  Others which a r e  a v a i l a b l e have been avoided because t h e y have been thought t o be not hardy enough* could and  Many of these  plants  be grown s u c c e s s f u l l y i f g i v e n a s u i t a b l e  location  adequate c a r e . Better  practical horticulture i n British  Columbia must depend p r i m a r i l y on t h e a p p l i c a t i o n o f the best s c i e n t i f i c methods o f o b t a i n i n g t h a t a r e a t our d i s p o s a l .  information  In t h i s i n v e s t i g a t i o n  every  attempt has been made t o use t h e t o o l s o f s c i e n c e s related to horticulture i n attacking problem.  Climatological  t i c a l analysis  a horticultural  methods, e s p e c i a l l y t h e s t a t i s -  o f temperature data, have been found  most u s e f u l . Of the numerous f a c t o r s which determine t h e s u i t a b i l i t y o f ornamental t r e e s and shrubs f o r part i c u l a r l o c a l i t i e s , low w i n t e r temperature i s undoubtedly v e r y important.  T h i s i s e s p e c i a l l y t r u e i f , as i n t h i s  i n v e s t i g a t i o n , the area under study i s c h a r a c t e r i z e d by marked c l i m a t i c d i v e r s i t y .  I n B r i t i s h Columbia  t h e r e i s a wide range i n the s e v e r i t y o f winter tempera-  -  k  ture i n d i f f e r e n t l o c a l i t i e s .  -  Around V i c t o r i a on the  southern t i p o f Vancouver I s l a n d the w i n t e r s a r e g e n e r a l l y m i l d enough t o permit the outdoor c u l t u r e o f n e a r l y any woody p l a n t from the temperate  zones o f the w o r l d .  At  P r i n c e George, toward the o t h e r extreme, o n l y a few n o t a b l y c o l d r e s i s t a n t t r e e s and shrubs w i l l  survive.  The purpose o f t h i s i n v e s t i g a t i o n i s t o p r o v i d e a f o u n d a t i o n f o r a sound a p p r a i s a l o f l o c a l i t i e s Columbia as t o s u i t a b i l i t y  of B r i t i s h  f o r the growth o f d i f f e r e n t  s p e c i e s of ornamental t r e e s and shrubs*  Although the  problem has a number o f important a s p e c t s ,  investigation  i s c o n f i n e d here t o t h e study o f low w i n t e r temperature as i t a f f e c t s the s e l e c t i o n o f woody ornamentals.  REVIEW OF LITERATURE One  would expect t h a t an a p p r e c i a b l e amount of i n -  v e s t i g a t i o n on t r e e s and  shrubs s u i t a b l e f o r B r i t i s h  Columbia would be under way,  c o n s i d e r i n g the youth of the  p r o v i n c e as a s e t t l e d a r e a .  U n f o r t u n a t e l y t h e r e has  little  d e t a i l e d work f o r s p e c i f i c The  Dominion Experimental  been  purposes. Farms S e r v i c e have taken  the l e a d i n t r y i n g out ornamental p l a n t s f o r d i f f e r e n t c l i m a t i c regions  i n Canada.  T h e i r work has been q u i t e  v a l u a b l e f o r Canada as a whole, e s p e c i a l l y the c o l d r e g i o n s which occupy the m a j o r i t y of the country*  Such work  a p p l i e s to the c o l d i n t e r i o r of B r i t i s h Columbia, but not to the warm c o a s t a l r e g i o n of the p r o v i n c e , where the population i s concentrated.  Some d e t a i l e d l o c a l work  been done at branch farms and t h i s i s published*  s t a t i o n s , but l i t t l e  climbers ( O l i v e r , 1944),  shrubs  and p e r e n n i a l s ( P r e s t o n ,  O l i v e r ' s b u l l e t i n s g i v e t a b l e s showing hardiness t r e e s and  of  From Ottawa have come b u l l e t i n s  hedges (Macoun, 1 9 3 1 ) , t r e e s ( O l i v e r , 1 9 4 5 ) ,  has  on and  1946). of  shrubs which have been t r i e d at d i f f e r e n t  the branch  farms and s t a t i o n s * In the H o r t i c u l t u r a l Branch of the  Provincial  Department o f A g r i c u l t u r e the major a t t e n t i o n has d i r e c t e d toward f r u i t  crops  been  r a t h e r than ornamentals*  I n t e r e s t i n the s u i t a b i l i t y of ornamentals has been f i n e d c h i e f l y to answering q u e r i e s from the p u b l i c .  eonDistrict  H o r t i c u l t u r i s t s undoubtedly have accumulated some good i n formation r e l a t i n g to i n d i v i d u a l d i s t r i c t s .  This  infor-  mation would be more u s e f u l i f i t were compiled and p u b l i s h e d f o r the use of people who the  are not f a m i l i a r with  province. There has been some attempt at The U n i v e r s i t y of  B r i t i s h Columbia to recommend p l a n t s s u i t a b l e f o r the province.  The l i s t  o f ornamental t r e e s and shrubs com-  p i l e d by F. E. Buck (1946) has been u s e f u l , but i t makes no d i s t i n c t i o n between d i f f e r e n t areas o f the p r o v i n c e . Brink and F a r s t a d (1949) i n an approach t o the problem o f recommending s u i t a b l e crop p l a n t s , have summarized physiography of the a g r i c u l t u r a l areas o f B r i t i s h and B r i n k (1950) has o r g a n i z e d some c l i m a t o l o g i c a l  the Columbia, infor-  mation f o r the use of a g r i c u l t u r a l i n v e s t i g a t o r s i n the first  of a s e r i e s of four p u b l i c a t i o n s .  Muirhead  (unpub.)  has done some o r i g i n a l work i n h i s i n v e s t i g a t i o n o f s u i t a b l e s t r e e t t r e e s f o r Vancouver.  There i s promise of an  i n c r e a s e d i n t e r e s t i n l o c a l problems o f t h i s n a t u r e . In the  Columbia  e x p l o r a t i o n of l o c a l p o s s i b i l i t i e s has progressed more  rapidly. of  the American S t a t e s south of B r i t i s h  Grant and Grant (1943) have g i v e n a good summary  the newer ideas i n a book on t r e e s and shrubs f o r the  P a c i f i c Northwest. Washington  Snyder's (no date) l i s t  i s a p p l i c a b l e to p a r t s of B.C.,  g i v e any d e t a i l s of c l i m a t i c s u i t a b i l i t y .  o f shrubs f o r but i t does not Graham and  McMinn (1941) have c o n s i d e r e d shrubs and v i n e s f o r the Pacific  coast*  McMinn and Maino (1935) i n c l u d e  i n t h e i r account o f t r e e s of the P a c i f i c  ornamentals  coast.  Numerous a r t i c l e s i n semi-popular gardening magazines  c o n t a i n v a l u a b l e but s c a t t e r e d fragments of i n -  formation on the c u l t u r e o f t r e e s and shrubs i n the P a c i f i c Northwest. on rhododendron  Grant (1944), f o r example, has w r i t t e n  c u l t u r e i n the a r e a .  The study o f c l i m a t e i n r e l a t i o n t o the growth of p l a n t s has a t t r a c t e d wide a t t e n t i o n i n the l a s t f i v e y e a r s , owing t o the s t i m u l u s of the new p l a n t ecology.  The f i r s t  comprehensive  twenty-  science of  quantitative  c l a s s i f i c a t i o n of c l i m a t e by Thornthwaite (1931) i s w e l l known.  The a p p l i c a t i o n o f T h o r n t h w a i t e s system t o a 1  p a r t i c u l a r problem such as the s e l e c t i o n o f t r e e s and shrubs should be preceded by c a r e f u l c o n s i d e r a t i o n o f the factors involved.  Any one f a c t o r such as temperature i s  d e a l t with v e r y g e n e r a l l y i n such a complex c l a s s i f i c a t i o n ; one temperature c a t e g o r y i n c l u d e s almost a l l t h e B r i t i s h Columbia  stations.  Since d i f f e r e n c e s i n w i n t e r temperature  are v e r y important i n the s e l e c t i o n o f t r e e s and shrubs, T h o r n t h w a i t e s c l a s s i f i c a t i o n has a l i m i t e d use i n t h i s 1  k i n d of work.  A new  c l a s s i f i c a t i o n by Thornthwaite (1948)  has appeared, and t h i s has been a p p l i e d to a of the c l i m a t e s of Canada by Sanderson  classification  (1948).  Another development i n the s c i e n c e of i s the s t a t i s t i c a l  approach*  climatology  Although s t a t i s t i c a l methods  have not been used as e x t e n s i v e l y as they might i n c l i m a t o l o g i c a l work, there has been an i n c r e a s e d attempt apply such methods to c l i m a t i c s t u d i e s i n the l a s t p a r t i c u l a r l y f o r m i l i t a r y purposes. t e x t c o v e r i n g fundamentals and statistical wider use  to decade,  An a u t h o r i t a t i v e  recent a p p l i c a t i o n s of  c l i m a t o l o g y by Conrad (1944) has  stimulated a  of these methods, e s p e c i a l l y i n r e l a t i o n to  agriculture.  F o s t e r (1948) has demonstrated the p o s s i -  b i l i t i e s of the s t a t i s t i c a l  approach i n h i s book on  hydrology.  Brink (1950) emphasizes the value of a thorough a p p r a i s a l of the c l i m a t e o f B r i t i s h Columbia f o r the e f f i c i e n c y of a g r i c u l t u r a l p r o d u c t i o n .  improving  Quoting  Land8berg (1946) he shows t h a t c l i m a t e i s i n essence  an  i n e x h a u s t i b l e n a t u r a l resource which, s i n c e i t i s f a i r l y constant  over a p e r i o d of y e a r s , can be t r e a t e d as a  calculable  risk. W r i t i n g s with  s p e c i f i c r e f e r e n c e to the B.  c l i m a t e have been r a t h e r numerous.  C.  Connor d e a l t with  temperature and p r e c i p i t a t i o n i n an e a r l y p u b l i c a t i o n (1915), and more r e c e n t l y (1949) has d i s c u s s e d the free period.  A summary of the B. C. Climate  frost-  by Denison  (1925) i s found i n the Monthly Weather Review.  Koeppe  (1931) i n c l u d e d some d e t a i l e d remarks about the c l i m a t e s of  d i s t r i c t s of B r i t i s h climate.  Columbia i n h i s book on the Canadian  The work o f Brink (1950) i s mentioned above. C h a r a c t e r i s t i c s of mountain c l i m a t e s o f Western  North America have been d i s c u s s e d by F. S. Baker (1944). The behaviour  o f temperature i n mountains has been t r e a t e d  f u l l y by P e a t t i e (1936). The h i s t o r y o f t h e development of methods o f c l a s s i f y i n g p l a n t s a c c o r d i n g t o c l i m a t i c requirements and of c l a s s i f y i n g c l i m a t e s a c c o r d i n g t o t h e i r s u i t a b i l i t y t o p l a n t s i s a long one d a t i n g i n t o a n t i q u i t y and a s s o c i a t e d with t h e o r i g i n and development of b o t a n i c a l gardens.  