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UBC Theses and Dissertations

Climate and outbreaks of the forest tent caterpillar in Ontario Daniel, Colin John 1990

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CLIMATE AND OUTBREAKS OF THE FOREST TENT CATERPILLAR IN ONTARIO by COLIN JOHN DANIEL B . A . S c , The U n i v e r s i t y o f Waterloo, 1985  A t h e s i s submitted i n p a r t i a l f u l f i l l m e n t o f the  requirements f o r the degree o f MASTER OF SCIENCE in  THE FACULTY OF GRADUATE STUDIES (Department  o f Zoology)  We accept t h i s as conforming to t h e r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA June,  1990  © C o l i n John D a n i e l ,  1990  In  presenting this  degree at the  thesis  in  University of  partial  fulfilment  of  of  department  this thesis for or  by  his  or  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying  the  representatives.  an advanced  Library shall make it  agree that permission for extensive  scholarly purposes may be her  for  It  is  granted  by the  understood  that  head of copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department  of  ^tO^^  The University of British Columbia Vancouver, Canada  DE-6 (2/88)  ABSTRACT  A review of the current understanding of f o r e s t tent caterpillar  (Malacosoma  disstria  Hbn.) p o p u l a t i o n dynamics  i n O n t a r i o s u g g e s t s t h a t two c l i m a t i c f a c t o r s , t h e t e m p e r a t u r e a t t h e time o f l a r v a l f e e d i n g and t h e minimum temperature through the w i n t e r , p l a y important r o l e s i n d e t e r m i n i n g o u t b r e a k s . Comparing t h e p a t t e r n o f d e f o l i a t i o n t o s i m i l a r l y s c a l e d temperature r e c o r d s over 41 y e a r s i n O n t a r i o shows no r e l a t i o n s h i p between t h e y e a r t o y e a r dynamics o f o u t b r e a k s and e i t h e r t h e t e m p e r a t u r e t h r o u g h t h e l a r v a l f e e d i n g p e r i o d o r t h e minimum o v e r w i n t e r i n g temperature. A long-term a n a l y s i s suggests t h a t  outbreaks  are l e s s s e v e r e i n t h o s e r e g i o n s w i t h low o v e r w i n t e r i n g t e m p e r a t u r e s and a p a t c h y d i s t r i b u t i o n o f h o s t . T h i s l a t t e r f i n d i n g , combined w i t h an a n a l y s i s o f t h e synchrony and s p r e a d o f d e f o l i a t i o n , s u g g e s t s t h a t a d u l t d i s p e r s a l may p l a y an i m p o r t a n t r o l e i n s h a p i n g t h e dynamics o f o u t b r e a k s .  ii  TABLE OF CONTENTS  LIST OF TABLES  V  LIST OF FIGURES  vi  ACKNOWLEDGEMENTS  X  1. INTRODUCTION  1  2. CURRENT UNDERSTANDING  5  L i f e History  5  History  6  o f Outbreaks  Host P r e f e r e n c e  7  Impact upon H o s t s  8  Egg M o r t a l i t y  8  Larval Mortality  9  Pupal M o r t a l i t y  12  Adult Dispersal  .•  13  Summary  14  3. PATTERN OF OUTBREAKS  16  D e f o l i a t i o n Maps  16  Maps and I n s e c t Abundance  22  Pattern of Defoliation  25  Summary  32  iii  TABLE OF CONTENTS  (continued)  4. CLIMATE AND FOREST COMPOSITION  33  L a r v a l F e e d i n g Temperature  34  O v e r w i n t e r i n g Temperature  56  F o r e s t C o m p o s i t i o n and Long-Term C l i m a t e  63  Summary  78  5. DISCUSSION  79  L a r v a l F e e d i n g Temperature  79  O v e r w i n t e r i n g Temperature  88  Host A v a i l a b i l i t y  91  Long-Term C l i m a t e  92  Other F a c t o r s  95  6. CONCLUSIONS AND RECOMMENDATIONS  105  7. LITERATURE CITED  107  APPENDIX A. S u c c e s s i v e y e a r o v e r l a y s o f d e f o l i a t i o n maps  113  APPENDIX B. F e e d i n g degree-days and d e f o l i a t i o n f o r 16 s t a t i o n s  124  APPENDIX C. Minimum o v e r w i n t e r i n g t e m p e r a t u r e and d e f o l i a t i o n f o r 16 s t a t i o n s APPENDIX D. D e t a i l s o f t h e d a t a a n a l y s i s  iv  129 134  LIST OF  I.  Studies  TABLES  p r o v i d i n g evidence of the r e l a t i o n s h i p  between f o r e s t t e n t c a t e r p i l l a r the temperature  outbreaks  through the e a r l y l a r v a l  and feeding  period II.  35  A c t u a l h a t c h d a t e s a n d t h o s e p r e d i c t e d by M i n n e s o t a model f o r v a r i o u s  t i m e s and  the  locations  in Ontario D-I.  D-II.  Proportion  40 o f area d e f o l i a t e d each year,  for  t h e 20 c l i m a t e s t a t i o n s  The  l o c a t i o n of the Atmospheric  Service  climate  1948-88, 138  s t a t i o n s used  Environment  i n the a n a l y s i s  . .  140  D - I I I . P r e d i c t e d h a t c h d a t e e a c h y e a r , 1948-88, f o r t h e 20 D-IV.  141  F e e d i n g d e g r e e - d a y s e a c h y e a r , 1948-88, f o r t h e 20  D-V.  climate stations  climate  stations  143  Minimum o v e r w i n t e r i n g  temperature  1 9 4 8 - 8 8 , f o r t h e 20 c l i m a t e  v  each  stations  year, 145  L I S T OF FIGURES  1.  Annual maps o f t h e a r e a w i t h i n which moderate t o s e v e r e d e f o l i a t i o n has o c c u r r e d i n O n t a r i o , 1948-1988  2.  18  T o t a l a r e a w i t h i n which moderate t o s e v e r e d e f o l i a t i o n has o c c u r r e d each y e a r i n O n t a r i o , 1948-88  3.  26  Composite maps showing t h e t o t a l e x t e n t o f t h e moderate t o s e v e r e d e f o l i a t i o n f o r each o f t h e f o u r p r o v i n c e - w i d e o u t b r e a k s from 1948-88  4.  27  The number o f o u t b r e a k s t h a t have o c c u r r e d t h r o u g h o u t t h e p r o v i n c e from 1948-88  5.  28  The l o c a t i o n o f t h e c e l l s d e f i n i n g t h e 4 o u t b r e a k r e g i o n s a t each o f 3 s c a l e s  6.  30  The p r o p o r t i o n o f l a n d a r e a d e f o l i a t e d w i t h i n  each  o f t h e 4 o u t b r e a k r e g i o n s , a t 3 d i f f e r e n t s c a l e s . . 31 7.  The l o c a t i o n o f t h e 20 c l i m a t e s t a t i o n s  36  8.  The p r e d i c t e d h a t c h date each y e a r f o r 4 o f t h e 20 climate stations  9.  41  The mean h a t c h d a t e , 1948-88, f o r each o f t h e 20 climate stations  -. .  10. The mean number o f f e e d i n g degree-days,  42  1948-88,^  f o r each o f t h e 20 c l i m a t e s t a t i o n s  45  11. The f e e d i n g degree-days each y e a r f o r 4 o f t h e 20 climate stations  46  vi  L I S T OF FIGURES  (continued)  12. The f e e d i n g degree-days and t h e p r o p o r t i o n o f area d e f o l i a t e d each year f o r 4 o f the 20 c l i m a t e stations  48  13. R e l a t i o n s h i p between the change i n percentage o f defoliated all  area and the f e e d i n g degree-days, f o r  s t a t i o n s and years w i t h a non-zero change i n  defoliation  50  14. The e f f e c t o f v a r y i n g the c e l l  s i z e on the  r e l a t i o n s h i p between the change i n percentage o f defoliated all  area and the f e e d i n g degree-days, f o r  s t a t i o n s and years w i t h a non-zero change i n  defoliation  51  15. The e f f e c t o f changing the c l i m a t i c measure on the r e l a t i o n s h i p between the change i n percentage o f defoliated all  area and the f e e d i n g degree-days, f o r  s t a t i o n s and years w i t h a non-zero change i n  defoliation  53  16. The d i s t r i b u t i o n o f 4-year averages o f f e e d i n g degree-days p r i o r t o i n i t i a l initial  i n c r e a s e years and  decrease years  55  17. The mean o f the minimum o v e r w i n t e r i n g temperature, 1948-88, f o r each o f the 20 c l i m a t e s t a t i o n s  . . . .  58  18. The minimum o v e r w i n t e r i n g temperature and t h e p r o p o r t i o n o f area d e f o l i a t e d each year f o r 4 o f the  20 c l i m a t e s t a t i o n s  vii  59  L I S T OF FIGURES  (continued)  19. R e l a t i o n s h i p between t h e change i n p e r c e n t a g e o f d e f o l i a t e d a r e a and t h e minimum o v e r w i n t e r i n g temperature, non-zero  f o r a l l s t a t i o n s and y e a r s w i t h a  change i n d e f o l i a t i o n  61  20. The e f f e c t o f v a r y i n g t h e c e l l s i z e on t h e r e l a t i o n s h i p between t h e change i n p e r c e n t a g e o f d e f o l i a t e d a r e a and t h e minimum o v e r w i n t e r i n g temperature, non-zero  f o r a l l s t a t i o n s and y e a r s w i t h a  change i n d e f o l i a t i o n  62  21. C e l l system f o r t h e f o r e s t i n v e n t o r y i n O n t a r i o  . .  65  22. The y e a r i n w h i c h t h e s t a n d i n f o r m a t i o n was r e c o r d e d f o r each c e l l i n t h e f o r e s t i n v e n t o r y  66  23. P r o p o r t i o n o f each c e l l ' s a r e a c l a s s i f i e d  as  non-forested  68  24. P r o p o r t i o n o f each c e l l ' s f o r e s t e d a r e a t h a t i s c l a s s i f i e d as e i t h e r mixedwood o r hardwood 25. Breakdown o f t h e deciduous component i n each  ....  69  cell  by genus  71  26. The l o n g - t e r m p a t t e r n s o f d e f o l i a t i o n and c l i m a t e , 1948-88, f o r each o f t h e 20 c l i m a t e s t a t i o n s  ....  76  27. R e l a t i o n s h i p between t h e number o f y e a r s o f d e f o l i a t i o n and t h e l o n g - t e r m c l i m a t e ,  1948-88,  f o r t h e 20 c l i m a t e s t a t i o n s  77  28. The f e e d i n g degree-days and t h e p r o p o r t i o n o f a r e a d e f o l i a t e d each year f o r Sioux Lookout  viii  81  LIST OF FIGURES (continued)  29. The d i s t r i b u t i o n o f maximum f e e d i n g degree-day v a l u e s i n a p e r i o d 2-4 y e a r s p r i o r t o i n i t i a l i n c r e a s e y e a r s and i n i t i a l decrease y e a r s 30. The p r o b a b i l i t y o f h a v i n g an above  84  average  f e e d i n g - d e g r e e day v a l u e as a f u n c t i o n o f t h e p e r i o d o f successive years considered 31. The minimum o v e r w i n t e r i n g t e m p e r a t u r e  85 and t h e  p r o p o r t i o n o f a r e a d e f o l i a t e d each y e a r f o r Fort Frances  90  32. The f e e d i n g degree-days each y e a r f o r p a i r s o f n e i g h b o u r i n g and d i s t a n t s t a t i o n s  97  33. The s p a t i a l c o r r e l o g r a m s f o r t h e annual v a l u e s o f f e e d i n g degree-days and minimum o v e r w i n t e r i n g temperature  100  ix  ACKNOWLEDGEMENTS  I would l i k e  t o t h a n k G o r d Howse o f t h e F o r e s t  and  Disease Survey  and  f o r p r o v i d i n g me w i t h t h e d e f o l i a t i o n  Mike Applejohn, Al  (FIDS) f o r h i s s u p p o r t a n d h o s p i t a l i t y ,  Dave C o n s t a b l e ,  and hatch  I would a l s o l i k e  Institute  for their  P o w e r f o r p r o v i d i n g me w i t h facilities;  access t o t h e i r  computer  was p r o v i d e d  c o m p u t i n g . The  b y M i k e Webb o f t h e  Atmospheric Environment S e r v i c e , while Ontario  Ministry  forest  inventory.  Natural  Sciences  of Natural  John Osborne o f t h e  Resources allowed  me t o u s e t h e  My s t u d i e s a t U.B.C. w e r e s u p p o r t e d b y a and Engineering  Research  Council  scholarship.  I would l i k e Ludwig f o r t h e i r  reading  Mike  L a r r y O'Brien and C o l i n Brethour f o r t h e i r  temperature data  Klinkenberg  National  support and h o s p i t a l i t y :  u n e n d i n g h e l p w i t h my l o n g d i s t a n c e  postgraduate  f o r which  t o t h a n k t h e FIDS  T e c h n o l o g y Development Group a t t h e Petawawa Forestry  data.  Wayne I n g r a m , B o b S a j a n a n d  K e i z e r s h o w e d me t h e f i e l d s i d e o f t h e S u r v e y ,  I am g r a t e f u l .  Insect  t o thank Tad U l r i c h ,  T i m Webb a n d Don  d i s c u s s i o n s . J o s h Korman a n d B r i a n  c o n t r i b u t e d both through d i s c u s s i o n s and by  my t h e s i s  draft.  My many s u p e r v i s o r s , B u z z  Holling,  C a r l W a l t e r s a n d J u d y M y e r s , e a c h c o n t r i b u t e d i n t h e i r own way  t o my e c o l o g i c a l u p b r i n g i n g .  for  your patience  and support.  x  Finally,  thank you Cheryl  CHAPTER 1 INTRODUCTION Four b l i n d men a r e l e d i n t o a c o u r t y a r d t o e x p e r i e n c e an e l e p h a n t f o r t h e f i r s t t i m e . The f i r s t g r a s p s t h e t r u n k and d e c l a r e s t h a t e l e p h a n t s are f i r e h o s e s . The second t o u c h e s an e a r and m a i n t a i n s t h a t e l e p h a n t s a r e r u g s . The t h i r d w a l k s i n t o i t s s i d e and b e l i e v e s t h a t e l e p h a n t s a r e a k i n d o f w a l l . The f o u r t h f e e l s a l e g and d e c i d e s that elephants are p i l l a r s . Parable,  from O ' N e i l l e t al. (1986, p.3)  Many s t u d i e s o f f o r e s t i n s e c t p o p u l a t i o n  dynamics can  be c l a s s i f i e d as " l o c a l " ; i . e . s m a l l e r i n b o t h t e m p o r a l and s p a t i a l s c a l e t h a n many o f t h e p a t t e r n s whose  underlying  mechanisms t h e y a r e t r y i n g t o u n c o v e r . C o n s i d e r , f o r example, s t u d i e s o f t h e p o p u l a t i o n t e n t c a t e r p i l l a r , Malacosoma few h e c t a r e s  disstria  dynamics o f t h e f o r e s t Hbn. U s i n g p l o t s o f a  m o n i t o r e d over 3 t o 5 y e a r s , v a r i o u s c l i m a t i c  f a c t o r s have been a s s o c i a t e d w i t h y e a r - t o - y e a r mortality  changes i n  (Hodson, 1941; W i t t e r e t al., 1975). These s t u d i e s  have p r o v i d e d  some i n s i g h t i n t o t h e p o p u l a t i o n  dynamics t h a t  o c c u r over an a r e a t h e s i z e o f a s t a n d and over a t i m e span o f a few y e a r s . Now suppose t h a t we a r e i n t e r e s t e d i n e x p l a i n i n g t h e year-to-year  changes i n abundance, b u t over an a r e a t h a t  spans s e v e r a l t h o u s a n d square k i l o m e t r e s . We have now expanded our s p a t i a l s c a l e w e l l beyond t h a t o f t h e l o c a l s t u d i e s . W h i l e c l i m a t i c f a c t o r s may be c a p a b l e o f i n d u c i n g changes i n m o r t a l i t y i n a p a r t i c u l a r l o c a t i o n o r y e a r ,  -1-  i ti s  not c l e a r whether they are s i g n i f i c a n t i n d e t e r m i n i n g t h e changes i n abundance t h a t have o c c u r r e d over t h i s  larger  a r e a . F o r example, s e v e r a l l a r g e r s c a l e s t u d i e s have t h a t f o r e s t t e n t c a t e r p i l l a r outbreaks t i m e from l o c a l areas o f i n f e s t a t i o n  noted  seem t o s p r e a d (Brown, 1938;  Sippell,  1962; Hodson, 1977). T h i s suggests t h a t d i s p e r s a l may important  over  be  i n determining the s p a t i a l progression of  o u t b r e a k s . The r o l e o f d i s p e r s a l d i d not become e v i d e n t , however, u n t i l one l o o k e d beyond s e p a r a t e p l o t s and examined s e v e r a l s u c c e s s i v e r e g i o n a l d e f o l i a t i o n maps. Having expanded our s p a t i a l s c a l e from s t a n d t o r e g i o n , we can a l s o expand t h e t e m p o r a l  s c a l e . I n s t e a d o f l o o k i n g at  t h e y e a r - t o - y e a r changes i n abundance, c o n s i d e r t h e dynamics over t h r e e o r f o u r o u t b r e a k s . Do we d i s c o v e r any f a c t o r s a t t h i s s c a l e t h a t went u n n o t i c e d a t p r e v i o u s ones? S i p p e l l (1962), f o r example, l o o k e d a t t h r e e s u c c e s s i v e f o r e s t t e n t c a t e r p i l l a r outbreaks  i n O n t a r i o and n o t i c e d t h a t  d e f o l i a t i o n had n e v e r o c c u r r e d i n some p a r t s o f t h e p r o v i n c e . However, no attempt  was made t o e x p l a i n t h i s  p a t t e r n . A r e t h e dynamics a t t h i s s c a l e i n f l u e n c e d by t h e f o r e s t c o m p o s i t i o n a c r o s s t h e p r o v i n c e ? Or p o s s i b l y c l i m a t e ? A n o t h e r example o f t h e importance  of scale i n forest  entomology i n v o l v e s e a s t e r n spruce budworm, fumiferana  Choristoneura  (Clem.), r e s e a r c h . While many s t u d i e s , most  n o t a b l y t h e Green R i v e r p r o j e c t ( M o r r i s , 1963), have s t u d i e d t h e p o p u l a t i o n dynamics l o c a l l y , o t h e r work has examined t h e  -2-  p a t t e r n o f outbreaks at l a r g e r s c a l e s . B l a i s uncovered outbreak p a t t e r n s  i n t r e e r i n g s across  North America over t h e l a s t two c e n t u r i e s , t h a t recent extent has  (1968) eastern  and suggested  outbreaks have been i n c r e a s i n g i n frequency,  and s e v e r i t y . T h i s change i n t h e p a t t e r n  o f outbreaks  s i n c e been a s s o c i a t e d w i t h changes i n f o r e s t  composition, through h a r v e s t i n g , reforestation  (Blais,  1983). Other r e s e a r c h  l a r g e s c a l e outbreak p a t t e r n s , 1938-1980 from a c r o s s  has r e l a t e d  u s i n g d e f o l i a t i o n maps f o r  a l l o f e a s t e r n North America, t o  s i m i l a r l y scaled vegetative 1984;  f i r e p r o t e c t i o n and  and c l i m a t i c i n f o r m a t i o n  Hardy e t al., 1986). The r e s u l t s o f these  (Hardy,  analyses  f u r t h e r emphasize t h e p o t e n t i a l l a r g e s c a l e importance o f climate  and f o r e s t composition.  I t appears t h a t c a r r y i n g out analyses s c a l e should  a t more than one  be e n l i g h t e n i n g . However, f o r most f o r e s t  insects r e l a t i v e l y  few s t u d i e s have been done at l a r g e r  s p a t i a l and temporal s c a l e s , presumably due t o t h e difficulty  i n f i n d i n g and a n a l y s i n g  information.  scaled  One system f o r which such data e x i s t i s t h e  forest tent c a t e r p i l l a r i n Ontario. combined w i t h other explore  large  These data,  when  l o c a l s t u d i e s , o f f e r an o p p o r t u n i t y t o  t h e dynamics o f a system over l a r g e r s p a t i a l and  temporal s c a l e s , and form t h e b a s i s f o r t h i s t h e s i s . The  o b j e c t i v e o f t h i s t h e s i s i s t o assess t h e  contribution of large scaled information  -3-  t o our  understanding caterpillar understanding  o f t h e p o p u l a t i o n dynamics o f t h e f o r e s t t e n t i n O n t a r i o . To p r o v i d e a b a s e l i n e o f from w h i c h I can judge t h e added c o n t r i b u t i o n  o f t h i s i n f o r m a t i o n , I r e v i e w t h e l i f e h i s t o r y and t h e c u r r e n t t h o u g h t s on p o p u l a t i o n dynamics o f t h e f o r e s t t e n t caterpillar  i n Chapter 2. I t h e n p r e s e n t  41 y e a r s o f  p r o v i n c e - w i d e maps o f f o r e s t t e n t c a t e r p i l l a r d e f o l i a t i o n i n C h a p t e r 3. The maps p r o v i d e o n l y a c o a r s e p i c t u r e o f f o r e s t t e n t c a t e r p i l l a r abundance, and t h i s c h a p t e r b e g i n s w i t h a d i s c u s s i o n o f t h e u n c e r t a i n t y i n t h e map d a t a and t h e i m p l i c a t i o n s f o r my a n a l y s i s . These d a t a a r e t h e n used t o e x p l o r e how t h e dynamics o f o u t b r e a k s v a r y as a f u n c t i o n o f the s p a t i a l  and t e m p o r a l s c a l e over w h i c h t h e y a r e measured.  I n Chapter 4 I p r e s e n t defoliation  t h e r e s u l t s o f my a n a l y s e s  maps, i n c o n j u n c t i o n w i t h s i m i l a r l y  using the  scaled  climatic  and v e g e t a t i v e i n f o r m a t i o n , t o e x p l o r e some o f t h e  climatic  f a c t o r s t h a t have been p r e v i o u s l y a s s o c i a t e d w i t h  l o c a l changes i n abundance. F i n a l l y ,  i n C h a p t e r 5, I d i s c u s s  t h e f i n d i n g s o f C h a p t e r s 3 and 4 i n l i g h t o f t h e i d e a s presented  i n the literature  review.  -4-  CHAPTER 2 CURRENT UNDERSTANDING  A number o f s t u d i e s o f t h e f o r e s t t e n t c a t e r p i l l a r have been c a r r i e d out i n and around O n t a r i o over t h e l a s t y e a r s . From t h e s e s t u d i e s a consensus has been r e g a r d i n g t h e p o p u l a t i o n dynamics.  fifty  formed  The f o l l o w i n g c h a p t e r  reviews t h i s current understanding.  Life  History  The range o f t h e f o r e s t t e n t c a t e r p i l l a r , disstria  Malacosoma  Hiibner, extends from P.E.I, t o B r i t i s h Columbia and  from James Bay t o L o u i s i a n a (Stehr and Cook, 1968) . I n O n t a r i o , egg l a y i n g by t h e female moth u s u a l l y o c c u r s i n e a r l y t o m i d - J u l y . Female moths l a y a s i n g l e egg mass c o n t a i n i n g a p p r o x i m a t e l y 200 eggs. The egg mass i s l a i d as a band on t h e s m a l l t w i g s o f v a r i o u s deciduous t r e e s p e c i e s , u s u a l l y i n t h e upper crown ( W i t t e r , 1979).  Embryonic  development b e g i n s i m m e d i a t e l y and c o n t i n u e s f o r about t h r e e weeks u n t i l t h e p h a r a t e l a r v a e a r e f u l l y formed w i t h i n t h e egg. R e g a r d l e s s o f t h e t e m p e r a t u r e , t h e p h a r a t e l a r v a e t h e n undergo an o b l i g a t o r y 3 month d i a p a u s e  (Hodson and Weinman,  1945). The p o s t - d i a p a u s e p h a r a t e l a r v a e remain dormant t h r o u g h t h e w i n t e r , w i t h egg h a t c h c o i n c i d i n g r o u g h l y w i t h t h e b u d b u r s t o f t h e h o s t t r e e s i n May.  -5-  The  l a r v a l p e r i o d u s u a l l y l a s t s about 6 weeks, w i t h  o f t h e f e e d i n g o c c u r r i n g i n the f o u r t h and  fifth  (Hodson, 1941). Through t h e e a r l y i n s t a r s t h e  95%  instars  caterpillars  are g r e g a r i o u s ,  f e e d i n g t o g e t h e r on a s i n g l e t r e e . By  l a t e f o u r t h and  f i f t h i n s t a r s they become more independent  i n t h e i r f e e d i n g p a t t e r n s and,  given a shortage  the  i n the  food  s u p p l y , w i l l wander between t r e e s i n s e a r c h o f s u i t a b l e f o l i a g e . The  late instar larvae w i l l  f e e d upon most of t h e  d e c i d u o u s t r e e s n a t i v e t o c e n t r a l and n o r t h e r n By mid-  Ontario.  