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Analysis and modelling of interspecies competition during forest secondary succession Bellefleur, Pierre 1978

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Analysis and modelling of interspecies competiti during f o r e s t secondary succession by PIERRE BELLEFLEUR B.A. (Hon.). Uni v e r s i t y of Montreal, 1967 B.Sc. (Hon.), Uni v e r s i t y of Montreal, 1970 M.Sc, McGill U n i v e r s i t y , 1972 A THESIS SUBMITTED IN THE REQUIREMENTS DOCTOR OF PARTIAL FULFILLMENT OF FOR THE DEGREE OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES I n s t i t u t e of Animal Resource Ecology and Department of Zoology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1978 Copyright 1978, Pie r r e B e l i e f l e u r In present ing th i s thes i s in p a r t i a l f u l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ib ra ry sha l l make i t f r e e l y ava i l ab le for reference and study. I fu r ther agree that permission for extens ive copying of th i s thes i s fo r s cho la r l y purposes may be granted by the Head of my Department or by h i s representat ives . It i s understood that copying or pub l i c a t i on of th i s thes i s fo r f i nanc i a l gain sha l l not be allowed without my wr i t ten permiss ion. Department of Zoology, I n s t i t u t e of Animal Resource Ecology The Un iver s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Oate J u n e 1 6 t h 1 9 7 8 THESIS ABSTRACT The Coastal f o r e s t of southwestern B r i t i s h Columbia i s examined at three l e v e l s of i n t e r p r e t a t i o n : the Biogeoclimatic Subzone l e v e l , the p l o t l e v e l , and the si n g l e tree l e v e l . These lev e l s correspond to the three major s t r a t a of the population: the geographic range, the community, and the i n d i v i d u a l . The data base consists of 40 years of observations on 730 Permanent Sample Plots describing over 70,000 trees. The highest l e v e l of i n t e r p r e t a t i o n , the Biogeoclimatic Subzone l e v e l , covers several thousand square kilometers of extremely varied topography and climate. The t o t a l study area i s subdivided into f i v e main low elevation Biogeoclimatic Subzones. The age structure of each subzone i s analysed on an average span of 80 years and forest-type succession dynamics i s described. The very nature of f o r e s t succession from one type to another, with a f i n i t e number of p o s s i b l e forest-types over the time horizon, seems admirably suited for a f i n i t e - s t a t e Markov process. However, the Markov models cannot f i t adequately the observa-tions at the subzone l e v e l because t r a n s i t i o n p r o b a b i l i t i e s are not e n t i r e l y time-homogeneous and because there i s a wide range of communities and o r i g i n s of perturbation within a subzone. The sample plot o f f e r s an intermediate l e v e l of i n t e r p r e t a t i o n and i s considered s u f f i c i e n t l y homogeneous to represent larger units of f o r e s t . The e n t i r e f o r e s t can be described by the agglomeration of the fundamental u n i t s . The growth of a given species i s l i k e l y to be d i f f e r e n t i n a pure f o r e s t than i n a mixed one, and between d i f f e r e n t types of mixed f o r e s t s . Tree species constitute the pool of b i o t i c v a r i a b l e s with the highest biomass and are estimated to have a high b i o t i c impact on each other's growth. Each Biogeoclimatic Subzone i s divided into several plot-types which represent fundamental units of forest composition.. The growth of any given species shows, indeed, s i g n i f i c a n t v a r i a t i o n from one p l o t -type to another. The trends i n succession at the p l o t type l e v e l coincide c l o s e l y with those observed at the Biogeoclimatic Subzone l e v e l . Thus i t i s hypothesized that succession at the subzone l e v e l i s a consequence of v a r i a t i o n i n species growth rate between plot'types, due to s i t e condi-tions and competition. At the lowest stratum of the population, the growth, mo r t a l i t y , and regeneration of a s i n g l e tree are investigated. The growth rate of a tree i s dependent on i t s past h i s t o r y , on the c l i m a t i c and geographic compo-. nents c h a r a c t e r i z i n g a Biogeoclimatic Subzone, and on the other trees growing i n i t s immediate neighborhood. These variables have a very s i g n i f i c a n t e f f e c t on whether a tree l i v e s or dies i n any time period. The analysis indicates that recently dead stems appear to have a h i s t o r y of sub-standard growth when compared with the population. Moreover, the immediate neighborhood of dead stems corresponds to a s p e c i f i c composition and structure of the vegetation. On the other hand, new stems show large interspecies differences i n t h e i r preference f o r f o r e s t composition and structure of t h e i r immediate surroundings. The habitat composition arid structure leading to the mort a l i t y of a stem of one species may constitute a good habitat f o r the i v regeneration of a stem of another species. This i s viewed as a mechanism which gives r i s e to p l o t type succession, which i n turn leads to f o r e s t -type succession. The levels of the i n d i v i d u a l , of the community, and of the geographic range d i s p l a y consistent population dynamics. Succession appears to be explained by simple mechanisms involving competition f o r l i g h t and space; i t i s not necessary to postulate more complex s y n e r g i s t i c or antagonistic mechanisms of species i n t e r a c t i o n . V TABLE OF CONTENTS THESIS ABSTRACT ' •• i i L i s t of Figures .... . v i i i L i s t of Tables . -ix AC KNOWLEDGEMENTS x GENERAL INTRODUCTION x i CHAPTER I ' * i ABSTRACT \ 2 RESUME* • 3 INTRODUCTION 4 DATA SAMPLING 6 The data base 6 Study area 7 Description of the data 7 1) Tree parameters 14 2) Plot parameters • ..14 Assessment of the data •-. ....15 METHODS . . .17 The analysis of succession 17 The Markov approach to succession 18 The underlying assumptions to the Markov process 23 RESULTS AND DISCUSSION 24 The Markov simulation 24 Dry Douglas-fir Subzone ....26 Wet Douglas-fir Subzone 39 Dry Western Hemlock Subzone 43 Wet Western Hemlock Subzone 45 Fog Western Hemlock Subzone 46 CONCLUSION .... • . .47 LITERATURE CITED 50 v i CHAPTER II • 54 ABSTRACT ,. • 55 RESUME . . 56 INTRODUCTION . 57 DATA AND METHODS 58 Heterogeneity within subzones • • • •. •• 58 D e f i n i t i o n of the c l a s s i f i c a t i o n scheme 61 RESULTS AND DISCUSSION .63 Dynamics of f o r e s t stands 63 Douglas-fir Zone .....63 Western Hemlock Zone 75 Plot type c l a s s i f i c a t i o n ....... 76 Analysis of basal area growth v a r i a t i o n 83 Dry Douglas-fir Subzone .• ..85 Major species (Table 10) ........ 85 Minor species (Table 11) - 87 Wet Douglas-fir Subzone ......89 Major species (Table 12) .....89 Minor species (Table 13) 91 Dry Western Hemlock Subzone 94 Major species (Table 14) ........ 94 Minor species (Table 15) . ... ..96 Wet Western Hemlock Subzone 98 Major species (Table 16) 98 Minor species (Table 17) ..102 Fog Western Hemlock Subzone 102 Major species (Table 18) ' ...102 Minor species (Table 19) . ... 105 S i t e index v a r i a t i o n .107 v i i CONCLUSION . . . . . . . 113 LITERATURE CITED .. . . ..115 CHAPTER III ' .116 .. ABSTRACT . . ... . . . . .... ... . .. . . . , .117 RESUME • . • . . .118 INTRODUCTION •••••• • • -1-19 DESCRIPTION OF THE DATA • 120 THE CHOICE OF AN APPROACH ....121 Li t e r a t u r e review 121 Methods . . . .... 122 RESULTS AND DISCUSSION 127 Regression models 127 M o r t a l i t y and regeneration analysis .134 Mo r t a l i t y i n d i c a t o r s ..134 Regeneration in d i c a t o r s 137 Succession trends 139 CONCLUSION . • ' 141 LITERATURE, CITED- . ' • • 144 CHAPTER IV: Synthesis and conclusion- 147 APPENDIX A . . -152 APPENDIX B .. ...153 APPENDIX C .159 v i i i LIST OF FIGURES 1. Plots of Vancouver Island .8 2. Plots of the Queen Charlotte Islands .10 3. D i s t r i b u t i o n of major tree species 13 4. T r a n s i t i o n p r o b a b i l i t y matrix evaluation • ....22 5. Markovian simulation of succession 27 6. Mean species r e l a t i v e abundance .64 7. P_. menziesii s i t e index d i s t r i b u t i o n ..108 8. T. heterophylla s i t e index d i s t r i b u t i o n ....110 9. Indices of competition .....124 ix LIST OF TABLES 1. Subzone c l i m a t i c parameters . .. 12 2. D i s t r i b u t i o n of the sample p l o t s 16 3. I n i t i a l stand-type frequencies 25 4. Theoretical subzone steady-states ............ .40 5. Plot types of the Dry Douglas-fir Subzone 77 6. Plot types of the Wet Douglas-fir Subzone 79 7. Plot types of the Dry Western Hemlock Subzone ....80. 8. Plot types of the Wet Western Hemlock Subzone ........81 9. Plot types of the Fog Western Hemlock Subzone 82 10. Anova of major species, Dry Douglas-fir Subzone 86 11. Anova of minor species, Dry Douglas-fir Subzone ....88 12. Anova of major species, Wet Douglas-fir Subzone .90 13. Anova of minor species, Wet Douglas-fir Subzone ......92 14. Anova of major species, Dry Western Hemlock Subzone 95 15. Anova of minor species, Dry Western Hemlock Subzone ....97 16. Anova of major species, Wet Western Hemlock Subzone .-...99 17. Anova of minor species, Wet Western Hemlock Subzone ....103 18. Anova of major species, Fog Western Hemlock Subzone .......... 104 19. Anova of minor species, Fog Western Hemlock Subzone 106 20. Mean subzone s i t e indices ' 112 21. Regression models 128 22. Anova table on regression models ....130 23. M o r t a l i t y i n d i c a t o r s .................................... 135 24. Regeneration ind i c a t o r s 138 ACKNOWLEDGEMENTS I wish to thank Fred Bunnell, Alan Chambers, Dave Handley, George Hochbaum, Buzz H o l l i n g , Ed Packee, Randall Perterman, Don Reimer, Nick Sonntag, William Thompson, Carl Walters, and Con Wehrhahn f o r reviewing and c r i t i s i z i n g my manuscript. I am s p e c i a l l y g r a t e f u l to Don Reimer of MacMillan Blbedel Limited, Forestry D i v i s i o n , f or providing the whole data base and a l l kinds of encouragement and support. Ed Packee provided four years of c r i t i c i s m and was an endless source of information. I acknowledge the National Research Council of Canada f o r a scholarship and C a r l Walters for a research assistantship during my doctoral program. x i GENERAL INTRODUCTION Succession appears to be a c e n t r a l concept i n both animal and plant ecology. In i t s broadest sense, succession can be defined as a repeatable sequence of dominant species i n an ecosystem. This concept i s , however, perceived with a d i f f e r e n t f l a v o r according to the scale at which the ecosystem i s observed. On a very small scale, large areas of vegetation can appear to be rather homogeneous, while on a large scale the heterogeneity of the communities and the v a r i a b i l i t y among in d i v i d u a l s become obvious. The problem i s then to evaluate how perspectives about the forces acting during secondary succession change with the l e v e l of i n t e r p r e t a t i o n . The coastal forest of southwestern B r i t i s h Columbia i s large enough to o f f e r observations from a very small to a very large scale. The general hypothesis of t h i s study i s that, although the perception of succession might be quite d i f f e r e n t at the scale of the Biogeoclimatic Subzone, at the scale of the forest stand, and at the scale of the i n d i v i d u a l tree, each l e v e l of i n t e r p r e t a t i o n must be consistent with the others. Furthermore, there must be some underlying mechanism responsible for the population dynamics observed at each l e v e l . The Biogeoclimatic Subzone l e v e l i s studied i n Chapter I, the pl o t l e v e l , i n Chapter I I , and the i n d i v i d u a l tree l e v e l , i n Chapter I I I . 1 Analysis and modelling of interspecies competition during forest secondary succession. Pierre B e l l e f l e u r CHAPTER I A Markov model of forest-type succession after disturbance i n Coastal B r i t i s h Columbia. 2 ABSTRACT Succession models were b u i l t f o r f i v e Biogeoclimatic Subzones of the coastal f o r e s t of B r i t i s h Columbia from a data bank of 730 p l o t s . Each p l o t was characterized by a forest-type every f i v e years and prob-a b i l i t i e s of moving from one type to another over the next f i v e years were calculated. The models tested the hypothesis that the future state of the f o r e s t , given past and present states, i s not f i x e d , but i s determined by a set of t r a n s i t i o n p r o b a b i l i t i e s based only on the present state of the f o r e s t . P_. menziesii stand-types showed a very slow decrease i n the Dry Douglas-fir Subzone to the advantage of T. p l i c a t a , t h i s decrease being f a s t e r i n the wet subzone where T. heterophylla stand-types succeeded a f t e r 100 years; t h i s succession occurred a f t e r 50 years i n the Dry Western Hemlock Subzone. In the wet part of t h i s subzone, T. heterophylla stand-types always stayed prominent with minor succession possibly occurring from P_. s i t c h e n s i s stand-types to A. amabilis. In the Fog Subzone, J_. p l i c a t a stand-types were more abundant soon af t e r disturbance, but T. heterophylla stand-types would progressively take over. The models did not adequately r e p l i c a t e the observations and f a i l e d to produce r e a l i s t i c long-term p r e d i c t i o n s . T r a n s i t i o n p r o b a b i l i t i e s were not e n t i r e l y time-homogeneous and the models were too general i n r e l a t i o n to the d i v e r s i t y of communities, types of disturbance, and patterns of invasion. Using t h i s type of data, i t i s concluded that f o r e s t succession i s not a Markov process. RESUME 3 On a construit des modeles de succession pour cinq sous-zones biogeoclimatiques de l a f o r e t cStiere de Colombie Britannique a p a r t i r d'une banque de donnees de730 p l a c e t t e s . Le type f o r e s t i e r de chaque pla c e t t e a ete determine a tous les cinq ans et les p r o b a b i l i t e s de t r a n s i t i o n d'un type a un autre durant les prochaines cinq annees ont ete calculees. Les modeles ont teste l'hypothese selon l a q u e l l e l ' e t a t futur de l a f o r e t , connaissant ses etats passe et present, n'est pas f i g e , mais p l u t 6 t determine par un ensemble de p r o b a b i l i t e s de t r a n s i t i o n basees seulement sur l ' e t a t actuel de l a f o r S t . Le type f o r e s t i e r P_. menziesii a diminue tres lentement dans l a sous-zone seche du sapin de Douglas au p r o f i t de J_. p l i c a t a et plus r a p i -dement dans l a sous-zone humide ou le type J_. heterophylla l u i succede apres 100 ans; cette meme succession se produit egalement dans l a sous-zone seche de l a pruche de l'ouest apres 50 ans. Dans l a p a r t i e humide de cette sous-zone, l e type f o r e s t i e r J_. heterophylla est demeure pro-eminent tandis qu'une succession mineure pouvait se produire du type P_. s i t c h e n s i s au type A. amabilis. Dans l a bande brumeuse de l a zone, le type T. p l i c a t a e t a i t l e plus abondant immediatement apres perturbation mais le type J_. heterophylla pourrait l u i succeder. Les modeles n'ont pas reproduit fidelement les observations et n'ont pu produire de predictions r e a l i s t e s a long terme. Les probabi-l i t e s de t r a n s i t i o n ne furent pas rigoureusement constantes et les modeles furent trop imprecis quant a l a v a r i e t e des communautes, des types de per-turbation et d'invasion des especes. On a conclu que l a succession fo-r e s t i e r e n'est pas Markovienne, selon les observations analysees. 4 INTRODUCTION There exists no precise theory to p r e d i c t the response of disturbed e c o l o g i c a l systems. Yet very large ecosystems subjected to natural and man-made disturbances are r o u t i n e l y exploited and a better understanding of t h e i r b i o t i c responses i s required. The P a c i f i c Coastal Mesothermal Forest (Krajina 1969) of B r i t i s h Columbia (Canada) has been exploited for over a century and recently c o l l a t e d data permit the study of succession a f t e r disturbance for a time range covering the f o r e s t r o t a t i o n . Raup (1967) pointed out that most fo r e s t s have a constant h i s t o r y of f i r e s , disease, insect pests, and w i n d f a l l s . Cooper (1913) showed how Abies balsamea ( L O M i l l , was preponderant soon a f t e r w i n d f a l l and was then out-competed by Betula p a p y r i f e r a Marsh., although t h i s species never became abundant due to low germination performance. Henry and Swan (1974) reconstructed f o r e s t succession f o r 300 years and found that disturbance was more important i n creating compositional changes than was autogenic succession. Morris (1963) and H b l l i n g e t a l . (1975) showed that the spruce budworm can cause up to 100% m o r t a l i t y i n stands over hundreds of hectares. Kilgore (1973) and Viereck (1973) found that w i l d f i r e s were a key f a c t o r i n the generation of new successions and i n the control of species composition. Flaccus (1959) studied the revegetation and the succession of species on 29 landslides i n the White Mountains of New Hampshire and showed the gradual replacement of pioneer species by t r a n s i t o r y species by age 70. Recently Horn (1976) has studied the e f f e c t of d i f f e r e n t patterns of devastation on succession, Slatyer and Connell (1976) have documented the patterns of c o l o n i z a t i o n a f t e r 5 perturbation, and Shugart et_ al_. (1973) have looked at the feedback e f f e c t of disturbance on pioneer species. Man i s the major b i o t i c agent a f f e c t i n g the f o r e s t (Kimmins 1972). Bartos (1973) has shown how f i r e and cutting cause the aspen (Populus  tremuloides Michx.) community to revert to early successional stages. Likens et_ a l . (1970) have made a d e t a i l e d study on the e f f e c t s of c l e a r -cutting and herbicides on s o i l nutrient contents and c y c l i n g . They showed that c l e a r c u t t i n g can produce high nutrient losses from s o i l s before the rate of nutrient u t i l i z a t i o n by early successional species reaches the rate of supply. Cole and Gessel (1968) and Gessel et a l . (1973) studied the impact of c l e a r c u t t i n g and even-age management on fo r e s t p r o d u c t i v i t y and mineral c y c l i n g . They found a 54 to 60% increase i n the amount of water i n the s o i l a f t e r c l e a r c u t t i n g . There i s abundant l i t e r a t u r e on other examples of human disturbance to the f o r e s t . E a r l y stages of succession including mosses, liverworts, annuals and s h o r t - l i v e d perennials, shrubs and tree seedlings were studied by Mueller-Dombois (1965), Kellman (1969), and Dyrness (1973). The present data set did not provide observations on understory vegetation and i t s i n c l u s i o n i n the models was not p o s s i b l e . In his study covering a l l vegetation s t r a t a , Kellman (1969) found that no p r e d i c t i o n could be made as to f l o r i s t i c organization at d i f f e r e n t stages of succession because of the highly stochastic process of propagule d i s p e r s a l i n minor vegetation. For the purpose of p r e d i c t i n g l a t e r stages of f o r e s t suc-cession, i t appears to be safer to wait u n t i l a f t e r the apparently hap-hazard stage of early competition among minor vegetation and tree saplings. 6 The purpose of t h i s paper i s to provide a synthesis of the succes-sion dynamics of the coastal f o r e s t of southwestern B r i t i s h Columbia a f t e r disturbance, at the scale of the Biogeoclimatic Subzone. As a f i r s t approach a small-scale analysis i s judged necessary to encompass the general behaviour of t h i s large ecosystem (1.3 x 10 5 km 2). The time horizon (the period of time over which modelling i s applied) required to perceive the dynamics of the system must be kept rather short, by neces-s i t y , since the cutting r o t a t i o n i s assumed to be s i x t y to eighty years. Under these conditions, an adequate model of succession should be general, synthetic and dynamic; general, due to the s i z e and v a r i a b i l i t y of the study area and because d e t a i l s are useless at t h i s l e v e l of i n t e r p r e t a t i o n ; synthetic, because i n t e g r a t i o n over several l e v e l s of response i s neces-sary; dynamic, because growth processes of a community generate constant changes i n environmental conditions and because forecasting techniques r e l y on an orderly flow of events from one time period to the next. DATA SAMPLING The data base The data f o r t h i s study were c o l l e c t e d by MacMillan Bloedel Limited, Forestry D i v i s i o n , on t h e i r Tree Farms and Tree Farm Licences i n coastal B r i t i s h Columbia. Some of the oldest p l o t s were established by Powell River Company and by the B r i t i s h Columbia Forest Service. The p l o t s are part of the Company's Permanent Sample Plot and Spacing Assessment Plot programs. They are located mainly i n the Powell River region, on a few 7 islands of the Johnstone S t r a i t , and at many locations on Vancouver Island and on the Queen Charlotte Islands. The p l o t s are grouped i n clusters of v a r i a b l e s i z e i n the d i f f e r e n t Biogeoclimatic Zones (Packee 1974). The p o s i t i o n of the clusters on Vancouver Island and the adjacent mainland, and on the Queen Charlotte Islands are shown (Figures 1 and 2). Study area The study area i s c l a s s i f i e d into four Biogeoclimatic Zones: Coastal Douglas-^fir, Coastal Western Hemlock, Subalpine Mountain Hemlock, and Alpine. The study pl o t s are r e s t r i c t e d to the f i r s t two zones, the lower elevation zones (^lOOOm.), each of which i s further divided into a dry and a wet subzone (Krajina 1965, 1969; Packee 1974, 1976). Packee (1974) also recognizes a Fog Western Hemlock / S i t k a Spruce Subzone at low elevation along the west coast of Vancouver . Island and on the Queen Charlotte Islands, within the Western Hemlock Zone. The main c l i m a t i c parameters forming the basis for c l a s s i f i c a t i o n of these f i v e subzones are l i s t e d i n Table 1. The d i s t r i b u t i o n of major tree species i n each sub-zone appears i n Figure 3. Description of the data The Forestry D i v i s i o n of MacMillan Bloedel Limited has established the Permanent Sample Plot program as a complement to i t s inventory system to assess timber production, f o r e s t r o t a t i o n , and annual allowable cut, and the Spacing Assessment Plot program as a t o o l for experimenting with stocking, thinning, f e r t i l i z a t i o n , and p l a n t i n g . The p l o t s are r e c t -angular or square, and vary from 0.04 to 0.8 hectares i n area. They are grouped i n c l u s t e r s of 2 to 10 p l o t s , i n several management blocks i n FIGUBE 1 L o c a t i o n o f the sample p l o t s c f Vancouver I s l a n d and the adjacent i s l a n d s and mainland. The Bio-g e o c l i m a t i c Subzcnes a f t e r Fackea (1974) are i n d i c a t e d by the map t e x t u r e . The s i z e of the c l u s t e r marker i n d i c a t e s the approximate number cf p l o t s per c l u s t e r . The subzones without any sample p l o t s have not been i n c l u d e d . 128° 127° 126° 125° 124° 123° W. 1 0 FIGURE 2 loca t i o n of the sample plots on the Queen Charlotte Islands. The Biogeoclimatic Subzcnas af t e r Packee (personnal communication) are i n d i -cated by the map texture. The size of the c l u s t e r marker indicates the approximate number of plots per c l u s t e r . The subzonas without any sample plots have not been included. The i n s e r t shews the r e l a t i v e position of Van-couver Island and the Queen Charlotte Islands. 12 i r EICGECCLTMATIC ZONE EIOGECCLIMATIC SUEZONE PRECIPITATION (cm) Annual Total Moist. D e f i c i t 1 DRIEST MONTH WETTEST MONTH ANNUAL SNOWFALL SNOW IN % OF ANN. PREC. climate (KCPPEN)2 6 6 - 1 0 2 1 3 . a temperature (°C) MEAN ANNUAL ANNUAL EANGE (MEAN MONTHLY) MEAN JANUARY MEAN JULY NUMBER CF FROST-FREE DAYS r — + -e l e v a t i c n (M) WINDWARD LEEWABD Coastal Douglas-fir Dry Wet 1 0 2 - 1 5 2 9.3 1 . 5 - 4 . 8 1 2 . 7 - 2 6 . 4 2 5 - 1 0 7 4-10 CSB (+DRIEST CFB) 9-11 1 2 - 1 8 1-4 1 6 - 1 9 1 5 0 - 2 5 0 0 - 1 5 0 0 - 4 5 0 Coastal Western Hemlock Dry 1 6 5 - 2 8 0 6.2 I Ret | +-I ! I 2 8 0 - 6 6 5 ! 2.7 | -j Fog -I <1 65 0.4 3 - 1 6 . 5 2 8 - 1 1 7 1 3 - 7 5 0 1-38 CFB (+ MILDEST DFB) 5-9 9-21 -4 TO 5 13- 1 8 1 2 0 - 2 5 0 C - 9 0 0 4 5 0 - 1 0 5 0 •+ \ I | 0-150 L 1 TABLE 1 The main c l i m a t i c parameters which are used tc c l a s s i f y the Bioqeoclimatic Zones (Krajina 1 9 6 5 , 1 9 6 9 , Packee 1 9 7 4 ) . The Fog Western Hemlock / Sitka Spruce sutzone i s after Packee ( 1 9 7 4 ) . Knowledge of the climax species i s also needed to c o r r e c t l y assess the zone and the subzone. 1 Mean Annual Moisture D e f i c i t with 200 mm of s o i l water storaqe capacity (Packee 1 9 7 6 ) . 2 Koppen's c l a s s i f i c a t i o n can be found i n S t r a h l e r <1 969). 13 D R Y D O U G L A S - F I R Subzone W E T D O U G L A S - F I R Subzone 0-4 -0 -0-6 D R Y W E S T E R N H E M L O C K 0-4 Subzone 0 0-8 1 W E T W E S T E R N H E M L O C K 0 • 4 -j Subzone 0 0-8 F O G W E S T E R N H E M L O C K 0-4" Subzone ^0-Th Pm Tp Ps Ag Aa Ar Pc F I G U R E 3 F r e q u e n c y d i s t r i b u t i o n of the seven most abundant tree s p e c i e s i n each B i o g e o c l i m a t i c Subzone based on i m m a t u r e plot data. The subset of unthinned plots only was used i n the computation. Species m a r k e d in a dashed line have a frequency of l e s s than 0.01. Th: T. heterophylla, Pm: P_. me n z i e s i i , Tp: T. p l i c a t a , Ps: P_. s i t c h e n s i s , Ag: A. grandis, Aa: A. amabilis, Ar: A. rubra, Pc: P. contorta. 14 each Biogeoclimatic Subzone (except i n the Alpine and Subalpine Zones). The t o t a l f o r e s t area managed by the Company i s approximately 1.4 x 10 6 hectares. The program was started during the 1930's, and oldest p l o t s have yielded observations over a period of more than 40 years. Plots are remeasured at five-year i n t e r v a l s . An i n i t i a l pool of 730 natural regeneration p l o t s , with over 70,000 trees, was a v a i l a b l e for t h i s study. 1) Tree parameters The following variables are taken or measured f o r each tree at least 4 cm i n DBH (Diameter at Breast Height, 1.4 m from ground l e v e l ) : tree number, species name, DBH, stem and butt c h a r a c t e r i s t i c s , tree defects, crown c l a s s , and pathological f a c t o r s . Breast height i s marked on the tree and DBH i s measured with a diameter tape to the nearest 0.25 cm. In addition, the age and the h e i g h t a r e measured on enough trees to assess the p l o t age and height. These trees are chosen randomly i n each of the canopy s t r a t a : dominant, co-dominant, intermediate, and suppressed. 