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Phytoecological impacts and management implications of the Douglas-Fir Tussock Moth near Kamloops, British.. 1977

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PHYTOECOLOGICAL IMPACTS AND MANAGEMENT IMPLICATIONS OF THE DOUGLAS-FIR TUSSOCK MOTH NEAR KAMLOOPS, BRITISH COLUMBIA by ANDREW ORTON MAJAWA B.S.F. (Hons), U n i v e r s i t y o f • B r i t i s h Columbia, 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY i n the Department of FORESTRY We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1977 <£) Andrew Orton Majawa, 1977 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements f' an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree tha the L ibrary sha l l make it f ree l y ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th is thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is fo r f inanc ia l gain sha l l not be allowed without my written permission. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date 2 7 ^ AfrJL, (177 ABSTRACT Seven outbreaks of Douglas-fir tussock moth, Ovgyia pseudotsugata McDunnough, have recurred i n the i n t e r i o r of B r i t i s h Columbia since 1915. But l i t t l e i s known about t h e i r impacts on renewable resources i n affected stands. A study wassundertaken to examine e f f e c t s of the most recent outbreak on understory vegetation and tree p r o d u c t i v i t y near Kamloops, B r i t i s h Columbia. Dry weight forage production was sampled from lmA c i r c u l a r p l o t s under various l e v e l s of stand crown cover (0-96%) and density (0-45.9m /ha), as modified by d e f o l i a t i o n . Crown cover was determined using a moosehorn, and from v e r t i c a l photographs obtained with a 160° lens mounted on a conventional camera. Stand density was determined using a 20 factor prism. Increment cores were obtained at breast height, and r a d i a l growth analysed under the Addo-X. Ring width behaviour was compared with occurrence of past outbreaks. The e c o l o g i c a l l i t e r a t u r e on 0. pseudotsugata was reviewed. N e g l i g i b l e amounts of forage were obtained from many plot s with undefoliated trees. In d e f o l i a t e d p l o t s with l i v e trees, t o t a l forage 2 production ranged from 0.0 under 96% crown cover and 45.9 m /ha density 2 to 648.9 kg/ha under 50% crown cover and 16.0 m /ha density. The average y i e l d i n small openings was 3667.4 kg/ha. High v a r i a b i l i t y was evident. In one stand, two years following i t s d e f o l i a t i o n and consequent death, t o t a l forage y i e l d s exceeded those from nearby small openings. Forage y i e l d data were described better by logarithmic models - i i - than by hyperbolic ones, at 95% p r o b a b i l i t y . Impacts on tree growth were not demonstrable one year following d e f o l i a t i o n . Many trees recovered even from complete d e f o l i a t i o n . Insect outbreaks and periods of slow tree growth coincided, but quite i n c o n s i s t e n t l y . Apparently, most scattered i n f e s t a t i o n patches develop independently of each other. Grazing values should increase i n s e r i o u s l y d e f o l i a t e d stands even without range seeding. On poor s i t e s and i n stands managed pr i m a r i l y f o r forage production, outbreaks of 0. pseudotsugata may be l e f t alone without n e c e s s a r i l y endangering remote stands. Selective control favoring better s i t e s managed f o r tree production should improve e f f i c i e n c y of investi n g scarce funds i n protection of the inventory. Tree growth and insect outbreaks may be under the influence of some regional c l i m a t i c f a c t o r , but l o c a l factors are also important. A need remains f or long term impact studies on tree growth, forage y i e l d and nutrient status, and other resources. - i i i - ACKNOWLEDGEMENTS I thank the committee which supervised me on my graduate program, including this project: Drs. K. Graham and J.H.G. Smith of the Faculty of Forestry; Dr. R.M. Strang of the Faculty of Forestry and Department of Plant Science; and Dr. J.H. Myers of the Department of Plant Science and Institute of Animal Resource Ecology. Dr. Graham was my principal advisor. He and F.A.O. of the United Nations supported me on the program arid project financially. Dr. Smith lent me his camera and moosehorn which I used to estimate stand crown cover; he and Mr. Z. Srejic assisted me in analyses of tree radial growth data. Drs. Graham and Smith encouraged me when the going got tough. Dr. Strang lent me some equipment for vegetation clipping. Through her inquisition of forestry terminology, Dr. Myers necessitated my clarifying some important concepts. I also thank Dr. A. Kozak and Mrs. K. Hejjas of the Faculty of Forestry for invaluable help in s t a t i s t i c a l modeling of forage yield data on stand characteristics. Dr. R.F. Shepherd of the Pacific Forest Research Center, Victoria, started me on this project. Dr. A. McLean and Mr. L. Haupt, Canada Department of Agriculture, Kamloops, kindly made available laboratory f a c i l i t i e s for my use. Mr. R. Chan, Balco Industries Ltd., Kamloops, and Mr. V. Craig, B.C. Forest Service, Kamloops, provided me with useful information. Gunter Schmidt helped me collect most of the data, and kept me company in the f i e l d . I am very grateful to a l l of you. - i v - I should also thank a l l the I met and talked to i n the f i e l d , f o r i n the s p e c i f i c study area. loggers, ranchers and graziers t e l l i n g me some of t h e i r experiences - v - TABLE OF CONTENTS Page ABSTRACT i ACKNOWLEDGEMENTS i i i TABLE OF CONTENTS v LIST OF TABLES - v i LIST OF FIGURES v i i i INTRODUCTION . 1 THE INSECT 3. ECOLOGICAL IMPACTS 5 THE STUDY AREA 8 METHODS . . . 16 Understory vegetation . . . . . . . 1 6 Tree growth, s u r v i v a l and salvaging . . . . 20 RESULTS 24 DISCUSSIONS ~ 69 Impacts . . . . . . . . . . 69 Epidemiology . . . . . . . . . 107 Cost of an outbreak . . . . . . . . 118 Resource use c o n f l i c t s and pest management strategy . 124 CONCLUSION 130 LITERATURE CITED 132 APPENDIX ' 140 S c i e n t i f i c names of plants . . . . . . 141 - v i - LIST OF TABLES Page Table 1. Ecological conditions prevalent in tree plots where understory vegetation was clipped . 19 Table 2. Extent of sampling for his t o r i c a l radial tree growth, effects of defoliation by Douglas-fir tussock moth on tree growth and understory forage yields . . . . . . . 22 Table 3. Extent of sampling for Douglas-fir resilience to, and salvageability of stands following defoliation by Douglas-fir tussock moth 23 Table 4. Average dry weight forage yields in the study 3.X* 6 3, 27 Table 5. Average dry weight biomass of understory vegetation in tree patches in the study area 28 Table 6. Grass yields under various stand stocking and density classes-. . . . . • 30 Table 7. Forb yields under various stand stocking and density classes . . . . . . . 32 Table 8. Shrub yields under various stand stocking and density classes . . . . . . . 34 Table 9. Total forage yields under various stand stocking and density classes 36 Table 10. Hyperbolic models significant at 95 percent probability level: forage yields . . . 41 Table 11. Logarithmic^ models significant at 95 percent probability level: forage yields . . . 43 Table 12. Radial growth at breast height in Ponderosa pine and Douglas-fir on a medium site at Mountain View . . . . . . 60 Table 13. A comparison of forage yields from openings in two forest associations in the Interior Douglas- f i r zone . . . . . . . . 72 Table 14. A comparison of forage yields in several plots at Mountain View. . . . . . . 75 - v i i - Page Table 15. Percent forage composition under crown cover, by stand density classes . . . . . 87 Table 16. Average percent change i n tree growth at breast height following d e f o l i a t i o n i n 1975 at Mountain View . . . . . . . 91 Table 17. Average percent change i n tree growth at breast height by tree s i z e following d e f o l i a t i o n i n 1975 at Mountain View . . . . . 92 Table 18. Recovery of completely d e f o l i a t e d trees i n a stand at Heffley Creek h i l l s i d e , and dynamics of t h e i r growth . . . . . . . 99 Table 19. Recovery of completely d e f o l i a t e d trees on a southeast facing dry s i t e , and dynamics of t h e i r growth . . . . . . . . 100 Table 20. Sur v i v a l of a l l completely d e f o l i a t e d Douglas- f i r trees t a l l i e d i n the study . . . . 100 Table 21. Average regeneration stocking i n experimental plo t s under canopy and i n adjacent protected openings . . . . . . . . 102 Table 22. Stand composition of Douglas-fir trees i n de f o l i a t e d stands before and following salvage logging . . . . . . . 105 Table 23. D i s t r i b u t i o n of Douglas-fir tussock moth cocoons i n l i g h t l y and heavily d e f o l i a t e d trees . . 113 - v i i i - LIST OF FIGURES Page Figure 1. Major outbreaks of Douglas-fir tussock moth i n western North America . . . . . Figure 2. A model of i n t e r r e l a t i o n s h i p s between important f a c t o r s i n t e r a c t i n g i n an outbreak of Douglas-fir tussock moth . . . . Figure 3. Extent of the outbreak i n the study area; sample l o c a l i t i e s indicated (inside back cover) Figure 4. A fisheye view of a part of Cherry Creek - 1974 Figure 5. Cherry Creek - 1975 . . . . . Figure 6. T y p i c a l Indian Gardens country . Figure 7. A part of Mountain View . . . . Figure 8. A representative fisheye view of Dairy Creek Figure 9. Heffley Creek - Top: h i l l s i d e ; Bottom: roadside Figure 10. Relationship between grass y i e l d s and stand density . . . . . . . Figure 11, Relationship between forb y i e l d s and stand density . . . . . . . Figure 12. Relationship between shrub y i e l d s and stand density . . . . . . . Figure 13. Relationship between grass y i e l d s and stand shocking . . . . . . . Figure 14. Relationship between forb y i e l d s and stand stocking . . . . . . . Figure 15. Relationship between shrub y i e l d s and stand stocking . . . . . . . Figure 16. Relationship between grass y i e l d s and stand shocking . . . . . . . Figure 17. Relationship between forb y i e l d s and stand - s'.toc - ix - Page Figure 18. Relationship between shrub yields and stand "stocking . . . . . . . . 53 Figure 19. Relationship between dry weight biomass and stand density . . . . . . . 54 Figure 20. Relationship between dry weight biomass and stand.stocking . . . . . . . 55 Figure 21. Relationship between dry weight biomass and stahdis|ocking . . . . . . . 56 Figure 22. Relationship between total forage yields and stand density . . . . . . 57 Figure 23. Relationship between total forage yields and standtstoeking . . . • • • • 58 Figure 24. Relationship between total forage yields and stand.stocking . . . . . . . 59 Figure 25. Behaviour of earlywood width in Ponderosa pine. 61 Figure 26. Behaviour of earlywood width in Douglas-fir . 62 Figure 27. Behaviour of latewood width in Ponderosa pine . 63 Figure 28. Behaviour of latewood width in Douglas-fir . 64 Figure 29. Ring width behaviour in Ponderosa pine . . 65 Figure 30. Ring width behaviour in Douglas-fir . . . 66 Figure 31. Behaviour of latewood/Ring in Ponderosa pine . 67 Figure 32. Behaviour of latewood/Ring in Douglas-fir. . 68 Figure 33. Response of understory vegetation at Mountain View . . . . . . . . . 76 , a) Top: Fisheye view - Foreground: Trees ~ defoliated and dead two years ago (1974) *V'* *> ©Background: Negligibly defoliated. . 76 Bottom: Photograph from the interphase between the dead and undefoliated parts of the stand . . . . . . 76 - x - Page Figure 33. b) Fisheye and ordinary views of forage response i n one p l o t i n foreground (a, above). Forage y i e l d s (kg/ha): Y g = 66.0; Y f = 278.5; Y s = 129.9, under % CC 39 m, 4 0 i e r l s , and basal area of 20.7m2/ha (dead trees) . . . . 77 c) Zone of t r a n s i t i o n between the d e f o l i a t e d and undefoliated parts. Note very sparse vegetation i n the understory. Bottom: A dense, undefoliated p l o t near Cherry Creek - 1975. Forage y i e l d s (kg/ha): Yt=0.0 Figure 36. Understory vegetation response under a d e f o l i a t e d now dead, open grown Douglas-fir tree at Cherry Creek - 1975. "ayp': Tree c h a r a c t e r i s t i c s : Diameter = 86.5cm; height = 26.5m; crown width = 14m; ~ . age >150 years. . . . ;'lTo.p^le,ClQ>Ve3cup'iivi'ew^4.nirsuiraner.-u Bottom: Close up view, i n winter Note the apparent d e l i n e a t i o n of the zone of response by crown pro j e c t i o n . Downy brome and Pine grass most abundant. 78 d) Understory vegetation i n the undefoliated part of the stand. Forage y i e l d s (kg/ha): Y g =14.9; Y f = Y s = 0.0, under % CC = 7 2 . ^ = lens a n d basal area 25.3m2/ha. . 78 Figure 34. A conceptual model showing response behaviour •:: b.f'-"forage y i e l d s i n two hypothetical, d e f o l i a t e d stands with d i f f e r e n t density l e v e l s 81 Figure 35. Top: A dense, completely d e f o l i a t e d p l o t at Dairy Creek. Forage y i e l d s (kg/ha): Y =10.0; Yf = Y s = 0.0, one year following d e f o l i a t i o n . Basal area = 2:7.6m2/ha; % CC = 44m> 5 0 i e n s . Forage y i e l d s l i k e l y to increase d r a s t i c a l l y i n time i f most trees die. . . . . 83 83 84 85 85 Figure 37. Some def o l i a t e d Douglas-fir trees infested with bark beetles. Size preference evident. Note t h r i v i n g Ponderosa pine . 97 - x i - Figure 38. Lush current year needle crop on small Douglas f i r trees, following complete d e f o l i a t i o n during the previous year. Evidence of good ' recovery unless r e d e f o l i a t e d ! Top, middle: Cherry Creek . . . . Bottom: Indian Gardens . . . . Figure 39. Abundance of cones on the ground; but no regeneration was evident i n some openings. Behind the range/pole i s undefoliated p l o t : Forage y i e l d s (kg/ha): Y t = 51.6; % CC = 67 m, 6 4 ^ e n s . Cherry Creek, 1974 Figure 40. Structure of r e s i d u a l stands following salvage logging. Marginal tree s i z e Ca. 20cm. .'• Top r ^ Z f i e y r f o e k s p u b l i c prop rr'tyV Top: Heffley Creek, public property Bottom: Mountain View, pri v a t e property (Mr. Inskip). Logging progressing into the devastated area. . . . . Figure 41. Shotgun e f f e c t : t y p i c a l nature of Douglas-fir tussock moth i n f e s t a t i o n on a landscape Figure 42. Active ant colonies . . . . . Top: Cherry Creek - 1975; colony behind the range pole . . . . Bottom: Mountain View; colony behind the log piece 1. r-Nbte rsome de'fbliafioh- ;ihqadj aeent - x i i - In the past, we have often worked on the premise that a l l insect and disease outbreaks are detrimental and must be c o n t r o l l e d . Perhaps i n most instances t h i s has been true, but the e f f e c t of the outbreak on w i l d l i f e and a e s t h e t i c resources may have been a p o s i t i v e f a c t o r that needs more recognition. A j u s t i f i c a t i o n f o r Federal funds must now be very c a r e f u l l y considered and prepared. The President's O f f i c e of Management and Budget i s not p a r t i c u l a r l y impressed by the general statement that m i l l i o n s of acres of trees are i n f e s t e d by i n s e c t s and that a large volume of timber i s dying. Nor i s i t impressed that many l i v e l i h o o d s are t i e d d i r e c t l y to the f o r e s t resource or with s i m i l a r arguments. What does impress the o f f i c e are s p e c i f i c b e n e f i t s that can be derived from the expenditure of a l t e r n a t i v e amounts of Federal d o l l a r s . In other words, the b e n e f i t - c o s t evaluation i s d i r e c t l y associated with the proposed project. We must never forget that every d o l l a r appropriated for forest i n s e c t and disease p r o t e c t i o n i s one l e s s d o l l a r a v a i l a b l e f o r medical research, mass t r a n s i t , flood r e l i e f assistance or s i m i l a r needs. We must be i n a p o s i t i o n to point out what e f f e c t s are s p e c i f i c a l l y associated with f o r e s t pests or p o l l u t a n t s when no c o r r e c t i v e action i s taken. And we must be able to quantify the b e n e f i t s that w i l l acrue ... under a l t e r n a t i v e l e v e l s of spending for f o r e s t pest management and environmental q u a l i t y evaluation a c t i v i t i e s . When we have good information, we can make good decisions .... The value of general estimates f o r a n a l y t i c a l purposes i s small. We need r e l i a b l e comprehensive data of f o r e s t i n s e c t and disease losses (and b e n e f i t s ) that w i l l stand up to close s c r u t i n y . If t h i s information were now a v a i l a b l e we could evaluate our losses more r e a l i s t i c a l l y and use scarce funds and manpower more e f f i c i e n t l y .... John R. McGuire, Chief, U.S. Forest Service. At the 1974 Symposium on the Spruce budworm, Alexandria, Virginia. - 1 - INTRODUCTION The l a t e s t outbreak of Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough (Lepidoptera: L i p a r i d a e ) , i n the i n t e r i o r of B r i t i s h Columbia i s the most devastating of a l l seven recorded outbreaks which have recurred there since about 1915. Outbreaks have occurred quasi-synchronously over a wide geographic region i n western North America. They also occur quite r e g u l a r l y with a mode of about eight years between outbreaks i n many places i n southern B r i t i s h Columbia (Fig. 1). Outbreaks are confined to the i n t e r i o r Douglas-fir"'" forest,,', s p e c i f i c a l l y to the ecotone between lower elevation Ponderosa pine and higher elevation Douglas-fir types. C r i t i c a l synecological data for zonal ecotones here are lacking (Tisdale and McLean, 1957) even now. Because plants continually contend with each other i n the tension zone, there i s no stable association i n the s t r i c t sense of the term. Notwithstanding, an edaphoclimatic "climax" association may be defined here as Douglas-fir-Ponderosa pine-Blue bunch wheatgrass, for purposes of t h i s t h e s i s . No region i n the province has more renewable natural resource values and uses converging upon the forest than the southern i n t e r i o r . C r i t i c a l values include timber, f i s h , range and forage for w i l d as well as domestic ungulates, aesthetics, s o i l and watershed. Inasmuch as various sectors of the p u b l i c make overlapping demands on the resources within an ecosystem, c o n f l i c t s e x i s t i n t h e i r management. Compatibility i s possible, but i t i s not as evident as c o n f l i c t s . As various "̂  S c i e n t i f i c names of plants are a v a i l a b l e i n appendix. CHASC -U i ; . : ; i : ! ! ! i u.u LlLIOOPT j|j C A C M t C ^ L f c l j c j ! SAVCWA !; | NORTH THOMSON KAMLOOPS Hi MONTE LAKk j :. SALMON A R M |; ARMSTROA/G- ! I! VEHNON i [i KkdwA/A ! i i WfSTBANk _ T ;:fENT|CTO/M ! ; : 'OKAM«rAM L-DQ . OLALLA QSOHOQS • ! H M l III i ! I I I ! I II M i l l ! Ii j l iP J iiilj 01 l i i l l l l ! ;:CASCAJ)C 7. OKAWQ-AN N.F. • COLV/Ut NF^JM) i:r.:_:::;' i ..̂  . • PA LLP as E . j±|q:h-jx| : UMhTlLLP. wr YOSEMlTI A/ F STANISLAUS N.F. /V.F. BOISE *. |. BOISE COUNTY N E V A D A pu.M.BOUbT NF 'VltiEttFR PEAK .P:jx0xt i l l |T I P i l l -2. /5 '120 ! : « i ! ! 