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Competition between paper birch and douglas-fia in two different biogeoclimatic zones of British Columbia Wang, Jian Rang 1997

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COMPETITION BETWEEN PAPER BIRCH AND DOUGLAS-FIR IN TWO D E F E R E N T BIOGEOCLEVIATIC ZONES OF BRITISH COLUMBIA By Jian Rang Wang B. Sc. Northwestern College of Forestry, 1982 M. Sc. Northwestern College of Forestry, 1987 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department of Forest Sciences (^Faculty of Forestry) We accept this thesis as conforming to the required standard The University of British Columbia June 1997 © Jian Rang Wang, 1997 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) 11 ABSTRACT Variation in the relative competitive abilities of plant species between different environments (such as climate) has been proposed as a control of the species composition of plant communities. This thesis examines whether the competitive abilities of paper birch and Douglas-fir vary with climate from a coastal site to a southern interior site in British Columbia. The overall hypothesis is that paper birch would be more competitive at the interior site and Douglas-fir would be more competitive at the coastal site. The study examined several components of this variation in competition. Seedlings of paper birch (Betula papyrifera Marsh.) and Douglas-fir {Pseudotsuga menziesii [Mirb.] Franco) were planted in pots at different densities either as pure culture (1, 2, 4 and 6 seedlings per pot) or as mixed culture (2, 4, 6 seedlings per pot in a 1:1 ratio). The study was established at each of two sites (Adams Lake in the southern interior and Malcolm Knapp Research Forest on the coast) representing one biogeoclimatic subzone in each of two different biogeoclimatic zones (Interior Cedar-Hemlock zone (ICH) and Coastal Western Hemlock zone (CWH), respectively). There was no replication of the study sites. The experiment was run for two growing seasons (1993 and 1994). Seasonal net photosynthetic rates of the two species were measured. Douglas-fir seedlings continued photosynthesis year-round at the coastal site but only photosynthesized seven months at the interior site (because of snow cover, photosynthesis was only measured for seven month but was assumed to negligible beneath the snow). Paper birch had active photosynthesis for only six months at the coastal site and five months at the interior site. Assuming that photosynthesis of mature conifers at the interior site was limited in the winter by low temperature, this suggests that winter photosynthesis by Douglas-fir at the coastal site contributes significantly to its carbon gain and competitive ability. Douglas-fir had higher photosynthetic NUE and WUE at the coastal site than at the interior site. However it had higher biomass-based NUE at the iii interior site. Paper birch had higher nitrogen use efficiency (NUE) and water use efficiency (WUE) at the coastal site than at the interior site. Douglas-fir seedlings had significantly larger basal diameter and height at the coastal site than at the interior site throughout the growing season. Paper birch seedlings were taller in the early part of the growing season at the coastal than at the interior site, but there was no significant difference in basal diameter between the two sites. Douglas-fir had significantly larger foliage, root, shoot and total biomass per plant at the coastal site than at the interior site. However, it had a lower root/shoot ratio at the coastal site, while the opposite was true for birch. The birch foliage, shoot, root and total biomass decreased significantly with increasing density at both sites, suggesting strong intra-specific competition. Douglas-fir experienced less intra-specific competition at both sites, and had greater negative effects on paper birch in terms of growth and biomass production at the coastal site than at the interior site. Paper birch had greater negative effects on Douglas-fir at the interior site than at the coastal site. Douglas-fir had greater RGR at the coastal site than at the interior site. In contrast, paper birch had greater a RGR at the interior site than at the coastal site. Douglas-fir had significantly greater relative competitive ability at the coastal site when grown in mixed culture with paper birch. In contrast, paper birch had.greater competitive ability at the interior site. Stem analysis of height growth patterns of the two species showed that height of Douglas-fir exceeded height of paper birch at about 45-50 years after stand establishment at the interior site. In comparison, Douglas-fir