2) Plot parameters The slope angle, slope aspect, p o s i t i o n on slope, and p l o t area are determined. The following are c a l c u l a t e d from the tree data: forest-type, p l o t cover, s i t e height, s i t e age, s i t e index (for Pseudotsuga menziesii (Mirb.) Franco 1, and Tsuga heterophylla (Raf.) Sarg.). The Biogeoclimatic Zone i s assessed, based on the climax species and p l o t l o c a t i o n . For each tree species, the number of stems and basal area are calculated on a per p l o t and per hectare b a s i s , f o r each DBH .class. Between measurements English species names are given i n Appendix A. population parameters such as ingrowth ( r e a l i z e d regeneration), m o r t a l i t y , and thinning are calculated on a f i v e year b a s i s . A l l changes i n tree s i z e and basal area, and the rates of change are also computed. The d i s -t r i b u t i o n of sample pl o t s i s shown i n Table 2. Assessment of the data Since large bodies of data s i m i l a r to t h i s one are i n c r e a s i n g l y a v a i l a b l e , i t i s important to c a r e f u l l y assess t h e i r merits and l i -mitations f o r e c o l o g i c a l studies. The main advantages of t h i s data assemblage are: 1. The a v a i l a b i l i t y of a data set r i c h with the expertise of several thousand man-days i s invaluable to the e c o l o g i s t . It allows him to focus on t h e o r e t i c a l ideas and on ana-l y t i c a l aspects rather than on time-consuming data a c q u i s i t i o n . 2. The large sample s i z e , the long range of observations and the uniformity i n the f i e l d procedures assure a high l e v e l of s t a t i s t i c a l r e l i a b i l i t y f o r most parameters. 3. The geographic area sampled i s on a Biogeoclimatic Region l e v e l - the P a c i f i c Coastal Mesothermal Forest (Krajina 1969) . This allows elaboration of g e n e r a l i t i e s pertinent to the whole region, and also concentration on between-zone v a r i a t i o n . 4. The data were obtained from MacMillan Bloedel Limited i n a form prepared f o r computer an a l y s i s , already v e r i f i e d and edited. 16 ""BIOGEOCLIMATIC ZONE BIOGEOCLIMATIC SUBZONE % T o t a l A r e a 1 A l l PLOTS Number of P l o t s % c f T o t a l Sampling P e r i o d Sampling Eange (years) UNTHINNEB PLOTS Number of P l o t s % c f T o t a l Number of t r e e s Average number of t r e e s per p l o t C o a s t a l D o u g l a s - f i r Dry 5.5 + 100 14 1955-71 16 71 11 4070 57 Wet , + 9.0 + 198 27 1946-73 27 -+ 167 26 12964 77 C o a s t a l Western Hemlock Dry 13.0 + 157 21 1935-72 37 142 22 10076 70 Wet 40.0 t 2.2 255 35 1932-72 40 248 38 21774 87 Fog .j ! TOTAL I — - i ^ 69 .72 20 3 1967-72 5 19 3 1 154 60 730 100 — I 647 100 500381 j TABLE 2 D i s t r i b u t i o n o f the sample p l o t s per B i o g e o c l i -matic Subzone. The complete sample c o n s i s t s of 730 p l o t s , some of which have been th i n n e d f o r ex p e r i m e n t a l purposes. Some a n a l y s e s use the complete sample, and others use the subsample cf 647 unthinned p l o t s . 1 A f t e r Packee (1976). 2 The Mountain Hemlock, A l p i n e , and Urbane B i o g e o c l i m a t i c Zones c o v e r the remaining 30.3?* area. 17 There are however some noteworthy l i m i t a t i o n s i n using inventory-type data f o r e c o l o g i c a l analysis: 1. Some parameters such as height and age are not systematically measured f o r each tre e , but only f o r a random subset of the p l o t . As a consequence, species with a low frequency are sometimes not measured and a s i g n i f i c a n t age v a r i a t i o n i n t h i s case could suggest a r t i f i c i a l patterns of succession. 2. Environmental variables (micro-climate, pedology, fauna, etc.) are u s u a l l y lacking from inventory sampling, and t h e i r absence makes i t impossible to r e l a t e the f o r e s t structure to environmental v a r i a t i o n between p l o t s . (This kind of information i s , however, being incorporated progres-s i v e l y into the sampling procedures of MacMillan Bloedel Limited.) 3. Understory f l o r a i s not recorded. This seems to be the most serious lack i n the data set since i t i s widely recognized that understory vegetation i s a better i n d i c a t o r of s i t e p o t e n t i a l than early se r a i tree composition. METHODS The analysis of succession Various studies on succession i n r e l a t i o n to disturbance were men-tioned e a r l i e r . Several other studies on f o r e s t succession are published and some authors have reviewed the matter. Harbo (1972), i n his t h e s i s , reviewed at length the pre-1970 work on succession. Shugart et_ a l . (1973) 18 used a set of d i f f e r e n t i a l equations based on stand dynamics to model large f o r e s t areas. Their approach takes advantage of the concept of rate of change and gives some in s i g h t into management. Vitousek and Reiners (1975) analysed the nutrient r e t e n t i o n towards climax i n re-l a t i o n to the importance of each nutrient to plant growth. They de-veloped and r e f i n e d the concept of biomass accumulation (Rodin and B a z i l e v i t c h 1967; Odum 1969) and they discussed other nutrient c y c l i n g studies. Whittaker (1953, 1957, 1970), Odum (1969, 1971), and Drury and Nisbet (1971, 1973) have discussed successional patterns quite throughly. Four elements are es s e n t i a l to a complete d e f i n i t i o n of succession. (1) Succession i s a property-of a system. None of the elements of the system considered separately can give a v a l i d p i c t u r e of succession. (2) Succession consists of a change i n the net rate of increase of species. As Horn (1974) pointed out, t h i s i s the condition without which one could not perceive succession. (3) The controls over succession are eit h e r e x t r i n s i c to the system: f i r e , f l ooding, c l i m a t i c changes etc., or i n -t r i n s i c : competition, predation etc. F i n a l l y , (4) there i s a c e r t a i n convergence of the system towards a r e l a t i v e l y steady state, the so-called climax, where species composition seems to change over a much longer time scale than i n e a r l i e r stages of succession. The Markov approach to succession From the e s s e n t i a l c h a r a c t e r i s t i c s of succession emerges the general concept of t r a n s i t i o n of the f o r e s t from one " s t a t e " to another. Two conditions bound the choice of states: t h e i r number must be f i n i t e and they must describe the conditions of the f o r e s t at any time. For the 19 study of large regions, Shugart et a l . (1973) used a f i n i t e number of cover-states or forest-types. Waggoner and Stephens (1970) and Stephens and Waggoner (1970) c l a s s i f i e d the f o r e s t into f i v e types "according to which of the f i v e classes had the most stems on the t r a c t " . Once the forest-types are i d e n t i f i e d , repeated observations at regular time i n -t e r v a l s on several sampling pl o t s show t r a n s i t i o n s from one type to another during the course of succession. MacArthur (1958, 1961) suggested that succession could be viewed as a plant-by-plant replacement process amenable to the Markovian approach. This approach views state t r a n s i t i o n s as a p r o b a b i l i s t i c phenomenon, where the future of any s i t e i s not f i x e d , but i s determined by a set of p r o b a b i l i t i e s of moving to another state over time. Anderson (1966), Olson and C r i s t o f o l i n i (1966), and Horn (1974, 1975a, 1975b, 1976) have a l l used t h i s method i n t h e i r studies of succession. Recently Horn (1975b) and Noble and Slatyer (1976) have reviewed t h i s approach for plant suc-cession. Mathematical treatments of the Markov process are found i n Bharucha-Reid (1960), Kemeny and S n e l l (1960), and H i l l i e r and Lieberman (1967). As Waggoner and Stephens (1970) point out, sets of extensive obser-vations i n time and space necessary f o r the v e r i f i c a t i o n of the t r a n s i t i o n p r o b a b i l i t i e s are rare. However the data f o r t h i s study seem s u i t a b l e for the task. Due to the absence of data on understory f l o r a , a f o r e s t -type c l a s s i f i c a t i o n was used and each p l o t was characterized on the basis of the tree species with the largest number of stems and, a l t e r -n a t i v e l y , with the largest basal area. This was done f o r each measurement 20 on a five-year i n t e r v a l basis and the stand-type ( a stand of a given forest-type) frequencies were plotted across stand age, for each Biogeoclimatic Subzone i n terms of stems and basal area. The sampling period v a r i e s f or each Biogeoclimatic Subzone and the maximum i s 40 years (Table 2 ). Since young and old stands were sampled, data were pl o t t e d across stand age to show v a r i a t i o n s i n stand-type frequency as a function of stand age rather than as a function of an a r b i t r a r y time-scale such as calendar year. This permits the re-construction of a long-lived ecosystem from observations of p l o t s of d i f f e r e n t age measured over the same period of time. However, t h i s approach has one i m p l i c a t i o n that complicates the extraction of t r a n s i t i o n s from the data. Consider two adjacent f o r e s t stands 25 and 70 years of age r e s p e c t i v e l y , observed at five-year i n t e r -vals f or 40 years. If a t r a n s i t i o n i s observed within any of the two stands, t h i s i s recorded. A d d i t i o n n a l l y the l a s t observation of the youngest stand, taken at age 6 5 , can be merged with the f i r s t obser-vation of the oldest stand, taken at 70, .as an implied t r a n s i t i o n . H i s t o r i c a l l y , most work on f o r e s t succession i n North America i s based on implied t r a n s i t i o n s (Drury and Nisbet 1973) . Ecologists have measured forests of d i f f e r e n t ages and have assumed that the oldest ones represented the state towards which the young forests were progressing. This approach has been proven adequate i n older forests of Europe and i n s h o r t - l i v e d ecosystems. When hundreds of stands of d i f f e r e n t ages are pooled together, the t o t a l age span i s increased, but implied t r a n s i t i o n s cannot be determined. Therefore, some t r a n s i t i o n s are bound to be missing from a t r a n s i t i o n matrix generated from the observed t r a n s i t i o n s alone. However, p r i o r b i o l o g i c a l knowledge of the system and published work can contribute to produce p r i o r estimates of the t r a n s i t i o n s . A subset of the observed t r a n s i t i o n s can then be used to modify the p r i o r estimates through the use of Bayes' r u l e (see Thompson and Vertinsky 1975) and to y i e l d the f i n a l t r a n s i t i o n p r o b a b i l i t y matrix. If E i s the p r i o r estimates matrix, and 0 the observed matrix, the function f such that f [E,O] = T, the f i n a l t r a n s i t i o n matrix, i s simply: f [E,O] = ( E ( i , j ) - 0 ( i , j ) ) / (E t o t a l ( i ) - 0 t o t a l ( i ) ) f o r a l l i ' s and j ' s , where i and j represent rows and columns r e s p e c t i v e l y . The same weight i s given to the observa-tions and to the estimates by s e t t i n g each column t o t a l of the estimates equal to the column t o t a l of the observations. Therefore, t h i s simply makes the t r a n s i t i o n matrices a l i t t l e more l i k e l y to succeed i n modelling the data. Figure 4 gives an example of the c a l c u l a t i o n f or the t r a n s i t i o n s i n stems i n the Dry Western Hemlock Subzone. Matrices are documented i n Appendix B. From the e c o l o g i c a l viewpoint, the meaning of a t r a n s i t i o n pro-b a b i l i t y matrix i s as follows. A l l observations of a given forest-type, the P. menziesii type f o r instance, represent pl o t s which may belong to d i f f e r e n t communities on the basis of t h e i r understory vegetation, and which may have d i f f e r e n t o r i g i n s depending on the source of perturbation. Some of these plots may have the p o t e n t i a l to remain the P_. menziesii type, while others might progressively become the Thuja p l i c a t a Donn or the J_. heterophylla type for instance. Therefore, a l l the p o s s i b i -l i t i e s are i m p l i c i t within the t r a n s i t i o n matrix and the observed and assumed p o s s i b i l i t i e s are included i n the matrix i n terms of p r o b a b i l i t i e s . 22 P. menziesii 100 A. rubra 0 T. heterophylla 4 T. p l i c a t a 2 A- qrandis 0 TOTAL 106 0 MATRIX Observations 1 0 0 0 5 0 0 0 0 129 0 0 0 3 2 0 0 0 0 3 6 132 2 3 E MATRIX Estimates 98 1 0 0 0 0 5 0 0 0 6 0 129 1 0 2 0 3 1 0 0 0 0 0 3 106 6 132 2 3 T MATRIX Transitions P. menziesii 533 A. rubra 0 T. jheterophylla 48 T. p l i c a t a 19 A. grandis 0 TOTAL 1000 167 0 0 0 83 3 0 0 0 0 977 200 0 0 23 800 0 0 0 0 1000 1000 1000 1000 1000 FIGUBE 4 Tr a n s i t i o n p r o b a b i l i t y matrix evaluation. The estimated matrix (E) i s modified by the observed matrix (0) to produce the f i n a l t r a n s i t i o n pro-b a b i l i t y matrix (T) using Bayes' r u l e . The t r a n s i t i o n s are expressed from the column stand-type at time t , to the row stand-type at time t+1. P r o b a b i l i t i e s have been multiplied by 1,000 for presentation in the table. The column stand-types are the same as the row stand-types. 23 This makes the Markov process very powerful and very general. Once the t r a n s i t i o n p r o b a b i l i t y matrix of a system i s determined, the Markov process allows the computation of the steady-state of the system, i f i t e x i s t s . In other words, i f f o r e s t succession i s to reach a state of climax where there i s v i r t u a l l y no change i n forest-types over a long period of time, t h i s state can be predicted. This assumes, of course, that the system i s t r u l y Markovian. The underlying assumptions to the Markov process The coastal f o r e s t succession could be treated as a f i n i t e state Markov process i f i t shows the following four properties ( H i l l i e r and Lieberman 1967) : (1) The system can take only a f i n i t e number of s t a t e s . Clas-s i f y i n g each sample p l o t into forest-types gives a t h e o r e t i c a l maximum number of 24 states over the e n t i r e study area. A maximum of eight forest-types were found i n any Biogeoclimatic Subzone. (2) The t r a n s i t i o n p r o b a b i l i t i e s of the system must be the same for each time i n t e r v a l , i . e . they must be time-homogenous. This was tested by comparing the p r o b a b i l i t y matrices from five-year period to five-year period for the time horizon considered i n each Biogeoclimatic Subzone. The number of five-year time periods i s 8 for the Dry Douglas-f i r Subzone, 16 f o r the Wet Douglas-fir Subzone, 18 f o r the Dry Western Hemlock Subzone, 15 for the Wet Western Hemlock Subzone, and 5 for the Fog Western Hemlock Subzone. An adapted chi-square s t a t i s t i c f o r Markov matrices ( B i l l i n g s l e y 1961) was used to t e s t the s i m i l a r i t y of the t r a n s i t i o n s f o r a l l the time periods, for each subzone, i n terms of stems 24 and basal area. The expected matrix was computed from a weighted average of the complete sample. Two matrices out of 16 i n the Wet Douglas-fir Subzone were s i g n i f i c a n t l y d i f f e r e n t (p = 0.01) from the expected matrix, 2 out of 18 i n the Dry Western Hemlock Subzone, 1 out of 15 i n the Wet Western Hemlock Subzone, and none i n the two remaining subzones. So time-homogeneity i s not rigourous i n 3 subzones out of 5, although the departures from homogeneity are small. (3) The system must have the Markovian property. A system i s said to have the Markovian property i f the conditional p r o b a b i l i t y of any future state, given any past and present state, depends only on the present state of the system. This i s an hypothesis that w i l l be tested. If a model based on the Markov process f i t s the observations w e l l , i t suggests that the system might be Markovian; i f the model does not f i t the observations, i t i s very l i k e l y that the system i s simply not Mar-kovian. (4) A set of i n i t i a l p r o b a b i l i t i e s f or a l l states must e x i s t . The p r o b a b i l i t i e s of the f o r e s t to be i n any state i s t h e o r e t i c a l l y unknown at the o r i g i n of the observations. However the frequency d i s t r i b u t i o n can be taken as representative of the p r o b a b i l i t i e s . Table 3 gives the i n i t i a l frequencies of each stand-type for a l l the Biogeoclimatic Sub-zones . RESULTS AND DISCUSSION The Markov simulation Simulation runs were made from the t r a n s i t i o n matrices and the 25 DGUGLAS-FIK WESTERN HEMLOCK Dry Wet Dry Wet Fog STEMS Pseudotsuga m e n z i e s i i 92 78 65 0 0 Ts.uga het er.c£hy 11a 0 8 26 67 33 Thuja g l i c a t a 0 9 0 8 67 A In us r u b r a 4 5 9 4 0 P i c e a s i t c h e n s i s 0 0 0 21 0 Pinus c o n t o r t a 4 0 0 0 0 A.b.ies jgrandis 0 0 0 0 0 Abj.es a ma b i l l s 0 0 0 0 0 TOTAL 100 1 CO 1 00 100 100 BASAL AREA Pseudotsuqa m e n z i e s i i 92 77 68 0 0 Ts ucja h e t e r o p h y l l a 0 18 28 75 33 Thuja p l i c a t a 0 0 0 0 67 Alnus rubra 4 5 4 0 0 P i c e a s t i c h e n s i s 0 0 0 25 0 Pinus c c n t o r t a 4 0 0 0 0 Abies ^ r a n d i s 0 0 0 0 0 Abies a m a b i l i s 0 0 0 0 0 TOTAL 100 100 100 100 100 TABLE 3 I n i t i a l stand-type f r e q u e n c i e s f o r each Biogeo-c l i m a t i c Subzone i n percentage. Ihe stand-type i s d e f i n e d as the s p e c i e s with the ab s o l u t e ma-ximum number of stems or a b s o l u t e maximum ba s a l a r e a . 26 r e s u l t s compared with the observations. The Markovian nature of the simulation has two important features. F i r s t , the whole system of stand-types i s simulated simultaneously and the rate of change of frequency i n each stand-type i s dependent on a l l other stand-type,' behaviour. Secondly, the frequencies change asymptotically to a steady-state. The Markovian process emphasises the i n t e r r e l a t i o n s h i p s between species rather than t h e i r frequency d i s t r i b u t i o n . Figure 5 (A to J) shows the simulated frequency curves and the observed data points i n number of stems and i n basal area a l t e r n a t i v e l y f o r each subzone. A two-tailed Kolmogorov-Smirnov s t a t i s t i c (K-S test) was used to t e s t the goodness of f i t between observations and p r e d i c t i o n s . Most frequency curves were found to f i t the data well (p = 0.05), with some exceptions that w i l l be discussed for each subzone. Dry Douglas-fir Subzone Although some observations f a l l o f f the predicted curve of P_. men- z i e s i i , none of the curves are rejected by the K-S t e s t . The p r o b a b i l i t y of P_. menziesii stems dominating the stand i s very high i n young stands (0.92) and declines slowly with stand age to reach 0.61 at age 75 (Figure 5 A). Alnus rubra Bong, and Pinus contorta Dougl. each have a p r o b a b i l i t y of 0.04 i n young stands and A. rubra decreases to 0.02 while P_. contorta increases to 0.16 by age 75. T. p l i c a t a does not dominate any stand at early stages but increases progressively to 0.21 by age 75. There are two major differences i n t h i s pattern when the proba-b i l i t i e s are calculated i n terms of dominance by basal area (Figure 5 B) rather than by number of stems. The p r o b a b i l i t y f or P_. menziesii does not decrease as f a s t : 0.92 at age 35 and 0.72 at age 75. This means 27 FIGURE 5 Markovian simulation of succession. The results are presented a l t e r n a t i v e l y i n number of stems and in basal area for each subzone: A Cry Dcuglas-fir Subzone (stems) B Dry Douglas-fir Subzone (basal C Wet Douglas-fir Subzone (stems) D "Wet Douglas-fir Subzone (basal area) E Dry Western Hemlock Subzone (stems) F Dry Western Hemlock Subzone G Wet Western Hemlock Subzone H Wet Western Hemlock Subzone I Fcg Western Hemlock Subzone J Fcg Western Hemlock Subzone . rea) (basal area) (ste ms) (basal area) (stems) (basal area) Each graph shows the observed data points with the following symbols, and the simulated curves with i d e n t i c a l larger symbols: P. menziesii • J» heterophylla O T. £licata A A. rubra .. X P. s i t c h e n s i s f A. m a c r cjg h_y 11 u m X P. c enter t a 0 A. 3randis (in the Wet Dcuqlas-fir Subzone) ......+ A. amabilis (in the Wet Western Hemlock Subzone) I 29 CQ CU '9) A3N3n03yj 3dAi-QNt)lS STAND-TYPE FREQUENCY (STEMS) n 0£ STAND-TYPE FREQUENCY (B. A.) (SW31S) A0N3R03cU 3dAl-QNBlS 8) A3N3n03HJ 3dAl -QNdiS STRND-TYPE FREQUENCY (STEMS) o 35 I ^ 1 1 1 1 -—I 1 1 1 1- O CU '9) A3N3flD3cU 3dAl-QNUiS STAND-TYPE FREQUENCY (STEMS) 9£ CO '9) A0N3P03c!3 3dAi-QNUlS 38 that there are 11% more P_. m e n z i e s i i stand-types that dominate i n terms of b a s a l area than i n terms of stems at age 75. At t h i s stand age, J_. p l i c a t a shows, to the c o n t r a r y , a lower stand-type frequency i n terms of b a s a l area (0.09) than i n number of stems (0.21). Therefore, even though J_. p l i c a t a i s i n c r e a s i n g i t s number of stems due to i t s a b i l i t y to regenerate i n the shade, P_. m e n z i e s i i d i s p l a y s a.better b a s a l area growth r a t e per stem. A. r u b r a shows the same ki n d of behaviour i n both u n i t s of measurement; i t s frequency of dominance i s 0.04 at age 35 and 0.02 at age 75. Packee (personal communication) b e l i e v e s t h a t A. rubra can dominate more commonly on c e r t a i n s i t e s , and he argues t h a t lack of s u f f i c i e n t sampling on those s i t e s m i ght•explain the low observed f r e -quencies. No other t r e e species i n t h i s subzone have been found able to dominate the stands e i t h e r i n number of stems or b a s a l area. K r a j i n a (1969) p o i n t s out t h a t P_. m e n z i e s i i i s shade t o l e r a n t i n t h i s subzone, except on h y g r i c edatopes. As the subzone i n general i s x e r i c to mesic, i t leaves l i t t l e room f o r h y g r i c species to dominate the wettest s i t e s , and t h i s i s the r o l e that J_. p l i c a t a p l a y s . I t s increase i n frequency w i t h stand age might be a t t r i b u t e d to i t s a b i l i t y to reproduce i n the shade on both wet and dry s i t e s . Packee (1976) re p o r t s that T. p l i c a t a i s commonly found on r e l a t i v e l y dry s i t e s , o f t e n i n a s s o c i a t i o n w i t h Arbutus m e n z i e s i i Pursh, but only i n the Dry Douglas-f i r Subzone. P. c o n t o r t a has a chance to dominate on the most x e r i c s i t e s and K r a j i n a (1969) mentions that i t would be overtaken by shade t o l e r a n t J_. p l i c a t a at about 50 years i n terms of stems. Packee (1974) c l a s s i f i e s P_. m e n z i e s i i and T. p l i c a t a as major climax s p e c i e s , A. rubra as a minor s e r a i s p e c i e s , and P. c o n t o r t a as a major s e r a i s p e c ies. The r e s u l t s of 39 the model seem to c o n t r a d i c t h i s c l a s s i f i c a t i o n of P_. m e n z i e s i i . A l -though t h i s species i s dominant i n more than 90% of the stands a f t e r d i s t u r b a n c e , the p r o p o r t i o n of P_. m e n z i e s i i stand-types decreases s t e a d i l y t h e r e a f t e r . P_. m e n z i e s i i should be c l a s s i f i e d , on t h i s b a s i s , as a pioneer. Long-term p r o j e c t i o n s based on the model show J_. p l i c a t a and P_. c o n t o r t a to become climax species (Table 4). This i s l i k e l y to cast serious doubts on the v a l i d i t y of the model. Indeed, i t i s argued that the decrease of P. m e n z i e s i i , and the consequential increase of T. p l i c a t a and P_. c o n t o r t a , i s an a r t e f a c t generated by a higher species d i v e r s i t y i n the o l d e s t p l o t s (above 55 years i n the D o u g l a s - f i r Zone) o r i g i n a t i n g mainly from n a t u r a l d i s t u r b a n c e s : wind, f i r e , i n s e c t s , disease (Packee, personal communication) . The younger p l o t s are n e a r l y pure P_. m e n z i e s i i • Therefore, the model i s based on biased data and cannot be used f o r pre-d i c t i o n s of the steady s t a t e . In the l i g h t of t h i s b i a s , Pakee's (1974) c l a s s i f i c a t i o n mentioned e a r l i e r appears to be exact. Packee a l s o mentions that Abies grandis (Dougl.) L i n d l . can be a major climax species on s u i t a b l e s o i l s , but t h i s species d i d not dominate any of the stands. The lack of A. grandis p l o t s i n t h i s data set might be due to the past sampling procedures of the Company, which d i d not focus on t h i s species (Packee, personal communication). Wet D o u g l a s - f i r Subzone Three species curves f a i l e d the K-S t e s t of f i t i n t h i s subzone: P_. m e n z i e s i i , J_. p l i c a t a , and Acer macrophyllum Pursh. The l a t t e r d i d not f i t w e l l because i t u s u a l l y does not c o n s t i t u t e a f o r e s t - t y p e i n t h i s area (with two exceptions i n the o r i g i n a l d a t a ) , and was not included i n 40 EO0GLAS-FIR WESTERN HEMLOCK Dry Wet Dry Wet Foq EXPECTED TIME: 400 430 400 1000 100 Pseudotsuqa m e n z i e s i i 2 30 0 0 0 Tsucja hetercrjh_jrlla 0 35 90 33 100 Thuja, p l i c a t a 58 22 10 0 0 Alnus rubra 0 0 0 0 0 Picea s i t c h e n s i s 0 0 0 0 0 Pinus c c n t c r t a 40 0 0 0 0 Abies g r a n d i s 0 13 0 0 0 Abies a m a b i l i s 0 0 0 67 0 TABLE 4 Expected time c f t h e o r e t i c a l s t e a d y - s t a t e and p r o b a b i l i t y d i s t r i b u t i o n of stand-types f o r each subzone at time of s t e a d y - s t a t e i n terms of stems. the graphs. Here F_. m e n z i e s i i dominates c l e a r l y and decreases s t e a d i l y w i t h stand age from a p r o b a b i l i t y of 0.78 at 20 years to 0.34 at 100 years (Figure 5 C). Again, the decrease i s smaller i n b a s a l area (Figure 5 D). T. h e t e r o p h y l l a has a p r o b a b i l i t y of 0.08 at age 20, and s l i g h t l y overtakes P_. m e n z i e s i i at age 100 w i t h a l e v e l of 0.38. However P_. m e n z i e s i i i s s t i l l w e l l ahead of T. h e t e r o p h y l l a i n basal area. K r a j i n a (1969) s t r e s s e s that P_. m e n z i e s i i achieves a higher f o r e s t production here than i n the dry subzone w h i l e J_. h e t e r o p h y l l a grows r a t h e r p o o r l y . The discrepancy between the p r e d i c t i o n s and the observations f o