Yet  only d u r i n g the t w e n t i e t h century have attempts been made to put these c l i m a t i c s t u d i e s on a q u a n t i t a t i v e b a s i s . The  development o f a p l a n t growth r e g i o n map by  F. L. Mulford of the United S t a t e s Department of A g r i c u l t u r e was  an e a r l y attempt t o c l a s s i f y t h e U n i t e d S t a t e s f o r  plants.  O r i g i n a l l y intended as a b a s i s f o r recommending  roses and s t r e e t t r e e s , M u l f o r d s 1  system was m o d i f i e d and  r e f i n e d with the a i d o f many s p e c i a l i s t s i n the U.S.D.A. The  o r i g i n a l t h i r t e e n r e g i o n s were i n c r e a s e d to t h i r t y - t w o  (Mulford, 1926).  Van D e r s a l (1938) g i v e s a d e t a i l e d  account of Mulford's  system, with c h a r a c t e r i z a t i o n s o f the  d i f f e r e n t r e g i o n s under (a) c l i m a t e a c c o r d i n g t o Thornthwaite 's C l a s s i f i c a t i o n , (b) l e n g t h o f growing season; and (c) average annual snow cover. the complexity  o f Mulford's  These d e s c r i p t i o n s r e v e a l  system and the d i f f i c u l t i e s  - 10 t h a t would be i n v o l v e d i n a p p l y i n g t h i s system t o B r i t i s h Columbia.  The c l i m a t e s of the regions occupying mountainous  areas are v e r y d i v e r s e , sometimes d e f y i n g  description.  Mulford*s system undoubtedly has p r a c t i c a l v a l u e f o r areas of r e g u l a r c l i m a t e , but i t i s too complex t o be u s e f u l i n d i s t i n g u i s h i n g growth r e g i o n s i n B r i t i s h  Columbia.  D e r s a l (1938, 1942) has a p p l i e d Mulford's growth  Van  regions  t o h i s work w i t h American woody p l a n t s , l i s t i n g t h e r e g i o n s f o r which each p l a n t i s recommended. Another q u a n t i t a t i v e approach t o t h e c l a s s i f i c a t i o n of p l a n t s f o r c l i m a t e was the development  of a system o f  winter h a r d i n e s s zones f o r c u l t i v a t e d t r e e s and shrubs by A l f r e d Rehder o f the A r n o l d Arboretum.  I n f o r m a t i o n about  the hardiness of d i f f e r e n t s p e c i e s had been  steadily  accumulating as a r e s u l t o f the i n t r o d u c t i o n and t e s t i n g of p l a n t s from the East through the b o t a n i c a l gardens of Europe and America.  Rehder  (1927) made t h i s  information  a v a i l a b l e i n h i s manual on c u l t i v a t e d t r e e s and shrubs. He d i v i d e d North America i n t o eight c l i m a t i c  zones based on  the "lowest mean temperature o f the c o l d e s t month".  The  numeral f o r the c o r r e s p o n d i n g zone ( I - V I I I ) was g i v e n w i t h the d e s c r i p t i o n o f each s p e c i e s i n the manual.  A plant of  Zone I I I would be hardy i n Zones I I I t o V I I I , but not i n Zones I t o I I .  In the second e d i t i o n o f h i s manual (1940)  Rehder e x p l a i n e d the b a s i s of h i s c l a s s i f i c a t i o n somewhat differently.  The number o f zones was reduced t o seven, and  - 11 these zones were based on t h e "annual minimum temperature". The average annual minimum temperature l i s t e d f o r the different  zones i s as f o l l o w s : Zone I:  A map  exceeding  -50°P  II:  -50°  to  -35°  III:  -35°  to  -20°  IV:  -20°  to  -10°  V:  -10°  to  -5°  VI:  -5°  to  • 5°  VII:  •5°  to  flO°  showing the approximate l o c a t i o n of these  zones i n North America i s i n c l u d e d with the manual. map  i s adapted from a map  This  o f average annual minimum tem-  p e r a t u r e i n the A t l a s of American A g r i c u l t u r e ( 0 . E. Baker, 1936).  The u s e f u l n e s s of R e h d e r s map 1  f o r d e t e r m i n i n g the  zone of a p l a c e i s l i m i t e d by t h e s m a l l s c a l e and the l a c k of d e t a i l i n o u t l i n i n g the zones.  I t i s c l e a r from  Rehder s 1  e x p l a n a t i o n of h i s system t h a t he b e l i e v e s many other f a c t o r s b e s i d e s w i n t e r temperature have an important b e a r i n g on the h a r d i n e s s of p l a n t s . The g e n e r a l r e c o g n i t i o n of Rehder*e work on c u l t i v a t e d t r e e s and shrubs has been  taxonomic accompanied  by a wide acceptance of h i s w i n t e r h a r d i n e s s zones as a b a s i s f o r c l a s s i f y i n g woody p l a n t s a c c o r d i n g t o c l i m a t e , Wyman (1938) r e f e r r e d to Rehder s 1  as standard f o r the U n i t e d S t a t e s .  w i n t e r h a r d i n e s s zones He a s s i g n e d somewhat  - 12 m o d i f i e d r a t i n g s based on Render's in  hisl i s t  o f hedge p l a n t s .  system t o each s p e c i e s  Grant and Grant (1943)  have extended h i s zones from seven t o t e n t o i n c l u d e the m i l d c o a s t a l areas o f t h e P a c i f i c Northwest, and t h e y assigned h a r d i n e s s r a t i n g s t o each s p e c i e s i n t h e i r of  plants f o r t h i s area.  list  The q u a n t i t a t i v e b a s i s f o r t h e  extended zones i s not g i v e n i n t h e i r e x p l a n a t i o n o f their modification. W r i t i n g s d e s c r i b i n g i n v e s t i g a t i o n s o f the nature of w i n t e r i n j u r y and the f a c t o r s  influencing  w i n t e r h a r d i n e s s have been v e r y e x t e n s i v e ( I m p e r i a l Bureau of P l a n t Breeding and G e n e t i c s . 1939; L e v i t t . 1941).  Some d i s c u s s i o n s o f the problem o f w i n t e r h a r d i -  ness i n r e l a t i o n t o ornamental p l a n t s a r e those of Bowers (1947), Crane (1947), Skinner (1944), and Teuscher (1941). The assessment  o f w i n t e r i n j u r y t o ornamental  p l a n t s a f t e r p a r t i c u l a r l y extreme w i n t e r s has been g i v e n some a t t e n t i o n i n recent years by t h e Royal H o r t i cultural Society.  Reports were p u b l i s h e d a f t e r the  w i n t e r s of 1939-40 (R.H.S., 1941), 1940-41 ( B a l f o u r , 1 9 k l \ and 1946-47 (Harrow, 1948; R.H.S., 1948).  The F r o s t  Damage Survey conducted a f t e r the 1946-47 w i n t e r was used as a guide f o r t h e survey conducted i n c o n n e c t i o n w i t h this  investigation.  * 13 ANALYSIS OF THE SUBJECT Development  of the Method  The i n t e r a c t i n g f a c t o r s which determine t h e r e l a t i o n o f a plant  t o i t s environment a r e known t o be  extremely complex*  Even t h e study o f c l i m a t i c  effects  involves  many f a c t o r s , none o f which a c t s by i t s e l f .  theless,  these d i f f e r e n t f a c t o r s must be separated f o r  purposes o f i n v e s t i g a t i o n .  Never-  A g e n e r a l approach t o a com-  p l i c a t e d problem i s u n l i k e l y t o b r i n g about progress i n any f i e l d o f s c i e n c e *  material  A specific  approach  allows the s e l e c t i o n o f the most v i t a l f a c t o r f o r i n v e s t i gation,  and consequently l e a d s t o a thorough knowledge o f  one important phase o f the problem. The environmental f a c t o r s of c u l t i v a t e d p l a n t s  influencing  may be grouped under two main headings:  edaphic f a c t o r s and c l i m a t i c f a c t o r s . m o d i f i e d g r e a t l y when p l a n t s vation,  the growth  While s o i l s can be  a r e grown under c l o s e  culti-  the c l i m a t i c f a c t o r s a r e much more d i f f i c u l t t o  control. The groups o f c l i m a t i c f a c t o r s cultivated plants  include  and the movement of a i r .  m o i s t u r e , l i g h t , temperature, Moisture i n the s o i l i s  r e l a t i v e l y easy t o r e g u l a t e , naturally  affecting  e s p e c i a l l y when i t i s  i n short supply d u r i n g the growing season. A t -  mospheric humidity u s u a l l y  i s not important i f t h e amount  1 4 *•  m  of s o i l moisture i s p r o p e r l y a d j u s t e d .  The e f f e c t s o f  wind can be reduced by s h e l t e r i n g arrangements, adequate  although  s h e l t e r o f t e n i n v o l v e s the growing of wind  r e s i s t a n t p l a n t s where they w i l l p r o t e c t the more susc e p t i b l e ones.  L i g h t can be i n c r e a s e d o n l y w i t h some  d i f f i c u l t y , but i t i s e a s i l y reduced by shading measures. Temperature  is difficult  t o modify u n l e s s p l a n t s a r e grown  i n some type o f s t r u c t u r e . L i g h t i s not u s u a l l y a l i m i t i n g f a c t o r i n t h e growth o f ornamental woody p l a n t s , except i n s p e c i a l circumstances.  Temperature  remains the most c r i t i c a l and  the l e a s t e a s i l y m o d i f i e d environmental f a c t o r the growth o f woody  affecting  ornamentals.  W i t h i n t h e temperate  zones d i f f e r e n c e s i n w i n t e r  temperature between areas have a great i n f l u e n c e on the kinds of woody p l a n t s which can be grown s u c c e s s f u l l y . Although the extent o f winter i n j u r y i s o f t e n determined by many complex f a c t o r s , extremely c o l d temperatures i n severe winters a r e p r i m a r i l y r e s p o n s i b l e f o r the s e r i o u s economic l o s s e s which l i m i t the number of s p e c i e s o f ornamental woody p l a n t s i t i s p r a c t i c a l t o grow i n a specified  locality. A c l i m a t i c study o f an area such as B r i t i s h  Columbia where the topography  i s extremely v a r i e d and  i r r e g u l a r i n v o l v e s c e r t a i n problems which do not assume importance i n a study of a more g r a d u a l l y changing and  - 15 f a i r l y uniform  -  area l i k e the c o n t i n e n t a l p l a i n s .  Meteoro-  l o g i c a l s t a t i o n s are not r e p r e s e n t a t i v e o f areas between them when they mountains.  