exceeded paper birch in height at about 25-30 years at the coastal site. Difference in height growth patterns of the two species at the two sites contributed to the explanation of differences in the persistence of paper birch in mixtures between these two biogeoclimatic subzones. Other factors between the two different study areas, such as differences in frequencies of natural fire, insect outbreak iv and forest diseases, may also be important in determining why paper birch is more abundant in the ICH zone. TABLE OF CONTENTS Abstract i Table of Contents List of Tables i List of Figures Acknowledgments xiv Chapter 1. Introduction 1 1.1 Ecophysiological characteristics of evergreen and deciduous species 2 1.2 Competition between species in mixed stands 4 1.3 Competitive ability of competing species 5 1.4 Research questions 6 1.5 The rationale for the study 7 1.6 Objectives and hypotheses 8 Chapter 2. Study sites and ecology of the species : 10 2.1 The study sites 10 2.2 Ecology of the species 12 2.2.1. Paper birch 12 2.2.2. Douglas-fir 13 2.2.2.1 Coastal Douglas-fir 14 2.2.2.2. Interior Douglas-fir 14 Chapter 3. Seasonal physiology of Douglas-fir and paper birch seedlings 15 3.1 Introduction 15 3.2 Methods 17 3.2.1 Research sites 17 3.2.2 Experimental design 17 3.2.3 Net photosynthetic rates 20 3.2.4 Specific leaf area (SLA) and total leaf area 20 3.2.5 Water use efficiency (WUE) and nitrogen use efficiency (NUE) 21 3.2.6 Soil temperature and soil moisture 21 3.2.7. Statistical analysis 22 3.3 Results 22 3.3.1 Seasonal soil temperature and soil moisture 22 3.3.2 Seasonal patterns of leaf photosynthesis 23 3.3.3 NUE and WUE 27 3.3.4 Specific leaf area (SLA) 37 3.4. Discussion 30 3.4.1 Soil temperature and soil moisture 30 3.4.2 Photosynthesis and stomatal conductance 31 3.4.3 Photosynthesis, NUE and WUE 34 3.4.4 Photosynthesis and SLA 36 3.5 Conclusions 36 Chapter 4. Growth and biomass allocation of Douglas-fir and paper birch seedlings 38 vi 4.1 Introduction 38 4.2 Material and methods 40 4.2.1 Plant material and experimental design 40 4.2.2 Seedling measurements 40 4.2.3 Statistical analysis 42 4.3 Results 43 4.3.1 Seasonal growth patterns without intra- and inter-specific competition 43 4.3.1.1 Height and basal diameter growth 43 4.3.1.2. Biomass production 45 4.3.1.3. Biomass allocation 48 4.3.2 Climatic and density effects on biomass production in pure culture 51 4.3.3. Climate and density effects on biomass production in mixed culture 57 4.3.4. Relationships between foliage and total biomass, and root and shoot biomass 61 4.4 Discussion 64 4.4.1 Competition, growth and biomass production 64 4.4.2 Competition and above- and below-ground biomass allocation 66 4.5 Conclusions 68 Chapter 5 Growth analysis of paper birch and Douglas-fir seedlings at the coastal and interior sites 70 5.1 Introduction 70 5.2. Material and methods 71 5.2.1. Experimental design and measurements 71 5.2.2. Data analysis 72 5.3 Results 73 5.3.1 Seasonal changes of RGR 73 5.3.2 Effects of climate, species and density on growth indices 76 5.4. Discussion 82 5.4.1. Differences between species 83 5.4.2. Individual versus competitively grown seedlings 83 5.4.3 RGR and biomass allocation 84 5.5. Conclusions 85 Chapter 6. Competition between Douglas-fir and paper birch 86 6.1 Introduction 86 6.2 Materials and Methods 89 6.2.1 Plant materials and study sites 89 6.2.2 Competition experimental design 89 6.2.2.1. Sequential harvest competition experiment 89 6.2.2.2. Replacement series 89 6.2.3. Resource complementarity 90 6.2.4. Competitive ability 91 vii 6.2.5. Intra- and inter-specific competition 92 6.2.6. Competition intensity 93 6.2.7. Statistical analysis 94 6.3. Results 95 6.3.1 Inter-specific competition from the mixture experiment 95 6.3.2 Inter-specific competition from the replacement series 97 6.3.3 Reciprocal yield analysis 101 6.3.4. Competition intensity 104 6.4 Discussion 105 6.5. Conclusions 107 Chapter 7. Height growth patterns of Douglas-fir and paper birch in two different biogeoclimatic zones in B. C 108 7.1. Introduction 108 7.2. Methods : 110 7.2.1 Study sites 110 7.2.2 Sample trees and stem analysis 111 7.2.3 Model development 112 7.3. Results 112 7.4. Discussion 121 7.5 Conclusions 123 Chapter 8. General Discussion and conclusions 124 8.1 Comparison of plant traits 124 8.2 The role of disturbances in sustaining paper birch-Douglas-fir mixtures 128 8.3 Limitations on the experimental design of the study 130 8.4 Douglas-fir and paper birch mixedwood management 132 References 134 Appendix 1 149 Appendix 2 159 Appendix 3 165 List of Tables Table 2.1. Monthly climatic data from the two research sites 11 Table 3.1. The 