r P_. men- z i e s i i , between age 45 and 75 (Figures 5 C and D), has a twofold expla-n a t i o n . The o l d e s t p l o t s were f i r s t measured i n the 1930's and were loc a t e d as a f u n c t i o n of road a c c e s s i b i l i t y , i . e . i n v a l l e y bottoms, where higher'moisture content favored J_. p l i c a t a over P_. m e n z i e s i i . Thus the observations show an abrupt d e c l i n e f o r F_. m e n z i e s i i a f t e r about age 70. This i s compounded by the b i a s mentioned e a r l i e r whereby the higher species d i v e r s i t y of the o l d e s t p l o t s produces an a r t i f i c i a l decrease of P_. m e n z i e s i i at o l d e r ages. The Markov model r e f l e c t s t h i s decrease by converging a s y m p t o t i c a l l y towards a s t e a d y - s t a t e , s t a r t i n g from a high frequency at e a r l y stand age. This r e s u l t s i n a smooth and steady d e c l i n e corresponding c l o s e l y t o the observations i n the e a r l y and l a t e stages, but departing g r e a t l y i n the middle stages. J_. p l i c a t a increases i t s dominance i n stems w i t h stand age and even at a f a s t e r r a t e i n b a s a l area. This suggests a b e t t e r moisture a v a i l a -b i l i t y and a higher s o i l n u t r i e n t content than i n the dry subzone, and a b e t t e r uptake by J_. p l i c a t a than by J_. h e t e r o p h y l l a . According to K r a j i n a (1969), J_. p l i c a t a needs r i c h e r s o i l s than J_. h e t e r o p h y l l a , and the o l i g o t r o p h i e edatopes r e q u i r e d f o r J_. h e t e r o p h y l l a are very r a r e i n t h i s subzone. Packee (1976) a t t r i b u t e s the lower frequency of T. p l i c a t a to moisture d e f i c i t . The s i m u l a t i o n f a i l e d to r e p l i c a t e the three peaks observed at age 80, 85, and 90 -on the graph i n stems f o r T. p l i c a t a . I t i s noteworthy that P i c e a s i t c h e n s i s (Bong.) Carr. never appears to domi-nate i n stems i n any stand, yet i t s b a s a l area dominance increases s t e a -d i l y w i t h time, seemingly t a k i n g advantage of the moisture. The absence of dominance i n the stem model agrees w i t h K r a j i n a ' s (1969) remark that P_. s i t c h e n s i s i s very r a r e i n t h i s subzone. I t s presence i n the b a s a l area model agrees on the other hand w i t h Phelps 1 (1973) contention that P_. s i t c h e n s i s may dominate on s i t e s where the s o i l s are w e l l d r a i n e d , f a i r l y r i c h i n n u t r i e n t s , and continuously moist. As f a r as number of stems goes, Packee (1974) does not mention P_. s i t c h e n s i s e i t h e r as a s e r a i or as a climax species. A. grandis increases i t s frequency of stem do-minance from n i l at age 20 to 0.08 by age 100, but has no chance to dominate i n ba s a l area i n t h i s area, w i t h i n the studied time h o r i z o n . K r a j i n a (1969) showed that eutrophic c o n d i t i o n s are necessary f o r A. gran- d i s to a t t a i n a good growth, while Packee (1976) argues that s o i l moisture i s a more important f a c t o r . As i n the dry subzone, A. rubra may dominate i n few young stands, but not i n older ones. Packee's (1974) c l a s s i f i c a t i o n f o r t h i s subzone i s : P_. m e n z i e s i i and J_. p l i c a t a are major climax s p e c i e s , A. grandis i s an edaphic major climax s p e c i e s , J_. h e t e r o p h y l l a i s a minor climax s p e c i e s , and A. rub r a i s a major s e r a i s p e c i e s . The r e s u l t s agree q u a l i t a t i v e l y w i t h t h a t , 43 w i t h the exception of J_. h e t e r o p h y l l a which tends to become a major climax species on moist s i t e s of o l d er stands. Kellman (1969), working i n an area mid-way between the Wet D o u g l a s - f i r Subzone and the Dry Western Hemlock Subzone, found species frequency s i m i l a r to these at age 13, 42, and 100, w i t h an expected T. p l i c a t a - T. h e t e r o p h y l l a climax. However, due to the b i a s i n the d a t a , i t i s l i k e l y t hat P_. m e n z i e s i i does not decrease as much as shown here, and consequently J_. p l i c a t a and J_. hete- r o p h y l l a would both have a lower frequency at higher ages; t h i s makes the use of the model f o r e x t r a p o l a t i o n unsafe. The t h e o r e t i c a l steady-s t a t e i n stems would be reached i n t h i s subzone at about 430 years of age (see Table 4 ) , i f the f o r e s t were t r u l y Markovian. Dry Western Hemlock Subzone No curve was r e j e c t e d by the K-S t e s t i n t h i s subzone, although the curves f o r P_. m e n z i e s i i and J_. h e t e r o p h y l l a do not v i s u a l l y seem to f i t the observations: the t e s t i s not very robust. There i s a remarkable s h i f t from a high frequency (0.66) of P_. m e n z i e s i i and low frequency of J_. hete- r o p h y l l a (0.26) at age 20 to 0.22 f o r P_. m e n z i e s i i and 0.68 f o r T. hetero- p h y l l a at age 10 (Figure 5 E ) . This s h i f t a l s o occurs i n b a s a l area, a l -though much more s l o w l y (Figure 5 F ) . Discrepancies between observations and p r e d i c t i o n s of frequencies of T. h e t e r o p h y l l a and P_. m e n z i e s i i are l i k e l y caused by an oversampling i n the v a l l e y bottoms, 30 and 40 years ago, because of b e t t e r road a c c e s s i b i l i t y (Packee, personal communication). V a l l e y moisture overemphasized frequency of T. h e t e r o p h y l l a p l o t s over P_. m e n z i e s i i p l o t s . Since p l o t s were not sampled before 20 years of age T. h e t e r o p h y l l a p l o t s now 50 years or older are overrepresented i n the observations. This might s l i g h t l y exaggerate the upward trend of 44 T_. h e t e r o p h y l l a i n the older ages, although there i s no doubt that T. h e t e r o p h y l l a i s t a k i n g over P_. m e n z i e s i i i n terms of stems. Again A. rubra may dominate young stands o n l y , and J_. p l i c a t a more f r e q u e n t l y dominates older stands, w i t h a maximum p r o b a b i l i t y of 0.10. Here P_. m e n z i e s i i can be a major climax s p e c i e s , but e d a p h i c a l l y c o n t r o l l e d (Packee 1974), or e l s e a major s e r a i s p e c i e s ; J_. p l i c a t a i s a major climax s p e c i e s , and A. r u b r a i s again a major s e r a i s p e cies. Graphs show J_. h e t e r o p h y l l a to become a major climax s p e c i e s , and t h i s agrees w i t h Packee's c o n t e n t i o n , although present r e s u l t s give more in f o r m a t i o n concerning the d e f i n i t e succession t o J_. h e t e r o p h y l l a . There i s a t h r e e f o l d explanation f o r t h i s s h i f t . (1) The f a c t that P_. menzie-s i i i s e d a p h i c a l l y c o n t r o l l e d and i s c o m p e t i t i v e l y s u p e r i o r on x e r i c s i t e s favors i t s appearance j u s t a f t e r disturbance. (2) The seedlings of J_. h e t e r o p h y l l a are s e n s i t i v e to heat and t h e i r establishment succeeds b e t t e r i n the shade of P_. m e n z i e s i i . Thereafter J_. h e t e r o p h y l l a i s able to continue regenerating i n the shade. (3) Unless there are frequent openings i n the canopy, the s e e d l i n g s u r v i v a l of P_. m e n z i e s i i i s threatened. K r a j i n a (1969) describes P. m e n z i e s i i as a d e f i n i t e pioneer species i n the subzone, and T. h e t e r o p h y l l a as a c l i m a t i c climax s p e c i e s . There were two i s o l a t e d observations of A. grandis that were not p o s s i b l e to simulate and were de l e t e d from the graphs. I t i s expected that the Markovian ste a d y - s t a t e w i l l not appear before 400 y e a r s , w i t h p r o b a b i l i t y d i s t r i b u t i o n of 0.90 f o r T. h e t e r o p h y l l a and 0.10 f o r T. p l i c a t a (see Table 4). For the same reasons as above, long term e x t r a p o l a t i o n s are c e r t a i n l y unsafe. 45 West Western Hemlock Subzone A l l curves i n t h i s subzone f i t the observations according t o the K-S t e s t . This subzone e x h i b i t s very slow changes and no s i g n i f i c a n t d i f f e r e n c e s between the evaluations i n number of stems and b a s a l area (Figure 5 G and H) . The dominance of J_. h e t e r o p h y l l a i s p r a c t i c a l l y constant w i t h i n the time h o r i z o n at a frequency of about 0.7 w h i l e Abies amabilis (Dougl.) Forbes succeeds to an e a r l y dominance of P. s i t c h e n s i s i n about 0.20 of the stands. J_. p l i c a t a may dominate i n -f r e q u e n t l y (0.08) i n e a r l y ages, but i s soon succeeded by A. a m a b i l i s . No stand dominated by P_. m e n z i e s i i was found here and K r a j i n a (1969) p o i n t s out that P_. m e n z i e s i i i s indeed s t r o n g l y outcompeted by T. hete- r o p h y l l a , J_. p l i c a t a , and A. a m a b i l i s . He a l s o s t r e s s e s that the climax J_. h e t e r o p h y l l a has i t s best production here. The frequency of stands dominated by A. ama b i l i s i s very low i n younger stands. K r a j i n a (1969) st a t e s that i t i s shade r e q u i r i n g i n mesic and d r i e r edatopes. Macbean (1941, i n Packee 1976) p o i n t s out that i t s regeneration i s very poor i n stands f o l l o w i n g c l e a r c u t t i n g , which i s the case i n the younger p l o t s . P_. s i t c h e n s i s might be outcompeted by A. ama b i l i s s i n c e the former i s shade i n t o l e r a n t i n dense stands ( K r a j i n a 1969) , although i t w i l l p e r s i s t on f l u v i a l bottomlands where i t s growth i s best (Packee 1976). Packee (1974) assigns species as f o l l o w s : T. h e t e r o p h y l l a , A. ama- b i l i s , and J_. p l i c a t a are major climax s p e c i e s , A. rubra i s a major s e r a i s p e c i e s , and P_. s i t c h e n s i s an edaphic minor s e r a i s p e c i e s . Since the changes i n frequency d i s t r i b u t i o n are so slow, i t would t h e o r e t i c a l l y take a very long time (about 1000 years, see Table 4) to reach a st e a d y - s t a t e . 46 Fog Western Hemlock Subzone J_. p l i c a t a and J_. h e t e r o p h y l l a share the dominance of the young stands w i t h a p r o b a b i l i t y of 0.67 and 0.33 r e s p e c t i v e l y i n number of stems and a l s o i n b a s a l area (Figure 5 I and J) . Very soon J_. hetero- p h y l l a succeeds i n a l l the stands, and dominates everywhere. But t h i s subzone has the smallest number of p l o t s (see Table 2) and the s h o r t e s t p e r i o d of o b s e r v a t i o n s , and the data do not represent w e l l the exact s i t u a t i o n . Packee (1974) assigns T. p l i c a t a and J_. h e t e r o p h y l l a as major climax s p e c i e s ; the r e s u l t s agree w i t h h i s c l a s s i f i c a t i o n of T. h e t e r o p h y l l a , but show J_. p l i c a t a to be a pioneer. He a l s o assigns A. amabilis as a major climax s p e c i e s , which was never observed i n the few stands of the study area i n t h i s subzone. He a l s o c l a s s i f i e s P_. s i t c h e n s i s as a major s e r a i species and Phelps (1973) r e p o r t s that P_. s i t c h e n s i s occurs more f r e q u e n t l y i n mixture than i n pure stands, and that the asso-c i a t e d species u s u a l l y assume dominance, which the r e s u l t s seem to confirm. I t i s obvious that there are too few p l o t s i n t h i s subzone. K r a j i n a (1969) s t a t e s that P_. s i t c h e n s i s has i t s best growth along the ocean i n the Wet C o a s t a l Western Hemlock Subzone, which corresponds to Packee's (1974) Fog Western Hemlock / S i t k a Spruce Subzone. This i s also supported by Phelps (1973) and Packee (1976). The absence of P_. s i t c h e n s i s stand-types i s , t h e r e f o r e , very s u r p r i s i n g . On the other hand, Packee (1976) r e p o r t s that t h i s species i s u s u a l l y a s s o c i a t e d w i t h J_. h e t e r o p h y l l a which o f t e n dominates the stand. Hence the high frequency of J_. h e t e r o p h y l l a stand-types would r e f l e c t the presence of P_. s i t c h e n s i s . The data and the model show T. p l i c a t a s t r i c t l y as a pioneer and Packee (1974, 1976) s t a t e s that i t i s d e f i n i t e l y a major climax species. 47 There are too few p l o t s i n the data set to make a b e t t e r assessment of the s i t u a t i o n and the e x t r a p o l a t i o n to an e x c l u s i v e J_. h e t e r o p h y l l a climax i s u n l i k e l y . CONCLUSION Forest succession The general trends of the succession i n each subzone are c l e a r w i t h i n the p e r i o d of o b s e r v a t i o n s , although the r a t e s of change are exaggerated by a c e r t a i n b i a s i n the data s e t . Over the whole study area, only P_. m e n z i e s i i shows a large d i f f e r e n c e between i t s abundance i n stems and i n b a s a l area. I t s stand-type frequency i s always higher i n terms of basal area than i n terms of stems. A. rubra always appears as a pioneer which may dominate up to 10 percent of the stands i n a l l but the Fog Western Hemlock Subzone, and i s always p r o g r e s s i v e l y outcompeted. J_. p l i c a t a behaves l i k e a pioneer species i n the Wet Western Hemlock Sub-zone, and i s s l o w l y succeeded by A. amabilis and J_. h e t e r o p h y l l a . The data show the same behaviour i n the Fog Western Hemlock Subzone, but i n t h i s case the behaviour i s an a r t e f a c t s i n c e T. p l i c a t a i s climax i n t h i s r e g i o n . In other subzones, the frequency of J_. p l i c a t a stand-types i n -creases w i t h stand age. In the Dry D o u g l a s - f i r Subzone, the slow decrease of P_. m e n z i e s i i from a high i n i t i a l frequency, and the equivalent increase of T_. p l i c a t a and P_. c o n t o r t a are i n f a c t much smaller i n terms of b a s a l area. P_. men- z i e s i i behaves l i k e an e f f i c i e n t pioneer and maintains i t s supremacy w e l l over the r o t a t i o n p e r i o d . K r a j i n a (1969) notes that P_. m e n z i e s i i i s shade 48 t o l e r a n t i n the d r i e r c l i m a t e s , which might e x p l a i n the low frequency of T_. p l i c a t a and P_. c o n t o r t a stand-types. In the Wet D o u g l a s - f i r Subzone on the other hand, P_. m e n z i e s i i appears a l s o as a pioneer, but T. hetero-p h y l l a overtakes i t r a p i d l y . A large p r o p o r t i o n of the h a b i t a t s of t h i s subzone are moist and P_. m e n z i e s i i i s s h a d e - i n t o l e r a n t on these edatopes. Yet i t s b a s a l area i s the highest of a l l species throughout the f o r e s t r o t a t i o n . P_. s i t c h e n s i s and J_. p l i c a t a show a b a s a l area p r o g r e s s i v e l y l a r g e r than the b a s a l area of T. h e t e r o p h y l l a d e s p i t e t h e i r lower number of stems. P. m e n z i e s i i a l s o occurs abundantly at the e a r l y stages of succession i n the Dry Western Hemlock Subzone but the number of stems of J_. hetero- p h y l l a predominates by age 55. Here again the decrease i n b a s a l area of P_. m e n z i e s i i f o l l o w s i t s decrease i n stems at a much slower pace and i t s b a s a l area maintains predominance over J_. h e t e r o p h y l l a . J_. p l i c a t a i n -creases i t s frequency up to n e a r l y ten percent of the stands by age 110. In the Wet Western Hemlock Subzone, P_. m e n z i e s i i i s never seen to c o n s t i -t u t e a stand-type. The trends observed f o r a l l species i n t h i s subzone are s i m i l a r i n terms of stems and b a s a l area. J_. h e t e r o p h y l l a dominates over the r o t a t i o n w i t h a constant frequency of about 70 percent. The P. s i t c h e n s i s stand-type has a higher frequency at e a r l y ages, and A. ama- b i l i s i s more frequent a f t e r 40 years. In the Fog Western Hemlock Sub-zone; the T. p l i c a t a stand-type predominates at e a r l y stages and i s l a r g e -l y overtaken by J_. h e t e r o p h y l l a a f t e r 35 years of age; t h i s i s an a r t i f a c t and J_. p l i c a t a should remain up to the climax stage. 49 The Markov model The Markov model i s not s a t i s f a c t o r y f o r any subzone except the Wet Western Hemlock Subzone, which i s the one where the fewest changes occur. The model f a i l s to f i t the observations and does not produce r e a l i s t i c p r e d i c t i o n s . I t shows what would happen i f the f o r e s t were Markovian and i t s long-term p r e d i c t i o n s are s u f f i c i e n t l y u n l i k e l y to suggest, f o r the f o l l o w i n g reasons, that f o r e s t succession i s not Markovian: (1) the t r a n s i t i o n p r o b a b i l i t i e s were not found to be en-t i r e l y time-homogenous. (2) The model i s much too general as f a r as d i v e r s i t y of communities and o r i g i n s of p e r t u r b a t i o n are concerned. A d i f f e r e n t model would be necessary f o r each k i n d of dis t u r b a n c e , each type of community, and each kind of s i t e . (3) The model does not allow species i n v a s i o n . This could be r e c t i f i e d by making i t a m u l t i -step model w i t h as many t r a n s i t i o n p r o b a b i l i t y matrices as l i f e - h i s t o r y s t r a t e g i e s i d e n t i f i e d w i t h i n the l i f e of the f o r e s t . (4) Even i f succession were Markovian over the p e r i o d of observations, the t r a n s i t i o n p r o b a b i l i t i e s are u n l i k e l y to stay constant a f t e r f o r e s t m a t u r i t y . Noble and S l a t y e r (1976) have pointed but that time homogeneity of t r a n s i t i o n p r o b a b i l i t i e s i s c o u n t e r - i n t u i t i v e , at l e a s t over long periods of time. This precludes any e x t r a p o l a t i o n or any p r e d i c t i o n of a steady-state i f i t occurs outside the p e r i o d of observations. Using t h i s p a r t i c u l a r k i n d of observations, i t i s concluded that f o r e s t succession i s not Markovian. The f u t u r e of a given f o r e s t - t y p e cannot be determined s o l e l y on the ba s i s of i t s present s t a t e , and i t s p r e d i c t i o n n e c e s s i t a t e s a sound knowledge of how the f o r e s t got there i n the f i r s t p l a c e . LITERATURE CITED 50 Anderson, M. C. 1966. 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F i s h e r , and R. S. P i e r c e . 1970. E f f e c t s o f f o r e s t c u t t i n g and h e r b i c i d e • treatment on n u t r i e n t budgets i n the Hubbard Brook wa-tershed ecosystem. E c o l . Monogr. 40:23-47 MacArthur, R. H. 1958. A note on s t a t i o n a r y age d i s t r i b u t i o n s i n s i n g l e - s p e c i e s populations i n a community. Ecology 39:146-147 MacArthur, R. H. 1961. Community. In: P. Gray (ed.) The encyclope-d i a of the b i o l o g i c a l s c i e n c e s , pp. 262-264. Reinhold, New-York. M o r r i s , R. F. (ed.) 1963. The dynamics of spruce budworm popula-t i o n s . Men. Entomo. Soc. Can. 31:1-332 Mueller-Dombois, D. 1965. I n i t i a l stages of secondary succession i n the c o a s t a l D o u g l a s - f i r and western hemlock zones, pp. 38-41 i n : V. J . K r a j i n a (ed.) 1965. Ecology of Western North America. Univ. Of B r i t i s h Columbia. Dept. of Bot. Noble, I. R. and R. 0. S l a t y e r . 1976. Successionnal modelling. 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Monogr. 23:41-78 Whittaker, R. H. 1957. Recent e v o l u t i o n of e c o l o g i c a l concepts i n r e l a t i o n to the eastern f o r e s t s of North America. Am. J . Bot. 44:197-206 Whittaker, R. H. 1970. Communities and ecosystems. MacMillan, London, Ontario. 162 p. A n a l y s i s and modelling of i n t e r s p e c i e s competition during f o r e s t secondary succession. P i e r r e B e l l e f l e u r CHAPTER I I The a n a l y s i s of t r e e growth v a r i a t i o n w i t h i n d i f f e r e n t p l o t types i n C o a s t a l B r i t i s h Columbia. 55 ABSTRACT R e l a t i v e abundance and r e l a t i v e b a s a l area of each major t r e e species were p l o t t e d against stand age and compared w i t h stand-type succession data f o r f i v e B i o g e o c l i m a t i c Subzones o f B r i t i s h Columbia. Forest heterogeneity w i t h i n each subzone was broken down by c l a s s i f y i n g sample p l o t s i n t o s t a t i s -t i c a l l y defined p l o t types i n which t r e e composition was assumed to give an image of s i t e c o n d i t i o n s and competition regimes. The bas a l area growth v a r i a t i o n o f t r e e species was compared among p l o t types by a n a l y s i s of variance and i t s c o r r e l a t i o n w i t h stand age and s i t e index was t e s t e d . F i n a l l y , the s i t e index d i s t r i b u t i o n of each subzone was analysed and cor-r e l a t e d w i t h subzone c h a r a c t e r i s t i c s . The time s e r i e s of species r e l a t i v e abundance revealed the same type of species behaviour as the stand-type succession data of the previous chapter but gave more d e t a i l s about l e s s abundant s p e c i e s . Two to seven p l o t types per subzone were s u f f i c i e n t to c l a s s i f y a l l p l o t s . Tree species o c c u r r i n g i n more than one p l o t type showed s i g n i f i c a n t d i f f e r e n c e s i n t h e i r b a s a l area growth which could not be e n t i r e l y accounted f o r by stand age and s i t e index. The response of co-occurring species was found to vary between subzones and mean subzone s i t e index was h i g h l y c o r r e l a t e d w i t h s o i l moisture d e f i c i t . I t was concluded that the v a r i a t i o n i n growth r a t e s due to d i f f e r e n c e s i n s i t e c o n d i t i o n s and competition regimes i s one of the agents generating succession. 56 RESUME On a trac e l'abondance r e l a t i v e et l a surface t e r r i e r e r e l a t i v e des p r i n c i p a l e s especes arborescentes en f o n c t i o n de l'age des s t a t i o n s et l'on a compare ces courbes avec l e s donnees de succession des s t a t i o n s - t y p e s dans c i n q sous-zones biogeoclimatiques de Colombie B r i t a n n i q u e . L'hetero-geneite de l a fore"t a l ' i n t e r i e u r des sous-zones a ete r e d u i t e en c l a s s i -f i a n t l e s p l a c e s - e c h a n t i l l o n s en places-types ou l a composition arbores -cente donnerait une bonne idee des c o n d i t i o n s du s i t e et du regime de com-p e t i t i o n . La v a r i a t i o n dans l a cro i s s a n c e en surface t e r r i e r e des essences arborescentes a ete comparee entre l e s places-types par analyse de variance et sa c o r r e l a t i o n avec l'age des s t a t i o n s et avec l ' i n d i c e de s i t e f u t te s t e e . E n f i n , l a d i s t r i b u t i o n de l ' i n d i c e de s i t e de chaque sous-zone f u t analysee et c o r r g l e e avec l e s a t t r i b u t s de l a sous-zone. L ' e v o l u t i o n de l'abondance r e l a t i v e des especes a r e v e l e l e meme genre de comportement que l e s donnees sur l a succession des s t a t i o n s - t y p e s du c h a p i t r e precedent, avec p l u s de d e t a i l s sur l e s especes moins abondantes. De deux a sept places-types par sous-zone f u r e n t s u f f i s a n t e s pour c l a s s i f i e r toutes l e s p l a c e s - e c h a n t i l l o n s . Les especes retrouvees dans pl u s d'une place-type ont montre des d i f f e r e n c e s s i g n i f i c a t i v e s dans l e u r c r o issance en surface t e r r i e r e i n e x p l i c a b l e s par seulement l'Sge des s t a t i o n s et l ' i n -d i c e de s i t e . La reponse des especes en coexistence v a r i e entre l e s sous-zones et l ' i n d i c e de s i t e moyen est c o r r e l e au manque d'humidite du s o l . On a conclu que l a v a r i a t i o n des taux de croissance due aux d i f f e r e n c e s de co n d i t i o n s du s i t e et des regimes de competition est l'un des agents q u i engendre l a succession. 57 INTRODUCTION In the previous chapter, secondary succession was analysed at the l e v e l of f o r e s t stand-types i n the Coas t a l D o u g l a s - f i r and the Co a s t a l Western Hemlock zones and subzones of B r i t i s h Columbia. Markov models f a i l e d to adequately f i t the observations and i t was concluded that f o r e s t succession was seemingly not Markovian. I t appeared that the main reason f o r the inadequacy of the Markov approach was that i t n e c e s s i t a t e d p o o l i n g together p l o t s that belonged to d i f f e r e n t communities, s i n c e understory v e g e t a t i o n was not a v a i l a b l e to d i s t i n g u i s h them. However, v a r i a t i o n i n t r e e composition might be s u i t a b l e to d i s t i n g u i s h p l o t s i n t o broad c a t e g o r i e s . Species o c c u r r i n g - i n more than one category are l i k e l y to respond and to compete d i f f e r e n t l y . These sets of c o n d i t i o n s under Which competition takes place w i l l be termed "competition regimes". The o b j e c t i v e s of t h i s chapter are: (1) To monitor the composition of each subzone f o r the r o t a t i o n p e r i o d , i n terms of r e l a t i v e abundance and r e l a t i v e b a s a l area f o r each major t r e e s p e c i e s . (2) To compare these observations w i t h the stand-type succession data mentioned above. (3) To separate each subzone i n t o major competition regimes. (4) To analyse the growth v a r i a t i o n of each species among the d i f f e r e n t competi-t i o n regimes w i t h i n each subzone at the l e v e l of the f o r e s t stand. (5) To t e s t c o r r e l a t i o n of t r e e growth with stand age and s i t e index. (6) To analyse s i t e index d i s t r i b u t i o n f o r each subzone and to t e s t i t s c o r r e l a t i o n w i t h subzone c h a r a c t e r i s t i c s . Achievement of these o b j e c t i v e s should permit to t e s t the f o l l o w i n g two hypotheses: (1) The growth of a given species i s i n f l u e n c e d by the 58 nature and abundance of other species growing i n the same stand. (2) The d i f f e r e n c e i n net r a t e of p o p u l a t i o n growth of d i f f e r e n t t r e e populations i s s u f f i c i e n t to t r i g g e r t r a n s i t i o n from one p l o t type to another, and hence t o generate succession. DATA AND METHODS Heterogeneity w i t h i n subzones The data set used f o r t h i s study i s part of the data bank of MacMillan Bloedel L i m i t e d , F o r e s t r y D i v i s i o n , and was described i n the previous chapter. I t c o n s i s t s of 730 Permanent Sample P l o t s and Spacing Assessment P l o t s , a l l l o c a t e d w i t h i n the C o a s t a l D o u g l a s - f i r and C o a s t a l Western Hemlock zones of B r i t i s h Columbia. In the previous chapter, each f o r e s t p l o t was assigned a stand-type, depending on which species had the absolute maximum stem count and b a s a l area. That approach had the advantage of c a t e g o r i z i n g the whole f o r e s t i n t o d i f f e r e n t s t a t e s and permitted monitoring and s i m u l a t i o n of the succession from one s t a t e to another through a f i n i t e - s t a t e Markov model. However, i t concealed a l o t of i n f o r m a t i o n about species whose abundance was always too low to c o n s t i t u t e a stand-type. The r e l a t i v e abundance of each t r e e species was t h e r e f o r e p l o t t e d against stand age to show i t s dynamics w i t h i n the v a r i o u s subzones. The species r e l a t i v e abundance ( i n percentage) was chosen over absolute abundance on the b a s i s of the unequal t o t a l number of observations at each f i v e - y e a r measurement. The comparison of these r e s u l t s w i t h stand-type frequency d i s t r i b u t i o n w i l l be discussed l a t e r . 