'Jti 4-0 < P P P i a I i mi 1 M : H : i:|:i:q; Jx ixjxtd: x t TO I ! i.i.U. t t b :px I XE Xtxn: TO 16 * j j x q x X J X X T i ? M i l 1 •|-|~HT 1 1 1 1 ! M i ! I I 60 P P 11 I i I! I 11 1 Mil m : l±t| rr 75 ESI "TTT M i I i Pi I LIGHT SEVERE ! i M M | ] S | j I j I Figure 1. Major outbreaks of Douglas-fir tussock moth i n western North America. The chart represents outbreaks recorded i n numerous accessible l i t e r a t u r e . Main sources: Sufcden, 1957; Canadian Forestry Service's Forest Insect and Disease Survey reports; U.&.D.A.-U.S.D.I. ... Douglas-fir tussock moth pest management plan, 1973). - 3, - resource values converge on an ecosystem, so do t h e i r managers and users. Since 1973, when the current outbreak surfaced, concern has been expressed about i t s impact on the ecosystem. Arguments about the impacts are mainly empirical, and are compartmentalized often with groups promoting p o l a r i z e d views. Some graziers and w i l d l i f e managers contend that d e f o l i a t i o n i s b e n e f i c i a l because i t r e s u l t s i n increased understory forage y i e l d and q u a l i t y . Some forest managers, on the other hand, maintain that notwithstanding the low s i t e q u a l i t y of infested stands, the wood, f i b e r and watershed values exceed those of other sympatric resources. The problem of resource use becomes more complex as various public i n t e r e s t s become involved. Many arguments are based on i n t u i t i o n and empirical evidence. S p e c i f i c data are lacking. As some arguments are speculative, they may provide questionable ground on which resource management decisions are based. The need for relevant data i s obvious. This thesis investigates and reports some r e a l and p o t e n t i a l e c o l o g i c a l impacts of Douglas-fir tussock moth outbreaks i n a part of the Kamloops Forest D i s t r i c t , i n the B r i t i s h Columbia i n t e r i o r . The data should aid resource managers there i n making well-founded decisions regarding outbreaks. The thesis also examines some e c o l o g i c a l aspects of the i n s e c t , and discusses a r a t i o n a l approach towards a strategy f o r i t s management. The insect The Douglas-fir tussock moth i s a native of western North America where i t i s one of the most destructive forest d e f o l i a t o r s . It was described by McDunnough (1921) from a holotype or specimen of - 4 - several paratypes from Chase, B.C. I t was he who separated the insect from Hemerocampa vetusta gulosa complex. In the American l i t e r a t u r e , the insect i s s t i l l sometimes referred to as Hemerocampa pseudotsugata (Grant et a l . , 1975; Harwood, 1975). In Canada, the genus Orgyia appears to have been completely accepted since about 1961. The l i f e cycle of the insect varies along ecoclines within i t s wide geographic habitat. Adults emerge, mate and lay eggs within a short period i n summer. The eggs, i n diapause, remain unhatched throughout the winter. Larvae emerge i n spring and begin feeding i n the upper and outer parts of tree crowns. The larvae trek to those parts immediately following emergence. The apparent photopositive reaction i s possibly triggered by hunger (tension) as i n Eastern spruce budworm, Choristpneura fwniferana (Wellington, 1948). In the European Orgyia antiqua the photopositive reaction i s i n h i b i t e d by some t a c t i l e sensors i n the forelegs: at the end of a branch, absence of t a c t i l e s t i m u l i leads larvae to revert to exploratory maneuver (Z a n f o r l i n , 1970) so that the insect does not f a l l o f f . Five l a r v a l i n s t a r s may have one l e s s - are most common. Although as many as seven i n s t a r s have been mentioned (U.S.D.A., 1973b), t h i s has not been ascertained 2 i n the s c i e n t i f i c l i t e r a t u r e . Sexual dimorphism of non-sexual c h a r a c t e r i s t i c s i s exhibited by adult Douglas-fir tussock mo ths: tf<? have normal lepidopterous wings, and nonfunctional v e s t i g i a l ones. 2 It i s well known that rearing insects on low q u a l i t y food may increase the number of l a r v a l moults (Leonard, 1970). To what extent the endocrine system - corpora allata^>' e'edysia! Jglands - i s influenced by the food i s not c l e a r . - 5 - Host "preference" also v a r i e s by region. In B.C., Douglas- f i r i s the preferred host; sympatric trees such as Ponderosa pine are r a r e l y attacked. The preference for Douglas-fir was implied by McDunnough (1921) i n his c l a s s i c a l paper where he reported some rearing r e s u l t s . The preference i s evident also from Forest Insect and Disease Survey records, and f i e l d observations. In the U.S. P a c i f i c Northwest, White f i r and Grand f i r are preferred, but Douglas-fir i s often attacked (Eaton and Struble, 1957). Other hosts there and farther south include Western l a r c h , Western hemlock, Subalpine f i r and Engelmann spruce (Balch, 1932; U.S.D.A., 1973b). The insect also feeds on l e s s e r vegetation e s p e c i a l l y when tree f o l i a g e i s depleted. Beckwith (1976) points out that whether the v a r i a t i o n i n host preference r e f l e c t s b i o l o g i c a l races of the insect i s not known. Ec o l o g i c a l impacts E c o l o g i c a l impacts can be evaluated by assessment at three stages i n the sequence of events: before, during and following a p p l i c a t i o n of the e c o l o g i c a l force. P o t e n t i a l impacts are evaluated before the a c t i v i t y . In the U.S., t h i s i s often done as a necessary part of environmental project f e a s i b i l i t y analysis under the 1960 Federal National Environmental P o l i c y Act Section 102. The r e s u l t i n g Environmental Impact Statements attempt to predict outcomes of s o c i o e c o l o g i c a l s i g n i f i c a n c e . The U.S. Forest Service has already undertaken impact studies for a few f o r e s t insects including the Douglas-fir tussock moth. The voluminous 1973 Draft Environmental Impact Statement for the tussock moth (U.S.D.A., 1973b) i n the P a c i f i c Northwest - 6 - centered on whether and how the insect should be c o n t r o l l e d . A b e n e f i t - cost r a t i o of 13 (D.A. Graham, 1974) c l e a r l y j u s t i f i e d c o n t r o l . However, i t was d i f f i c u l t to decide on how to c o n t r o l the insect because, as Harwood (1975) pointed out, a f t e r a survey of the l i t e r a t u r e Stark found very few " s c i e n t i f i c papers" on t h i s insect pest. Impacts and t h e i r magnitudes vary with i n t e n s i t y , frequency, severity and timing of the respective e c o l o g i c a l force. Impacts are also a function of the ecosystem prevalent when the force i s applied. Figure 2 i l l u s t r a t e s possible r e l a t i o n s h i p s between many factors involved i n determining the impact of an outbreak of Douglas- f i r tussock moth. The model becomes more complex when a management decision i s superimposed on the system. Some of the r e l a t i o n s h i p s are hypothetical, but they should be appreciated by decision makers and resource managers involved i n the problem. The tussock moth d i r e c t l y a f f e c t s . v a r i o u s parts of the vegetation. This, i n turn, a f f e c t s the stand of which secondary vegetation may be a major component. The extent to which impacts are evident at various l e v e l s of stand, forest etc. i n the hierarchy depends mainly on the s p a t i a l or geographic extent of an i n f e s t a t i o n . Reciprocal impacts are r e a l : I i n f e r from.data presented by Condrashoff and Grant (1962) that depletion of tree f o l i a g e r e s u l t s i n a change of preference for o v i p o s i t i o n and diapause to parts of trees nearer to the ground, where predation may be intense. Weather, elevation and other external factors also influence impacts of d e f o l i a t i o n . As the model i n d i c a t e s , there i s an impact at any l e v e l i n the hierarchy. For a small outbreak, a pest management decision may - 7 - Management decision: Action/No-.- action Weather, site factors ilevation\ soil ) aspect Tree spp.: composition Lesser veg.: composition spatial arrangement yield growth condition survival quality reproduction availability FOREST RESOURCES ^ ^ o i l - w a t e r s h e ^ ^ GRAND ECOLOGICAL' IMPACT Figure 2. A model of interrelationships between important factors interacting in an outbreak of Douglas-fir tussock moth. Arrows indicate flow of influence; thickness of arrows indicates relative intensity or importance of influence. NOTE reciprocal impacts e.g. Trees—>Douglas-fir tussock moth. - 8 - probably be based on impacts at the stand l e v e l . For extensive outbreaks, however, i t i s necessary that decisions be made following analyses of impacts on resources at the regional l e v e l . Such analyses should provide the r a t i o n a l e or raison d'etre and i t s basis for the fundamental decision of control or no-control. U n t i l recently most e c o l o g i c a l impact analyses were pre- occupied with evaluating e f f e c t s of (chemical) c o n t r o l decisions, often bypassing the d i r e c t e c o l o g i c a l impacts of the insect i t s e l f . I t was often assumed a p r i o r i that damage was serious enqugh to warrant some con t r o l . Furthermore, emphasis was on in v e s t i g a t i o n s of e f f e c t s on the animal community, mainly b i r d s , f i s h and ungulates. Insects were examined i n followup studies by entomologists to determine e f f i c a c y of the control measures. Apparently, the long time i t takes for impacts to show i n some parts of the ecosystem discouraged serious research there. Thus, impacts on the plant community have l a r g e l y been ignored i n Douglas-fir tussock moth outbreaks. In t h i s thesis I emphasize impacts on the phytocoenose - the tree and l e s s e r vegetation. Even within t h i s r e s t r i c t i o n , for p r a c t i c a l reasons, the need for evaluating only the more important impacts i s evident. Other impacts are not ignored, however. The study area The study area i s i n what i s generally referred to as the North Thompson and Kamloops i n Forest Insect and Disease Survey reports. It i s MominWtedl-by unevenaged, mostly second growth Dougla s - f i r - Ponderosa pine stands. - 9 - The i n t e r i o r i s a part of the Dry Forest B i o t i c Area which i s " f a u n i s t i c a l l y most c l o s e l y related to, and indeed forms a northern extension of the Great Basin Complex" (Munro and McT. Cowan, 1947). No det a i l e d synecological studies relevant for the outbreak zonal ecotones are a v a i l a b l e i n the accessible l i t e r a t u r e . Broadly, the area i s a part of Rowe's (1972) M-l or Ponderosa pine Douglas-fir section of the Montane Forest Region, and Krajina's (1959, 1965) I n t e r i o r Douglas-fir Biogeoclimatic Zone, Dry or Pinegrass subzone. . I t approximates Beal's (1974) Pseudotsuga Agropyron Spicatum association - "a topoedaphic climax since both topography and s o i l are necessary f o r i t s establishment" - of the wetter Southern Cariboo Zone. In the Similkameen v a l l e y , the broad Pseudotsuga menziesii zone (McLean, 1969) embraces e c o l o g i c a l conditions common i n the study area. The ecotone does not exactly f i t i n any of Brayshaw's (1965) d i s t i n c t associations: It l i e s between h i s Pinus ponderosa - Agropyron Spicatum var. inerme and Pseudotsuga menziesii - Agropyron spicatum associations'. I consider the zonal ecotone as Pseudotsuga menziesii - Pinus ponderosae - Agropyron spicatum quasi-association, which represents a dynamic s i t u a t i o n and i s not t r u l y climax. Study p l o t s were r e s t r i c t e d to the southern part of the North Thompson Val l e y near Dairy.and Heffley.creeks, and Mountain View, and to the south of Kamloops Lake near Cherry Creek and Indian Gardens (Figure 3 - folded inside back cover). <Cdiamagrostis,rubescens was a minor part of the vegetation i n a few p l o t s . Other l e s s e r vegetation included Balsam root, Timber milk-vetch, J u negrassSagebrush, Needle- and-thread, and Kentucky bluegrass. Most of these plants are - 10 - invaders on overgrazed s i t e s . . In most, p l o t s , s o i l s were generally deep, f i n e to medium textured. A d e s c r i p t i o n of each stand follows. 3 Cherry Creek - 1974: This stand was severely d e f o l i a t e d i n 1974. Plots were located between 653 and 720 m elevation, and between 3 and 25 percent slope. Northeast facing slopes are dominant. The s o i l i s . deep, sandy loam. The forest f l o o r depth averaged 3.3cm; i n a few plo t s i t was as deep as 7.6cm. Two years following d e f o l i a t i o n , twenty three percent of trees t a l l i e d had been or was infested with bark beetles. The smallest tree infested had a breast height diameter of 7.9cm. Only one Ponderosa pine tree was in f e s t e d . C a t t l e and horses were grazing i n the area at the time of sampling. Plots for understory vegetation were, however, located where v i s u a l evidence indicated no grazing a c t i v i t y . (Figure 4). Cherry Creek - 1975: This stand was d e f o l i a t e d i n 1975. Plots were, located between 683 and 720m, and between 3 and 25 percent el e v a t i o n and slope r e s p e c t i v e l y . I t i s generally s i m i l a r to Cherry Creek - 1974. (Figure 5). Information of years when experimental stands were d e f o l i a t e d was given by Dr. R.F. Shepherd, Canadian Forestry Service, V i c t o r i a , B.C. Figure 5. Cherry Creek - 1975. - 12 - Indian Gardens: This i s a dry s i t e . The s o i l i s loamy clay with a few rock outcrops scattered throughout. The duff layer averaged 2.5cm i n depth. The stand approximates a pure Douglas-fir type as no Ponderosa pine trees were t a l l i e d i n the sample p l o t s . Plots were within 827 - 921m and 15 to 25 percent ranges of elevation and slope respectively. (Figure 6). Figure 6. T y p i c a l Indian Gardens country. - 13 - Mountain View: One stand sampled here was de f o l i a t e d i n 1975. The s o i l i s loamy clay. Plots were located between 518 and 636m, and between 5 and 20 percent elevation and slope respectively. The stand i s on a southeast facing slope. Some plots were located i n another stand which was d e f o l i a t e d i n 1974. V i r t u a l l y a l l trees were dead at time of sampling, two years l a t e r . A slope of 35 percent was quite common; elevation ranged from 647 and 671m. (Figure 7). Figure 7. A part of Mountain View. - 14 - Dairy Creek: The stand i s characterized by deep loamy clay s o i l , and a forest f l o o r averaging 6.4cm deep. In many plots the fo r e s t f l o o r was severely cracked, i n d i c a t i n g extreme dryness. Part of the stand was fenced off from grazing for the second consecutive year. The stand faces south. Elevation and slopes of plo t s were between 624 and 878m, and 5 and 20 percent r e s p e c t i v e l y . (Figure 8). Figure 8. A representative fisheye view of Dairy Creek. To face page 15 Figure 9. Heffley Creek. Top: h i l l s i d e Bottom: roadside  - 16 - Heffley Creek: Two stands both along the creek were sampled here. One stand on the north side of the creek was only l i g h t l y d e f o l i a t e d i n 1975. Elevation of 588m and slope of 20 percent were t y p i c a l . The other stand i s on the south side on a very steep h i l l s i d e . I refer to these stands as Heffley Creek - roadside and h i l l s i d e . The s o i l i s very deep sandy loam. On the h i l l s i d e , a steep slope of 88 percent makes the s o i l prone to mass wasting; deep ravines are common here. Probably the angle of repose i s not much less than the p r e v a i l i n g 42°. Depth of the f o r e s t f l o o r averaged 7.6cm. Bunchgrass i s exceptionally dense here. The tussock moth swept through t h i s stand i n 1975 and l e f t v i r t u a l l y a l l Douglas-fir trees completely d e f o l i a t e d . (Figure 9). Methods Understory vegetation In the l i t e r a t u r e i t i s evident that forage (= herbage) y i e l d on forested range land i s a function of i n t e r a c t i n g e c o l o g i c a l f a c t o r s . In t h i s thesis I studied the influence, of stand density and stocking as modified by d e f o l i a t i o n , on understory forage p r o d u c t i v i t y . In each l o c a t i o n , temporary plo t s were chosen i n a maximum of s i x groups of trees representing d i f f e r e n t e c o l o g i c a l conditions:- No d e f o l i a t i o n - high density, low density; P a r t i a l d e f o l i a t i o n - high density, low density; Complete d e f o l i a t i o n - high density, low density. D e f o l i a t i o n classes here r e f e r to the patch rather than i n d i v i d u a l trees, and the terms high and low density are r e l a t i v e . - 17 - For each p l o t and adjacent area i n the stand, I noted stand type, aspect, slope, elevation, s o i l s and the forest association. The purpose was to define part of the e c o l o g i c a l domain within which the data would be v a l i d . A l l p l o t s reported here were within the ranges of 517 to 921m and 3 to 88 percent for elevation and slope. From each pl o t center, a sweep was made with a prism of basal area factor 20, to obtain the number of " i n " trees. The patch density was determined using p r i n c i p l e s of v a r i a b l e p l o t sampling (Dilworth and B e l l , 1972). I t a l l i e d a l l " i n " trees t a l l e r than 1.4m or breast height and recorded the species, breast height diameter (dbh), height, whether i t was l i v e , dead or undetermined, recovery p o t e n t i a l i f d e f o l i a t e d , and presence or absence of secondary insects. For every crown I recorded the following: width, t o t a l length, length of dead portion or top k i l l , and of p a r t i a l l y d e f o l i a t e d , and undefoliated sections. The proportion of current year f o l i a g e was estimated o c u l a r l y . This was possible because of clear d i s t i n c t i o n i n color and p o s i t i o n of current and older f o l i a g e . 2 In the past, the use of 9.6 f t microplots was t r a d i t i o n a l among American range e c o l o g i s t s . Its o r i g i n dates back to 1949 when i t was proposed independently by Frischknecht and Plummer, and Campbell and Cassady. The r a t i o n a l e was that biomass from the p l o t i n grams i s equivalent to one tenth of y i e l d i n pounds expected from one acre, or 2 43560 f t . Later, Canadians adopted the same plo t s i z e so they could quickly judge the c a p a b i l i t y of t h e i r range land by comparing with 2 American data. Currently, lm p l o t s are used with increasing frequency 2 i n forage p r o d u c t i v i t y studies. Grams of biomass from a lm p l o t are - 18 - equivalent to one tenth of y i e l d i n conventional kilograms-per-hectare u n i t s . 