are separated  For t h i s reason,  by extensive ranges of broad zones i n r e s p e c t t o a  m e t e o r o l o g i c a l element such as temperature are to determine i n mountain r e g i o n s . meteorological  difficult  However, s i n c e the  s t a t i o n s u s u a l l y are l o c a t e d at lower  e l e v a t i o n s i n the g e n e r a l v i c i n i t y o f a g r i c u l t u r a l and  urban s e t t l e m e n t s , they may  lands  be q u i t e v a l u a b l e i n the  c l i m a t i c assessment of l i m i t e d areas around them.  Brink  (1950) d i s c u s s e s the l i t e r a t u r e d e a l i n g with mountain c l i m a t e s and the c a u t i o n which i s necessary r e l a t i n g t o mountainous  i n using  data  areas.  In view of the problems d i s c u s s e d above, the f o l l o w i n g approach was Low  adopted i n t h i s i n v e s t i g a t i o n :  w i n t e r temperature was  taken as the most  important  f a c t o r i n f l u e n c i n g the s e l e c t i o n o f ornamental  t r e e s and  shrubs f o r a l o c a l i t y , and  a recognized  p r e s s i o n of t h i s c l i m a t i c element was meteorological  s t a t i o n s of the  determined f o r most  province.  The l o c a l i t y surrounding s t a t i o n s was  ex-  one  or more meteorological  taken as the u n i t f o r i n v e s t i g a t i o n , and  meteorological  s t a t i o n was  L i t t l e attempt was  the  used as a r e f e r e n c e p o i n t .  made to i n d i c a t e r e l a t i o n s h i p s broader  than between d i f f e r e n t  localities.  . - 16 C e r t a i n methods were used to i n t e r p r e t the i n formation on low w i n t e r temperatures i n an o r i g i n a l  way.  These methods are the use of the w i n t e r r a t h e r than the calendar year as the u n i t i n c o n s i d e r i n g low temperature, the  a p p l i c a t i o n of s t a t i s t i c a l a n a l y s i s to express the  amount of v a r i a t i o n i n low temperature from one w i n t e r t o another, and the c o n v e r s i o n of s t a t i s t i c a l  estimates from  mathematical v a l u e s to convenient p r o b a b i l i t y e a s i l y understood by p r a c t i c a l workers without  ratios scientific  training* A survey was conducted t o o b t a i n an e s t i m a t e of the  i n j u r y t o ornamental t r e e s and shrubs f o l l o w i n g two  severe w i n t e r s .  The i n f o r m a t i o n o b t a i n e d was used t o  t e s t the u s e f u l n e s s o f low temperature data as a guide i n s e l e c t i n g woody ornamentals f o r h a r d i n e s s i n a  locality,  and t o get a c c u r a t e low temperature l i m i t s i n the P a c i f i c c o a s t a l r e g i o n f o r a number of ornamental  species*  Extreme Lowest Temperature Extreme lowest temperature o f the year The lowest recorded temperature d u r i n g a calendar year a t a p a r t i c u l a r m e t e o r o l o g i c a l s t a t i o n c a l l e d the annual minimum temperature by Baker  is  (1936).  Rehder (1940), u s i n g Baker's map o f average annual minimum temperature of the United S t a t e s as a b a s i s f o r h i s w i n t e r hardiness zone map,  f o l l o w s the nomenclature used by  - 17 Baker*  "Average annual minimum temperature" corresponds  t o what i s c a l l e d "annual averages o f extreme lowest temperature" by t h e Canadian M e t e o r o l o g i c a l S e r v i c e (1946). For t h e sake o f c l a r i t y t h e e x p r e s s i o n "extreme  lowest  temperature of the y e a r " i s used here i n s t e a d o f the exp r e s s i o n "annual minimum temperature". Rehder*s well-known w i n t e r h a r d i n e s s zones were to be determined f o r B r i t i s h Columbia it  l o c a l i t i e s , and i f  should prove f e a s i b l e , a map showing the d i s t r i b u t i o n  of these zones was to be c o n s t r u c t e d .  E x c e p t i n g some  long-term averages f o r the more important s t a t i o n s , the b a s i c data, averages o f extreme year, was not a v a i l a b l e .  lowest temperature of the  To get averages f o r a l l s t a t i o n s  i t was necessary t o search through m e t e o r o l o g i c a l  publi-  c a t i o n s f o r extreme  lowest temperatures f o r a ten-year  p e r i o d (1940-1949),  and t o average these r e a d i n g s .  Infor-  mation f o r the year 1940 was e x t r a c t e d from d a i l y minimum temperatures i n the Monthly Record of M e t e o r o l o g i c a l Observations (1940); f o r t h e years 1941-1948 from minimum temperatures i n the Climate of B r i t i s h (1941-1948);  monthly  Columbia  and f o r 1949 from monthly minimum temperatures  i n the Monthly Weather Map of the Dominion S e r v i c e (1949).  Meteorological  The i n f o r m a t i o n c o l l e c t e d and the averages  c a l c u l a t e d from these f i g u r e s have been compiled i n t o a t a b l e , which i s on f i l e a t the Department of H o r t i c u l t u r e , The U n i v e r s i t y of B r i t i s h Columbia.  F i g u r e s f o r the lowest  - 18 « temperatures recorded d u r i n g the r e c o r d c o l d s p e l l o f January, 1950, have been i n c l u d e d with the t a b l e f o r purposes of comparison* Average readings f o r the d i f f e r e n t  stations,  with the number o f years f o r which f i g u r e s were a v a i l a b l e d u r i n g the p e r i o d , are given i n Table 1. are a l s o shown on a map with the Appendix* i n f o r m a t i o n was  These averages  o f B r i t i s h Columbia  included  F i g u r e s f o r those s t a t i o n s f o r which  hot a v a i l a b l e f o r t e n c o n s e c u t i v e years  are c i r c l e d on the map,  s i n c e averages f o r s h o r t e r p e r i o d s  would not be r e l i a b l e i n making comparisons between averages o f neighbouring s t a t i o n s .  Averages covering  short  p e r i o d s were i n c l u d e d with the t a b l e s i n order t o g i v e a rough estimate f o r s t a t i o n s from which no i n f o r m a t i o n could otherwise be i n c l u d e d .  Long-term averages f o r some  s t a t i o n s were found i n the Canadian M e t e o r o l o g i c a l S e r v i c e Summary (1946), are given i n Table 1 as f i g u r e s i n b r a c k e t s a f t e r the name of the s t a t i o n .  The long-term averages are  g e n e r a l l y somewhat lower than the averages f o r the t e n year p e r i o d 1940-1949. A d e f i n i t e p a t t e r n i s evident i n the extreme  low-  est temperature of lowland s t a t i o n s i n the c o a s t a l r e g i o n . S t a t i o n s c l o s e to the open P a c i f i c on Vancouver  Island  and  the Queen C h a r l o t t e s have the highest averages, over 20°F. On e a s t e r n Vancouver I s l a n d averages range from over 20° i n the south around V i c t o r i a t o l e s s than 15° i n the middle part  19 TABLE 1 Ten Year Averages of Extreme Lowest Temperatures of t h e Year at B r i t i s h Columbia M e t e o r o l o g i c a l S t a t i o n s f o r the P e r i o d 1940-1949. Long Term Averages are g i v e n i n b r a c k e t s a f t e r names of S t a t i o n s f o r which they are a v a i l a b l e , (Degrees F a h r e n h e i t ) , STATION  YRS.  AV.  STATION  Abbotsford  10  11  Clayoquot  Agassis  10  14  Comox (A)  Creek) 10  11  Coquitlam  10  13  Cowichan  20  Cowichan Lake  A l b e r n i (Beaver A l b e r n i , Port Alliford  Bay  4  Armstrong  Atlin  (-38)  Baldonnel (-26)  B e l l a Coola  (1)  Lake Bay  25  5  13  10  14  10  19  8  16  10  -35  3  -18  Cranbrook (A) (-28)10  -23  6  -34  Crescent V a l l e y  10  -8  -39  Creston  10  -5  -28  Cultus Lake  4  12  Cumberland  9  11  9  1  10  Lake  9  Cranberry  10  Barkervillo  (21)  -14  10  Ashcroft  YRS. AV,  Big Creek  9  -30  Departure Bay  10  Blue R i v e r  3  -31  Dome Creek  10  -13  Dominion Observatory  10  21  Duncan  10  10  10  23  Fauquier  10  -2  Fernie  10  Bralorne  10  B r i t a n n i a Beach  10  18  B u l l Harbour  10  22  Cape S t . James  3  Carmi  0  -13  Chinook Cove  7  -16  Chute Lake  4  -23  20  Estevan  Finlay  Point  Forks  F o r t S t . James  3 10  21 -30  -21 -54 -32  - 20 * TABLE I - Cont. Yrs • Av.  STATION  Y r s . Av.  STATION  F t . S t . John (A) (-38)  9  -42  Ganges  S  19  Masset  Gerrard  9  -7  Merritt  10  -16  10  10  -23  10  15  10  -13  M i l l Bay (Nass R.)  9  4  -27  M i s s i o n Creek  6  -14  10  -14  Mission  8  10  -16  Nanaimo  4  14  Nelson  Hedley  10  -6  Newgate  Hedley (N.P.M.)  10  -17  9  7  10  11  7  -25  James I s l a n d  10  Jordan R i v e r  Glacier  (-19)  Golden Grand Forks  (-17)  Greenwood Haney  Hope ( L i t t l e Mt.)  McCulloch (14)  Flats  mm ()  10  16  10  3  8  *23  New H a z e l t o n (-29) 10  -24  (-4)  New Westminster  10  14  Ocean F a l l s  10  15  Okanagan Centre  10  3  22  Oliver  10  -3  5  21  Osprey Lake  10  -22  10  -8  Pachena  9  22  Kaslo.  10  0  7  17  Kelowna  10  -1  Pemberton  10  -8  Keremeos  10  -2  Penticton  10  -3  Kimberley  5  -21  Port Hardy (A)  5  19  Kleena Kleene  7  -34  Powell R i v e r  10  23  Langara  7  20  Premier  9  -2  10  -2  P r i n c e t o n (A)(-26) 10  -17  8  -27  P r i n c e George  -25  Hope (A) Invermere  Kamloops  Lytton McBride  (-13)  Point  P a t r i c i a Bay Meadows (-2)  (-40) 5  - 21 TABLE I - Cont Y r s . Av.  STATION  STATION  Y r s . Av. 8  -4  Tatlayoko Lake  10  -19  Telkwa  10  -20  -22  Terrace  10  ->2  10  -11  Ucluelet  Rock Creek  8  -13  Ucluelet  Rossland  9  •2  Vananda  Salmon Arm  10  -5  Vancouver  Shawnigan Lake  10  14  Vancouver (A)  10  Sidney  10  21  Vavenby  10  -20  9  -19  Vernon  10  -4  10  -24  6  Vernon(Coldstream)  9  -6  -25  Sooke  8  10  19  23  South S l o c a n  Warfield  (Trail)10  2  9  -6  Stave F a l l s  Westwold  14  9  -18  9  Steveston  10  9  15  3 10  7  -18  -5  10  2  10  -24  P r i n c e George (A)  7  *36  P r i n c e Rupert (11)  10  13  Quatsino  10  20  Quesnel  10  Revelstoke  Sinclair  (- 14)  Pass  Smithers Smithers  (A)  Stewart Summerland  (-6)  Tappen  3  20"  4  22  10  18  5  16  (A)  (13)  (-30)  Victoria  (20)  White Rock W i l l i a m s Lake Wistaria  14"  at Comox* There i s a g r a d u a l decrease on the Lower Mainland from over 15° near the G u l f of Georgia t o l e s s than 10° at Hope.  .- .  - 22 In the i n t e r i o r of B r i t i s h Columbia the  irregular  mountainous topography causes abrupt d i f f e r e n c e s i n averages of d i f f e r e n t s t a t i o n s *  Near the Okanagan, Arrow, and  Kootenay Lakes at low a l t i t u d e s , however, the averages are a l l near 0 ° .  In c e n t r a l B r i t i s h Columbia the a t a t i o n s  represented have averages below -25°F. A map  showing  the approximate l o c a t i o n of low  temperature zones i n the s e t t l e d p a r t of the c o a s t a l r e g i o n was  drawn up*  The areas r e p r e s e n t e d i n the f o u r zones are  roughly those areas i n which a r a b l e l a n d i s found a c c o r d ing to B r i n k and F a r s t a d (1949)*  The average extreme  temperature of the year f o r the m e t e o r o l o g i c a l w i t h i n these areas was  lowest  stations  used as the c h i e f b a s i s f o r the zones.  Each zone i n c l u d e s s t a t i o n s w i t h averages w i t h i n a 5° range; f o r example, 5° t o 10°.  This map  ( F i g u r e 4) f o l l o w s the  account of the w i n t e r i n j u r y survey. The soundness  of u s i n g a t e n year p e r i o d to get  a r e p r e s e n t a t i v e average of a c l i m a t i c element such as temperature i s not now  disputed*  The t e n year p e r i o d i s  widely used i n c l i m a t o l o g i c a l work, s i n c e a l o n g e r p e r i o d u s u a l l y i n v o l v e s an a p p r e c i a b l e amount o f c l i m a t i c  change.  Extreme lowest temperature of the w i n t e r For p r a c t i c a l purposes the extreme  lowest tem-  perature taken f o r each c a l e n d a r y e a r p r o v i d e s a s a t i s f a c t o r y b a s i s f o r the c a l c u l a t i o n of averages*  However,  t h i s b a s i s would not be s a t i s f a c t o r y f b r a study o f v a r i a t i o n  - 23 i n low temperature  between d i f f e r e n t w i n t e r s .  The  reason  f o r the e r r o r i s t h a t the calendar year s p l i t s the winter i n t o two  h a l v e s , so t h a t any w i n t e r may  twice or not a t a l l i n the d a t a .  be  represented  Since a measure of the  a c t u a l v a r i a t i o n from w i n t e r to w i n t e r was  required i n  order to get a s t a t i s t i c a l estimate of extreme lowest temperatures f o r important below),  stations i n B r i t i s h  Columbia  (see  data which would r e p r e s e n t each winter as a u n i t  had t o be o b t a i n e d . F i g u r e s f o r extreme lowest temperature  of the  winter at s e l e c t e d B. C. m e t e o r o l o g i c a l s t a t i o n s f o r the t e n - w i n t e r - p e r i o d from 1940-41 t o 1949-50 were Sources  of i n f o r m a t i o n were the same as f o r f i g u r e s  on the calendar y e a r .  A table giving this  i n Appendix 1.  based  Averages were c a l c u l a t e d f o r those  s t a t i o n s from which i n f o r m a t i o n was winters.  compiled.  Incomplete  available for the  compiled  ten  i n f o r m a t i o n i s found  s e r i e s of f i g u r e s are i n c l u d e d  with the t a b l e . S i n c e the r e c o r d low temperatures s p e l l of January,  1950,  cold  are i n c l u d e d i n the f i g u r e s  on the w i n t e r , but not i n those based averages  of t h e  on the year, the  from the former f i g u r e s are s l i g h t l y lower  those from the l a t t e r  than  figures.  A n a l y s i s of extreme lowest temperature The  based  a c t u a l v a r i a t i o n s i n extreme lowest  variations tempera-  t u r e from winter to w i n t e r can be r e p r e s e n t e d by means of  - 24 simple bar The  graphs, examples of which are seen i n F i g u r e  average f o r t e n winters i s used as the base, and  1.  the  d e v i a t i o n of the minimum temperatures from t h i s mean i s shown by a darkened column above or below the l i n e of mean, the l e n g t h of the the d e v i a t i o n .  column depending on the  s i z e of  Since the mean i s shown i n r e l a t i o n to  temperature s c a l e , comparison of the stations reveals  d i f f e r e n c e s i n the  the amount of v a r i a t i o n .  average as w e l l as i n  Although such graphs convey a  i n making q u a n t i t a t i v e p r e d i c t i o n s .  The  only  t a t i v e g e n e r a l i z a t i o n t o be made i s the g r e a t e s t the d e v i a t i o n s . was  spread at Vancouver during  little quanti-  spread of the  period  21°; at Summerland i t was 32°; at Quesnel 44°•  Differences this  The  the  graphs f o r d i f f e r e n t  c l e a r p i c t u r e of the a c t u a l v a r i a t i o n , they are of use  the  i n the amount of v a r i a t i o n are i n d i c a t e d  information,  but  a s a t i s f a c t o r y method of  by  approxi-  mating these d i f f e r e n c e s i s n e c e s s a r y . S t a t i s t i c a l a n a l y s i s p r o v i d e s the method which i s required.  A c a l c u l a t i o n of the  though expressing  standard  no a c t u a l d i f f e r e n c e s , c o n s t i t u t e s a  r e l i a b l e s t a t i s t i c a l measure of the The  amount of v a r i a t i o n .  probable s i z e of f u t u r e d e v i a t i o n s  d i c t e d from the matical  deviation,  can be r e a d i l y p r e -  standard d e v i a t i o n by the use  of mathe-  tables. Standard d e v i a t i o n from the average extreme  lowest temperature of the winter was  calculated for  ^1  302010o-  °F  :  30-  10-  °r  LILB  i n  VANCOUVER  M=IZ.8'F  (AIRPORT)  COWICHAN BAY M = na°f  100-  -10-  -10-  -20-  -20-30-  -30-  -40-  -HO~  -50-  -50SuHNERLftND  °F  QuESNEL  M^o.l'f  M = -24°f  °F  Figure 1. V a r i a t i o n i n extreme lowest temperature o f the winter during the t e n winter period from 1940-41 t o 1949-50 a t f o u r B r i t i s h Columbia meteorological s t a t i o n s . (to follow page 24)  s e l e c t e d B. C. m e t e o r o l o g i c a l  s t a t i o n s from which f i g u r e s  were a v a i l a b l e f o r the  ten w i n t e r s .  were made with the use  of the  Standard  following  deviation  formula:  n - 1  V  S S  Machine c a l c u l a t i o n s  =  x* „  (£*) n  where S S  =  the  sum  of the  S  s  the  sum  of  x  =  any  variate  and e.g.  n  2  squares..  r=. • the t o t a l number of v a r i a t e s .  Abbotsford. S S s  2 x*  _  r  Clx  )  2  n *  S t . dev. The  mean and  i s g i v e n i n Table I I . s t a t i o n s was interior  =  95  \/  - 20|i  2  6  *%*  ?  =  6  8  0  #  5  75.6  =8.7  standard d e v i a t i o n of each s t a t i o n The  standard d e v i a t i o n f o r  found t o be a p p r e c i a b l y  s t a t i o n s which are not  i n f l u e n c e of bodies of water.  smaller  where the winters are more severe g e n e r a l l y amount of v a r i a t i o n i n the  than that  a f f e c t e d by the I t i s evident  coastal of  moderating  that have a  areas greater  extreme lowest temperature  of  - 26  -  the winter than areas where the winters are more m i l d * gradual i n c r e a s e i n the standard  d e v i a t i o n as the average  extreme lowest temperature decreases  i s shown i n F i g u r e  which i l l u s t r a t e s g r a p h i c a l l y the mean and d e v i a t i o n f o r t e n s e l e c t e d 8*  C.  The  2,  standard  stations*  On t h e o r e t i c a l grounds a c a l c u l a t i o n of the standard d e v i a t i o n i s considered r e l i a b l e i f based on a random sample of s u f f i c i e n t numbers from a p o p u l a t i o n or group which i s normally d i s t r i b u t e d *  The t e n winter  series  here taken at random, though small i n numbers, i s s i m i l a r to the t e n year p e r i o d s from which s t a t i s t i c  estimates  of  v a r i o u s elements are made i n c l i m a t o l o g y (Conrad, 1948). There i s , however, some evidence extreme lowest  t h a t the d i s t r i b u t i o n of  temperatures i s not completely  normal.  In  r e g i o n s with a c l i m a t e s i m i l a r to that of Western Europe there i s some skewing t o the l e f t , extremely  caused by o c c a s i o n a l  c o l d p e r i o d s which are the r e s u l t of a p a r t i c u l a r  combination  of weather c o n d i t i o n s .  These c o n d i t i o n s are  a r c t i c a i r p e n e t r a t i o n s a s s o c i a t e d with c l e a r s k i e s and e f f e c t i v e snow cover*  C l e a r s k i e s and  an  a snow cover i n t e n -  s i f y the c o l d p e r i o d s i n i t i a t e d by a r c t i c a i r p e n e t r a t i o n s , causing phenomenally low temperatures w e l l out of the normal range to occur* d u r i n g the cold  These c o n d i t i o n s p r e v a i l e d at Vancouver s p e l l i n January, 1950*  Despite the f a c t t h a t the d i s t r i b u t i o n of extreme lowest  temperatures over a p e r i o d of winters  i s not q u i t e  F i g u r e 2. S t a t i s t i c a l e x p r e s s i o n o f extreme lowest temperature o f the w i n t e r a t t e n B r i t i s h Columbia meteorological stations. The b a r r e p r e s e n t s two standard d e v i a t i o n s , one above, and one below the mean. ( t o  f o l l o w  page 2 6 )  normal, c a l c u l a t i o n s r e l a t i n g t o the c e n t r a l p a r t s of the curve are expected t o be r e l i a b l e enough f o r p r a c t i c a l purposes. The n i n e t y percent p o i n t A p p l i c a t i o n o f s t a t i s t i c a l methods i n a n a l y s i s of  temperature data permits an approximation o f the r e l a t i o n  of the mean (or average) t o the range o f d e v i a t i o n s on which i t i s based.  The standard d e v i a t i o n o f t h e  extreme  lowest temperature of the w i n t e r i s a r e l i a b l e index o f the  amount o f v a r i a t i o n from the mean t o be expected.  Consequently, i f the mean and standard d e v i a t i o n are known, the at  p r o b a b i l i t y o f any p a r t i c u l a r low temperature o c c u r r i n g a s t a t i o n can be found by u s i n g s t a t i s t i c a l  tables.  However, t h i s t e c h n i c a l approach would confuse the  nurseryman  or p r a c t i c a l gardener who  with s t a t i s t i c a l  concepts.  