59 The main goal i s to f i n d i f one can detect whether the growth of a given species i s i n d i f f e r e n t to species composition i n the stand at the same time. Several cases may occur. A subject species may cover a wide range of abundance i n the stand, from a unique s e e d l i n g to absolute predominance. The r e s t of the stand may i n t u r n be d i s t r i b u t e d among v i r t u a l l y any number of other s p e c i e s , w i t h v a r y i n g r e l a t i v e abundance, thus c o n s t i t u t i n g s e v e r a l competition regimes. The d i f f e r e n c e i n r a t e of growth can be monitored at the l e v e l of each i n d i v i d u a l stem, and at the l e v e l of the s p e c i e s . Only the l a t t e r case i s considered i n t h i s chapter. Each B i o g e o c l i m a t i c Subzone as defined by K r a j i n a (1969) and Packee (1974, 1976) has a t h e o r e t i c a l l y homogeneous set of g e o c l i m a t i c c o n d i t i o n s . However, va r i o u s v e g e t a t i o n patterns r e v e a l a mosaic of h a b i t a t types w i t h i n each subzone (Daubenmire 1968, Daubenmire and Daubenmire 1968). Since most species can occur w i t h i n s e v e r a l v e g e t a t i o n p a t t e r n s , i t i s necessary to d i s t i n g u i s h t y p i c a l patterns which might o f f e r completely d i f f e r e n t s i t u a t i o n s from the viewpoint of competition. Packee (1976) has reviewed four major v e g e t a t i o n c l a s s i f i c a t i o n schemes which apply to southwestern B r i t i s h Columbia. Rowe's (1972) c l a s s i f i c a t i o n , based on the previous work of H a l l i d a y (1937), i s e s s e n t i a l l y a geographic d e s c r i p t i o n of the d i f f e r e n t f o r e s t regions of Canada. Southwestern B r i t i s h Columbia l i e s e n t i r e l y w i t h i n the Coast Forest Region of Subalpine Forest Region, and Rowe (1972) sub-d i v i d e s i t i n t o 4 Forest S e c t i o n s . These Sections are defined q u i t e a r b i t r a r i l y "from above" (Rowe 1972), i . e . f o l l o w i n g conspicuous geo-g r a p h i c a l e n t i t i e s , f o r the purpose of convenience, and represent broad 60 cover types of r a t h e r s t a b l e a s s o c i a t i o n s . Rowe (1972) mentions t h a t a c l a s s i f i c a t i o n "from below", i . e . based on e c o l o g i c a l knowledge of v e g e t a t i o n , would be d e s i r a b l e , but would r e q u i r e i n f o r m a t i o n not a v a i l a b l e on a large s c a l e . The S o c i e t y of American Forest e r s (1954) has described f o r e s t types and f o r e s t cover types f o r Canada and the United S t a t e s . Packee (1976) has i d e n t i f i e d 16 of these cover types r e l e v a n t to southwestern B r i t i s h Columbia. The cover types are defined on the b a s i s of present v e g e t a t i o n , r e g a r d l e s s of the p o t e n t i a l climax. The type name i s based on the species which c o n s t i t u t e s at l e a s t 50% of the stem composition, o r , i f more than one species predominates, the type i s given a binomial or t r i n o m i a l name. The composition of each type i s described without any q u a n t i t a t i v e assessment. F r a n k l i n and Dyrness (1969, 1973) published an e c o l o g i c a l study of the p l a n t communities of Washington and Oregon. Their c l a s s i f i c a t i o n i s based on the zone, d e f i n e d as the area covered by the c l i m a t i c climax a s s o c i a t i o n . The a s s o c i a t i o n s found i n each zone are described i n q u a l i -t a t i v e terms -- r a r e , o c c a s i o n a l , common, and abundant -- based on the presence of s p e c i e s . Seven of F r a n k l i n and Dyrness' (1973) zones occur i n southwestern B r i t i s h Columbia (Packee 1976). K r a j i n a (1969) c l a s s i f i e d the f o r e s t s of B r i t i s h Columbia i n t o B i o g e o c l i m a t i c Zones and Subzones. Packee (1974) f o l l o w e d t h i s c l a s s i -f i c a t i o n scheme f o r the c o a s t a l f o r e s t s i n d e f i n i n g d e t a i l e d boundaries at the l e v e l of the subzones f o r Vancouver Island and the adjacent main-land and i s l a n d s , and recognized a new subzone w i t h i n the Coas t a l Western Hemlock Zone, the Fog S i t k a Spruce - Western Hemlock Subzone. Packee (1976) 61 made some a d d i t i o n a l m o d i f i c a t i o n s to h i s c l a s s i f i c a t i o n , based on h i s f i n d i n g s t h a t moisture d e f i c i t w i t h 200 mm of s o i l water storage capa-c i t y was a good c l i m a t i c v a r i a b l e to d i f f e r e n t i a t e zones. D e f i n i t i o n of the c l a s s i f i c a t i o n scheme For the purpose of t h i s study, the c l a s s i f i c a t i o n scheme must be able to d i s t i n g u i s h between v e g e t a t i o n p a t t e r n s which present d i f f e r e n t competition regimes, where a competition regime i s defined by the number of t r e e species present i n a p l o t and by the abundance of each s p e c i e s . The measure of abundance should be based on an index as r e p r e s e n t a t i v e as p o s s i b l e of biomass. The assessment should be made on the b a s i s of present v e g e t a t i o n , without reference to the assumed climax, nor to under-s t o r y . F i n a l l y , the method should be q u a n t i t a t i v e and o b j e c t i v e so that p l o t s could be c a t e g o r i z e d by computer and groups be s t a t i s t i c a l l y des-c r i b e d . Since none of the c l a s s i f i c a t i o n schemes mentioned above s a t i s -f i e s a l l these requirements, a s u i t a b l e scheme was developed. S t r i c t l y speaking no two p l o t s i n a subzone are a l i k e , and each p l o t can c o n s t i t u t e a category of i t s own. This i s useless s i n c e i t y i e l d s as many categ o r i e s as there are p l o t s . At the other extreme, a l l the p l o t s can be considered s i m i l a r s i n c e they a l l belong to the same subzone. Somewhere between these extremes, p l o t s w i t h s i m i l a r composition should c o n s t i t u t e a s i m i l a r competition regime. I t i s argued t h a t , from the competition v i e w p o i n t , the s i n g l e most important parameter r e l e v a n t to any s p e c i e s ' growth i s the nature and abundance of competitors, assuming that environmental a t t r i b u t e s are homogeneous w i t h i n the p l o t boundaries. I f the maximum number of major p o t e n t i a l t r e e species i s 8 f o r i n s t a n c e , t h i s gives 255 p o t e n t i a l species combinations. In p r a c t i c e however, sin c e c e r t a i n combinations of species are b i o l o g i c a l l y i m p o s s i b l e , i t was found that a maximum of 7 groups was s u f f i c i e n t to conveniently sub-d i v i d e each subzone, provided l e s s abundant species were grouped together. The obvious choice of a measure of abundance i s t o t a l volume per spec i e s , but s i n c e the data set lack s t r e e height i n f o r m a t i o n f o r c e r t a i n s p e c i e s , the next best choice i s b a s a l area. For each p l o t , b a s a l area was c a l c u l a t e d f o r every species at each f i v e - y e a r measurement on a per hectare b a s i s . Species o c c u r r i n g i n a l l observations, w i t h a basal area r e p r e s e n t i n g at l e a s t 5% of the t o t a l of each observation are r e f e r r e d to as "major s p e c i e s " and were in c l u d e d i n the name of the p l o t type. Species w i t h smaller b a s a l area and which do not occur i n a l l observations are r e f e r r e d to as "minor s p e c i e s " . The presence of minor species was i n d i -cated i n the name of the p l o t type by a plus s i g n ( • ) i n s u f f i x . For a l l species o c c u r r i n g i n a number of p l o t types w i t h i n one subzone, one-way a n a l y s i s of vari a n c e was used to detect v a r i a t i o n i n growth v a r i a b l e s among p l o t types. The v a r i a b l e s analysed belong to two groups: age a t t r i b u t e s and bas a l area a t t r i b u t e s . The f i r s t group c o n s i s t s of the mean age of the p l o t s and the mean s i t e index f o r P_. m e n z i e s i i and J_. h e t e r o p h y l l a . The second group contains the mean f i v e - y e a r b a s a l area increment and the mean bas a l area of the subject s p e c i e s , the mean r a t i o of the two previous v a r i a b l e s , the mean t o t a l b a s a l area ( a l l t r e e s p e c i e s ) , and the mean r a t i o of bas a l area increment over t o t a l b a s a l area. The s i -te index d i s t r i b u t i o n was f u r t h e r analysed at the subzone l e v e l . 63 RESULTS AND DISCUSSION Dynamics of f o r e s t stands The changes i n mean species r e l a t i v e abundance against stand age are presented i n Figures 6 A to J . Results are shown as stem count percentages and b a s a l area percentages. As expected, these graphs are very s i m i l a r t o the graphs of the stand-type frequencies presented i n the previous chapter (Figure 5). Stand-type was defined as the species w i t h the maximum number of stems (or b a s a l area) i n a stand. Therefore the previous set of graphs (Figure 5) showed the p r o p o r t i o n of stands of each type at each f i v e - y e a r measurement and t h i s set shows the p r o p o r t i o n of stems of each species at each measurement. Obviously i f 90% of the Stems are P. m e n z i e s i i at age 35 f o r i n s t a n c e , chances are that a high p r o p o r t i o n of the stands w i l l be of the type P_. m e n z i e s i i . However species r e p r e s e n t i n g a low p r o p o r t i o n of the subzone t o t a l stems i n the species r e l a t i v e abundance graph might never c o n s t i t u t e a stand-type, and would never appear i n the stand-type graphs. A b r i e f d e s c r i p t i o n of the species behaviour i s given f o r each zone, and the r e l a t i o n to growth v a r i a t i o n w i l l be discussed l a t e r . D o u g l a s - f i r Zone The Dry D o u g l a s - f i r Subzone i s dominated by P_. m e n z i e s i i , but T. p l i c a t a increases s i g n i f i c a n t l y a f t e r 70 years (Figures 6 A and B), although t h i s trend i s exaggerated f o r reasons explained i n the previous chapter. A. rubra appears as a pioneer and n e a r l y vanishes at approxi-mately 60 years, w h i l e P_. co n t o r t a and T. h e t e r o p h y l l a seem to be 64 FIGURE 6 Mean s p e c i e s abundance at f i v e - y e a r measurements. The r e -s u l t s are presented a l t e r n a t i v e l y i n number of stems and i n b a s a l area f o r each subzcne: A Dry D o u g l a s - f i r Subzone (stems) E Dry D o u g l a s - f i r Subzone (basal area) C Wet D o u g l a s - f i r Subzone (stems) D Wet D o u g l a s - f i r Subzone ( b a s a l area) E Dry Western Hemlock Subzone (stems) F Dry Western Hemlock Subzone (basal area) G Wet Western Hemlock Subzone (stems) H Wet Western Hemlock Subzone (basal area) I Fcq Western Hemlock Subzone (stems) J Fcg western Hemlock Subzone (basal area) The symbols used f o r each s p e c i e s are: F. m e n z i e s i i • !• hetgPQ.phYila O T. £ 1 i cat a & A. rubra X JE« s i t c h e n s i s f J • roacrophyllum X P. c o n t o r t a ^ A. g r a n d i s (i n the Wet D o u g l a s - f i r Subzone) 4-A. a m a b i l i s (in the Wet Western Hemlock Subzcne) ...... ,4. i SPECIES RELATIVE BASAL AREA I 99 67 c n c o r - c D m s T r n c M ' — o 30NVQNnaV 3AHV~l3d S3D3dS SPECIES RELATIVE BASAL AREA O ^ P O C O J ^ C J I C D - J C O t D 89 69 33NV0NnaV 3AI±V13cJ S3l03dS SPECIES RELATIVE B A S A L AREA OZ. 71 30NVaNn9V 3AI±V33d S3l03dS 72 V 3 d V " W S V a 3 A I ± V 1 3 d S3 l03dS 73 3DNVQNnaV 3AI1V13U S3D3dS SPECIES RELATIVE B A S A L AREA PL 75 i n c r e a s i n g to reach 10% r e l a t i v e abundance by age 90. The recent work of Packee (1976) describes the succession from e a r l y i n v a s i o n by herbs and shrubs up to the t r e e stratum climax. Although he gives no q u a n t i -t a t i v e assessment, these r e s u l t s g e n e r a l l y agree w i t h h i s d e s c r i p t i o n . He recognizes the increase of T. p l i c a t a i n the appropriate f o r e s t type, and he p o i n t s out t h a t Quercus garryana Dougl. and Arbutus m e n z i e s i i Pursh. may be l o c a l l y important. These l a s t two species were extremely r a r e (<* 1%) i n the data s e t . The Wet D o u g l a s - f i r Subzone i s a l s o the domain of P_. m e n z i e s i i , but J_. h e t e r o p h y l l a may l o c a l l y be abundant at e a r l y stages, and J_. p l i c a t a at l a t e r stages (Figures 6 C and D) . The d e c l i n e of P_. m e n z i e s i i a f t e r age 60 i s exaggerated f o r reasons mentioned above. A. rubra invades e a r l y and tends to decrease, P_. s i t c h e n s i s , A. g r a n d i s , and A. macrophyllum are few. Packee (1976) contends that P_. s i t c h e n s i s i s s e r a i and suggests a climax of P_. m e n z i e s i i -- T. h e t e r o p h y l l a and l o c a l l y on the moister s i t e s , T. p l i c a t a -- T. h e t e r o p h y l l a -- A. grandis. Western Hemlock Zone J_. h e t e r o p h y l l a i s g e n e r a l l y more abundant i n the Dry Western Hemlock Subzone, even though P_. m e n z i e s i i may reach a r e l a t i v e abundance of 0.68 (Figures 6 E and F ) . A. rubra i s low and decreases f a s t , w h i l e T. p l i c a t a increases s t e a d i l y . A. grandis and A. macrophyllum are b a r e l y p e r c e p t i b l e . Packee (1976) recognizes that both A. rubra and P_. m e n z i e s i i are e a r l y invaders and he describes the climax as mainly P_. m e n z i e s i i (on dry s i t e s ) and J_. h e t e r o p h y l l a , w i t h J_. p l i c a t a l o c a l l y . 76 In the Wet Western Hemlock Subzone, T. h e t e r o p h y l l a i s the most abundant, A. rubr a and P_. m e n z i e s i i are not very abundant invaders, P_. s i t c h e n s i s i s s e r a i and A. am a b i l i s may form a l o c a l climax w i t h T. p l i c a t a and T. h e t e r o p h y l l a (Figures 6 G and H). These r e s u l t s agree with packee rs (1976) d e s c r i p t i o n , w i t h the exception of P_. s i t c h e n s i s which he seems to place l a t e r i n succession (although he gives no time s c a l e ) . The Fog Western Hemlock Subzone i s not very w e l l described by the data s e t , si n c e there are only 19 obs e r v a t i o n s , a l l between ages 35 and 60 (Figures I and J ) . I t shows an e a r l y i n v a s i o n by T. p l i c a t a , T. he- t e r o p h y l l a , and P_. s i t c h e n s i s . A f t e r 45 years, T. h e t e r o p h y l l a reaches a r e l a t i v e abundance of over 80%. P_. m e n z i e s i i and A. rubra show a r e l a t i v e abundance of about 1%. Packee (1976) assesses A. rubra as the main pioneer, f o l l o w e d by e i t h e r P_. s i t c h e n s i s or P_. s i t c h e n s i s -- T. he- t e r o p h y l l a (and o c c a s i o n a l l y P_. m e n z i e s i i ) , and a climax dominated by T. h e t e r o p h y l l a , l o c a l l y a s s o ciated w i t h J_. p l i c a t a , A. a m a b i l i s , or P_. s i t c h e n s i s . P l o t type c l a s s i f i c a t i o n The r e s u l t s of the c l a s s i f i c a t i o n described p r e v i o u s l y are presented f o r each subzone i n Tables 5 to 9. The t a b l e s show the number of p l o t s i n each p l o t type, a l l the t r e e species accounting f o r 1% or more of the mean bas a l area, the mean basal area (and standard d e v i a t i o n ) and the r e l a t i v e b a s a l area f o r each species. The Dry D o u g l a s - f i r Subzone i s subdivided i n t o four p l o t types (Table 5): Pm, Pmt, PmTp*, and PmTpTht . In a l l p l o t types, P_. m e n z i e s i i 77 M e t Type N Species mean E.A. (s) mean E.A. (>U B.A.) (m2/h) (%) 1) Fm 61 P. m e n z i e s i i 41. 6 (9.8) 99.2 2) Pm + 34 P. m e n z i e s i i 23.4 (13.0) 64.6 P. c e n t o r t a 7.4 (11.9) 19.6 A. rubra 4.2 (7.1) 14.0 3) P m T p + 23 P. m e n z i e s i i 23.8 (9.2) 79.9 2« p l i c a t a 3.7 (3.5) 10.8 £• rubra 1.3 (2.4) 4.3 A. g r a n d i s 0.3 (0.6) 1.8 T. ^ - t e r g p h y l l a 0.7 (0.9) 1.7 P. ccp.tor t a 0.7 (1.8) 1.4 F m T p T h + 7 P. m e n z i e s i i 32. 4 (14.6) 65.7 T. p l i c a t a 10.8 (6.2) 21.3 1. h e t e r o p h y l l a 4.8 (2.3) 9.3 A. rubra 1.6 (1.1) 3.8 TABLE 5 Fo r e s t p l o t types of the Dry D o u g l a s - f i r Subzone. The mnemonics f o r the p l o t types are d e r i v e d from the f i r s t l a t t e r of the genus and s p e c i e s o f each s p e c i e s oc-c u r r i n g i n each o b s e r v a t i o n with an abundance c f at l e a s t 5% c f the b a s a l area f o r the o b s e r v a t i o n . A p l u s s i g n (+) i n d i c a t e s t h a t other s p e c i e s are present with an abundance cf at l e a s t 1% of the b a s a l area, but not n e c e s s a r i l y i n each o b s e r v a t i o n . Values i n b r a c k e t s are the standard de-v i a t i o n s of the b a s a l a r e a . 78 accounts f o r at l e a s t 65% of the basal area. P_. co n t o r t a i s t y p i c a l of the Pm-* p l o t type, and T. p l i c a t a i s t y p i c a l of both PmTp* and PmTpTht p l o t types. J_. h e t e r o p h y l l a i s s l i g h t l y abundant (9.3%) only i n PmTpTh*. The Wet D o u g l a s - f i r Subzone has s i x p l o t types (Table 6): Pro*, PmTh+, PmTp+, PmThTp+, PmThAgTp*, and ThTp* . P_. m e n z i e s i i occurs i n a l l but the l a s t p l o t type, w i t h at l e a s t 41% of the bas a l area i n each. T. h e t e r o p h y l l a w i t h 20.5% to 56.5% of the bas a l area i s a major species i n four p l o t types and T_. p l i c a t a accounts f o r at l e a s t 14% i n the l a s t f o u r p l o t types. There are s i x p l o t types i n the Dry Western Hemlock Subzone (Table 7): Th*, PmTh, PmThArt, PmThTp, ThTpt, and Pm+. P_. m e n z i e s i i i s the most abundant species i n fou r out of s i x p l o t types, w i t h at l e a s t 51% i n b a s a l area, and J_. h e t e r o p h y l l a i s the most abundant i n the two other p l o t types, w i t h a minimum of 75% i n bas a l area. A. rubra and J_. p l i c a t a are the only other two species which can q u a l i f y as major s p e c i e s . The Wet Western Hemlock Subzone i s subdivided i n t o seven p l o t types, the highest number of a l l subzones (Table 8). They are: Th, ThPs*, ThAa, ThTp+, ThPsTpt, ThTpPm+, and ThPmt. T. h e t e r o p h y l l a i s the predominating major species i n a l l p l o t types, J_. p l i c a t a i s major i n three, and P_. men- z i e s i i and P_. s i t c h e n s i s i n two. Only two p l o t types were found i n the Fog Western Hemlock Subzone (Table 9): ThPs* and ThTp*. There are only 19 observations i n t h i s subzone and t h i s i s i n s u f f i c i e n t to r e v e a l i t s f u l l d i v e r s i t y . T_. h e t e r o p h y l l a i s by and large the most abundant i n both p l o t types. P_. s i t c h e n s i s i s a l s o found i n both. P_. m e n z i e s i i occurs i n ThPs+ only, and J_. p l i c a t a i n ThTpt only. P l c t Type N Species mean E.fi. (s) mean E.A. <>1S E.A.) N (m2/h) (%) 1) l?ra+ 110 2) PmTh+ 57 3) PmTp+ 38 4) PmThTp+ 61 5) PmThAgTp+ 16 6) ThTp+ 27 P. m e n z i e s i i A..rubra P. m e n z i e s i i 1• h e t e r o p h y l l a A. rubra R« m e n z i e s i i T. p l i c a t a P. s i t c h e n s i s A. g r a n d i s A. rubra 1. macrophyllum 2• heteroph y l l a P. m e n z i e s i i 2• h e t e r o p h y l l a T. p l i c a t a A. macrophyllum P. .menziesii 2• h e t e r o p h y l l a A. 3 r a n d i s T. p l i c a t a A. macrophyllum T. h e t e r o p h y l l a T. p l i c a t a P. s i t c h e n s i s A. rubra 36. 6 (11.3) 95.5 1. 2 (3.2) 3.1 26. 7 (13.1) 73.9 8. 3 (11.8) 20. 5 1. 7 (4.5) 4.5 28. 4 (8.9) 73.3 6. 6 (6.6) 13.9 2. 6 (8.7) 3.6 1. 8 (6.4) 3.2 1. 4 (2.7) 2.6 1. 1 (3.0) 2.2 0. 6 (0.8) 1.1 26. 8 (17.6) 54.4 12. 6 (10.0) 27. 1 8. 3 (8.5) 16.5 0. 8 (2.8) 1.3 26. 0 (17.5) 41.0 11. 7 (11.8) 21.5 11. 9 (8.4) 20.0 8. 4 (4. 1) 16.5 0. 8 (1.5) 1.2 22. 8 (19.9) 56. 5 15. 6 (16.7) 29.3 7. 2 (11.5) 10.9 1. 1 (1.7) 1.8 TAE1E 6 F o r e s t p l o t types of the Wet D o u g l a s - f i r Subzone. See Table 5 f o r e x p l a n a t i o n s . 80 F l c t Type N Species mean E.A. (s) mean E.A. (>1S B.A.) (m2/h) (%) 1) Th+ 25 2) FmTh 72 3) PmThAr+ 27 4) FmThTp 48 5) T h T p + 17 6) Pm+ 38 T. h e t e r o p h y l l a A. rubra P. m e n z i e s i i T. h s t e r o p . i y l l a P. m e n z i e s i i ! • h e t e r o p h y l l a A. rubra A. a r a n d i s P. m e n z i e s j i T. h e t e r o p h y l l a 1. p l i c a t a T. h e t e r o p h y l l a 1- p l i c a t a rubra .grandis P. m e n z i e s i i A. rubra £• j a c r o p h y l l u r a h e t e r o p h y l l a 52.1 (11.6) 98.1 0.5 (1.3) 1.0 24.6 (14.7) 61.6 18.6 (17.3) 37.0 21.3 (13.5) '50.8 17.1 (15.8) 35.1 4.2 (3.7) 10.3 1.1 (2.0) 3.2 31.1 (18.9) 51.5 17.6 (12.5) 32.4 8.7 (6.0) 14.7 37.2 (10.2) 75.3 10.6 (7.5) 21.6 0.5 (1.2) 1.2 0.8 (3.2) 1.2 30.7 (14.6) 92.2 1.7 (4.5) 5.0 0.7 (2.5) 1.7 0.4 (0.6) 1.1 TABLE 7 F o r e s t p l o t types of the Dry Western Hemlock Subzone. See Table 5 f o r e x p l a n a t i o n s . 81 P l c t Type N Species mean E.A. (s) mean E.A. (>1S B. A. ) (tnz/h) (%) 1) Th 70 J . heterophylla 61.6 (12.2) 97.7 2) ThFs + 56 1. P. h e t e r o p h y l l a s i t c h e n s i s r u b r a 34.5 28.8 3.4 (17.7) (20.7) (6.8) 52.5 41.0 5.7 3) ThAa 65 T. heterophylla a m a b i l i s 36.4 26.8 (21.4) (21.0) '57.4 42.0 <0 T h T p + 16 T. A. ibgtg£o,p,hylla. p l i c a t a a m a b i l i s 28.5 21.2 6.1 (16.0) (23.7) (11.9) 57.7 31.4 10.5 5) ThPsTp+ 32 T. P. !• A. e ro_ghy 11a s i t c h e n s i s p l i c a t a rubra 23.7 21.8 12.4 4.9 (14.0) (19.4) (7.8) (4.9) 38.2 32.3 21.2 8.3 6) ThTpPin + 17 T. P. h e t e r o p h y l l a _gli.cat a m e n z i e s i i rubra 29.2 9.7 9.2 1.3 (13.2) (6.4) (7.8) (2.1) 58.1 20.8 17.2 3.6 7) ThPm + 40 I . P. P. T. h§tero£h_ylla m e n z i e s i i s i t c h e n s i s p l i c a t a 52. 1 16.4 1.0 0.6 (14.7) (12.5) (3.0) (1.0) 74.4 22.0 1.5 1.0 TABLE 8 Forest p l c t types o'f the Wet Western Hemlock Subzone. See Table 5 f o r e x p l a n a t i o n s . 82 P l o t Type S Species mean E.A. (s) mean E.A. (>U B.A.) (tn2/h) (%) 1) ThEs + 12 h e t e r o p h y l l a 60.9 (8.4) 83.2 P. s i t c h e n s i s 11.1 (7.9) 14.3 P. m e n z i e s i i 1.6 (4.9) 1.9 2) ThTp + 7 T. i s t e r ojghy 1 l a 40.8 (24.7) 63.6 1. p l i c a t a 16.8 (15.2) 29.4 P. s i t c h e n s i s 2.9 (4.5) • 5.0 ! • rubra 1.1 (2.8) 1.7 TABLE 9 Fo r e s t p l c t types of the Fcg Western Hemlock Subzone. See Table 5 f o r e x p l a n a t i o n s . 83 There i s one important comment to make about t h i s c l a s s i f i c a t i o n method. The major species were used to b u i l d i t s s k e l e t o n , s i n c e , by d e f i n i t i o n , these species occur i n a l l observations. To avoid an i n f i n i t e number of c l a s s e s , minor species were grouped, and each one does not n e c e s s a r i l y occur i n each observation. For example, i n the Dry D o u g l a s - f i r Subzone (see Table 5 ) , the name of the second p l o t type, Pm-v, i n d i c a t e s t h a t each observation has to c o n t a i n P_. m e n z i e s i i , and e i t h e r P_. c o n t o r t a or A. r u b r a , or both. T h i s , u n f o r t u n a t e l y , i n f l a t e s the standard d e v i a t i o n of the minor species i n Tables 5 to 9, but the advantage of a l i m i t e d number of c l a s s e s f a r outweighs t h i s inconvenience In any case, minor species account f o r , at most, only 5% of the t o t a l b a s a l area. A n a l y s i s of b a s a l area growth v a r i a t i o n There are f i v e species t h a t occur i n more than one p l o t type and i n a l l p l o t s i n each case, w i t h i n one or more subzones: P_. m e n z i e s i i , J_. h e t e r o p h y l l a , J_. p l i c a t a , P_. s i t c h e n s i s , and A. a m a b i l i s . Since they are major s p e c i e s , i . e . they occur i n a l l observations of the p l o t types where they are found, i t i s p o s s i b l e to study the v a r i a t i o n of t h e i r basal area growth among va r i o u s p l o t types as described p r e v i o u s l y . D i f f e r e n t p l o t types are assumed t o represent d i f f e r e n t competition regimes. Since minor species do not occur i n a l l observations, a n a l y s i s of v a r i a n c e can be performed only on the subset of p l o t s i n which they do occur. This e x p l a i n s the d i s c r e p a n c i e s i n mean b a s a l area f o r these species between the set of t a b l e s d e s c r i b i n g the p l o t types (Tables 5 to and the set of t a b l e s of anova r e s u l t s (Tables 11, 13, 15, 17, and 19). 84 A l l data shown i n t h i s a n a l y s i s represent means f o r a l l p l o t s of a p l o t type, or o v e r a l l means when i n d i c a t e d . The stand age i s given i n case i t might be c o r r e l a t e d w i t h growth v a r i a b l e s ; a p o s i t i v e c o r r e l a t i o n w i t h growth increment could o v e r r i d e the treatment e f f e c t . S i t e i n d i c e s are mentioned f o r P_. m e n z i e s i i and T. h e t e r o p h y l l a , wherever both species occur; s i t e index i s used as a general i n d i c a t i o n of s i t e p r o d u c t i v i t y and could a l s o o v e r r i d e the e f f e c t of the treatment ( p l o t t y p e ) . Since the f o r e s t i s immature, the f i v e - y e a r increment i n bas a l area should be p r o p o r t i o n a l to ba s a l area, so a r a t i o of the f i v e - y e a r increment over b a s a l area i s a l s o given (as a percentage). This percent f i v e - y e a r i n -crement i s the most c r i t i c a l v a r i a b l e , since i t i s independent of the abundance of the s p e c i e s , and i s reasonably l i n e a r over the p e r i o d of time considered i n t h i s study. A s i g n i f i c a n t d i f f e r e n c e i n the bas a l area i t s e l f among p l o t types would be i n d i c a t i v e of the f i t n e s s of the species to each p l o t type. F i n a l l y the r a t i o ( i n percent) of the b a s a l area increment of a species (DBA) over the t o t a l b a s a l area ( a l l species) i n d i c a t e s a r a t e of change of a species over the whole community. The r e s u l t s of t h i s a n a l y s i s are discussed s e p a r a t e l y f o r each subzone. When there i s a s i g n i f i c a n t d i f f e r e n c e among treatments ( p l o t t y p e s ) , the extremes are given, otherwise the o v e r a l l mean i s used. Where age a t t r i b u t e s vary s i g n i f i c a n t l y , t h e i r c o r r e l a t i o n with b a s a l area growth a t t r i b u t e s i s given, i f r e l e v a n t . I t i s assumed that s i g n i f i c a n t d i f f e r e n c e s i n growth a t t r i b u t e s are due to treatments, i . e . d i f f e r e n c e i n competition regimes, only when there i s no s i g n i f i c a n t d i f f e r e n c e i n age a t t r i b u t e s or no s i g n i f i c a n t c o r r e l a t i o n between age a t t r i b u t e s and growth a t t r i b u t e s . 