t o l a t e - J u n e t h e f i f t h i n s t a r l a r v a e form  cocoons i n r o l l e d l e a v e s of any r e m a i n i n g  v e g e t a t i o n . They  remain as pupae f o r about 2 weeks, emerging as a d u l t moths in e a r l y to mid-July.  adult f l y i n g period l a s t s for  1-2  weeks, w i t h t h e moths becoming a c t i v e i n l a t e a f t e r n o o n  and  e a r l y evening  The  and c o n t i n u i n g t h e i r a c t i v i t y t h r o u g h o u t t h e  night.  H i s t o r y of  Records from 18 67 t o 1982  Outbreaks  suggest t h a t t h e r e have been  12 o u t b r e a k s i n O n t a r i o d u r i n g t h i s p e r i o d , w i t h t h e t i m e between t h e onset o f each o u t b r e a k r a n g i n g from 6 t o years  ( S i p p e l l , 1962;  and D i s e a s e  Annual R e p o r t s of t h e F o r e s t  Survey f o r 1948-1982). S i p p e l l  14  Insect  (1962) d e s c r i b e d  an o u t b r e a k a t a t y p i c a l l o c a t i o n i n O n t a r i o as c o n s i s t i n g of 2-3  y e a r s o f i n c r e a s i n g p o p u l a t i o n s , 1-2  -6-  y e a r s of h i g h  p o p u l a t i o n s and 1 year o f d e c l i n e . Brown (1938), (1962) and Hodson (1977) have a l l found t h a t  Sippell  outbreaks  g e n e r a l l y s p r e a d s o u t h and e a s t over t i m e , c o r r e s p o n d i n g t o t h e d i r e c t i o n o f p r e v a i l i n g winds.  Host P r e f e r e n c e  The p r e f e r r e d host s p e c i e s o f t h e f o r e s t t e n t c a t e r p i l l a r v a r i e s a c r o s s i t s range.  I n t h e n o r t h e r n and  western p a r t s o f Ontario, which are p r i m a r i l y w i t h i n t h e B o r e a l F o r e s t , t r e m b l i n g aspen (Populus  tremuloides)  p r e f e r r e d c h o i c e o f egg l a y i n g moths ( S i p p e l l , i s also true of the P r a i r i e provinces 1975)  and n o r t h e r n Minnesota  i s the  1957). T h i s  ( H i l d a h l and Campbell,  (Hodson, 1941). As one moves  f u r t h e r s o u t h , i n t o a r e g i o n w i t h mixed c o n i f e r o u s and deciduous  t r e e s , t h e p r e f e r e n c e f o r egg l a y i n g s h i f t s t o  a l s o i n c l u d e sugar maple, A c e r saccharum, Quercus  rubrus  and r e d oak,  ( F o r e s t I n s e c t and D i s e a s e Survey,  comm.). Other t r e e s p e c i e s on which eggs have been t o h a t c h and s u b s e q u e n t l y  pers. observed  f e e d i n c l u d e ( S i p p e l l , 1957;  Connola e t al., 1957): -willow  (Salix  species) ;  - l a r g e t o o t h aspen (Populus -pin  c h e r r y (Frunus  -black cherry -apple  (Prunus  (Malus s p e c i e s ) .  -7-  grandidentata);  pennsylvanica); serotina);  W h i l e eggs and young l a r v a e are c o n f i n e d p r i m a r i l y t o t h e a f o r e m e n t i o n e d s p e c i e s , wandering will  late i n s t a r larvae  f e e d upon v i r t u a l l y a l l deciduous t r e e s n a t i v e t o  O n t a r i o . L i t t l e i s known about t h e f a c t o r s t h a t  influence  t h e s e l e c t i o n o f h o s t s p e c i e s by t h e egg l a y i n g moths, a l t h o u g h Hodson (1941) and S i p p e l l  (1957) have b o t h  s u g g e s t e d t h a t t h e t i m i n g o f budbreak may  be an i m p o r t a n t  factor i n determining early l a r v a l m o r t a l i t y .  Impact upon Hosts  Two  s t u d i e s have a s s e s s e d t h e h o s t m o r t a l i t y and  growth  l o s s caused by f o r e s t t e n t c a t e r p i l l a r d e f o l i a t i o n (Duncan and Hodson, 1958; H i l d a h l and Reeks, 1960) . B o t h found t h a t s e v e r a l y e a r s o f d e f o l i a t i o n caused some growth l o s s , w i t h growth r e t u r n i n g t o p r e - d e f o l i a t i o n l e v e l s i n t h e  second  y e a r f o l l o w i n g an o u t b r e a k ' s c o l l a p s e . Tree m o r t a l i t y  was  generally considered n e g l i g i b l e .  Egg M o r t a l i t y  Most s t u d i e s have found egg m o r t a l i t y t o be  relatively  low t h r o u g h t h e c o u r s e o f an o u t b r e a k . M o r t a l i t y due t o egg p a r a s i t i s m has been found t o range from 0 t o 10% 1941; Connola e t al., 1972). One  1957;  (Hodson,  I v e s , 1971; W i t t e r and Kulman,  c l i m a t i c f a c t o r t h a t has been l i n k e d t o h i g h e r egg  -8-  m o r t a l i t y i s e x t r e m e l y low w i n t e r t e m p e r a t u r e s . A s t u d y of t h e s e a s o n a l v a r i a t i o n i n g l y c e r o l c o n t e n t o f eggs found t h a t t h e y c o u l d be c o o l e d t o -41°C  i n January w i t h o u t f r e e z i n g  (Hanec, 1966). A subsequent s t u d y i n n o r t h e r n M i n n e s o t a found egg m o r t a l i t y , from f a c t o r s o t h e r t h a n p a r a s i t i s m infertility,  and  t o v a r y from 0 t o 65% over a 9 y e a r p e r i o d  ( W i t t e r et a l . ,  1975). Egg m o r t a l i t y f o r t h e 5 y e a r s f o r  w h i c h t h e t e m p e r a t u r e d i d not drop below -4 0°C ranged from 0 t o 10%, w h i l e i n t h e 4 y e a r s where t e m p e r a t u r e s dropped below t h i s t h r e s h o l d m o r t a l i t y ranged from 10 t o 65%. Hodson (1941), however, has r e p o r t e d t h e p r e s e n c e o f l a r v a e i n areas w h i c h e x p e r i e n c e d t e m p e r a t u r e s as low as -47°C t h e p r e v i o u s winter. Other e x p e r i m e n t s e x a m i n i n g t h e p r e - h a t c h e f f e c t s o f t e m p e r a t u r e have shown t h a t eggs kept below 5°C w i l l hatch  never  (Hodson and Weinman, 1945), and eggs can s u r v i v e  exposure t o c o l d t e m p e r a t u r e s (as low as -20°C) a few days b e f o r e h a t c h i n g (Wetzel et a l . ,  1973; Raske, 1975).  Larval Mortality  Climatic  factors  L a b o r a t o r y e x p e r i m e n t s have shown t h a t l a r v a e a r e a b l e t o s u r v i v e t e m p e r a t u r e s as low as -12°C hatch  immediately a f t e r  ( I v e s , 1971). As p r o l o n g e d extreme t e m p e r a t u r e s such  -9-  as t h e s e a r e r a r e l y e n c o u n t e r e d i n t h e f i e l d t h r o u g h t h e l a r v a l s t a g e , t h e y a r e not thought t o be d i r e c t l y r e s p o n s i b l e f o r much l a r v a l m o r t a l i t y  (Raske,  1975).  Starvation There a r e s e v e r a l r e p o r t s o f s p r i n g storms d e s t r o y i n g h o s t f o l i a g e and s u b s e q u e n t l y c a u s i n g e a r l y i n s t a r m o r t a l i t y through s t a r v a t i o n  (Hodson,  larval  1941; B l a i s et al.,  1955; Connola e t al., 1957). Two o f t h e s e r e p o r t s a l s o i n c l u d e a mention o f areas a d j a c e n t t o t h o s e whose  foliage  was d e s t r o y e d where s t a r v a t i o n d i d not o c c u r (Hodson, 1941; B l a i s e t al., 1955). I n b o t h cases l a r g e b o d i e s o f water p r o v i d e d c o o l e r s p r i n g temperatures i n the adjacent areas, d e l a y i n g t h e h a t c h and h o s t budburst u n t i l a f t e r t h e storm. The i n d i r e c t e f f e c t o f t e m p e r a t u r e upon l a r v a l f e e d i n g may a l s o cause s i g n i f i c a n t l a r v a l m o r t a l i t y . Hodson  (1941)  found t h a t a t t e m p e r a t u r e s below 15°C l a r v a e do l i t t l e o r no f e e d i n g , and t h a t most o f t h e d e f o l i a t i n g i s done on days when t h e d a i l y maximum t e m p e r a t u r e exceeded 23°C. W e l l i n g t o n (1952) o b s e r v e d t h a t l a r v a e were most a c t i v e i n warm, humid weather,  and s u g g e s t e d t h a t y e a r s o f m o i s t , warm weather  d u r i n g the l a r v a l stage are f a v o u r a b l e f o r p o p u l a t i o n i n c r e a s e s . By e x a m i n i n g t h e maps o f c y c l o n i c c e n t r e s a t 2 l o c a t i o n s , W e l l i n g t o n (1952) showed t h a t i n t h e y e a r s p r i o r t o o u t b r e a k s t h e r e was an above average number o f passages o f warm, m o i s t a i r masses d u r i n g t h e l a r v a l s t a g e . I v e s  -10-  (1973) e x p l o r e d t h e r e l a t i o n s h i p between v a r i o u s t e m p e r a t u r e i n d i c e s and o u t b r e a k s , f o r 10 l o c a t i o n s , over a 40 y e a r p e r i o d . He s u g g e s t e d t h a t p o p u l a t i o n i n c r e a s e s were p r e c e d e d by a s i n g l e y e a r  (2 t o 4 y e a r s p r i o r ) w i t h above average  t e m p e r a t u r e s i n t h e 3 weeks f o l l o w i n g h a t c h , w h i l e p o p u l a t i o n d e c r e a s e s were p r e c e d e d by a y e a r w i t h average t e m p e r a t u r e s  below  (same y e a r , o r 1 t o 2 y e a r s p r i o r ) .  Hodson (1977) compared t e m p e r a t u r e r e c o r d s d u r i n g t h e 3 weeks f o l l o w i n g egg h a t c h t o c a t e r p i l l a r abundance over t h e c o u r s e o f 2 o u t b r e a k s a t 2 l o c a t i o n s i n M i n n e s o t a . He  found  t h a t t e m p e r a t u r e s were g e n e r a l l y above average 2 t o 3 y e a r s p r i o r t o t h e s t a r t o f o u t b r e a k s , and below average i n t h e y e a r s o f d e c r e a s i n g abundance. F i n a l l y , l a r v a l mortality i n high density populations has a l s o been a t t r i b u t e d t o l a t e i n s t a r s t a r v a t i o n ,  as  l a r v a e can exhaust t h e i r f o o d s u p p l y b e f o r e t h e i r development  i s complete  (Hodson,  1977; S i p p e l l ,  1957).  Disease N u c l e a r p o l y h e d r o s i s v i r u s has been p r e v a l e n t i n some populations, with epizootics  (and subsequent  larval  m o r t a l i t y ) most o f t e n o c c u r r i n g i n p o p u l a t i o n s t h a t have been a t h i g h d e n s i t i e s f o r s e v e r a l g e n e r a t i o n s ( S t a i r s , 1972). V i r u s i s t r a n s m i t t e d on t h e t r e e s and egg masses ( C l a r k , 1958), and t h e p u p a l p a r a s i t e Sarcophaga  aldrichi  may  1966).  a l s o be c a p a b l e of t r a n s m i t t i n g v i r u s  -11-  (Stairs,  Predation A study o f b i r d p r e d a t i o n d u r i n g one year o f a  northern  M i n n e s o t a o u t b r e a k showed t h a t a wide v a r i e t y o f b i r d s w i l l f e e d upon f o r e s t t e n t c a t e r p i l l a r l a r v a e al.,  (Fashingbauer  et  1957). W h i l e m o r t a l i t y due t o p r e d a t i o n i s t h o u g h t t o  be n e g l i g i b l e a t h i g h d e n s i t i e s , l i t t l e i s known o f i t s i m p o r t a n c e i n endemic y e a r s .  Pupal M o r t a l i t y  S e v e r a l s t u d i e s of p u p a l p a r a s i t i s m have found t h a t r a t e s i n c r e a s e over the course of an o u t b r e a k Connola e t al., al.,  1975;  1957;  S i p p e l l , 1957;  Hodson, 1977). The  (Hodson,  I v e s , 1971;  1941;  W i t t e r et  g e n e r a l consensus i s t h a t  these r a t e s reach t h e i r highest l e v e l s only a f t e r a p o p u l a t i o n d e c l i n e has been i n i t i a t e d by some o t h e r The  dominant p u p a l p a r a s i t e i s t h e f l e s h f l y ,  Sarcophaga aldrichi  factor.  aldrichi  Parker. While the p r e f e r r e d host of  i s t h e f o r e s t t e n t c a t e r p i l l a r , i t has  r e a r e d from t h e gypsy moth, Porthetria moth, Stilpnotia Choristoneura  dispar,  S.  a l s o been the  satin  salicls,  and t h e e a s t e r n s p r u c e budworm,  fumiferana  ( A r t h u r and C o p p e l , 1953). A d u l t  f l i e s appear i n mid t o l a t e May, p e r i o d l a s t i n g 3-4  w i t h the  prelarviposition  weeks. Once l a r v i p o s i t i o n b e g i n s  the  female f l y d e p o s i t s s i n g l e l a r v a i n t e r m i t t e n t l y onto t h e  -12-  cocoons of t h e f o r e s t t e n t c a t e r p i l l a r . A f t e r 8-12  days t h e  f u l l y f e d l a r v a drops t o t h e ground, where i t forms a puparium and  overwinters  Sippell  (Hodson, 1939).  (1957) r e c o r d e d r a t e s of p u p a l p a r a s i t i s m at  d i f f e r e n t l o c a t i o n s across Ontario o u t b r e a k . He  over t h e c o u r s e o f  16  an  found t h a t t h e r a t e at which cocoons were  p a r a s i t i z e d by  S. aldrichi  went from an average o f about  i n t h e f i r s t o u t b r e a k y e a r t o 75% i n t h e f o u r t h , w i t h  20%  rates  of t o t a l p u p a l p a r a s i t i s m f o r most s i t e s i n e x c e s s of 90% t h e l a t e r o u t b r e a k y e a r s . Hodson (1941) found t h a t r a t e s parasitism increased with distance o u t b r e a k s , and  from t h e c e n t r e o f  c o n c l u d e d t h a t S. aldrichi  Adult  of  local  populations  i n c r e a s e r a p i d l y where t h e r e are h i g h h o s t numbers and e x t e n d t h e i r range i n t o s u r r o u n d i n g  in  then  areas.  Dispersal  L i t t l e i s known about t h e d i s p e r s a l p a t t e r n s  of  adult  moths. Hodson (1941) found t h a t a d u l t s o f b o t h sexes l i v e d f o r about 5 days, w i t h moth emergence g e n e r a l l y over a two  occurring  week p e r i o d . Brown (1965) found moths i n A l b e r t a  t h a t had been c a r r i e d f o r at l e a s t 450  km by t h e  a i r a s s o c i a t e d w i t h a c o l d f r o n t , w h i l e Greenbank estimated  a n o t h e r mass movement of moths t o have  over a d i s t a n c e o f about 80  km.  -13-  turbulent (1954) occurred  Summary  The  f o l l o w i n g f a c t o r s are c u r r e n t l y thought t o  i n f l u e n c e t h e p o p u l a t i o n dynamics o f t h e f o r e s t t e n t c a t e r p i l l a r i n Ontario: 1. L a r v a l f e e d i n g t e m p e r a t u r e There i s e v i d e n c e s u g g e s t i n g t h a t t e m p e r a t u r e d u r i n g t h e e a r l y l a r v a l f e e d i n g p e r i o d i s an i m p o r t a n t determining  factor i n  l a r v a l s u r v i v a l , w i t h warm t e m p e r a t u r e s b e i n g  f a v o u r a b l e t o p o p u l a t i o n i n c r e a s e s . The s t u d i e s p r o v i d i n g t h i s e v i d e n c e have a l l been c o r r e l a t i v e , r e l a t i n g  patterns  o f o u t b r e a k s t o t e m p e r a t u r e r e c o r d s . However, r e s u l t s o f such c l i m a t i c s t u d i e s a r e o f t e n d i f f i c u l t t o i n t e r p r e t ( M a r t i n a t , 1987; Myers, 1988), p a r t i c u l a r l y when t h e number of a s s o c i a t i o n s considered are high t h e number o f o b s e r v a t i o n s 1952;  (such as I v e s , 1973), o r  a r e few (as w i t h W e l l i n g t o n ,  B l a i s e t al., 1955; Hodson, 1977).  2. O v e r w i n t e r i n g  temperature  A second c l i m a t i c h y p o t h e s i s  i s that pharate  larval  m o r t a l i t y i n c r e a s e s s h a r p l y i n t h o s e y e a r s when w i n t e r t e m p e r a t u r e s drop below -40°C ( W i t t e r e t al., 1975). T h i s f i n d i n g , however, i s based upon measurements made a t o n l y a s i n g l e l o c a t i o n , over t h e course  -14-  o f one o u t b r e a k .  3. P u p a l p a r a s i t i s m The r a t e o f p u p a l p a r a s i t i s m has been found t o r i s e over t h e c o u r s e o f an outbreak outbreak  and may c o n t r i b u t e t o  c o l l a p s e s . I t i s n o t c l e a r , however, whether t h e  p a r a s i t e s cause t h e p o p u l a t i o n changes o r s i m p l y r e s p o n d t o them. 4. Food s u p p l y and d i s e a s e D i s e a s e and e x h a u s t i o n o f t h e f o o d s u p p l y k i l l  late  i n s t a r l a r v a e i n some h i g h d e n s i t y p o p u l a t i o n s and have c o n t r i b u t e d t o t h e c o l l a p s e o f some o u t b r e a k s . 5. A d u l t  dispersal  D e f o l i a t i o n maps f o r v a r i o u s o u t b r e a k s  show an apparent  year-to-year spread i n the area d e f o l i a t e d , suggesting t h a t moth d i s p e r s a l may p l a y an i m p o r t a n t r o l e i n d e t e r m i n i n g t h e s p a t i a l p r o g r e s s i o n of outbreaks.  -15-  CHAPTER 3 PATTERN OF OUTBREAKS  The f o l l o w i n g c h a p t e r p r e s e n t s t h e f o r e s t t e n t c a t e r p i l l a r d e f o l i a t i o n maps f o r O n t a r i o from 1948 t o 1988. The f i r s t s e c t i o n o u t l i n e s t h e methods used t o g e n e r a t e t h e s e maps. T h i s i s f o l l o w e d by an assessment o f t h e q u a l i t y o f t h i s i n f o r m a t i o n : t h e r e l a t i o n s h i p between t h e maps and t r u e i n s e c t abundance, and t h e s c a l e a t w h i c h t h e maps can be m e a n i n g f u l l y i n t e r p r e t e d . F i n a l l y , t h e maps a r e used t o p r o v i d e a p i c t u r e o f t h e p r o v i n c e - w i d e s p a t i a l and t e m p o r a l pattern of outbreaks.  Defoliation  Maps  S i n c e 1948, r a n g e r s from t h e F o r e s t I n s e c t and D i s e a s e Survey a t F o r e s t r y Canada's Great Lakes F o r e s t r y C e n t r e have been mapping t h e e x t e n t o f d e f o l i a t i o n by t h e f o r e s t t e n t c a t e r p i l l a r i n O n t a r i o . T h i s mapping i s done by f o l l o w i n g f l i g h t l i n e s 5-10 km a p a r t back and f o r t h a c r o s s areas s u s p e c t e d o f b e i n g d e f o l i a t e d and s k e t c h i n g t h e a r e a s t h a t show moderate t o s e v e r e d e f o l i a t i o n . The mapping i s done each y e a r a f t e r t h e l a r v a e have f i n i s h e d t h e i r f e e d i n g and before the host t r e e s r e f o l i a t e . L o c a t i n g t h e e x a c t boundary between d e f o l i a t e d and nond e f o l i a t e d a r e a s i s somewhat s u b j e c t i v e , and v a r i e s  -16-  a c c o r d i n g t o each mapper's i n t e r p r e t a t i o n o f "moderate t o s e v e r e " and t h e t i m i n g o f t h e f l i g h t w i t h r e s p e c t t o i n s e c t f e e d i n g and h o s t r e f o l i a t i o n . I f a l a r g e a r e a has been d e f o l i a t e d , most s k e t c h mappers w i l l n o t t r y t o d e l i n e a t e n o n - d e f o l i a t e d stands  ( o f t e n non-host s p e c i e s ) w i t h i n t h e  general i n f e s t a t i o n boundaries.  Conversely,  small pockets of  d e f o l i a t i o n i n l o c a t i o n s f a r from any p r e v i o u s  defoliation  may n o t be r e c o r d e d . Each r a n g e r maps t h e d e f o l i a t i o n onto t o p o g r a p h i c  base  maps, u s u a l l y a t a s c a l e o f 1:100,000. The maps o f a l l t h e rangers  i n O n t a r i o a r e then combined each y e a r t o c r e a t e a  s i n g l e province-wide  map, u s u a l l y a t a s c a l e o f 1:1,584,000  (1 inch=25 m i l e s ) . I n some y e a r s areas o f d e f o l i a t i o n were mapped a c c o r d i n g t o t h r e e l e v e l s o f s e v e r i t y ( l i g h t , moderate and s e v e r e ) , w h i l e i n o t h e r y e a r s d e f o l i a t i o n was mapped a c c o r d i n g t o o n l y one (moderate t o s e v e r e ) . To compare one y e a r t o t h e n e x t , o r one outbreak have dropped t h e l i g h t c a t e g o r y  t o t h e next, I  from t h o s e maps where i t  e x i s t e d , and combined t h e moderate and s e v e r e c a t e g o r i e s . The  41 annual maps were t h e n d i g i t i z e d u s i n g t h e  ARC/INFO G e o g r a p h i c I n f o r m a t i o n System; t h e r e s u l t i n g maps a r e shown i n F i g u r e 1. A l l o f t h e maps i n t h i s t h e s i s a r e d i s p l a y e d u s i n g a Lambert Conformal p r o j e c t i o n ( s t a n d a r d p a r a l l e l s 44.5° and 53.5°, c e n t r a l m e r i d i a n  -17-  -85°).  F i g u r e 1. A n n u a l maps o f t h e a r e a in Ontario, 1948-1988.  within  which  moderate  to severe  defoliation  has  occurred  F i g u r e 1.  (continued)  F i g u r e 1.  (continued)  km 0  F i g u r e 1.  (continued)  500  1000  Maps and I n s e c t Abundance  The d e f o l i a t i o n maps p r o v i d e o n l y a c o a r s e p i c t u r e o f t h e changes i n abundance o f t h e f o r e s t t e n t c a t e r p i l l a r i n O n t a r i o . B e f o r e u s i n g t h e maps t o make i n f e r e n c e s about t h e dynamics o f t h e i n s e c t i n O n t a r i o , i t would be u s e f u l t o discuss the q u a l i t y of t h i s information. F i r s t c o n s i d e r t h e r e l a t i o n s h i p between a p a r t i c u l a r l e v e l o f d e f o l i a t i o n and f o r e s t t e n t c a t e r p i l l a r abundance each y e a r . R e c a l l  (from Chapter 2) t h a t 95% o f t h e f e e d i n g  o c c u r s i n t h e 4 t h and 5 t h i n s t a r s  (Hodson, 1941). As  d e f o l i a t i o n i s mapped a t t h e end o f t h e l a r v a l p e r i o d each y e a r , t h e l e v e l o f d e f o l i a t i o n i s thus an i n d e x o f t h e i n s t a r l a r v a l abundance. A study i n n o r t h e r n  late  Minnesota,  where l i k e much o f O n t a r i o t r e m b l i n g aspen i s t h e p r i m a r y h o s t s p e c i e s , d e t e r m i n e d t h a t each c a t e r p i l l a r consumes a p p r o x i m a t e l y 8.5 l e a v e s i n i t s l i f e t i m e  (Hodson, 1941). The  s t u d y a l s o e s t i m a t e d t h e number o f l e a v e s p e r t r e m b l i n g aspen t r e e as a f u n c t i o n o f t r e e d i a m e t e r ; t h i s v a r i e d  from  about 2 0 0 0 t o 2 0 0 0 0 f o r t h e range o f t r e e d i a m e t e r s i n t h e i r study p l o t s  (2.5 cm t o 18 cm d i a m e t e r a t b r e a s t h e i g h t ) . I n  another n o r t h e r n Minnesota  study, W i t t e r (1971)  determined  t h a t a t y p i c a l aspen dominated s t a n d had an average t r e e d i a m e t e r o f 8.7 cm, which c o r r e s p o n d s t o an average o f 1 0 0 0 0 l e a v e s p e r t r e e . From t h e s e f i g u r e s one can e s t i m a t e t h a t t h e number o f l a r v a e r e q u i r e d t o c o m p l e t e l y d e f o l i a t e an  -22-  area would need t o be about 1200 l e a v e s per t r e e / 8.5  l a r v a e per h o s t t r e e  (10000  l e a v e s per l a r v a e ) .  T h i s r e l a t i o n s h i p would v a r y somewhat from s t a n d  to  s t a n d a c c o r d i n g t o the s i z e s t r u c t u r e of i t s aspen component. I t may  a l s o be q u i t e d i f f e r e n t i n t h e  p a r t o f t h e p r o v i n c e , where sugar maple and oak important  h o s t s p e c i e s , as t h e l a r v a l f e e d i n g  f o r t h e s e o t h e r s p e c i e s may  are a l s o  requirements  d i f f e r from t h o s e of  aspen. F o r example, a study of f o r e s t t e n t f e e d i n g upon t u p e l o gum  southern  (Nyssa aquatica  trembling  caterpillar  L.)  trees i n  s o u t h e r n L o u i s i a n a found t h a t each l a r v a e consumed 3 t i m e s more l e a f a r e a t h a n was Minnesota  (Smith et al.,  consumed f o r t h e t r e m b l i n g aspen i n 1986).  