i s not f a m i l i a r  In a d d i t i o n , t h e r e i s a d i s -  advantage i n f i n d i n g the p r o b a b i l i t y of a given temperature r a t h e r than s e l e c t i n g a p r o b a b i l i t y and c a l c u l a t i n g the temperature corresponding to i t ; i f a s e l e c t e d  probability  i s employed, comparable temperature i n f o r m a t i o n can be c a l c u l a t e d f o r a l l the s t a t i o n s b e i n g s t u d i e d .  A proba-  b i l i t y which i s convenient f o r studying the problem o f s e l e c t i n g woody ornamentals would be the one chosen. simple method o f e x p r e s s i n g the s t a t i s t i c a l  i n f o r m a t i o n as  a p r o b a b i l i t y a p p r o p r i a t e f o r the a p p l i c a t i o n was For  A  desired.  these reasons a concept known as the n i n e t y  -28 percent p o i n t was f o r m u l a t e d . that temperature will fall  The n i n e t y percent p o i n t i s  above which the extreme lowest  temperature  i n approximately nine out o f t e n w i n t e r s , and  below which the extreme lowest temperature  will fall in  approximately one out o f t e n w i n t e r s , a c c o r d i n g t o mathematical  expectancy  based  on s t a t i s t i c a l a n a l y s i s of  temperatures  observed over a p e r i o d of w i n t e r s .  A one t o nine r a t i o was chosen because  satis-  f a c t o r y s u r v i v a l i n nine out o f t e n winters i s a reasonable l e v e l of success f o r woody ornamental  plants.  Many of the  most b e a u t i f u l shrubs a r e on the b o r d e r l i n e o f h a r d i n e s s for  most B r i t i s h Columbia l o c a l i t i e s ; an e n t h u s i a s t i c  gardener would be s a t i s f i e d with a one t o nine r i s k i n any p a r t i c u l a r winter.  Species which are not i n j u r e d a t the  n i n e t y percent p o i n t f o r a l o c a l i t y a r e expected  t o remain  unharmed i n nine out of t e n w i n t e r s when p l a n t e d with due regard f o r h o r t i c u l t u r a l requirements.  When f u l l y  t r e e s or shrubs are d e s i r e d , s p e c i e s with low  hardy  temperature  l i m i t s w e l l above the n i n e t y percent p o i n t should be selected. The n i n e t y percent p o i n t i s o f f e r e d as a p r a c t i c a l and of  convenient method of p r o v i d i n g a r e l i a b l e e x p r e s s i o n t h e low temperatures  place.  to be expected a t a p a r t i c u l a r  Whenever the approximate low temperature  l i m i t of  a p l a n t s p e c i e s i s known, a knowledge of the n i n e t y percent p o i n t o f the l o c a l i t y w i l l be u s e f u l i n e s t i m a t i n g the  F i g u r e 3» Normal frequency d i s t r i b u t i o n curve showing approximate p r o p o r t i o n s d i v i d e d by the n i n e t y percent p o i n t .  (to  f o l l o w page  28)  -  29  -  r i s k i n v o l v e d i n growing the p l a n t * A method of c o n v e r t i n g i n f o r m a t i o n i n terms of standard d e v i a t i o n t o i n f o r m a t i o n i n terms of the n i n e t y percent p o i n t was  developed*  The  n i n e t y percent p o i n t i s  found by s u b t r a c t i n g the standard d e v i a t i o n m u l t i p l i e d 1*3  by  from the average extreme lowest temperature of the  winter*  The  f a c t o r 1*3  i s based on a c a l c u l a t i o n of the  d e v i a t i o n which d i v i d e s a s e r i e s so t h a t g r e a t e r d e v i a t i o n s w i l l represent twenty percent of the t o t a l number of o b s e r v a t i o n s ( i . e . ten percent  i n each of the  According to a t a b l e given by Simpson and Eoe d e v i a t i o n of approximately  1.3  times the  tails)* (1939), a  standard  d e v i a t i o n d i v i d e s a normally d i s t r i b u t e d s e r i e s i n the above p r o p o r t i o n . rearranged  Part of t h i s t a b l e i s g i v e n below i n  form: Areas of the normal curve % area o u t s i d e  % area i n s i d e  deviation st.  23  17  19  81  For p r a c t i c a l purposes the f a c t o r 1.3 accurate t o correspond  dev.  1.10 1.30  is sufficiently  to the v a l u e where twenty percent  of the area i f o u t s i d e the l i m i t s .  The  d i v i s i o n of the  normal curve at the n i n e t y percent p o i n t i s shown by a diagram i n F i g u r e  3«  The f o l l o w i n g example i n d i c a t e s how  the n i n e t y  - 30 percent p o i n t i s c a l c u l a t e d : Abbotsford,  B. C.  Mean S t . dev.  90$ p o i n t  = =  9.5°F.  8.7  Mean - (1.3 x S t . dev.)  =  =  9.5° - (1.3 x 8.7)  =  9.5 - 11.3  =  - 0.8° F.  The n i n e t y percent  p o i n t f o r extreme lowest  temperature of t h e winter was c a l c u l a t e d f o r s e l e c t e d B. C. meteorological stations.  The mean, standard d e v i a t i o n ,  and n i n e t y percent p o i n t f o r each s t a t i o n i s found i n Table I I . TABLE I I . A n a l y s i s o f Low Temperature Data. Average extreme lowest temperature of the winter f o r the t e n w i n t e r p e r i o d from 1940-41 t o 1949-50, standard d e v i a t i o n , and n i n e t y percent p o i n t f o r s e l e c t e d B. C. M e t e o r o l o g i c a l Stations. Station  Mean  Abbotsford  9.5  Agassiz  13.2  A l b e r n i (Beaver A l b e r n i , Port Armstrong Bella  8.0 10.5 -17.9  Coola  Coquitlam  Greek)  Lake  Cowichan Bay Cranbrook (A)  0.3 12.4 17.8 -24.0  S t . Dev. 8.7  90$ P o i n t -1.8  10.5  -0.4  10.4  -5.5  8.3  -0.3  14.2  -36.4  10.4  -10.5  10.0  -0.6  6.3 14.9  9.6 -43.4  31 TABLE I I - Cont.  Station  Mean  S t . Dev.  9 0 % Point  Creston  -6.2  9.0  -17.8  Duncan  10.2  7.5  f  Fernie  -22.2  10.2  -35.5  Golden  -28.3  10.5  -42.0  Grand Forks  -16.0  10.0  -29.0  6.8  10.7  - 7.1  James I s l a n d  21.1  8.0  .•10.7  Kamloops  -11.0  14.2  -29.5  Kelowna  - 1.6  12.8  -18.2  Lytton  - 4.3  10.3  -17.7  McBride  -25.4  12.6  -41.8  14.9  7.9  Merritt  -17.7  14.6  -36.7  Nanaimo  14*8  6.7  6.1  New  12.0  8.1  1.5  16.3  9.7  3.7  Hope  Masset  Westminster  Ocean F a l l s  . f  0.4  4.6  Okanagan Centre  f  0.5  12.1  -15.2  Oliver  -  5.0  11.8  -20.3  0.4  9.3  -11.7  P r i n c e t o n (A)  -19.3  11.7  -34.5  P r i n c e Rupert  13.4  9.8  -24.8  15.1  Penticton  Quesnel  •  0.7  -44.4  -  -  32  TABLE I I - Cont.  Station  Mean  S t . Dev.  9 0 $ Point  Revelstoke  -11.8  10.3  -25.2  Salmon Arm  -  12.9  -24.4  20.0  7.2  10.6  0.1  11.0  -14.2  -3.9  10.4  -17.4  12.8  7.9  Vernon  -6.7  12.5  Victoria  21.2  8.8  9.8  White Rock  13.9  7.8  3.5  Sidney Summerland Terrace Vancouver  (A)  7.6  f  2.5  -23.0  The Winter injury Survey Purpose of the survey Low temperature  In? severe w i n t e r s had been s e l e c t e d  as the c h i e f f a c t o r l i m i t i n g the number of s p e c i e s o f ornamental woody p l a n t s which may  be grown i n a l o c a l i t y ,  and the degree of low temperature i n d i f f e r e n t had been a s c e r t a i n e d by c e r t a i n methods.  localities  In o r d e r t o  t e s t the value of t h i s c l i m a t i c data as a guide i n the s e l e c t i o n of plants f o r d i f f e r e n t  localities,  information  on i n j u r y t o ornamentals f o l l o w i n g severe w i n t e r s was needed.  This i n f o r m a t i o n could a l s o be used t o get  accurate low temperature l i m i t s i n the P a c i f i c  coastal  - 33 r e g i o n f o r a number of important  s p e c i e s o f ornamental  t r e e s and shrubs* The l a s t two winters were w e l l s u i t e d t o a survey of  Winter i n j u r y .  The Winter o f 1948-49 was the c o l d e s t  in  s i x years i n most p a r t s of t h e P r o v i n c e , and t h e Winter  of  1949-50 was the c o l d e s t on r e c o r d i n Western Canada.  Consequently, t h e r e was a good o p p o r t u n i t y t o check t h e hardiness o f those t r e e s and shrubs which were expected t o be badly i n j u r e d or k i l l e d i n severe w i n t e r s , as w e l l as those which are o n l y s l i g h t l y tender  i n some a r e a s .  D e s c r i p t i o n o f methods The formal winter i n j u r y survey was preceded by preliminary l e t t e r s to D i s t r i c t  H o r t i c u l t u r i s t s and t h e  p r i n c i p a l n u r s e r i e s of the p r o v i n c e .  R e p l i e s t o these  letters indicated sufficient interest  i n the s u b j e c t o f  winter i n j u r y t o ornamental p l a n t s to j u s t i f y c o m p i l i n g a form which would f a c i l i t a t e r e p l i e s and the subsequent analysis of information received. A list by choosing  o f one hundred and f o u r s p e c i e s was  compiled  from Rehder's Manual (1940) t h e more common  s p e c i e s of ornamental t r e e s and shrubs l i k e l y t o be i n j u r e d during severe winters i n the s e t t l e d areas o f B r i t i s h Columbia.  Almost a l l of these s p e c i e s a r e i n Zone V, VI  or V I I a c c o r d i n g to Rehder's w i n t e r hardiness The in  classification.  zone number, s c i e n t i f i c name and common name were g i v e n the l i s t .  Columns were p r o v i d e d f o r i n f o r m a t i o n on t h e  number of years p l a n t e d , damage a f t e r the winter o f 1948-  49 and a f t e r the winter o f 1949-50, and other remarks. The  system o f symbols used by the Royal  Horticultural  S o c i e t y (1948) was used t o i n d i c a t e t h e amount of i n j u r y . A form l e t t e r e x p l a i n i n g t h e reason f o r the survey was enclosed with each l i s t  sent o u t .  i n c l u d e d on the survey i s found  A list  o f the s p e c i e s  i n Appendix I I .  Survey forms were sent t o s i x t y - f i v e addresses i n B r i t i s h Columbia, i n c l u d i n g the Dominion  Experimental  Farms and S t a t i o n s , the D i s t r i c t H o r t i c u l t u r i s t s , and most of  the n u r s e r i e s .  