85 Since minor species occur on fewer p l o t types than major s p e c i e s , and i n fewer ob s e r v a t i o n s , very few s i g n i f i c a n t d i f f e r e n c e s among p l o t types were found f o r e i t h e r t h e i r age a t t r i b u t e s or growth a t t r i b u t e s . For minor s p e c i e s , only r e s u l t s w i t h some relevance to succession w i l l be discussed. Dry D o u g l a s - f i r Subzone Major species (Table 10) Four p l o t types c o n s t i t u t e t h i s subzone, and P_.' m e n z i e s i i occurs i n a l l of them (Table 5 and 10). Stand age ranges from 46.0 to 57.9 years, and P_. m e n z i e s i i s i t e index has an o v e r a l l mean of 25.9 m. The f i v e - y e a r b a s a l area increment of P_. m e n z i e s i i shows no s i g n i f i c a n t d i f f e r e n c e among p l o t types, i t s b a s a l area shows a s i g n i f i c a n t d i f f e -rence (23.4 - 41.6 m 2/h); and the r a t i o s of these two v a r i a b l e s vary s i g n i f i c a n t l y from 6.4% to 14.6%. The percent r a t e of increase shows no s i g n i f i c a n t c o r r e l a t i o n (p = 0.05) w i t h age or with basal area. Assuming that the d i f f e r e n c e i s due to the competition regime, the data show that the r a t e of increase (DBA) of P_. m e n z i e s i i i s the smallest i n the p l o t types (Pm, PmTpt) where P_. m e n z i e s i i i s the most abundant s p e c i e s , and the gre a t e s t i n the p l o t types (Pm+, PmTpTh+) where A. rubra shows i t highest decrease. This suggests t h a t P_. m e n z i e s i i growth i s favoured by the opening of the f o r e s t when the m o r t a l i t y of A. rubra becomes hi g h , a f t e r 40 or 50 years. As P_. m e n z i e s i i takes over A. r u b r a , P_. c o n t o r t a and J_. p l i c a t a i n c r e a s e c o n c u r r e n t l y , thus preventing P_. m e n z i e s i i from being the absolute dominant, except i n the Pm p l o t type. 86 Stand Pm Th T o t a l DBA/ P l o t Type Age SI 50 SI 50 DBA BA DBA/BA BA Tot BA (years) (m) (m) (m2/h/5y) (mz/h) (%/5y) (mZ/h) (%/5y) P. m e n z i e s i i 1) Pm 46. C 26.6 - 2.0 4 1,6 6.4 41.9 6.3 2) Pm + 50. 0 24. 8 - 3.6 23., 4 14.6 35. 8 10.4 3) PmTp + 50. 9 26. 0 - 1.8 2 3, -3 8.1 30. 6 6.5 «*) PmTpTh+ 57. 9 24.4 — 3.7 32. 4 12.7 49.7 8.8 O v e r a l l 48. 6 25. 9 - 2.5 32. 9 9.3 38. 6 7.6 F - r a t i c 3.1 0.9 - 0.7 26. 6 2.6 9.5 0.8 ** NS - NS ** * * *** NS J> p l i c a t a D PmTp + 50. 9 26. 0 - 1.2 3. 7 53.6 30. 6 4.4 2) PmTpTh+ 57. 9 24.4 — 2.8 10. 8 29. 1 49.7 5.9 O v e r a l l 52. 5 25. 6 - 1.6 5. 4 47.9 35. 0 4.7 F - r a t i c 1.4 0.5 — 9.0 15. 2 1 • 5 9. 4 0.7 NS NS - *** *** NS *** NS TABLE 10 One-way a n a l y s i s of v a r i a n c e of the major s p e c i e s a c r o s s d i f f e r e n t p l o t types of the Cry D o u g l a s - f i r Subzone. Data r e p r e s e n t means f o r a l l o b s e r v a t i o n s of a p a r t i c u l a r p l o t type. C h a r a c t e r i s t i c s o f p l o t types are giv e n i n Table 5. Fm = P. m e n z i e s i i . Th = T. h e t e r o p h y l l a . «SI 50' - s i t e index at base age 50. 'DBA1 = D e l t a BA = f i r s t d i f f e r e n c e i n basal area between two o b s e r v a t i o n s at 5 years i n t e r v a l . 'BA' •= b a s a l area of the s u b j e c t s p e c i e s . ' T o t a l EA* = t o t a l b a s a l area of a l l the s p e c i e s i n each o b s e r v a t i o n . P r o b a b i l i t y l e v e l s are as f o l l o w s : * = p<0.10, ** = p<0.05, *** - p<o.01, NS = not s i g n i f i c a n t . 87 J_. p l i c a t a occurs i n two p l o t types where stand age averages 52.5 years, and g_. m e n z i e s i i s i t e index, 25.6 m. The f i v e - y e a r increment v a r i e s s i g n i f i c a n t l y (1.2 - 2.8 m 2/h/5y), but i s p r o p o r t i o n a l to ba s a l area (3.7 - 10.8 m 2/h), and t h e i r r a t i o s are not s i g n i f i c a n t l y d i f f e r e n t . The very h i g h r a t e of increase of T. p l i c a t a (47.9%/5y) i n d i c a t e s a gradual succession of T. p l i e a t a over P_. m e n z i e s i i , r e s u l t i n g i n a t r a n -s i t i o n from the Pm p l o t type to PmTp+. The same conc l u s i o n was reached i n the stand-type succession data presented i n the previous chapter. The graphs of species r e l a t i v e abundance across age (see Figures 6 A and B) show i n f a c t that J_. p l i c a t a increases at the detriment of P_. m e n z i e s i i . In some stands, the t r a n s i t i o n goes from Pm to Pm+ where P_. c o n t o r t a may reach a r e l a t i v e abundance of 20%. t h i s trend i s a l s o i n agreement w i t h the succession data (previous c h a p t e r ) , and with the graph of species r e l a t i v e abundance across age (Figures 6 A and B). Minor species (Table 11) A. rub r a shows a s i g n i f i c a n t d i f f e r e n c e i n r a t e of increase over t o t a l b a s a l area (-0.5 - 1.6%/5y) c o r r e l a t e d w i t h stand age (r =-0.98, p = 0.1). This f a l l i n the r e l a t i v e basal area r a t e of increase confirms the pioneer r o l e of A. rub r a i n the community. I t s r a t e of increase r e -l a t i v e to the community becomes negative (-0.5%/5y) i n PmTpt, where P_. m e n z i e s i i a t t a i n s 6.5%/5y and T. p l i c a t a , 4.4%/5y. P_. c o n t o r t a i s found more abundantly i n the p l o t type without J_. p l i c a t a (Pm+) than i n the one w i t h t h i s species (PmTpt). This suggests d i f f e r e n t b a s i c requirements f o r these s p e c i e s , and K r a j i n a (1969) p o i n t s out t h a t T. p l i c a t a p r e f e r s eutrophic s o i l s and h y g r i c c o n d i t i o n s , whereas P_. co n t o r t a cannot t o l e r a t e 88 Stand Pm Th T o t a l DBA/ P l c t Type Age SI 50 SI 50 DBA BA DBA/BA BA Tot BA (years) (m) (m) (m2/h/5y) (m2/h) <%/5y) (mZ/h) (%/5y) A. rubra 1) Pm + 46. C 26. 8 - 0.4 7.6 -5.1 34.7 1.6 2) FmTp+ 61. 1 29. 5 - -0. 1 3. 4 -2.7 37.8 -0.5 3) PmTpTh+ 57. 9 24, 4 — 0.2 1.6 -6.6 49. 7 0.3 G v e r c . l l 52. 3 27. 0 - 0.2 5. 3 -4.8 38.5 0.8 F - r a t i o 5. 7 1.8 — 2.5 2. 9 0.0 3.7 2.7 *** NS - * * NS ** * £. c o n t o r t a D Pm + 55. 0 21.9 - 0.6 14. 8 7. 4 36. 8 1.4 2) PmTp + 68. 8 30. 5 — -0. 1 4. 2 1.8 50. 1 -0.1 O v e r a l l 57. 6 23. 5 - 0.4 12. 8 6.3 39.3 .1.1 F - r a t i o 3. 6 8.4 - 1.2 2.5 0.5 7. C 1.0 * *** — NS NS NS * * NS I'. t e ro_phy 1 l a D PmTp + 55. 0 27. 7 - -0. 1 1. 2 1.2 36. S -0. 1 2) PmIpTh+ 57. 9 24. 4 — -0.9 4.8 -9.5 49.7 -0.8 O v e r a l l 56. 0 26. 5 - -0.4 2. 4 -2.6 41.4 -0.3 F - r a t i o 0. 2 1.9 - 1. 1 27. 0 0.3 3. 3 0.4 NS NS - NS ** * NS * NS TABLE 11 Cne-way a n a l y s i s of v a r i a n c e of the minor s p e c i e s a c r o s s d i f f e r e n t p l c t types of the Dry D o u g l a s - f i r Subzone. Data r e p r e s e n t means f o r a l l occurrences of the s u b j e c t s p e c i e s i n a given p l c t type. C h a r a c t e r i s t i c s of p l o t types are given i n Table 5. For a b b r e v i a t i o n s , see Tabl e 10. 89 eutrophic s o i l s and r e q u i r e s d r i e r c o n d i t i o n s . J_. h e t e r o p h y l l a i s analysed as a minor species here although i t i s a major one i n the PmTpTh* p l o t type. No s i g n i f i c a n t d i f f e r e n c e s were found between the two p l o t types, except, of course, t h a t J_. h e t e r o p h y l l a i s more abundant i n the p l o t type where i t i s a major species. Figures 6 A and B show a decreasing p r o p o r t i o n of .A. rubr a basal area, p r e v i o u s l y observed i n the succession data, and a low and s t a b l e r e l a t i v e abundance of F_. co n t o r t a and J_. hete- r o p h y l l a . Wet D o u g l a s - f i r Subzone Major species (Table 12) P_. m e n z i e s i i i s found i n 5 out of 6 p l o t types w i t h i n which stand age ranges from 40.9 to 71.3 years, P_. m e n z i e s i i s i t e index averages 26.7 m., and J_. h e t e r o p h y l l a s i t e index v a r i e s from 18.3 to 27.4 m. The f i v e - y e a r b a s a l area increment has an o v e r a l l mean of 2.3 m2/h/5y, bas a l area ranges from 26.0 t o 36.5 m2/h, and the r a t e of increase shows no s i g n i f i c a n t d i f f e r e n c e among p l o t types, w i t h an o v e r a l l mean of 10.6%/5y. In a d d i t i o n , the r a t e of b a s a l area increase as a r a t i o of the whole community shows no s i g n i f i c a n t d i f f e r e n c e . The s i t u a t i o n i s s i m i l a r f o r T. h e t e r o p h y l l a , but here basal area increment shows a s i g n i f i c a n t d i f f e r -ence (0.02 - 2.5 m2/h/5y) as w e l l as the bas a l area (8.3 - 22.8 m 2/h), yet t h e i r r a t i o i s not s i g n i f i c a n t l y d i f f e r e n t and has an o v e r a l l mean of 5.9%/5y. On the other hand, the r a t i o of b a s a l area increment over t o t a l b a s a l area i s s i g n i f i c a n t and J_. h e t e r o p h y l l a reaches the highest r a t e of i n c r e a s e i n the ThTp/- p l o t type, the only one where there i s no P_. men- z i e s i i . suggesting mutual s i t e i n c o m p a t i b i l i t y . 90 Stand Pm Th P l c t Type Age SI 50 s i 5«: (years) (ID) (m) P. m e n z i e s i i 1) Pm + 46. 0 26. 6 -2) PmTh + 40.9 27.5 23.9 3) PmTp + 57. 0 25. 2 1 8. 3 <0 PmThTp+ 61. 1 26. 2 22. 4 5) PmThAgTp+ 71. 3 29.5 27.4 O v e r a l l 51. 1 26. 7 23. 4 F - r a t i o 16.9 1.9 4.2 * * * NS *** 1- heterc£hxlla 1) PmTh + 40. 9 27. 5 23. 9 2) PmThTp+ 61. 1 26. 2 22. 4 3) PmTh AgTp + 71.3 29. 5 27. 4 4) ThTp + 55. 6 21.3 22.9 O v e r a l l 54. 0 27. 1 23. 4 F - r a t i o 12. 9 1.5 2. 6 *** NS * 2. . p l i c a t a D PmTp + 57. 0 25. 2 18.3 2) PmThTp+ 61.1 26. 2 22. 4 3) PmThAgTp+ 71.3 29.5 27.4 4) ThTp + 55. 6 21.3 22.9 O v e r a l l 60. 1 26. 3 23. 1 F - r a t i c 2. 1 2.0 3.4 NS NS ** T c t a l DEA/ DBA EA DBA/BA BA Tot BA (m2/h/5y) (mz/h) (%/5y) (m2/h) (%/5y) 2. 5 36. 5 9.1 38. 4 8.4 2.4 26.7 13.5 37. 1 8.8 2.6 28. 4 10.5 42. 4 7.3 1. 7 26. 8 10.7 . 48. 8 4.8 1.9 26. 0 9.4 59. 1 3.3 2. 3 30. 8 10.6 42. 1 7.3 0. 5 8. 6 0.8 11.8 1.6 NS *** NS *** NS 0.6 8. 3 7.2 37. 1 2. 2 0.02 12. 6 3.2 48.8 1.1 0. 5 11.7 1.5 59. 1 1.0 2.5 22. 8 11.9 47. 2 8. 1 0.7 12. 7 5.9 45.4 2.7 6.3 7. 8 0.6 8. 2 7.6 *** *** NS ** * *** 1.5 6.6 40.0 42. 4 3.6 1.2 8. 3 22. 8 48. 8 3.3 1.3 8. 4 15.9 59. 1 2.5 1.4 15. 6 10.9 47. 2 3.1 1.3 9. 2 24. 4 48. 0 3.3 0.2 4. 9 3.3 3. 1 0.2 NS ** * ** ** NS TABLE 12 One-way a n a l y s i s of v a r i a n c e of the majcr s p e c i e s a c r o s s d i f f e r e n t p l o t types of the Wet D o u g l a s - f i r Subzone. Data r e p r e s e n t means f o r a l l o b s e r v a t i o n s of a p a r t i c u l a r p l c t type. C h a r a c t e r i s t i c s of p l o t types are given i n Table 6. For a b b r e v i a t i o n s , see Table 10. J_. p l i c a t a has a very s i g n i f i c a n t d i f f e r e n c e i n r a t e of growth among p l o t types, from 10.9 to 40.0%/5Y. I t s lowest r a t e of increase i s i n the ThTp* p l o t type, e x a c t l y where T. h e t e r o p h y l l a e x h i b i t s i t s highest r a t e of in c r e a s e . The highest r a t e of increase f o r J_. p l i c a t a appears i n the PmTp+ p l o t type, where P_. m e n z i e s i i i s the most abundant among a l l p l o t types i n which these two species c o e x i s t , and i n which J_. hete- r o p h y l l a i s p r a c t i c a l l y absent. Moreover, there i s a s i g n i f i c a n t c o r r e -l a t i o n of 0.99 (p = 0.05) between the r a t e of increase of J_. p l i c a t a and the r e l a t i v e abundance (% BA, Table 6 ) , of P_. m e n z i e s i i i n the 3 p l o t types where these species co-occur (PmTpt, PmThTp+, PmThAgTp+), and the r a t e of in c r e a s e i s c o n s i s t e n t l y 2 to 4 times higher f o r J_. p l i c a t a than f o r P_. m e n z i e s i i . These observations i n d i c a t e that the co n d i t i o n s which favour P_. m e n z i e s i i do not favour J_. h e t e r o p h y l l a , and that J_. p l i c a t a has some p o t e n t i a l to succeed P_. m e n z i e s i i , at l e a s t l o c a l l y , where J_. hetero- p h y l l a i s in f r e q u e n t . This can a l s o be observed i n the graph of the species r e l a t i v e abundance (see Figures 6 C and D), and t h i s trend was revealed by the succession data of the previous chapter. Minor Species (Table 13) No s i g n i f i c a n t d i f f e r e n c e s were found i n r a t e s of increase of minor species. A. r u b r a deserves a comment. The stand age v a r i e s g r e a t l y among p l o t types, and i s n e g a t i v e l y c o r r e l a t e d w i t h the r a t e of increase i n basal area (r = -0.92, p = 0.1). Although the d i f f e r e n c e i n r a t e of increase i n basal area i s not s i g n i f i c a n t , i t i s noteworthy that i t shows s u c c e s s i v e l y an increase (5.6%/5Y) and then a decrease (-6.4%/5Y) with time. This suggests t h a t the pioneer r o l e of A. rubra observed i n the 92 Stand Pm Th T o t a l DBA/ P l c t Type Age SI 50 SI 50 DBA BA DBA/BA BA Tot BA (years) (m) (m) (m^/h/Sy) (m2/h) (%/5y) {m2/h) (%/5y) A. rubra 1) Pm* 42.4 28.6 - i -0.05 4. 6 6.2 39.4 0.4 2) PmTh + 38. 6 31. 4 29. 0 0.5 6. 9 5. 6 40. 3 1.4 3) PmTp + 70. 8 29. 1 18. 3 -0.4 4. 1 -10. 7 49. 5 -0.6 4) ThTp + 79. 2 — 20. 3 -0.2 2. 5 -6.4 60.8 -0.5 O v e r a l l 53. 5 29. 4 22.5 -0.02 4. 6 0.7 45. 3. 0.3 F - r a t i c 23. 1 1.2 7.0 1.4 1.9 1.4 7. 5 2.1 *** NS *** NS NS NS ** * NS P. s i t c h e n s i s D PmTp + 77. 5 28. 2 18. 3 3. 2 25. 0 12.2 67. 9 4.4 2) ThTp + 83. 6 — 20. 0 1.7 17. 7 6.7 60.0 2.4 O v e r a l l 82. 0 28. 2 19.6 2.1 19. 6 8.2 62. 1 3.0 F - r a t i o 0. 9 - 0. 3 1.0 1.0 0.7 0. 6 0.9 NS — NS NS NS NS NS NS A. g r a n d i s D PmTp + 65. 0 31.0 - 0.7 11. 5 7.8 51.8 1.2 2) PmThAgTp+ 71. 3 2S.5 27.4 1.1 11. 9 14.2 59. 1 2. 1 O v e r a l l 69. 5 29. 9 27. 4 1.0 11. 8 12.5 57. 1 1.8 F - r a t i o 0. 5 0. 3 - 1.4 0. 0 1.4 1.6 1.7 NS NS - NS NS NS NS NS 1 M i s s i n g values f o r F i r or Hemlock S i t e Index are due to the absence o f the s p e c i e s i n the p l o t type. T a b l e 13... 93 (Cont'd) Stand Pm Th T o t a l DBA/ P l o t Type Age SI 50 SI 50 DBA EA DBA/BA BA Tot BA (years) (m) (m) <mVh/5y) (m^/h) (%/5y) (ra^/h) (%/5y) A. macrophyllum 1) PmTp + 65. 6 29.7 - 0.4 5.0 10.0 49.4 0.8 2) PmTpTh+ 69. 1 25. 8 23.7 0. 1 4. 7 29.0 48.2 0.5 3) PmThAgTp+ 67.5 33. 5 36.6 0.2 3.0 7.9 58. 5 0.4 O v e r a l l 67. 6 28. 5 26.0 0.2 4.5 18.7 50. 4 0.6 F - r a t i o 0. 1 3.9 22. 7 0.8 0. 2 0.8 0. 4 0.6 NS * * *** NS NS NS NS NS T A B U 13 One-way a n a l y s i s of va r i a n c e of the minor s p e c i e s a c r o s s d i f f e r e n t p l o t types of the Het D o u g l a s - f i r Subzone. Data r e p r e s e n t means f o r a l l occurrences of the s u b j e c t s p e c i e s i n a given p l o t type. C h a r a c t e r i s t i c s of p l o t types are given i n Table 6. For a b b r e v i a t i o n s , see Table 10. 94 Dry D o u g l a s - f i r Subzone i s s i m i l a r i n the Wet D o u g l a s - f i r Subzone. The graph of species r e l a t i v e abundance agrees w e l l w i t h t h i s view (Figures 6 C and D), and the succession data showed the same behaviour. P_. s i t c h e n - s i s , A. g r a n d i s , and A. macrophyllum do not show s i g n i f i c a n t d i f f e r e n c e i n any of the growth v a r i a b l e s . Dry Western Hemlock Subzone Major species (Table 14) J_. h e t e r o p h y l l a i s the most important species i n t h i s subzone and occurs i n 5 out of 6 p l o t types. Stand age (37.8 - 67.6 y ) , P_. men- z i e s i i s i t e index (26.3 - 39.6 m), and J_. h e t e r o p h y l l a s i t e index (24.3 -28.0 m) are a l l s i g n i f i c a n t l y d i f f e r e n t . Basal area increment (0.9 -4.3 m2/h/5y) and basal area (17.1 - 52.1 m2/h) a l s o vary s i g n i f i c a n t l y , and are c o r r e l a t e d (r - 0.94, p = 0.05), yet n e i t h e r one shows any s i g n i -f i c a n t c o r r e l a t i o n w i t h stand age, or s i t e index. The percent r a t e of increase i s h i g h l y s i g n i f i c a n t l y d i f f e r e n t among p l o t types, w i t h the highest values i n the two p l o t types where J_. p l i c a t a i s absent and F_. m e n z i e s i i present (PmTh, PrnThArf) , and the s m a l l e s t values where J_. he-t e r o p h y l l a i s e i t h e r forming pure stands (Th*) of where T. p l i c a t a i s abundant (PmThTp, ThTp*). This i n d i c a t e s that P_. m e n z i e s i i does not o f f e r much competition to J_. h e t e r o p h y l l a , and that J_. h e t e r o p h y l l a and T. p l i - c a t a compete s t r o n g l y w i t h T_. h e t e r o p h y l l a . A l l v a r i a b l e s f o r F_. m e n z i e s i i are s i g n i f i c a n t l y d i f f e r e n t among p l o t types. The mean stand age goes from 33.2 to 67.6 years. The basal area increment i s n e g a t i v e l y c o r r e l a t e d w i t h stand age (r =-0.96, p = 0.05) 95 Stand Pm Th T c t a l DBA/ P l c t Type Age SI 50 SI 50 DBA EA DBA/BA BA Tot BA (years) (m) (m) (mZ/h/Sy) (m2/h) (%/5y) (a^/h) (%/5y) 1 • JlSie rp^hy 11a 1) 2) 3) <*) 5) Th + PmTh PmThAr+ PmThTp ThTp + 56. C 45. 4 37. 8 67.6 49. 7 39.6 30. 6 32. 1 26.3 27. 4 27. 4 25.5 28.0 24. 3 26.9 O v e r a l l 51.7 29.6 2 6.0 F - r a t i o 9.6 * * * 6.9 *** 2. 9 ** P. m e n z i e s i i D 2) 3) PmTh PmThAr+ PmThTp Pm + 45. 4 37. 8 67. 6 33. 2 30. 6 32. 1 26. 3 27. 2 25. 5 28. 0 24. 3 O v e r a l l 47.5 29.0 25.5 F - r a t i o 18.8 *** 10.0 ** * 3. 7 ** T . j i l i c a t a D 2) PmThTp ThTp + 67. 6 49. 7 26.3 27. 4 24. 3 26. 9 O v e r a l l 62. 9 26.3' , 25. 2 F - r a t i o 8.7 *** 0.0 NS 0. 2 NS 4. 3 52. 1 9.1 53. 1 8.9 2. 2 18. 6 21. 9 43. 9 6.4 1.2 17. 1 14.9 44. 2 4.0 0. 9 17. 6 6.2 56. 2 2.2 3.0 37. 2 9.3 . 4*9.4 6.8 2. 1 24. 2 14.1 49. 3 5.3 11.2 32. 2 6.8 5. 0 5.4 *** ** * *** *** 3.3 24. 6 20.1 43. 9 13.2 3.6 21.3 21.3 44.2 11.2 1.2 31. 1 7.3 58. 2 2.6 5. 2 30. 7 22.3 33. 5 20.9 3.2 27. 1 17.4 45.5 11.7 6. 5 3. 5 7. 4 12. 0 15.1 *** * * * ** ** * *** 0.8 8. 7 12. 1 58. 2 1. 8 1.0 10. 6 9.5 49. 4 2.2 0.8 9. 2 11.4 55. 9 1.9 0.3 1. 2 0.3 4. 1 0.3 NS NS NS ** NS TABIE 14 One-way a n a l y s i s of v a r i a n c e of the rcajcr s p e c i e s a c r o s s d i f f e r e n t p l o t types cf the Dry Western Hemlock Sutzone. Data r e p r e s e n t means f o r a l l o b s e r v a t i o n s of a p a r t i c u l a r p l c t type. C h a r a c t e r i s t i c s of p l o t types are giv e n i n Table 7. For a b r e v i a t i o n s , see Table 10. 96 and shows i t s lowest value (1.2 m2/h/5y) i n the o l d e s t p l o t type (PmTh Tp). The percent r a t e of i n c r e a s e i s a l s o the lowest i n the o l d e s t p l o t type. However, t h i s p l o t type (PmThTp) i s a l s o the only P_. men- z i e s i i p l o t type w i t h a l a r g e p r o p o r t i o n of T_. p l i c a t a (14.7%), and J_. p l i c a t a i s at i t s best r a t e of i n c r e a s e (12.1%/5y). I t seems apparent i n the o l d e r p l o t s that the c o n d i t i o n s favour a r a p i d b a s a l area growth f o r J_. p l i c a t a r e f l e c t i n g both a l a r g e diameter increment and good rege-n e r a t i o n of t h i s s p e c i e s , while P_. m e n z i e s i i grows much slower than i n other p l o t types. The consequences can be seen on the graph of species r e l a t i v e abundance f o r the Dry Western Hemlock Subzone (Figures 6 E and F ) . Minor species (Table 15) A. rubra and A_. grandis are minor species i n the Dry Western Hemlock Subzone (Table 15). Both b a s a l area and b a s a l area increment over b a s a l area are s i g n i f i c a n t l y d i f f e r e n t f o r A. rubra. Even though stand age i s not s i g n i f i c a n t l y d i f f e r e n t among p l o t types, there i s a s i g n i f i c a n t negative c o r r e l a t i o n between stand age and basal area (r =-0.97, p = 0.05). Moreover, the two o l d e s t p l o t types show a very high m o r t a l i t y f o r A. r u b r a i n d i c a t e d by a r a t e of increase of -31.6%/5Y i n the Th* p l o t type, and -73.4%/5y i n the PmTpt. This again r e f l e c t s the pioneer behaviour of A. rubra whose r e l a t i v e abundance i s decreasing c o n s t a n t l y when p l o t t e d against age (Figures 6 E and F ) , as p r e v i o u s l y shown i n the stand-type succession data. A. grandis covers a very small b a s a l area i n the PmThArt p l o t type (2.5 m 2/h), and s l i g h t l y more i n PmTp+ (6.6 m 2/h); t h i s d i f f e r e n c e i s not s i g n i f i c a n t . 97 Stand Fro Th Total DBA/ Plot Tyre Age SI 50 SI 50 DBA BA DBA/BA BA Tot BA (years) (m) (m) (m2/h/5y) {m2/h) (%/5y) (mz/h) (%/5y) A. rubra D Th + 50. 0 — 29. 7 2) PmThAr+ 38, 3 32.3 28.0 3) T h T p + 51.3 27. 4 26. 7 4) Pm + 24. 0 33.5 -Overall 39.0 32.4 28.0 F-ratio 1.9 1.0 0.5 NS NS NS A . grandis D PmThAr+ 49. 2 29. 1 27.8 2) PmTp + 50. 0 — 30. 5 Overall 49. 3 29. 1 28. 3 F- r a t i c 0. 0 — 0.7 NS - *** -0. 8 3. 0 -31.6 55. 3 -1.7 -0.1 4. 9 4.9 44. 1 0.8 -1.0 2. 1 -73. 4 46.7 -2.4 0.6 12. 9 4.0 34. 5 1.9 -0.2 5.5 -8.0 44.3 0.3 0.9 12. 1 6.8 1. 4 1.5 NS ** * *** NS NS 0.5 2. 5 14.6 49.2 2.0 0.7 6. 6 5. 3 61.6 1.1 0.5 3.0 1 3 . 3 51. 0 1.8 0. 1 2. 4 0.4 0.6 0.2 NS NS NS NS NS TAEIE 15 One-vay analysis of variance of the minor species acrcss d i f f e r e n t plot types of the Dry Western Hemlock Subzone. Data represent means for a l l occurrences of the subject species in a given plct type. C h a r a c t e r i s t i c s of plot types are given i n Table 7. For abbreviations, see Table 10. 98 Wet Western Hemlock Subzone Major species (Table 16) T_. h e t e r o p h y l l a i s found i n a l l of the 7 p l o t types, and accounts f o r w e l l over h a l f the t o t a l b a s a l area, except i n ThPsTp* where i t i s only 38.2% (Table 8). The stand age v a r i e s from 42.8 to 60.6 years, and the T. h e t e r o p h y l l a s i t e index, from 21.5 to 29.9 m. The only c o r r e l a t i o n worth mentioning i n d i c a t e s a s l o w l y d i m i n i s h i n g percent r a t e of increase w i t h stand age (r = -0.70, p -.0.1). T. h e t e r o p h y l l a basal area increment as a r a t i o of t o t a l b a s a l area has an o v e r a l l mean of 4.8%/5y, but as a r a t i o of J_. h e t e r o p h y l l a b a s a l area, i t v a r i e s among p l o t types. I t has i t s highest r a t e of in c r e a s e (13.7%/5y) i n the ThPst p l o t type, where P_. s i t c h e n s i s a l s o reaches i t s highest v a l u e . This high r a t e of increase f o r both species i s probably due to the youth of t h i s p l o t type, and to high f i t n e s s to s i t e c o n d i t i o n s , but i t might a l s o r e v e a l a lack of intense competition between J_. h e t e r o p h y l l a and P_. s i t c h e n s i s . Among 5 p l o t types, Th, ThAa, ThTpt, ThPsTpt, and ThTpPm+, the r a t e of increase of T. h e t e r o p h y l l a i s very s t a b l e ( c i r c a 7.5%/5y), the lowest r a t e of increase (3.5%/5y) i s found i n the ThPm+ p l o t type, where P_. m e n z i e s i i i s the most abundant. This i n d i c a t e s e i t h e r mutual s i t e i n c o m p a t i b i l i t y or strong competition between these two s p e c i e s , and t h i s hypothesis i s r e i n f o r c e d by the observation that P_. m e n z i e s i i shows i t s lowest r a t e of increase (3.0%/5y) i n t h i s same p l o t type, and i t s highest (14.2%/5y) i n the ThTpPm+, where J_. h e t e r o p h y l l a i s s i g n i f i c a n t l y l e ss abundant (see Table 8). 99 Stand Pm Th Total DBA, Plct Type Age SI 50 SI 50 DBA BA DBA/BA BA Tot ] (years) (m) (m) (m2/h/5y) (m^/h) (%/5y) (m2/h) <%/5 heterophylla 1) Th 54.6 — 29.0 3.2 61.6 6.1 63. 0 6.0 2) ThPs + 42., 8 - 28. 3 3.0 34. 5 13.7 67. 2 6.4 3) ThAa 57. 1 - 26. 5 2.7 36. 4 7.3 63.5 5.0 <0 ThTp + 60. 6 - 21.5 1.3 28. 5 7.9 56. C 3.6 5) ThPsTp+ 43. 3 - 26. 1 1.6 23. 6 8.6 62. 9 2.7 6) ThTpPm+ 47.6 - 29.9 1.6 29. 2 7.4 49.4 4.4 7) ThEm + 59. 3 — 29. 8 1.6 52. 1 3.5 70.8 2.2 Overall 52. 2 • - 27.7 2.5 41. 9 7.9 63. 8 4.8 F- r a t i c 6.2 — 7.3 2.0 32.4 2.6 3. 6 1.7 *** - *** * *** ** *** NS £• £licata D ThTp + 60. 6 — 21.5 0.8 21.2 10.5 56. 0 2.3 2) ThPsTp+ 43. 3 - 26. 1 1.7 12. 4 12.4 62. 8 3.3 3) ThTpPm + 47. 6 — 29. 9 0.6 9. 7 2.6 49.5 1.4 Overall 48.7 - 26.0 1.2 13. 8 9.4 57. 7 2.6 F-ratio 5.4 — 8. 6 3.6 3. 5 3.5 2. 1 1.5 * * * . - *** ** ** ** NS NS £• menziesii D ThTpPm+ 47.6 - 29.9 1. 1 9.2 14.2 49.5 2.2 2) ThPm + 59. 3 — 29.8 0.5 16.4 3.0 70.7 0.7 Overall 55. 8 - 29.8 0.6 14. 2 6.4 64. 4 1.2 F- r a t i c 3.5 - 0.0 1.2 4. 8 3.8 26. 8 3.4 * - NS NS ** * *** * Table 16... 100 (Cont'd) Stand Pm Th Total DBA/ Plot Type Age SI 50 SI 50 DBA EA DBA/BA EA Tot BA (years) (m) (m) (n)2/h/5y) (m^/h) (%/5y) (mz/h) {%/5y) P. s i t c h e n s i s 1) ThPs + 42. 8 - 28. 4 3. 9 28. 8 17.9 67. 2 6.9 2) ThPsTp+ 43. 3 — 26. 1 3.3 21.8 15.3 62. 8 5.1 Overall 43. 0 - 27. 5 3.6 26. 3 17.0 65.6 6.3 F-rati o 0. 0 - 4. 6 0.7 2. 4 0.9 0. 9 1.2 NS - • ** NS NS NS NS NS TABLE 16 One-way analysis of variance of the major species across d i f f e r e n t plot types of the Wet Western Hemlock Subzone. Data represent means for a l l observations of a par t i c u l a r plot type. C h a r a c t e r i s t i c s of plot types are given in Table 8. For abreviations, see Table 10. 