2 Within each tree p l o t I systematically established four-lm microplots." C i r c u l a r p l o t s have the smallest perimeter per unit area (Van Dyne e_t al_. , 1963), and t h i s minimizes edge e f f e c t s which may bias r e s u l t s i n forage y i e l d studies. I used a metal loop to determine microplot boundary: Tree plot center Tree plot with imaginary, i r r e g u l a r l y shaped boundary enclosing a l l " i n " trees. microplot Microplots were established also i n openings. In each microplot a f i e l d a s s i s t a n t and I clipped a l l l e s s e r vegetation - shrubs, forb.s, grasses - rooted within the p l o t , at root c o l l a r . Tree seedlings were counted but not clipped. The three components of understory vegetation were separated i n the f i e l d , put i n bags and l a t e r stored i n a cold room. The vegetation was then dried at 50°C for 50 hours, and weighed to the nearest one hundredth of a gram - 19 - In the laboratory. We did t h i s part of the f i e l d work during the summer of 1976. We estimated crown cover under each pl o t i n two ways. One reading was obtained from above the center of each microplot using a moosehorn invented by Robinson (1947) and l a t e r described by Garrison"- (1949). For r e l i a b l e and precise moosehorn crown cover estimates, as many as f o r t y readings per one quarter acre p l o t are recommended (Robinson, 1947; Bonnor, 1968). Our readings f a l l within t h i s acceptable l i m i t . In sp i t e of d i f f i c u l t i e s involved i n holding the moosehorn v e r t i c a l l y and s t e a d i l y , e s p e c i a l l y i n adverse weather conditions i n the f i e l d , we found the technique quite precise (Table 1). Table 1 Ec o l o g i c a l conditions prevalent i n tree p l o t s where understory vegetation was clipped. Data for crown cover are based.on 172 microplots, and for basal area on 36 tree p l o t s . _ _ , _ - Percent crown cover Basal area (m /ha) moosehorn wide angle lens Mean 50. 10 50. ,90 21. 09 Minimum 0. 00 0. ,00 0. 00 Maximum 96. 00 90. ,00 45. 90 Stand, deviat. 28. 80 25, ,70 12. 20 Coef. of Var. 0. 58 0. .51 0. 58 - 20 - The second technique involved the use of hemispherical or' "fisheye" (160°) lens mounted on a conventional.Pentax camera (Brown and Worley, 1965; Bonnor, 1967), loaded with a high speed color s l i d e f i l m . I took crown photographs of each tree p l o t from ground l e v e l , and determined crown closure from p r i n t s . u s i n g a dot g r i d . This technique requires c l e a r skies, calm weather and some f a m i l i a r i t y with photography. I t becomes very expensive i f the f i e l d should be r e v i s i t e d to take more photographs so spoiled ones may be replaced. But i t provides a semi- permanent record of the p l o t s . The r i s k of a f i l m developer l o s i n g or even mixing up good photographs i s always present. Therefore, p l o t s should be marked, a l b e i t temporarily, and films developed as quickly as possible so that plots can be r e v i s i t e d quickly without d i f f i c u l t y i f required. The use of a f i x e d angle lens i n t h i s technique gives crowns of t a l l e r trees a better chance of being included i n a photograph. Yet i t i s recognized that shorter trees may have a shading influence of t h e i r own. This probably biases estimates of crown cover i n uneven aged stands, e s p e c i a l l y i f the angle i s narrow and tree p l o t s large. In t h i s study, most tree crowns appeared i n the photographs, as i n each patch v a r i a t i o n i n tree height was small. Tree growth, s u r v i v a l and salvaging. To investigate possible association between occurrence of outbreaks and trends i n tree r a d i a l growth, and e f f e c t s of the tussock moth on tree s u r v i v a l , we obtained increment cores from trees i n each tree p l o t . We cored two Douglas-fir trees - one tree of average dbh, the other of maximum dbh, and two Ponderosa pine trees both of average - 21 - dbh. One of the Ponderosa pine trees was. from i n s i d e , and the other outside the p l o t . The number of increment cores obtained i n each p l o t was v a r i a b l e as some p l o t s did not have any Ponderosa pine trees, and some trees outside one p l o t also served for another adjacent p l o t . Increment cores were preserved i n p l a s t i c straws; l a t e r I analysed them for earlywood, latewood width using the Swedish Tree Ring Machine, the Addo-X. Only two of 229 cores were discarded because of serious defect of rot at a p i t c h pocket. The freezing technique (Francis et a l . , 1972) used to detect r i n g s , i n rot pockets i s v a l i d for studies involving only r i n g counts for age and s i t e index determination. The technique i s inappropriate for studying. r i n g behaviour ..because i n s i t u moisture may cause changes i n c e l l width. For each Ponderosa pine tree outside the p l o t , we recorded s i m i l a r parameters as we did for each tree in s i d e the p l o t . Because of apparent high v a r i a b i l i t y i n tree growth, I suspected that in.order to detect r e l i a b l e impacts on tree r a d i a l growth, some intensive sampling of increment cores within one area was necessary. So i n addition to the above, I cored 40 trees for r i n g width behaviour analyses on a medium s i t e at Mountain View. I did t h i s a f t e r tree growth had ceased i n winter of 1976. I cored two trees from each of the following 20 treatments: Diameter classes (cm): <^15.0, 15.1-25.0, 25.1-35.0, >35.0; and for each diameter class the following crown conditions: Ponderosa pine c o n t r o l ; Douglas-fir d e f o l i a t i o n classes: c o n t r o l , 5-25%, 30-60%, >65%. A l l the cored trees had been d e f o l i a t e d i n 1975; they were l i v e at. time of sampling. The purpose was to examine h i s t o r i c a l c o r r e l a t i o n s between Table 2. Extent of sampling for hi s t o r i c a l radial tree growth, effects of defoliation by Douglas-fir tussock moth on tree growth and understory forage yields. Site quality - B.C. Forest Service: M - medium, L - Low, P - poor. Elevation % Site Tree Trees t a l l i e d Trees cored Cores Lesser veg. (m) Slope quality plots "::t, ZF analysed plots (incl. Tot. %F F Py open) Dairy.') iGreek 624-878- 19-26 Cherry Cr. - 1974 653-'7.20 3-25 - 1975 683-778 3-35 M-P P-L P-L 72 57 67 97 93 88 12 12 12 8 7 27 32 34 28 28 28 Heffley rCr.- Roadside 558 - Hillside 610 20 88 M M-P 2 3 13 100 100 12 16 Mountain View - 1974 617-671 35 M-P 2 20 100 - 1975 519-636 5-20 M 7 89 96 12 31 8 32 Growth response 561-702 Indian Gardens 872-921 5-20 15-26 M P 40 50 100 32 8 8 2 80 18 20 36 408 91 37 229 172 Table 3. Extent of sampling f o r Douglas-fir r e s i l i e n c e to, and salvage- a b i l i t y of stands following d e f o l i a t i o n by Douglas-fir tussock moth. Elevation On) % Slope No, S t r i p Size(m) Trees F t a l l i e d Py Trees F dead Py Avge Basi (m2/V Heffley Cr. H i l l s i d e 610 88 1 8x31 48 15 (unsalvaged) 610 80 2 12x40 121 3 21 — — H e f f l e y Cr. 824 5 1 9x214 44 3 2 (Balco-Salvage Oper.) 800 10 2 8x92 12 2 2 - - 800 10 3 8x122 79 1 31 - - 790 25 4 31x61 28 13 6 - - (adj. stands unlogged) Prism p l o t 790 20 1 8 - 1 - 37 793 25 2 14 - 6 - 32 793 25 3 12 - 2 - 28 793 10 4 5 5 - 1 23 793 32 5 4 4 — — 41 - 24 - past outbreaks and tree growth during corresponding periods, and tree growth responses to d i f f e r e n t i n t e n s i t i e s of d e f o l i a t i o n i n 1975. A l l increment cores were obtained at breast height. Table 2 shows the extent of sampling undertaken i n t h i s part of the project. Remarkable r e s i l i e n c e of Douglas-fir following d e f o l i a t i o n by the tussock moth i n western U.S. was implied i n the l i t e r a t u r e by Caroline and Coulter -"(19.75). My f i e l d observations suggested that mortality of infested trees varied mainly with s i z e and degree of d e f o l i a t i o n . Therefore t a l l i e s were taken of i n d i v i d u a l trees i n 2 representative s t r i p s at Heffley Creek - h i l l s i d e , where a l l trees had been completely d e f o l i a t e d i n 1975. The s t r i p s measured 8 x 31m and 12 x 40m. A t o t a l of 172 trees were t a l l i e d i n both s t r i p s . For each tree, we recorded the species, condition, dbh, height, crown width and length, recovery p o t e n t i a l (subjectively determined) and absence or presence of secondary in s e c t s . S t r i p s were also located i n areas where salvage logging had been undertaken. Trees from there were also used i n the r e s i l i e n c e study. This part of the study, done i n summer of 1976, also served for i n v e s t i g a t i n g the nature and impact of salvaging infested stands. (Table 3). Results The e f f i c i e n c y of a sampling system i s often estimated as the r e c i p r o c a l of the sample variance. The e f f i c i e n c y of system " i " r e l a t i v e to " j " i s given by o2 / a2 ->. S2 / S2 . when-costs of sampling per m i W r e not u%qual r, e f f i c l i n c y ^ i s ^ m o d i f I b B to'1/|txCV^](Freese, 1962) • where C - r sMtpling-' c'o'sfc 'per"utt-irt,CV^=: c o e f f i c i e n t of v a r i a t i o n . In this study, one film exposure cost on the average $0.15 for purchase, $0.12 for developing into transparencies, and $0.77 for developing into prints for dot grid analysis for a total of $1.04. The 2 sample unit under consideration i s one lm microplot where understory vegetation was clipped. Whereas one moosehorn reading was required for each microplot, four microplots f e l l within each tree plot whose crown cover was photographed. Thus each sample unit cost $0.26. Stocking estimates by the moosehorn and wide angle lens are compared in Table 1. The relative efficiency of the moosehorn system: RE , = (C x CV2) lens moosehorn 2 (C x CV ) moosehorn = 26C x 0.512 1C x 0.582 = 20.10 Although i t produces a higher sample variance, the moosehorn is more efficient than the photographic system by more than twenty times. I have ignored capital costs of the equipment, incidentals of mailing films and slides and riskg. of losing a film, slides or prints. The relative efficiency of the moosehorn calculated above i s therefore a conservative estimate. - 26 - Basal area and percent crown cover may be b i o l o g i c a l l y r e l a t e d , but c o r r e l a t i o n analysis showed the two v a r i a b l e s to be s t a t i s t i c a l l y independent (r = 0.26). The wide range of basal area under s i m i l a r l e v e l s of stocking or crown cover (Smith, 1974) and vice versa, i s i n d i c a t i v e of the complex dynamics of stand development. The low c o r r e l a t i o n between stocking and density i s not unexpected because each varies with aspect, slope, elevation, s o i l s and other factors which are unaccounted for here. In the f i r s t 46 microplots sampled, forage was not separated into grass, forbs and shrubs because of l i m i t e d manpower. However, i t was possible l a t e r to i s o l a t e the vegetation from 126 p l o t s . In developing regressions for t o t a l biomass I used the data from a l l 172 p l o t s , while for regressions describing grass, forbs and shrubs I used data from 126 p l o t s . This means that regression c o e f f i c i e n t s i n models of the three components are not additive to those of t o t a l biomass. Tables 4, 5, 6, 7, 8, 9 summarize the y i e l d data from a l l p l o t s . Evidently, v a r i a t i o n i n y i e l d decreases i n the order of grass, forbs and shrubs, and with increasing stocking and density. [Note that c o e f f i c i e n t s of v a r i a t i o n are not percentages]. In subsequent s t a t i s t i c a l analyses variables are defined as follows: Independent v a r i a b l e s : 2 : Basal area (m /ha) X£ : Percent crown cover by moosehorn X : Percent crown cover by wide angle lens - 27 - Dependent v a r i a b l e s : Y : T o t a l forage y i e l d Y : Grass y i e l d g Y^ : Forb y i e l d Y : Shrub y i e l d s A l l y i e l d s are dry weight (Kg/ha) as described i n methods. Table 4 Average dry weight forage y i e l d s i n the study area. Data are based on 126 microplots, except for t o t a l which are based on 172 micropolots. Grass Yie l d s (Kg/ha) Forbs Shrubs To t a l Mean Minimum Maximum Stand, dev. Coef. of Var. 88.5 0.0 743.0 139.3 1.57 47.8 0.0 599.0 108.6 2.28 48.6 159.8 0.0 0.0 534.5 1175.4 97.7 216.3 2.01 1.35 Table 5. Average Dry weight biomass (kg/ha) of understory vegetation i n tree patches i n the study area. Each moosehorn and y i e l d datum i s based on 4 microplots. Basal area % Crown Cover Grass Forbs Shrubs Total (m2/ha) moosehorn lens Cherry Cr. 1974 0.0 13.8 16.1 18.4 25.3 27.5 29.8 Cherry Cr. 1975 0.0 16.1 20.7 23.0 23.0 29.8 41.3 Indian Gardens 0.0 16.1 23.0 29.8 46.0 0 0 - 25 39 - 63 63 - 28 69 - 67 64 - 68 63 - 41 55 - 0 0 48.9 49 64 - 40 42 - 20 36 - 60 66 - 70 40 37.6 40 51 - 0 0 260.6 53 57 306.8 70 62 6.1 70 53 80.8 70 50 0.0 - - 207.8 - - 112.0 - - 51.6 - - 126.5 - - 0.0 - - 24.7 - - 250.1 126.5 178.9 354.3 - - 84.9 - - 60.6 - - 80.0 - - 50.6 3.6 12.5 53.7 - - 125.5 32.3 252.5 545.4 19.6 30.6 357.0 0.0 31.4 37.5 4.5 0.0 85.3 0.0 0.0 0.0 Table 5 continued. Basal area % Crown Cover ' Grass Forbs Shrubs Total (m2/ha) moosehorn lens Dairy Cr. 0 .0 0 0. 417 .3 344 .3 142, .7 904 .3 18 .4 68 74 12 .6 0 .0 0. .0 12 .6 23 .4 75 75 303 .5 8 .1 9 .7 321 .3 25 .3 61 45 90 .5 21 .8 0. .0 112 .3 27 .5 44 50 10 .0 0 .0 0 .0 10 .0 34 .4 69 68 6 .8 0 .0 0 .0 6 .8 36 .7 70 60 38 .7 0 .0 0 .0 38 .7 Mountain View 0 .0 0 0 102 .2 262 .1 120 .5 484 .8 13 .8 61 62 53 .9 57 .4 9 .0 120 .3 23 .0 60 71 3 .9. 83 .0 28 .1 115 .0 23 .0 61 49 28 .8 1 .5 0 .0 30 .3 23 .0 88 78 15 .7 0 .8 19 .8 36 .3 39 .8 91 90 2 .3 0 .5 8 .1 10 .9 41 .3 45 55 44 .5 8 .6 0 .0 53 .1 Dead '74 20 .4 39 40 66 .0 278 .5 129 .9 474 .4 25 .3 72 72 14 .9 0 .0 0 .0 14 .9 Hef f l e y Cr. - Road 0 .0 0 0 62 .7 86 .9 272 .4 422 .0 13 .8 76 75 19 .0 13 .7 60 .5 93 .2 16 .1 83 67 4 .7 0 .0 0 .0 4 .7 H i l l 0 .0 0 0 554 .4 61 .6 132 .2 748 .2 20 .7 52 57 104 .9 10 .5 0 .0 115 .4 20 .7 64 58 48 .2 10 .7 68 .0 126 .9 20 .7 71 75 77 .8 0 .0 2 .0 79 .8 Table;.6. Grass y i e l d s (kg/ha) under various stand stocking and density. Crown cover data are from moosehorn % CC class 1: 0-10; 2: 11-30; 3: 31-70; 4: 71-96. Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 46.0 Crown cover cla s s 1 >2 .3 '4 :1 •. /2: I, 3 k 4 •. l ; " 2 3 3 4 4 .1 1.1 2 3 4 30.7 13.6 6.3 6.4 0.5 21.9 35.7 25.8 0.0 0.0 76.6 526.4 11.5 23.3 83.5 0.0 0.0 2.7 234.5 0.0 80.5 9.3 63.4 13.5 88.6 217.6- 380.4 119.1 181.7 57.9 20.4 67.7 248.5 388.5 124.1 37.7 0.0 0.0 36.5 169.1 0.0 76.7 0.0 0.0 0.0 193.6 276.0 72.1 42.0 0.0 0.0 0.0 364.6 0.0 42.9 28.5 6.6 0.0 9.0 263.0 5.7 44.8 0.0 43.1 . 0.0 221.1 0.0 14.1 11.1 44.1 360.3 45.1 15.7 16.4 108.2 412.4 0.0 22.1 10.6 272.6 0.0 11.0 10.0 623.7 15.5 4.0 0.0 124.0 0.0 57.9 180.0 0.0 0.0 Table 6 continued Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 Crown cover class 1 2 3 4 1 2 3 4 53.2 136.0 18.7 51.5 34.9 0.0 75.9 0.0 0.0 25.0 112.6 29.2 48.9 85.4 91.0 101.0 52.2 8.1 621.4 8.2 743.0 5.7 206.9 197.0 396.0 6.0 41.4 175.0 85.5 77.0 1.0 128.7 83.0 23.1 - 34.4 34.5 - 46.0 1 2 3 4 1 2 3 4 Mean 215.92 St.dev. 205.59 Coef Var. 0.95 90.13 55.35 116.00 109.4 1.29 1.98 40.30 44.18 42.44 58.21 1.05 1.32 24.87 5.36 37.71 8.01 1.08 1.49 Table 7. Forb y i e l d s (kg/ha) under various stand stocking and density. Crown cover data are from moosehorn. % CC class 1: 0-10; 2: 11-30; 3: 31-70; 4: 71-96. Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 46.00 Crown cover class '•; 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 254.8 499.7 0.0 0.0 0.0 0.9 0.0 34.0 0.0 0.0 18.5 0.0 0.0 0.0 0.0 0.0 0.0 197.8 0.0 0.0 0.0 13.6 0.0 0.0 178.7 78.4 0.0 12.6 0.0 0.0 0.0 110.5 0.0 32.4 0.0 17.3 0.0 0.0 18.7 0.0 21.7 54.4 0.0 0.0 1.8 0.0 0.0 0.0 20.3 0.0 0.0 0.0 52.4 0.0 0.0 0.0 0.0 0.0 0.0 40.5 0.0 16.9 0.0 0.0 0.0 36.2 0.0 0.0 0.0 0.0 578.6 0.0 0.0 0.0 0.2 74.4 124.6 2.3 0.0 599.0 146.0 1.0 0.0 125.3 39.5 2.2 0.0 304.3 5.8 33.4 421.7 0.0 0.0 267.9 15.3 0.0 54.5 56.0 0.0 225.0 141.2 0.0 Table 7 continued Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 46.00 Crown cover class , 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 25.2 130.2 0.0 37.5 300.7 0.0 60.0 183.2 0.0 61.1 18.9 76.0 0.2 1.1 0.0 108.1 0.0 41.7 0.4 0.0 0.0 42.1 0.0 0.0 Mean 151.07 St.dev. 167.17 Coef.Var. 1.11 40.13 5.00 70.61 10.66 1.76 2.13 6.30 3.43 15.13 6.88 2.40 2.01 0.02 0.23 0.06 0.64 3.00 2.78 Table 8. Shrub yi e l d s (kg/ha) under various stand stocking and density. Crown cover data are from moosehorn. %CC class 1: 0-10; 2: 11-30; 3: 31-70; 4: 71-95. Basal area ( m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 46.0 Crown cover class 1 2 3 4 1 . 2 : 3 44 i.l .2 3 3 , 4 .. 1 : 2 3 4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 131.8 122.5 125.7 0.0 27.5 0.0 0.0 147.5 0.0 0.0 0.0 22.4 0.0 0.0 178.5 0.0 6.3 0.0 0.0 0.0 0.0 58.5 0.0 0.0 0.0 0.0 0.0 0.0 331.4 32.3 18.6 0.0 0.0 0.0 34.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 192.4 0.0 0.0 0.0 0.0 0.0 9.0 534.5 0.0 36.1 0.0 0.0 0.0 283.2 0.0 20.8 0.0 0.0 236.5 0.0 27.2 0.0 0.0 117.3 0.0 13.0 0.0 0.0 9.4 18.0 0.0 217.1 34.4 121.8 0.0 35.9 0.0 0.0 0.0 0.0 0.0 165.4 0.0 0.0 280.5 0.0 0.0 Table 8 continued Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 46.0 Crown cover cla s s 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 141.0 0.0 0.0 393.8 306.1 12.9 321.0 153.2 0.0 233.9 60.1 0.0 34.9 18.2 136.9 102.1 249.0 0.0 108.1 0.0 0.0 0.0 0.0 259.1 0.0 0.0 7.9 Mean 174.20 St. Dev. 133.97 Coef Var. 0.77 33.49 18.20 74.80 33.77 2.23 1.97 0.0 5.54 undefined .,11.08 2.00 0.0 5.41 undefined 12.09 2.24 Tab)le 9. Total forage y i e l d s (kg/ha) under various stand stocking and density. Crown cover data are from moosehorn. %CC cla s s 1: 0 - 1 0 ; 2: 11-30; 3: 31-70; 4: 71-95. Basal area ( m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 46.0 Crown cover 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 186.5 111.3 163.5 124.6 57.6 0.5 235.0 34.3 124.5 182.5 0.0 132.6 59.2 132.4 147.0 111.4 298.5 20.5 59.8 89.5 0.0 285.5 181.5 85.4 38.6 6.4 147.4 23.6 105.5 0.0 226.7 126.2 59.5 137.2 323.2 0.0 0.0 13.5 348.0 69.7 50.5 0.0 20.5 0.0 63.4 20.4 445.8 99.4 33.4 386.7 0.0 0.0 57.9 0.0 326.7 59.3 98.9 420.9 22.8 35.7 0.0 34.3 386.6 20.0 11.6 40.3 23.3 111.0 0.0 0.0 193.6 513.2 66.9 72.1 80.5 45.3 0.0 9.0 609.4 60.7 42.9 131.7 181.7 0.0 838.4 100.6 97.8 124.1 55.0 0.0 540.5 80.0 34.9 131.1 0.0 44.1 1175.4 86.5 42.9 62.3 0.0 108.4 604.1 32.5 37.4 28.5 6.6 871.6 3.4 30.0 0.0 43.1 966.1 6.3 128.0 11.1 464.2 648.9 91.3 16.4 601.7 234.5 0.0 10.6 Table 9 continued ... Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 48.0 Crown cover cla s s 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 .486.5 296.0 18.7 '386.5 248.5 0.0 441.9 201.4 0.0 444.0 276.0 .42.1 407.0 0.0 91.0 394.9 5.7 8.1 717.4 0.0 955.9 45.71i 457.0 124.6 612.2 155.4 89.4 5.8 0.0 151.3 90.9 141.2 336.1 43.9 128.7 Table 9 continued Basal area (m2/ha) 0.0 - 11.5 11.6 - 23.0 23.1 - 34.4 34.5 - 48.0 Crown cover cla s s 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 90.9 548.9 539.3 295.5 45.3 108.0 197.7 6.0 83.1 175.4 85.5 Mean 518.08 St. Dev. 256.63 Coef Var. 0.50 117.33 141.02 133.33 79.07 61.37 146.04 145.55 108.35 0.52 1.04 1.09 1.37 83.85 37.12 92.15 50.10 8.58 100.81 50.05 44.15 58.37 12.22 1.20 1.35 0.50 1.17 1.42 - 39 - Scattergrams (Figures 10 to 24 i n c l u s i v e ) indicated non- l i n e a r r e l a t i o n s h i p s between the dependent and independent v a r i a b l e s . Therefore, s t r i c t l i n e a r models were not examined for regression modeling. Constants i n X + 1 and Y + 1 i n hyperbolic and logarithmic analyses re s p e c t i v e l y are used to avoid mathematical problems because i n some cases X and Y equaled zero. The logarithmic transformation makes variances along the regression l i n e more uniform. For the logarithmic model, the standard errors of the estimate were transformed into nonlogarithmic form. The transformation procedure i s as follows: The SEE = \ | SS /df r r N where SS^ = sum of squares r e s i d u a l df = degrees of freedom r e s i d u a l r Transformation: SS n E j = l (7j + 1) - 10 (b 0 + p i X i j ) .th , . j 2 = j forage y i e l d n = number of observations Y. = Y , ; f i n d i v i d u a l l y J j ' g J ' j ' S j X_̂  = i 1 * * 1 independent v a r i a b l e ; i = 1, 2 here b Q , b^ = regression c o e f f i c i e n t s defined formally. - 40 - = n-m-1 m = number of independent variables i n the s i g n i f i c a n t model under consideration. 