In order t o cover s e t t l e d  localities  which were not represented by t h e above addresses, a number o f forms were sent t o f l o r i s t s , gardeners;  growers, and amateur  o r i f no i n f o r m a t i o n as t o a s u i t a b l e  was a v a i l a b l e , the form was addressed  recipient  t o the l o c a l  post-  master. The  i n f o r m a t i o n r e c e i v e d i n r e p l y was t r a n s f e r r e d  to  a master form.  in  g e o g r a p h i c a l order and the s p e c i e s i n the order  appear on the l i s t .  The master form l i s t e d the l o c a l i t i e s they  T h i s method of compiling the data  allowed comparisons of the behaviour  o f any s p e c i e s i n  d i f f e r e n t l o c a l i t i e s t o be made a t a g l a n c e . Result s Twenty-five  winter i n j u r y survey forms were r e -  turned with the requested  information f i l l e d  forms were r e t u r n e d with no i n f o r m a t i o n .  The  in.  A few  response  - 35 v a r i e d c h i e f l y a c c o r d i n g t o the p a r t of the p r o v i n c e which the r e p l y came.  R e p l i e s from the i n t e r i o r  were l e s s complete than those s i n c e the m a j o r i t y of the  u s u a l l y grown i n the i n t e r i o r .  the i n t e r e s t s and  districts  from c o a s t a l d i s t r i c t s ,  s p e c i e s on the l i s t  r e p l y a l s o depended on how  from  The  are  not  thoroughness of the  c l o s e to the s u b j e c t of  t r a i n i n g of the r e c i p i e n t were.  study Keen  amateurs gave the most adequate i n f o r m a t i o n on l e s s common ornamentals.  Experimental  p l a n t i n g dates  Farms were able to g i v e  of mature specimens.  accurate  Nurserymen p r o v i d e d  i n f o r m a t i o n on comparative damage to a number of  species  grown under s i m i l a r c o n d i t i o n s i n the same l o c a t i o n . D e t a i l s o f i n j u r y a f t e r the winter cluded  i n some of the  of  1948-49  were i n -  replies.  A comprehensive r e p o r t on the i n f o r m a t i o n accumulated by means of the winter i n j u r y survey t h i s i n v e s t i g a t i o n . The pected  i s beyond the scope of  f i n d i n g s of the survey are  ex-  to be v a l u a b l e f o r f u t u r e r e f e r e n c e , s i n c e the i n -  formation  c o n s t i t u t e s the beginning  of a permanent r e c o r d  of the behaviour of ornamental species i n severe i n B r i t i s h Columbia. survey forms, and  The  l e t t e r s of r e p l y , r e t u r n e d  the master form have been f i l e d at the  Department of H o r t i c u l t u r e , The Columbia.  U n i v e r s i t y of  British  Examples of the r e p o r t s which were used as  b a s i s of the c o n c l u s i o n s are presented The  winters  extent  the  below.  of i n j u r y to woody ornamental p l a n t s  - 36 i n d i f f e r e n t l o c a l i t i e s of B r i t i s h Columbia winter of 1949-50 was lowest temperatures  a f t e r the  r e l a t e d more or l e s s c l o s e l y to the  recorded d u r i n g the winter a t the  nearest m e t e o r o l o g i c a l s t a t i o n s .  I n j u r y t o some s p e c i e s  corresponded c l o s e l y with the low temperatures p l a n t s had been s u b j e c t e d .  to which the  I n j u r y to other s p e c i e s d i d  not appear t o be c o r r e l a t e d with low temperature  except  over a wide range. For example, Cedrus a t l a n t i c a was  r e p o r t e d un-  i n j u r e d at Sidney (S°F.), s l i g h t l y i n j u r e d a t New  Westminster  (-1°), and k i l l e d a t Nelson (-16°)j W i s t a r i a s i n e n s i s  was  r e p o r t e d u n i n j u r e d a t Hope (-11°), s l i g h t l y i n j u r e d at Keremeos (-23°) and b a d l y i n j u r e d a t Vernon (-31°). other hand. Cryptomeria .laponica was  On the  r e p o r t e d u n i n j u r e d at  Port A l b e r n i (-7°), s l i g h t l y i n j u r e d at V i c t o r i a (6°), and s l i g h t l y to badly i n j u r e d at Vancouver (0°); Mahonia a q u i f o l i u m was  r e p o r t e d s l i g h t l y i n j u r e d at V i c t o r i a (6°),  u n i n j u r e d a t Hope (-11°), and s l i g h t l y i n j u r e d at Keremeos (-23°)•  The above temperatures  are the lowest recorded  during the w i n t e r of 1949-50. The amount of i n j u r y to low-growing  shrubs depended  on the depth of snow around the p l a n t s d u r i n g the c o l d weather.  At Vancouver the l e a v e s of Cotoneaster m i c r o p h y l l a  were burned where they were exposed, touched where the snow covered them. leaved evergreens was  but completely un- > Most i n j u r y to broad-  d i r e c t l y r e l a t e d t o the amount of  - 37 exposure t o the b r i g h t sun d u r i n g t h e c o l d weather* the coast^ Prunus Laurocerasus.  At  Prunus l u s i t a n i c a .  Camellia j a p o n i c a and many other s p e c i e s o f t e n showed severe  s c o r c h i n g on the sunny s i d e of the p l a n t , but no  damage on the shaded p a r t s *  I n j u r y t o c o n i f e r s , on the  other hand, was w i d e l y d i s t r i b u t e d over the p l a n t , o r concentrated  on t h e s i d e exposed t o wind*  to exposure t o wind was evident  Injury related  i n l a r g e specimens o f  Cryptomeria .japonica and Sequoiadendron giganteum at Vancouver. Conclusions The  general extent  of i n j u r y i n c e r t a i n l o c a l i t i e s  was g r e a t e r -than the extreme lowest winter,  temperature of t h e  compared with t h a t of other l o c a l i t i e s ,  indicate.  V i c t o r i a with  6° F., Vancouver w i t h 0°, and Port  A l b e r n i with -7° a l l r e c e i v e d approximately amount of damage*  would  t h e same  Along the east coast of Vancouver  I s l a n d , although  temperatures lower than a t V i c t o r i a were  recorded,  g e n e r a l i n j u r y was n o t i c e a b l e .  little  Modifying  f a c t o r s such as exposure t o wind, amount of sunshine d u r i n g the c o l d weather, and depth of the snow cover are judged r e s p o n s i b l e .  In the i n t e r i o r of B r i t i s h  Columbia  somewhat lower temperatures than those a t the coast were r e q u i r e d i n producing  s i m i l a r i n j u r y f o r the same s p e c i e s .  An approximate estimate  o f the low temperature  l i m i t s was made f o r f i f t y - s i x s p e c i e s of ornamental t r e e s  38 and  shrubs i n the P a c i f i c c o a s t a l area*  numerous d i s c r e p a n c i e s a r e evident  Even though  i n the i n f o r m a t i o n  provided by t h i s survey, a g e n e r a l c o n c l u s i o n as t o the approximate temperature at which a p l a n t i s reasonably safe from damage can be made.  T h i s was done by comparing  r e p o r t s of i n j u r y t o each s p e c i e s with the lowest peratures recorded a t the corresponding  stations.  temThe low  temperature l i m i t s determined a r e given with the l i s t o f s p e c i e s i n Appendix I I .  F i g u r e 4. Approximate low temperature zones i n the s e t t l e d c o a s t a l r e g i o n , based on average extreme lowest temperature (ten-year p e r i o d 1940-49); areas zoned a r e a r a b l e lands as d e f i n e d by B r i n k and F a r s t a d .  -  39  -  DISCUSSION D i s c u s s i o n s o f the d i f f e r e n t methods which were employed have been given with the e x p l a n a t i o n s o f the methods*  For t h i s s e c t i o n t h e r e remains a g e n e r a l  discussion of conclusions* C e r t a i n m o d i f i c a t i o n s should be made i n Rehder's system of winter hardiness applied i n B r i t i s h  zones when t h i s  Columbia.  According  system i s  to the f i g u r e s  c a l c u l a t e d here, averages o f extreme lowest  temperature  of the year f o r s t a t i o n s i n the c o a s t a l area o f B. C. (see F i g u r e 4) a r e above the range given f o r Zone V I I by Rehder. and  Yet i n f o r m a t i o n from the winter i n j u r y  survey  g e n e r a l o b s e r v a t i o n s i n d i c a t e t h a t most s p e c i e s  listed  as Zone VI or V I I by Rehder are not f u l l y hardy i n t h i s area.  One way of overcoming the d i f f i c u l t y would be to  a l t e r the s c a l e used by Rehder; l o c a l i t i e s with extreme o lowest  temperature averages above 20 F. would be i n c l u d e d  i n Zone V I I and those with averages between 10° and 20° i n Zone VI. percent  Another method would be t o use t h e n i n e t y  p o i n t of a s t a t i o n , i n s t e a d o f averages, t o  correspond  with averages g i v e n i n t h e s c a l e used by Rehder. In a d d i t i o n t o m o d i f i c a t i o n s i n t h e s c a l e f o r  the zones, however, m o d i f i c a t i o n s a r e necessary the hardiness The  i n many of  zone r a t i n g s assigned t o s p e c i e s by Rehder.  necessary m o d i f i c a t i o n s could be made by checking t h e  zones assigned by Rehder with the i n f o r m a t i o n on low  -  40 -  temperature l i m i t s of s p e c i e s i n the P a c i f i c  coastal region  as g i v e n i n Appendix I I . Low temperature zones i n B r i t i s h Columbia  and  low temperature l i m i t s f o r s p e c i e s i n t h i s area a r e not s t a t e d here i n terms of Rehder's  zones because t h i s  infor-  mation i s c o n s i d e r e d more Valuable i f expressed i n terms of temperature.  C a u t i o n was  found necessary s i n c e  system d i d not f i t i n t o the p a t t e r n i n B r i t i s h  Rehder's  Columbia.  I f temperature i n f o r m a t i o n f o r B. C. were s t a t e d i n the symbols  o f Rehder's  system, the accuracy of some, o f the  i n f o r m a t i o n would be l o s t , owing t o the i m p e r f e c t i o n s of that system when a p p l i e d to  B.C.  The u t i l i t y of the n i n e t y percent p o i n t depends on how  concept  important a f a c t o r low temperature i s as a  cause of w i n t e r i n j u r y , on how  r e p r e s e n t a t i v e the low  temperature i n f o r m a t i o n i s f o r a l o c a l i t y , and on  how  p r e c i s e l y low temperature l i m i t s of p l a n t s p e c i e s can be determined.  The r e s u l t s of the w i n t e r i n j u r y survey  i n d i c a t e that low temperature may  be m o d i f i e d by a number  of other f a c t o r s i n i t s e f f e c t s on p l a n t s .  