101 J_. p l i c a t a occurs as a major species i n 3 p l o t types, where stand age goes from 43.3 to 60.6 years, and J_. h e t e r o p h y l l a s i t e index, from 21.5 to 29.9 m. Basal area r a t e of i n c r e a s e , basal area, and percent r a t e of i n c r e a s e a l l vary s i g n i f i c a n t l y among p l o t types. There i s no s i g n i f i c a n t c o r r e l a t i o n between any of these v a r i a b l e s . T o t a l b a s a l area and J_. p l i c a t a increment over t o t a l b a s a l area do not vary s i g n i -f i c a n t l y . The lowest b a s a l area r a t e of increase (2.6%/5y) f o r T. p l i - c ata i s . found i n the ThTpPmt p l o t type, the only p l o t type where P_. men- z i e s i i c o e x i s t s w i t h J_. p l i c a t a , and where P_. m e n z i e s i i achieves i t s best r a t e of increase (14.2%/5y). This can be i n t e r p r e t e d as a s u p e r i o r com-p e t i t i v e a b i l i t y of P_. m e n z i e s i i over J_. p l i c a t a i n t h i s p l o t type, or by b e t t e r response of P_. m e n z i e s i i to the s i t e c o n d i t i o n s . P_. s i t c h e n s i s i s found i n two p l o t types, but none of the growth v a r i a b l e s r e f l e c t any s i g n i f i c a n t d i f f e r e n c e . There i s a strong predominance of J_. h e t e r o p h y l l a over a l l p l o t types. T. h e t e r o p h y l l a can e i t h e r form the climax by i t s e l f or by asso-c i a t i o n w i t h A. amabilis or T_. p l i c a t a . This i s a l s o what i s suggested by the graph of species r e l a t i v e abundance against stand age (Figures 6 G and H), where T_. h e t e r o p h y l l a accounts f o r 60 to 70% of the t o t a l b a s a l area at a l l ages. P_. s i t c h e n s i s and A. amabilis f l u c t u a t e around the 15% l e v e l , and P_. m e n z i e s i i , J_. p l i c a t a and A. r u b r a , around the 5% l e v e l . The succession data of the previous chapter showed much the same, w i t h emphasis on the p o s s i b i l i t y of A. a m a b i l i s t a k i n g over the low frequency stand-types at o l d e r stand ages. 102 Minor species (Table 17) A. ru b r a appears again as a minor s p e c i e s , and i t s basal area and bas a l area increment d i s p l a y no s i g n i f i c a n t d i f f e r e n c e among p l o t types. Although i t s b a s a l area i s s l i g h t l y l a r g e r i n older p l o t types, i t s r a t e of increase becomes negative (-2.1%/5y), and A. rubra i s deemed to be outcompeted by s e r a i and climax s p e c i e s , as i n a l l p r e v i o u s l y c o n s i -dered subzones. I t s behaviour i s shown i n Figures 6 G and H. A_. amabi- l i s i s a major species i n ThAa, but a minor one i n ThTp*; f o r t h i s rea-son i t i s discussed as a minor s p e c i e s . Only the J_. h e t e r o p h y l l a s i t e index shows a s i g n i f i c a n t d i f f e r e n c e between the two p l o t types, but no s i g n i f i c a n t c o r r e l a t i o n w i t h other v a r i a b l e s can be e s t a b l i s h e d . I t was found t h a t A. amabilis occupies 42.0% of the t o t a l b a s a l area i n the ThAa p l o t type (Table 8 ) , and c o n s t i t u t e s a climax w i t h T. h e t e r o p h y l l a . Packee (1976) p o i n t s out that A. am a b i l i s w i l l become a climax dominant i n the colder p o r t i o n of the subzone, provided no major disturbance occurs, but w i l l be of l e s s e r importance i n more maritime (lower eleva-t i o n ) p o r t i o n s of the subzone. Fog Western''Hemlock Subzone Major species (Table 18) T. h e t e r o p h y l l a i s the only species found i n a l l observations. A l l v a r i a b l e s show s i g n i f i c a n t d i f f e r e n c e s between the two p l o t types, but there are too few observations to detect any s i g n i f i c a n t c o r r e l a t i o n s . T. h e t e r o p h y l l a has a r a t e of increase of 0.3%/5y i n the ThPs* p l o t type, and 12.8%/5y i n the ThTpt p l o t type. This i n d i c a t e s that T. h e t e r o p h y l l a 103 Stand Pm Th Total DBA/ Plot Type Age SI 50 SI 50 DBA BA DBA/BA BA Tot BA (years) (m) (ro) (m*/h/5y) (m^/h) (%/5y) (m2/h) (%/Sy) A. rubra 1) ThPs* 46. 0 - 27. 9 0.3 9. 1 -2. 1 67. 9 0.7 2) IhPsTp+ 40. 0 - 25.6 0.6 7. 9 6.7 60.1 1.? 3) ThTpl?ai + 26. 7 — 35. 1 0.6 3. 7 14.9 40.8 1.7 Overall 41. 0 - 27. 8 0.5 7. 9 3.8 61. 1 1.0 F-ratio 10.2 - 10.5 0.5 1.6 2.4 8. 7 0.8 *** — *** NS NS NS *** NS A. amabilis D ThAa 57. 1 — 26. 4 2.1 26. 8 9.2 6 3. 5 3.6 2) ThTp + 53. 3 — 19.8 1.4 16. 3 12.8 69. 2 4.0 Overall 56. 8 - 25. 9 2. 1 25. 9 9.5 64. 0 3.6 F-ratio 0.2 - 7.0 0.7 1.4 1.1 0.3 0. 1 NS - *** NS NS NS NS NS TABLE 17 One-way analysis of variance of the minor species across d i f f e r e n t plot types of the Wet Western Hemlock Subzone. Data represent means for a l l occurrences of the subject species in a given plot type. C h a r a c t e r i s t i c s of plot types are given i n Table 8. For abbreviations, see Table 10. 104 Stand Pm Plct Type Age SI 50 (years) (m) Th Total DBA/ SI 50 DBA EA DBA/BA BA Tot BA (m) (m2/h/5y) (m2/h) (%/5y) (m*/h) (%/5y) 5• hgtergph^lla 1) ThPs + 51.7 - 35.3 0. 2 6C. 9 0.3 74. 0 0.3 2) ThTp + 43. 6 — ?9. 2 3. 3 40. 8 12.8 61. 8 5.6 Overall 48.7 - 33.7 1.3 53. 5 4.9 69. 5 2.2 F-rati o 12.2 — 20. 0 13. 6 6. 8 18.0 8. 0 16. 1 ** * - ** * *** ** *** ** TABLE 18 One-way analysis of variance of major species on di f f e r e n t p l c t types of the Fog Western Hemlock Subzone. Data represent means for a l l observations o f a par t i c u l a r plot type. C h a r a c t e r i s t i c s of plct types are given i n Table 9. For abreviaticns, see Table 10. 105 might outcompete J_. p l i c a t a , and P_. s i t c h e n s i s might l a t e r i n t e r f e r e w i t h the p r o g r e s s i o n of J_. h e t e r o p h y l l a . Since J_. p l i c a t a was found only i n the ThTp+ p l o t type, i t i s impossible to compare i t s p e r f o r -mance, but the graph of species r e l a t i v e abundance (Figure 6) i n d i -cates that the high r a t e of i n c r e a s e of T_. h e t e r o p h y l l a allows i t to overtake T. p l i c a t a l a t e r . T. p l i c a t a then f a l l s to the l e v e l of 10% r e l a t i v e abundance (Figures 6 I and J ) , and P_. s i t c h e n s i s increases s l i g h t l y to reach a l e v e l under 10%. P_. m e n z i e s i i and A. r u b r a are merely t r a c e s ( < 2 % ) . The stand-type data showed that i n f a c t P_. s i t -chensis was never abundant enough to c o n s t i t u t e a stand-type and that J_. h e t e r o p h y l l a overtakes T. p l i c a t a by age 45. In the previous chapter, the u n l i k e l i n e s s of the r a r i t y of J_. p l i c a t a was discussed and was a t t r i -buted to i n s u f f i c i e n t sampling i n t h i s subzone. The r o l e of major climax species as s t a t e d by Packee (1976) was agreed upon. Minor species (Table 19) P_. s i t c h e n s i s i s considered a minor species f o r the same reason given f o r A. a m a b i l i s i n the Wet Western Hemlock Subzone. I t s b a s a l area i s s i g n i f i c a n t l y l a r g e r i n ThPst where i t i s a major s p e c i e s , 13.3 m2/h, against 5.1 m2/h i n ThTp+ where i t i s a minor s p e c i e s . However, i t s r a t e of i n c r e a s e i s s m a l l e r , though not s i g n i f i c a n t l y i n the ThPs* p l o t type, where J_. h e t e r o p h y l l a i s more abundant. This r e f l e c t s anta-gonism between J_. h e t e r o p h y l l a and P_. s i t c h e n s i s . Figures 6 I and J i n d i c a t e that the p r o p o r t i o n of i t s b a s a l area over a l l the p l o t s of the subzone f l u c t u a t e s very l i t t l e around the 10% l e v e l . The stand-type data showed th a t P. s i t c h e n s i s was never the most abundant species i n 106 Stand Pm Th Total DEA/ Plct Type Age SI 50 SI 50 DBA BA DBA/BA BA Tot BA (years) (m) (m) ( m V h/Sy) (m2/h) l%/5y) (m^/h) (%/5y) P. si t c h e n s i s 1) ThPs + 52. 0 - 36. 9 0.8 13. 3 6.0 75. 7 1.0 2) ThTp + ao. c — 31.2 1.0 5. 1 11.7 60. a 1.7 Overall 48.6 - 35.3 0.8 10. 9 7.6 71.3 1.2 F-ratio 23. 5 - 10.0 0. 1 5. 0 2.2 8. a 0.8 ** * - *** NS ** NS ** NS TABIE 19 One-way analysis of variance of the minor species across dif f e r e n t plot types of the Fcg Western Hemlock Subzcne. Data represent means for a l l occurrences of the subject species in a given plct type. C h a r a c t e r i s t i c s of plct types are given i n Table 9. For abbreviations, see Table 10. 107 any stand. S i t e index v a r i a t i o n S i t e index v a r i a t i o n was never s i g n i f i c a n t l y c o r r e l a t e d w i t h basal area growth. Although s i t e index of even-aged stands i s con-s i d e r e d an expression of s i t e q u a l i t y ( C u r t i s et_ al_. 1974) , i t s e v a l u a t i o n takes only age and height i n t o account. The absence of c o r r e l a t i o n between s i t e index and bas a l area growth does not i n v a l i -date s i t e index as a measure of s i t e p r o d u c t i v i t y s i n c e height i s as important as bas a l area i n the computation of p r o d u c t i v i t y . I t seems r a t h e r to suggest, as i s g e n e r a l l y accepted, that b a s a l area growth and height growth are c o n t r o l l e d by d i f f e r e n t s i t e f a c t o r s . Perhaps height growth i s more s e n s i t i v e to physico-chemical s i t e f a c t o r s w h i l e b a s a l area growth i s more s e n s i t i v e to b i o t i c f a c t o r s such as composition and d e n s i t y of v e g e t a t i o n . The d i s t r i b u t i o n of s i t e i n d i c e s i n 10 f e e t (3.03 m) c l a s s e s , at age 50, are given per subzone, f o r P_. m e n z i e s i i and J_. h e t e r o p h y l l a (Figure 7 and 8), and the subzone means and standard d e v i a t i o n s are l i s t e d (Table 20). There i s a s i g n i f i c a n t d i f f e r e n c e (p = 0.01) among the subzone means f o r P_. m e n z i e s i i and J_. h e t e r o p h y l l a s i t e i n d i c e s , showing an increase i n s i t e index from the d r i e s t to the moistest subzone. Packee (1976) demonstrated that the mean annual moisture d e f i c i t w i t h 200 mm of s o i l water storage c a p a c i t y was the most s u i t a b l e v a r i a b l e f o r d i f f e r e n t i a t i n g subzones. Moisture d e f i c i t (Table 20) has a s i g n i f i c a n t c o r r e l a t i o n w i t h P. m e n z i e s i i s i t e index (r = 0.95, p = 0.05), and w i t h T. h e t e r o p h y l l a s i t e index (r = 0.82, p = 0.1). This s t r o n g l y 108 FIGURE 7 S i t e i n d e x d i s t r i b u t i o n p e r 10 f e e t ( 3 . 0 3 m) c l a s s e s f o r P. m e n z i e s i i a t age 5 0 . The c o m p u t a t i o n i s b a s e d on a r e -g r e s s i o n c u r v e d e v e l o p e d by M a c M i l l a n B l o e d e l L i m i t e d (1 9 7 5 I n t e r n a l R e p o r t ) . DRY DOUGLAS-FIR WET DOUGLflS-FIR 5 j 4 -3 --2 --1 .5 .4 .3 .2 .1 + 0 I " KT 1 + 20 40 60 80 100 120 340 160 20 40 60 80 100 120 140 160 DRY WESTERN HEMLOCK 5 j 4 -3 --2 •-1 --0. WET WESTERN HEMLOCK .5 T .3 + .2 + .1 + FOG WESTERN HEMLOCK .5 T .4 + .3 + .2 + 1 + I I I I I 1 I 1 I • f - r - f 20 40 60 80 100 120 1 40 160 20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160 R menziesii S I T E INDEX (50) 110 FIGURE 8 Site index d i s t r i b u t i o n per 10 feet ( 3 . 0 3 to) classes for T. heterophylla at age 50,. The computation i s based cn a regression curve developed by KacMillan Dloedel Limited ( 1 9 7 5 Internal Report). D R Y D O U G L R S - F I R W E T D O U G L R S - F I R 5 j A-• 3 - • 2 -1 -+ + -+-+-. 5 . 4 . 3 2 -.1 -0 i r p r i i T 1 2 0 4 0 GO 80 100 1 20 1 40 160 20 40 SO 80 100 120 140 160 D R Y W E S T E R N H E M L O C K W E T W E S T E R N H E M L O C K F O G W E S T E R N H E M L O C K 5 T 4 + 3 + 2 + 1 + d . 5 T .4 + . 3 + . 2 .1 + tl . 5 T .4 + . 3 .2 I + 4-f-f 2 0 4 0 6 0 90 100 120 140 160 20 4 0 6 0 80 100 120 140 160 2 0 40 6 0 8 0 100 120 140 160 T. heterophylla S I T E I N D E X ( 5 0 ) 112 SUBZONE Pro SITE INDEX Th SITE INDEX MD n mean s n mean s mean (m) (m) (mm) Dry Douglas- • f i r Subzone 71 25. 9 (5.6) 10 25. 3 (5.6) 134 Set Dcuglas-• f i r Subzone 143 27.1 (6.4) 74 23. 9 (6.6) 93 Dry Western Hemlock Subzone 82 29.1 (6. 2) 96 26.2 (4.8) 62 Wet Western Hemlock Subzone 36 34.2 (5.2) 229 28. 0 (5.0) 27 Fog Western Hemlock Subzone 2 38.1 (2.2) 19 33.7 (4.8) 4 TABLE 20 Mean s i t e indices and mean annual moisture d e f i c i t per subzcne. Site indices for P. menziesii and T. heterophylla at age 50 (MacMillan Bloedel Limited 1975 Internal Report). MC i s the mean annual moisture d e f i c i t with 200 mm of s o i l water storage capacity (Packee 1976). Values in brackets a r e t h e standard deviations o f s i t e indices. 113 suggests that moisture a v a i l a b i l i t y i s one of the main determinants i n height growth f o r P_. m e n z i e s i i and J_. h e t e r o p h y l l a , and l i k e l y f o r the other species i n t h i s a n a l y s i s . CONCLUSION B i o g e o c l i m a t i c Subzones can be o b j e c t i v e l y subdivided i n t o p l o t types which are s t a t i s t i c a l l y defined on the ba s i s of present canopy v e g e t a t i o n . D i f f e r e n c e s i n p l o t types are assumed to modify the dynamics of competition and the basal area growth performance o f species. Q u a n t i t a t i v e d i f f e r e n c e s among p l o t types were found i n the r a t e of b a s a l area growth of species which cannot be s o l e l y a t t r i b u t e d to s i t e index as a measure of p r o d u c t i v i t y nor to s i t e age. Results of a n a l y s i s of va r i a n c e are p a r t i c u l a r l y c o n c l u s i v e f o r the major s p e c i e s , P_. m e n z i e s i i , J_. h e t e r o p h y l l a , J_. p l i c a t a , and P_. s i t c h e n s i s , and f o r two minor s p e c i e s , P_. c o n t o r t a and A. rubra . No s i g n i f i c a n t e f f e c t of P_. m e n z i e s i i and J_. h e t e r o p h y l l a s i t e index on bas a l area growth could be detected at the p l o t l e v e l . S i g n i f i c a n t d i f f e r e n c e s i n s i t e index appear at the subzone l e v e l and seem to r e f l e c t the s o i l moisture regime. B i o t i c and a b i o t i c s i t e f a c t o r s vary g r e a t l y w i t h i n one B i o g e o c l i -matic Subzone. The data d i d not allow t e s t i n g f o r exact s i t e f a c t o r s that favor the growth of a species while i n h i b i t i n g the growth of another. At e a r l y stages of secondary succession, species i n v a s i o n and p a r t i -c u l a r l y , species establishment are c o n t r o l l e d by a b i o t i c s i t e c o n d i t i o n s . 114 Later on, t r e e composition creates a s i t u a t i o n where s p e c i e s , j u s t be-cause they grow, have to compete f o r resources. Therefore, t r e e compo-s i t i o n i s an image of both a b i o t i c s i t e f a c t o r s a l l o w i n g or not the presence of v a r i o u s s p e c i e s , and b i o t i c components a l l o w i n g or not t h e i r coexistence. The inferences on succession drawn from these r e s u l t s agree w i t h the species r e l a t i v e abundance observed throughout the r o t a t i o n p e r i o d and w i t h the stand-type succession data of the previous chapter. Moreover, species performance might vary from one B i o g e o c l i m a t i c Subzone to another, w i t h i n s i m i l a r p l o t types. The presence of P_. m e n z i e s i i i n the Wet D o u g l a s - f i r Subzone, f o r i n s t a n c e , seems to correspond w i t h a poor growth of -J_. h e t e r o p h y l l a . No such observation was made i n the Dry Western Hemlock Subzone, whereas the opposite f o r T. h e t e r o p h y l l a was found i n the Wet Western Hemlock Sub-zone. The r e l a t i o n s h i p s between these r e s u l t s suggest that the o v e r a l l f o r e s t succession observed and modelled at the subzone l e v e l i s p a r t l y due to the dynamics of i n t e r s p e c i e s competition observed at the p l o t l e v e l . This study has brought forward some evidence t h a t b a s a l area growth of a species v a r i e s according to t r e e composition as c h a r a c t e r i z e d by p l o t types. I t was not meant to assess the r e l a t i v e c o n t r i b u t i o n of the v a r i a t i o n due to a b i o t i c f a c t o r s w i t h that due to competition; however, i t i s very l i k e l y t h a t both are e q u a l l y important. 115 LITERATURE CITED C u r t i s , R.O., D.J. DeMars, and F.R. Herman. 1974. Which dependent v a r i a b l e i n s i t e index -- height -- age r e g r e s s i o n s ? Forest S c i . 20: 74-87. Daubenmire, R. 1968. Pl a n t communities. Harper § Row. New York. 300 p. Daubenmire, R. and J.B. Daubenmire. 1968. Forest v e g e t a t i o n of eastern Washington and northern Idaho. Wash. State Univ. Agr. Exp. Sta. B u l l . # 60. 104 p. F r a n k l i n , J.F., and C.T. Dyrness. 1969. Vegetation of Oregon and Washing-ton. U.S.D.A. For. Res. Pap. PNW-80. P o r t l a n d , Oregon. 216 p. F r a n k l i n , J.F., and C.T. Dyrness. 1973. N a t u r a l v e g e t a t i o n of Oregon and Washington. U.S.D.A. For. Res. Serv. Gen. Tech. Rept. PNW-8. 417 p. H a l l i d a y , W.E.D. 1937. A f o r e s t c l a s s i f i c a t i o n f o r Canada. Can. For. Serv. B u l l . 89. K r a j i n a , V.J. 1969. Ecology of f o r e s t t r e e s i n B r i t i s h Columbia. E c o l . Western North Amer. 2:1-147. Univ. of B r i t i s h Columbia. Dept. of Bot. Packee, E.C. 1974. The B i o g e o c l i m a t i c Subzones of Vancouver I s l a n d and the adjacent mainland and i s l a n d s . MacMillan Bloedel Li m i t e d For. Res. Notes. 11 p. + app. Packee, E.C. 1976. An e c o l o g i c a l approach toward y i e l d o p t i m i z a t i o n through species a l l o c a t i o n . Ph.D. t h e s i s . Univ. of Minnesota. 740 p. * app. Rowe, J.S. 1972. Forest regions of Canada. Can. For. Serv. Publ. 1300. x • 172 p. Socie t y of American F o r e s t e r s . 1954. Forest cover types of North America ( e x c l u s i v e of Mexico). Soc. Amer. For. Washington, D.C. 67 p. A n a l y s i s and modelling of i n t e r s p e c i e s competition during f o r e s t secondary succession. P i e r r e B e l l e f l e u r CHAPTER I I I The r e l a t i o n s h i p s between m u l t i - s p e c i e s competition and s i n g l e t r e e replacement. 117 ABSTRACT The e f f e c t of i n t e r s p e c i e s competition was examined on a s i n g l e t r e e b a s i s . The data c o n s i s t e d of over 2,000 observations from 12 Permanent Sample P l o t s where the coordinates of each t r e e were known. Indices of competition r e p r e s e n t i n g h o r i z o n t a l and v e r t i c a l f o r e s t s t r u c t u r e were computed f o r each t r e e . Regression models of y e a r l y diameter increment were b u i l t to evaluate the c o n t r i b u t i o n of diameter, age, s i t e index, subzone l o c a t i o n , s e v e r a l competition i n d i c e s and i n t e r -a c t i o n s of some of these terms, f o r P_. m e n z i e s i i , T. p l i c a t a , and T. h e t e r o p h y l l a . The most s i g n i f i c a n t v a r i a b l e s a f f e c t i n g t r e e growth, m o r t a l i t y , and r e g e n e r a t i o n , were determined by a n a l y s i s of v a r i a n c e . The r e s u l t s of the r e g r e s s i o n models showed that estimates based on present s i t e c o n d i t i o n s were s i g n i f i c a n t only when used alone, w i t h -out v a r i a b l e s i n d i c a t i v e of the past h i s t o r y of the t r e e . I t was found that the r e l a t i o n s h i p between the competition regime and the present s t a t e of a t r e e seems t o be cause and e f f e c t a p p l i e d over the e n t i r e l i f e - s p a n of the t r e e . The most powerful i n d i c a t o r s of the impact of competition were found i n the t r e e i t s e l f , and were evaluated by i t s diameter and long-term diameter increment i n comparison with the whole po p u l a t i o n . M o r t a l i t y and regeneration of each species were found to vary through time i n response to the immediate neighborhood of the i n -d i v i d u a l t r e e ; t h i s seems to be the mechanism which generates succession at the p o p u l a t i o n l e v e l . 118 RESUME On a examine l ' e f f e t de l a competition i n t e r s p e c i f i q u e au niveau de l ' a r b r e . Les donnees forment plus de 2,000 observations provenant de 12 p a r c e l l e s permanentes ou l'on connait l e s coordonnees de ehaque t i g e . On a c a l c u l e des i n d i c e s de competition tenant compte de l a s t r u c t u r e h o r i z o n t a l e et v e r t i c a l e de l a f o r e t pour chaque arbre. On a c o n s t r u i t des modeles de r e g r e s s i o n de 1'accroissement annuel en d i a -metre pour evaluer l a c o n t r i b u t i o n du diametre, de l'Sge, de l ' i n d i c e de s i t e , de l a l o c a t i o n de l a sous-zone, de p l u s i e u r s i n d i c e s de competition et des i n t e r a c t i o n s de quelques-uns de ces termes pour P_. m e n z i e s i i , J_. p l i c a t a et J_. h e t e r o p h y l l a . On a determine l e s v a r i a b l e s l e s plus s i -g n i f i c a t i v e s pour l a c r o i s s a n c e , l a m o r t a l i t e et l a regeneration par analyse de v a r i a n c e . Les r e s u l t a t s des modeles de r e g r e s s i o n ont montre que l e s p r e d i c -t i o n s basees sur l e s c o n d i t i o n s a c t u e l l e s du s i t e sont s i g n i f i c a t i v e s seulement s i u t i l i s e e s s e u l e s , sans 1 ' i n c l u s i o n de v a r i a b l e s r e f l e t a n t l e passe de l ' a r b r e . On a trouve que l a r e l a t i o n entre l e regime de compe-t i t i o n et l ' e t a t a c t u e l de l ' a r b r e en est une de cause a e f f e t durant l a v i e e n t i e r e de l ' a r b r e . C'est dans l ' a r b r e lui-meme que l'on a trouve l e s m e i l l e u r e s i n d i c a t i o n s de 1'impact de l a competition qui est r e v e l e par son diametre et son accroissement en diametre en comparaison de l a pop u l a t i o n . On a trouve que l a m o r t a l i t e et l a regeneration de chaque espece v a r i e n t selon l e v o i s i n a g e immediat de chaque arbre; i l semble que ce s o i t l a l e mecanisme qui engendre l a succession au niveau de l a po p u l a t i o n . 119 INTRODUCTION The e f f e c t of i n t e r s p e c i e s competition on succession i s o f t e n taken f o r granted, on the b a s i s of b i o l o g i c a l common sense (Dansereau 1957, Horn 1974), and many conclusions about i t s importance are based on s p e c u l a t i o n ( M i l l e r 1967). The lack of knowledge about i n t e r s p e c i e s competition obscures the mechanisms which lead to the i n h i b i t i o n of growth as p o p u l a t i o n d e n s i t y increases (Stewart and Levin 1973) . Compe-t i t i o n , as a process of p l a n t p o p u l a t i o n dynamics, has been concealed by more obvious processes, l i k e s uccession, and has t h e r e f o r e been ne-g l e c t e d by i n v e s t i g a t o r s ( P i c k e t t 1976). F l u c t u a t i o n s i n p o p u l a t i o n -d e n s i t y should be explained by processes a c t i n g at the community l e v e l (Decker 1959). The attempt to e l u c i d a t e the mechanism of succession at the p h y s i o l o g i c a l l e v e l of the p l a n t represents a step below the p o p u l a t i o n l e v e l and leaves p a r t l y unexplained the events observed i n the community. The importance of i n t e r s p e c i e s competition i n p o p u l a t i o n dynamics has been s t r e s s e d by many i n v e s t i g a t o r s , , yet s t a t i s t i c a l evidence i s l a c k i n g to confirm the hypothesis of u n d e r l y i n g mechanisms by which competition would lead to succession. This hypothesis r e q u i r e s a demonstrated m o d i f i c a t i o n of the response of an i n d i v i d u a l p l a n t to the presence of d i f f e r e n t competitors i n i t s immediate neighborhood. More-over, i t should be shown th a t p a r t i c u l a r combinations of p l a n t s can i n h i b i t the growth of a s p e c i f i c p l a n t and induce i t s m o r t a l i t y . This chapter attempts to t e s t the f o l l o w i n g hypotheses f o r a f o r e s t community of C o a s t a l B r i t i s h Columbia. (1) The growth, the suppression, 120 and the regeneration of a s i n g l e t r e e are r e l a t e d to the f o r e s t compo-s i t i o n i n i t s immediate neighborhood. (2) The decrease i n r a t e of growth of a t r e e i s p r o g r e s s i v e and can be used to p r e d i c t i t s m o r t a l i t y . (3) The r e l a t i o n s h i p between r a t e of growth and f o r e s t composition i s species-s p e c i f i c . (4) The replacement of dead trees by tre e s of the same or d i f f e r e n t species can be p r e d i c t e d by the neighborhood composition. (5) Dead tre e s are f r e q u e n t l y replaced by tre e s of other species and t h i s mechanism generates the succession observed at the l e v e l of the f o r e s t stand. DESCRIPTION OF THE DATA The data c o n s i s t s of a set of 12 Permanent Sample P l o t s from the data bank of MacMillan Bloedel L i m i t e d , F o r e s t r y D i v i s i o n . The p l o t s belong to the fou r major B i o g e o c l i m a t i c Subzones of Coas t a l B r i t i s h Columbia; two p l o t s are i n the Dry D o u g l a s - f i r Subzone, s i x i n the Wet D o u g l a s - f i r Subzone, three i n the Dry Western Hemlock Subzone, and one p l o t i s i n the Wet Western Hemlock Subzone. Nine p l o t s have an area of 0.04 hectare and t h r e e , 0.08 hectare. P l o t parameters were measured three or four times at f i v e - y e a r i n t e r v a l s . T h e i r f o r e s t d e n s i t y ranges from 1,317 to 1,947 stems per hectare, and the s i t e index (base age 50) v a r i e s from 14 to 38 m f o r P_. m e n z i e s i i , and from 12 to 33 f o r J_. hete- r o p h y l l a . The age of the p l o t s ranges from 15 years at the f i r s t mea-surement to 114 years at the l a s t measurement. Standard inventory-type parameters, described i n Chapter I , were measured f o r each t r e e . In 121 a d d i t i o n , the p o s i t i o n of each t r e e was c a l c u l a t e d and recorded on stem maps. Since the main goal of t h i s study i s the a n a l y s i s of f o r e s t i n t e r -species c o m p e t i t i o n , sample p l o t s were chosen on the b a s i s of t r e e species d i v e r s i t y . The number of t r e e species per p l o t v a r i e s from three to s i x ; a t o t a l of nine species were found: P_. m e n z i e s i i , T_. p l i c a t a , T_. hetero- p h y l l a , A. r u b r a , A. g r a n d i s , and l e s s abundantly, A. macrophyllum, Pinus  monticola Dougl., Cornus n u t t a l l i i Audubon, and Prunus emarginata Dougl. THE CHOICE OF AN APPROACH L i t e r a t u r e Review There are a v a r i e t y of d e t e r m i n i s t i c models f o r s i n g l e s p e c i e s : Pinus taeda L. ( C l u t t e r 1963), P. m e n z i e s i i (Newnham 1964, P a i l l e 1970, Goulding 1972, B e l l a 1971, M i t c h e l l 1971, A r n e y 1972), P i c e a glauca ( M i t c h e l l 1969), P_. c o n t o r t a (Lee 1967), T. h e t e r o p h y l l a ( L i n 1969). These models use e i t h e r a t r e e - d i s t a n c e dependent or t r e e - d i s t a n c e independant approach (Munro 1973), and they a l l deal w i t h i n t r a s p e c i e s competition. The main f e a t u r e common to these models i s the concept of "zone of i n f l u e n -ce" ( K r a j i c e k et al.1961, Vezina 1963, Opie 1968). The zone of i n f l u e n c e of a t r e e i s defined as an area on the ground re p r e s e n t i n g the v e r t i c a l p r o j e c t i o n of the crown or of the r o o t s . I t i s , t h e r e f o r e , the assumed h o r i z o n t a l extent to which a t r e e can gather l i g h t , water and n u t r i e n t s . P e r t i n e n t reviews of f o r e s t stand s i m u l a t i o n modelling are numerous (Jaquette 1972, Honer 1972, F r a n k l i n et al_. 