1/2 n (b Q + Z b ± X i ; j) tn-m-1] (y + 1) - 10 x The models reported below (Tables 10, 11) were s i g n i f i c a n t at 95 percent p r o b a b i l i t y l e v e l . Analyses were by l e a s t squares technique - elimination procedure. Some dependent variables are described by two s i g n i f i c a n t models; the models are i n the order they were encountered through elimination. The second model i s shown for checking how much p r e c i s i o n i s l o s t by dropping one s i g n i f i c a n t v a r i a b l e . This becomes relevant when i t may be costly to measure a v a r i a b l e . C o e f f i c i e n t s of determination are noftfan'sf drifted "to iriOnldgarithmic form: therefore i t would be unwise to compare f i t n e s s of hyperbolic with 2 logarithmic models using R values. I t i s acceptable to compare between logarithmic models using these values. Better f i t of logarithmic models i s evident. Yields are also shown graphically i n figures 10 — 24 i n c l u s i v e . Enlarging p l o t s i z e by combining data from 4 microplots (Table 5) did not reduce standard errors s i g n i f i c a n t l y . This resulted i n an increase of standard errors i n some logarithmic models. Apparently, - 41 - Table 10. Hyperbolic models probability l e v e l : s i g n i f i c a n t at forage y i e l d s . 95 percent Y = b 0+b 1x 1+b 2(i/x 1+i) SEE 2 %R F Y t = 141.356-2 .9378X-J+365 . 387 (l/X^+l) 147.212 54.238 100.150 : 71.7137+444.595 ( 1 / X ^ l ) 148.468 53.178 193.097 Y g = 47.9099+170.009 (1/X +1) 123.035 22.633 36.275 Y f = 15.1861+136.377 (1/X^+l) 95.1174 23.952 -.39.056 Y s = 9.0021+165.614 (1/X +1) .'73.6212 43.673 96.143 Y = b +b1X0+b. (l/X.+l) o 1 z z z Y t = 169.248-1.4151X2+345.092 (1/X2+1) 146.974 54.386 100.748 : 81.902+164.971 (1/X2+1) 148.661 53.060 192.135 Y g = 52.4075+164.584 (1/X2+1) 123.304 22.295 35.578 Y f = 144.7689-1.8557X 92.9141 27.430 46.881 Y s = 13.2240+161.056 (1/X2+1) 73.7918 43.410 95.126 Y = b +b1X.+b„ (1/X.+1) + b„X„+b. (l/X.+l) o i l / 1 J Z 4 Z Y t = 167.764+348.384 (1/X +1)-1.5260X2 146.269 54.820 102.538 • 71.7132+444.595 (1/X +1) 148.468 53.178 193.079 Y g = 47.9099+170.009 (1/Xj+l) 123.035 22.633 36.275 Y f = 259.417-5. 9193X^-3363.590 (1/X +1) +3255.490 (1/X2+1) 92.359 29.454 16.979 • 18.5076+133.330 (1/X2+1) 95.048 24.060 39.295 Y s = 9.0091+165.614 (1/Xj+l) 73.621 43.673 96.143 - 42 - Table 10 continued... Y = b +b.X,+b. (1/X +1) o 1 3 2 J SEE 2 %R F Y t = 200.798-1.8972X3+314.084 (1/X3+1) 147.617 53.986 99.138 Y g = 52.3948+164.643 (1/X3+1) 123.293 22.308 35.605 Y f = 144.550-1.9323X 94.103 25.567 42.529 Y s 13.216+161.093 (1/X3+1) 73.783 43.426 95.181 Y b +b1X1+b0(l/X1+l)+b_X_+b(1/X.+1) Y t = 304.978-3.6461X -2.0709X +209.885 (1/X +1) 145.208 55.739 70.521 170.698-3.4118X +344.718 (1/X3+1) 146.959 54.395 100.788 Y g = 213.932-3.1847X -1.1880X3 121.524 25.131 20.643 190.743-4.9396XX 123.509 22.037 35.047 Y f = 144.550-1.9323X 94.103 25.567 42.592 Y s = 9.0021+165.614 (1/X +1) 73.621 43.673 96.145 - 43 - Table 11. Logarithmic^Q models s i g n i f i c a n t at 95 percent p r o b a b i l i t y l e v e l : forage y i e l d s . log(Y+l) = = b +b,Xn o 1 1 SEE 2 %R F log(Y t+l) = 2.5699-0.0423X1 130.590 34.410 89. 189 log(Y +1) = 2.0582-0.0349X1 44.104 27.171 46. 262 log(Y f+l) = 1.6524-0.0443X1 :16.505 39.514 81. 007 log(Y s+l) = 1.6258-0.0452X1 13.373 38.477 77. 550 log(Y+l) = o 1 2 log(Y t+l) = 2.5206-0.0167X2 124.434 29.930 72. 610 log(Y +1) = 2.0173-0.0130X2 41.084 20.364 31. 709 log(Y f+l) = 1.7835-0.0201X2 22.399 43.455 95. 293 log(Y s+l) = 1.5435-0.0163X2 10.810 26.955 43. 745 log(Y+l) = V b l X l + b 2 X 2 log(Y t+l) = 2.7357-0.0289X1-0.0089X2 200.815 39.428 55. 003 : 2.5699-0.0423X1 145.987 34.410 89. 189 log(Y +1) = 2.0582-0.0349X1 44.108 27.171 46. 262 log(Y f+l) = 1.8897-0.0228X^0.0131X2 29.945 48.619 58. 195 • 1.7835-0.0208X2 22.398 43.455 95. 293 log(Y s+l) = 1.6258-0.0452X1 13.375 38.477 77. 550 - 44 - Table 11 continued... log(Y-KL) = b +b,X3 o 1 . . SEE 2 %R F log(Y t+l) = 2.6169-0.0185X3 150.326 28.968 69.328 log(Y +1) o = 2.1062-0.0154X3 50.601 24.320 39.842 log(Y f+l) = 1.7829-0.0209X 22.409 40.560 86.614 log(Y g+l) = 1.6382-0.0189X 13.662 31.089 55.941 log(Y+l) b +b 1X 1+b„X. o 1 1 2 3 log(Y t+l) = 2. 7749-0.0296X --0.0093X3 221.696 38.655 53.245 2.5699-0.0423XX 130.590 34.407 89.174 log(Y +1) = 2.2138-0.0232X1--0.0080X3 66.179 30.605 27.124 • 2.0582-0.0350X1 44.104 27.171 46.262 log(Y f+l) = 1.9013-0.0255X -•0.0128X3 30.869 47.446 55.522 : 1.7829-0.0209X 22.409 40.560 84.614 log(Y s+l) = 1.7902-0.0327X -•0.0084X3 21.353 41.725 44.034 1.6258-0.0452X 13.373 38.477 55.473  - 46 - FIG. 1 1 . RELATIONSHIP BETWEEN FORB YIELDS PND 5TPND DENSITY Y=(49.916 * 0 . 9 0 3 * ) - ! 45.0 0.0 S.D -1 10.0 X1 —1-*— 15.0 20.0 25.0 30.0 STAND BRSPL PREP (SQ.M/HR) 35.0 40.0 50 - 47 - F1G.1 2 RELATIONSHIP BETWEEN SHRUB YIELDS AND STAND DENSITY Y=(42.247 K 0 . 9 0 1 ) - 1 . or JZ X a i Oo $ CO £° CO in cn- T 10.0 -r 1 20.0 25.0 STAND 0RSAL AREA 30.0 ISQ.M/HAJ 15.lT -1 50.0 - 48 - - 49 - - 50 - 3* FIG . l 5. RELRTI0N5HIP BETWEEN SHRUB YIELDS AND STOCKING Y=134.954 * 0 . 9 6 3 X ) - 1 , 40.0 ;CROWN COVER 60.0 MOOSEHORN 00.0 ~ l — 90.0 ~1 100.0  52 - FIG. 17- RELATIONSHIP BETWEEN FORB YIELDS AND STOCKING Oo t— X CD Q I CD Oo Y=(60.660 X 0.953 20.0 30.0 40.0 50.0 60.0 70.0 X CROWN COVER - WIDE-ANGLE LENS 80.0 -M—tjl so.o 100.0 - 53 - 1G. 18. RELATIONSHIP BETWEEN SHRUB YIELDS RND STOCKING Y r ( 4 3 . 4 7 1 X 0-.957 J - l , 20.0 I 30.0 40.0 50.0 J CROWN COVER - W1DE- 60.0 ANGLE LENS 70.0 BO.O 90.0 100.0 - 54 - - 55 - o FIG. 20- RELATIONSHIP-BETWEEN DRY WT. BIOMASS AND STOCKING GR: Y = U 0 4 . 0 6 4 X 0 . 9 7 ] 1-1. F O : Y=(60 .744 X 0 . 9 5 5 ) - ] . S H : Y=(34 .954 X 0 . 9 6 3 ) - ] . 40.0 50.0 60.0 XCR0WN COVER - MOOSEHORN T 70.0 BO.O i 90.0 100.0 - 56 - . RELATIONSHIP BETWEEN DRV WT. BIOMASS AND STOCKING GR: Y = U 2 7 . 7 0 3 X 0 . 9 6 5 X ) - 1 . F O : Y=C60.660 X 0 . 9 5 3 X ) - ] . S H : Y=(43.471 X 0 . 9 5 7 X ) - ] . GRASS FQRB5 SHRUBS  FIG. 23. RELATIONSHIP BETWEEN TOTAL FORAGE YIELDS AND STOCKING 1 Y=(331.589 X 0 . 9 6 2 X ) - ] . 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 60.0 90.0 100 ;CROWN COVER - MOOSEHORN - 59 - Table 12. Radial growth (.01mm) at breast height l n Ponderosa pine and Douglas-fir on a medium s i t e at Mountain view. Trees were defoliated i n 1975; increment cores were.extracted, i n winter 1976. Each average i s based on 16 cores. Lw: latewood; Ew: earlywood; R: ";otal annual ring. Diameter class (cm) Averages . v , * i 5 1 5 . 1 - 2 5 . 0 2 5 . 1 - 3 5 . 0 >35' Deg.of Yr.of - x . • de f o l : growth Lw . Ew R." Lw/R Lw Ew R Lw/R Lw Ew R Lw/R Lw Ew R Lw/R Lw Ew R Lw/R P y 0 1975 9.8 33.0 42.8 .228 18.8 69.8 88.5 .212 14.3 46.8. 61.0 .234 20.2 80.0 100.8 .206 15.9 57.4 73.3 .217 1976 20.3 56.0 76.3 .266 . 22.3 64.0 86.3 .258 15.0 50.0. 65.0 .231 38.0 98.5 136.5 .278 23.9 67.1 91.0 .262 DF 0 1975 30.5 66.5 .97 .0 .314 32.3 87.3 119.5 .270 27.3 98.5 125.3 .217 17.5 74.5 92.0 .190 26.9 81.7 108.6 .248 1976 12.3 38.8 50.5 .243 6.8 14.5 21.3 .318 33.0 52.3. 85.3 .387 8.5 23.5 32.0 .266 15.1 32.1 47.3 .320 L 1975 9.5 25.8 35.3 .270 18.5 46.8 65.3 .284 15.3' 44.8 60.0 .254 13.3 52.0 65.3 .203 14.1 42.3 56.4 .250 1976 6.0 11.5 17.5 .343 14.0 42.5 56.5 .248 14.3 27.8 42.0 .339 11.3 43.3 54.5 .206 11.4 31.3 42.6 .267 M 1975 20.3 57.8 78.0 .200 15.3 . 4 5 . 8 61.0 .250 38.8 104.5 143.3 .271 47.0 80.8 127.8 .368 30.3 72.6 102.5 .290 1976 19.8 54.3 74.0 .267 . 21.5 78.3 99.8. .216 17.8 83.5 101.3 .175 29.0 95.0 124.0 .234 22.0 77.8 99.8 .221 H 1975 36.5 80.5 117.0 .312 31.5 88.3 119.8 .263 .. 16.0 57.0 73.0 . .219 9.3 35.3. 44.5 .208 23.3 65.3 88.6 .263 1976 22.0 57.8 79.8 .276 18.5 88.0 106.5 .174 10.0 35.5 45.5 .220 6.3 22.3 28.5 .219 14.2 50.9 65.1 /218        03 - 69 - more p r e c i s i o n may be obtained by increasing the number of sample p l o t s , instead of plo t s i z e . Data on r a d i a l growth i n trees i n 1975 and following that year's d e f o l i a t i o n are summarized i n table 12. Figures 25 — 32 i n c l u s i v e represent h i s t o r i c a l r a d i a l growth at breast height i n trees from the whole study area during the past century. The Douglas-fir curves are based on 150, and the Ponderosa pine curves on 79 increment cores. Discussion Impacts Understory forage y i e l d s and t h e i r v a r i a b i l i t y decrease with increasing stand basal area and percent crown cover. The general trends evident i n the r e s u l t s presented here are common i n the l i t e r a t u r e , but apparently, mathematical, models best describing forage y i e l d s vary. Dodd (1969) found a good l i t of simple l i n e a r models between percent crown cover and forage y i e l d s i n "undisturbed" stands i n higher elevation P. menziesii - oalamagrostis association a few miles northwest of Kamloops. He admitted that curves would describe the data better. Nevertheless he applied l i n e a r models " f o r being more useful ( s i c p. 51)." Later Dodd e_t a l . (1972) f i t both l i n e a r and semi- logarithmic, models on the same data and found both models s i g n i f i c a n t . But because the SEE are i n d i f f e r e n t u n i t s , i t i s not clear which form of model describes the data better. - 70 - A high l i n e a r c o r r e l a t i o n (r = 0.985) between forage y i e l d s and stocking i n Ponderosa pine stands i n eastern Washington was reported by McConnell and Smith (1970). Pase (1958), Jameson (1967) and others have found nonlinear r e l a t i o n s h i p s between y i e l d s and stand density and stocking. Gaines e_t al_. (1954) reported a second degree parabola with 2 "k" p o s i t i v e ( l i n e a r : y = b Q + b^x + b^x ) as describing forage y i e l d s on stand density: but they cautioned that the upturn i n the curve might have been due to inadequacy of data. On the other hand, they c o r r e c t l y alluded to the p o s s i b i l i t y that the upturn might have s i g n i f i e d a point beyond which stand density was increasing at the expense of stocking, thus making more space and l i g h t a v a i l a b l e f or forage production. Jameson (1967) c i t e d a t h i r d degree or cubic parabola^ ("linear: 2 3 y = b Q + b^x + b^x + b^x ) as giving a best f i t of h i s forage y i e l d s on stand density and stocking. A b i o l o g i c a l hypothesis for the shape of the continuous function i s d i f f i c u l t to conceive. These data were obtained under i n s i t u or undisturbed crown cover conditions. In the Southern Pine Region, herbaceous growth i s also inversely related to stand density and crown closure; and forage, y i e l d s are highest i n openings ( B l a i r and Brunett, 1976). In my analyses, standard errors of the hyperbolic functions are much higher than those of logarithmic functions. Both types of models are s i g n i f i c a n t . They describe the data adequately. Because of high errors associated with them, the hyperbolic models would give very wide confidence i n t e r v a l s i f used for p r e d i c t i o n . The logarithmic models are i n v a r i a b l y better f i t t i n g . The c o e f f i c i e n t s of determination are misleading here because of differences i n units of the dependent - 71 - v a r i a b l e i n the two kinds of models. In t h e i r work i n Montana F o o t h i l l s Bunchg'rass Ranges, Van Dyne et a l . (1963) used c o e f f i c i e n t s of v a r i a t i o n to conclude that grasses and forbs were less v a r i a b l e than shrubs. In general, Muegler (1976) concluded s i m i l a r l y . In my study area, grasses are most v a r i a b l e , and forbs more var i a b l e than shrubs. Basal area and crown cover are required to p r e d i c t t o t a l forage y i e l d s w e l l . But separate predictions of grass, forbs and shrubs require only basal area. •The importance of basal area i s not unexpected, as i t i s i n d i c a t i v e of s i t e q u a l i t y and b i o l o g i c a l capacity. In most of the multiple regression models c o e f f i c i e n t s of determination and SEE indicate that crown cover can be ignored i n p r e d i c t i n g forage y i e l d s without n e c e s s a r i l y l o s i n g much p r e c i s i o n . This does not mean crown cover i s not important i n determining forage y i e l d s ; i t means basal area i s more important. Table 13 shows forage y i e l d s for two forest associations within the I n t e r i o r Douglas-fir Zone. Only y i e l d s from openings are compared because of lack of stand density data i n Dodd (1969), and because of possible i n t e r a c t i o n between density and stocking i n t h i s study. Williams Lake i s far t h e r north, cooler and more moist than Pass Lake. As my data are from a d r i e s t area of the three, they f a l l within reasonable expected ranges. At most, 54 percent of the v a r i a t i o n i n t o t a l forage y i e l d s was due to basal area and percent crown cover. These independent v a r i a b l e s accounted for even smaller amounts of the v a r i a t i o n i n separate y i e l d s of grass, forbs and shrubs. L i k e l y , other factors are important i n determining forage production i n t h i s ecotone. Gains et a l . (1954) showed a very high c o r r e l a t i o n between grass and forb - 72 - Table 13 A comparison of forage y i e l d s (Kg/ha) from openings i n two forest associations i n the I n t e r i o r Douglas- f i r Zone. Data for Pass and Williams Lakes extracted and further analysed from Dodd (1969). Data for the other association are from s i x l o c a l i t i e s studied here. Pseudotsuga - Calamagrostis Pseudotsuga - P.Ponderosa - Pass Lake (Dry s i t e ) Williams Lake Agropyron spp. N. Thompson Valley - So. of Kamloops Lake 632.8 459.4 932.5 1538.8 Avge(s:.: 674.9 207.8 354.3 545.4 904.3 484.7 422.0 Avge.:486.4 y i e l d s and forest l i t t e r amounts. A thick mor forest f l o o r may Imother vegetatively regenerating plants; i t makes mineral s o i l i n a c c e s s i b l e to seeds. Severson and Kranz (1976) reported very poor logarithmic f i t of forage y i e l d data on basal area i n aspen stands. While the y i e l d s decreased as proportion of Ponderosa pine increased, p r e d i c t a b i l i t y increased. They employed a double sampling technique of r a t i o estimation to obtain dry weight from fresh weight of forage, instead of drying a l l samples. Therefore i n t h e i r regression analysis - 73 - they actually used forage yield estimates. It is not indicated, whether the error associated with the use of estimates was accounted for. It is not known whether the insignificance of their models was associated with the double sampling procedure. Notwithstanding, the authors are of the opinion that their models, were insignificant because they did not t a l l y the most important independent variable. Probably in Aspen and other vegetatively regenerating stands, "roots, total biomass or growth" are more predictive of forage yields than basal area or crown cover. Increases of understory vegetation yields in response to tree defoliation by Douglas-fir tussock moth are evident. Greatest increases should be expected in cooler and more moist microsites in the ecotone, nearer the Pseudotsuga calamagrostis association and along creeks. On dry sites, where yields are ordinarily low, forage produc- tion may increase several fold, but i t does not amount to much except possibly where complete defoliation results in mortality of large groups of trees. In their exploratory work, Tisdale and McLean (1957) observed forage yields under several canopies and basal area levels in several seres in the interior. They noted a pioneer aspen sere with 2 basal area of 2 0 . 7 m /ha yielded an average of 270 kg/ha of forage, and 2 the climax Douglas-fir sere with a basal area of 5 2 . 1 m /ha yielded only 114 kg/ha. Forage yields in transition seres of Lodgepole pine and mixed conifer/aspen were not given. In a pine stand which was k i l l e d by D&ndroctonus beetles, probably D. ponderosae (monticolae)3 forage yields were "... 50 percent greater than for comparable site occupied by a b n o r m a l stand of Pinus." This appears to be the f i r s t - 74 - time an.insect was recognized and documented i n the l i t e r a t u r e as an important e c o l o g i c a l force i n range management i n the i n t e r i o r . Munro and McT. Cowan (1947) had recognized logging and f i r e i n th i s regard. Transmissivity of i n s o l a t i o n , and basal area i n Ponderosa pine stands are s i g n i f i c a n t l y r e l a t e d i n a hyperbolic fashion (Solomon et a l . , 1976). Reducing stand density provides more l i g h t to the understory. Following d e f o l i a t i o n , more moisture and l i g h t are a v a i l a b l e under the canopy; and animals frequent dead patches thereby e f f e c t i n g s o i l s c a r i f i c a t i o n . In one stand, two years following i t s death, forage y i e l d s exceeded those i n openings (Table 14; Figure 33). This also i l l u s t r a t e s the importance of moving shade provided by the dead trees or snags. In adjacent undefoliated stands, forage y i e l d s were extremely low. Not only does d e f o l i a t i o n provide more l i g h t and moisture to understory vegetation, i t also makes available more nutrients which leach out of the forest f l o o r and f r a s s . When d e f o l i a - t i o n r e s u l t s i n tree mortality, competition - for these resources i s greatly reduced and understory vegetation f l o u r i s h e s . Dolph (1973) gave an empirical estimate of about 7,900 animal unit months as the magnitude of range benefits following a tussock moth outbreak i n the U.S. P a c i f i c Northwest. From h i s data, i t i s not clear whether these benefits are from 70.5 thousand or 80.thousand hectares. D e f o l i a t i o n may have d i f f e r e n t e f f e c t s on forage q u a l i t y and y i e l d . Increases i n y i e l d do not n e c e s s a r i l y imply increased capacity for range land. In a black tupelo forest i n the southern U.S. extensive d e f o l i a t i o n by the f o r e s t tent c a t e r p i l l a r , Matacosomaid%sstv£ay-'•reduced wild game, population. This was r e f l e c t e d i n hunters' success. Besides i t s Table 14. A comparison of forage y i e l d s (kg/ha) i n several pl o t s at Mountain View. The two stands merge into each other on the same side of a main haul road, have the same slope, aspect etc. Note higher average y i e l d s (534) under dead trees and crown cover 50%; c f . average y i e l d s (485) i n openings. Dead Stand, Defoliated Undefoliated Stand Openings 2 years before Basal area (m2/ha) 25.3 25.3 % Cr. cover 20 32 50 55 56 64 84 84 Grass 13.6 112.6 85.4 52.2 0.0 10.0 6.6 43.1 124.0 180.0 53.2 51.5 Forbs 499.7 130.2 300.7 183.2 0.0 0.0 0.0 .0.0 304.3 421.7 267.9 54.5 Shrubs 0.0 306.1 153.2 60.1 0.0 0.0 0.0 0.0 35.9 0.0 165.4 280.5 Tot a l 513.3 548.9 539.3 295.5 0.0 10.0 6.6 43.1 464.2 601.7 486.5 386.5 To face page 76 Figure 33. Response of understory vegetation at Mountain View. a) Top: Fisheye view - Foreground: Trees d e f o l i a t e d and dead two years ago (1974). Bottom: Pho,tmgry.^h'. f ̂ Background: N e g l i g i b l y d e f o l i a t e d . Bottom: Photograph from the interphase between the dead and undefoliated parts of the stand.  