Nevertheless,  f o r most woody ornamental p l a n t s p e c i e s , the amount of damage f o l l o w i n g a severe w i n t e r corresponds approximately to the low temperatures which have been endured. The low temperature l i m i t s determined are s t a t e d w i t h i n f i v e degrees f o r most s p e c i e s .  P l a n t s w i l l not  - 41 always s u r v i v e temperatures at or above the low temperature l i m i t a , u n l e s s they a r e grown with due regard f o r h o r t i c u l t u r a l requirements.  They may s u r v i v e lower temperatures  i f they a r e given s p e c i a l p r o t e c t i o n , or i f other f a c t o r s modifying temperature a r e i n favour of t h e i r  survival.  Thus, the low temperature l i m i t s must be c o n s i d e r e d approximate, and the method used to determine them a rough one. The s t a t i s t i c a l methods used i n the a n a l y s i s of temperature data, on the other hand, a r e r e l a t i v e l y exact. The temperature data on which t h e s t a t i s t i c a l  analysis  i s based, however, i s taken to r e p r e s e n t a r a t h e r e x t e n s i v e area (the l o c a l i t y around a m e t e o r o l o g i c a l  station).  Although t h e r e may be many s l i g h t d i f f e r e n c e s w i t h i n a l o c a l i t y , these d i f f e r e n c e s can be accounted f o r by an experienced person who i s f a m i l i a r w i t h the l o c a l  topography.  Minor c o r r e c t i o n s i n the n i n e t y percent p o i n t t o account f o r these d i f f e r e n c e s could be made by adding or s u b t r a c t i n g f i v e t o t e n degrees, a c c o r d i n g to the amount o f the d i f f e r e n c e expected. Consequently, the main l i m i t a t i o n i n t h e p r a c t i c a l a p p l i c a t i o n of the n i n e t y percent p o i n t i n s e l e c t i n g woody ornamentals i s the d i f f i c u l t y i n g e t t i n g p r e c i s e low temperature l i m i t s f o r the plant concerned.  species  The n i n e t y percent p o i n t would be d i f f i c u l t  to use w i t h s p e c i e s which have i l l - d e f i n e d low temperature  limits*  42 -  I t must be admitted that many ornamental  do not have as w e l l - d e f i n e d Nevertheless,  l i m i t s as had been expected*  w i t h i n i t s l i m i t a t i o n s the n i n e t y  p o i n t concept provides  species  percent  a r e l i a b l e method of e s t i m a t i n g  the chances o f s u r v i v a l i n a p a r t i c u l a r p l a c e f o r most of our important ornamental t r e e s and shrubs. Other a p p l i c a t i o n s of the n i n e t y percent  point  are suggested by a glance a t f i e l d s o f study r e l a t e d t o this investigation. point  The idea behind the n i n e t y  i s t o express the mean and standard  percent  d e v i a t i o n of a  s e r i e s i n terms of the d e v i a t i o n which corresponds t o a selected p r o b a b i l i t y . any  T h i s idea should  be a p p l i c a b l e t o  study of low temperature, and p o s s i b l e t o other  series  of a s i m i l a r n a t u r e . Within  h o r t i c u l t u r e , commercial f r u i t  growing  i n v o l v e s many f a c t o r s s i m i l a r to those s t u d i e d here i n r e l a t i o n t o the s e l e c t i o n of woody ornamentals. temperature l i m i t s of woody f r u i t  The low  p l a n t s a r e w e l l known*  I f the r i s k s i n v o l v e d i n growing a c e r t a i n type of t r e e fruit  i n a given l o c a t i o n were c a l c u l a t e d , the investment  of l a r g e sums o f money i n new p l a n t i n g s could be made with a f u l l e r knowledge of the changes i n v o l v e d . i n regard i n orchard  The r i s k  t o low w i n t e r temperature, an important f a c t o r c u l t u r e , c o u l d be estimated by comparing t h e  low temperature corresponding t o a s e l e c t e d p r o b a b i l i t y f o r t h i s l o c a t i o n with the low temperature l i m i t of the p l a n t to be grown*  43 SUMMARY To meet the need f o r r e l i a b l e i n f o r m a t i o n on the s u i t a b i l i t y of s e t t l e d areas of B r i t i s h for different  Columbia  s p e c i e s of ornamental t r e e s and shrubs, a  study o f low winter temperature as i t a f f e c t s the s e l e c t i o n of woody ornamentals f o r l o c a l i t i e s o f the p r o v i n c e was made. Average  extreme lowest temperature o f the year  f o r each B. C. M e t e o r o l o g i c a l s t a t i o n was c a l c u l a t e d f i g u r e s compiled f o r the ten-year p e r i o d 1940-49*  from  Average  f i g u r e s were arranged on a map of B r i t i s h Columbia f o r g e o g r a p h i c a l comparison.  A map showing approximate low  temperature zones f o r s e t t l e d p a r t s o f the c o a s t a l  region  was c o n s t r u c t e d . Average  extreme lowest temperature of the w i n t e r  f o r each o f s e l e c t e d m e t e o r o l o g i c a l s t a t i o n s was  cal-  c u l a t e d from f i g u r e s compiled f o r the t e n - w i n t e r p e r i o d from 1940-41 t o 1949-50.  The amount o f v a r i a t i o n i n  extreme lowest temperature from winter t o w i n t e r was approximated s t a t i s t i c a l l y by c a l c u l a t i n g the standard d e v i a t i o n f o r each s t a t i o n .  As expected, the c o a s t a l  s t a t i o n s were found t o have a g e n e r a l l y lower standard d e v i a t i o n than i n t e r i o r  stations.  A new concept c a l l e d the n i n e t y percent p o i n t was employed to p r o v i d e a s t a t i s t i c a l  e x p r e s s i o n o f low  m  44  temperature i n simple terms.  The n i n e t y percent p o i n t i s  that temperature above which the extreme lowest temperature of  a station w i l l f a l l  i n approximately nine out of t e n  w i n t e r s , and below which the extreme lowest temperature will fall  i n approximately one out o f t e n w i n t e r s , a c c o r d i n g  to  mathematical expectancy based on s t a t i s t i c a l  analysis  of  temperatures observed over a p e r i o d o f w i n t e r s .  This  concept combines the i n f o r m a t i o n t o be o b t a i n e d from the average extreme lowest temperature and the standard deviation. the  The n i n e t y percent p o i n t i s found by s u b t r a c t i n g  standard d e v i a t i o n m u l t i p l i e d by 1 . 3 from t h e average  extreme lowest temperature of the w i n t e r f o r the s t a t i o n . A survey was conducted t o o b t a i n an estimate o f the  i n j u r y t o ornamental t r e e s and shrubs i n B r i t i s h  Columbia  f o l l o w i n g two severe w i n t e r s .  The i n f o r m a t i o n was  used t o t e s t the u s e f u l n e s s of low temperature data as a guide i n s e l e c t i n g woody ornamentals f o r h a r d i n e s s i n a l o c a l i t y , and t o get a c c u r a t e low temperature l i m i t s i n t h e P a c i f i c c o a s t a l r e g i o n f o r a number o f ornamental  species.  Low temperature i n f o r m a t i o n was found u s e f u l w i t h i n l i m i t a t i o n s as an i n d i c a t i o n o f the amount o f w i n t e r i n j u r y to woody ornamentals t o be expected i n a l o c a l i t y i n B r i t i s h Columbia. in  Many s p e c i e s r e a c t t o g i v e n temperatures  a p r e d i c t a b l e way under most c o n d i t i o n s .  Some s p e c i e s  behave as though f a c t o r s o t h e r than low temperature are mainly r e s p o n s i b l e f o r the extent o f i n j u r y .  —  45  -  LITERATURE CITED  BAKER, F. S., 1944.  Mountain climates of the Western  United States, Ecolog. Monoer. 14:223-254. BAKER, 0. E., 1936.  A t l a s of American A g r i c u l t u r e  Physical basis  f  f  c l i m a t e Washington, U. S. Govt. t  P r i n t i n g Off., p. 9, f i g . 7. BALFOUR, F., 1941.  Low temperatures i n January,  1941  i n S. E. Scotland and t h e i r e f f e c t on shrubs and t r e e s , Rov. Hort. Soc. Jour. 66:230-236. BOWERS, C. G., 1947.  Rhododendron notes; f a c t o r s a f f e c t -  ing hardiness, Nat. Hort. Mag. 26:231-237. BRINK, V. C., 1950.  Climates of B r i t i s h Columbia f o r  a g r o l o g i s t s , part l  f  some general f e a t u r e s of  the climates. U n i v e r s i t y of B r i t i s h Columbia, Agronomy Dept., Technical  Communication.  BRINK, V. C. and L. FARSTAD, 1949*  The physiography o f  the a g r i c u l t u r a l areas of B r i t i s h Columbia,. S c i . A g r i c . 29:273-301. BRITISH COLUMBIA, Dept. of A g r i c u l t u r e , Climate o f B r i t i s h Columbia. V i c t o r i a , B. G., 1941 t o 1948. BUCK, F. E., 1946.  A p a r t i a l l i s t of ornamental t r e e s  and shrubs recommended f o r landscape use i n the province of B r i t i s h Columbia  f  U n i v e r s i t y of  B r i t i s h Columbia, mimeographed f o l d e r , r e v . ed. CANADA, M e t e o r o l o g i c a l S e r v i c e , 1940.  Monthly record  of m e t e o r o l o g i c a l o b s e r v a t i o n s  T  Toronto, Canada.  January, 1940 t o March, 1941. CANADA, M e t e o r o l o g i c a l S e r v i c e , 1946.  Climate  summaries  f o r selected meteorological s t a t i o n s i n the Dominion o f Canada. v o l . 1, Toronto, Canada,  (1946) CANADA, M e t e o r o l o g i c a l S e r v i c e , 1949. Monthly weather map  t  January, 1949 t o February, 1950.  CRANE, H. L., 1947. F a c t o r s i n f l u e n c i n g t h e h a r d i n e s s o f woody p l a n t s , N o r t h . Nut Growers Assn. Report. 1947: 30-37 CONNOR, A. J . , 1915. The temperature and p r e c i p i t a t i o n of B r i t i s h Columbia, Canadian M e t e o r o l o g i c a l S e r v i c e , Ottawa, Canada. CONNOR, A. J . and s t a f f , 1949. The f r o s t f r e e season i n B r i t i s h Columbia. Canadian M e t e o r o l o g i c a l S e r v i c e , Toronto, Canada. CONRAD, V. A., 1944. Methods i n c l i m a t o l o g y . Harvard U n i v e r s i t y P r e s s . DAUBENMIRE, R. F., 1947. P l a n t s and environment, New York, Wiley,  Chap. 4 .  DENISON, F. N., 1925. The c l i m a t e o f B r i t i s h Columbia, Monthly Weather Review FOSTER, E . E., 1948. R a i n f a l l MacMillan, 1948.  53-354. and r u n o f f . New York,  GRAHAM, E., and H. McMINN, 1941.  