1972, Smith 1973, Munro 1973). 122 Pl a n t p h y s i o l o g i c a l modelling (Hesketh and Jones 1976, McKinion et_ al_. . 1975), although extremely r i c h i n d e t a i l s about the mechanics of a p l a n t , r e v e a l l i t t l e about p l a n t to p l a n t i n t e r a c t i o n , and even l e s s about a m u l t i - s p e c i e s s i t u a t i o n . A g r i c u l t u r a l p l a n t modelling i s a l s o concerned p r i m a r i l y w i t h monocultures (Stern 1965, Mead 1967). There are s e v e r a l models concerned with f o r e s t m u l t i - s p e c i e s modelling (Nelson 1965, Duncan et al_. 1967, Waggoner and Reifsnyder 1968, B o t k i n et a l . 1970, Whittaker et al_. 1974, Stout et a l . 1975). In these, the i n v e s t i g a t o r i s u s u a l l y faced w i t h a number of parameters v a r y i n g together to determine, at any i n s t a n t , p a r t of the behaviour of a group of sp e c i e s . M u l t i p l e r e g r e s s i o n techniques are t h e r e f o r e widely used, and have proven to be q u i t e powerful. However, m u l t i - s p e c i e s models are mostly developed at the l e v e l of the whole stand, using a t r e e - d i s t a n c e independent approach. This approach i s s u f f i c i e n t f o r growth and y i e l d s t u d i e s , but inadequate to examine p l a n t to p l a n t i n t e r -a c t i o n . In view of the o b j e c t i v e s of t h i s study, a t r e e - d i s t a n c e dependent approach seems to be necessary to i n v e s t i g a t e the response of a s i n g l e p l a n t to a number of b i o t i c parameters. M u l t i p l e r e g r e s s i o n and a n a l y s i s of v a r i a n c e can then be a p p l i e d to evaluate the v a r i a b i l i t y and r e l a t i v e importance of va r i o u s parameters. Methods Height growth and diameter growth show d i f f e r e n t p h y s i o l o g i c a l r e s -ponses. The l a t t e r i s more s e n s i t i v e to the den s i t y of the f o r e s t (Kramer and Kozlowski 1960) and i s of the greatest i n t e r e s t f o r 123 competition s t u d i e s . The hypothesis that the r a t e of growth of a s i n g l e t r e e i s r e l a t e d to competition from d i f f e r e n t species i n i t s neighborhood i m p l i e s a p r e c i s e measurement of competition due to each. Two main types of competition index are found i n the f o r e s t l i t e r a t u r e . The f i r s t type i s based on i n d i v i d u a l t r e e competition and u s u a l l y evaluates i n t r a s p e c i e s competition. The second type.deals w i t h i n t e r -species competition, but i s g e n e r a l l y c a l c u l a t e d at the species l e v e l . For t h i s study, an index of competition based on s i n g l e t r e e s was derived from the i d e a of i n t r a s p e c i e s competition i n d i c e s by e x t e n t i o n of the concept from one to s e v e r a l species. The c l a s s i c a l approach i s presented by B e l l a (1969) and Moore et_ al_. (1973). I f the subject t r e e i s denoted S and i t s diameter DS, there e x i s t s a zone of diameter ZS, p r o p o r t i o n a l to DS, defined as the zone of i n -f l u e n c e of S (Figure 9 A). S i m i l a r l y , each competitor j of species i , denoted C ( i , j ) , has a diameter D C ( i , j ) and a zone of i n f l u e n c e of diameter Z C ( i , j ) . When ZS i s overlapped by Z C ( i , j ) , i t i s assumed that S and C ( i , j ) compete f o r the same resources w i t h i n the area of overlap 0 ( i , j ) . The summation of overlap of t r e e s of species 1 i s Sum ( 0 ( 1 , j ) ) , f o r j = l . . . n , where n i s the number of competitors of species 1 w i t h subject t r e e S. The r a t i o of the area of overlap of species 1 to the area of S i s Sum ( 0 ( 1 , j ) ) / A S , f o r j = l . . . n , where AS i s the area of the zone of i n f l u e n c e of S. The r a t i o of the overlap due to a l l species i s t h e r e f o r e Sum ( 0 ( i , j ) ) / A S , f o r j = l . . . n and i = l...m, where m i s the number of species competing w i t h S. The computation of the area of overlap was adapted f o r m u l t i - s p e c i e s from Arney (1972). 124 FIGURE 9 A. G e o m e t r i c a l r e p r e s e n t a t i o n o f t h e a r e a s o f o v e r l a p b e t w e e n a s u b j e c t t r e e and i t s c o m p e t i t o r s . DS = DBH o f t h e s u b j e c t t r e e . ZS = d i a m e t e r o f t h e z o n e o f i n f l u e n c e o f t h e s u b j e c t t r e e . C C ( i , j ) - DBH o f t h e j t h t r e e o f t h e i t h c o m p e t i n g s p e c i e s . Z C ( i , j ) = d i a m e t e r o f t h e z o n e o f i n f l u e n c e o f t h e j t h t r e e c f t h e i t h c o m p e t i n g s p e c i e s . C ( i , j ) = a r e a o f o v e r l a p b e t ween t h e j t h t r e e o f t h e i t h c o m p e t i n g s p e c i e s and t h e s u b j e c t t r e e . R e f e r t o t e x t f o r f o r m u l a e . B. G e o m e t r i c a l r e p r e s e n t a t i o n o f t h e h e i g h t r a t i o o f t h e c o m p e t i n g t r e e s o v e r t h e s u b j e c t t r e e . S - s u b j e c t t r e e . c < i / 1 ) = 1th t r e e o f t h e i t h c o m p e t i n g s p e c i e s . HS = h e i g h t o f t h e s u b j e c t t r e e . H C ( j ) = h e i g h t c f t h e j t h t r e e . R e f e r t o t e x t f c r f o r m u l a e . 125 126 The p o t e n t i a l area of overlap due to unknown competitors l o c a t e d outside the p l o t borders creates a b i a s (Monserud and Ek 1974, M a r t i n _et_ al_. 1977). The method of m i r r o r image from the border was used, w i t h the r e f l e c t i o n l i n e passing through the border, and the c a l c u l a t e d over-lap was weighted i n p r o p o r t i o n to the d i s t a n c e of the subject t r e e from each of the two c l o s e s t borders. Since sample p l o t s are r e c t a n g u l a r , t h i s procedure performed s a t i s f a c t o r i l y when compared with e v a l u a t i o n using d i s t a n c e and s i z e of trees outside the borders. A simple index of v e r t i c a l competition was a l s o c a l c u l a t e d . The height of the subject t r e e i s denoted HS, and the height of a competitor HC(j) (Figure 9 B). No species d i s t i n c t i o n was made f o r the competitors' height. The average height of the competitors i s Sum(HC(j))/n, f o r j = l . . . n and the height r a t i o of competitors over subject t r e e i s Sum (HC(j))/n/HS, f o r j = l . . . n . The purpose of t h i s index i s t o i n d i c a t e whether the subject t r e e i s t a l l e r than i t s competitors (index<1) or i s under t h e i r shade (index >1), and i n what p r o p o r t i o n . The DBH (diameter at breast height) of each t r e e was measured at f i v e - y e a r i n t e r v a l s and the average y e a r l y DBH increment was c a l c u l a t e d . The age of each t r e e was evaluated from r e g r e s s i o n equations based e i t h e r on measured age, f o r canopy t r e e s , or on DBH, f o r ingrowth t r e e s . The status of the t r e e was recorded as ingrowth (DBH <4 cm at l a s t measurement), l i v e , or dead. The subzone to which the p l o t belongs was recorded as a presence-absence f a c t o r . To evaluate the i n f l u e n c e of the presence of n d i f f e r e n t species on the diameter growth of a subject t r e e , r e g r e s s i o n equations of the 127 f o l l o w i n g form were b u i l t : INCREMENT ( i , j ) = f(Sum (0(1,1), Sum (0(2,1))... Sum (Q(n , i ) ) ) f o r each subject t r e e i of each species j . Other p r e d i c t o r s such as DBH2 and DBH/age were a l s o used i n some models. The purpose of the exe r c i s e was not to reach a high c o e f f i c i e n t of determination ( R 2 ) , but to determine the c o n t r i b u t i o n of v a r i o u s p r e d i c t o r s i n the equation. P r e d i c t o r c o n t r i b u t i o n was t e s t e d by a n a l y s i s of vari a n c e of the addi-t i o n a l sum of squares due to the p r e d i c t o r . F i n a l l y , the s t a t i s t i c a l s i g n i f i c a n c e of i n t e r a c t i o n s between p r e d i c t o r "species overlap r a t i o " and p r e d i c t o r "subzone" were t e s t e d . RESULTS AND DISCUSSION Regression models To f i n d out the usefulness of d i s t i n g u i s h i n g between the overlap r a t i o due to each competing s p e c i e s , as opposed to the t o t a l overlap r a t i o , two simple r e g r e s s i o n models were b u i l t (Table 21, Model 1 and 2). Model 1 pools a l l competitor species i n t o o v e r a l l overlap (SUMOR); Model 2 separates overlaps by competitor species (0PM, OTP, etc.). Both models in c l u d e DBH, age, and subzone l o c a t i o n as a d d i t i o n a l independent v a r i a b l e s . The a n a l y s i s of va r i a n c e (Table 22, Model 2 versus Model 1) confirms the s i g n i f i c a n c e of a d d i t i o n a l sum of squares due to a d d i t i o n a l f a c t o r s considered i n Model 2, w i t h the exception of J_. p l i c a t a model. I t i s , t h e r e f o r e , u s e f u l t o know e x a c t l y which species i s competing against P_. m e n z i e s i i and T_. h e t e r o p h y l l a . T_. p l i c a t a appears l e s s s e n s i t i v e to 128 1) Y = (K, DBH, AGE, SUMOE, DEF, WDF, DSH, WWH) B E 2 (Pm) = 0.f>4 5 ( l p ) = 0.508 (Th) = 0. 410 2) Y = (K, DBH, WWH) E AGE, OPM, OTP, CTH, OAG, OAR, OAM, DDF, WDF, DWH, R 2 (Pm) = 0.656 (Ip) - 0.513 (Th) = 0.430 3) Y = (K, DBH, AGE, OEM, OTP, CTH, DDF, WDF, DWH, WWH) B R 2 (Pm) = 0.655 ( l p ) = 0.510 (Th) = 0.425 4) Y = (K, DBH, AGE, SUMOB*HR, OEM, OTP, OTH, DDF, WDF, DWH, WWH) E 2 (Pm) = 0.655 (Tp) = 0.510 (Th) = 0. 425 5) Y = (K, DBH, AGE, OEM, OTP, OTH) B E 2 (Pm) = 0.630 (Tp) = 0.186 (Th) = 0.413 6) Y = (K, DBH, GTF*DDF AGE, OEM, OPM*WBF, OTP, CTH, DDF, WDF, DWH, OTP*WDF, OTH*W CF, CPM*DWH, WWH, OPM *DDF, OTP*DWIl, OTH*DWH, OPK*WWH, CTP*WWH, CTH*WWH) B R 2 (Pm) ='0.664 (Tp) = 0.508 (Th) = 0.427 7) Y = (K, DBH, DBH 2, DEH/AGE, SUMOE, OEM, OTP, OTH, F S I T E , HSTTE, DDE, WDF, DWH, WWH) B E 2 (Pm) = 0. 765 (Tp) = 0.684 (Th) = 0.506 129 ( C o n t ' d ) TABLE 21 R e g r e s s i o n m o d e l s u s e d i n t h i s s t u d y . R 2 i s g i v e n f o r t h r e e s u b j e c t s p e c i e s : P. m e n z i e s i i , T. p l i c a t a , a nd %• h e t e r c p h y l l a r e s p e c t i v e l y . V a r i a b l e names a r e a s f o l -l o w s : AGE: b r e a s t age c f t h e t r e e ( y e a r s ) E: v e c t o r o f r e g r e s s i o n c o e f f i c i e n t s DBH: d i a m e t e r a t b r e a s t h e i g h t (mm) DEE: C r y D o u g l a s - f i r S u b z o n e (0 o r 1) DWH: Dry W e s t e r n H e m l c c k S u b z o n e (0 o r 1) F S I T E : s i t e i n d e x f o r P. m e n z i e s i i , (age 50) (m) HSITE: s i t e i n d e x f o r T. h e t e r o p h y l l a , (age 50) (m) HE: h e i g h t r a t i o K: t h e c o n s t a n t 1 GAG: o v e r l a p r a t i o due t o A. g r a n d i s CAM: o v e r l a p r a t i o due t o A. m a c r o p h y l l u m CAR: o v e r l a p r a t i o due t o A. r u b r a CPM: o v e r l a p r a t i o due t o P. m e n z i e s i i OTH: o v e r l a p r a t i o due t c T. h e t e r o p h y l l a OTP: o v e r l a p r a t i o due t o T. p l i c a t a SUMOB: t o t a l o v e r l a p r a t i o ( a l l s p e c i e s ) WDF: Wet D o u g l a s - f i r S u b z o n e (0 o r 1) WWH: Wet W e s t e r n H e m l c c k S u b z o n e (0 o r 1) Y: a v e r a g e y e a r l y d i a m e t e r i n c r e m e n t i n t h e l a s t f i v e y e a r s (mm) 130 M o del S o u r c e d f MS F - r a t i o MODEL 2 v e r s u s MODEL 1 P. A d d i t i o n a l E r r o r R e g r e s s i o n 5 657 12. 15 3.01 4. 04 *** T. p l i c a t a A d d i t i o n a l E r r o r R e g r e s s i o n 5 377 4.10 5. 16 0.80 NS 1' h g t e ^ i r o p h y l l a a d d i t i o n a l E r r o r R e g r e s s i o n 4 400 4.58 1. 29 3.55 **# MODEL 3 v e r s u s MODEL 1 P. m e n z i e s i i A d d i t i c n a l E r r o r R e g r e s s i o n 2 660 26.92 3.01 8.94 *** p l i c a t a A d d i t i o n a l E r r o r R e g r e s s i o n 2 380 4.82 5. 15 0.93 NS h e t e r o p h y l l a A d d i t i o n a l E r r o r R e g r e s s i o n 2 402 6. 44 1.29 4.99 *** MODEL 4 v e r s u s MODEL 3 P. m e n z i e s i i A d d i t i o n a l E r r o r R e g r e s s i o n 1 659 1. 05 3.01 0.35 NS T. p _ l i c a t a A d d i t i c n a l E r r o r R e g r e s s i o n 1 379 0.17 5. 16 0.03 NS T . l>2lsro_p_h_y_ 1 l a A d d i t i o n a l E r r o r R e g r e s s i o n 1 40 1 0. 12 1.30 0.09 NS T a b l e 2 2 . . . 131 ( C o n t ' d ) M o d a l S o u r c e d f MS F - r a t i c MODEL 3 v e r s u s MCEEL 5 P.. m e n z i e s i i A d d i t i o n a l R e g r e s s i o n 4 34. 75 1 1 .54 *** E r r o r 660 3.01 T. p l i c a t a A d d i t i o n a l R e g r e s s i o n 4 24.61 4.78 *** E r r o r .380 5. 15 2» h e t e r o p h y l l a A d d i t i o n a l R e g r e s s i o n 3 3.51 2.72 *** E r r o r 402 1.29 MODEL 6 v e r s u s MODEL 3 P. m e n z i e s i i A d d i t i o n a l R e g r e s s i o n 11 4.62 1.55 NS E r r o r 649 2.98 T. J 2 l i c a t a A d d i t i o n a l R e g r e s s i o n 11 0.78 0. 15 NS E r r o r 369 5.32 T. h e t e r o p h y l l a A d d i t i o n a l R e g r e s s i o n 8 0.31 0.23 NS E r r o r 394 1.32 MODEL 7 v e r s u s MODEL 3 P. m e n z i e s i i A d d i t i o n a l R e g r e s s i o n 4 158.7 77.03 *** E r r o r 656 2.06 T. p l i c a t a A d d i t i o n a l R e g r e s s i o n 4 177.7 51.68 *** E r r o r 376 3.36 T. h e t e r o p h y l l a A d d i t i o n a l R e g r e s s i o n 4 18.49. 16.51 *** E r r o r 398 1.12 TABLE 22 A n a l y s i s o f v a r i a n c e t a b l e on r e g r e s s i o n racdels. The a n a -l y s i s t e s t s t h e s i g n i f i c a n c e o f t h e v a r i a t i o n a c c o u n t e d f o r by t h e f i r s t m o d e l o v e r and abo v e t h a t a c c o u n t e d f o r by t h e s e c o n d m o d e l . 132 t h i s l e v e l of d e t a i l i n t h i s model. The large number of p r e d i c t o r s i n the models, and the low occurrence of some species made the s o l u t i o n of the models p o s s i b l e only f o r three species: P_. m e n z i e s i i , J_. h e t e r o p h y l l a , and J_. p l i c a t a . Model 3 (Table 21) shows that i t i s p o s s i b l e to d e l e t e the low frequency species as p r e d i c t o r s i n Model 2, and s t i l l o b t a i n a more powerful model than Model 1. Model 4 t e s t s an agglomerate index of competition, defined as t o t a l overlap r a t i o times the height r a t i o . The u n d e r l y i n g hypothesis i s that the average y e a r l y increment should be i n v e r s e l y p r o p o r t i o n a l to the t o t a l overlap r a t i o , as w e l l as to the height r a t i o , s i n c e the overlap on both the h o r i z o n t a l and the v e r t i c a l plane of the crown i s assumed d e t r i m e n t a l to diameter increment. A n a l y s i s of v a r i a n c e shows that t h i s p r e d i c t o r does not add s i g n i f i c a n t i n f o r m a t i o n (Table 22, Model 4 versus Model 3). The n e c e s s i t y of i n c l u d i n g the B i o g e o c l i m a t i c Subzone from which each observation came was t e s t e d by removing t h i s i n f o r m a t i o n from Model 3 (Table 21, Model 5). The a n a l y s i s of varia n c e supports the hypothesis that the a d d i t i o n a l i n f o r m a t i o n provided by the subzone l o c a t i o n i s h i g h l y s i g n i f i c a n t (Table 22, Model 3 versus Model 5). Model 6 was deri v e d from Model 3 to t e s t a p o s s i b l e i n t e r a c t i o n between the overlap r a t i o s and the B i o g e o c l i m a t i c Subzones. I t was hypothesized t h a t P_. men- z i e s i i , T_. p l i c a t a , and T_. h e t e r o p h y l l a might have a t o t a l l y d i f f e r e n t impact as competitors from one subzone to another (Table 21, Model 6). The a n a l y s i s of va r i a n c e i n d i c a t e s , however, that these i n t e r a c t i o n s are not s i g n i f i c a n t (Table 22, Model 6 versus Model 3). Some p r e d i c t o r s were added to Model 3 to t e s t t h e i r s i g n i f i c a n c e . DBH2 was inc l u d e d as a 133 r e f l e c t i o n of the geometric increase of basal area; DBH/Age as an i n d i -cator of the average growth over the l i f e of the t r e e ; P_. m e n z i e s i i and J_. h e t e r o p h y l l a s i t e i n d i c e s , as i n d i c a t o r of s i t e p r o d u c t i v i t y ; and f i n a l l y the t o t a l overlap r a t i o was rei n t r o d u c e d i n the model to repre-sent the r e s i d u a l b i t s of inf o r m a t i o n due to competitors other than P_. m e n z i e s i i , T. p l i c a t a , and T., h e t e r o p h y l l a (Table 21, Model 7). As expected, the i n c l u s i o n of these four p r e d i c t o r s was very h i g h l y s i g n i -f i c a n t (Table 22, Model 7 versus Model 3 ) . This model gives high m u l t i p l e c o r r e l a t i o n c o e f f i c i e n t s (R = 0.87 f o r P_. m e n z i e s i i , R = 0.83 f o r J_. p l i c a t a , and R = 0.71 f o r J_. h e t e r o p h y l l a ) , and i s w e l l s u i t e d to estimate the y e a r l y DBH increment f o r these species over a large d i v e r -s i t y of s i t u a t i o n s . I n t e r e s t i n g l y enough, p r e d i c t o r s l i k e p a r t i a l and t o t a l o v e r l a p s , and subzone l o c a t i o n are not s i g n i f i c a n t i n t h i s model (Appendix C, Model 7 ) , while they were s i g n i f i c a n t i n models where DBH 2 and DBH/Age were not introduced as p r e d i c t o r s . S i t e i n d i c e s were s i g n i -f i c a n t i n only h a l f of the cases. The highest p r e d i c t i v e power, achieved by DBH 2 and DBH/Age, has a c l e a r b i o l o g i c a l meaning. DBH2 i s d i r e c t l y p r o p o r t i o n a l to basal area and represents the cumulative growth of the t r e e over i t s e n t i r e l i f e s p a n . DBH/Age gives the average DBH increment over the l i f e of the t r e e and r e v e a l s the h i s t o r y of i t s f a i l u r e s or successes. The p r e d i c t o r s c a r r y so much of the past growth h i s t o r y of the t r e e that other p r e d i c t o r s r e p r e s e n t i n g only present c o n d i t i o n s are i n s i g n i f i c a n t i n comparison. When the strong p r e d i c t o r s are not included i n the model, weak p r e d i c t o r s become s i g n i f i c a n t s i n c e they d e s c r i b e the present c o n d i t i o n s through subzone l o c a t i o n , s i t e index, and competition regime. 134 M o r t a l i t y and regeneration a n a l y s i s . A l l dependent v a r i a b l e s mentioned above were submitted to one-way analyses of v a r i a n c e to t e s t f o r p o s s i b l e d i f f e r e n c e s among species and among status (ingrowth,, l i v e , dead) of stems w i t h i n each species. Two u s e f u l types of i n d i c a t o r s were found. M o r t a l i t y i n d i c a t o r s are v a r i a b l e s that show s i g n i f i c a n t d i f f e r e n c e s between l i v e and dead stems of the same age and s p e c i e s ; s i n c e some measurements were made j u s t before the death of t r e e s , i t i s p o s s i b l e to compare each v a r i a b l e , DBH f o r i n s t a n c e , between l i v e and dead stems and to p r e d i c t the p r o b a b i l i t y of m o r t a l i t y of a l i v e stem whose value f o r that v a r i a b l e approaches the average value of dead stems. Regeneration i n d i c a t o r s are competition i n d i c e s that show s i g n i f i c a n t d i f f e r e n c e s between species i n the category of the ingrowth stems; they i n d i c a t e the c o n d i t i o n s under which a given species does and does not regenerate. M o r t a l i t y i n d i c a t o r s m e n z i e s i i i s the only species whose dead stems show a DBH s i g n i f i c a n t l y smaller than the average f o r l i v e stems (Table 23). The overlap r a t i o due to J_. p l i c a t a i s s i g n i f i c a n t l y smaller on dead stems than on l i v e ones while the overlap r a t i o due to T. h e t e r o p h y l l a i s s i g n i f i c a n t l y l a r g e r on dead stems. This i n d i c a t e s that a surrounding of J_. h e t e r o p h y l l a i s g e n e r a l l y associated w i t h the suppression and death of P_. m e n z i e s i i stems. The average y e a r l y DBH increment over the f i v e years preceding death i s s i g n i f i c a n t l y s m a l l e r , i n d i c a t i n g a p r o g r e s s i v e growth r e d u c t i o n before death. The average growth r a t e over the t o t a l l i f e s p a n of the t r e e , DBH/Age, i s a l s o s i g n i f i c a n t l y smaller f o r dead stems, which s t r o n g l y suggests a long and p r o g r e s s i v e accumulation of the e f f e c t s of 135 INDICATOR STATUS Pm Tp Th Aq Ar YINC L i v e Dead F - r a t i o 2.7 .93 11 ***. 2.5 0.1 2.1 NS 1 . 8 0.9 8.1*** 1.8 . 84 -.5 4.0*** DBH DEH/AGE OFM OTP OTH SIZES L i v e 234 178 165 274 244 Dead 175 178 182 266 200 F - r a t i o 12*** 0.0 NS 1.1 NS 0. 1 NS 0.5 NS L i v e 3.8 2.9 2.5 4.8 4.0 Dead 2.5 2.2 2.4 4.8 2.3 F - r a t i o 11*** 0.5 NS 0.2 NS 0.0 NS 4.4 ** L i v e . 36 ,.49 .42 .25 . 17 Dead . 36 ,. 51 .63 .67 . 07 F - r a t i o 0.0 NS 0.0 NS 3.9 * * 1.8 NS 0.2 NS L i v e . 18 „ 30 . 20 . 05 .02 Dead .04 28 .17 .01 . 11 F - r a t i o 3.7 ** 0.0 NS 0.1 NS 0.7 NS 2.2 NS L i v e .18 . 16 .18 . 10 Dead .40 0.0 .10 - . 23 F - r a t i o 4.6 ** 0.6 NS 1.4 NS - 1.2 NS L i v e . 94 1.6 1.3 1.1 . 95 Dead 1.1 2.7 1.9 2.5 1.5 F - r a t i o 1.5 NS 2.4 NS 10*** 12*** 3.8 * TAELE 23 One-way a n a l y s i s o f v a r i a n c e o f m o r t a l i t y i n d i c a t o r s b e t -ween l i v e and dead s t e m s . R e f e r t o T a b l e 21 f o r d e f i n i t i o n o f i n d i c a t o r s . Pm = P_. m e n z i e s i i , Tp = T. p i i c a t a t Th = T. h e t e -r o p h y l l a , Ag=A • g r a n d i s t Ar = A.. r u b r a . 136 the neighborhood competitors. No m o r t a l i t y i n d i c a t o r shows any s t a t i s t i c a l s i g n i f i c a n c e i n the case of X- p l i c a t a . However, there were only four dead J_. p l i c a t a stems out of 377 observations. The low number of observations i n t h i s c l a s s i n d i c a t e s c l e a r l y that the m o r t a l i t y i n J_. p l i c a t a occurs l a t e r than i n P_. m e n z i e s i i , s i n c e the average age of T. p l i c a t a i s not s i g n i f i c a n t l y lower than P_. m e n z i e s i i . Three i n d i c a t o r s are s i g n i f i c a n t f o r T. h e t e r o p h y l l a . The average y e a r l y increment i n the f i v e years preceding death i s only h a l f of the value f o r l i v e stems. The overlap r a t i o due to P. m e n z i e s i i i s s i g n i f i -c a n t l y l a r g e r on dead stems. The height r a t i o of the competitors i s a l s o s i g n i f i c a n t l y higher around dying stems. Therefore stems which are over-lapped and are s h o r t e r than the average, and w i t h a DBH increment smaller than the average, d i e . The height r a t i o i s the only v a l i d i n d i c a t o r f o r A. g r a n d i s . Yet the overlap r a t i o due to P_. m e n z i e s i i , although not s t a t i s t i c a l l y s i g n i -f i c a n t , i s an i n d i c a t i o n that P_. m e n z i e s i i overlap i s c o r r e l a t e d w i t h m o r t a l i t y i n A. grandis. The dead stems of A. rubra show that the average DBH increment over t h e i r e n t i r e l i f e s p a n , DBH/Age, i s s i g n i f i c a n t l y smaller than f o r l i v e stems; t h i s i n d i c a t e s that the competition e f f e c t of surrounding stems was a c t i n g f o r a long time. In the f i v e years preceding m o r t a l i t y , the average DBH increment becomes n i l . The competitors around dead stems are, on the average, 1.5 times as t a l l , as opposed to 0.95 around l i v e stems. 137 Regeneration i n d i c a t o r s One-way a n a l y s i s of variance among species i n d i c a t e s that A. rubra regenerates a new stem only when the t o t a l overlap r a t i o i s near zero (Table 24). This confirms the pioneer r o l e of A. rubra which was already demonstrated i n the two previous chapters. The height r a t i o f u r t h e r i n d i c a t e s t h a t the competitors are s h o r t e r , as would be expected during e a r l y stages of succession. P_. m e n z i e s i i a l s o r e q u i r e s low t o t a l overlap r a t i o to grow a new stem. The overlap r a t i o due to P_. m e n z i e s i i , J_. h e t e r o p h y l l a , and J_. p l i - c a t a , r e s p e c t i v e l y , r e f l e c t s the order i n which these species w i l l compete against P_. m e n z i e s i i . The height r a t i o l a r g e r than 1 means th a t other stems were present before or c o n c u r r e n t l y w i t h P_. m e n z i e s i i ; i t i s only l o g i c a l to suggest that A. rubra was preceding i t . The next l e s s t o l e r a n t species i n regard to t o t a l overlap i s T_. h e t e r o p h y l l a . Yet the overlap r a t i o due to P_. m e n z i e s i i suggests that t h i s l a t t e r species was present f i r s t and surrounds the new stems of J_. h e t e r o p h y l l a . The height r a t i o of 2.0 i n d i c a t e s the head s t a r t of e a r l y i n v aders, e i t h e r preceding or growing f a s t e r than T_. h e t e r o p h y l l a . J_. p l i c a t a i s l e s s abundant as a neighbor of the new stems of J_. hetero- p h y l l a , and w i l l p l a y i t s r o l e l a t e r . Next i n overlap t o l e r a n c e i s A. g r a n d i s , which occurs only i n the Dry D o u g l a s - f i r Subzone. P_. m e n z i e s i i i s t h e r e f o r e i t s main competitor and no co-occurrence w i t h J_. p l i c a t a nor with T. h e t e r o p h y l l a was observed i n the sample. The height r a t i o c l a s s i f i e s A. grandis as a l a t e invader l i k e l y t o succeed P_. m e n z i e s i i l o c a l l y . 138 INDICATOR Pm IP Th Ag Ar F- r a t i o SDMOR .53 .94 .76 . 93 . 02 20 .0 *** OPM .37 . 46 .45 . 93 .001 10 . 5 *** OTP . 18 .38 .16 - .02 9 .7 *** OTI1 . 32 .25 . 26 - .002 ' 2 .9 ** HR 1.2 2.2 2.0 1.7 .85 50 .0 *** TABLE 24 One-way analysis of variance of regeneration i n d i c a t o r s between species. Refer to Table 21 for d e f i n i t i o n cf i n d i -cators. Ingrowth data only were used in t h i s analysis. Pm= P.. menziesii. Tp = T_• p l i c a t a . Th = T.. heterophylla , Ag = A.. grand i s t Ar = A.. rubra . 139 The most t o l e r a n t regenerator i n regard to overlap i s J_. p l i c a t a which can regenerate even when 94% of i t s zone of i n f l u e n c e i s over-lapped. The most severe competitor on a new stem of J_. p l i c a t a i s P_. m e n z i e s i i , f o l l o w e d by T.