To face page 77 Figure 33. Response of understory vegetation at Mountain View. b) Fisheye and ordinary views of forage response in one plot in foreground (a, above). Forage yields (kg/ha): Y g = 66.0; Y = 129.9, under % CC 39m, 40 lens, and basal area of 20.7m2/ha (dead trees). - 77 - To face page 78 Figure 33. Response of understory vegetation at Mountain View. c) T6p.<:̂  Zone of t r a n s i t i o n between, the d e f o l i a t e d and undefoliated parts. Note very sparse vegetation i n the understory. d) Bottom: Understory vegetation i n the undefoliated part of the stand. Forage y i e l d s (kg/ha): Y =14.9; Y = Y =0.0, under % CC = 72.0m = g f s lens and basal area 25.3m2/ha.  - 79 - adverse e f f e c t s on the trees, d e f o l i a t i o n encouraged growth of less desirable brush and vines. Apparently, t h i s caused w i l d l i f e to abandon the devastated stands for safer ones with overstory (R.C. Morris, 1976). In the Douglas-fir tussock moth s i t u a t i o n , the patchy nature of i n f e s t a t i o n s makes i t possible for w i l d l i f e to f i n d refuge i n the general area of an outbreak. Because of possible recovery by some de f o l i a t e d trees, the question of stand development following d e f o l i a t i o n i s obviously important i n our attempts to determine magnitudes of the range benefits accruing following d e f o l i a t i o n . . How much d e f o l i a t i o n , and at what frequency can a Douglas-fir tree continue growing or l i v i n g ? What i s the recovery p o t e n t i a l of the d e f o l i a t e d tree? I t appears we must reduce crown cover to le s s than f i f t y percent i n order to r e a l i s e geometric increases i n forage y i e l d . Eddlemann and McLean (1969) also define f i f t y percent crown cover as a c r i t i c a l l e v e l i n Ponderosa pine stands. How long can the y i e l d increasesWe maintained? In an e c o l o g i c a l study of f i r e disturbance i n the southern U.S., B l a i r and Brunett (1976) concluded that kind, i n t e n s i t y and length of i n t e r v a l s (frequency) between disturbance are the most important factors i n determining stand composition. This may be true for c h r o n i c a l l y i n f e s t e d Douglas-fir stands i n the i n t e r i o r . Let us suppose we are dealing with a stand with seventy percent crown cover. Crown cover must be reduced to f i f t y percent to r e a l i z e s i g n i f i c a n t increased forage-, y i e l d s . Also suppose crown cover i s f o r t y - f i v e percent following d e f o l i a t i o n . While we needed to reduce crown cover by more than twenty percent, a l l the stand requires - 80 - now i s a f i v e percent - probably two years - gain of fo l i a g e to revert to i t s condition of low understory forage y i e l d s . Often we are dealing with stands uneven i n age, height, stocking and health. When these variables are superimposed on the crown cover i n our example above, i t becomes obvious that we cannot j u s t i f i a b l y generalise about impacts of the d e f o l i a t i o n on forage beyond the statements made here. Moreover, the dynamics of stand development are complex (Smith, 1974) enough without superimposing upon them an extra e c o l o g i c a l force. Figure 34 i s a conceptual model of forage response behaviour i n two susceptible stands. Stand a}y has higher density than stand, b,' - for s i m p l i c i t y , assume other factors are equal. The differe n c e i n density i s r e f l e c t e d i n higher i n s i t u forage y i e l d s i n stand b , Y. > Y Various degrees of d e f o l i a t i o n increase forage y i e l d s to bo ao ° d i f f e r e n t l e v e l s . Assume equal degrees of d e f o l i a t i o n i n both stands: ."defoliation r e s u l t s i n higher forage y i e l d s i n stand b, Y, . > Y .. At bx ax very low degrees of d e f o l i a t i o n , the difference i n p r o d u c t i v i t y between the two stands narrows, (Y. r-. - Y c) < (Y, _ - Y _ ) . Following d e f o l i a - bo ao; b l a l t i o n , the tendency i s f o r the stand to revert to i t s o r i g i n a l state: y i e l d approaches the o r i g i n a l l e v e l , Y, .—^Y, , Y .—*Y . Probably • ° bx ' bo a x ' ao both stands require about the same period to revert to the o r i g i n a l state of forage p r o d u c t i v i t y ; and following a low degree of d e f o l i a t i o n , that state would be reached i n a shorter period of.time than following higher degrees of d e f o l i a t i o n s , ta^'pi^t\:)^' t b 6 < < ^ 2 * C b l ' a n C* t « t < t Cl e a r l y , increased d e f o l i a t i o n benefits grazing i n 3D Q./. 3.1. at l e a s t two e x p l i c i t ways: by increasing y i e l d s more or less immediately, and by sustaining the y i e l d s for a longer period. —I 1 1 1 1 1 1 20 30 40 50 60 75 90 Degree of D e f o l i a t i o n (%) Figure 34. A conceptual model showing response behaviour of forage y i e l d s i n 2 defo l i a t e d stands with d i f f e r e n t density l e v e l s . Stand a; Stand b. B A A > B A B ; Y F E > Y 3 Q - 82 - Low forage y i e l d s i n , and i n a c c e s s i b i l i t y of thick tree patches (Fig. 35) to domestic and wild ungulates which are of concern i n t h i s ecotone (McLean e_t a l . , 1970) , leads one to question whether such patches should be included i n range land inventory. C r i s s - c r o s s i n g by dead trees f a l l e n a f t e r t h e i r d e f o l i a t i o n may impede a c c e s s i b i l i t y , but only to a smaller extent. Only patches occupied by dead trees and trees s e r i o u s l y d e f o l i a t e d to the extent which requires many years to regain suppressive crown cover represent a r e a l i s t i c increase i n the inventory. In southern Alabama, Gaines e_t a l . (1954) mentioned i n d i v i d u a l Longleef pine trees between 18 and 36 cm dbh. i n f l u e n c i n g grass production within a maximum distance of only 2.4 meters from the trunk - crown- widths were not given. On the other hand a group of trees, presumably of s i m i l a r s i z e , influences grass production within a broader zone of 9 m from the f o r e s t edge. The difference i s probably due to microclimatic influence of the f o r e s t "wall". By c o r o l l a r y , following d e f o l i a t i o n , more forage may be r e a l i z e d from along f o r e s t walls than under i n d i v i d u a l open grown trees. Figure 36 shows an impressive response of understory forage under a dead, more than 150 year-old open grown Douglas-fir tree of 86.5cm dbh and 14m crown width, near Cherry Creek. C l e a r l y the zone of response was delineated by the crown. Such response r e f l e c t s also a greater supply of nutrients from frass and needles following d e f o l i a t i o n . Within a stand, increasing crown cover r e s u l t s i n reduced forage y i e l d s ; but i t favors grass production at the expense of forbs and shrubs. This i s true for most l e v e l s of stand density. The same To face page 83 Figure 35. Top: A dense, completely d e f o l i a t e d p l o t at Dairy Creek. Forage y i e l d s (kg/ha): Y = 10.0; Y f = Y =0.0, one year following d e f o l i a t i o n . Basal area = 2 27.6m /ha; % CC = 44m, 50 lens. Forage y i e l d s l i k e l y to i n c r e a s e . d r a s t i c a l l y i n time i f most trees die. Bottom: A dense, undefoliated p l o t near Cherry Creek - 1975. Forage y i e l d s (kg/ha) Yfc = 0.0 - 83 - To face page 84 Figure 36. Understory vegetation response under a d e f o l i a t e d , now dead, open grown Douglas-fir tree at Cherry Creek - 1975. a. Tree C h a r a c t e r i s t i c s : Diameter = 86.5 cm; height = 26.5 m; crown width = 14 m; age 150 years. - 84 - To face page 85 Figure 36. b. Top: Close up view, i n summer. Bottom: Close up view, i n winter. Note the apparent de l i n e a t i o n of the zone of response by crown projection. Downy brome and Pine grass most abundant. A - 86 - conclusion i s evident from examining forage composition under 1 s i m i l a r stocking l e v e l s on increasing density; Stand density and stocking, and probably other factors have an interacting, e f f e c t on forage y i e l d and composition (Table 15). At lower stocking and density l e v e l s grass i s l e s s dominant, but i t s t i l l constitutes a higher porportion of biomass than forbs and shrubs. In many cases reduction i n tree growth following d e f o l i a t i o n i s considered so common that i t i s often assumed and used to j u s t i f y i n s e c t control measures. The loss i n tree production i s relevant only i n s urviving trees; losses due to mortality may be higher. Tree form may be impared by top k i l l and formation of spikes, bayonets and forks. This i s s i g n i f i c a n t i n young stands. In 1973 extensive top k i l l i n a fo r t y one hectare stand near Osoyoos was noted i n a Forest Insect and Disease Survey Annual Report. D e f o l i a t i o n may reduce photosynthetic surface enough to a f f e c t tree growth. T h e o r e t i c a l l y , serious reduction i n tree growth should be expected because the tussock moth d e f o l i a t e s from above, where current year needles and t h e i r biomass are concentrated ( S i l v e r , 1962; Smith, 1970). Gordon (1962) studied competitive e f f e c t s of common understory species on tree r a d i a l growth i n the "east side pine type" i n C a l i f o r n i a . Removal of bunchgrass resulted i n increased radial.growth i n widely scattered Ponderosa and J e f f r e y pine trees. Possibly, i n my study area, increased p r o d u c t i v i t y of understory forage following d e f o l i a t i o n may prevent r e s i d u a l trees from r e a l i s i n g s i g n i f i c a n t growth increment. In h i s analysis of 4 dominant and codominant coastal Douglas-fir trees, S i l v e r (1962).found the current Table 15. Percent forage composition under crown cover, by stand density classes. Crown cover classes: 1: 0-10% (mostly openings); 2: 11-30%; 3: 31-70%; 4: >71%. Maximum CC = 95% for moosehorn, 90% for wide angle lens. - indicates no plots obtained i n treatment. Data from 172 p l o t s . Basal Area Class ( 2 m /ha) 0 - 11.5 11.6 - 23 .0 23.1 - 34. 4 34.5 - 50.0 Crown cover class 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 Moosehorn Grass 40 _ 3 51 49 100 87 83 - - 96 92 Forbs 28 - - - - 97 27 8 0 13 7 - - <1 4 Shrubs 32 - - - 0 22 43 0 0 10 - - 4 4 Wide angle lens - ^ - Grass 40 _ - 49 67 - 84 100 - - 91 21 Forbs 38 _ - 30 17 - 11 0 - - 9 4 Shrubs 32 — _ — - — 21 16 — — 5 0 _ _ 0 75 - 88 - year f o l i a g e i n the upper 1/3 amounted to over 12 percent more than i n the lower 2/3. The current year f o l i a g e i s preferred food by the tussock moth (Beckwith, 1976).. Further analysis of S i l v e r ' s data shows there are more needles per l i n e a r 2.5 cm (1 inch) of f o l i a t e d twigs i n the lower 2/3: Tree number 1 2 3 4 No. of needles per l i n e a r 2.5cm. Top 1/3: 261 230 229 257 Bottom 2/3: 290 161 299 273 This implies more d i l u t i o n of current year f o l i a g e i n the lower parts of the crown; a higher concentration provides a better chance for the i n s e c t to locate good food i n the upper crown. We may suppose that weather and both forage and tree growth are r e l a t e d ; but McLean and Smith (1973) were unable to f i n d s i g n i f i c a n t c o r r e l a t i o n between forage y i e l d s and tree ring growth. The high v a r i a t i o n i n y i e l d s and r i n g width behaviour i s a t t r i b u t e d to l o c a l conditions or microsite. We may assume that weather d i r e c t l y a f f e c t s the tussock moth as well as tree growth. The insect also a f f e c t s trees so that the impact on tree growth i s l i k e l y a summation of at l e a s t climate and d e f o l i a t i o n . Trees a f f e c t the insect i n a feedback fashion: - 89 - As Koerber and Wickman (19.70) emphasized, an outbreak may only magnify the impact of the weather i f the weather correlated with the outbreaks retards tree growth. The Duff and Nolan (1953) concept i s not h e l p f u l i n i s o l a t i n g impacts of several e x t r i n s i c . o r "environmental";.^factors such as insects and weather. So I examined impacts on tree growth by analysing r i n g growth behaviour i n Ponderosa pine and undefoliated Douglas-fir trees, as controls, and i n trees d e f o l i a t e d to d i f f e r e n t degrees. Various workers have examined tree growth following s i l v i c u l t u r a l treatments such as pruning, thinning and f e r t i l i z a t i o n , and following n a t u r a l and man-made, disasters of d e f o l i a t i o n . E f f e c t s of pruning, were examined, i n Douglas-fir. by S;€ein v(,1955) -and Staebler (1963; 1964). Pruning from below up to 25 percent of the l i v e crown increased diameter growth.at breast height, i n d i c a t i n g the pruned branches were a burden to the tree. Increased se v e r i t y of pruning almost i n v a r i a b l y reduces growth. In Lodgepole pine d e f o l i a t e d by the Lodgepole.needleminer, Coleoteehrvites (Evagora) starki, reduction of r a d i a l increment i s immediately evident i n upper parts of the stem, but there i s a two year, lag at breast height (Stark and Cook, 1957). For Grand f i r , Douglas-fir and Engelmann Spruce d e f o l i a t e d by western Spruce budworm, Chor-Lsteneura oecidenetaliss C.B. Williams (1967) found parts of the stem near the ground were.more "complacent" i n e x h i b i t i n g reduction than parts higher up. Douglas-fir showed the l e a s t reduction. Although generally tree growth i s d i r e c t l y proportional to amount of f o l i a g e present ( M i t c h e l l , 1975), i t isr; necessary to evaluate, the feeding behaviour of a d e f o l i a t o r , and the needle crop d i s t r i b u t i o n - 90 - within the crown configuration in order to postulate some theoretical expectations for impacts of defoliation. Radial growth impacts include missing and discontinuous rings (O'Neal, 1962; 1963), immediate and delayed reduction in ring width, no response and increased ring width (Staebler, 1963; Polge and Garros, 1971). Polge and Garros explained the increase as due to mobilization of stored food in parenchyma. But cambial activity (and hyperactivity) i s due to growth regulators rather than stored carbohydrates (Kozlowski, 1969). Webb and Kilpatrick.(1976) found significant reduction in starch content in Douglas-fir trees defoliated by the tussock moth near my study area. K. Graham (1963) was of the opinion.that increased radial growth is l i k e l y due to lower rates of transpiration and translocation following defoliation. Except.in extreme cases, temperature in the stem is unlikely to increase fast enough.to negate the increase in growth by promoting faster, rates of metabolism. Since growth in Douglas-fir is determinate, and since in this species most photosynthates are stored in buds and needles, effects of defoliation in one year should not be evident in earlywood the following year. Effects.should, however, be evident in latewood because i t s formation largely depends on current year photosysthates. Tables 16 and 17 summarize data of tree radial growth at breast height in 1976 at Mountain View. Defoliation occurred there in 1975. I have attempted to use 1974 and 1975 radial.growth in defoliated Douglas-fir trees, and 1976 growth in undefoliated trees as controls in examining possible reduction, in radial growth at breast height following defoliation. Ponderosa pine gained more radial increment in 1976 than in - 91 - Table 16. Average percent change i n tree r a d i a l growth at breast height following d e f o l i a t i o n at Mountain View i n 1975. Top: Growth i n 1976 as percent change from 1975 growth i n the same trees. Bottom: 1976 growth i n d e f o l i a t e d trees as percent of 1976 growth i n undefoliated Douglas-fir trees. Ponderosa pine Douglas-fir Deg. of d e f o l i a t i o n : 0 0 Low Medium High Lw +50 -44 -19 -27 -39 Ew +17 -61 -26 + 8 -22 Ring +24 -57 -25 - 3 -27 Lw/Ring +21 +29 + 7 -25 -17 Lw 76 146 94 Ew 98 242 155 Ring 90 211 138 Lw: latewood; Ew: earlywood. Data are based on 16 cores i n each c l a s s . - 92 - Table 17. Average percent change in tree radial growth at breast height by tree size, following defoliation in 1975 at Mountain View. Growth in 1976 as: Top: Percent change from 1975 growth in the same trees; Bottom: Percent change from 1974 growth in the same trees. Diameter class (cm) «15 . 15.1 - 25-.0 25.1 - 35.0 >35 Deg.iiofree • . iJdefol^vdei.Lw;' Ew R Lw Ew R Lw Ew R Lw Ew R P 0 +107 +70 +78 + 1 9 - 8 - 3 + 5 + 7 + 7 + 8 3 +23. +35 y ' - ' DF 0 - 60 -42 -50 -79 -83 -82 +21 -47 -32 - 51 -69 -65 L - 37 -55 -50 -32 - 9 -14 - 7 -38 -30 - 15 -17 -17 M - 3 - 6 - 0 . 2 + 4 1 +70 +64 -54 -20 -29 - 38 +5 - 3 H - 40 -28 -32 +41 -0.03 -11 -38 -38 -38 - 32 -37 -36 P 0 +178 +79 +98 + 2 9 - 6 +0.4+7 -20 -15 +111 +42 +56 y DF 0 -60 -51 -53 -67 -822 -79 - 2 -33 -24 - 36 -58 -53 L -20 -14 -.46 + 2 -16 -12 0 -27 -20 + 8 -20 -17 M + 8 -12 - 8 +62 +21 +28 -57 +11 -13 + 2 +30 +22 H -20 -18 -19 - 8 - 0 . 