Ornamental shrubs  and woody vines of the P a c i f i c coast, Berkeley, C a l . , G i l l i c k Press. GRANT, J . A., 1944.  Rhododendrons i n the P a c i f i c  Northwest/ Home Gard. 3(6):  13-14.  GRANT, J . A. and C. L. GRANT, 1943.  Trees and shrubs  f o r P a c i f i c Northwest gardens, S e a t t l e , McCaffrey P u b l i s h i n g Co. HARROW, R. L., 1948.  The e f f e c t of f r o s t i n the winter  of 1946-47 on vegetation, Rov. Hort. Soc. Jour. 63(1.1) :389. IMPERIAL BUREAU OF PLANT BREEDING AND GENETICS, 1939. Bibliography on c o l d r e s i s t a n c e i n p l a n t s  f  Cambridge, England, School of A g r i c u l t u r e . KOEPPE, C. E., 1931.  The Canadian climate ,  Bloomington, 111., LANDSBERG, H., 1946.  McNight•and McNight.  Climate as a n a t u r a l resource,  S c i . Month. 63(4):293-298. LEVITT, J . , 1941.  1946.  F r o s t k i l l i n g and hardiness i n p l a n t s ,  Minneapolis, Burgess P u b l i s h i n g Co. MACOUN, W. T., 1931. A g r i c . B u i . 142 MULFORD, F. L., 1920.  Hedges and t h e i r uses, Dom.  Dept.  (N.S.), Ottawa, Canada. Street trees,  U. S. Dept.  A g r i c . B u i . 6*16, Washington, U. S. Govt. P r i n t . Off.  -  -  48  MULFORD, F. L., 1926. Trees f o r r o a d s i d e p l a n t i n g , U. S. Dept. A g r i c . Farm B u i . 1482, Washington, U. S. Govt. P r i n t . O f f . MUIRHEAD, G. D., (unpubl.).  An e v a l u a t i o n o f t h e  s t r e e t t r e e s i n t h e u n i v e r s i t y area o f Vancouver, B. C , U n i v e r s i t y o f B r i t i s h Columbia, Graduating essay, 1 9 5 0 . McMINN, H. E . and MAINO, E., 1 9 3 5 . An i l l u s t r a t e d guide t o P a c i f i c Coast t r e e s , U n i v e r s i t y o f C a l i f o r n i a Press. OLIVER, R. W.,  1 9 4 4 . Ornamental shrubs and woody  c l i m b e r s more commonly used f o r landscape purposes throughout Canada, Dom. Dept. A g r i c . P u b l . 7 1 3 , Farmer's B u i . 100, Ottawa, OLIVER, R. W.,  Canada.  1 9 4 5 . Deciduous t r e e s and c o n i f e r s  more commonly used f o r ornamental purposes throughout Canada, Dom. Dept. A g r i c . Farmer's B u i . 4 9 , Ottawa,  Canada.  PEATTIE, R., 1 9 3 6 . Mountain geography: a c r i t i q u e and f i e l d study, Harvard U n i v e r s i t y  Press.  PRESTON, I . , 1 9 4 6 . Herbaceous p e r e n n i a l s f o r Canadian gardens, Dom. Dept. A g r i c . Farmers' B u i . , 138, Ottawa,  Canada.  REHDER, A., 1 9 2 7 . Manual o f c u l t i v a t e d t r e e s and shrubs hardv i n North America, New York, MacMillan, 1 s t ed.  REHDER, A., 1 9 4 0 . M a n u a l o f  cultivated trees  s h r u b s hardy i n N o r t h America,, MacMillan,  New Y o r k ,  2nd e d .  ROYAL HORTICULTURAL S O C I E T Y , cold s p e l l ,  1939-40,  1941.  Effect  Rov. Hort Soc.  66:207-209.  of  the  Jour.  i  ROYAL HORTICULTURAL SOCIETY, survey,  and  1946-47,  1948.  Rov. Hort.  Frost  Soc.  damage  Jour.  63:390-415, 439-448. SANDERSON, M a r i e , according to tion, SIMPSON,  The c l i m a t e s  1948. the  new T h o r n t h w a i t e  S^jlgrisj.  Canada classifica-  28:501-517.  G . L . and R O E , A . , 1939.  zoology,  of  New Y o r k ,  Quantitative  McGraw H i l l ,  1st e d .  p. 137. SKINNER, F . L . , 1944. Nat. SNYDER,  H o r t . Mag.  Hardiness i n  23^236.  J o h n C . , no d a t e .  landscape Dept. of TEUSCHER,  plantings  Agric.  plants,  Ornamental shrubs i n Washington. U .  cooperating with State  for S.  College  Washington, Pullman, Washington. H . , 1934.  Hardiness i n plants,  New Y o r k B o t . G a r d . THORNTHWAITE,  35:121-131.  C . W . , 1 9 3 1 . The c l i m a t e s  America a c c o r d i n g to Geogr. Rev.  Jour.  a new  21:633-655.  of North  classification.  - 50 -  THORNTHWAITE, C. W., 1948. An approach toward a r a t i o n a l c l a s s i f i c a t i o n of c l i m a t e .  Geogr.  Rev. 38:55-94. VAN DERSAL, W.R.,  1938. Native woodv p l a n t s o f  the United States. U. S. Dept. A g r i c . Misc. Publ. 303, Washington, U. S. Govt. P r i n t . O f f . VAN DERSAL, W. R., 1942. Ornamental American shrubs. Oxford U n i v e r s i t y Press. WYMAN, D., 1938. Hedges, screens and windbreaks, New York, McGraw H i l l .  ft APFEHDIX  APPENDIX I. Ertreme Lowest (Temperature of the Winter at Selected B. C. Meteorological Stations for the Ten-Winter Period from 1940-41 to 1949-50. Averages are given for stations from which information was available for a l l ten winters. (Degrees Fahrenheit). station  1940 41- 42- 43-44-45- 46-4V- 48- 49- Average 49 44 45 46 50 -41 42 43 47 48  Abbotsford (A) 21 22 Agassis Alberni (Beaver Cfc) 19 20 Alberni, Port -8 Armstrong Ashcroft -23 Barkerville -23 Bella Coola 5 Comox 22 Coquitlam Lake 24 Cowichan Bay -12 Cranbrook (A} 7 Creston Cultus Lake Cumberland 17 Dominion Obser25 vatory Duncan 15 Pernio -18 Golden -15 Grand Forks -6 Haney _ 17 Hope James Island 26 Jordan Biver Eamloops 2 9 Kelowna 7 Seremeos Zimberley Lytton 0 MeBrlde -20 Masset 20 -2 Merritt Hanairao 24 Nelson 10 20 New Westminster 18 Ocean Falls 9 Okanagan Centre 11 Oliver Penticton 10 Port lardy (A) Powell River 27  -1 22 15 18 -4 25 9 -3 17 12 9 17 -5 -39 -12  11 20 8 13 -5  -23 -45 7 -5  -17 -22 15 9  14 5 18 11 -22 -41 0 -18  24 20 26 21 ^12 -19 -4 4  13  -3  22  16  9 7 19 3 17 5 2 20 -6 -16 -26 -20 -52 4 ^10 19 9 19 4 24 13 -16 -22 -10 8 15 3  8 19 16 12 -17 -15 -26 4 13 18 20 -20 -3 15 15  24 7 28 26 23 14 21 9 19 13 19 9 7 14 -9 -18 -12 -20 -21 -17 -30 -31 -40 -18 -26 -17 -30 -25 -7 -30 -12 -10 -8 -18 -11 9 18 -8 20 12 12 13 -3 12 17 25 25 7 29 27 27 26 17 20 0 -27 2 2 -2 -20 -10 -9 4 ^15 2 9 10 10 0 -17 6 2 7 -5 1 -8 -18 -18 1 -15 6 4 6 ^11 0 -19 -43 -8 -20 -12 -35 -28 26 22 19 4 12 21 5 -6 -33 -8 -2 -11 -21 -16 13 6 22 19 20 13 15 12 5 10 0 1 -13 6 21 17 18 16 -1 7 11 23 25 27 22 3 22 -1 9 -5 Z 6 -16 15 11 -21 -10 1 3 0 3 3 0 9 -10 -4 4 7 11 14 22 23 30 28 28 25 11 13 26  9 -6 +9.5 12 -2 13.2 +8.0 6 -14 10.5 7 -7 -27 -44 -17.9 -22 -35 -12 -20 +0.3 1 -6 12.4 4 -6 6 17.8 15 -24.0 -35 -41 -13 -20 - 6.2 11 -5  2 -5 -38 -39 -36 -47 -25 -33 9 -5 4 -11 20 8 19 4 -20 -37 -12 -24 -10 -22 -32 -40 -9 -25 -23 -46 6 14 -30 -46 13 3 2 -16 -1 12 17 5 -4 -22 -17 -23 -7 -16 17 6  10.2 -22.2 -28.3 -16.0 +6.8 21.1 -11.0 -1.6 -3,1 -4.3 -25.4 14,9 -17.7 14.8 +1.7 12.0 16.3 +0.5 -5.0 +0.4  APPENDIX I-Cont.  Station  1940 -41  Princeton (A) -9 Prince George (A) Prince Rupert 15 Qnesnel -17 Revelstoke -3 6 Salmon Arm 26 Sidney Smither8 -20 17 Stave Falls Steveston 10 Summerland Terrace 3 Vancouver (A) 20 Vernon 1 Victoria 28 W&rfield ((Trail) 11 21 White Rock Williams Lake -15  44- 4541- 42- 43-• Tins 42 43 45 46  -16 -37 •- i i -11 -28 22 1 26 24 -13 —<3i> -10 -12 -12 -30 0 -6 -1 -26 0 5 22 10 28 24 -21 -32 •-11 -17 10 -3 20 18 2 21 11 9 7 -13 10 6 -3 -10 14 15 3 21 21 2 -25 4 4 7 31 28 25 3 -16 13 5 2 22 19 17 -13 -42--12 -10  4647  4748  4849  4950  Avers  -9 -25 21 -10 -1 3 26  -22 -52 -3 -43 -14 -15 13  -14 -39 10 -23 -10 -5 24  -22 -46 12 -33 -15 -13 19  -42 -58 3 -52 -27 -30 8  13.4 -24.8 -11.8 -7.6 20.0  19 13 7 -3 16 2 25 5 18 -24  12 -2 -2 -17 5 -7 17 -2 8  14 16 2 -6 18 -4 26 4 19  -7 -2 9 -13 19 -5 12  -22 -21 0 -31 6  +0.1 -3.9 12.8 -6.7 21.2  1  13.9  -19.3  APPMDIX II Species of frees and Shrubs Approximate low temperature determined from information given for certain species. Botanical Fame  Included i n the Winter Injury Surrey, 1950. limits i n the Paeifie coastal region, as obtained by means of the survey, are (Degrees Fahrenheit).  Low Temp, Limit  Taxus baceata -5 to 46 §• cuspldata -10 to +5 Cephalotaxus drupacea var. fastiglata Araucaria araucana 0 to +5 Abie8 plnsapo A. conoolor Cedrus atlantiea -5 to +5 C. deodara +5 to +10 Pinus radiata Sequoia sempervirens +5 to +10 Sequoiadendron giganteum +5 to +10 Cryptomeria japonica -5 to +10 Cunninghamla lanceolata fhujopsis dolobrata Cupres8us arizonica C. macrocarpa +10 to +15 Chamaecyparia lawsoniana 0 to +10 Juniperus app, Salix oablonica Garrya e l l i p t i c a Juglans regie -5 to +5 Carya Pecan Quercus Virginians Peonia suffruticosa X Clematis jackmani Mahonia aquifolium Berber!s buxifolia X B. stenophylla -5 to +5 B. darwini +5 to +10 B. Tfcoribexgl X Magnolia Soulangeana M. grandiflora +5 to +10 M. stellata Carpentaria californlea Umbellularia ealifornica Hydrangea macrophylla var. Hortensis 0 to +10 Escallonia rubra +10 to +15 X langleyensis +15 to +20  Botanical Fame  Low Temp. Limit  Ootoneaster Franeheti +10 to+15 0 , miorophylla +5 to +15 Pyraeantha eoccinea P. crenato-serrata Photlnia serrulate +15 to +20 Stranvaesia Davidiana +5 to +10 Boss vars, Prmms triloba PruBUS lusitanica +10 to +15 Prunus Laurocerasus +15 to +20 Cereis Sillquastrum +10 to +15 Spartium junceum +10 to +15 Laburnum anagroldes Indlgofera spp. Wistaria sinensis +5 to +10 Ohoisya ternata +15 to +20 Skimmla japonica +5 to +10 Sarcococca spp. +5 to +10 Pachysandra terminal!s Buxus sempervirens +5 to +10 B. miorophylla Ilex aquifolium +5 to +10 1. opaea Euonymus Fortune! var. radieans 0 to +10 E. japonica +5 to +10 Pachystima myrsinites Acer palmaturn X Oeanothus Delilianus +15 to+20 C. velutinus +5 to+10 T i t i s vinifera -5 to +5 Hibiscus 8yriaeus +5 to +10 Camellia japonica +15 to +20 Camellia Sa sanq.ua Hypericum calyeinum +5 to +10 Tamarix anglica 0 to +5 Clstus ladanlferus +5 to +10 Opuntia spp. Daphne laureola +5 to +10 Eucalyptus Gunnii +10 to +15 Fuchsia magellaniea var. Biehartonii +10 to +15  APPMDIX I I - Cont.  Botanical Same  Low Temp. Limit  Botanical Name  Hedera helix +5 to +10 Buddlela Davldi Fatsia japonica +10 to +15 Rosemarinus officinalis Aralla chinensis Aucuba japonica •10 to +15 Salvia officinalis Lit ho speranim Cornua H u t t a l l i i diffusum Rhododendron spp.(half Paulowala tomentosa hardy spp.) Arbutus Kensiesli +5 to +10 Hebe spp. Viburnum Davldi Aret08taphylo8 Viburnum tinus tomentosa X Abelia grandiflora Vaecinium ovatum Olearia Haastii Forsythla spp. Ruscus aculeatus Ligustrum lucidum Oamanthus i l i c l f o l i u s Jasmlnum nudlflorum +5 to +10  Low Temp. Limit +10 to +15  +10 to +15 +10 •10 +15 +15 •10  to +20 to +15 to +20 to +20 to +15  

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