These problems a s i d e , we now  have a rough e s t i m a t e  of  t h e l a t e l a r v a l d e n s i t i e s r e q u i r e d t o cause complete d e f o l i a t i o n i n an a r e a . However, t h e s k e t c h maps o f F i g u r e 1 do not show complete d e f o l i a t i o n , but r a t h e r a r e a s w i t h i n which moderate t o s e v e r e d e f o l i a t i o n has  occurred.  So what  i s t h e r e l a t i o n s h i p between an a r e a marked as m o d e r a t e l y t o s e v e r e l y d e f o l i a t e d and t h e p e r c e n t a g e d e f o l i a t i o n ? Based upon t h e d i f f e r e n c e between t h e w e i g h t s of on d e f o l i a t e d and n o n - d e f o l i a t e d t r e e s , Ives  leaves  (1971) found  t h a t t h e t r u e d e f o l i a t i o n f o r s t a n d s c l a s s i f i e d from the a i r as m o d e r a t e l y t o s e v e r e l y d e f o l i a t e d ranged from 60-100%. T h i s would c o r r e s p o n d t o l a r v a l d e n s i t i e s o f at l e a s t  -23-  700-1200 l a r v a e per t r e e i n t h e a r e a s t h a t are c l a s s i f i e d  as  m o d e r a t e l y t o s e v e r e l y d e f o l i a t e d . Note t h a t t h i s i s t h e minimum l a r v a l d e n s i t y which w i l l cause moderate t o s e v e r e d e f o l i a t i o n ; Hodson (1941) has  r e p o r t e d l a r v a l d e n s i t i e s as  h i g h as 8000 p e r t r e e i n some s t a n d s .  But t h e s k e t c h mappers  f i l t e r out s m a l l e r p o c k e t s o f d e f o l i a t e d and  non-defoliated  a r e a s ; t h e y do not always d e l i n e a t e n o n - d e f o l i a t e d w i t h i n l a r g e r i n f e s t a t i o n s and can miss s m a l l e r  areas  isolated  p o c k e t s of d e f o l i a t i o n . T h i s i m p l i e s t h a t t h e u n c e r t a i n t y i n l a r v a l densities associated with a p a r t i c u l a r l e v e l  of  d e f o l i a t i o n i s s c a l e dependent. At a s t a n d l e v e l t h e maps have a r e l a t i v e l y weak l i n k t o l a r v a l d e n s i t i e s ; when a p a r t i c u l a r s t a n d i s mapped as d e f o l i a t e d , i t does not n e c e s s a r i l y mean t h a t t h e r e were h i g h l a r v a l d e n s i t i e s . T h i s s u g g e s t s t h a t t h e maps w i l l be o f more use larger scaled analyses.  I t i s d i f f i c u l t to decide  for  upon t h e  minimum s c a l e o f a n a l y s i s , however, w i t h o u t  knowing more  about t h e f i l t e r i n g p r o c e s s o f t h e r a n g e r s .  Because o f  s c a l e at w h i c h t h e r a n g e r s f l y t h e i r f l i g h t l i n e s  the  (5-10km),  and t h e s c a l e a t w h i c h the p r o v i n c e - w i d e maps were p r o d u c e d (1:1,584,000), i n t e r p r e t i n g t h e maps at a s c a l e as f i n e 10km  by 10km  would be of l i t t l e v a l u e . A s c a l e o f about  100km by 100km i s p r o b a b l y  more a p p r o p r i a t e .  F i n a l l y , w h i l e the maps g i v e us a crude measure o f absolute  as  abundance of l a t e i n s t a r l a r v a e f o r an a r e a i n  g i v e n y e a r , t h e y are p r o b a b l y  -24-  b e s t used as a measure o f  the any the  change i n abundance a t a p a r t i c u l a r l o c a t i o n from one y e a r t o t h e n e x t . F o r example, c o n s i d e r a 100km by 100km a r e a f o r w h i c h 50% o f t h e a r e a i s d e f o l i a t e d one y e a r and o n l y 10% o f t h e a r e a i s d e f o l i a t e d t h e y e a r a f t e r . A l t h o u g h t h e r e may be considerable uncertainty regarding the absolute density of l a r v a e each year,, one can be more c e r t a i n t h a t t h e r e was a d e c r e a s e i n abundance between mappings.  Pattern of  Defoliation  The p r o v i n c e - w i d e t i m e s e r i e s o f d e f o l i a t i o n shows t h a t t h e r e have been t h r e e o u t b r e a k s s i n c e 1948, w i t h a f o u r t h c u r r e n t l y underway ( F i g u r e 2 ) . A t t h i s s c a l e t h e f o r e s t t e n t c a t e r p i l l a r would appear t o be a p e r i o d i c d e f o l i a t o r , t h e peak y e a r s o f d e f o l i a t i o n h a v i n g o c c u r r e d a t e x a c t l y 13 year i n t e r v a l s . Each outbreak has c o n s i s t e d o f 4-6 y e a r s o f i n c r e a s i n g d e f o l i a t i o n , f o l l o w e d by r o u g h l y t h e same number of decreasing years. F i g u r e 3 shows t h e d i f f e r e n c e i n s p a t i a l e x t e n t o f each o f t h e s e o u t b r e a k s . By o v e r l a y i n g t h e f o u r maps o f F i g u r e 3, one sees t h a t w h i l e t h e p a t t e r n o f d e f o l i a t i o n appears t o be p e r i o d i c a t a p r o v i n c e - w i d e s c a l e , t h e r e a r e many a r e a s t h a t have had o n l y one o r two o u t b r e a k s t h r o u g h t h i s 41 y e a r period  ( F i g u r e 4 ) . I n f a c t t h e r e would appear t o be a number  o f r e g i o n s w i t h i n which t h e dynamics,  at least  q u a l i t a t i v e l y , appear t o be q u i t e s i m i l a r over t h e f u l l 41  -25-  300000 -i  J  200000  or  cc CD  <  100000 H  1940  1950  1960  1970  1980  Year  F i g u r e 2. T o t a l area w i t h i n which moderate t o severe d e f o l i a t i o n has o c c u r r e d each year i n O n t a r i o , 1948-88  -26-  1990  /  L-  1  19 8 3 - 81  km i  500  i  — i  1000  3 . Composite maps showing the t o t a l e x t e n t of the moderate t o severe d e f o l i a t i o n f o r each o f the f o u r province-wide outbreaks from 1948-88. F i g u r e  -27-  F i g u r e 4. The number o f o u t b r e a k s t h a t h a v e o c c u r r e d t h r o u g h o u t t h e p r o v i n c e f r o m 1948-88. ( N o t e : t h i s map c r e a t e d b y o v e r l a y i n g t h e 4 maps o f F i g u r e 3.)  -28-  was  year p e r i o d . These are most r e a d i l y seen from t h e 1972-82 map  o f F i g u r e 3, where t h e r e are t h r e e q u i t e  outbreak  r e g i o n s and a f o u r t h area  separate  (North-Centre)  w i t h no  defoliation. T h i s d i f f e r e n c e between r e g i o n s s u g g e s t s  t h a t the  dynamics ( i . e . t h e p e r i o d i c i t y , s e v e r i t y and d u r a t i o n o f outbreaks)  may  be a f u n c t i o n of the s c a l e and l o c a t i o n a t  w h i c h t h e y are measured. To e x p l o r e t h i s f u r t h e r I chose f o u r l o c a t i o n s a c r o s s t h e p r o v i n c e , each o f which c e n t e r e d w i t h i n one o f f o u r g e n e r a l outbreak 5).  was  regions  (Figure  G i v e n t h e s e f o u r l o c a t i o n s I then c r e a t e d a time s e r i e s  of d e f o l i a t i o n f o r three s p a t i a l s c a l e s . Using c e l l s of 3 different sizes  (100x100 km,  200x200 km and 400x400  km),  c e n t e r e d a t each o f t h e f o u r l o c a t i o n s , I c a l c u l a t e d t h e p r o p o r t i o n o f l a n d a r e a w i t h i n a c e l l t h a t was  defoliated  each y e a r . The Looking  r e s u l t s o f t h i s a n a l y s i s are shown i n F i g u r e  6.  f i r s t a c r o s s t h e rows o f t h i s f i g u r e , one sees t h a t  t h e p a t t e r n o f d e f o l i a t i o n f o r a p a r t i c u l a r l o c a t i o n does not change a p p r e c i a b l y over s c a l e s o f 100-400 km. down t h e columns, however, one  Looking  sees t h a t t h e dynamics do  change from one r e g i o n t o t h e n e x t . W h i l e t h e North-West r e g i o n e x h i b i t s the province-wide  p e r i o d i c i t y , the  other  r e g i o n s s u f f e r e d l i t t l e or no d e f o l i a t i o n i n a t l e a s t one t h e f i r s t t h r e e o u t b r e a k s . Whenever d e f o l i a t i o n does  -29-  of  F i g u r e 5. The l o c a t i o n of the c e l l s d e f i n i n g the 4 outbreak r e g i o n s (North-West, North-Centre, North-East and SouthEast) at each o f 3 s c a l e s (100x100 km, 200x200 km and 400x400 km).  -30-  100km x 100km  200km x 200km  400km x 400km  1  I  rl  N-W  N-C i  c .o  3? o  M—  CD  Q  —  1940  A L l fil / 1860  1860  1970  1980  1990  1940  J L 1960  J  4  N-E  —rT.  S-E I960  1970  1980  1990  1940  1950  1960  1970  1B80  1990  Year  F i g u r e 6. The p r o p o r t i o n o f l a n d area d e f o l i a t e d w i t h i n each o f t h e 4 outbreak r e g i o n s , a t 3 d i f f e r e n t s c a l e s . See F i g u r e 5 f o r d e t a i l s o f r e g i o n and s c a l e l o c a t i o n s .  o c c u r i n a r e g i o n , however, t h e p a t t e r n o f d e f o l i a t i o n i s roughly synchronized across the e n t i r e province. The p o p u l a t i o n dynamics o f t h e f o r e s t t e n t  caterpillar  appear t o be homogeneous over areas t h a t a r e w i t h i n a p p r o x i m a t e l y 50-200km o f each o t h e r . W h i l e t h e r i s e s and f a l l s a r e somewhat synchronous  over d i s t a n c e s g r e a t e r t h a n  t h i s , t h e s e v e r i t y o f o u t b r e a k s would appear t o v a r y c o n s i d e r a b l y at t h i s l a r g e r s p a t i a l s c a l e . This suggests t h a t f a c t o r s which a r e homogeneous over t h i s s m a l l e r (200 km) s c a l e , y e t v a r y from one r e g i o n t o t h e next w i t h i n t h e p r o v i n c e , may p l a y an i m p o r t a n t r o l e i n s h a p i n g t h e o b s e r v e d pattern of outbreaks.  Summary  The a r e a s w i t h i n which d e f o l i a t i o n by t h e f o r e s t t e n t c a t e r p i l l a r has o c c u r r e d each y e a r have been mapped i n O n t a r i o from 1948 t o 1988. These maps p r o v i d e an i n d e x o f t h e l a t e l a r v a l d e n s i t i e s each y e a r , and a r e b e s t used as a measure o f r e l a t i v e changes i n abundance f o r l a r g e r s c a l e d a n a l y s e s . The p a t t e r n o f d e f o l i a t i o n i n O n t a r i o s u g g e s t s t h a t , w h i l e o u t b r e a k s appear p e r i o d i c a l l y a t a p r o v i n c e - w i d e scale, there i s considerable variation i n t h e i r from r e g i o n t o r e g i o n and outbreak t o o u t b r e a k .  -32-  severity  CHAPTER 4 CLIMATE AND FOREST COMPOSITION  Recent r e v i e w s  suggest t h a t s t u d i e s o f t h e f o r e s t t e n t  c a t e r p i l l a r p r o v i d e e v i d e n c e o f how weather can p l a y an important  r o l e i n t r i g g e r i n g f o r e s t i n s e c t outbreaks  ( M a r t i n a t , 1987;  Wallner,  1987). I n p a r t i c u l a r t h e r e i s  e v i d e n c e t o suggest t h a t b o t h t h e t e m p e r a t u r e t h r o u g h t h e e a r l y l a r v a l f e e d i n g p e r i o d , and t h e minimum t e m p e r a t u r e t h r o u g h t h e w i n t e r , may determine when and where o u t b r e a k s occur i n Ontario  (see Chapter 2 ) .  F o r t h e most p a r t , however, t h e s e s t u d i e s have i n v o l v e d observations  a t o n l y a few p o i n t s i n space and t i m e . I n t h e  f o l l o w i n g chapter,  41 y e a r s o f l a r g e s c a l e d d e f o l i a t i o n  w i l l be u s e d i n c o n j u n c t i o n w i t h m a c r o - c l i m a t i c composition  data  and f o r e s t  i n f o r m a t i o n t o e x p l o r e some o f t h e p r e v i o u s l y  d e v e l o p e d hypotheses r e g a r d i n g t h e r o l e o f c l i m a t e i n outbreaks.  The a n a l y s i s w i l l b e g i n by e x a m i n i n g t h e  r e l a t i o n s h i p between t h e y e a r - t o - y e a r  changes i n d e f o l i a t i o n  and b o t h t h e t e m p e r a t u r e d u r i n g l a r v a l f e e d i n g and t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e . The l o n g - t e r m  pattern of  o u t b r e a k s w i l l t h e n be compared t o p a t t e r n s o f c l i m a t e and host  availability.  -33-  L a r v a l Feeding Temperature  S e v e r a l s t u d i e s have p r o v i d e d e v i d e n c e l i n k i n g t h e r i s e s and f a l l s o f o u t b r e a k s t o t h e t e m p e r a t u r e t o w h i c h t h e e a r l y i n s t a r l a r v a e a r e exposed  (Table I ) . With t h e  e x c e p t i o n o f t h e s t u d y by I v e s (1973), whose r e s u l t s a r e somewhat d i f f i c u l t  t o i n t e r p r e t , t h e s e f i n d i n g s a r e based  upon o n l y a few i s o l a t e d o b s e r v a t i o n s o f p o p u l a t i o n changes. The l o c a l n a t u r e o f t h i s work makes i t d i f f i c u l t the  to assess  s i g n i f i c a n c e o f such a f a c t o r over a l a r g e r s p a t i a l  and  t e m p o r a l s c a l e . W h i l e u n f a v o u r a b l e c l i m a t e may be c a p a b l e o f i n d u c i n g h i g h e r l a r v a l m o r t a l i t y i n a p a r t i c u l a r l o c a t i o n or y e a r , i t i s not c l e a r whether  i t has d e t e r m i n e d changes i n  abundance i n O n t a r i o . To i n v e s t i g a t e t h i s r e l a t i o n s h i p f u r t h e r I w i l l use  two  s o u r c e s o f i n f o r m a t i o n : annual maps o f t h e areas w i t h i n w h i c h moderate t o s e v e r e d e f o l i a t i o n o c c u r r e d i n O n t a r i o from 1948 t o 1988  (as o u t l i n e d i n C h a p t e r 3 ) , and d a i l y  maximum and minimum t e m p e r a t u r e d a t a , from t h e A t m o s p h e r i c Environment  S e r v i c e o f Environment  Canada, f o r a network  of  20 s t a t i o n s a c r o s s t h e p r o v i n c e over t h i s same p e r i o d (Figure 7 ) . Two  criteria  were used i n s e l e c t i n g t h e c l i m a t e  s t a t i o n s t o be used i n t h i s a n a l y s i s . F i r s t ,  s t a t i o n s were  s e l e c t e d such t h a t t h e y were a p p r o x i m a t e l y 200 km a p a r t , a l t h o u g h t h i s was not always p o s s i b l e i n t h e n o r t h e r n p a r t  -34-  Table I S t u d i e s p r o v i d i n g evidence o f t h e r e l a t i o n s h i p between f o r e s t t e n t c a t e r p i l l a r o u t b r e a k s and t h e temperature through t h e e a r l y l a r v a l f e e d i n g p e r i o d .  Reference  Location  E x t e n t of Observations  Findings  Hodson (1941)  Northern Minnesota  2 locations 1 outbreak  C o l d , wet weather f o r 3 weeks a f t e r hatch; high l a r v a l m o r t a l i t y .  B l a i s e t al. (1955)  Manitoba & N-W O n t a r i o  2 locations 1 outbreak  P r o l o n g e d c o l d and wet f o l l o w i n g h a t c h ; outbreak c o l l a p s e d .  Ives  Ontario & Prairies  several locations and outbreaks  Years p r i o r t o s t a r t o f outbreaks warmer than y e a r s p r i o r t o c o l l a p s e s .  Minnesota  2 locations 2 outbreaks  Warm i n y e a r s p r i o r t o s t a r t o f o u t b r e a k s cool i n years p r i o r t o c o l l a p s e s .  (1973)  Hodson (1977)  Figure 7. The l o c a t i o n of t h e 20 c l i m a t e s t a t i o n s . S o l i d boxes i n d i c a t e t h e 4 s t a t i o n s whose r e s u l t s w i l l be d i s p l a y e d t h r o u g h o u t t h e remainder o f t h e t h e s i s .  o f t h e p r o v i n c e . Second,  s t a t i o n s were s e l e c t e d based upon  t h e completeness o f t h e i r r e c o r d from 1948 t o 1988.  To  e x t e n d t h e p e r i o d o f r e c o r d f o r t h o s e s t a t i o n s which were e i t h e r m i s s i n g r e c o r d s o r were r e p l a c e d o v e r t i m e w i t h a s t a t i o n nearby, s t a t i o n s w i t h i n 20 km o f each o t h e r were t r e a t e d as a s i n g l e  location.  G i v e n such a d a t a s e t , t h e f i r s t s t e p I f o l l o w e d i n t e s t i n g the importance of the e a r l y l a r v a l f e e d i n g t e m p e r a t u r e was t o p r e d i c t t h e s t a r t o f t h e l a r v a l s t a g e f o r each o f t h e 20 c l i m a t e s t a t i o n s and 41 y e a r s u s i n g a s i m p l e h a t c h model.  I t h e n c a l c u l a t e d a measure o f how f a v o u r a b l e  t h e s p r i n g t e m p e r a t u r e was t h r o u g h t h e e a r l y p a r t o f t h e l a r v a l p e r i o d f o r each s t a t i o n and y e a r . T h i s c l i m a t i c i n d e x was t h e n compared t o changes i n d e f o l i a t i o n , t o see i f c l i m a t i c a l l y f a v o u r a b l e l o c a t i o n s and y e a r s c o r r e s p o n d e d w i t h i n c r e a s e s i n abundance and u n f a v o u r a b l e ones w i t h decreases.  Hatch model Two models p r e d i c t i n g t h e h a t c h d a t e o f eggs from d a i l y maximum and minimum t e m p e r a t u r e d a t a have been d e v e l o p e d f o r the f o r e s t tent c a t e r p i l l a r use a heat u n i t development.  ( I v e s , 1973; Hodson, 1977); b o t h  (or degree-day)  concept t o p r e d i c t  egg  Such models a r e w i d e l y used f o r p r e d i c t i n g  i n s e c t development  (Wagner e t al.,  1984)  and are based upon  t h e f o l l o w i n g p r i n c i p l e s : t h e r e i s some t e m p e r a t u r e  -37-  t h r e s h o l d below which no egg development w i l l  occur;  whenever t h e t e m p e r a t u r e exceeds t h i s t h r e s h o l d , t h e r e l a t i o n s h i p between temperature and t h e r a t e o f development is linear accumulate  ( A l l e n , 1976). F o r h a t c h t o o c c u r t h e eggs must a f i x e d number o f heat u n i t s , where t h e heat  u n i t s a r e c a l c u l a t e d as t h e degree-days above t h e development t h r e s h o l d . B o t h o f t h e e x i s t i n g models, were d e v e l o p e d u s i n g r e c o r d e d h a t c h d a t e s t o e s t i m a t e t h e parameters  of the  model. The model d e v e l o p e d by Ives (1973), u s i n g r e c o r d s from A l b e r t a , p r e d i c t s t h a t h a t c h w i l l o c c u r each y e a r once t h e number o f degree-days above a t h r e s h o l d o f 4.4°C (40°F), s t a r t i n g on A p r i l 27th, exceeds 61.1°C-days (110°F-days). The model d e v e l o p e d by Hodson (1977), u s i n g r e c o r d s from Minnesota  (which b o r d e r s n o r t h - w e s t e r n O n t a r i o ) , has  d i f f e r e n t parameters.  T h i s model r e q u i r e s an a c c u m u l a t i o n o f  44.4°C-days (80°F-days), above a t h r e s h o l d o f 7.8°C (46°F), and b e g i n n i n g March 1 s t . B o t h models c l a i m t o be a b l e t o p r e d i c t t h e h a t c h date t o w i t h i n 2-3 days o f t h e t r u e d a t e . As n e i t h e r model had been t e s t e d i n O n t a r i o , I compared p r e d i c t e d and r e c o r d e d h a t c h d a t e s , f o r b o t h models, a t v a r i o u s l o c a t i o n s and t i m e s a c r o s s t h e p r o v i n c e . A t r i a n g u l a r approximation  ( I v e s , 1973)  was  used t o c a l c u l a t e  t h e degree-days from d a i l y maximum and minimum  temperature  d a t a . F o r t h o s e t e s t l o c a t i o n s more t h a n 50km from a c l i m a t e s t a t i o n , h a t c h d a t e s were e s t i m a t e d u s i n g a d i s t a n c e  -38-  w e i g h t e d average o f t h e p r e d i c t e d v a l u e s f o r t h e two n e a r e s t stations. T a b l e I I compares t h e a c t u a l h a t c h d a t e s t o t h o s e p r e d i c t e d by t h e M i n n e s o t a model. W i t h one e x c e p t i o n t h e p r e d i c t e d h a t c h d a t e s f o r t h i s model are w i t h i n 5 days o f t h e a c t u a l d a t e s . As t h e eggs from a s i n g l e egg band g e n e r a l l y h a t c h over t h e c o u r s e o f a 2-3 day p e r i o d  (Raske,  1974), i t would be d i f f i c u l t t o p r e d i c t t h e h a t c h d a t e o f the f o r e s t tent c a t e r p i l l a r , using only macroclimatic t e m p e r a t u r e d a t a , w i t h much g r e a t e r a c c u r a c y . The  Alberta  model, which does not b e g i n a c c u m u l a t i n g degree-days A p r i l 27th, c o n s i s t e n t l y p r e d i c t e d hatch dates w e l l  until after  t h e r e c o r d e d ones. T h i s model's l a t e s t a r t i n g d a t e f o r heat u n i t a c c u m u l a t i o n p r o b a b l y e x p l a i n s i t s poor performance, h a t c h d a t e s b e f o r e May  as  1 s t are q u i t e common i n O n t a r i o .  The M i n n e s o t a model was t h e r e f o r e used t o p r e d i c t t h e h a t c h d a t e s a t each o f t h e 20 c l i m a t e s t a t i o n s from 1948 1988.  to  The p r e d i c t e d d a t e s f o r any one s t a t i o n v a r y over a  range o f about 30-40 days from y e a r t o y e a r  ( F i g u r e 8 ) . The  s p a t i a l v a r i a t i o n i n h a t c h d a t e s i s shown by t h e d i s t r i b u t i o n o f l o n g - t e r m mean h a t c h d a t e s a c r o s s t h e province  ( F i g u r e 9 ) . Note t h e d e l a y i n h a t c h date t h a t  o c c u r s as one moves towards t h e g e n e r a l l y c o o l e r n o r t h e r n and c e n t r a l p a r t s o f t h e p r o v i n c e .  -39-  Table I I  A c t u a l hatch dates and those p r e d i c t e d by the Minnesota model f o r v a r i o u s times and locations i n Ontario.  Location  Fort  Frances^  Fort  Frances^  Cedar Lake Nagagami Bancroft Earlton Muskoka Muskoka  Year  1967 1968 1969 1970 1971 1972 1973 1974 1953 1966 1967 1974 1978 1988  A c t u a l Hatch Date Source  Actual Date "  Witter et al. (1972)  May May May May May May May May May May May May May May  Mattson and E r i k s o n (1978)  B l a i s et al. (1955) H a l l (1967) Livesey (1968) MacLeod et al. (1975) Anonymous (1978) G. Howse (pers. comm.)  1  22 1 2 13 7 12 7 17 8 24 1 18 8 3  Model Date  Difference (Model-Actual)  May May Apr May May May May May May May May May May May  -4 +1 -2 +5 -1 -2 -1 +1 -1 0 + 11 +4 +5 +3  18 2 30 18 6 10 6 18 7 24 12 22 13 6  A c t u a l date represents estimated date of 50% hatch. As the average time between s t a r t and 90% hatch i s 2 days (Raske, 1974) , 1 day was added t o the date of those sources r e p o r t i n g only the hatch s t a r t . A c t u a l hatch dates were recorded near I n t e r n a t i o n a l F a l l s , Minnesota (about 10 km from F o r t Frances, O n t a r i o ) .  Kenora (1)  Year  F i g u r e 8. The p r e d i c t e d h a t c h date each y e a r f o r 4 o f t h e 20 c l i m a t e s t a t i o n s (the s t a t i o n numbers from F i g u r e 7 a r e g i v e n i n b r a c k e t s ) . Hatch d a t e s a r e d i s p l a y e d as J u l i a n days b e g i n n i n g March 1 s t . Shading shows t h e h a t c h d a t e each y e a r r e l a t i v e t o May 8 (day 70), t h e mean f o r a l l s t a t i o n s and years.  -41-  F i g u r e 9. The mean h a t c h date, 1948-88, f o r each o f t h e 20 c l i m a t e s t a t i o n s . Dates a r e d i s p l a y e d as J u l i a n days b e g i n n i n g March 1 s t .  -42-  Feeding  degree-days  The n e x t s t e p was t o c a l c u l a t e an i n d e x o f f a v o u r a b l e t h e t e m p e r a t u r e was  how  f o r feeding i n the e a r l y part  of t h e l a r v a l s t a g e . The i n d e x I chose i s based upon s e v e r a l findings. First,  l a b o r a t o r y e x p e r i m e n t s and  field  o b s e r v a t i o n s suggest t h a t l a r v a e do not f e e d a t t e m p e r a t u r e s below 15°C,  and most d e f o l i a t i o n o c c u r s on days when  t e m p e r a t u r e s a r e i n excess o f about 23°C (Hodson,  1941).  F u r t h e r m o r e W e l l i n g t o n (1950), i n a s t u d y o f t h e r e l a t i o n s h i p between a i r t e m p e r a t u r e s and t h e s u r f a c e t e m p e r a t u r e s o f f o l i a g e , found t h a t a t t e m p e r a t u r e s between 15°C  and 26°C t r e m b l i n g aspen l e a v e s were no more t h a n  above t h e a i r t e m p e r a t u r e  1.6°C  (whereas c o n i f e r o u s f o l i a g e was  as  much as 8°C h i g h e r ) . T h i s suggests t h a t , f o r f o r e s t t e n t c a t e r p i l l a r , m a c r o c l i m a t i c temperature o b s e r v a t i o n s are a r e l a t i v e l y good measure o f t h e t e m p e r a t u r e t o which l a r v a e are  exposed w h i l e f e e d i n g . The i n d e x I d e c i d e d t o use i s s i m i l a r t o t h a t  p r e v i o u s l y d e v e l o p e d by I v e s (1973); i t uses a heat u n i t concept t o d e t e r m i n e t h e number o f degree-days  that  accumulate each y e a r above a t h r e s h o l d f e e d i n g t e m p e r a t u r e . U s i n g d a i l y maximum and minimum t e m p e r a t u r e d a t a , t h e i n d e x i s c a l c u l a t e d as t h e number o f degree-days o f 15°C the  (or " f e e d i n g " degree-days)  above a t h r e s h o l d  t h a t accumulate d u r i n g  f i r s t 3 weeks a f t e r h a t c h . A h i g h v a l u e i n d i c a t e s a  warm, o r f a v o u r a b l e e a r l y l a r v a l f e e d i n g p e r i o d w h i l e a low  -43-  v a l u e i n d i c a t e s a l e s s f a v o u r a b l e y e a r . Only 3 weeks a f t e r h a t c h a r e c o n s i d e r e d as t h i s i s how  l o n g newly h a t c h e d  l a r v a e a r e thought t o be a b l e t o s u r v i v e w i t h o u t food  (Smith  and Raske, 1968) . Based upon t h e p r e d i c t e d h a t c h d a t e s I c a l c u l a t e d t h e f e e d i n g degree-days t h a t have accumulated  a t each o f t h e 2 0  s t a t i o n s from 1948 t o 1988. U n l i k e t h e h a t c h d a t e s , however, a s t r o n g n o r t h - s o u t h or east-west g r a d i e n t i n t h e i r l o n g term means does not e x i s t  ( F i g u r e 10). However, t h e number  o f f e e d i n g degree-days at each s t a t i o n v a r i e s c o n s i d e r a b l y from one y e a r t o t h e next  Comparing c l i m a t e and  ( F i g u r e 11).  defoliation  Next I compared t h e d e f o l i a t i o n maps t o t h e f e e d i n g degree-days f o r each s t a t i o n and year  (or " s t a t i o n - y e a r " ) .  As t h e d e f o l i a t i o n i s mapped a t t h e end o f t h e l a r v a l each y e a r  stage  ( u s u a l l y mid- t o l a t e - J u n e ) , i t p r o v i d e s an  i n d i c a t i o n o f each y e a r ' s l a t e i n s t a r l a r v a l abundance. Whether o r not t h e l a t e l a r v a l d e n s i t i e s i n an a r e a i n c r e a s e d o r d e c r e a s e d between y e a r s can be seen by comparing  the p r o p o r t i o n of a f i x e d s i z e d area t h a t i s  d e f o l i a t e d i n one y e a r  (say, y e a r t-1) t o t h e p r o p o r t i o n o f  t h a t same a r e a d e f o l i a t e d i n t h e next y e a r  (year  I c a l c u l a t e d t h e a r e a d e f o l i a t e d f o r each  fc).  station-year  by c e n t e r i n g c e l l s t h a t were 100km by 100km i n s i z e at each o f t h e 20 s t a t i o n s and c a l c u l a t i n g t h e p r o p o r t i o n o f t h e  F i g u r e 10. The mean number o f f e e d i n g degree-days, 1948-88, f o r each o f t h e 20 c l i m a t e s t a t i o n s .  Kenora ( 1 ) 120 -  i  1940  1950  1960  Armstrong  1970  1980  1990  1980  1990  (5)  120 -l  80 -  1940  1950  1960  1970  F i g u r e 11. The f e e d i n g degree-days each y e a r f o r 4 o f t h e 20 c l i m a t e s t a t i o n s . Shading shows t h e degree-days each y e a r r e l a t i v e t o 25°C-days, t h e mean f o r a l l s t a t i o n s and y e a r s .  -46-  l a n d a r e a i n each c e l l t h a t was d e f o l i a t e d each y e a r .  The  importance of the l a r v a l f e e d i n g temperature i n determining p o p u l a t i o n i n c r e a s e s o r d e c l i n e s was t e s t e d by comparing  the  change i n d e f o l i a t e d a r e a , from y e a r t - 1 t o y e a r t , t o t h e f e e d i n g degree-days  i n year t f o r each  station-year.  F i g u r e 12 shows t h e t i m e s e r i e s o f f e e d i n g degree-days and d e f o l i a t i o n f o r 4 o f t h e 20 s t a t i o n s  (see Appendix B f o r  r e m a i n i n g 16 s t a t i o n s ) . I f t h e l a r v a l f e e d i n g t e m p e r a t u r e i s i m p o r t a n t i n d e t e r m i n i n g when and where o u t b r e a k s r i s e fall,  one would expect h i g h e r f e e d i n g degree-days  and  f o r those  s t a t i o n - y e a r s where t h e a r e a d e f o l i a t e d i n c r e a s e d from y e a r t o - y e a r t h a n f o r t h o s e s t a t i o n - y e a r s where t h e d e f o l i a t i o n decreased. A s i m p l e r way  o f examining t h i s r e l a t i o n s h i p i s t o p l o t  t h e change i n d e f o l i a t i o n , from y e a r t-1 t o y e a r t , a g a i n s t t h e f e e d i n g degree-days  i n year t f o r a l l s t a t i o n s  and  y e a r s . R e c a l l , however, t h a t i n Chapter 3 I s u g g e s t e d t h e l a r v a l d e n s i t i e s c o u l d be as h i g h as 500-1000 l a r v a e p e r h o s t t r e e and s t i l l not show any moderate t o s e v e r e d e f o l i a t i o n . So i f t h e d e f o l i a t i o n remains t h e same from  one  y e a r t o t h e n e x t , i t i s v e r y d i f f i c u l t t o know whether o r not t h e l a r v a l d e n s i t i e s i n c r e a s e d , d e c r e a s e d , o r t h e same. F o r t h i s reason I compared o n l y t h o s e y e a r s f o r which t h e r e was a non-zero from y e a r t-1 t o y e a r t .  -47-  remained  station-  change i n d e f o l i a t i o n  Kenora (1)  j  i 1940  i 1950  i 1960  i 1970  i 1980  i \j 1990  1980  1990  North B a y (14)  1940  1950  1960  1970  Year  F i g u r e 12. The f e e d i n g degree-days and t h e p r o p o r t i o n o f a r e a d e f o l i a t e d each y e a r f o r 4 o f t h e 20 c l i m a t e s t a t i o n s . Shading shows t h e degree-days each y e a r r e l a t i v e t o 25°C-days, t h e mean f o r a l l s t a t i o n s and y e a r s . Dark l i n e shows t h e p e r c e n t d e f o l i a t i o n .  -48-  F i g u r e 13 shows the f e e d i n g degree days f o r y e a r s  of  i n c r e a s i n g and d e c r e a s i n g d e f o l i a t i o n a t a l l 20 s t a t i o n s , from 1948-88. A g a i n , determining  i f the f e e d i n g t e m p e r a t u r e were  p o p u l a t i o n change, one would e x p e c t t o  see  d e c r e a s e s i n d e f o l i a t i o n a s s o c i a t e d w i t h low degree-day y e a r s and/or i n c r e a s e s a s s o c i a t e d w i t h h i g h degree-day y e a r s . T h i s p l o t shows no s i g n of such a r e l a t i o n s h i p . There were s e v e r a l s t a t i o n - y e a r s w i t h v e r y few degree-days  and  i n c r e a s e s i n d e f o l i a t i o n , and o t h e r s w i t h h i g h degree-day t o t a l s and d e f o l i a t i o n  decreases.  Sensitivity analysis To t e s t t h e s e n s i t i v i t y o f t h e s e r e s u l t s t o changes i n t h e measure o f abundance, I v a r i e d t h e s c a l e over w h i c h t h e d e f o l i a t i o n was  measured. T h i s i n v o l v e d c h a n g i n g t h e s i z e of  t h e 100km by 100km s t a t i o n c e n t e r e d c e l l t o s i z e s o f 50km by 50km and 200km by 200km. The  r e s u l t s o f t h e s e changes shows  t h a t t h e l a c k o f a r e l a t i o n s h i p between f e e d i n g degree-days and changes i n d e f o l i a t i o n i s not s e n s i t i v e t o s m a l l changes i n t h e s c a l e over which the d e f o l i a t i o n i s measured  (Figure  14) . Next I l o o k e d at t h e e f f e c t of changes i n t h e measure. The  climatic  f e e d i n g degree-day index i s b a s e d upon 3  p a r a m e t e r s : t h e s t a r t of the l a r v a l p e r i o d  (as p r e d i c t e d by  t h e h a t c h model), the f e e d i n g t h r e s h o l d t e m p e r a t u r e and the p e r i o d o f i n f l u e n c e (3 weeks). To t e s t  -49-  the  (15°C)  Degree Days  F i g u r e 13. R e l a t i o n s h i p between t h e change i n p e r c e n t a g e o f d e f o l i a t e d a r e a and t h e f e e d i n g degree-days, f o r a l l s t a t i o n s and y e a r s w i t h a non-zero change i n d e f o l i a t i o n . V e r t i c a l l i n e shows t h e mean number o f f e e d i n g degree-days f o r a l l s t a t i o n s and y e a r s .  -50-  100  •  •  •  (a)  • • •  •  :  •  •  •  •  • •  Alj::  0 -—:  •• •  •  «  _•___:.„  • • •  •  •  •  x: O c o  ]io  •  •  c  CO  •  • •  CD CJ)  •  •  a  •  ., - .. . t. .  •100  50  0  100  (b)  100  Q  B  0  .  •100  50  100  Degree D a y s  F i g u r e 14. The e f f e c t o f v a r y i n g the c e l l s i z e on the r e l a t i o n s h i p between the change i n percentage o f d e f o l i a t e d area and the f e e d i n g degree-days, f o r a l l s t a t i o n s and years w i t h a non-zero change i n d e f o l i a t i o n . Area d e f o l i a t e d i s c a l c u l a t e d at c e l l s i z e s o f : (a) 50km by 50km; (b) 200km by 200km.  - 5 1 -  robustness of the r e s u l t s t o these v a l u e s , I repeated the a n a l y s i s u s i n g more c o n s e r v a t i v e e s t i m a t e s o f each parameter.  T h i s i n v o l v e d t h e f o l l o w i n g changes t o my i n d e x :  t h e s t a r t o f t h e f e e d i n g p e r i o d was d e l a y e d f o r one week a f t e r t h e p r e d i c t e d h a t c h d a t e ; t h e f e e d i n g t h r e s h o l d was l o w e r e d from 15°C t o 10°C; t h e p e r i o d f o r a c c u m u l a t i n g degree-days was extended  from 3 t o 4 weeks.  F o r each o f t h e s e changes I s t i l l  found no r e l a t i o n s h i p  between i n c r e a s e s and d e c r e a s e s i n d e f o l i a t i o n and t h e temperature  through the l a r v a l p e r i o d (Figure 15).  Years p r i o r t o i n c r e a s e s To t h i s p o i n t my a n a l y s i s has compared changes i n d e f o l i a t i o n t o the l a r v a l feeding temperature  f o r t h e same  year. Given the high l a r v a l d e n s i t i e s r e q u i r e d t o b r i n g about n o t i c e a b l e d e f o l i a t i o n , i t i s q u i t e p o s s i b l e t h a t t h e most i m p o r t a n t c l i m a t i c i n f l u e n c e o c c u r s s e v e r a l y e a r s b e f o r e any d e f o l i a t i o n i s r e c o r d e d . B o t h W e l l i n g t o n (1952) and I v e s  (1973) have t e s t e d t h i s i d e a f o r t h e f o r e s t t e n t  c a t e r p i l l a r by e x a m i n i n g t h e c l i m a t e i n t h e y e a r s p r i o r t o defoliation. Exploring this p o s s i b i l i t y involves distinguishing between t h o s e y e a r s i n which d e f o l i a t i o n f i r s t began t o increase subsequent  (or decrease) increasing  a t a p a r t i c u l a r s t a t i o n , and (or d e c r e a s i n g ) y e a r s .  "Initial  i n c r e a s e " y e a r s were s a i d t o o c c u r f o r a s t a t i o n i n y e a r t -52-  (a)  -100  200  (b) CD CC  c  CO  _c O c o  ~M o o Q  200  (c)  200  Degree D a y s  F i g u r e 15. The e f f e c t o f changing t h e c l i m a t i c measure on t h e r e l a t i o n s h i p between t h e change i n p e r c e n t a g e o f d e f o l i a t e d a r e a and t h e f e e d i n g degree-days, f o r a l l s t a t i o n s and y e a r s w i t h a non-zero change i n d e f o l i a t i o n . F e e d i n g degree-days a r e c a l c u l a t e d u s i n g : (a) 1 week d e l a y a f t e r h a t c h ; (b) f e e d i n g t h r e s h o l d o f 10°C; (c) 4 week p e r i o d o f i n f l u e n c e . V e r t i c a l l i n e s show t h e mean number o f f e e d i n g degree-days f o r a l l s t a t i o n s and y e a r s .  -53-  when t h e r e was an i n c r e a s e i n d e f o l i a t i o n from y e a r t-1 t o y e a r t, w i t h no i n c r e a s e i n d e f o l i a t i o n a t t h a t s t a t i o n i n the previous three years  (years t-3 t o t - 1 ) . S i m i l a r l y ,  " i n i t i a l d e c r e a s e " y e a r s were t h o s e y e a r s showing a d e c r e a s e i n d e f o l i a t i o n i n t h e c u r r e n t y e a r and no d e c r e a s e s i n previous 3 years. I f t h e f e e d i n g t e m p e r a t u r e does i n i t i a t e e i t h e r t h e r i s e o r t h e d e c l i n e o f o u t b r e a k s , one would expect t o see h i g h e r f e e d i n g degree-days i n t h e y e a r s p r e c e d i n g  initial  i n c r e a s e years than i n the years preceding i n i t i a l  decrease  y e a r s . To e x p l o r e t h i s p o s s i b i l i t y I used a 4 y e a r  average  (years t - 3 t o t i n c l u s i v e )  o f f e e d i n g degree-days a t each  s t a t i o n as my c l i m a t i c i n d e x f o r year t . I t h e n compared t h e new i n d e x v a l u e s f o r t h o s e s t a t i o n - y e a r s showing i n c r e a s e s t o t h o s e showing i n i t i a l d e c r e a s e s  initial  (Figure 16).  These r e s u l t s show no d i f f e r e n c e between t h e 4 y e a r  average  of f e e d i n g degree-days p r i o r t o r i s e s and t h o s e p r i o r t o c o l l a p s e s o f o u t b r e a k s . Twenty o f t h e 39 i n i t i a l i n c r e a s e years  (51%) were preceded by a 4 year average t h a t was above  t h e mean f o r a l l s t a t i o n s i n i t i a l decrease years  and y e a r s . S i m i l a r l y , 21 o f 39  (54%) were p r e c e d e d by a 4 y e a r  average above t h e mean.  -54-  10  I  10  I  -20  1  1  -15  1  1  -10  1  1  1  -5  1  i  1  0  1  '  1  5  Degree D a y s -  10  r  1  15  i  i  20  25  30  Mean  F i g u r e 16. The d i s t r i b u t i o n o f 4 - y e a r a v e r a g e s o f f e e d i n g d e g r e e - d a y s p r i o r t o : (a) i n i t i a l i n c r e a s e y e a r s ; (b) i n i t i a l d e c r e a s e y e a r s . Degree-days a r e d i s p l a y e d r e l a t i v e t o 25°C-days, t h e mean number o f f e e d i n g d e g r e e - d a y s f o r a l l s t a t i o n s and y e a r s .  -55-  Overwintering  Temperature  The second c l i m a t i c f a c t o r examined was t h e o v e r w i n t e r i n g t e m p e r a t u r e . There are two s t u d i e s which t o g e t h e r suggest t h a t t h i s c o u l d i n f l u e n c e p o p u l a t i o n change. Hanec (1966) showed t h a t a s e a s o n a l v a r i a t i o n i n g l y c e r o l c o n t e n t a l l o w s f o r e s t t e n t c a t e r p i l l a r eggs t o be s u p e r c o o l e d t o t e m p e r a t u r e s as low as -41°C, below which they w i l l  f r e e z e . A subsequent s t u d y o f f o r e s t t e n t  c a t e r p i l l a r p o p u l a t i o n dynamics i n n o r t h e r n M i n n e s o t a ( W i t t e r et al.,  1975)  found egg m o r t a l i t y , from f a c t o r s  o t h e r t h a n p a r a s i t i s m and i n f e r t i l i t y ,  t o v a r y from  0-65%  o v e r a 9 y e a r p e r i o d . Comparing egg m o r t a l i t y t o t h e c o l d e s t t e m p e r a t u r e t h r o u g h t h e p r e v i o u s w i n t e r , a sharp r i s e i n m o r t a l i t y f o r t h o s e y e a r s i n which t h e t e m p e r a t u r e dropped below -40°C was d i s c o v e r e d . Egg m o r t a l i t y f o r t h e 5 y e a r s f o r w h i c h t h e t e m p e r a t u r e d i d not drop below -4 0°C  ranged  from 0-10%, w h i l e i n t h e 4 y e a r s where t e m p e r a t u r e s dropped below t h i s t h r e s h o l d , m o r t a l i t y ranged from 10-65%. T h i s s u g g e s t s t h a t t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e may p l a y an i m p o r t a n t r o l e i n t h e c o l l a p s e o f f o r e s t t e n t c a t e r p i l l a r o u t b r e a k s ( W i t t e r , 1979). However e v i d e n c e i s based upon o b s e r v a t i o n s a t a s i n g l e  location  o v e r t h e c o u r s e o f a s i n g l e outbreak, supplemented  by  i s o l a t e d r e p o r t s o f h i g h egg m o r t a l i t y a t o t h e r l o c a t i o n s ( P r e n t i c e , 1954; Gautreau, 1964). To examine t h e r o l e o f the  -56-  minimum o v e r w i n t e r i n g t e m p e r a t u r e as an i n f l u e n c e on p o p u l a t i o n change over my 41 year s t u d y p e r i o d i n O n t a r i o , I used t h e d e f o l i a t i o n maps a l o n g w i t h d a i l y minimum t e m p e r a t u r e d a t a . As W e l l i n g t o n (1950) has shown t h a t t h e d a i l y minimum t e m p e r a t u r e o f f o r e s t t e n t c a t e r p i l l a r egg masses i s g e n e r a l l y w i t h i n 1°C o f t h e a i r t e m p e r a t u r e , m a c r o c l i m a t i c t e m p e r a t u r e o b s e r v a t i o n s s h o u l d p r o v i d e a good measure o f t h e minimum t e m p e r a t u r e s e x p e r i e n c e d by t h e eggs. To t e s t t h e importance o f t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e I d e t e r m i n e d t h e minimum d a i l y t e m p e r a t u r e  each  w i n t e r , from 1947/1948 t o 1987/1988, f o r each o f t h e 20 c l i m a t i c s t a t i o n s a c r o s s t h e p r o v i n c e . I t h e n compared t h e change i n d e f o l i a t i o n , from one y e a r t o t h e n e x t , t o t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e f o r each  station-year.  F i g u r e 17 shows t h e l o n g - t e r m means o f t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e s a t each o f t h e 20 s t a t i o n s . There i s a l a r g e r e g i o n t o t h e n o r t h and c e n t r e o f t h e p r o v i n c e where t e m p e r a t u r e s , on average, f a l l below t h e -40°C t h r e s h o l d . F o r much o f t h e p r o v i n c e , however, t e m p e r a t u r e s r a r e l y drop below -40°C. F i g u r e 18 shows t h e time s e r i e s o f minimum o v e r w i n t e r i n g t e m p e r a t u r e s and t h e a r e a d e f o l i a t e d each year f o r 4 o f t h e 20 s t a t i o n s  (see Appendix C f o r r e m a i n i n g 16  s t a t i o n s ) . I f t h e o v e r w i n t e r i n g t e m p e r a t u r e i s an i m p o r t a n t f a c t o r i n c a u s i n g c o l l a p s e s o f o u t b r e a k s , t h e n one would e x p e c t t o see d e c r e a s e s i n d e f o l i a t i o n f o r t h o s e y e a r s w i t h  -57-  F i g u r e 17. The mean o f t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e , 1948-88, f o r each o f t h e 20 c l i m a t e s t a t i o n s .  -58-  Kenora (1) 100  1940  1950  1970  1960  1980  1990  Armstrong (5) -10  100  -40  50  -70 1940  1950  1960  1970  1980  1990  CD  55  i  c .o  ~C0 CD CL  E  CD  Kapuskasing (9) -10 -,  -40 -  -70 1940  100  J 1950  50  1960  1970  North B a y  1980  CD  Q  0 1990  (14)  -10 -i  1940  Ho  100  1950  1960  1970  1980  1990  Year  F i g u r e 18. The minimum o v e r w i n t e r i n g t e m p e r a t u r e and t h e p r o p o r t i o n o f a r e a d e f o l i a t e d each y e a r f o r 4 o f t h e 20 c l i m a t e s t a t i o n s . F o r each y e a r t , t e m p e r a t u r e i s t h e minimum f o r t h e w i n t e r o f y e a r t - 1 t o y e a r t . Shading shows the t e m p e r a t u r e r e l a t i v e t o -40°C. Dark l i n e shows t h e percent d e f o l i a t i o n .  -59-  l o w e r o v e r w i n t e r i n g t e m p e r a t u r e s , i n p a r t i c u l a r t h o s e below -40°C. F u r t h e r m o r e , one might expect t o see fewer i n c r e a s e s in defoliation  f o r those s t a t i o n s  and y e a r s where t h e  t e m p e r a t u r e dropped below t h i s t h r e s h o l d . A s i m p l e way o f e x p l o r i n g t h i s i s t o p l o t t h e change i n defoliation,  from y e a r t - 1 t o t , a g a i n s t t h e minimum  t e m p e r a t u r e o c c u r r i n g between t h e s e d e f o l i a t i o n mappings (which I r e f e r t o as t h e minimum t e m p e r a t u r e f o r y e a r t ) . As with the p l o t s  f o r the l a r v a l feeding temperature, t h i s i s  done o n l y f o r t h o s e s t a t i o n - y e a r s f o r w h i c h t h e r e was z e r o change i n d e f o l i a t i o n  from one y e a r t o t h e n e x t .  F i g u r e s 19 and 20 show t h e r e s u l t s a l l 20 s t a t i o n s , calculated  o f such a p l o t f o r  from 1948 t o 1988, w i t h  at 3 d i f f e r e n t  a non-  spatial scales.  defoliation When one c o n s i d e r s  a l l of the outbreaks i n the p r o v i n c e through t h i s p e r i o d , t h e r e i s no apparent r e l a t i o n s h i p  between t h e o v e r w i n t e r i n g  t e m p e r a t u r e and d e c r e a s e s i n d e f o l i a t i o n . R e g a r d l e s s o f t h e s c a l e o v e r w h i c h t h e d e f o l i a t i o n i s measured, one  sees  s e v e r a l s t a t i o n - y e a r s w i t h minimum t e m p e r a t u r e s w e l l below -40°C and i n c r e a s e s i n d e f o l i a t i o n . F u r t h e r m o r e , t h e r e a r e many s t a t i o n - y e a r s f o r w h i c h t h e t e m p e r a t u r e s were w e l l above -40°C and y e t d e f o l i a t i o n substantially.  -60-  still  decreased  100  CD CD  •  c  CTJ  JZ  O a _o  • • •• • • •• •  w  _ f  •  •  y . . •  0  ~M  •• • •  o o  Q  -100 -60  -50  -40  -30  -20  -10  Temperature  F i g u r e 19. R e l a t i o n s h i p between t h e change i n p e r c e n t a g e o f d e f o l i a t e d a r e a and t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e , f o r a l l s t a t i o n s and y e a r s w i t h a non-zero change i n d e f o l i a t i o n . Area d e f o l i a t e d i s c a l c u l a t e d at a c e l l s i z e of 100km by 100km. V e r t i c a l l i n e shows t h e -40°C t h r e s h o l d .  -61-  (a)  100  CD CD  c CO  -100  o c o  3i  (b)  100  o "CD O  0 -•  -100  Temperature  F i g u r e 20. The e f f e c t of v a r y i n g the c e l l s i z e on t h e r e l a t i o n s h i p between the change i n percentage o f d e f o l i a t e d area and t h e minimum o v e r w i n t e r i n g temperature, f o r a l l s t a t i o n s and years with a non-zero change i n d e f o l i a t i o n . Area d e f o l i a t e d i s c a l c u l a t e d at c e l l s i z e s o f : (a) 50km by 50km; (b) 200km by 200km.  -62-  F o r e s t C o m p o s i t i o n and Long-Term C l i m a t e  Recall that the severity  o f o u t b r e a k s has d i f f e r e d  c o n s i d e r a b l y from one r e g i o n t o a n o t h e r a c r o s s t h e p r o v i n c e (see F i g u r e 4 i n C h a p t e r 3 ) . There a r e many p a r t s o f t h e province,  f o r example, t h a t have been d e f o l i a t e d  i n 3 or 4  o u t b r e a k s s i n c e 1948, w h i l e o t h e r areas have shown no n o t i c e a b l e d e f o l i a t i o n t h r o u g h t h i s p e r i o d . To t h i s p o i n t I have o n l y compared c l i m a t e t o t h e y e a r - t o - y e a r  changes i n  forest tent c a t e r p i l l a r populations. This section's m u l t i outbreak a n a l y s i s w i l l temporal scale,  e x p l o r e t h e dynamics a t a d i f f e r e n t  and l o o k a t why some p a r t s o f t h e p r o v i n c e  have had many o u t b r e a k s w h i l e o t h e r s have had none. To do t h i s I compared t h e l o n g - t e r m  s p a t i a l pattern of  d e f o l i a t i o n i n the province t o the pattern of l a r v a l feeding t e m p e r a t u r e s , o v e r w i n t e r i n g t e m p e r a t u r e s , and f o r e s t composition.  T h i s was a c c o m p l i s h e d u s i n g 3 sources o f  i n f o r m a t i o n : annual d e f o l i a t i o n maps, d a i l y maximum and minimum t e m p e r a t u r e d a t a s i n g l e province-wide  ( f o r 20 c l i m a t i c s t a t i o n s ) , and a  forest  inventory.  Host a v a i l a b i l i t y The f i r s t  stage i n t h i s a n a l y s i s was t o a s s e s s t h e  a v a i l a b i l i t y o f host a c r o s s t h e p r o v i n c e . T h i s was accomplished using a forest  i n v e n t o r y p r o v i d e d by F o r e s t r y  Canada's F o r e s t Resource Data Program ( f o r more d e t a i l s see  -63-  Anonymous, 1988). The i n v e n t o r y was d e r i v e d from s t a n d  level  f o r e s t t y p e maps; such maps g e n e r a l l y use a e r i a l photography, i n c o n j u n c t i o n w i t h f i e l d s a m p l i n g , t o d e l i n e a t e and c l a s s i f y s t a n d s . The s t a n d l e v e l maps were a g g r e g a t e d t o a g r i d system w i t h c e l l s c o r r e s p o n d i n g t o p r o v i n c i a l t o w n s h i p s i n t h e south and e a s t , and w i t h 10km by 10km c e l l s i n t h e n o r t h and west ( F i g u r e 2 1 ) . The i n v e n t o r y was c o m p i l e d  u s i n g t h e most r e c e n t a v a i l a b l e s t a n d d a t a , as  o f 1986, f o r each p a r t o f t h e p r o v i n c e . F i g u r e 22 shows t h a t most c e l l s were i n v e n t o r i e d between 1972 and 1986. F o r each s t a n d i n t h e i n v e n t o r y v a r i o u s a t t r i b u t e s a r e recorded.  Those r e l e v a n t t o my a n a l y s i s i n c l u d e d :  1. F o r e s t Type The f o r e s t t y p e i s c l a s s i f i e d a c c o r d i n g t o one o f 3 c a t e g o r i e s : softwood (76-100% o f t h e canopy i s c o n i f e r o u s ) ; mixedwood (26-75% c o n i f e r o u s ) ; hardwood (0-25% c o n i f e r o u s ) . 2. Predominant Genus The most abundant genus i n t h e s t a n d . T h i s i s c l a s s i f i e d a c c o r d i n g t o 12 c a t e g o r i e s , o f w h i c h t h e deciduous c a t e g o r i e s a r e : poplar birch  (Populus  species);  ( B e t u l a s p e c i e s ) ; maple (Acer s p e c i e s ) ; o t h e r  broadleaved  species.  3. A r e a The s t a n d ' s  f o r e s t e d area.  -64-  Figure 22. recorded  The y e a r i n w h i c h t h e s t a n d i n f o r m a t i o n f o r each c e l l i n the forest inventory.  -66-  was  Recall  (from Chapter 2) t h a t the h o s t p r e f e r r e d by  the  f o r e s t t e n t c a t e r p i l l a r i n t h e n o r t h e r n and w e s t e r n p a r t s of t h e p r o v i n c e i s t r e m b l i n g aspen (Populus f u r t h e r south t h i s preference maple, Acer 1957;  saccharum,  tremuloides);  s h i f t s t o a l s o i n c l u d e sugar  and r e d oak,  F o r e s t I n s e c t and D i s e a s e  Quercus  rubra  (Sippell,  Survey, p e r s . comm.).  The  f i r s t step i n a s s e s s i n g the d i s t r i b u t i o n of host across p r o v i n c e was was  t o d e t e r m i n e t h e p r o p o r t i o n o f each c e l l  the  that  c l a s s i f i e d as f o r e s t e d . F i g u r e 23 shows t h a t , f o r most  o f t h e p r o v i n c e , 80% or more o f the a r e a i s f o r e s t e d . In the southern  p a r t o f the p r o v i n c e , however, t h e r e i s a drop i n  t h e f o r e s t e d a r e a . The  l a n d use here i s p r i m a r i l y urban  a g r i c u l t u r a l , and the f o r e s t e d areas t h a t do e x i s t  and  are  g e n e r a l l y s m a l l , i s o l a t e d woodlots. The  n e x t s t e p was  t o determine t h e c o m p o s i t i o n  f o r e s t e d a r e a s . U s i n g the f o r e s t type a t t r i b u t e , I  of the estimated  t h e p r o p o r t i o n o f each c e l l ' s area t h a t had a s i g n i f i c a n t d e c i d u o u s component. T h i s was  a c c o m p l i s h e d by  calculating  t h e p r o p o r t i o n o f t h e f o r e s t e d area i n each c e l l t h a t  was  c l a s s i f i e d as e i t h e r mixedwood or hardwood. F i g u r e 24 shows t h a t most o f t h e p r o v i n c e has a s u b s t a n t i a l d e c i d u o u s component, a l t h o u g h t h e p r o p o r t i o n o f stands t h a t are mixed or d e c i d u o u s i n c r e a s e s as one moves s o u t h . To get a p i c t u r e o f the breakdown of t h i s deciduous f o r e s t by genus, I d e t e r m i n e d t h e p r o p o r t i o n of t o t a l d e c i d u o u s dominated a r e a t h a t was  dominated by each o f t h e f o u r genus c a t e g o r i e s . For  -67-  F i g u r e 23. P r o p o r t i o n  of  each  forested.  -68-  cell's  area  classified  as  non-  F i g u r e 24. P r o p o r t i o n c l a s s i f i e d as f o r e s t canopy  of each c e l l ' s f o r e s t e d area that i s e i t h e r m i x e d w o o d o r h a r d w o o d ( i . e . >25% o f t h e i s deciduous) .  -69-  p o p l a r t h i s was c a l c u l a t e d a s : (area c l a s s i f i e d as p r e d o m i n a n t l y p o p l a r ) (area c l a s s i f i e d as p r e d . p o p l a r + b i r c h + maple + other) T h i s p r o p o r t i o n was c a l c u l a t e d i n t h e same way f o r each o f t h e o t h e r 3 d e c i d u o u s c a t e g o r i e s , p r o v i d i n g an e s t i m a t e o f t h e p r o p o r t i o n o f t h e d e c i d u o u s t r e e component i n each c e l l a t t r i b u t a b l e t o each genus. F i g u r e 25 shows t h a t , t h r o u g h most o f t h e n o r t h e r n and w e s t e r n p a r t o f t h e p r o v i n c e , p o p l a r dominates t h e f o r e s t ' s d e c i d u o u s component. In s o u t h e r n O n t a r i o , however, maple i s much more significant. G i v e n t h a t t r e m b l i n g aspen i s t h e most common o f t h e p o p l a r s p e c i e s i n O n t a r i o , and sugar maple t h e most common maple (Rowe, 1972) , t h i s a n a l y s i s s u g g e s t s  that there i s  h o s t a v a i l a b l e a c r o s s most o f t h e p r o v i n c e . The o n l y e x c e p t i o n i s t h e s o u t h e r n p a r t o f t h e p r o v i n c e where, although t h e f o r e s t i s p r i m a r i l y deciduous, little  there i s very  f o r e s t e d area.  D e f o l i a t i o n and c l i m a t e To compare t h e l o n g - t e r m  patterns of d e f o l i a t i o n t o  t h o s e o f t h e two c l i m a t i c i n d i c e s , I f i r s t c a l c u l a t e d a long-term  measure o f t h e d e f o l i a t i o n f o r each c l i m a t e  s t a t i o n . The measure I s e l e c t e d was t h e t o t a l number o f years o f d e f o l i a t i o n ,  from 1948 t o 1988. T h i s was c a l c u l a t e d  as t h e number o f y e a r s i n which non-zero d e f o l i a t i o n was  -70-  F i g u r e 25.  Breakdown o f t h e d e c i d u o u s component i n each c e l l by genus. C a l c u l a t e d as t h e p r o p o r t i o n o f e a c h c e l l ' s deciduous dominated a r e a t h a t i s dominated by: (a) p o p l a r ; (b) b i r c h ; (c) m a p l e ; (d) o t h e r b r o a d l e a v e d s p e c i e s .  -71-  F i g u r e 25.  (continued)  -72-  F i g u r e 25.  (continued)  F i g u r e 25.  (continued)  -74-  r e p o r t e d w i t h i n a 100km by 100km c e l l c e n t e r e d upon each o f t h e 20 s t a t i o n s . I a l s o c a l c u l a t e d l o n g - t e r m  means, u s i n g  a n n u a l v a l u e s from 1948 t o 1988, f o r b o t h t h e number o f f e e d i n g degree days and t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e a t each s t a t i o n . F i g u r e 2 6 shows t h e l o n g - t e r m  spatial pattern of  d e f o l i a t i o n , f e e d i n g degree-days and minimum o v e r w i n t e r i n g t e m p e r a t u r e . There i s no apparent r e l a t i o n s h i p between t h e long-term  mean number o f f e e d i n g degree-days and t h e number  o f y e a r s o f d e f o l i a t i o n . However t h e r e i s some e v i d e n c e t h a t t h e a r e a s w i t h mean minimum o v e r w i n t e r i n g t e m p e r a t u r e s near o r below -40°C a r e d e f o l i a t e d l e s s o f t e n . In t h e a n a l y s i s o f h o s t a v a i l a b i l i t y I showed t h a t there i s r e l a t i v e l y l i t t l e  f o r e s t e d area i n the southern  p a r t o f the province. This could e x p l a i n the southern  limit  o f d e f o l i a t i o n seen so c l e a r l y i n C h a p t e r 2 (see F i g u r e 4 ) , and i n t h e map o f l o n g - t e r m  defoliation  (Figure 26). Given  t h a t t h e f i v e southern-most c l i m a t i c s t a t i o n s f a l l w i t h i n t h i s urban/agricultural region one p l o t s t h e l o n g - t e r m  (see F i g u r e s 7 and 23), i f  d e f o l i a t i o n a g a i n s t each o f t h e  c l i m a t i c i n d i c e s f o r the remaining  stations, a relationship  between t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e and t h e frequency  o f d e f o l i a t i o n i s more e v i d e n t  ( F i g u r e 2 7 ) . Once  a g a i n , t h e r e i s s t i l l no r e l a t i o n s h i p between t h e long-term p a t t e r n o f d e f o l i a t i o n and f e e d i n g degree-days.  -75-  F i g u r e 26. The long-term p a t t e r n s o f d e f o l i a t i o n and c l i m a t e , 1948-88, f o r each o f t h e 20 c l i m a t e s t a t i o n s : (a) t o t a l years o f d e f o l i a t i o n ; (b) mean number o f f e e d i n g degree-days; (c) mean minimum o v e r w i n t e r i n g temperature.  -76-  20  -i  (a)  c  o  _l—I  o M—  CD  Q  10  CO ca  CD  0 15  20  25  — i 35  30  Degree D a y s  20  (b)  c o  ^—»  o Q  10  o CO \_ crj  CD >  -rB  -50  -40  -30  8-20  Temperature  F i g u r e 27. R e l a t i o n s h i p between t h e number o f y e a r s o f d e f o l i a t i o n and t h e long-term c l i m a t e , 1948-88, f o r t h e 20 c l i m a t e s t a t i o n s : (a) mean f e e d i n g degree-days; (b) mean minimum o v e r w i n t e r i n g t e m p e r a t u r e . Open c i r c l e s r e p r e s e n t the s t a t i o n s w i t h i n the non-forested p a r t of southern Ontario.  -77-  Summary  T h i s a n a l y s i s shows no r e l a t i o n s h i p between y e a r - t o y e a r changes i n d e f o l i a t i o n and e i t h e r t h e l a r v a l  feeding  t e m p e r a t u r e o r t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e . The l o n g - t e r m s u s c e p t i b i l i t y o f an a r e a , as measured by t h e number o f y e a r s o f non-zero d e f o l i a t i o n , v a r i e s c o n s i d e r a b l y across t h e p r o v i n c e . While t h i s s p a t i a l v a r i a t i o n i n s u s c e p t i b i l i t y appears t o be u n r e l a t e d t o t h e mean l a r v a l f e e d i n g t e m p e r a t u r e , i t may be r e l a t e d t o b o t h t h e p r o p o r t i o n o f an a r e a t h a t i s f o r e s t e d , and t h e mean annual minimum w i n t e r t e m p e r a t u r e .  -78-  CHAPTER 5 DISCUSSION  The l a c k o f a r e l a t i o n s h i p between t h e two c l i m a t i c f a c t o r s and t h e y e a r - t o - y e a r dynamics o f o u t b r e a k s  appears  t o be i n c o n s i s t e n t w i t h t h e p r e d i c t i o n s o f p a s t s t u d i e s . I w i l l b e g i n t h i s c h a p t e r w i t h some comments on how such a c o n t r a d i c t i o n might a r i s e . I w i l l t h e n examine t h e p o s s i b l e r o l e o f c l i m a t e and f o r e s t c o m p o s i t i o n i n d e t e r m i n i n g t h e long-term s u s c e p t i b i l i t y of d i f f e r e n t p a r t s of the province. F i n a l l y , t h e r o l e o f o t h e r f a c t o r s i n d e t e r m i n i n g when and where o u t b r e a k s o c c u r w i l l be d i s c u s s e d .  L a r v a l Feeding  Temperature  As i n t h i s a n a l y s i s , a l l o f t h e p a s t s t u d i e s l i n k i n g the l a r v a l f e e d i n g temperature  t o r i s e s and c o l l a p s e s i n  o u t b r e a k s have been c o r r e l a t i v e . Such s t u d i e s a r e always prone t o d i s c o v e r i n g s p u r i o u s r e l a t i o n s h i p s : t h e fewer t h e number o f o b s e r v a t i o n s , t h e g r e a t e r t h e chance o f f i n d i n g a r e l a t i o n s h i p t h a t does not e x i s t . But even i f t h e r e l a t i o n s h i p s uncovered  i n such s t u d i e s do e x i s t , i t becomes  i n c r e a s i n g l y d i f f i c u l t t o g e n e r a l i z e t h e f i n d i n g s beyond t h e bounds o f t h e s t u d y as t h e number o f o b s e r v a t i o n s d e c r e a s e s . F o r t h r e e o f t h e p a s t s t u d i e s t h a t have suggested t h e importance  of t h e l a r v a l feeding temperature, the  -79-  c o n c l u s i o n s have been based upon o b s e r v a t i o n s t h r o u g h one two  outbreaks  B l a i s et al., t h e one al.  a t o n l y one or two 1955;  l o c a t i o n s (Hodson,  or  1941;  Hodson, 1977). As an example, c o n s i d e r  study f o r which I a l s o have d a t a : t h a t o f B l a i s e t  (1955), w h i c h l i n k e d t h e c o l l a p s e o f an outbreak  north-western  in  O n t a r i o t o c o l d weather s h o r t l y a f t e r h a t c h .  F i g u r e 28 shows t h e time s e r i e s o f f e e d i n g degree-days d e f o l i a t i o n f o r S i o u x Lookout, a s t a t i o n w i t h i n t h e i r  and study  a r e a . From t h i s we see v e r y few degree-days and a drop i n d e f o l i a t i o n i n 1953,  the year o f t h e i r s t u d y , w h i c h  agrees  w i t h t h e i r f i n d i n g s . T h i s p a t t e r n d i s a p p e a r s , however, when one  l o o k s a t more p o i n t s i n space and t i m e . I f t h e  f e e d i n g temperature outbreak  were an i m p o r t a n t  larval  factor i n causing  c o l l a p s e s , one would expect t o see fewer i n c r e a s e s  i n d e f o l i a t i o n t h a n decreases  f o r t h o s e s t a t i o n s and  years  w i t h low f e e d i n g degree-day a c c u m u l a t i o n s . W h i l e F i g u r e 13 showed s e v e r a l d e c l i n e s f o r s t a t i o n - y e a r s w i t h few days,  as i n S i o u x Lookout i n 1953,  degree-  i t showed j u s t as many  d e f o l i a t i o n i n c r e a s e s i n the c o o l e r y e a r s . Furthermore, l a r g e number o f outbreaks  c o l l a p s e d i n years w i t h high  degree-day t o t a l s . T h i s suggests t h a t t h e r e are o t h e r t h a n t h e temperature  factors  during l a r v a l feeding that  c o n t r i b u t e t o outbreak d e c l i n e s .  -80-  a  F i g u r e 28. The f e e d i n g d e g r e e - d a y s a n d t h e p r o p o r t i o n o f area d e f o l i a t e d each year f o r Sioux Lookout ( s t a t i o n 3 ) . O u t b r e a k c o l l a p s e was l i n k e d t o t h e t e m p e r a t u r e d u r i n g l a r v a l f e e d i n g i n 1 9 5 3 . S h a d i n g shows t h e d e g r e e - d a y s e a c h y e a r r e l a t i v e t o 25°C d a y s , t h e n mean f o r a l l s t a t i o n s a n d y e a r s . D a r k l i n e shows t h e p e r c e n t d e f o l i a t i o n .  -81-  Years p r i o r t o i n c r e a s e s A p o s s i b l e e x p l a n a t i o n f o r the d i s c r e p a n c y between my f i n d i n g s and t h o s e o f p r e v i o u s s t u d i e s i s t h e l o c a l n a t u r e o f t h e o b s e r v a t i o n s i n t h e p r e v i o u s s t u d i e s . However not a l l s t u d i e s have been so l i m i t e d i n t h e number o f o b s e r v a t i o n s . Ives  (1973) used r e c o r d s o f o u t b r e a k s  and t e m p e r a t u r e  f o r 10  s t a t i o n s i n t h e P r a i r i e p r o v i n c e s and O n t a r i o , from 1930 1970,  t o show t h a t o u t b r e a k s were preceded  by a s i n g l e  to year  (2 t o 4 y e a r s e a r l i e r ) w i t h a h i g h number o f f e e d i n g degreedays. T h i s s t u d y had,  i n my view, p r o v i d e d t h e most  c o n v i n c i n g e v i d e n c e o f t h e importance temperature  of the l a r v a l feeding  i n d e t e r m i n i n g t h e y e a r - t o - y e a r dynamics o f the  forest tent c a t e r p i l l a r . Does t h i s same p a t t e r n appear w i t h my data? To check t h i s f o r t h e 20 s t a t i o n s i n my i n c r e a s e " years  study, I l e t " i n i t i a l  (as d e f i n e d i n Chapter  b e g i n n i n g o f an outbreak  4) d e f i n e t h e  at a s t a t i o n . S i m i l a r l y ,  I let  " i n i t i a l d e c r e a s e " y e a r s d e f i n e t h e end o f o u t b r e a k s , b e i n g y e a r s showing a decrease decreases  i n d e f o l i a t i o n w i t h no  i n t h e p r e v i o u s 3 y e a r s . For e v e r y  i n c r e a s e and d e c r e a s e  year  initial  (year t ) , I t h e n d e t e r m i n e d  h i g h e s t annual degree-day v a l u e i n t h e p r e v i o u s 2-4 (years t-2,  those  years  t-3 and t-4) . T h i s a l l o w e d me t o determine  h i g h e s t v a l u e o f t h e f e e d i n g degree-days i n t h e 2-4 p r i o r t o b o t h t h e b e g i n n i n g and end o f  -82-  outbreaks.  the  the  years  F i g u r e 29 shows t h e d i s t r i b u t i o n o f v a l u e s f o r t h e h i g h e s t annual  f e e d i n g degree-day v a l u e i n t h e 2 - 4  years  p r i o r to i n i t i a l  i n c r e a s e and d e c r e a s e y e a r s , f o r a l l 20  stations.  o f the 36 i n i t i a l i n c r e a s e y e a r s  Thirty  (83%)  were  p r e c e d e d by a t l e a s t one year o f above average degree-days. T h i s would appear t o be c o n s i s t e n t w i t h t h e I v e s t h a t t h e r e be a s i n g l e year o f f a v o u r a b l e  hypothesis  feeding  temperatures p r i o r to the beginning of outbreaks.  However  t h e d i s t r i b u t i o n o f maximum f e e d i n g degree-days p r i o r t o i n i t i a l d e c r e a s e y e a r s shows t h e same p a t t e r n . Here 35 t h e 40  i n i t i a l decrease years  (or 88%)  of  were p r e c e d e d by  one  or more above average degree-day y e a r s . Years w i t h above average f e e d i n g degree-days o c c u r j u s t as o f t e n p r i o r t o the end o f o u t b r e a k s  as t h e y do p r i o r t o s t a r t .  This suggests  t h a t over a p e r i o d o f 3 s u c c e s s i v e y e a r s ,  t h e p r o b a b i l i t y o f h a v i n g a t l e a s t one warm y e a r may q u i t e h i g h . To examine t h i s more c l o s e l y , the p r o b a b i l i t y  be  I looked at  how  o f h a v i n g an above average f e e d i n g degree-  day y e a r v a r i e d as a f u n c t i o n o f t h e p e r i o d o f s u c c e s s i v e y e a r s c o n s i d e r e d . I d e t e r m i n e d t h e h i g h e s t annual degree-day v a l u e t h r o u g h  a l l p o s s i b l e p e r i o d s of 1 t o 4  c o n s e c u t i v e y e a r s , u s i n g t h e f e e d i n g degree-days at a l l s t a t i o n s  feeding  and y e a r s . F i g u r e 30 shows t h a t as  calculated one  i n c r e a s e s t h e l e n g t h o f t h e p e r i o d over which t h e maximum annual v a l u e i s determined,  t h e chance o f f i n d i n g an above  average v a l u e i n c r e a s e s d r a m a t i c a l l y . I f t h e s t a r t o f  -83-  Degree D a y s -  Mean  F i g u r e 29. The d i s t r i b u t i o n o f maximum f e e d i n g degree-day v a l u e s i n a p e r i o d 2-4 years p r i o r t o : (a) i n i t i a l i n c r e a s e y e a r s ; (b) i n i t i a l decrease y e a r s . Degree-days are d i s p l a y e d r e l a t i v e t o 2 5 ° C - d a y s , the mean number o f f e e d i n g degreedays f o r a l l s t a t i o n s and y e a r s .  -84-  1.0 -i (a) maximum 0.8  0.6  lQ CO .O O CL  (b) a v e r a g e 0.4  -  0.2  0.0  o  —r 3  i  4  5  Period (years)  F i g u r e 30, The p r o b a b i l i t y o f h a v i n g an above average f e e d i n g - d e g r e e day v a l u e as a f u n c t i o n o f t h e p e r i o d o f s u c c e s s i v e y e a r s c o n s i d e r e d . The two measures a r e : (a) t h e maximum annual v a l u e i n t h e p e r i o d ; (b) t h e average v a l u e over t h e p e r i o d .  -85-  o u t b r e a k s bear no r e l a t i o n s h i p t o t h e f e e d i n g t e m p e r a t u r e s i n the preceding  y e a r s , one would s t i l l e x p e c t t o f i n d a  s i n g l e warm y e a r i n t h e p r e c e d i n g  2-4  y e a r s f o r 80% of t h e  cases. This could e x p l a i n the d i f f e r e n c e i n conclusions r e g a r d i n g the e f f e c t of the l a r v a l feeding temperature of t h i s s t u d y and t h a t of Ives An a l t e r n a t i v e way  (1973).  