2 - 1 -47 -31 -35 - 51 -44 -46 Lw: Latewood; Ew: earlywood; R: Total annual ring. Data arelbased on 4 cores in each class. - 93 - 1975. The opposite i s true for. sympatric Douglas-fir. In d e f o l i a t e d trees, within the f i r s t year, reduction i n r a d i a l growth was les s than i n undefoliated Douglas-fir trees. The reduction i s apparently not correlated with tree s i z e . D e f o l i a t i o n seems to have retarded immediate growth reduction. Evidently at breast height, there i s a lag of more than one year i n Douglas-fir growth- following d e f o l i a t i o n . Impacts at breast height may be more dramatic i n c h a r a c t e r i s t i c s other than r a d i a l growth. It may be speculated that d e f o l i a t i o n early i n the growing.season r e s u l t s i n nutrients being rechannelled from branch tip s to the trunk. In the past century., trees i n the study area experienced two periods of good growth and three of poor growth (Figures 25 to 32, i n c l u s i v e ) . These graphs and s i g n i f i c a n t c o r r e l a t i o n c o e f f i c i e n t s of 0.6, 0.8, 0.7 for earlywood, latewood and r i n g width of Douglas-fir and Ponderosa pine i n d i c a t e that the two species experienced s i m i l a r r a d i a l growth trends. Generally, Douglas-fir grew f a s t e r than Ponderosa pine trees. But during periods of depression, growth of Douglas-fir was reduced more than Ponderosa pine. Superimposing North Thompson.and Kamloops h i s t o r i c a l out- breaks (Figure 1) on the r a d i a l growth behaviour graphs, i t i s note- worthy that three outbreaks occurred during low growth periods (depres- sions), and one during a isemifavo'fable period;!. A depression may accommodate more than one outbreak. Because we know nothing about the specific.outbreak h i s t o r y of these trees, we cannot state whether or not d e f o l i a t i o n played a r o l e i n the growth depressions. I t i s not even known i f the outbreaks occurred.in the general v i c i n i t y . Some . A , - 94 - growth depressions precede the beginning of.outbreaks, i n d i c a t i n g that growth reduction i n Douglas-fir i s not n e c e s s a r i l y a r e s u l t of outbreaks. Probably some common fa c t o r ( s ) a f f e c t s r a d i a l growth behaviour i n the two species. The factor i s probably a macro one since trees used i n t h i s h i s t o r i c a l analysis are from a wide area. The coincidence of some outbreaks with depressions i n tree growth suggests a s i m i l a r factor also a f f e c t s i n s e c t populations. But apparent inconsistency i n the coincidence suggests a macro factor i s not the only important one. The o v e r a l l factor may.set the stage within which several cofactors function to determine insect population trends. More conclusive statements cannot be made from t h i s analysis without the r i s k of making tenuous assumptions. A knowledge of h i s t o r y of the trees or stands studied here would have made th i s part of the project more than exploratory. The d i f f i c u l t i e s of assigning cause-effect r e l a t i o n s h i p s when enough information i s not known are evident i n the following chart. Probably the most spectacular impact, of Douglas-fir tussock moth outbreaks i s the sometimes extensive, v i s u a l l y obvious tree m o r t a l i t y they i n f l i c t on.the landscape. In Forest Insect Disease Survey records, reports of extensive mortality near Vernon were recorded i n the following years: 1921-1922, 1929—1930, 1938-1939, and 1945. M o r t a l i t y near Chase, Armstrong, Hedley and other places was noted i n various years. Many workers i n the U.S. also have expressed.concern about the destructive power of the Douglas-fir tussock moth. D.A. Graham (1974) stated that the insect can cause mo r t a l i t y one year following d e f o l i a t i o n i n unnamed host, and contrasted The two species respond s i m i l a r l y to the same or di f f e r e n t factors Yes Working hypothesis: Radial growth behaviour and outbreaks l i k e l y respond to a common eco l o g i c a l f a c t o r ( s ) Other factors play important roles i n outbreak occurrence Working hypothesis: Radial growth behaviour and insect populations are determined by, or respond d i f f e r e n t l y to the same or di f f e r e n t ecological factors • No ± Lack of c o r r e l a t i o n may be due to high v a r i a b i l i t y i n the population: Regroup trees into smaller populations or increase sampling i n t e n s i t y Trees are complecent: Possibly the hypothesized i n t e r - action between climate, trees and insects may be v a l i d Impacts may be i n terms of other than r a d i a l growth behaviour. - 96 - t h i s with Balsam f i r which can to l e r a t e as many.as three consecutive years of d e f o l i a t i o n by spruce budworm. In 1949, a Forest Insect and Disease Survey report noted that i n Monte Creek and Duck Ranger D i s t r i c t s , d e f o l i a t e d trees between 35.5 and 40.6 cm dbh were also.attacked and k i l l e d by the Douglas-fir beetle, Dendrootonus pseudotsugae. In western U.S.A., a range of mor t a l i t y from 66 percent to 95 percent has been a t t r i b u t e d to bark beetles i n tussock moth defoliated:stands (Wlckman, 1958; 1963; Wickman et^ a l . , 1973; D.A. Graham, 1974; C a r o l i n and Coulter, 1975). Size "preference'', by the beetles was not indicated i n the FIDS reports; but i t was evident i n my study area (Figure 37). The 1949 Forest Insect and Disease report also suggested that Douglas-fir i s highly r e s i l i e n t to tussock moth d e f o l i a t i o n . I t stated that a l l (Ponderosa) pines which had been d e f o l i a t e d , presumably by the tussock moth, were dead i n contrast to Douglas-fir. which recovered quickly. A 1964 Forest Insect and Disease report: "... (Douglas-fir) trees which were almost denuded (of f o l i a g e ) i n 1963 grew a surprising, amount of f o l i a g e . " More recently, C a r o l i n and. Coulter (1975) have shown that i n the U.S. P a c i f i c Northwest, Grand f i r i s damaged more than Douglas-fir even when insect density i s . equal i n the upper 1/3 of the crown i n both species. The authors did.not speculate on possible, reasons for th i s d i f f e r e n c e . Is i t due to c e r t a i n differences i n lengths.of time needle crops are retained on the two species, or to differences i n f o l i a g e (age) d i s t r i b u t i o n i n . t h e i r crowns? Wright (1974) had observed that a c t u a l l y the greater damage to Grand f i r stands was due to d i f f e r e n t i a l d e f o l i a t i o n by the tussock moth. But to state, as he d i d , without Figure 37. Some d e f o l i a t e d Dougi" - 97 - Figure 37. Some de f o l i a t e d Douglas-fir trees infested with bark beetles. Size preference evident. Note t h r i v i n g Ponderosa pine. further comment that s u s c e p t i b i l i t y increased with Douglas-fir component i n the Blue Mountains seems contradictory, and serves to confuse the s i t u a t i o n . The question of what l e v e l of acute or chronic d e f o l i a t i o n i s necessary before Douglas-fir trees succumb i s relevant i n assessing mortality impacts more p r e c i s e l y . In the P a c i f i c Northwest, f i f t y percent d e f o l i a t i o n was indicated to be the threshold i n unnamed species To face page 98 Figure 38. Lush current year needle crop on small Douglas-fir trees, following complete d e f o l i a t i o n during the previous year. Evidence of good recovery unless r e d e f o l i a t e d ! Top', middle: Cherry Creek, Bottom: Indian Gardens  - 99 - U.S.D.A., 1973b). I did not.embark on an estimation of a threshold because of d i f f i c u l t i e s involved i n estimating d e f o l i a t i o n l e v e l s p r e c i s e l y . Instead, I examined recovery of Douglas-fir trees which had been completely d e f o l i a t e d i n the preceding year. Color and p o s i t i o n of current year needles f a c i l i t a t e d my c l a s s i f y i n g a tree i n t h i s category. Good recovery rates are evident i n small trees (Figure 38) , and mortality i s most serious only among large trees (Tables 18, 19, 20). Table 18 Recovery of completely d e f o l i a t e d trees i n a stand at Heffley Creek h i l l s i d e (M-site q u a l i t y ) , and dynamics of t h e i r growth. Data are based on. 170 trees from 2 representative s t r i p s . Trees were t a l l i e d one year following d e f o l i a t i o n . Diameter class (cm) <5.0 5.1-10.0 10.1-15.0 15.1-20.0 20.1-25.0 % Survival 76 72 80 66 50 Avge diam (cm) 2.8 7.1 11.4 17.5 23.1 Avge height (m) 2.6 7.0 10.6 13.4 16.5 Avge Cr. length (m) 1.5 3.8 4.4 5.4 6.0 Avge Cr. width (m) 1.3 2.3 3.4 4.6 5.5 Diam/Cr. l g t h 1.9 2.0 2.6 3.2 3.9 Diam/Cr. width 2.2 3.1 3.4 3.8 4.2 Ht/Cr. l g t h 1.7 1.8 2.4 2.5 2.8 Ht/Cr. wdth 2.0 3.0 3.1 2.9 3.0 - 100 - Table 19 Recovery of completely d e f o l i a t e d trees on a southeast facing dry s i t e , and dynamics of t h e i r growth. Data are based on 158 trees - residuals from salvage logging. Trees were t a l l i e d one year following d e f o l i a t i o n . Diameter class (cm) <5.-0 5.1-10.0 10.1-15.0 15.1-20.0 20.1-25.0 % Survival 76 68 76 82 66 Avge diam (cm) 3.1 7.6 12.5 17.3 20.8 Avge height (m) 3.0 8.3 11.7 13.4 16.7 Avge Cr. length (m) 1.6 3.3 6.1 8.2 8.3 Avge Cr. wdth (m) 1.3 1.7 2.3 2.7 3.4 Diam/Cr. l g t h 1.9 2.0 2.1 2.1 2.5 Diam/Cr. wdth 2.4 4.5 5.4 6.4 6.1 Ht/Cr. l g t h 1.9 2.2 1.9 1.6 2.0 Ht/Cr. wdth 2.3 4.9 5.1 5.0 4.9 Table 20 Survival of a l l , completely d e f o l i a t e d Douglas-fir trees t a l l i e d i n the study. Data are based on 466 trees ffrom most plot s and.strips i n the study area. Trees were t a l l i e d one year following d e f o l i a t i o n . Diameter class (cm) • *.fl * ' 5 i-.T-rr.n- l f f j - i ' 5 ij 15 i - ? r ' , . <5 .0 5.1-1070 1011-T5.0 -15 .1-20.0 21."l-25.0 >25.1 Trees t a l l i e d 152 136 109 44 17 8 Trees l i v i n g 113 98 79 37 12 4 % Sur v i v a l 74 71 64 84 71 50 - 101 - Apparently, the larger the tree.the lower the chances of recovery as l e v e l s of d e f o l i a t i o n increases. Older stands t r a d i t i o n a l l y have low sto c k i n g . l e v e l s ; increased mortality following d e f o l i a t i o n further reduces stocking to lower l e v e l s . This i s advantageous from the point of view of graziers as increased understory forage y i e l d s may be r e a l i z e d . The r a t i o - o f dbh/crown length or width increases with tree s i z e , i n d i c a t i n g the crown becomes r e l a t i v e l y smaller. The r a t i o i s higher on d r i e r and poorer s i t e s , where a smaller crown may serve to minimize evapotranspiration. In many stands i n the ecotone, trees are widely spaced so that competition seems i n s i g n i f i c a n t . The chance of some trees being released following d e f o l i a t i o n of others i s remote, except i n a few thi c k patches. Vincent. (1962) observed release of Balsam f i r s i n stands i n f e s t e d with Spruce budworm i n the we l l known Green River Watershed i n New Brunswick. He thought the evidently slow release of advance Balsam, f i r regeneration was due to more l i g h t penetrating through, and reduction of competition following d e f o l i a t i o n . Advance Douglas-fir regeneration i s not immune to d e f o l i a t i o n by the tussock moth, but most of i t recovers w e l l . Harwood (1975) was of the opinion that severe Douglas-fir d e f o l i a t i o n a f f e c t s cone bearing trees and seed production for some time. Vincent (1962) also alluded to the need for seed a v a i l a b i l i t y immediately p r i o r to d e f o l i a t i o n for successful natural regeneration i n Black spruce stands. In the study area, under dense stands and high crown cover tree regeneration was uncommon. The denseness of - 102 - these patches made them i n a c c e s s i b l e to ungulates. The f o r e s t f l o o r and l i t t e r layer remained undisturbed and thick. Reduction of stocking and density by d e f o l i a t i o n would make stands accessible to ungulates. S c a r i f i c a t i o n e f f e c t s should be evident i n increased forage y i e l d s and regeneration. In protected openings, high stocking of Douglas-fir regeneration was common. Ponderosa pine regeneration was very scarce even when cones were c l e a r l y abundant on the ground (ITable" 21, Figure 39). Whether.the Ponderosa pine seeds were eaten by mice and s q u i r r e l s Table 21 Average regeneration stocking i n experimental pl o t s under canopy and i n adjacent protected openings. Averages are based on 4 p l o t s under canopy, and between 4 and 10 p l o t s in.openings. Only the 8 tree pl o t s out of 36 had regeneration. 2 Regeneration stocking (No./m ) Tree p l o t Adjacent protected opening Basal area %CC F Py F Py z o . moose (mz/ha) 13.8 39 2.0 - 0.0 16.0 64 1.5 - 2.5 16.0 63 0.5 - 7.6 - 18.4 69 0.5 - 1.3 20.7 42 5.0 - 7.4 2.0 23.0 36 3.3 - 5.1 25.3 64 0.5 - 7.8 41.3 51 2.5 - 3.0 - 103 - Figure 39. Abundance of cones on the ground; but no regeneration was evident i n some openings. Behind the range pole i s undefoliated p l o t Forage y i e l d s (kg/ha): Yfc = 51.6; %CC = 67 67 , 64, . Cherry Creek, 1974. m lens ' more than were Douglas-fir seeds, or whether there were differences i n seed v i a b i l i t y between the two species i s not known. The low regeneration stocking under high crown cover regardless of the stand density implies that l i g h t i s l i m i t i n g for Douglas-fir regeneration i n the ecotone. For adequate natural regeneration, seed a v a i l a b i l i t y p r i o r to d e f o l i a t i o n appears necessary. - 104 - Salvaging dead or dying trees reduces loss of timber volume and value. Unlike the process of salvaging bark beetle infested trees salvaging tussock moth k i l l e d trees does not drain insect numbers from i n f e s t e d stands. I t may i n fact serve as a means of d i s p e r s a l for the insect i f salvaging i s c a r r i e d out during the summer month's".- The a b i l i t y to salvage i s constrained by s i z e and pattern of an outbreak, which i n turn a f f e c t economics of harvesting. Except i n second growth, a c c e s s i b i l i t y i s a c o s t l y problem e s p e c i a l l y for the small (gypo) operator. The age and s i z e of infested stands, and of dead trees also determine the f e a s i b i l i t y of salvaging. In C a l i f o r n i a , extensive outbreaks i n true f i r stands often r e s u l t i n a race against Scolytus and Tetropivm beetles, and decay. Hidden defects of wetwood (Wickman and Scharpf, 1972) are also important. In a C a l i f o r n i a study, 81 percent of t o p k i l l e d trees had wetwood along the whole tree compared to only 2 percent i n uninfested stands. Wetwood reduces timber q u a l i t y , as i t leads to excessive checking and collapse, and gluing d i f f i c u l t i e s due to uneven d i s t r i b u t i o n of moisture at e q u i l i - brium following drying. The race against time also i s serious when logging i s r e s t r i c t e d to c e r t a i n times of the year, due to excessive snow, wet ground or other reasons. In my study area, i f salvaging were r e s t r i c t e d to dead trees or patches harvesting costs would probably be p r o h i b i t i v e unless those people who b e n e f i t from increased forage y i e l d contributed. Quality of dead Douglas-fir trees i s probably not impaired within the f i r s t year following d e f o l i a t i o n . Most of the logging i n devastated stands i s s e l e c t i v e inasmuch as only trees larger than economic marginal s i z e are removed (Table 22; -. 105, - Figure 40). The stand structure i s consequently changed. Many large undefoliated Ponderosa pine trees are removed together with Douglas-fir trees for economic reasons. As much as 16 percent of the volume removed from several settings by an operator was "mix". U t i l i z a t i o n stands were quite low. A cruise i n stands adjacent 2 to a s e t t i n g indicated a gross volume of 178m /ha. From a volume/ weight r a t i o , Balco Industries, a l o c a l f i r m estimated as having 3 extracted only 31m /ha, or about 20 percent of the volume. Such y i e l d s are due to low-poor s i t e q u a l i t y , possibly stand immaturity and the f a c t that only salvageable material was removed. Experienced cattlemen were of the stern opinion that skidding or t r a c t o r logging serves to s c a r i f y the s o i l , and i s b e n e f i c i a l because t h i s i s l i k e l y to increase forage y i e l d s even without range seeding. Table 22 Stand composition of Douglas-fir trees i n d e f o l i a t e d stands before and following salvage logging. Data are from 4 representative s t r i p s near Heffley Creek. Diameter class (cm) <5.0 5.1-10.0 10.1-15.0 15.1-20.0 20.1-25.0 >25 Percentage of trees i n class Before logging 6 25. 25 23 2 19 Following logging 26 34 31 7 2 0 To face page 106 Figure 40. Structure of r e s i d u a l stands following salvage logging. Marginal tree s i z e Ca. 20 cm. Top: Heffley Creek, public property. Bottom: Mountain View, private property (Mr. Inskip). Logging progressing into the devastated area. - 106 - - 107 - Salvaging may have impacts on the bird community. Birds of the primitive coniferous forest are almost a l l insectivorous. Removal of the forest enhances establishment of mountain and western bluebirds and other graminivorous birds, many of which prefer inhabiting coniferous forest - grassland ecotones (Thomas and McCluskey, 1974). They are mostly cavity nesters, and heavy herbaceous flora provides desirable cover. To the extent that snags may be c r i t i c a l for survival of these birds, care should be taken during salvaging to preserve some dead trees. Some insects may have a serious negative impact on bird populations as much as birds have on the insects. Defoliation may expose bird nests to the extent where ̂ nsolationmmay'be lethal-to ' nestlings, and may lead parent birds to abandon their pregeny. This impact was mentioned in a Gypsy moth, %yndnhc.ia (Porthetria) dispav, outbreak in eastern U.S.A. (Commonwealth of Massachussetts, 1908). K. Graham (1963, p. 251) refers to some European literature on this impact. Epidemiology Regulation of insect numbers reflects, in part, an impact of the insects on themselves. Knowledge of insect epidemiology enables economic entomologists to forecast trends of insect populations, and future damage so that appropriate action may be taken. The knowledge is necessary for formulating rational pest control policies and strategies. - 108 - L i f e cycle and sexual.dimorphism of the Douglas-fir tussock moth have already been mentioned i n a previous section. Several studies have been undertaken i n examining aspects of population dynamics of t h i s i n sect. The c y c l i c a l nature of outbreaks i n several locati o n s i s quite s t r i k i n g . So i s the synchronous nature of outbreaks between locations over a wide l a t i t u d i n a l range from New Mexico to Kamloops. This d i s t r i b u t i o n i n time and space, and the wingless nature 4 of (j) adults make i t u n l i k e l y f o r these populations to be re l a t e d g e n e t i c a l l y . For populations which are close to each other, i n a b i l i t y of theO^ to f l y reduces frequency of gene flow between them. Genetic r e l a t i o n s h i p would require consistent dispers a l of c?c?, which i s highly u n l i k e l y f or populations farther apart than 2500 km - between New Mexico and Kamloops! Evidence indicates most populations are "independent" of each other. Even within a stand, growth of one population i s not n e c e s s a r i l y re l a t e d to trends i n another population. Mason (1974) has shown t h i s i n f i f t y p l o t s i n a 121ha stand. He employed R.F. Morris's (1963) analysis.of Trend Index [I = ^ /N ^] and concluded that for populations within a stand, the f i r s t , second and t h i r d year, the trend indices were 7, 3, <1 r e s p e c t i v e l y . He also showed i n a dynamic population model, N = f (density), that more than 80 percent of the changes i n numbers during one year were due to changes.in the same population, during, the preceding year. This meant that contagion was i n s i g n i f i c a n t or. immigration equaled emigration i n numbers and q u a l i t y . 4 Dr. R.R. Mason, For. Sc. Lab., C o r v a l l i s , Oregon, U.S.A. Concurs with t h i s view i n personal correspondence. - 109 - In spite of the fac t that dependence has not been demonstrated, views implying i t ' e x i s t s are not uncommon i n the popular l i t e r a t u r e . Opinions such as "... the tussock moth can j u s t eat i t s way to those f i r s on our c o a s t , a n d "... D i s t r i c t Forest Ranger said the (Douglas- f i r tussock) moths were t r a v e l l i n g toward a large stand of v i r g i n timber..." are i l l founded. They represent a misunderstanding of an important issue. We know the tussock moth does not swarm l i k e l o c u s t s ! The h i s t o r i c a l frequency of the tussock moth on the coast i s n e g l i g i b l e . In f a c t the insec t may have never inhabited much of the coast. Unfortunately the alarmist views sometimes serve the: purpose of marshaling public support and sympathy for what would otherwise be u n j u s t i f i a b l e control measures. Livingstone and-Tunnock (1973) were convinced . that surveys c l e a r l y showed great p o t e n t i a l for the insect to spread. It i s not clear whether they were worried about devastation of susceptible stands by autochthonus or "migrating" i n s e c t s . Despite t^is.'amb'iguitNy,, the b e l i e f was used i n an argument i n attempts to persuade the U.S. Environmental Protection Agency to grant permission for the l a t e s t D.D .T. - a e r i a l . spray i n the P a c i f i c Northwest (see U.S.D.A. 1973b). In Western U.S.A., where the tussock moth has been i n t e n s i v e l y studied, three population phases, v i z . release—>peak—>decline are so commonly referred to as to suggest they are a constant feature of the in s e c t . The idea and terminology appear to. have originated from ^ The Oregonian. 3rd November, 1972. The Oregon Journal. 