- p l i c a t a and f i n a l l y J_. h e t e r o p h y l l a . The very high height r a t i o f o r J_. p l i c a t a i n d i c a t e s t h a t a l l competitors are, on the average, 2.2 times as t a l l as the ingrowth of T. p l i c a t a . This height r a t i o i s the l a r g e s t of a l l s p e c i e s , which suggests that J_. p l i c a -t a i s the species able to regenerate the l a t e s t i n the stand. This i s an i n d i c a t i o n of a very high shade t o l e r a n c e , and t h e r e f o r e , of the presence of J_. p l i c a t a i n the o l d e r v e g e t a t i o n . The c a p a c i t y of T_- p l i c a -t a to t o l e r a t e a broad spectrum of moisture c o n d i t i o n s i s a l s o a s e l e c t i v e advantage f o r regeneration under dense cover. Succession trends A t y p i c a l dead stem of P_. m e n z i e s i i has a smaller DBH than the average stem; i t s l i f e average DBH increment i s smaller than l i v e stems; i t s DBH increment i n the f i v e years preceding death i s very s m a l l ; i t s most severe competitors are J_. h e t e r o p h y l l a and P_. m e n z i e s i i stems, and the competing stems are t a l l e r . P_. m e n z i e s i i ingrowth r e q u i r e s good sun-l i g h t exposure as i n d i c a t e d by i t s low t o l e r a n c e to t o t a l overlap r a t i o , which makes i t a t y p i c a l pioneer to be succeeded by more shade-tolerant species. The requirement f o r good s u n l i g h t exposure f u r t h e r suggests t o l e r a n c e to d r i e r s i t e s . For A. r u b r a , the t y p i c a l dead stem has a l i f e average DBH increment smaller than l i v e stems; the DBH increment i s h i g h l y reduced during the f i v e years preceding death and the dead stems are much sho r t e r than the 140 average. The ingrowth stem does not t o l e r a t e any overlap and i s only s l i g h t l y s h o r t e r than the surrounding stems. Therefore, among the sample p l o t s , A. r u b r a .is an e a r l y invader which i s r a p i d l y replaced by s e r a i or climax s p e c i e s . I t competes w i t h other pioneers such as P_. m e n z i e s i i . I t was shown, i n Chapter I (Figure 5 ) , that A. r u b r a can hold out P_. m e n z i e s i i i n a small p r o p o r t i o n of the stands (< 5%), u n t i l about age 60. The dead stems of T. h e t e r o p h y l l a do not show a l i f e average DBH increment any s m a l l e r than other stems; t h e i r DBH increment preceding m o r t a l i t y i s very reduced; t h e i r most severe competitors are F_. m e n z i e s i i stems, and the dead stems can be much shor t e r than t h e i r competitors. The ingrowth can t o l e r a t e a large amount of o v e r l a p , u s u a l l y provided by stems of P_. m e n z i e s i i and o l d e r T. h e t e r o p h y l l a stems, and grows i n deep shade, w i t h high surrounding competitors. T. h e t e r o p h y l l a i s t h e r e f o r e a s e r a i species l i k e l y to remain i n the climax v e g e t a t i o n , and i s preceded, on these sample p l o t s , by A. rubra or _P. m e n z i e s i i , or both. J_. h e t e r o p h y l l a can a l s o be present as a pioneer i f c o n d i t i o n s are u n s u i t a b l e f o r , or there i s no seed source of P. m e n z i e s i i . The dead stems of A. g r a n d i s , on the sample p l o t s , have only one c h a r a c t e r i s t i c which d i s t i n g u i s h e s them from the average l i v e stem: they are very much shor t e r than the surrounding stems. The ingrowth can t o l e r a t e a large amount of o v e r l a p , a l l coming from P_. m e n z i e s i i i n t h i s case, and from stems which are much t a l l e r . A. grandis was found only i n the Dry D o u g l a s - f i r Subzone among the sample p l o t s and was found l o c a l l y w i t h P_. m e n z i e s i i i n the older v e g e t a t i o n . 141 Within-the sample, there were only four dead stems of J_. p l i c a t a and they showed no s i g n i f i c a n t c h a r a c t e r i s t i c (Tables 23). Yet t h i s low m o r t a l i t y on p l o t s 114 years o l d i s i t s e l f an i n d i c a t i o n that T. p l i c a t a w i l l p e r s i s t during l a t e r stages of succession. The ingrowth shows a very high t o l e r a n c e to overlap (Table 24); i t s main competitors are P_. m e n z i e s i i and other stems of J_. p l i c a t a ; the height of the average competitor can be very much higher than the ingrowth. J_. p l i c a t a seems the most shade t o l e r a n t among the f i v e species analysed at the stem l e v e l and i t occupies a place i n the older v e g e t a t i o n i n p l o t s dominated by P_. m e n z i e s i i or J_. h e t e r o p h y l l a . CONCLUSION There i s strong evidence that the growth of a s i n g l e stem i s a f f e c t e d by f o r e s t composition i n i t s immediate neighborhood. Diameter growth increment i s a r e s u l t of s i t e c o n d i t i o n s and competition regimes, both past and present. The c o n t r i b u t i o n of present s i t e c o n d i t i o n s was studied through t r e e composition, subzone l o c a t i o n , and s i t e index. Pre-sent competition regime was estimated by competition i n d i c e s which took i n t o account the h o r i z o n t a l d i s t r i b u t i o n of the crowns and roots and the v e r t i c a l d i s t r i b u t i o n of the crowns of a l l t r e e species. I t was found that three species - P. m e n z i e s i i , J_. h e t e r o p h y l l a , and J_. p l i c a t a - were most i n d i c a t i v e of competition from crown and root overlap s i n c e they represented 92% of the t o t a l stem abundance i n the sample p l o t s . Cumu-l a t i v e e f f e c t s of past s i t e c o n d i t i o n s and past competition regimes over 142 the l i f e s p a n of a t r e e were r e f l e c t e d by DBH, DBH 2, and DBH/Age, which were the best p r e d i c t o r s f o r diameter increment. Estimates based on present c o n d i t i o n s were found s i g n i f i c a n t only when used alone, without the p r e d i c t o r s DBH 2 and DBH/Age. No matter how small the competition i n d i c e s were, and t h e r e f o r e sometimes s t a t i s t i c a l l y n o n - s i g n i f i c a n t , i t was the everyday impact created by d e t r i m e n t a l competition which, i n the long run, cumulated i n terms of small DBH and small DBH increment. Although subzone l o c a t i o n and overlap r a t i o s were s i g n i f i c a n t , i n the absence of stronger p r e d i c t o r s , t h e i r i n t e r a c t i o n was not s i g n i f i c a n t . This i n d i c a t e s that the mechanism of competition might be the same i n a l l subzones, and that d i f f e r e n c e s i n ve g e t a t i o n between subzones would be due to other f a c t o r s , such as s o i l and c l i m a t e of the subzone r e g u l a t i n g the a v a i l a b i l i t y of s o l a r r a d i a t i o n , water, and n u t r i e n t s . Regression models revealed that DBH, DBH 2, and DBH/Age were the best p r e d i c t o r s of present diameter increment; the a n a l y s i s of m o r t a l i t y showed that a high competition index, a DBH below average, and a diameter increment below average were good i n d i c a t o r s of m o r t a l i t y . These r e s u l t s are s i m i l a r to those of Monserud (1976) who found that DBH, diameter increment, and competition index were the best v a r i a b l e s to d i s t i n g u i s h between l i v e and dead stems, although the m o r t a l i t y f u n c t i o n he derived from them was not s p e c i e s - s p e c i f i c . M o r t a l i t y and regeneration i n d i c a t o r s were s t r o n g l y c o r r e l a t e d w i t h f o r e s t composition and s t r u c t u r e (geometric p o s i t i o n of each t r e e and d i s t r i b u t i o n s of DBH and h e i g h t ) , and were s p e c i e s - s p e c i f i c . Pioneer and s e r a i species could be recognized on 143 the b a s i s of t h e i r t o l e r a n c e to f o r e s t composition and s t r u c t u r e i n t h e i r surroundings. The c o r r e l a t i o n between high competition i n d i c e s and m o r t a l i t y , and between low competition i n d i c e s and regeneration i n a s p e c i e s - s p e c i f i c manner p o i n t s out a mechanism more l i k e l y dependent on the l o c a l competition regime around each stem than on s i t e f a c t o r s . S t a r t i n g from an assumed equal seed d i s t r i b u t i o n , s i t e c o n d i t i o n s allow only some species to grow at f i r s t , and s i n c e competition i s very severe on these e a r l y invaders, t h e i r d e n s i t y decreases q u i c k l y . S i -multaneously, shade c o n d i t i o n s (set by f o r e s t composition and s t r u c t u r e ) determine p r o b a b i l i t i e s of r e g e n e r a t i o n of these species and i n v a s i o n by other species. This mechanism a p p l i e s to the lowest l e v e l of the f o r e s t p o p u l a t i o n , a s i n g l e t r e e , and i t s e f f e c t s produce succession as can be observed at the p l o t l e v e l and at the B i o g e o c l i m a t i c Subzone l e v e l . A-b i o t i c c h a r a c t e r i s t i c s of the subzone determine f o r e s t composition from which competition shapes the trend of succession by a mechanism indepen-dent of the subzone. I t i s , t h e r e f o r e , unnecessary to invoke more com-pl e x explanations to l i n k together s i g n i f i c a n t i n t e r a c t i o n s from the s i n g l e t r e e to the e n t i r e subzone. 144 LITERATURE CITED Arney, J.D. 1972. Computer s i m u l a t i o n of D o u g l a s - f i r t r e e and stand growth. Can. For. Ser. Pac. For. Res. Cen. I n t . Rep. BC-27. 79 p. B e l l a , I.E. 1969. Competitive influence-zone overlap: a competition model f o r i n d i v i d u a l t r e e s . Can. Dept. F i s h . For. B i -monthly Res. 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Research on coniferous f o r e s t ecosystems - a symposium. U.S.D.A. Forest S e r v i c e . P o r t l a n d , Oregon. 322 p. Goulding, C.J. 1972. Si m u l a t i o n techniques f o r a s t o c h a s t i c model of the growth of D o u g l a s - f i r . Ph.D. t h e s i s . F a c u l t y of F o r e s t r y , U.B.C. 234 p. Hesketh, J.D., and J.W. Jones. 1976. Some comments on computer simula-t o r s f o r p l a n t s . E c o l . Model. 2: 235-247 Honer, T.G. 1972. A team approach to sim u l a t o r research and development w i t h i n the Canadian F o r e s t r y S e r v i c e , pages 109-114 i n : Proceedings: t r e e growth s i m u l a t i o n workshop. T.G. Honer, ed. For. Man. I n s t . Rep. FMR-25. Ottawa. 116 p. 145 J a q u e t t e , D.L. 1972. Mathematical models f o r c o n t r o l l i n g growing b i o l o -g i c a l p o p u l a t i o n s : a survey. Operation Research. 20: 1142-1151. K r a j i c e k , J.E., K.A. Brinkman, and S.F. G i n g r i c h . 1961. Crown competition -a measure of d e n s i t y . For. S c i . 7: 35-42. Lee, J.Y. 1967. Stand models f o r lodgepole pine and l i m i t s to t h e i r a p p l i c a t i o n . Ph.D. t h e s i s . F a c u l t y of F o r e s t r y , U.B.C. 182 p. M a r t i n , G.L., A.R. Ek, and R.A. Monserud. 1977. Co n t r o l of p l o t edge b i a s i n f o r e s t stand growth s i m u l a t i o n models. Can. J . For. Res. 7 : 100-105. McKinion, J.M., J.W. Jones, and J.D. Hesketh. 1975. A system of growth equations f o r the continuous s i m u l a t i o n of p l a n t growth. Trans, of the ASAE. 18: 975-984. Mead, R. 1968. Measurement of competition between i n d i v i d u a l p l a n t s i n a p o p u l a t i o n . J . E c o l . 56: 35-45. M i l l e r , R.S. 1967. P a t t e r n and process i n competition, pages 1-74 i n : Advances i n e c o l o g i c a l research. J.B., Cragg, ed. Academic Press. London and New York. 311 p. M i t c h e l l , K.J. 1969. Simu l a t i o n of the growth of even-aged stands of white spruce.. B u l l . No. 75. Yale Univ. Sch. For. New Haven, Connecticut. 48 p. M i t c h e l l , K.J. 1971. D e s c r i p t i o n and growth s i m u l a t i o n of D o u g l a s - f i r stands. Can. For. Ser. P.P.R.C. I n t . Rep. BC-25. Monserud, R.A. 1976. Simu l a t i o n of f o r e s t t r e e m o r t a l i t y . Forest S c i . 22: 438-444. Monserud, R.A. and A.R. Ek. 1974. P l o t edge bias i n f o r e s t stand growth s i m u l a t i o n models. Can. J . For. Res. 4: 419-423. Moore, J.A., C A . Budelsky, and R.C. Sc h l e s i n g e r . 1973. A new index r e p r e s e n t i n g i n d i v i d u a l t r e e competitive s t a t u s . Can. J . For. Res. 3: 495-500. Munro, D.D. 1973. Modelling f o r managed stands. B.C.F.S. Report on p r o j e c t #65-6872. 22 p. Nelson, T.C. 1965. Growth models f o r stands of mixed species composition. Proc. Soc. Am. Forester s Meeting 1964: 229-231. Newnham, R.M. 1964. The development of stand model f o r D o u g l a s - f i r . Ph.D. t h e s i s . F a c u l t y of F o r e s t r y , U.B.C. 201 p. 146 i Opie, J.E. 1968. P r e d i c t a b i l i t y of i n d i v i d u a l t r e e growth usi n g v a r i o u s d e f i n i t i o n s of competing ba s a l area. For. S c i . 14: 314-323. P a i l l e , G. 1970. D e s c r i p t i o n and p r e d i c t i o n of m o r t a l i t y i n some c o a s t a l D o u g l a s - f i r stands. Ph.D. t h e s i s . F a c u l t y of F o r e s t r y , U.B.C. 300 p. P i c k e t t , S.T.A. 1976. Succession: an e v o l u t i o n a r y i n t e r p r e t a t i o n . Amer. Natur. 110: 107-119. Smith, S. 1973. A review and e v a l u a t i o n of mathematical programming and computer s i m u l a t i o n a p p l i e d to whole f o r e s t s and i n d i -v i d u a l f o r e s t stands. Report to the P r o d u c t i v i t y Committee of the B.C.F.S. Unpublished manuscript. 49 p. Stern, W.R. 1965. The e f f e c t of d e n s i t y on the performance of i n d i -v i d u a l p l a n t s i n subterranean c l o v e r swards. Aust. J . A g r i c . Res. 16: 541-555. Stewart, F.M. and B.R. Le v i n . 1973. P a r t i t i o n i n g of resources and the outcome of i n t e r s p e c i f i c competition: a model and some general c o n s i d e r a t i o n s . Am. Nat. 107: 171-198. Stout, B.B., J.M. Deschenes, and L'.F. Ohmann. 1975. M u l t i - s p e c i e s models of a deciduous f o r e s t . E c o l . 56: 226-231. Vezina, P.E. 1963. More about the Chron. 39:. 313-317. Waggoner, P.E. and W.E. Reifsnyder humidity and evaporation Meteor. 7: 400-409. "crown competition f a c t o r . " For. . 1968. Simu l a t i o n of the temperature, p r o f i l e s i n a l e a f canopy. J.Appl. Whittaker, R.H., F.H. Bormann, G.E. Li k e n s , and T.G. Siccama. 1974. The Hubbard Brook ecosystem study: f o r e s t biomass and produ c t i o n . E c o l . Monogr. 44: 233-252. A n a l y s i s and modelling of i n t e r s p e c i e s competition during f o r e s t secondary succession. P i e r r e B e l l e f l e u r CHAPTER IV Synthesis and c o n c l u s i o n . 148 The perception of succession at the B i o g e o c l i m a t i c Subzone l e v e l r e q u ired observations over a long p e r i o d of time. The l e v e l of r e s o l u t i o n was r a t h e r broad and the observations revealed trends r a t h e r than d e t a i l s . Pioneer and s e r a i r o l e s of species could be i d e n t i f i e d i n each subzone, although the r a t e s of change might have been exaggerated due to unequal sampling i n t e n s i t y over space. Markov models were unable to d u p l i c a t e the observed changes i n t r e e species composition i n adequate d e t a i l . The major problems that were unsolved at t h i s l e v e l were l i n k e d w i t h the v a r i a b i l i t y i n the kinds of d i s t u r -bance which i n i t i a t e d succession, i n the types of communities, and i n the kinds of s i t e s , and were f u r t h e r l i n k e d w i t h the p r o b a b i l i t y of species i n v a s i o n . Therefore, t h i s l e v e l of i n t e r p r e t a t i o n appeared e s s e n t i a l l y g l o b a l and d e s c r i p t i v e and d i d not suggest any s p e c i f i c p o p u l a t i o n dynamic mechanisms. I t s main value was the overview provided f o r each subzone and the comparison of patterns of succession among them. Observations at the p l o t l e v e l made the community s t r u c t u r e immediately obvious, no matter what scheme was used to c l a s s i f y communities. Tree composition was used to d i s c r i m i n a t e between communi-t i e s s i n c e i t was the only p o s s i b l e way to do so i n the absence of data on understory v e g e t a t i o n . In a d d i t i o n , t h i s way of d e f i n i n g communities o f f e r e d the advantage of s i m p l i c i t y and f i e l d p r a c t i c a b i l i t y . The growth of any given species could be c l e a r l y seen to vary from one community to another; t h i s performance appeared to be s u b z o n e - s p e c i f i c . Trends i n species succession could be i n f e r r e d only i n d i r e c t l y at t h i s 149 l e v e l , but they c o i n c i d e d c l o s e l y w i t h those observed at the B i o g e o c l i m a t i c Subzone l e v e l . The long-term overview provided by the B i o g e o c l i m a t i c Subzone l e v e l was, however, l o s t at the p l o t l e v e l . On the other hand, some mechanism of species replacement through e i t h e r f a c i l i t a t i o n or i n h i b i t i o n emerged more or l e s s c l e a r l y , s i n c e growth was a f f e c t e d by t r e e composition which, i n t u r n , was a f f e c t e d by s i t e f a c t o r s and by i n t r a - and i n t e r s p e c i e s competition. The p l o t l e v e l of i n t e r p r e t a t i o n was s u p e r i o r to the B i o g e o c l i m a t i c Subzone l e v e l i n i t s a b i l i t y to r e v e a l the s t r u c t u r e of communities and the r o l e they pl a y i n promoting species replacement. Un f o r t u n a t e l y , due to the absence of appropriate data on s i t e f a c t o r s , i t was not p o s s i b l e to t e s t whether or not a b i o t i c f a c t o r s such as m i c r o c l i m a t e , s o i l heterogeneity, and l o c a l topography played a more important r o l e than p l a n t to p l a n t i n t e r a c t i o n s . I t seemed that t h i s problem could be solved e i t h e r by f i e l d experimentation or by observations at a l e v e l of i n t e r p r e t a t i o n where s i t e f a c t o r s could be kept r e l a t i v e l y homogeneous. With present inventory techniques of v e g e t a t i o n sampling, sample p l o t s had to be chosen to be r e l a t i v e l y homogeneous to represent t y p i c a l communities and to maximize d i f f e r e n c e s between them. This o f f e r e d the i n v a l u a b l e advantage of ensuring a c e r t a i n constancy of the s i t e f a c t o r s w i t h i n any sample p l o t and made i t reasonable to assume that a l l t r e e s of a p l o t were subject to the same a b i o t i c c o n d i t i o n s . I t was shown that suppression and m o r t a l i t y of t r e e s was s t r o n g l y dependent upon the composition of the surrounding t r e e s . Dead stems 150 showed a h i s t o r y of sub-standard growth which was c o r r e l a t e d w i t h competition from i t s neighbors suggesting that the accumulation of d e t r i m e n t a l e f f e c t s produced a s t r e s s which, i n the long run, l e d to below-average growth. The c o n d i t i o n s f o r regeneration were a l s o determined by the neighboring v e g e t a t i o n and those c o n d i t i o n s which were associated w i t h the m o r t a l i t y of a t r e e of a given species could be associated w i t h the regeneration of another species. At t h i s l e v e l of i n t e r p r e t a t i o n , i t was a l s o p o s s i b l e to show that the best growth p r e d i c t o r s r e f l e c t e d the past h i s t o r y of the t r e e , which i s , not s u r p r i s i n g l y , a non-Markovian c o n c l u s i o n . This general mechanism of s e l e c t i v e suppression and s e l e c t i v e replacement of stems seemed, furthermore, the same from one subzone to the other. The d i f f e r e n c e s i n v e g e t a t i o n between subzones should then be due to other f a c t o r s , such as the a v a i l a b i l i t y of s o l a r r a d i a t i o n , water, and n u t r i e n t s . The i n t e r p r e t a t i o n at the i n d i v i d u a l t r e e l e v e l was the only one which suggested a mechanism, broadly described as i n t e r - t r e e competition, which was able to account f o r changes i n the net r a t e of change of populations through m o r t a l i t y and regeneration. This mechanism i s r e s p o n s i b l e f o r the repeatable sequence of dominant species observed at the two higher l e v e l s of i n t e r p r e t a t i o n . Whether competition can be q u a l i f i e d as a "mechanism" i s debatable. I f one looks at i t from a p h y s i o l o g i c a l viewpoint, concepts such as n u t r i e n t c y c l i n g , i o n exchange c a p a c i t y , and a l l e l o p a t h i c substances would suggest more hypotheses on the chemical mechanics of i n h i b i t i o n and f a c i l i t a t i o n . T h i s , 151 however, i s beyond the scope of t h i s study which meant to i n v e s t i g a t e the f o r e s t from the p o p u l a t i o n dynamics viewpoint. From t h i s view, competition i s indeed a mechanism si n c e i t accounts f o r part of the f o r c e s behind m o r t a l i t y and regeneration of species. I t was not p o s s i b l e to demonstrate that f a c i l i t a t i o n mechanisms r a t h e r than i n h i b i t o r y mechanisms such as comeptition are necessary to e x p l a i n secondary succession. 152 APPENDIX A Species names used in the analyses (after Krajina 1969) CODE EOTANICAL NAME ENGLISH NAME Aa Jbies amabilis (Dougl.) Porbes A9" Abies grandis (Dougl.) L i n d l . Am Acer macrophyllum Pursh Ar Alnus rubra Bcng. Arbutus menziesii Pursh Corn us n u t t a l l i i Audubon Ps Picea s i t c h e n s i s (Bcnq.) Carr Pc Pinus contorta Douql. Pinus mcnticcla Douql. Prunus emarcjinajra Dougl. Pm Pseudotsu,ga menziesii (Mirb. ) Franco puercus garryana Dougl. Tp Thuja p l i c a t a Donn Th Tsu<ja heterophylla (Raf.) Sarg. Amabilis f i r Grand f i r Broadleaf maple Red alder P a c i f i c madrona Western flowering dcqwood Sitka spruce Lcdgepcle pine Western white pine B i t t e r cherry Dcuglas-fir Garry oak Western redcedar Western hemlcck IPPJIDIX B 153 T r a n s i t i o n matrices used in the Markov models. Bows and columns represent stand types in the order of the species l i s t . Observations and es-timates are counts. Transitions are p r o b a b i l i t i e s of moving from the column stand-type to the row stand-type in a time i n t e r v a l of f i v e years,. The t r a n s i t i o n matrix has been mul-t i p l i e d hy 103. SPECIES'. THUJA PLICATA ALNUS RUBRA PSEUDOTSUGA MENZIESII PINUS CONTORTA STEMS OBSERVATIONS: 9 0 1 0 0 3 0 . 0 0 0 103 0 0 0 0 9 9 3 104 9 ESTIMATES'. 9 1 5 0 0 2 0 0 0 0 95 0 0 0 4 9 9 3 104 9 TRANSITIONS'. 1000 115 30 0 0 885 0 0 0 0 950 0 0 0 20 1000 1000 1000 1000 1000 BASAL AREA 1 0 0 0 0 4 1 0 0 0 111 0 0 0 0 8 1 4 112 8 1 3 0 0 0 0 2 0 0 0 106 0 0 1 3 8 1 4 112 8 DO 400 0 0 0 500 15 0 0 0 970 0 0 100 15 1000 1000 1000 1000 1000 1. DRY DOUGLAS*FIR SUBZONE. SPECIES: PSEUDOTSUGA MENZIESII TSUGA HETEROPHYLLA THUJA PLICATA ALNUS RUBRA ABIES GRANDIS ACER MACROPHYLLUM PICEA SITCHENSIS STEMS OBSERVATIONS: 211 3 0 0 1 0 0 5 53 1 0 0 0 0 2 2 38 0 1 0 0 0 0 0 3 0 0 0 0 0 1 0 3 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 1 218 58 40 3 5 2 1 ST MATES: 180 3 0 0 0 0 0 30 53 1 2 0 0 0 8 2 24 0 1 0 0 0 0 0 2 0 0 0 0 0 15 0 4 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 1 218 58 40 3 5 2 1 RANSITIONS: 896 52 0 0 100 0 0 80 914 25 250 0 0 0 24 34 775 0 200 0 0 0 0 0 750 0 0 0 0 0 200 0 700 0 0 0 0 0 0 0 1000 0 0 0 0 0 0 0 1000 1000 1000 1000 1000 1000 1000 1000 155 ; 5 3 3 S 3 3 ! : : i I I I = S 3 ! 3 I 5 3 2 S r J 3 3 5 S 5 3 S r 3 BASAL AREA 248 0 0 0 0 0 0 1 42 1 0 0 0 0 1 0 20 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 7 250 42 21 3 2 1 7 228 0 0 3 0 0 0 1 29 1 0 0 0 0 21 0 20 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 1 0 0 13 0 0 0 0 7 250 42 21 3 2 1 7 952 0 0 500 0 0 0 4 850 50 0 0 0 0 44 0 950 0 0 0 0 0 0 0 500 0 0 0 0 0 0 0 1000 0 0 0 0 0 0 0 1000 0 0 150 0 0 0 0 1000 1000 1000 1000 1000 1000 1000 1000 3 2 2 3 3 3 3 3 3 = 3 = 3 = ; : = 3 3 3 3 . 3 3 3 3 3 2 3 2 3 2 3 3 3 3 2. WET DOUGLASnFIR SUBZONE. SPECIES:: PSEUDOTSUGA MENZIESII ALNUS RUBRA TSUGA HETEROPHYLLA THUJA PLICATA ABIES GRANDIS STEMS BASAL AREA OBSERVATIONS'. 100 1 0 0 0 145 0 2 0 0 0 5 0 0 0 0 3 0 0 0 0 129 0 0 5 0 89 0 0 2 0 3 2 0 1 0 0 1 0 0 0 0 0 3 0 0 0 0 4 106 6 132 2 3 151 3 91 1 4 ESTIMATES: 98 1 0 0 0 145 0 4 0 4 0 5 0 0 0 0 2 0 0 0 6 0 129 1 0 5 0 87 0 0 2 0 3 1 0 1 0 0 1 0 0 0 0 0 3 0 1 0 0 0 106 6 132 2 3 151 3 91 1 4 TRANSITIONS'. 933 167 0 0 0 960 0 32 0 500 0 833 0 0 0 0 800 0 0 0 48 0 977 200 0 33 0 968 0 0 19 0 23 800 0 7 0 0 1000 0 0 0 0 0 1000 0 200 0 0 500 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 3 3 3 2 3 3 3 3 3 2 2 3 3 3 2 2 2 2 3 3 3 3 3 2 3 3 3 3 3 2 3 3 3 3 3 2 2 3 3 2 3 3 2 3 3 3 3 3 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3. DRY WESTERN HEMLOCK SUBZONE. SPECIES'. TSUGA HETEROPHYLLA THUJA PLICATA ABIES AMABILIS PICEA SITCHENSIS ALNUS RUBRA STEMS OBSERVATIONS: 249 0 0 1 0 0 10 0 1 0 0 0 39 0 0 1 0 0 21 0 0 0 0 0 4 250 10 39 23 4 ESTIMATES: 249 0 0 1 1 0 6 0 1 0 0 4 39 5 0 1 0 0 16 0 0 0 0 0 3 250 10 39 23 4 UNSITIONS: 996 0 0 43 100 0 800 0 43 0 0 200 1000 100 0 4 0 0 814 0 0 0 0 0 900 1000 1000 1000 1000 1000 BASAL AREA 234 0 0 0 0 0 13 1 0 0 0 0 34 0 0 3 1 0 33 0 0 0 0 0 4 237 14 35 33 4 234 0 4 0 0 0 13 1 0 0 0 0 30 20 0 3 1 0 13 0 0 0 0 0 4 237 14 35 33 4 987 0 50 0 0 0 929 29 0 0 0 0 921 300 0 13 71 0 700 0 0 0 0 0 1000 1000 1000 1000 1000 1000 4. WET WESTERN HEMLOCK SUBZONE. SPECIES'. TSUGA HETEROPHYLLA THUJA PLICATA STEMS BASAL AREA OBSERVATIONS'. 17 0 17 0 0 3 0 3 17 3 17 3 ESTIMATES'. 17 3 0 0 17 3 17 3 0 0 17 3 TRANSITIONS'. 1000 550 1000 550 0 450 0 450 1000 1000 1000 1000 5. FOG WESTERN HEMLOCK SUBZONE. APPENDIX C 159 P a r t i a l regression c o e f f i c i e n t s (B) and F-rat i o s for Model 5 and Model 7_ In a l l cases F(0.05) = 5.02 and F(0.01) = 7,88 MODEL 5 Y = K + DBH + AGE + OPM + OTP + OTH F. menziesii 0.631 df - 1, 664 E: F: 4.7 .014 253 628 -.075 454 -- 65 25 0.26 3-3 .083 -670 1- p l i c a t a R2 = 0.486 df = 1, 384 E: F: 2-3 .019 44 310 -.044 97 -. 30 2- 5 -.58 11 .290 1. 1 1- heterophylla R2 = 0.413 df = 1, 405 E: F: 2.7 .009 152 176 -.032 142 -. 42 18 0.085 0-6 -. 32 5. 1 APPENDIX C. (Cont'd) 160 MODEL 7 Y = K + DBH + EBH2 + DBH +SUMOR+ OPM + OTP + OTH /AGE + FSITE+HSITE+ CDF + WDF + DWH + WWH P. menziesii P.* ~ 0.765 df = 1, 656 D: -.33 .004 -.001 1-04 -.28 -. 19 0-07 -.03 -.03 -.03 -.25 0. 14 -. 29 0. 40 F: 0.42 5.03 7.0 52 9 5. 4 2.3 -32 0. 10 1.2 1.8 .38 . 13 -57 1.0 T. p l i c a t a B 2 = 0-684 df=1. 376 B: 1.80 0.017 -.002 1- 1 -. 27 0. 18 -. 11 --02 -.09 -.12 0.27 1- 4 -1.1 -. 6 F: 4.6 26 17 219 1. 9 0. 58 .43 .007 4.1 6.3 .22 7. 3 3.9 1. 1 T. heterophylla H 2 = 0.506 df = 1, 398 B: .079 .009 -.002 .9 1 -- 06 -.36 -. 03 -.34 -.09 .059 -. 19 -.46 1. 1 F: .04 8.9 14 16 9 0. 16 4.0 .05 3.9 19 7.2 -81 6. 1 .33 

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