of examining the e f f e c t  of  t e m p e r a t u r e p r i o r t o o u t b r e a k s i s t o use an average o f t h e f e e d i n g degree days over a f i x e d number o f y e a r s p r i o r t o the s t a r t of d e f o l i a t i o n  (as i n W e l l i n g t o n , 1952). I f t h e  f e e d i n g degree-days are above average i n one  or more o f t h e  y e a r s p r i o r t o t h e s t a r t o f an o u t b r e a k , t h e  multi-year  average s h o u l d a l s o be above average. U n l i k e t h e  previous  measure, however, such an average i s not b i a s e d by  the  l e n g t h o f t h e p e r i o d over which i t i s measured ( F i g u r e 3 0 ) . I t i s f o r t h i s r e a s o n t h a t i n Chapter 4 I chose t o t e s t i d e a t h a t t h e f e e d i n g t e m p e r a t u r e may  the  i n i t i a t e outbreaks,  the years p r i o r t o the f i r s t n o t i c e a b l e d e f o l i a t i o n ,  in  using  t h e average of t h e f e e d i n g degree-days i n t h e 4 y e a r s  prior  t o i n i t i a l i n c r e a s e s . R e c a l l t h a t the r e s u l t s o f t h i s analysis  ( F i g u r e 16)  showed no d i f f e r e n c e between t h e 4 year  average of f e e d i n g degree days p r i o r t o t h e r i s e s  (51% above  t h e mean) and t h e d e c l i n e s (54% above t h e mean), p r o v i d i n g f u r t h e r e v i d e n c e t h a t t h e r e are f a c t o r s o t h e r t h a n t h e temperature d u r i n g l a r v a l feeding that c o n t r i b u t e to o u t b r e a k r i s e s and d e c l i n e s .  -86-  I n d i c e s and  Insects  A l t h o u g h t h e r e does not appear t o be any  relationship  between changes i n d e f o l i a t i o n and my f e e d i n g t e m p e r a t u r e i n d e x , one cannot assume t h a t t h e f e e d i n g t e m p e r a t u r e has no r o l e i n s h a p i n g t h e y e a r - t o - y e a r dynamics o f o u t b r e a k s . As i n a l l b i o c l i m a t i c s t u d i e s o f t h i s form, i t i s always p o s s i b l e t h a t t h e measure o f c l i m a t e I have chosen does not r e p r e s e n t t h e f e e d i n g c o n d i t i o n s as e x p e r i e n c e d by t h e insect. The i n d e x used here was chosen t o match t h a t o f previous studies  ( I v e s , 1973; Hodson, 1977)  upon f i e l d o b s e r v a t i o n s o f h a t c h i n g r a t e s feeding habits  (Hodson, 1941)  and was (Hodson,  based 1977),  and s t a r v a t i o n e x p e r i m e n t s  (Smith and Raske, 1968). The s e n s i t i v i t y a n a l y s i s s e r v e d t o e x p l o r e how  c o n t i n g e n t my r e s u l t s were upon v a r i o u s  assumptions r e g a r d i n g t h e i n f l u e n c e of t e m p e r a t u r e on t h e feeding larvae. F i r s t l y , w h i l e t h e h a t c h model i s a b l e t o p r e d i c t t h e h a t c h date t o w i t h i n a few days, i t i s not c l e a r a t e x a c t l y what p o i n t a f t e r h a t c h t h e l a r v a l f e e d i n g b e g i n s t o be i n f l u e n c e d by c l i m a t e . T h i s prompted me t o d e l a y t h e p e r i o d over which I c a l c u l a t e d t h e f e e d i n g degree-days  f o r a week  a f t e r h a t c h , and t o t r y e x t e n d i n g i t from 3 t o 4 weeks. F u r t h e r m o r e , t h e t e m p e r a t u r e below which t h e l a r v a e w i l l f e e d i s not known p r e c i s e l y . To account f o r t h i s I t r i e d  -87-  not  l o w e r i n g t h e f e e d i n g t h r e s h o l d from 15°C t o 10°C. I a l s o t e s t e d t h e s e n s i t i v i t y o f my f i n d i n g s t o t h e c h o i c e o f s c a l e over which t h e d e f o l i a t i o n  (and t h u s abundance) i s measured  f o r each s t a t i o n and y e a r . The c h o i c e o f 100km by 100km was d i c t a t e d by t h e n a t u r e o f t h e d e f o l i a t i o n d a t a . The r e s o l u t i o n o f t h e d e f o l i a t i o n d a t a makes i n t e r p r e t a t i o n o f t h e maps a t s c a l e s f i n e r t h a n t h i s d i f f i c u l t 2 ) , w h i l e s c a l e s much l a r g e r t h a n t h i s  (see Chapter  (say 1000km by  1000km) would n o t c a p t u r e t h e r e g i o n a l v a r i a t i o n i n b o t h d e f o l i a t i o n and c l i m a t e . Thus w h i l e l a r g e changes i n t h e s c a l e o f a n a l y s i s were not c o n s i d e r e d , s m a l l e r changes i n t h e a r e a over w h i c h t h e d e f o l i a t i o n was measured were examined. None o f t h e s e changes produced any n o t i c e a b l e d i f f e r e n c e s i n the c l i m a t e - d e f o l i a t i o n r e l a t i o n s h i p s . This suggests that t h e f i n d i n g s are r e l a t i v e l y i n s e n s i t i v e t o some o f t h e assumptions  of the indices.  Overwintering  Temperature  As w i t h t h e s t u d i e s t h a t have s u g g e s t e d t h e importance of the l a r v a l f e e d i n g temperature, evidence f o r t h e r o l e of t h e o v e r w i n t e r i n g temperature i n t h e c o l l a p s e o f o u t b r e a k s i s p r i m a r i l y c o r r e l a t i v e . The s t r o n g e s t e v i d e n c e comes from r e c o r d s o f egg m o r t a l i t y t h r o u g h a s i n g l e o u t b r e a k , 1965 t o 1972, a l o n g t h e M i n n e s o t a - O n t a r i o b o r d e r  -88-  from  (Witter et  al.,  1 9 7 5 ) .  Frances,  These o b s e r v a t i o n s were a l l r e c o r d e d near F o r t  O n t a r i o , f o r which the time s e r i e s of d e f o l i a t i o n  and o v e r w i n t e r i n g temperatures t h i s study  (Figure 3 1 ) .  The  were c a l c u l a t e d as p a r t of  d e f o l i a t i o n and  overwintering  temperature data seem t o agree w i t h W i t t e r ' s f i n d i n g s ,  and  are indeed s u g g e s t i v e of a r e l a t i o n s h i p between the o v e r w i n t e r i n g temperature and the d e c l i n e of The  outbreaks.  r e l a t i o n s h i p disappears, however, when one  looks at  c o l l a p s e s a c r o s s the e n t i r e p r o v i n c e over the l a s t  4 1 years.  I f the o v e r w i n t e r i n g temperature were an important  factor i n  c a u s i n g the d e c l i n e of outbreaks,  to  one would expect  fewer years o f i n c r e a s i n g d e f o l i a t i o n than d e f o l i a t i o n f o r years w i t h temperatures  see  decreasing  f a l l i n g below  - 4 0 ° C .  F i g u r e 1 9 showed t h a t while some d e c l i n e s do occur i n years w i t h minimum o v e r w i n t e r i n g temperatures those  from  1 9 6 5 - 1 9 7 2  at F o r t Frances,  below  - 4 0 ° C ,  as  increases i n  d e f o l i a t i o n o c c u r r e d j u s t as o f t e n as decreases c o l d e r y e a r s . The  such  i n these  l a r g e number of d e c l i n e s t h a t o c c u r r e d at  s t a t i o n - y e a r s w i t h temperatures  w e l l above  - 4 0 ° C  is a  f u r t h e r i n d i c a t i o n of the importance of f a c t o r s other the o v e r w i n t e r i n g temperature i n c a u s i n g p o p u l a t i o n declines.  - 8 9 -  than  1940  1950  1960  1970  1980  1990  Year  F i g u r e 31. The minimum o v e r w i n t e r i n g t e m p e r a t u r e and t h e p r o p o r t i o n o f a r e a d e f o l i a t e d each y e a r f o r F o r t F r a n c e s ( s t a t i o n 2 ) . H i g h egg m o r t a l i t y and low minimum o v e r w i n t e r i n g t e m p e r a t u r e s were r e c o r d e d i n 1966, 1968 and 1972. Shading shows t h e t e m p e r a t u r e r e l a t i v e t o -40°C. Dark l i n e shows t h e p e r c e n t d e f o l i a t i o n .  -90-  Host A v a i l a b i l i t y  Outbreaks  appear t o be r e s t r i c t e d t o r e g i o n s i n t h e  p r o v i n c e w i t h c o n t i n u o u s t r a c t s o f deciduous and mixed f o r e s t s . W h i l e t h e c l i m a t e and s p e c i e s c o m p o s i t i o n o f s o u t h e r n O n t a r i o appear t o be conducive t o o u t b r e a k s , t h e fragmented  n a t u r e o f i t s f o r e s t e d areas appears t o l i m i t  t h e i r s e v e r i t y . F u r t h e r evidence of the p o s s i b i l i t y of outbreaks o c c u r r i n g i n t h i s area, i f s u f f i c i e n t  forest  cover  e x i s t e d , i s t h e r e p o r t s of l o c a l outbreaks throughout the U n i t e d S t a t e s (Hodson, 1941; Connola e t al., et al.,  1987).  Outbreaks dominated  1957; Rejmanek  have been as severe i n t h e c o n i f e r o u s  f o r e s t s o f n o r t h - w e s t e r n O n t a r i o (where t r e m b l i n g  aspen i s t h e p r i m a r y host) as i n t h e more s o u t h e r l y mixed and deciduous  forests  (where sugar maple d o m i n a t e s ) .  Wherever t h e r e i s c o n t i n u o u s l y f o r e s t e d a r e a , t h e r e would appear t o be a s u f f i c i e n t l y h i g h p r o p o r t i o n o f h o s t t r e e s t o s u p p o r t an o u t b r e a k . T h i s homogeneity o f h o s t a v a i l a b i l i t y a c r o s s t h e p r o v i n c e suggests t h a t s p e c i e s c o m p o s i t i o n i s not a major f a c t o r i n d e t e r m i n i n g t h e s u s c e p t i b i l i t y to  of a region  f o r e s t t e n t c a t e r p i l l a r outbreaks. This f i n d i n g i s surely  s c a l e dependent, however. I f one were t o a s s e s s t h e susceptibility  o f i n d i v i d u a l s t a n d s , f o r example, one might  e x p e c t a h i g h e r p r o p o r t i o n o f t h e t r e e s t o be a l l h o s t o r  -91-  non-host, and t h u s f i n d t h e s p e c i e s c o m p o s i t i o n t o have a g r e a t e r i n f l u e n c e upon t h e s t a n d ' s s u s c e p t i b i l i t y .  Long-Term C l i m a t e  W h i l e t h e r e i s no apparent r e l a t i o n s h i p between t h e l o n g - t e r m mean l a r v a l f e e d i n g t e m p e r a t u r e and t h e s e v e r i t y of  o u t b r e a k s a c r o s s the p r o v i n c e , t h e r e i s some i n d i c a t i o n  of  a r e l a t i o n s h i p between t h e minimum o v e r w i n t e r i n g  t e m p e r a t u r e and s e v e r i t y o f o u t b r e a k s . The  north-central  p a r t o f t h e p r o v i n c e , w i t h annual minimum t e m p e r a t u r e s t h a t f r e q u e n t l y f a l l below -40°C, has shown l i t t l e  defoliation  from 1948 t o 1988. Note t h a t one s h o u l d t r e a t t h e r e s u l t s o f t h i s l o n g - t e r m comparison o f o v e r w i n t e r i n g t e m p e r a t u r e s o u t b r e a k s e v e r i t y w i t h c a u t i o n . As t h e c l i m a t e a t any  and  one  s t a t i o n i s r e l a t e d t o t h a t at t h e n e i g h b o u r i n g ones, t h e measures at each o f t h e 20 s t a t i o n s a r e not  independent.  Such a u t o c o r r e l a t i o n amongst v a r i a b l e s t e n d s t o e x a g g e r a t e the  presence of r e l a t i o n s h i p s  ( C l i f f and Ord,  1981).  G i v e n t h e absence o f a r e l a t i o n s h i p between t h e o v e r w i n t e r i n g t e m p e r a t u r e and t h e y e a r - t o - y e a r p o p u l a t i o n dynamics, how  c o u l d the o v e r w i n t e r i n g temperature  influence  an a r e a ' s l o n g - t e r m s u s c e p t i b i l i t y t o o u t b r e a k s ? I t may  be  t h a t w h i l e w i n t e r m o r t a l i t y r a t e s a r e r a r e l y h i g h enough t o be t h e p r i m a r y cause of outbreak c o l l a p s e s t h r o u g h o u t most of  t h e p r o v i n c e , t h e y may be h i g h enough i n t h e n o r t h -  -92-  c e n t r a l p a r t o f t h e p r o v i n c e t o p r e v e n t d e n s i t i e s from e v e r r e a c h i n g l e v e l s t h a t would cause n o t i c e a b l e d e f o l i a t i o n . G i v e n f e c u n d i t i e s o f about 150 t o 200 eggs p e r a d u l t (Hodson, 1941; W i t t e r e t al., 1975) and a sex r a t i o o f a p p r o x i m a t e l y 1:1 ( S i p p e l l , 1957; W i t t e r , 1979),  generation  m o r t a l i t y r a t e s o f c l o s e t o 99% a r e r e q u i r e d t o b r i n g about a d e c l i n e i n abundance. The h i g h e s t r e p o r t e d  overwintering  m o r t a l i t y r a t e f o r f o r e s t t e n t c a t e r p i l l a r i s 65%, which o c c u r r e d i n a y e a r w i t h a minimum t e m p e r a t u r e o f -43°C ( W i t t e r e t al., 1975). F u r t h e r m o r e , t h e s u p e r c o o l i n g p o i n t of -40°C p r o v i d e s o n l y an i n d i c a t i o n o f t h e t e m p e r a t u r e a t w h i c h m o r t a l i t y becomes s i g n i f i c a n t ; t h e d i r e c t e f f e c t o f low t e m p e r a t u r e s on egg m o r t a l i t y i s n o t known. The l e t h a l l i m i t o f low t e m p e r a t u r e s f o r h i b e r n a t i n g i n s e c t s i s n o t f i x e d ; t h e p r o b a b i l i t y o f f r e e z i n g i n c r e a s e s as t h e t e m p e r a t u r e d e c r e a s e s and t h e exposure t i m e i n c r e a s e s  (Salt,  1961). As such, a r e a s which e x p e r i e n c e o n l y b r i e f p e r i o d s o f t e m p e r a t u r e s below -40°C may s t i l l have q u i t e h i g h egg s u r v i v a l . Eggs w i t h i n a r e a s w i t h l o n g e r , more f r e q u e n t p e r i o d s o f e x p o s u r e , such as t h e n o r t h - c e n t r a l p a r t o f t h e p r o v i n c e , w i l l have a h i g h e r p r o b a b i l i t y o f f r e e z i n g . T h i s might f u r t h e r e x p l a i n t h e reduced s u s c e p t i b i l i t y o f such areas t o d e f o l i a t i o n . A c o n t r o l l e d e x p e r i m e n t , measuring egg m o r t a l i t y i n r e l a t i o n t o e x p o s u r e s o f v a r y i n g extremes and d u r a t i o n s , would h e l p a s s e s s t h e p o t e n t i a l r o l e o f t h e o v e r w i n t e r i n g  -93-  t e m p e r a t u r e i n l i m i t i n g the s e v e r i t y of o u t b r e a k s .  As  s u p e r c o o l i n g p o i n t o f the eggs v a r i e s s e a s o n a l l y ,  the  m o r t a l i t y r a t e may  the  a l s o be a f u n c t i o n of b o t h t h e t i m i n g of  t h e exposure and t h e p r i o r t e m p e r a t u r e s . These f a c t o r s c o u l d a l s o be a c c o u n t e d f o r when c a l c u l a t i n g t h e  temperature-  mortality relationship. I f t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e does i n f l u e n c e the s e v e r i t y of f o r e s t tent c a t e r p i l l a r outbreaks i n O n t a r i o , one would expect t o see a s i m i l a r p a t t e r n f o r o t h e r p a r t s of Canada. D e f o l i a t i o n d a t a , s i m i l a r t o t h a t used i n t h i s study, 1923  e x i s t s f o r the P r a i r i e provinces  ( H i l d a h l and Reeks, 1960;  t h i s s u s c e p t i b i l i t y hypothesis  as f a r back as  I v e s , 1971) . A good t e s t of would be t o compare  temperature data across these provinces t o t h e i r p a t t e r n s  of  outbreak s e v e r i t y . I f t h e d i s t r i b u t i o n of minimum w i n t e r t e m p e r a t u r e s does i n f l u e n c e t h e s u s c e p t i b i l i t y of r e g i o n s t o f o r e s t t e n t c a t e r p i l l a r outbreaks, important  one would a l s o e x p e c t i t t o  i n determining  be  the long-term p a t t e r n of outbreaks  f o r o t h e r f o r e s t d e f o l i a t o r s . One  example o f a f o r e s t i n s e c t  showing a s i m i l a r r e l a t i o n s h i p between t e m p e r a t u r e  and  o u t b r e a k s i s t h e w i n t e r moth, Operophtera  in  Scandinavia.  MacPhee (1967) has  brumata,  shown t h a t w i n t e r moth  egg  m o r t a l i t y i n c r e a s e s s i g n i f i c a n t l y when t e m p e r a t u r e s are near i t s s u p e r c o o l i n g p o i n t of -35°C, w i t h 10% m o r t a l i t y o c c u r r i n g at -32.2°C and  100% m o r t a l i t y -36.7°C. When t h e  -94-  l o n g - t e r m p a t t e r n o f d e f o l i a t i o n by t h e w i n t e r moth i n Norway and Sweden  (from 1862-1967) was compared t o t h e  d i s t r i b u t i o n o f mean minimum w i n t e r t e m p e r a t u r e s ,  outbreaks  were found t o be c o n c e n t r a t e d w i t h i n r e g i o n s w i t h mean minimum w i n t e r t e m p e r a t u r e s Furthermore,  above -33°C (Tenow,  1972).  w i t h i n l a r g e r a r e a s o f d e f o l i a t i o n t h e r e were  o f t e n b e l t s o f undamaged f o r e s t a l o n g r i v e r s and l a k e s , where h i g h e r o v e r w i n t e r i n g m o r t a l i t y was a t t r i b u t e d t o l o c a l accumulations  o f c o l d a i r (Tenow,  Other  1981).  Factors  My a n a l y s i s so f a r i n d i c a t e s t h a t , w h i l e c l i m a t e and f o r e s t c o m p o s i t i o n may determine t h e s u s c e p t i b i l i t y o f an a r e a t o f o r e s t t e n t c a t e r p i l l a r o u t b r e a k s , t h e y a r e not s o l e l y r e s p o n s i b l e f o r y e a r - t o - y e a r changes i n abundance. The f o l l o w i n g s e c t i o n d i s c u s s e s t h e p o s s i b l e importance  of  o t h e r f a c t o r s i n d e t e r m i n i n g t h e y e a r - t o - y e a r dynamics o f outbreaks.  Synchrony o f o u t b r e a k s In Chapter  3 I showed how r i s e s and f a l l s o f o u t b r e a k s  o c c u r i n a r e l a t i v e l y synchronous manner a c r o s s t h e e n t i r e province factor  (see F i g u r e 6 ) . T h i s suggests t h a t a c l i m a t i c  (or f a c t o r s ) p r i m a r i l y r e s p o n s i b l e f o r t h e s e dynamics  s h o u l d a l s o a c t s y n c h r o n o u s l y over a s i m i l a r s p a t i a l e x t e n t .  -95-  As c l i m a t e at one l o c a t i o n i n space and t i m e i s o f t e n r e l a t e d t o t h a t at n e i g h b o u r i n g l o c a t i o n s ( F i g u r e 32), c l i m a t i c f a c t o r s c o u l d c o n c e i v a b l y cause synchronous changes i n abundance over q u i t e l a r g e a r e a s . One  way  t o examine the  p o t e n t i a l of a c l i m a t i c f a c t o r f o r c a u s i n g such  synchronous  changes i n abundance i s t o examine t h e degree t o w h i c h i t s n e i g h b o u r i n g v a l u e s are c o r r e l a t e d . I f a f a c t o r i s p r i m a r i l y r e s p o n s i b l e f o r t h e y e a r - t o - y e a r changes i n abundance,  one  would expect t h e s p a t i a l e x t e n t over w h i c h i t s n e i g h b o u r i n g v a l u e s are c o r r e l a t e d t o match t h e e x t e n t over w h i c h t h e changes i n abundance are  synchronized.  In g e n e r a l , i f h i g h v a l u e s f o r a p a r t i c u l a r v a r i a b l e at one  l o c a l i t y a r e c o r r e l a t e d w i t h h i g h v a l u e s nearby, t h e  variable i s said to exhibit positive  spatial  a u t o c o r r e l a t i o n . I f h i g h and low v a l u e s a l t e r n a t e ,  the  s p a t i a l a u t o c o r r e l a t i o n i s n e g a t i v e , w h i l e i f t h e v a l u e s are independent t h e a u t o c o r r e l a t i o n w i l l be z e r o . C o n s i d e r t h a t a c l i m a t i c i n d e x i s a random v a r i a b l e , X, t h a t has been measured a t n p o i n t s i n space and t i m e . The v a l u e f o r a p a r t i c u l a r l o c a t i o n i ( i n space and time) s i m p l e model o f t h e s p a t i a l i n t e r d e p e n d e n c e would be x  i  ( C l i f f and Ord, =  where  P £ w  Xj  ±j  j  J  1981): +  e±  J  -96-  i s t h e n x^. among t h e  A {x^}  (a) 3 1 0  1940  1950  1960  km  1970  1980  1990  1980  1990  CO  >«  CO Q CD CD te>  CD Q  (b)  1940  1950  1480  1960  km  1970  Year  F i g u r e 32. The f e e d i n g degree-days each y e a r f o r p a i r s o f n e i g h b o u r i n g and d i s t a n t s t a t i o n s . S t a t i o n s a r e s e p a r a t e d by: (a) 310 km; (b) 1480 km.  -97-  WJ_J = 1  i f i i s s p a t i a l l y adjacent t o j , 0  otherwise;  {£^} a r e independent and i d e n t i c a l l y d i s t r i b u t e d variates; p i s a measure o f t h e o v e r a l l s p a t i a l  autocorrelation.  The most commonly used measure o f s p a t i a l a u t o c o r r e l a t i o n i s Moran's I s t a t i s t i c  ( C l i f f and Ord,  1981), w h i c h i s e x p r e s s e d a s :  =  I  ( II  c.. ) / ( s  w  ±1  2  II  i  i1  )  where c  ij  x  =  (  =  x  I  i~ X£  ~  (j x  /  '  n ;  i  s  2  = I  (x± -  x) / 2  n .  i  W i t h h i g h p o s i t i v e a u t o c o r r e l a t i o n I w i l l be c l o s e t o 1; w i t h no a u t o c o r r e l a t i o n t h e e x p e c t a t i o n (Upton and F i n g l e t o n ,  of I i s - l / ( n - l )  1985), w h i c h approaches 0 f o r l a r g e  v a l u e s o f n. The a d j a c e n c y w e i g h t s  define the distance  over w h i c h t h e a u t o c o r r e l a t i o n i s measured. F o r example, t o measure t h e a u t o c o r r e l a t i o n a t a d i s t a n c e  o f 100 km, one  might s e t t h e WJ_J t o 1 f o r a l l i and j t h a t a r e 50 t o 150 km apart  (and i n t h e same y e a r ) . One can t h e n g e n e r a t e a  s p a t i a l c o r r e l o g r a m , showing t h e a u t o c o r r e l a t i o n as a f u n c t i o n o f d i s t a n c e , by c a l c u l a t i n g Moran's I f o r a range of distance  classes.  -98-  As a measure o f the s c a l e over which t h e l a r v a l  feeding  t e m p e r a t u r e and t h e o v e r w i n t e r i n g t e m p e r a t u r e might cause synchronous changes i n abundance, I c a l c u l a t e d t h e correlogram  f o r t h e annual v a l u e s of b o t h t h e s e  i n d i c e s . As t h e 20  spatial  climatic  c l i m a t i c s t a t i o n s used t o t h i s p o i n t in'  t h e a n a l y s i s were chosen so as t o be about 200  km  apart,  they provide l i t t l e data f o r c a l c u l a t i n g the a u t o c o r r e l a t i o n a t d i s t a n c e s o f 0 t o 200  km.  To g e n e r a t e a  correlogram  a c r o s s t h e f u l l range o f d i s t a n c e s , I used 88 s t a t i o n s across the province. Although  many o f  climatic these  s t a t i o n s had o n l y enough t e m p e r a t u r e d a t a t o g e n e r a t e v a l u e s f o r a few y e a r s , they s t i l l p r o v i d e d  index  valuable  i n f o r m a t i o n r e g a r d i n g the a u t o c o r r e l a t i o n a t s m a l l e r distance classes. F i g u r e 33  shows t h e r e s u l t i n g c o r r e l o g r a m s  f o r the  a n n u a l v a l u e s o f t h e f e e d i n g degree-days and minimum o v e r w i n t e r i n g t e m p e r a t u r e s . For the  overwintering  temperature index, the r e g u l a r gradient i n values  (from  n o r t h t o south) l e a d s t o the c h a r a c t e r i s t i c p a t t e r n o f h i g h negative  a u t o c o r r e l a t i o n s at t h e l a r g e r d i s t a n c e c l a s s e s  ( S o k a l and Oden, 1 9 7 8 ) . For b o t h i n d i c e s t h e r e i s  little  p o s i t i v e a u t o c o r r e l a t i o n between t h e v a l u e s r e c o r d e d l o c a t i o n s s e p a r a t e d by more t h a n 500 For t h e n o r t h - w e s t e r n  at  km.  and s o u t h e r n p a r t s o f t h e  p r o v i n c e , which are more t h a n 1000  km a p a r t , t h e f e e d i n g  o v e r w i n t e r i n g t e m p e r a t u r e s each year are t h u s g e n e r a l l y  -99-  and  Distance (km)  F i g u r e 33. The s p a t i a l c o r r e l o g r a m s f o r t h e a n n u a l v a l u e s o f : (a) f e e d i n g d e g r e e - d a y s ; (b) minimum o v e r w i n t e r i n g temperature.  -100-  u n r e l a t e d . I f temperature  was s o l e l y r e s p o n s i b l e f o r t h e  y e a r - t o - y e a r dynamics, one would have e x p e c t e d t h e synchrony to  have been l i m i t e d t o a range o f about 500 km. T h i s  p r o v i d e s f u r t h e r e v i d e n c e o f t h e importance  of other  factors  b e i n g r e s p o n s i b l e f o r l i n k i n g t h e dynamics o f o u t b r e a k s across the province.  Years o f i n c r e a s i n g abundance Why t h e n have t h e o u t b r e a k s synchronously  appeared and d i s a p p e a r e d so  across the e n t i r e province? Consider f i r s t the  i n c r e a s e phase o f o u t b r e a k s . I f one o v e r l a y s p a i r s o f d e f o l i a t i o n maps f o r s u c c e s s i v e y e a r s , t h e f o l l o w i n g p i c t u r e emerges (see Appendix A ) : s m a l l p o c k e t s o f d e f o l i a t i o n  first  appear i n a few i s o l a t e d l o c a t i o n s ( o f t e n r e f e r r e d t o as " e p i c e n t r e s " - see W a l l n e r , 1987); t h e e p i c e n t r e s u s u a l l y appear s y n c h r o n o u s l y  across the province  ( w i t h i n 1-2 y e a r s  o f each o t h e r ) ; t h e l o c a t i o n s o f t h e e p i c e n t r e s v a r y from outbreak spreads  t o outbreak;  t h e d e f o l i a t i o n i n subsequent y e a r s  r a p i d l y outwards.  This spreading pattern of d e f o l i a t i o n i s s i m i l a r t o t h a t observed 198 6)  f o r t h e e a s t e r n spruce budworm (Hardy e t  al.,  and s u g g e s t s t h a t a d u l t d i s p e r s a l may p l a y an  i m p o r t a n t r o l e i n t h e r i s e phase o f o u t b r e a k s . T h i s would a l s o e x p l a i n the e a r l i e r f i n d i n g t h a t outbreaks  do n o t  appear i n t h e p a r t o f t h e p r o v i n c e w i t h o n l y s m a l l , i s o l a t e d patches  o f h o s t . A l t h o u g h l i t t l e i s known o f t h e d i s p e r s a l  -101-  response of f o r e s t t e n t c a t e r p i l l a r moths, t h e r e are r e p o r t s of moths b e i n g t r a n s p o r t e d hundreds of k i l o m e t r e s 1965;  Raske, 1976) . Such a process  (Brown,  could p o t e n t i a l l y  homogenize the p a t t e r n of outbreaks over a r e l a t i v e l y scale. Simulation spruce  s t u d i e s of the p o p u l a t i o n dynamics of the  budworm i n New  Brunswick have suggested t h a t moth  d i s p e r s a l p l a y s an important  r o l e i n t h a t system's  synchronous p a t t e r n of outbreaks  (Clark, 1979).  While the d e f o l i a t i o n maps are suggestive  of the  presence of e p i c e n t r e s , from which outbreaks then more e x t e n s i v e  large  spread,  r e c o r d s of abundance i n the non-outbreak  years would h e l p t o b e t t e r e s t a b l i s h t h e i r e x i s t e n c e . L i g h t t r a p r e c o r d s of endemic p o p u l a t i o n l e v e l s between outbreaks i n Minnesota i n d i c a t e t h a t low d e n s i t i e s of moths were present  i n a l l o f the endemic years  over much of the  area  p r e v i o u s l y d e f o l i a t e d (Hodson, 1977). Apparently  populations  do not go l o c a l l y e x t i n c t between outbreaks,  rather  remain at low  but  l e v e l s throughout the endemic y e a r s . One  could  e s t a b l i s h a network of pheromone t r a p s , as has been done p r e v i o u s l y i n A t l a n t i c Canada it  (Pendrel, 1984), and  monitor  over a p e r i o d of years p r i o r t o the next outbreak i n  O n t a r i o . T h i s may  provide  some v a l u a b l e  r e g a r d i n g the presence of e p i c e n t r e s . One  information c o u l d a l s o set  an egg mass c o l l e c t i o n program, over the same network of stations, to provide e a r l y epidemic  f u r t h e r abundance i n f o r m a t i o n i n the  years.  -102-  up  G i v e n t h a t t h e s e e p i c e n t r e s do e x i s t , and can be l o c a t e d i n t h e e a r l y s t a g e s o f an outbreak, one c o u l d b e t t e r a s s e s s t h e r o l e o f f o r e s t c o m p o s i t i o n and c l i m a t e i n t r i g g e r i n g o u t b r e a k s . Furthermore,  t h e d e f o l i a t i o n maps  c o u l d be used t o g e n e r a t e models f o r p r e d i c t i n g t h e y e a r - t o year p r o g r e s s i o n o f outbreaks  (as i s c u r r e n t l y b e i n g done by  F o r e s t r y Canada f o r t h e hemlock l o o p e r i n Newfoundland - M. Power, p e r s . comm.). D e v e l o p i n g b i o l o g i c a l l y  meaningful  p r e d i c t i v e models f o r t h e f o r e s t t e n t c a t e r p i l l a r ,  however,  w i l l r e q u i r e a f a r b e t t e r u n d e r s t a n d i n g o f t h e a d u l t moth dispersal  response.  Years o f d e c r e a s i n g abundance C o n s i d e r t h e n o n - c l i m a t i c f a c t o r s t h a t have been s u g g e s t e d as i m p o r t a n t i n c a u s i n g o u t b r e a k s t o d e c l i n e : p u p a l p a r a s i t i s m , d i s e a s e and t h e f o o d s u p p l y . C e r t a i n l y Sippel's  (1957) e x t e n s i v e r e c o r d o f i n c r e a s e s i n p u p a l  p a r a s i t i s m by t h e f l e s h f l y ,  Sarcophaga  aldrichi,  over t h e  c o u r s e o f an o u t b r e a k suggest t h a t t h i s f a c t o r c o u l d p l a y an important r o l e i n t h e d e c l i n e o f outbreaks. Rates o f pupal p a r a s i t i s m i n e x c e s s o f 90% i n t h e l a t e o u t b r e a k y e a r s have f r e q u e n t l y been r e c o r d e d i n O n t a r i o and M i n n e s o t a 1941;  Sippell,  (Hodson,  1957; Hodson, 1977).  Very l i t t l e d a t a have been c o l l e c t e d f o r t h e o t h e r two f a c t o r s , however, making i t d i f f i c u l t t o a s s e s s t h e i r i n c a u s i n g d e c l i n e s . I f h i g h e r S. aldrichi  -103-  role  attack rates  occurred  f o r t h o s e pupae t h a t  starvation  or d i s e a s e ,  would o v e r s t a t e  the  declines.  It  quite  dependent  factors  is  then  fly's  were p r e v i o u s l y  the  c o n t r i b u t i o n to  possible  act  high rates  that  together to  two  weakened  of  parasitism  population  o r more s u c h  bring  by  about  the  density  end o f  an  outbreak.  Food supply, conceivably 3.  cause the  The d i s p e r s a l  dynamics  p u p a l p a r a s i t i s m and d i s e a s e  of  of  synchronous  S.  aldrichi  (which,  as  as  aldrichi,  fly's  The f o o d s u p p l y ,  dynamics  are  dispersal, large  separate  a l r e a d y homogenized  the  The d e f o l i a t i o n effects  an  given  of these  factors;  outbreak.  -104-  the  the  such  the  as over  do l i t t l e is  to  required  v a r i a t i o n over  be  outbreak  limiting  will what  can  l i n k e d to  by p r o c e s s e s  maps a l o n e  Chapter  link  virus  that  synchronously  more i n f o r m a t i o n c o n c e r n i n g t h e i r of  in  all  disease  may i n t u r n be  c o u l d a l s o become  areas.  could  nuclear polyhedrosis  t r a n s m i t t e d by Si dispersal).  shown  could p o t e n t i a l l y  neighbouring areas,  transmission  declines  could  the  is  course  CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS  The  r e s u l t s o f t h i s t h e s i s suggest t h a t  maps a r e a v a l u a b l e source  defoliation  o f i n f o r m a t i o n i n t h e study o f  f o r e s t i n s e c t p o p u l a t i o n dynamics. When combined w i t h  other  l a r g e s c a l e d i n f o r m a t i o n they provide a unique view o f t h e dynamics o f such systems. The v a l u e o f t h e s e maps has been i l l u s t r a t e d i n two ways. F i r s t l y , t h e maps have been used t o examine t h e i m p o r t a n c e o f f a c t o r s t h a t were p r e v i o u s l y i d e n t i f i e d as important  t h r o u g h o n l y a l i m i t e d number o f s m a l l e r s c a l e d  o b s e r v a t i o n s . T h i s was done i n a s s e s s i n g t h e r o l e o f b o t h t h e l a r v a l f e e d i n g t e m p e r a t u r e and t h e o v e r w i n t e r i n g temperature i n determining  year-to-year  changes i n  abundance. The r e s u l t s o f t h i s a n a l y s i s suggest t h a t year-to-year  these  dynamics cannot be s o l e l y a t t r i b u t e d t o t h e  v a r i a t i o n i n t h e s e two c l i m a t i c f a c t o r s . The maps were a l s o used t o e x p l o r e t h e i m p o r t a n c e o f f a c t o r s t h a t might go u n n o t i c e d a t s m a l l e r s c a l e s . A l o n g t e r m a n a l y s i s examined t h e r o l e o f t h e l a r v a l  feeding  t e m p e r a t u r e and t h e o v e r w i n t e r i n g t e m p e r a t u r e i n d e t e r m i n i n g t h e s u s c e p t i b i l i t y o f d i f f e r e n t areas t o o u t b r e a k s .  The  r e s u l t s o f t h i s a n a l y s i s suggest t h a t t h e o v e r w i n t e r i n g t e m p e r a t u r e may p l a y an i m p o r t a n t long-term  r o l e i n determining  this  s u s c e p t i b i l i t y . F u r t h e r study o f t h e r e l a t i o n s h i p  -105-  between c o l d t e m p e r a t u r e s and egg m o r t a l i t y , f o r t h e f o r e s t t e n t c a t e r p i l l a r and o t h e r  f o r e s t i n s e c t s , would h e l p  greatly i n assessing the overwintering  temperature's  importance. The  synchrony o f o u t b r e a k s , and t h e i r apparent  year-to-  y e a r s p r e a d , s u g g e s t s t h a t a d u l t d i s p e r s a l may l i n k t h e dynamics o f o u t b r e a k s over l a r g e a r e a s .  Developing  b i o l o g i c a l l y m e a n i n g f u l models o f t h e d i s p e r s a l such as t h o s e o f C l a r k  process,  (197 9) f o r t h e s p r u c e budworm, would  h e l p t o b e t t e r a s s e s s i t s i m p o r t a n c e . T h i s , however,  will  require a f a r b e t t e r understanding of the f o r e s t tent c a t e r p i l l a r ' s d i s p e r s a l r e s p o n s e . T e s t i n g t h e s e models w i l l a l s o r e q u i r e more i n f o r m a t i o n  regarding  t h e s p a t i a l and  temporal p a t t e r n of i n s e c t d e n s i t i e s i n the p r e - d e f o l i a t i o n years. F i n a l l y , t h e d e f o l i a t i o n maps suggest t h a t  outbreaks  may b e g i n i n a few d i s t i n c t e p i c e n t r e s . W h i l e d e f o l i a t i o n may f i r s t appear o n l y a t t h e s e s o - c a l l e d e p i c e n t r e s , t h e h i g h l a r v a l d e n s i t i e s r e q u i r e d t o b r i n g about any n o t i c e a b l e d e f o l i a t i o n i n d i c a t e t h a t o u t b r e a k s a r e w e l l underway any  d e f o l i a t i o n i s recorded. Better records  population  before  o f endemic  l e v e l s would h e l p t o e s t a b l i s h t h e e x i s t e n c e o f  t h e s e e p i c e n t r e s , and a l l o w one t o b e t t e r a s s e s s t h e importance of other composition,  f a c t o r s , such as c l i m a t e and f o r e s t  i n t r i g g e r i n g t h e i r development.  -106-  CHAPTER 7 LITERATURE CITED  A l l e n , J.C. 1976. A m o d i f i e d s i n e wave method f o r c a l c u l a t i n g degree days. E n v i r o n m e n t a l E n t o m o l o g i s t 5: 388-396. Anonymous, 1978. S p r i n g Survey B u l l e t i n . 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I n : P r o c e e d i n g s , new and improved t e c h n i q u e s f o r m o n i t o r i n g and e v a l u a t i n g s p r u c e budworm p o p u l a t i o n s . U n i t e d S t a t e s Department o f A g r i c u l t u r e , F o r e s t S e r v i c e , N o r t h e a s t e r n S t a t i o n , G e n e r a l T e c h n i c a l Report NE-88. Hardy, Y., M. M a n v i l l e and D.M. S c h m i t t 1986. An a t l a s o f s p r u c e budworm d e f o l i a t i o n i n E a s t e r n N o r t h A m e r i c a : 1938-80. U n i t e d S t a t e s Department o f A g r i c u l t u r e , M i s c e l l a n e o u s P u b l i c a t i o n No. 1449. H i l d a h l , V. and I.M. Campbell 1975. F o r e s t t e n t c a t e r p i l l a r and t h e P r a i r i e p r o v i n c e s . Canadian F o r e s t r y S e r v i c e , N o r t h e r n F o r e s t Research C e n t r e , Report NOR-X-135. H i l d a h l , V. and W.A. Reeks 1960. 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Great Lakes E n t o m o l o g i s t 11: 59-61.  -109-  M o r r i s , R.F. (ed.) 1963. The dynamics of e p i d e m i c s p r u c e budworm p o p u l a t i o n s . Memoirs of the E n t o m o l o g i c a l S o c i e t y o f Canada 31. Myers, J.H. 1988. Can a g e n e r a l h y p o t h e s i s e x p l a i n p o p u l a t i o n c y c l e s of f o r e s t L e p i d o p t e r a ? Advances i n E c o l o g i c a l R e s e a r c h 18: 179-242. O ' N e i l l , R.V., D.L. D e A n g e l i s , J.B. Waide, T.F.H. A l l e n 1986. A H i e r a r c h i c a l Concept of Ecosystems. Monographs i n P o p u l a t i o n B i o l o g y 23 (R.M. May e d . ) , P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n , New J e r s e y . P e n d r e l , B.A. 1984. P o p u l a t i o n d i s t r i b u t i o n o f t h e f o r e s t t e n t c a t e r p i l l a r (Malacosoma disstria) i n the Maritimes 1984 d e s c r i b e d t h r o u g h pheromone t r a p p i n g . 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P o p u l a t i o n dynamics o f t h e f o r e s t t e n t c a t e r p i l l a r (Malacosoma disstria) i n a water t u p e l o (Nyssa Aquatica) forest: a s i m u l a t i o n model. E c o l o g i c a l M o d e l l i n g 39: 287-305. Rowe, J.S. 1972. F o r e s t Regions of Canada. Canadian F o r e s t r y S e r v i c e P u b l i c a t i o n No. 1300. S a l t , R.W. 1961. P r i n c i p l e s of i n s e c t c o l d - h a r d i n e s s . A n n u a l Review o f Entomology 6: 55-74. S i p p e l l , W.L. 1957. A study of t h e f o r e s t t e n t c a t e r p i l l a r and i t s p a r a s i t e complex i n O n t a r i o . U n p u l i s h e d Ph.D. T h e s i s , U n i v e r s i t y of M i c h i g a n , Ann A r b o r , M i c h i g a n . S i p p e l l , W.L. 1962. Outbreaks of t h e f o r e s t t e n t c a t e r p i l l a r , a p e r i o d i c d e f o l i a t o r of b r o a d - l e a v e d t r e e s i n O n t a r i o . Canadian E n t o m o l o g i s t 94: 408-416.  -110-  Smith, G.J. and A.G. Raske 1968. S t a r v a t i o n e x p e r i m e n t s w i t h f i r s t i n s t a r f o r e s t t e n t c a t e r p i l l a r l a r v a e . Canadian F o r e s t r y S e r v i c e B i - m o n t h l y Research Notes 24: 39. Smith, J.D., R.A. Goyer and J.P. Woodring 1986. I n s t a r d e t e r m i n a t i o n and growth f e e d i n g i n d i c e s o f t h e f o r e s t t e n t c a t e r p i l l a r , Malacosoma disstria (Lepidoptera: L a s i o c a m p i d a e ) , r e a r e d on t u p e l o gum. A n n a l s o f t h e E n t o m o l o g i c a l S o c i e t y o f America 79: 304-307. S o k a l , R.R. and N.L. Oden 1978. S p a t i a l a u t o c o r r e l a t i o n i n b i o l o g y . I . Methodology. B i o l o g i c a l J o u r n a l o f t h e L i n n e a n S o c i e t y 10: 199-228. S t a i r s , G.R. 1966. T r a n s m i s s i o n o f v i r u s i n t e n t c a t e r p i l l a r p o p u l a t i o n s . Canadian E n t o m o l o g i s t 98: 1100-1104. S t a i r s , G.R. 1972. P a t h o g e n i c microorganisms i n t h e r e g u l a t i o n o f f o r e s t i n s e c t p o p u l a t i o n s . Annual o f Entomology 17: 355-372.  Review  S t e h r , F.W. and E.F. Cook 1968. A r e v i s i o n o f t h e genus Malacosoma Hiibner i n N o r t h America ( L e p i d o p t e r a : L a s i o c a m p i d a e ) : S y s t e m a t i c s , b i o l o g y , immatures and p a r a s i t e s . U n i t e d S t a t e s N a t i o n a l Museum B u l l e t i n 276. Tenow, 0. 1972. The o u t b r e a k s o f Oporinia autumnata Bkh. and Operophthera spp. (Lep., Geometridae) i n t h e S c a n d i n a v i a n mountain c h a i n and n o r t h e r n F i n l a n d 18621968. Z o o l o g i s k a B i d r a g F r a n U p p s a l a , Supplement 2. Tenow, 0. 1981. T o p o c l i m a t i c l i m i t a t i o n s t o t h e o u t b r e a k s o f Epirrita (=0porinia) automnata (Bkh.) ( L e p i d o p t e r a : Geometridae) near t h e f o r e s t l i m i t o f t h e mountain b i r c h i n F e n n o s c a n d i a . I n P. M o r i s s e t and S. P a y e t t e eds. T r e e - L i n e E c o l o g y . P r o c e e d i n g s o f t h e N o r t h e r n Quebec T r e e - L i n e Conference, N o r d i c a n a No. 47. C e n t r e d'etudes n o r d i q u e s , U n i v e r s i t e L a v a l , Quebec, pp. 159164 . Upton, G.J. and B. F i n g l e t o n 1985. S p a t i a l d a t a a n a l y s i s by example. Volume 1: P o i n t P a t t e r n and Q u a n t i t a t i v e Data. John W i l e y & Sons: C h i c h e s t e r . Wagner T.L., H.I. Wu, P.J. Sharpe, R.M. S c h o o l f i e l d and R.N. C o u l s o n 1984. M o d e l i n g i n s e c t development r a t e s : a l i t e r a t u r e r e v i e w and a p p l i c a t i o n o f a b i o p h y s i c a l model. A n n a l s o f t h e E n t o m o l o g i c a l S o c i e t y o f America 77: 208-225. W a l l n e r , W.E. 1987. F a c t o r s a f f e c t i n g i n s e c t p o p u l a t i o n dynamics: d i f f e r e n c e s between outbreak and non-outbreak s p e c i e s . Annual Review o f Entomology 32: 317-340.  -Ill-  W e l l i n g t o n , W.G. 1950. E f f e c t s o f r a d i a t i o n on t h e t e m p e r a t u r e o f i n s e c t s and h a b i t a t s . S c i e n t i f i c A g r i c u l t u r e 30: 209-234. W e l l i n g t o n , W.G. 1952. A i r mass c l i m a t o l o g y o f O n t a r i o N o r t h of Lake Huron and Lake S u p e r i o r b e f o r e o u t b r e a k s o f t h e spruce budworm and t h e f o r e s t t e n t c a t e r p i l l a r . Canadian J o u r n a l o f Zoology 30: 115-127. W e t z e l , B.W., H.M. Kulman and J.A. W i t t e r 1973. E f f e c t s o f c o l d t e m p e r a t u r e s on h a t c h i n g o f t h e f o r e s t t e n t c a t e r p i l l a r . Canadian E n t o m o l o g i s t 105: 1145-1149. W i t t e r , J.A. 1971. Bionomics o f t h e f o r e s t t e n t c a t e r p i l l a r , Malacosoma disstria Hbn. U n p u b l i s h e d Ph.D. T h e s i s , U n i v e r s i t y o f Minnesota, S t . P a u l . W i t t e r , J.A. 197 9. The f o r e s t t e n t c a t e r p i l l a r ( L e p i d o p t e r a : Lasiocampidae) i n M i n n e s o t a : a case h i s t o r y r e v i e w . Great Lakes E n t o m o l o g i s t 12: 191-197. W i t t e r , J.A. and H.M. Kulman 1972. M o r t a l i t y f a c t o r s a f f e c t i n g eggs o f t h e f o r e s t t e n t c a t e r p i l l a r . Canadian E n t o m o l o g i s t 104: 705-710. W i t t e r , J.A., H.M. Kulman, and A.C. Hodson 1972. L i f e f o r the f o r e s t tent c a t e r p i l l a r . Annals of the E n t o m o l o g i c a l S o c i e t y o f A m e r i c a 65: 25-31.  tables  W i t t e r , J.A., W.J. Mattson and H.M. Kulman 1975. N u m e r i c a l a n a l y s i s o f a f o r e s t t e n t c a t e r p i l l a r outbreak i n n o r t h e r n M i n n e s o t a . Canadian E n t o m o l o g i s t 107, 837-854.  -112-  APPENDIX A S u c c e s s i v e year o v e r l a y s o f d e f o l i a t i o n maps  Appendix A p r o v i d e s a p i c t u r e o f t h e y e a r t o y e a r changes i n t h e s p a t i a l p a t t e r n o f d e f o l i a t i o n . F o r each p a i r o f s u c c e s s i v e y e a r s , from 1948-49 t o 1987-88, t h e d e f o l i a t i o n maps have been o v e r l a i d . The r e s u l t i s a s e r i e s o f 40 maps c l a s s i f i e d as f o l l o w s  ( f o r a y e a r t-1 and y e a r t  overlay): area d e f o l i a t e d only i n year t - 1 ; P area d e f o l i a t e d only i n year t ; •  a r e a d e f o l i a t e d i n b o t h y e a r t - 1 and y e a r t .  i  -113-  -114-  -115-  -116-  -117-  - 1 1 8 -  -119-  -120-  -121-  -122-  -123-  APPENDIX B F e e d i n g degree-days  and d e f o l i a t i o n f o r 16  stations  Appendix B shows t h e f e e d i n g degree-days and t h e p r o p o r t i o n o f a r e a d e f o l i a t e d each y e a r , from 1948-88, f o r 16 o f t h e 20 c l i m a t e s t a t i o n s . The o t h e r 4 s t a t i o n s a r e shown i n F i g u r e 12. Shading shows t h e f e e d i n g degree-days r e l a t i v e t o 25°C-days, t h e mean f o r a l l s t a t i o n s and y e a r s . Dark l i n e shows t h e p e r c e n t d e f o l i a t i o n .  -124-  Fort F r a n c e s (2) 100  1940  1950  1960  1970  Sioux Lookout  1980  1990  (3) 100  •50  1940  1950  1960  1970  1980  1990  C e n t r a l Patricia (4) 120 T  r 100  80 40  0 1940  1950  1960  1970  1980  Thunder B a y (6) 100  -50  Year  -125-  Moosonee (7) 100  Hornepayne (8) 100  1980  CO  >-  C  ed O  _o  Chapleau (10)  CD CD CD CD  100  C)  Q  Q  -50  1940  1950  1960  1970  1980  0 1990  Earlton (11) 100  Year  -126-  Sault S t e . Marie  (12)  120  100  80 50  40 0 1940  1960  1970  1980  0 1990  Gore B a y (13) 100  CO >> CO  1950  1970  1980 \o  c  Q  CD CD i_ CD CD  o  M u s k o k a (15) 100  3§ o  "CD  Q  -50  Ottawa  (16) 100  - 50  Year  -127-  Q  Wiarton (17) r 100  1940  1950  Peterborough (18) 100 -50  1970  CO >>  CO Q  CD C D i_ CO CD  I S  c o  London (19)  ii 100  o  ^CD  Q  Q  1970  Woodslee (20) 100  1980  Year  -128-  APPENDIX C  Minimum o v e r w i n t e r i n g temperature and d e f o l i a t i o n f o r 16  stations  T h i s appendix shows the minimum o v e r w i n t e r i n g temperature and the p r o p o r t i o n o f area d e f o l i a t e d  each year,  from 1948-88, f o r 16 o f the 20 c l i m a t e s t a t i o n s .  The other 4  stations  are shown i n F i g u r e 18. Shading shows t h e  temperature r e l a t i v e t o -40°C. Dark l i n e shows t h e p e r c e n t defoliation.  -129-  Fort F r a n c e s (2) r 100  -10  50  -40 -70 1940  1950  J3-i  1960  1970  Sioux Lookout  1980  1990  (3)  -10  100  -40  50  -70 1940  r 1950  1960  1970  1980  M-0 1990 c O  Central Patricia (4) r 100  -10 -40 -70 1940  mjt uimij  1950  1960  1970  IL  1980  - 50  w*  •0 1990  Thunder B a y (6) -10 -,  100  50  1990  -130-  n o  o Q  M o o s o n e e (7) •10  100  -l  -50  -40 •70 1940  1950  1960  1970  1980  1990  H o m e p a y n e (8) -10 -i  100  -40  50  -70 1940  1950  1960  1970  1980  *H-0 1990 c _o  C h a p l e a u (10) -10  100  -i  M o M—  CD  -40 -70 1940  50  1950  1960  1970  1980  •0 1990  Earlton (11) r  Year  100  Q  Sault Ste. Marie (12) 100  10  50  -40 -70 1940  1950  1960  1970  1980  •0 1990  Gore Bay (13) 100  -10 -i  1940  1950  1960  1970  1980  1990  Muskoka (15) -10  r 100  -40  50  -70 1940  Ix 1950  1960  1970  1980  1990  Ottawa (16) -10  100  n  -50  1940  Year  -132-  Wiarton (17) 100  1940  1950  Peterborough  (18) 100  1940  1950  1960  1970  1980  1990  CD  oN  ZS  C  "5  o  CD CL  E CD  ^—<  London (19) -10  100  -40 -70 1940  • 50  1950  1960  1970  1980  1990  Woodslee (20) -10  100  -i  -40 -70 1940  •50  1950  1960  1970  Year  -133-  1980  •0 1990  o  %  APPENDIX D Details  Defoliation  o f t h e data  analysis  Data  The d e f o l i a t i o n maps were p r o v i d e d by F o r e s t r y Canada's F o r e s t I n s e c t and D i s e a s e Survey F o r e s t r y Centre  (FIDS) a t t h e Great  Lakes  (GLFC) i n S a u l t S t e . M a r i e , O n t a r i o . The  O n t a r i o FIDS c r e a t e a p r o v i n c e - w i d e d e f o l i a t i o n map each y e a r by combining a l l o f t h e i n d i v i d u a l r a n g e r s k e t c h maps onto a s i n g l e O n t a r i o base map. From 1948 t o 1974 t h e s c a l e of t h e p r o v i n c e - w i d e base maps was 1:1,267,200 (1 i n c h = 20 m i l e s ) , w h i l e t h e s c a l e from 1975 t o 1988 was  1:1,584,000  (1 i n c h = 25 m i l e s ) . A l l o r i g i n a l base maps used a Lambert Conformal p r o j e c t i o n  ( s t a n d a r d p a r a l l e l s o f 44.5° and 53.5°,  c e n t r a l m e r i d i a n o f -85°). The d i f f e r e n t l e v e l s o f d e f o l i a t i o n r e p o r t e d on t h e o r i g i n a l maps v a r i e d from one y e a r t o t h e n e x t . Some y e a r s showed o n l y one c a t e g o r y o f d e f o l i a t i o n  (moderate t o severe)  w h i l e o t h e r s showed as many as t h r e e c a t e g o r i e s ( l i g h t , moderate and s e v e r e ) . To s t a n d a r d i z e t h e s e maps I i g n o r e d t h e a r e a s marked as " l i g h t " and combined t h e o t h e r areas into a single  "moderate t o s e v e r e " c a t e g o r y .  There were two y e a r s f o r which no p r o v i n c e - w i d e composite maps e x i s t e d : 1958 and 1985. Maps f o r t h e s e y e a r s were r e - c r e a t e d u s i n g t h e annual O n t a r i o FIDS r a n g e r  -134-  r e p o r t s ; w h i l e t h e 1985 r e p o r t s showed some d e f o l i a t i o n , no d e f o l i a t i o n was r e p o r t e d i n 1958. A l l o f t h e d e f o l i a t i o n maps were d i g i t i z e d u s i n g t h e ARC/INFO G e o g r a p h i c I n f o r m a t i o n System. The r e g i o n a l maps f o r 1985 were combined and t r a n s f o r m e d  t o t h e same  p r o j e c t i o n as t h o s e o f t h e o t h e r y e a r s . F o r d i s p l a y purposes a l l o f t h e maps were o v e r l a y e d upon an O n t a r i o base map p r o v i d e d by t h e FIDS Technology Development Group a t F o r e s t r y Canada's Petawawa N a t i o n a l F o r e s t r y I n s t i t u t e . To g e n e r a t e  t h e d e f o l i a t i o n time s e r i e s i n t h i s  thesis,  a 10 km by 10 km g r i d system was c r e a t e d f o r t h e p r o v i n c e . By o v e r l a y i n g t h e O n t a r i o base map on t h i s g r i d I d e t e r m i n e d t h e l a n d a r e a w i t h i n each o f t h e g r i d ' s 10 km by 10 km cells.  I t h e n d e t e r m i n e d t h e d e f o l i a t e d a r e a each y e a r , f o r  each c e l l , by o v e r l a y i n g each y e a r ' s d e f o l i a t i o n map on t h e g r i d system. To generate  a time s e r i e s f o r a p a r t i c u l a r  a r e a , I t h e n summed t h e l a n d and d e f o l i a t e d a r e a s o f a l l t h e c e l l s corresponding  t o t h e a r e a i n q u e s t i o n . The p e r c e n t  d e f o l i a t i o n over t h e area f o r each y e a r t was t h e n c a l c u l a t e d as: (% d e f o l i a t i o n )  t  = (total defoliated area) (total land a r e a )  t  x 100%  t  The p e r c e n t d e f o l i a t i o n  f o r each o f t h e 20 s t a t i o n s and  41 y e a r s , a t a s c a l e o f 100 km by 100 km, i s g i v e n i n Table D-I.  -135-  Temperature Data D a i l y maximum and minimum t e m p e r a t u r e d a t a were p r o v i d e d by t h e Canadian C l i m a t e C e n t r e , a d i v i s i o n o f Environment Canada's A t m o s p h e r i c Environment S e r v i c e  (AES).  A c a t a l o g u e showing a l l o f t h e AES s t a t i o n l o c a t i o n s and approximate p e r i o d s o f r e c o r d was used t o s e l e c t 88 s t a t i o n s a c r o s s t h e p r o v i n c e . These were s e l e c t e d t o g i v e a network o f s t a t i o n s t h a t would p r o v i d e c o n t i n u o u s t e m p e r a t u r e d a t a , from 1947-88, f o r t h e e n t i r e p r o v i n c e . To e x t e n d t h e p e r i o d o f r e c o r d f o r t h o s e s t a t i o n s which were e i t h e r m i s s i n g r e c o r d s o r were r e p l a c e d o v e r t i m e w i t h a s t a t i o n nearby, s t a t i o n s w i t h i n 20 km o f each o t h e r were t r e a t e d as a s i n g l e l o c a t i o n . The completeness o f t h e r e c o r d f o r each s t a t i o n was t h e n d e t e r m i n e d by r a n k i n g t h e s t a t i o n s a c c o r d i n g t o t h e number o f y e a r s f o r w h i c h t h e f e e d i n g degree-days and t h e minimum o v e r w i n t e r i n g t e m p e r a t u r e c o u l d be e v a l u a t e d . F o r t h e f e e d i n g degree-days, a s t a t i o n and year  (or " s t a t i o n - y e a r " ) was deemed t o have s u f f i c i e n t d a t a  i f a c o n t i n u o u s r e c o r d o f d a i l y maximum and minimum t e m p e r a t u r e s e x i s t e d from March 1 t o June 30. S i m i l a r l y , a s t a t i o n - y e a r q u a l i f i e d f o r c a l c u l a t i n g t h e minimum o v e r w i n t e r i n g temperature i f a continuous r e c o r d o f d a i l y minimum t e m p e r a t u r e s e x i s t e d from December 1 (of t h e p r e v i o u s year) t o March 31.  -136-  Two c r i t e r i a were then used t o s e l e c t t h o s e s t a t i o n s t h a t would be used f o r f u r t h e r a n a l y s i s . F i r s t ,  stations  were s e l e c t e d such t h a t t h e y were a p p r o x i m a t e l y 200 km a p a r t . Second,  s t a t i o n s were s e l e c t e d based upon t h e  completeness o f t h e i r r e c o r d . T h i s l e d t o t h e network o f 20 s t a t i o n s used i n t h i s t h e s i s  (Table D - I I ) .  The c a l c u l a t e d h a t c h d a t e s , f e e d i n g degree-days and minimum o v e r w i n t e r i n g t e m p e r a t u r e s f o r each o f t h e 20 s t a t i o n s and 41 y e a r s a r e g i v e n i n T a b l e s D - I I I , D-IV and D-V r e s p e c t i v e l y . The minimum o v e r w i n t e r i n g t e m p e r a t u r e f o r each s t a t i o n - y e a r i s t h e minimum t e m p e r a t u r e r e c o r d e d a t t h e s t a t i o n between December 1 and March 31. Hatch d a t e s and f e e d i n g degree-days were c a l c u l a t e d u s i n g t h e f o r m u l a s g i v e n i n Chapter 4. A t r i a n g u l a r a p p r o x i m a t i o n was used t o e s t i m a t e t h e degree-days  each day from maximum and minimum  t e m p e r a t u r e d a t a . T h i s a p p r o x i m a t i o n uses t h e f o l l o w i n g formula  (Ives,  1973):  degree days = (max + min) 2  =  - th  (max - th) 2 (max - min)  =0  th < min; mm  < th < max;  th > max;  where max = d a i l y maximum t e m p e r a t u r e ; min th  = d a i l y minimum  temperature;  = t h r e s h o l d temperature.  -137-  T a b l e D-I  P r o p o r t i o n of area d e f o l i a t e d each year, 1948-88, f o r the 20 c l i m a t e s t a t i o n s . Values are the percentage of t o t a l land area d e f o l i a t e d , at a s c a l e of 100 km by 100 km. S t a t i o n numbers are those given i n F i g u r e 7.  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  Year 48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  65  66  67  68  0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0  1 0 31 0 0 0 0 0 0 0 0 11 9 0 10 0 0 0 0 0  0 2 66 0 0 0 2 3 14 1 0 47 46 8 36 0 0 31 0 0  3 21 89 0 0 0 0 15 21 23 4 95 99 37 98 2 0 34 0 0  80 97 93 0 19 57 0 53 59 43 11 74 83 79 24 35 74 22 0 0  35 70 0 0 18 49 0 87 96 88 67 1 0 92 4 85 31 21 0 0  0 0 0 0 0 0 0 5 1 29 96 0 0 4 0 0 12 2 0 0  0 0 0 0 0 0 0 0 0 0 92 0 0 0 0 0 0 0 0 0  0 0 0 1 0 0 0 0 0 0 31 0 0 0 0 0 0 0 0 0  0 0 0 2 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  50 7 94 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  98 100 100 56 67 88 62 95 90 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 5 11 0 0 15 1 6 16 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 48 0 0 0 0 0 0 0 0 0 5 8 20 3 47 0 0 0 0  0 54 0 0 0 0 0 0 0 0 0 9 25 0 0 0 0 0 0 0  0 15 0 0 0 0 0 0 0 0 0 7 29 0 0 0 0 0 0 0  64  Table D-I  (continued)  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  Year 69  70  71  72  73  74  75  76  77  78  0 18 0 0 0 0 0 0 0 0 0 0 11 0 0 0 0 0 0 0  0 20 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 22 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 0 1 0 0 0 0 0 0 0 13 0 0 1 0 0 0 0 0 0  0 0 0 0 0 0 0 2 0 0 16 0 0 2 0 0 0 0 0 0  0 0 0 0 0 0 1 18 53 0 22 0 0 31 11 0 0 4 0 0  43 0 0 0 0 0 4 12 62 0 0 0 3 30 77 0 40 17 0 0  81 100 0 0 20 100 28 0 0 0 2 6 1 14 2 6 64 90 0 0 2 1 0 6 16 16 10 33 84 0 0 3 0 66 0 15 0 0 0 0  79  80  81  14 2 95 0 0 6 0 0 5 0 0 0 3 0 0 0 0 0 0 0  0 0 0 0 0 11 0 0 0 0 4 0 2 0 0 0 0 0 0 0  0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0  82  0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0  83  0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0  84  85  86  87  88  0 0 0 0 0 7 0 0 0 0 12 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 19 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 26 0 1 11 0 0 0 0 0 0  0 1 0 0 0 0 0 0 0 0 29 2 12 72 29 0 0 5 0 0  0 30 0 0 0 0 0 0 0 0 0 4 56 90 67 1 1 31 0 0  Table D-II  The l o c a t i o n o f t h e A t m o s p h e r i c Environment S e r v i c e (AES) c l i m a t e s t a t i o n s used i n t h e a n a l y s i s . S t a t i o n numbers a r e t h o s e g i v e n i n F i g u r e 7.  Stn. #  AES Id.  1 2 3 4 4 5 6 7 8 9 10 10 10 11 12 12 12 13 14 15 16 17 18 18 19 20  6034075 6022475 6037775 6011305 6016525 6040325 6048261 6075425 6053570 6073960 6061358 6061359 6061361 6072225 6057589 6057590 6057592 6092925 6085700 6115525 6106000 6119500 6166416 6166418 6144475 6139600  Latitude Longitude deg. min. deg. min. 49 48 50 51 51 50 48 51 49 49 47 47 47 47 46 46 46 45 46 44 45 44 44 44 43 42  48 37 7 30 27 17 22 16 14 25 50 50 49 42 32 32 28 53 22 58 19 45 20 14 2 13  94 93 91 90 90 88 89 80 84 82 83 83 83 79 84 84 84 82 79 79 75 81 78 78 81 82  -140-  22 25 54 9 12 54 19 39 48 26 26 26 21 51 30 20 30 34 25 18 40 6 19 21 9 44  Name  KENORA A FORT FRANCES SIOUX LOOKOUT A CENTRAL PATRICIA PICKLE LAKE ARMSTRONG A FT WILLIAM PT ARTHUR A MOOSONEE HORNEPAYNE KAPUSKASING CHAPLEAU CHAPLEAU CHAPLEAU A EARLTON A SAULT STE MARIE SAULT STE MARIE 2 SAULT STE MARIE GORE BAY A NORTH BAY A MUSKOKA A OTTAWA A WIARTON A PETERBOROUGH PETERBOROUGH A LONDON A WOODSLEE  Table D-III P r e d i c t e d hatch date each year, 1948-88, f o r the 20 c l i m a t e s t a t i o n s . Hatch dates are g i v e n as the J u l i a n days beginning March 1 s t . S t a t i o n numbers are those given i n F i g u r e 7.  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  Year 48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65  66  67  68  73 64 75  61 60 62  85  69  88  74  55 52 57  68 68 69  83 82 94  58 57 58  78 75 80 78 75  62 78 58 69 83 102 66 84 70 80 66 76 70 70 61 70 61 70 61 70 58 68 57 67 59 55 67 52 65 50  95 84 98  71 64 73  70 64 84 91 87 76 85  82 82 75 82 78 72 61 62 62 60 52 49  60 62 60  81 78 83 80 79 77 77 74 77 67 56 64 60 61 54 48  88 80 96 88 87  77 66 76 78 78 78 88 77  65 64 65 64 69 75 67 65 64 65 63 66 66 62 59 61 58  71 67 71 78 79 73 84 71 70  77 76 75 75 73 60 64 60  68 59 72 77 86 77 86 78 79 76 77 77 77 73 66 65 64  84 83 87  88 85 88 88 84 83 83 93 82 81 76 71 77 74 67 65  71 50 73 77 77 72 95 74 75 75 68 68 73 67 52 51 64 51 50 49  81 80 81  73 61 83 77 64 66 64 65 65 65 63 63 62 59 57  61 60 66 72 71 67 91  75 74 76  83 81 94 78 75  89 86 91 94 97 87 101 97 98 96 91 91 91 90 82 75 76 75 72 64  57 56  48 34  53 48  86 79 88 92 93 90 93 92 90 89 90 88 89 86 79 75 62 62 46 40  73 63 75 86 87 74 75 75 75 75 69 73 73 53 47 47 47 45 44 35  74 74 71 65 55 55 56 56 51  75 63 68 69 64 63 68 63 60 59  60 61 55 60 55 51 44 42  68 59 59 66 57 55 55 55 56 54 53  70 71 71 72 72 68 67 64 67 64 56 49  76 75 76 75 74 70 74 73 72 67  70 72 71 69 68 68 69 65 66 63  91 85 85 87 83 85 83 84 85 83 81 76 81 75 66 51  Table D-III  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  (continued)  Year 69  62 61 67 87 89 76 100 84 88 88 83 79 . 83 76 65 65 68 58 52 47  70  71  72  73  74  75  76  77  78  79  80  81  82  83  84  85  86  87  88  83 79 84 90 92 83 94 79 83 81 74 61 75 64 61 61 61 59 59 57  73 67 75 86 89 76 90 84 89 87 76 78 78 76 76 72 76 69 69 55  71 71 73  78 67 80  82 79 88  63 62 64 65  88  73 68 50 59 67 59 72 68 60 61 60 68 61 60  70 89 63 63  73 75 72 67 61 60 59 59 58 56 50 56 51 45  51 67  75 78 77 75 74 70 76 74 72 63  68 66 75 82 82 76 93 83 82 82 80 80 81 80 48 44 48 47 41 35  47 45 48 51  62 64 62 52 50 50 51 47 43 41  56 53 60 62 63 62 81 65 73 64 65 65 65 63 63 62 66 62 64 55  67 65 72 76  71 69 70 49 49 49 48 48 47 45  86 83 87 88 91 87 79 91 79 79 74 77 72 69 57 57 69 56 55 53  60 60 63 75  66  67 67 77 78 80 78 88 83 79  53 56 57 70  95 85 96 85 88 82 83 81 82 79 60 60 59 58 57 48  56 55 63 68 73 64 82  79 71 82 89  87 83 8.7 83 80 80 70 71 68 63 53 53 52 52 50 46  70 59 75 78 83 74 94 85 77  63 61  78 78 83 74 78 78 77 78 78 77 75 74 77 73 67 61  71 73 76 78 79 74 81 74 74 78 72 78 73 71 71 67 71 68 66 63  69 80 75 75 69 70 70 69 66 67 66 66 65 54  82 79 69 76 68 68 67 72 72 66 60 65 62 59 55  95 83 90 80 81 83 75 72 67 75 67 62 58  70 64 62 61 57 54 54 51 46  51 51 49 49 50 48 47 46 48 46 46  Table D-IV Feeding degree-days each year, 1948-88, f o r the 20 c l i m a t e s t a t i o n s . Degree-days are i n °C-days. S t a t i o n numbers are those given i n F i g u r e 7.  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  Year 48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65  66  67  68  49 18 45  13 22 7  34  25  26  28  47 47 26  12 19 7  17 21 55  23 25 24 24 48  6 7 22 9 14 9 14 5 4 4 9 10 4 11 15 33  6 7 35 6 7 7 18 14 8 18 26 41  43 22 68  11 11 56 45 30 18 27  16 14 29 28 49 34 45 29 23 27 15 49 20 19 18 34  30 25 15 20 17  18 16 21 29 15 9 22 23  38 36 30 20 7 13 11 24 30 38 38 29 22 30 30 41 28  12 22 13 6 9 9 17 10 9  36 55 40 33 55 49 54 37  8 10 12 19 19 14 7 26 24 42 40 37 22 20 6 9 2  22 24 18  18 22 17 15 28 22 40 16 26 55 33 38 23 26 19 30  28 2 19 7 2 15 18 13 12 10 10 9 11 8 3 3 8 2 8 12  61 57 32  9 8 29 9 5 11 14 8 8 13 31 34 32 37 51  10 16 12 4 11 10 25  30 30 25  40 47 18 19 31  27 99 35 90 20 101 89 18 66 17 54 13 33 67 14 68 17 67 15 65 56 10 62 15 62 22 30 26 22 12 11 27 16 22 37 17 27  60 72  13 5  28 30  44 36 40 41 28 28 37 38 41 47 58 45 56 63 36 33 1 3 4 6  8 3 11 15 11 5 21 20 25 17 15 8 7 6 4 5 3 6 5 11  26 19 8 3 12 8 3 7 9  45 13 19 32 23 29 28 29 29 36  28 29  24 19 10 21 10 12 13 14 4 16 11 16  10 17 9 8 5 20 26 13 22 36 44  22 21 29 16 14 28 31 47 29 25 19 16  2 11 12 8 15 25 17 32 32 28  23 16 7 28 36 44 29 37 50 58  18 18 14 12 16 15 27 22 17 28 38 43 31 33 18 3  Table D-IV  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  (continued)  Year 69  70  71  72  73  74  75  76  77  78  79  80  81  82  83  4 8 11 9 5 13 15 13 11 20 26 13 17 18 8 11 11 15 13 23  59 44 49 64 42 28 40 37 31 34 13 5 9 6 14 20 12 25 34 52  15 12 22 38 39 14 33 34 53 39 18 17 13 17 25 34 16 33 25 13  74 92 77  23 13 23  21 36 22 16 22 37 33 43 31 37 25 22 39 2 5 1 12 13 17  49 49 59 73 45 31 22 49  47 54 42 37 23 28 11 17 33  25 13 9 1 4 9 9 11 15 34  46 42 22 6 9 15 8 13 17 34  67 48 34 64 56 80 43 67 62 21  41 28 34 26 27 25 15 39 18 19 23 12 3 20 25 26 18 24 31 37  39 25 33 40 35 35 12 23 32 33 24 25 20 20 21 22 13 25 32 19  23 23 35 21 18 26 20 26 29 28 39 27 23 37 5 2 3 3 2 8  8 9 15 46  16 26 12 35 25 19 12 8 7 5 2 6 5 5 13 18  31 13 52 51 59 22 65 83 42  10 15  47 41 12 53 51 57 55 51 36 50 50 62 34 47 39 36  29 50 35 19 21 28 20 52 50 50 59 38 34 59 67 93 47 71 69 59  44 27 13 18 33 30 31 32 18 23 32 25 29 45 51  21 102 17 44 5 6 9 5 9 11 4 9 10 10  85  86  87  88  1 2 4 9  19 23 14 5  51 24 59 48  26 26 17 5  22 31 16 17  20 4 4 7 4 4 8 3 3 5 8 8 5 7  10 20 8 11  43 25 40 39 16 15 12 12 21 31 22 29 21 18  8 14  10 11 32 25 24 33 28 17 18 24 29 16 23 12  84  18 18 8 16 27 18 21 37 60  3 4 12 11 5 12 14 21 9 16 16  Table D-V Minimum overwintering temperature each year, 1948-88, f o r the 20 c l i m a t e Temperatures are i n °C. S t a t i o n numbers are those given i n F i g u r e 7.  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  stations.  Year 48  49  50  51  52  53  54  55  -36. 1 -40. 0 -40. 6 -38. 9 -36.1 -35 .0 -38 .9 -36 .1 -38. 9 -37. 8 -41. 1 -33.9 -34 .4 -40 .0 -37 .2 -37. 2 -42. 2 -41. 7 -41. 7 -39.4 -38 .3 -40 .0 -37 .2 -50 .0 -46. 1 -42. 8 -47. 8 -48. 3 -42.8 -40 .0 -49 .4 -42 .2 -38. 3 -34. 4 -40. 6 -41. 1 -32.2 -32 .8 -35 .0 -36 .7 -46. 7 -36. 1 -46. 7 -41. 7 -38.3 -35 .6 -41 .7 -42 .8 -46. 1 -45. 0 -43. 9 -44. 4 -38.9 -37 .2 -42. 2 -41. 1 -42. 2 -38. 9 -37.2 -36 .7 -42 .8 -41 .7 -40. 0 -43. 9 -45. 0 -41,1 -38 .9 -42 .2 -39. 4 -33. 9 -40. 6 -45. 0 -41.7 -35 .0 -40 .0 -38. 9 -28. 9 -36. 7 -28.9 -28 .9 -30 .6 -30. 0 -26. 1 -30. 0 -31. 7 -33.3 -25 .6 -27 .8 -26 .1 -35. 6 -31. 7 -36. 7 -35. 6 -34.4 -30 .0 -32 .2 -29 .4 -36. 1 -30. 6 -32. 2 -38. 9 -34.4 -27 .8 -31 .7 -30 .6 -33. 3 -25. 0 -30. 6 -33. 3 -31.1 -25 .0 -29 .4 -29 .4 -30. 0 -20. 0 -22. 2 -22. 8 -23.3 -18 .9 -23 .3 -24 .4 -33. 3 -25. 6 -33. 3 -28.3 -21 .1 -27 .8 -27 .2 -26. 7 -20. 0 -22. 8 -24. 4 -20.0 -21 .1 -20 .6 -23 .3 -21.7 -17 .2 -18 .9 -19 .4 -15. 6 -21. 1  56 -37.2 -39.4 -39.4 -40.6 -41.1 -33.3 -38.3 -35.6 -37.8 -42.8 -40.0 -26.1 -23.9 -32.2 -34.4 -30.6 -22.8 -27.2 -22.2 -20.0  57  58  59  60  -37.2 -33. 9 -35. -38.3 -33. 3 -37. -41.7 -38. 3 -38. -45. 6 -53. -50.0 -44. 4 -45. -38.3 -31. 7 -34. -45.0 -42. 8 -38.  6 8 3 9 0 4 3  -42.2 -40. 0 -45.0 -39.4 -33. 9 -29. 4 -32.2 -34.4 -28. 3 -32.2 -28. 3 -35. 6 -25. 0 -23.9 -23. 3 -32.2 -25. 0 -23.3 -25. 6 -25.6 -20. 6  2 8 6 3 8 9 6 0 2 1 0 6  -37. -42. -35. -28. -27. -33. -35. -30. -27. -31. -25. -20.  61  -33. 3 -37 .2 -31. 7 -37 .2 -34. 4 -38 .3 -42. -32. -40. -41. -39. -42. -36. -23. -31. -32. -33. -27. -23. -30. -21. -21.  8 2 0 1 4 2 1 9 1 2 9 8 9 0 1 1  -41 .7 -33 .3 -42 .8 -42 .8 -41 .7 -36 .1 -26 .7 -28 .9 -33 .3 -28 .3 -26 . 1 -27 .2 -26 .1 -23 .3  T a b l e D-V  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  (continued)  Year 62 -38 -38 -38 -43 -44 -36 -40 -41 -44 -44 -45 -35 -30 -33 -33 -32 -32 -33 -22 -23  .3 . 9 .3 .9 .4 .7 .6 .7 .4 .4 .0 .0 .0 .9 .9 .2 .8 .9 .2 .3  63  64  65  6 8 3 2 4 3 2  -32. -35. -38. -42. -42. -31. -38. -42.  8 6 9 2 8 7 3 2  -40. 0 -41. 7 -32. 2 -32. 8 -31. 1 -34. 4 -28. 3 -31. 1  -41. -36. -30. -26. -31. -34. -27. -23.  7 7 6 7 7 4 8 3  6 -23. 1 -21.  3 1  -40. -37. -43. -47. -49. -38. -42.  -25. -26.  -34.4 -40.6 -41.1 -43.9 -37.8 -40.0 -44.4 -44.4 -40.0 -41.1 -34.4 -32.2 -35.0 -36.1 -29.4 -26.7 -28.3 -23.9 -22.2  66  67  -40.6 -36. 7 -43.3 -40. 6 -41. 7 -46.1 -47.2 -48. 3 -44.4 -46. 1 -35.0 -39. 4 -39.4 -46. 1 -41.1 -41. 7 -40. 6 -44. 4 -41.7 -44. 4 -41. 7 -42.2 -29.4 -35. 0 -32. 8 -28.9 -31.7 -36. 1 -35. 6 -33.9 -27.2 -31. 7 -27. 2 -26.1 -30. 0 -25.0 -24. 4 -25.0 -22.2 -20. 6  68  69  -41.7 -41.1 -43.3 -51.2 -48.3 -38.3 -43.3 -42.8 -45.6 -43.9 -39.4 -33.9 -33.3 -37.8 -35.0 -32.8 -25.6 -34.4 -22.8 -22.2  -33.3 -37.2 -34.4 -38.9 -39.4 -30.0 -38.3 -37.8 -38.3 -41.1 -38.3 -24.4 -25.6 -31.7 -30.0 -30.6 -18.9 -26.7 -22.8 -19.4  70 -37 -38 -38 -42 -47 -40 -43 -43 -42 -42 -42 -35 -32 -33 -37 -28 -25 -31 -31 -23  71 .2 .3 .3 .2 .2 .0 .3 .9 .8 .8 .2 .0 .2 .3 .2 .9 .0 .7 .7 .9  -36. -35. -37. -46. -43. -34. -44. -41. -40. -40. -41. -35. -32. -32. -36. -32. -26. -35. -25. -22.  72 1 6 2 1 9 4 4 7 6 0 7 0 8 2 7 2 7 6 6 8  -41.7 -41.1 -41.1 -42.8 -42.8 -37.2 -41.7 -40.6 -40.6 -44.4 -39.4 -35.6 -30.6 -36.1 -39.4 -30.0 -25.6 -31.7 -23.3 -25.0  73  74  -33. -38. -41.  3 -38. 9 -36. 1 -45.  -43. -34. -38. -40. -40. -40. -40. -30. -26. -31. -36. -27. -26. -27. -23. -21.  3 4 9 6 0 0 6 6 7 1 1 8 1 2 9 1  -47. -36. -43. -41. -43. -43. -42. -35. -29. -30. -31. -27. -27. -31. -23. -22.  75 3 -33. 9 1 -33. 3 0 -39. 4 -48 . 3 8 -48. 9 7 -35. 0 3 -42. 2 1 -42. 8 3 -42. 2 3 -40. 6 2 -38. 9 0 -32 . 2 4 -26. 7 0 -32. 8 1 -33. 9 2 -29. 4 2 -22. 8 1 -25. 6 9 -20. 0 8 -20. 6  Table D-V  Stn. #  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  (continued)  Year 76  77  78  79  80  81  82  -36.1 -36.7 -36.1 -43.9 -41.7 -31.1 -38.9 -42.2 -47.2 -41.1 -42.2 -30.6 -33.3 -37.2 -38.3 -31.7 -29.4 -36.1 -30.6 -22.2  -36.0 -37.2 -39.5 -48.3 -44.4 -37.9 -40.0 -40.6  -33.6 -36.1 -36.7 -43.3 -40.7 -37.3 -39.6 -38.0 -40.0  -34.9 -33.5 -35.7 -39.8 -43.9 -31.6 -34.8 -39.0 -36.0  -38.7 -34.6 -38.0 -37.5 -43.2 -42.0 -40.5 -43.3 -39.7 -47.7 -40.4 -36.9 -41. 6 -40.0 -42.0 -47.0  -38.4 -35.0 -35.2 -32.8 -39.8 -27.9 -36.4 -37.1 -25.7 -24.4  -40.1 -29.4 -28.7 -28.5 -32.6 -25.4 -31.6 -33.9 -29.5 -25.5  -37.6 -40.0 -39.4 -40.6 -45.0 -39.0 -41.5 -40.0 -42.0 -42.0 -39.9 -38.7 -36.5 -34.5 -41.5 -29.3 -34.8 -37.8 -25.9 -22.0  -30.4 -30.1 -28.0 -30.6 -34.3 -26.0 -30.7 -29.1 -21.7 -20.0  -41.2 -44.8 -35. 9 -36.8 -32.2 -36.9 -37.7 -38.4 -38.4 -39.2 -30.7 -35.2 -33.0 -26.5 -36.2 -32.0 -26.1 -26.5 -26.0 -23.0  83  84  85  86  87  88  -30. -32. -39. -41.  1 5 0 9  -38 -37 -40 -41  .0 .5 .9 .1  -40. -38. -42. -43.  0 -33 5 -36 0 -37 8  .5 .0 .4  -35 -36 -36 -42  .1 .0 .4 .2  -34. -34. -37. -38.  4 5 9 6  -35. -40.  .6 .2 .0 .0  -36. -36.  4 -35 9 -38  .7 .3  -33 -34  .7 .6  -39.  4 -34 3 -40 -43 0 -44  -39.  0 -39  .5  -38  .0  -36. -39. -39. -39.  7 6 5 0  -37. -26. -25. -26. -31. -23. -21. -26. -19. -15.  4 6 2 3 5 6 4 1 3 0  .3 .9 .6 .5  -36. -32. -35. -29.  3 3 3 5  - 2 9 .4 -27 .5 -37 .9 - 2 8 .8 -27 .0  -26. -25. -26. -24. -26.  .1 .9 .0 .4 .0 .7 .8 .6 .2  -34 -30 -27 -32 -33 -27 -20 -29 -23  .7 .0 .2 .3 .0 .4 .4 .5 .7  -35. -28. -29. -33. -37. -29. -22. -28. -19.  7 4 2 3 8 4 6 6 6  -41 -32 -32 -33  -36 -35 -28 -32 -35 2 -26 3 -24 5 -29 9 -25 0  

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