18th Ju l y , 1947. (Courtesy of Dr. R.R. Mason, personal correspondence). - 110 - Greenbank (1963) in his work, with eastern Spruce budworm. Most tussock moth infestations are recorded as lasting three years (U.S.D.A., 1973a) - hence the so called three year cycle. Wickman ejt al_. (1973) ascertained the cycle in five separate case studies. Each phase is considered to last one year. This time dimension may serve to warn resource managers about the state of an outbreak, but i t is not l i k e l y representative of a l l populations. The preparatory (release) phase probably lasts longer than one year. It i s d i f f i c u l t to define what constitutes a release phase because the very low population levels imply d i f f i c u l t i e s of detecting the insect. A "shotgun effect" (Figure 41) so common on infested landscape suggests the three year cycle may be unrealistic. It i s evident in Figure 1 that outbreaks may last for as long as five years. As D.A. Graham (1974) pointed out, in one.infested patch the cycle may be a three year one, but i t may be longer in a stand or forest with several patches. The infesta- tion patch we see up the h i l l i s not necessarily i n the same phase as the one down the valley. The quasisynchronous occurrence of outbreaks over great distances leads one to suggest that some regional factor determines, at least in part, the outbreaks. If this were true one would suspect effects of the same factor, to be expressed in other organisms. If this subsidiary postulate were shown to be true, i t would lend credence to the principal hypothesis. Rejection is not "derogatory" to the primary hypothesis, however (Peddie, 1938). This area i s examined through tree ring analyses reported elsewhere in this thesis. The Douglas-fir tussock moth is a "hitchhicker" (Wolfenbarger, - I l l - Figure 41. Shotgun e f f e c t : t y p i c a l nature of Douglas-fir tussock moth i n f e s t a t i o n on a landscape. - 112 - 1946) on people, animals, automobiles and i n wind, i n the l a r v a l stage. Probably mortality i s high i n the transportation medium unless t r a v e l i s r e s t r i c t e d to the t e r r e s t r i a l zone (Berland, 1935), or active plankton zone (Wellington, 1945) - more than 2 km above ground and 7°C. The r e c i p r o c a l influence of trees on the tussock moth indicated i n the i n t e r a c t i o n t r i a n g l e on page .88 i s r e a l . I t represents "resistance" or feedback common between l i v i n g systems. I have encountered i n the l i t e r a t u r e two sets of data which although not intended to i l l u s t r a t e t h i s concept, i l l u s t r a t e i t w e l l i n the tussock moth s i t u a t i o n . Condrashoff and Grant (1962) reported t h e i r survey on d i s t r i b u t i o n of diapause s i t e s ( l a r v a l coccoons) i n stands d e f o l i a t e d by the tussock moth near Vernon, B.C. In a stand with trees denuded of t h e i r f o l i a g e , the understory vegetation i s favored for o v i p o s i t i o n s i t e s ; Douglas-fir regeneration being the preferred plants. Number of cocoons on the reproduction averaged more than twice the number on Choke cherry and Douglas maple combined. In a stand where the overstory i s completely d e f o l i a t e d , emerging larvae immediately feed on - the reproduction. The d i s t r i b u t i o n of cocoons w i t h i n a Douglas-fir tree v a r i e s with the degree to which the tree was d e f o l i a t e d (Table 23). In general, Luck andDBahlsten'(1967) arid Dahlsten et^ a l . (1970) concluded s i m i l a r l y for cocoon d i s t r i b u t i o n i n White f i r . Heavier d e f o l i a t i o n r e s u l t s i n a s h i f t i n r e l a t i v e "preference" of the insects for the bark and lower parts of the tree as o v i p o s i t i o n and refuge s i t e s . On these s i t e s and on the favored understory vegetation, probably predation and other mortality factors are more intense. The d i s t r i b u t i o n also i l l u s t r a t e s the need for - 113 - Table 23 D i s t r i b u t i o n of Douglas-fir tussock moth cocoons i n l i g h t l y and heavily d e f o l i a t e d trees. (Modified from Condrashoff and Grant, 1962). Crown stratum Upper Middle Lower Bark Degree of d e f o l i a t i o n Light Heavy 189 156 . 74 196 80 223 16 139 s t r a t i f y i n g the sampling design along the v e r t i c a l axis for purposes of sampling tussock moth populations. Also i t i s necessary to change the i n t e n s i t y of sampling i n various parts of the crown and tree as the degree of d e f o l i a t i o n changes. By enhancing a i r c i r c u l a t i o n and formation of thermals i n the f o r e s t , intensive d e f o l i a t i o n by the tussock moth promotes i t s chances for d i s p e r s a l . This improves the chances of s u r v i v a l f o r both emigrants and residuals when food i s s t i l l a v a i l a b l e . But t h i s may also reduce the r e s i d u a l populations to a point where b i o t i c agents can bring them down, e s p e c i a l l y when stress i s prevalent i n the r e s i d u a l s . Current year needles are eaten f i r s t during the release phase. During peak and decline phases only older needles which probably have lower food q u a l i t y are a v a i l a b l e . Beckwith (1976) free-fed and force-fed - 114 - tussock moth larvae on f o l i a g e from.different crown s t r a t a of three hosts. I tabulate h i s data to i l l u s t r a t e a r e c i p r o c a l impact: Host Source of f o l i a g e % Survival *Free feeding *Forced feeding Douglas-fir Top 100 100 Bottom 100 100 Grand f i r Top 100 100 Bottom 100 90 Subalpine f i r Top 90 80 Bottom 100 70 *Free feeding: On current year f o l i a g e *Forced feeding: On older f o l i a g e . Forced feeding simulated the s i t u a t i o n following release phase when mostly low q u a l i t y needles would be a v a i l a b l e . The low nutrient q u a l i t y and probably r e l a t i v e quantity i n the older f o l i a g e was indicated by high frass production. Exhaustion of food may be s u i c i d a l when d i s p e r s a l i s not possible. Exhaustion of high q u a l i t y food reduces s u r v i v a l rates, (see also Mason and. Thompson, 1971), and probably q u a l i t y which may be r e f l e c t e d i n fecundity. Food quantity a f f e c t s s i z e of adults, thereby t h e i r fecundity. Leonard (1970) advanced a provocative hypothesis on several aspects of population regulation i n the l i p a r i d , Lymantria dispar. He reasonably.suggested that starvation enhances d i s p e r s a l . But to state - 115 - that "at high density dispersal., i s induced p r i o r to the crush of the population" i s misleading because i t implies d i s p e r s a l i s "induced" s o c i a l l y . o r otherwise from within the population. Yet i t i s c l e a r that environmental forces are necessary f o r d i s p e r s a l . He also suggested that during evolution, loss of wings i n the Oj^ was accompanied by population flushes or wide f l u c t u a t i o n s . The flushes appear s e l f d estructive, but because sta r v a t i o n enhances d i s p e r s a l , they are a mechanism which ensures gene.flow.and maintenance of v a r i a b i l i t y i n the populations. At high density d i s p e r s a l i s induced before the population.crashes and t h i s sows the seeds for new populations. This erroneously implies that whenever we detect a population crash, the insects have a c t u a l l y gone elsewhere. Whether or not loss of wings i n Douglas-fir tussock mothQ^ was compensated for by development of d i s p e r s a l mechanisms i n larvae, the loss has not been very c o s t l y as gene flow and mating are f a c i l i t a t e d by the being almost stationary and producing a sex pheromone, and the hairy nature of the larvae for a e r i a l d i s p e r s a l . Several b i o t i c agents have been recorded with increasing frequency i n the f i e l d during the decline phase. Most of them have been i d e n t i f i e d from rearing projects. Apparently, the most important agent i s a.nuclear polyhearal v i r u s (NPV). In Forest Insect and Disease Survey Annual Reports, a condition.was described i n 1939 as a w i l t disease; in.1945 as.a v i r u s ; i n 1954 as a polyhedral v i r u s , and i n 1955 as NPV. In 1952, a b i o l o g i c a l control attempt with a v i r u s - probably NPV - was undertaken against the tussock moth i n B.C. NPV has also"been implicated i n decline of several outbreaks i n the U.S.A. - 116 - Through a l i f e table - factor .analysis approach, Mason and Thompson (1971) found for a v i r u s d^F.of 41 percent. Hughes and Addison (1970) have i d e n t i f i e d two s t r a i n s of NPV i n the tussock moth. The v i r u s prevents o v i p o s i t i o n by <j) tussock moths (Dahlsten, et a l . , 1970): i t i s not clear whether t h i s i s due to e f f e c t s on oocyte development, hormonal control of sexual development and a c t i v i t y , or behaviour. Martignoni e_t al_. (1969) found a cytoplasmic polyhedral v i r u s i n Douglas f i r tussock moths. Where NPV has been claimed to cause s i g n i f i c a n t m o r t a l i t y , i t has often done so a f t e r severe damage has already been i n f l i c t e d by the tussock moth. The v i r u s appears to l e t the insect get out of hand. Long lags are probably c h a r a c t e r i s t i c between populations of these two organisms. Stress may be necessary before the pest succumbs to the v i r u s . Is stress provided by food shortages, and increase i n pest density? Is high density required as a s u f f i c i e n t means of disease transmission i n the population? Notwithstanding our lack of understanding of such points, NPV i s registered now i n the U.S.A. for use against the Douglas-fir tussock moth. Circumstancial evidence indicates a red ant, Formica intergroides, protects trees from d e f o l i a t i o n by the tussock moth. Active ant colonies (Figure 42) were encountered i n the study area. Their s c a r c i t y and uneven d i s t r i b u t i o n i n affected stands were apparent. Macroclimatic factors r e l a t e d to aspect and elevation, and microsite factors r e l a t e d to stand structure may l i m i t establishment of colonies i n the study area. Hughes (1975) showed such environmental factors to be l i m i t i n g f o r colonies of two insect predators, Formica rufa and To face page 117 Figure 42. Active ant colonies. Top: Cherry Creek - 1975; colony behind the range pole. Bottom: Mountain View; colony behind the log piece. Note some d e f o l i a t i o n i n adjacent trees. - 117 - - 118 - F. lugubris i n Wales. Formica intergroides appears to "displace f o r c e f u l l y tussock moth larvae from branches.^ In the Coniferous Biome of North America some of the l a r g e s t groups of birds feed on leaf eating i n s e c t s . O r i o l e s , Vireos are common in the i n t e r i o r of B r i t i s h Columbia, but t h e i r predatory influence may be i n s i g n i f i c a n t i n reducing i n s e c t numbers. Turc'ek (1948) i n Checkslovakia noted that toxic gypsy moth larvae are eaten by birds including o r i o l e s and s t a r l i n g s . In-Germany, hole nesting and other birds also eat gypsy moths (Luhl and Watzek, 1976). So the presence of a toxin i n Douglas-fir tussock moth larvae may make them poor, but not u n l i k e l y candidate for b i r d s ' food. Cost of an outbreak A decision to protect or to not protect forest resources has primary and external benefits as w e l l as costs. E x t e r n a l i t i e s are an important c h a r a c t e r i s t i c of the forest resource and decisions - governing i t s management. T r a d i t i o n a l l y , managers measure q u a n t i t a t i v e l y these benefits and costs, commonly i n monetary terms. In a managed forest', d i r e c t costs of an outbreak are r e a l as they represent assaults on c a p i t a l investments made i n i t . In a natural f o r e s t , on the other hand, losses are r e a l only to the extent that we recognize the current market value of the crop, and the cost of time during which the crop occupies the land. Time i s not a free resource: t h i s concept i s acknowledged i n a l l investment decisions i n part by the use of discount rates. This ^ Observation by Dr. R.F. Shepherd, personal communication. - 119 - i s true also for conventional cash flow stand analyses. C l e a r l y , value losses are sustained whether damage i s done to natural or man-made stands. Investments to reduce these losses are e s s e n t i a l l y not d i f f e r e n t from any other i n forest management. Because forest protection must compete with other c u l t u r a l treatments for scarce funds, there i s need to express costs and benefits i n terms of a common parameter. This i s necessary also for analysing f e a s i b i l i t y of, and ranking investment projects to decide between a l t e r n a t i v e s . How do we a c t u a l l y measure losses and benefits i n an outbreak? We face two basic problems here: (i) i d e n t i f y i n g sources of benefits and costs, e s p e c i a l l y external ones, and ( i i ) quantifying them. The sources may be more complex than was indicated by Stark (1975). D i f f i c u l t i e s involved i n quantifying benefits and costs, e s p e c i a l l y external ones such as s o i l p r otection and aesthetics, were evident at the 1974, 25th Annual Western Forest Insect Work Conference, at Salt Lake C i t y , Utah, i n discussions by several resource economists (Curtis, 1974; Michalson, 1974; Rivas, 1974; R.G. Williams, 1974). These d i f f i c u l t i e s are r e a l ; yet there i s undeniable need for undertaking economic analyses to ensure maximum returns from investments. Economic analyses of s p e c i f i c insect problems are scarce i n the l i t e r a t u r e . As we are unable to quantify convincingly many costs and b e n e f i t s , the best we can do i s use c l a s s i c a l c r i t e r i a of Benefit-Cost r a t i o , Internal Rate of Return, Net Present Value only as guides i n the investment decision. Many forest protection decisions are made on a "gut f e e l i n g " , or f o r p o l i t i c a l , s t r a t e g i c or speculated reason such as the argument that f i r e hazard i s a problem i n d e f o l i a t e d stands. - 120 - In B.C., the p u b l i c , as the major owner of the forest resource, bears most of these losses. But some segments of society sustain higher immediate losses than others. The cost of an outbreak to a forest worker represents reduction i n income as a r e s u l t of depletion of the resource following d e f o l i a t i o n . The cost of an outbreak to d i f f e r e n t workers may vary because of i n s i t u differences i n t h e i r income. The more income one foregoes the higher the cost. For an i n d i v i d u a l who becomes i l l from c o n j u c t i v i t u s , dermatitis, pulmonary and other ailments caused by toxins from the base of tussock mothl'.s u r t i c a t i n g h a i r s (Gilmer, 1923; U.S.D.A., 1973b; personal observation ), h i s costs may be s i g n i f i c a n t l y higher. The cost to a grazier may even be o f f s e t by increased forage following d e f o l i a t i o n . Consider los s of a Christmas tree crop at P r i t c h a r d , B.C. (FIDS, 1948), and of s h e l t e r b e l t s around farms and residences i n Idaho and Washington (Tunnock, 1973): the tree farmers and residents did not sustain equal loss e s . For a f o r e s t r y enterprise which i s dependent on backward i n t e g r a t i o n of the resource for s u r v i v a l and competitive a b i l i t y , an outbreak i s a matter of l i f e or death. These differences i n sustained costs stem mainly from the e x t e r n a l i t y c h a r a c t e r i s t i c of the resource, and i t s s p e c i f i c ownership pattern. In landscape architecture and urban f o r e s t r y , quantifying value of a damaged tree i s equally c o n t r o v e r s i a l . The value may be equated with the amount of money an owner i s prepared to pay i n order to save the tree. But various owners would spend d i f f e r e n t amounts of g I witnessed a f a l l e r complain of serious skin i r r i t a t i o n while logging a devastated stand owned by a Mr. Inskip, at Mountain View. This was i n the stand shown i n figure 40 - bottom. - 121 - money f o r the same tree. I t i s generally agreed that one of the follow- ing i s the r e a l loss to insect k i l l : ( i) the current market value of the tree regardless of h i s t o r i c a l costs; or ( i i ) the cost of e s t a b l i s h - ing a new tree up to the age, s i z e and value of the dead one immediately p r i o r to i t s destruction. These concepts are often used i n forest property compensation. Aesthetic values of trees i n the wilderness are even more d i f f i c u l t to quantify. The value of trees i n a park may be assessed by v i s i t o r use. But what i s the value of trees along a p u b l i c highway? Evaluation of values here becomes a problem of evaluating mainly s o c i a l a t t i t u d e s . Wickman and Renton (1975) explored two simple methods of evaluating cost of one outbreak i n a P i n e - F i r campground with 8 u n i t s , i n C a l i f o r n i a . ( i ) Following tree mortality, cleaning up was required to reduce f i r e hazard, and danger to camp users. F e l l i n g of dead and dying trees, and slash disposal cost $90.00. Topping top k i l l e d trees cost $100.00. The t o t a l cost was $190.00 ($23.75 per u n i t ) , ( i i ) There were 370 trees i n the campground, or 46.2 trees per unit. The replacement value of each unit was given as $1500.00. Assuming the Pine and F i r trees have equal aesthetic appeal, the value of each tree equals $33.00. A t o t a l of 25 trees were k i l l e d by the tussock moth outright: t o t a l value l o s t i n mortality equals $825.00. To t h i s should be added the cost of tree f e l l i n g and topping ($190.00) • from ( i ) . T o t a l loss amounts to $1015.00 ($126.00 per u n i t ) . - 122 - The f i r s t procedure i s unacceptable as i t ignores replacement costs. Both procedures u n r e a l i s t i c a l l y ignore possible reduction i n v i s i t o r use related to lower aesthetic value, and annoyance caused by the tussock moth. I submit that the r e a l cost of an outbreak i s heavily dependent on "whose horse i s getting gored". Recently a new concept c a l l e d Allowable Cut E f f e c t , dubbed ACE, has appeared i n the f o r e s t r y l i t e r a t u r e (Schweitzer ejt a l . , 1972). The concept i s not subscribed to unanimously. The concept: i n a regulated forest with some old growth where y i e l d s are constrained a r t i f i c i a l l y and regulated, any s i l v i c u l t u r a l treatment which increases y i e l d i n second growth should j u s t i f y our reaping benefits of increased y i e l d immediately i n the old growth. The immediacy of these benefits r e s u l t s i n highly favorable Internal Rates of Return. ACE i s r e a l , and i s demonstrable i n conventional stand analyses. The fact that i t can be traced to i n s i t u a r t i f i c i a l constraint on the y i e l d does not n u l l i f y i t s r e a l i t y . S t r i c t l y on the basis of conventional investment cash flow analysis applied to protection of forest inventory, B e l l e_t a l . (1975) implied that we often exaggerate the cost of an outbreak. While ACE i s used to promote some stand improvement investments, i t can be used to discourage others such as protection of inventory: " . . . l i k e the two edged sword, ACE can cut i n both d i r e c t i o n s . " B e l l et a l . (1975) used data from a case study of the l a t e s t tussock moth outbreak i n the Umatilla National Forest. The U.S. Forest Service had estimated the damage there to be over two m i l l i o n d o l l a r s . But B e l l and h i s associates argued as follows:- In that outbreak, nonsalvageable mortality - 123 - amounted to about 1.2 m i l l i o n board feet (fbm) every year for the next r o t a t i o n of 115 years, or 1.2 m i l l i o n fbm -''"of the allowable annual cut i n the management u n i t . The los s was c a l c u l a t e d according to the f a m i l i a r Hanzlik formula, which i s now obsolete i n that area. At the market value of $62.00 per thousand fbm, the loss was $74,400.00 annually. In cash flow investment theory, t h i s represents a ser i e s of annual payments for a terminable period of 115 years. Assuming a reasonable discount rate of 10 percent, and using the appropriate 9 investment model to discount to the present, the loss amounted to only $744,000 (cf. more than $2,000,000.00). only by the present generation. I t i s equivalent to using zero discount rate. As i n depreciation theory, these costs should be spread over a meaningful period - a crop r o t a t i o n i n t h i s case. Insect damage may not r e s u l t i n as much losses as we often think. Because of higher timber values and shorter rotations on better s i t e s , discounted losses are l i k e l y to be higher there. Such s i t e s deserve higher p r i o r i t y i n protection. Losses on poorer s i t e s may be very low; benefits accruing from increased forage production following d e f o l i a t i o n make the losses even smaller. This i s an argument for leaving outbreaks on poorer s i t e s to run t h e i r course. If we invest money on such s i t e s , the opportunity cost we incur may be too high. The younger the stand ^ V = r / i I ( l + i ) n - l [ where V = discounted value; r = annual payment; O I - . . \ n I B e l l e_t a l . did not give t h e i r model. Results obtained from t h i s one were s l i g h t l y d i f f e r e n t f rom t h e i r s . Reduction of the discounted loss i s indisputable! The undiscounted loss i s so high because the cost i s borne i = discount rate; 10% = 0.1; n = number of years- r o t a t i o n . - 124 - when i t i s damaged, the less value we lose through mortality. For various reasons, discount rates lower than 10 percent are more r e a l i s t i c . But to exclude discounting at a l l i s unacceptable. When outbreaks are recurrent, as they are within some management u n i t s , loses may overlap and magnify over a sing l e r o t a t i o n . Because values of stands d i f f e r by l o c a t i o n and other c h a r a c t e r i s t i c s , and because discount rates also d i f f e r i n time, we obviously need d e t a i l e d evaluation of ben e f i t s and costs f o r each s p e c i f i c problem.in-order ,to determine i t s r e a l magnitude before attempting serious control measures. A blanket control project i n the study area i s u n j u s t i f i e d . I t may also be undesirable when we examine benefits accruing to forage production i f an outbreak i s l e f t alone on some s i t e s . u... involvement i n resource protection from insects and diseases has been oriented toward protecting commercial timber values. Where these values are low ... but where watershed, w i l d l i f e , e s t h e t i c s and r e c r e a t i o n a l values of a :vigorous forest are high, we need to rethink our p r i o r i t i e s . " John R. McGuire, Chief, U.S. Forest Service, 1976. Resource use c o n f l i c t s and pest management strategy I t i s unwise to advocate pest management strategies without considering the land or resource use pattern i n an outbreak area. Mere v i s u a l impacts on trees should not ne c e s s a r i l y lead to invoking of pest suppressive measures. Sometimes for various reasons i t i s more sensible to leave an outbreak alone unless i t threatens.valuable stands. Where several resources are involved on the same land, as i n the B.C. i n t e r i o r , i t i s important that we consider a l l resources, not only one. - 125 - It may be easier to decide on the strategy when the sympatric resources are compatible. In t h i s section I w i l l consider two apparently " c o n f l i c t i n g " resources i n the study area - forage and tree production - i n developing a strategy for managing the Douglas-fir tussock moth. In my arguments, I w i l l r e l y heavily on the data and foundation established i n preceding sections. Inasmuch as land tenure i s i n d i c a t i v e of land use p r i o r i t i e s , when protection of f o r e s t inventory i s considered i t i s imperative that we consider the resource values and t h e i r r e l a t i v e importance i n the whole. The relevance of forest land tenure - the interphase between for e s t law and economics - i n forest resource use i s apparent, e s p e c i a l l y i n expanding scope of forest resource management. On the Canadian scene, most forest land tenures such as those i n the p u b l i c domain are i n d i c a t i v e of r e l a t i v e magnitudes of resource values on the respective land. Within the I n t e r i o r Douglas-fir Zone about 3.2 m i l l i o n forested hectares were being used for grazing twenty years ago. This included a l l the lower zonal ecotones. In contrast, there were 1.2 m i l l i o n hectares of open range most of them below the timber l i n e (Sloan, 1956; T i s d a l e and McLean, 1957). More recently Pearse (1976) put the t o t a l area of usable forested range land at about 6.7 m i l l i o n hectares, most of which are i n the Kamloops and Cariboo Forest D i s t r i c t s . Evidently, the i n t e r i o r forests are important sources of forage. In the open range, forage production i s the dominant, and often the only tenured use. Tenure on forest land i s v a r i a b l e . The study area i s surrounded by several Public Sustained Y i e l d Units (PSYU) and Tree Farm - 126 - Licences (TFL). A l l of my study p l o t s were within the Kamloops PSYU (No. 31). Within the u n i t , some land i s p r i v a t e l y owned. P.S.Y.U.'s and T.F.L.'s are dominant at higher elevation, where wood and f i b r e production are primary uses, and forage r i g h t s are usually for one year i n the form of grazing permits. In the ecotone, many stands are managed under 21 year grazing leases; here forage production is.dominant over timber production. But logging may be undertaken i n emergency to salvage timber values through Timber Sale contracts while the lease i s s t i l l v a l i d . The forested land covered by these leases i s administered under the Land Act, and i s of low s i t e q u a l i t y f o r timber production. Many of the d e f o l i a t e d stands were on such land (Table 2). The low s i t e q u a l i t y i s evident also i n low timber y i e l d s extracted during logging. On most of the p r i v a t e l y owned forest land, grazing i s the dominant, but not n e c e s s a r i l y the only use. Tnasmuchcasithe-public makes^various.ioverlapping demands on the ecosystem, c o n f l i c t s i n resource use and management are Abound to a r i s e . One of the most serious and oldest c o n f l i c t s here involves range and timber values. Professional resource managers, graziers and others have been involved i n the c o n f l i c t . As early as 1920 the pro- v i n c i a l minister responsible for f o r e s t resources, the Hon. T.D. P a t t u l l o , stated that of the forested land 3.8 hectares were p o t e n t i a l l y s u i t a b l e f o r a g r i c u l t u r e and would be put to farming (probably forage production) a f t e r timber harvesting. The withdrawal seems not to have materialized to a s i g n i f i c a n t extent as there were 3.5 m i l l i o n hectares of forested range land t h i r t y - s i x years l a t e r (Sloan, 1956). In h i s Royal Commission reports, Chief J u s t i c e Sloan (1945, 1956) considered the - 127 - issue of multiple use, e s p e c i a l l y i n the i n t e r i o r , as one of the most (C c o n t r o v e r s i a l i n management of the p r o v i n c i a l f o r e s t resource. I t was during the 1955-1957 commission hearings that the controversy between range and timber i n t e r e s t s reached i t s apogee. " I t i s c h i e f l y i n r e l a t i o n to grazing on crown forest land that c o n f l i c t s of i n t e r e s t a r i s e . (The use of) the land for production of timber, c a t t l e , the extraction of minerals and a v a i l a b l e water ... w i l l create ... unfortunate, although presently avoidable consequences". (Sloan, 1956; p. 681). It i s f a l l a c i o u s to believe that resource c o n f l i c t s are due s o l e l y to mismanagement, contrary to the Argument of Crown Counsel, section 199 (Anon. 1956): "One witness said /%,±tia%ty'' that there was room for both loggers and cattlement i f the matter i s properly managed." In a b r i e f , a Mr. T.G. W i l l i s , an agrologist with the then Dominion A g r i c u l t u r e : "Their (graziers') other problem i s the encroachment of the f o r e s t on t h e i r grazing land. Stockmen have been a g i t a t i n g t h i s matter for a number of years, so far without any tangible r e s u l t s . " "Jack (Lodgepole) pine, willow and alder" are blamed for the forest encroachment. In concurring with these opinions, Sloan c a l l e d these trees trespassers, and erroneously considered the encroachment problem more serious than overgrazing. The same attitud e had been set i n h i s e a r l i e r report - (Sloan, 1945; p. 164). But as f o r e s t e r Alan Moss t e s t i f i e d : "We (the i n t e r i o r f o rest industry) are j u s t as touchy about encroachment of ( s i c ) f o r e s t land by grazing land as the c a t t l e industry i s on the encroachment of grazing land by f o r e s t r y " (Sloan, 1956; p. 699). - 128 - In view of the broad frame of reference f o r the commission, i t i s su r p r i s i n g that equally important questions of forage y i e l d s and q u a l i t y , timber y i e l d s and s o i l conservation influences by e c o l o g i c a l forces (e.g. insects) other than logging appear:to have l a r g e l y been ignored. The broadening scope of forest resource management necessitates that the basic objective of pest control measures be one of minimising damage or losses not n e c e s s a r i l y to one, but several, resources i n the ecosystem. Because control measures have beneficial.and detrimental e x t e r n a l i t i e s , we need to think i n terms of the whole system. The resources considered are probably v a r i a b l e i n space and time, and they are not of equal importance. Any.attempt to evaluate impacts i n a forest ecosystem necessarily.involves i n v e s t i g a t i n g parameters c l o s e l y associated.with the resources of i n t e r e s t . The pest management strategy should take into account, among other things, the extent of and v a r i a t i o n i n the resources and impacts of the damage. On poor.and low s i t e s , control of the Douglas-fir tussock moth would be j u s t i f i e d i f the objective was to decimate populations from p o t e n t i a l epicenters. But contagious spread i n t h i s i n s e c t i s i n s i g n i f i c a n t (Mason and Thompson, 1971; Mason, 1974; Wickman et a l . , 1973). I f (passive) contagious spread was s i g n i f i c a n t , i t would l i k e l y be f o r long distances. Presence of the insect i n major v a l l e y s i n the area, where cross v a l l e y and north<—^south winds are common suggests some populations are probably r e l a t e d , but i n a way which i s d i f f i c u l t to predict, from d i s p e r s a l patterns. So f a r the evidence indicates that patches so.common .on the landscape represent d i f f e r e n t native or autochthonus populations. C o n t r o l l i n g the f o c i i s sound only to the - 129 - extent that i t prevents damage of resources within the i n f e s t a t i o n patch. The "nip-in-the-bud" concept (Stehr, 1968) i s not relevant beyond the patch because decimating the insects i n one patch does not a f f e c t those inv,another. The three year cycle may describe adequately i n d i v i d u a l populations, but i n the f i e l d often populations are not i n phase with each other. On the landscape longer cycles are not uncommon. A broadcast control treatment i s i n e f f i c i e n t unless i t i s applied only on the good and medium s i t e s and when most populations are i n the same vulnerable phase, before eruption or c r i s i s . As populations are "independent" and i n f e s t a t i o n s l a s t f o r a few years, c o n t r o l i s l i k e l y to be spread over as many years. Some stands may have to be treated more than once. High rates of tree mortality are probably due to chronic i n f e s t a t i o n s . It should not be assumed that every tree which has been stripped of i t s f o l i a g e w i l l . die. I t i s u n r e a l i s t i c to invoke c o n t r o l measures i n a stand during the f i r s t year of i n f e s t a t i o n on grounds that we'are preventing trees from dying. Most outbreaks i n the past collapsed n a t u r a l l y , although often a f t e r ;severe ri damage had already beenj i n f l i c t e d . Most control attempts were undertaken during the outbreak phase. Since most populations are not i n phase with each other, claims of successful control.from a s i n g l e broadcast treatment may be suspect. L i k e l y the populations would have collapsed n a t u r a l l y , as they have many times i n the past. Any spurious claim of successful control i s dangerous from at le a s t two angles: i t j u s t i f i e s expenditures unwisely spent, and sets a precedent;on,: which future control attempts w i l l be based on the premise that " i t worked the l a s t time". - 130 - A d e c i s i o n .which advocates no c o n t r o l i n some areas requires l e s s cash outlay. I t a l s o . r e a l i z e s benefits i n forage y i e l d s . On south and east facing slopes providing winter refuge for mule deer, the decision assumes s p e c i a l dimension. High increases i n forage y i e l d s should be expected, on mesic s i t e s with deep sandy loam s o i l s . Such s i t e s may produce high timber values but c o n t r o l should not n e c e s s a r i l y be the rule.there, e s p e c i a l l y when the stands are managed p r i m a r i l y for forage, or w i l d l i f e refuge. Conclusion By reducing stand stocking and density, the Douglas-fir tussock moth increases range forage production. S i g n i f i c a n t gains should be expected on mesic s i t e s , i n more i n t e n s i v e l y c h r o n i c a l l y i n f e s t e d stands, and i n dead patches of trees. Salvaging i n f e s t e d stands increases the b e n e f i t s , e s p e c i a l l y when followed by range seeding. Tree s u r v i v a l i s affected.by d e f o l i a t i o n , and i s related to s i z e and possibly other f a c t o r s . E f f e c t s on tree r a d i a l growth at breast height.are not s i g n i f i c a n t during the f i r s t year following d e f o l i a t i o n . I did not investigate e f f e c t s beyond the f i r s t year.- It i s true that various degrees of contagious spread of tussock moth populations by wind d i s p e r s a l of the larvae are i n e v i t a b l e . Nevertheless.the strong p o s s i b i l i t y remains that e x i s t i n g widespread populations have t h e i r own independent c a p a b i l i t y of erupting under the blanket conditions of weather systems which favor population - 131 - increase generally. Delayed eruptions i n some l o c a l i t i e s do not n e c e s s a r i l y signify.that, they originated from "hot spots", but may s i g n i f y that the microsite conditions, were somewhat les s favorable, and thus created a l a g . Advocating a broadcast control of the pest i s unwise because i t leads to .spending money on low q u a l i t y s i t e s and on s i t e s which are managed p r i m a r i l y for forage production. I t also prevents r e a l i z a t i o n of range b e n e f i t s . Suppression measures.may not. prevent remote stands from being.infested because contagious spread.is not common. Selective c o n t r o l , with better s i t e s given priority., w i l l improve e f f i c i e n c y of i n v e s t i n g scarce funds. There is' need for undertaking similar, studies i n other affected l o c a l i t i e s to obtain data.from.a wider base more representa- t i v e of the I n t e r i o r Douglas-fir Dry Subzone. Because outbreaks are recurrent, i t i s relevant to study impacts i n a long term mission oriented research. But we need to know the s p e c i f i c h i s t o r y of stands, and possibly i n d i v i d u a l trees, i f we are to state long term impacts confidently. There i s also need to examine changes i n forage y i e l d and q u a l i t y at the species l e v e l to provide most meaningful data to range and wildlife-managers and graziers. 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The i n h i b i t i o n of l i g h t o r i e n t a t i n g reactions i n c a t t e r p i l l a r s of Lymantriidae3 Lymantria dispar and Orgyia antiqua (Lepidoptera). Monit. Zool. I t a l . 4(1): 1-19. Mason, R.R. and C.G. Thompson. 1971. of the Douglas-fir tussock (Lepidoptera:Lymantrii dae) Collapse of an outbreak population moth '.Hemerocampa pseudotsugata U.S. For. Serv. Res. Note PNW-139, 10p. - 140 - i Appendix - 141- SCIENTIFIC. NAMES OF PLANTS Trees Balsam f i r Black cottonwood Black spruce Black tupelo Choke Cherry Abies balsamea (L.) M i l l . Populus trichocarpa Torr. & Gray Picea mariana ( M i l l . ) BSP Nyssa sylvatiaa Marsh. Prunus virginiana var. melanocavpa (A. Nels.) Sarg. Douglas-fir ( i n t e r i o r ) Pseudotsuga menziesii (Mirb.) Franco var. glauoa Douglas maple Engelmann spruce Grand f i r J e f f r e y pine Longleaf pine Ponderosa pine Subalpine f i r Western hemlock Western l a r c h White f i r Acer globurum Torr. var.douglasii (Hook) Dipp. Picea engelmannii Parry Abies grandis (Dougl.) L i n d l . Pinus geffreyi Grev. & Balf. Pinus palustris M i l l . Pinus ponderosa Laws. Abies lasiooarpa (Hook) Nutt. Tsuga heterophylla (Raf.) Sarg. Larix occidentalis Nutt. Abies conoolor Gord. & Glend. Understory vegetation Balsam root Balsamrhiza sagitata Nutt. Blue bunch wheat-grass Agropyron spicatum (Pursh) Scribn. & Smith. Downy brome Bromus tectorium L. June grass Koeleria cristata (L.) Pers. - 142 - Kentuky bluegrass Needle-and-thread Pine grass Sagebrush Timber milk-vetch Poa pratensis L. Stypa Qomata T r i n . & Rupr. Calamagrostis rubesaens Buckl. Artemesia tridentata Nutt. Astragalus miser Dougl. ex Hook I N A T I O N A L T O P O G R A P H I C S Y S T E M B R I T I S H C O L U M B I A SECOND STATUS EDITION—July 15th, 1968. S H E E T 92 V N E Surveyed Crown Land in flooded areas Surveyed land in flooded areas which has been alienated Surveyed Timber Lease. Licence, or Berth Induin Reserve Government Reserve Land District Boundary Provincial Forest Boundary Tree Farm L Municipality Water Supply Area Park Park less than 10 acres Campground Forest Service Lookout Post Office School Church Hospital Building Cemetery Mine Dyke Historic Monument On the above index,maps published with district lot land status are coloured yellow. Land Commissioner's OJJice is located at Kamloops. Mineral Claims arc not shown on this sheet. District land lot numbers 24 Sections within Townships 2 4 K A M L O O P S L A K E , B. C S H E E T 9 2 1 /NE S E C O N D S T A T U S EDITION

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