5x4x2 factorial experiment design 18 Table 3.2 Monthly mean soil water potential and temperature on the two study sites in 1994 23 Table 3.3. Analysis of variance for photosynthetic rates (A, pmol m~2 s_1), stomatal conductance (gs, mol m~2 s~l), water use efficiency (WUE) and nitrogen use efficiency (NUE) of Douglas-fir and paper birch at the coastal and interior sites. Data were from the one-seedling-per-pot treatment 26 Table 4.1 Characteristics (mean±SE) of the seedlings of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) at the start of the experiment. Based on 30 randomly selected seedlings 41 Table 4.2. Foliage, shoot and root biomass (mean±SE, g per plant) and root/shoot ratios of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in pure culture at four densities at the interior and coastal sites harvested in August, 1994 52 Table 4.3. F-values from three-way ANOVA of plant biomass variables in pure culture in the competition experiment. The data were from the August harvest, 1994 53 Table 4.4. Foliage, shoot, root and total biomass (mean±SE, g per plant), and root/shoot ratios of paper birch (PB), and coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in mixed culture at three densities at the interior and coastal sites 58 Table 4.5. F-values from three-way ANOVAs of plant biomass variables in mixed culture in the competition experiment. The data were from the harvest in August, 1994 61 Table 4.6. Linear regression relationships between Total biomass (Tb) and foliage biomass (Fb), height (Ht) and basal diameter (Bd), and root biomass (Rt) and shoot biomass (St) for paper birch (PB) and Douglas-fir (DF) growing at two different sites 63 Table 5.1. Relative growth rate (RGR), leaf area ratio (LAR), leaf weight ratio (LWR) and root weight ratio (RWR) (mean±E) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in pure culture at four densities at the interior and coastal sites harvested in August, 1994 77 IX Table 5.2. Relative growth rate (RGR), leaf area ratio (LAR), leaf weight ratio (LWR) and root weight ratio (RWR) (mean±SE) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in mixed culture at four densities at the interior and coastal site harvested in August, 1994 78 Table 5.3. F-values from three-way ANOVAs of parameters from plant growth analysis in the competition experiment. The data were from the August harvest 79 Table 6.1 The relative yield of mixture (RYM), relative yield per plant (RYP), relative yield total (RYT) and relative crowding coefficient (RCC) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) from the mixed culture at the two different sites 96 Table 6.2. Relative yield per plant (RYP), relative yield total (RYT), relative crowding coefficient (RCC) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) from the replacement experiment at the two different sites 99 Table 6.3 Mean competition intensity in the coastal and interior sites for paper birch and Douglas-fir, and the statistical comparison of means between the two sites 104 Table 7.1. Characteristics of sample trees of Douglas-fir and paper birch at the two sites -. 113 Table 7.2. Height growth model fitting statistics for paper birch and Douglas-fir at the coastal and interior sites, respectively 116 Table 8.1 Typical characteristics of paper birch and Douglas-fir grown at the two different sites (coastal and interior) summarizing information presented in the thesis 125 X List of Figures Figure 3.1. Random layout of the pot experiment and field condition at UBC Research Forest site. The same layout was used at the interior site 19 Figure 3.2. Mean mid-day seasonal photosynthetic rates of paper birch and Douglas-fir (I-DF for the interior site and C-DF for the coastal site) in the two different biogeoclimatic zones. Bars indicate +1 SE of mean. Data were from the one-seedling-per-pot treatment 24 Figure 3.3. (a) photosynthetic NUE; (b) NUE based on the yield as total biomass per unit of foliage nitrogen; and (c) WUE of paper birch, coastal and interior Douglas-fir at two different sites. Bars represent mean ±1 SE of mean. Data were from the one seedling-per-pot treatment 28 Figure. 3.4. The relationships between leaf area (cm^ ) and leaf dry weight (g) of paper birch (a) and Douglas-fir (b). Data were from the one seedling per pot treatment. Data were from one-seedling-per-pot treatment 29 Figure 3.5. The relationships between photosynthetic rate (A) and stomatal conductance (gs) of paper birch (P) and Douglas-fir (D) based on data measured in May 3 and 19, 1995 at the two different sites 33 Figure 4.1. Seasonal growth patterns of mean height (a, b) and basal diameter (c, d) of paper birch and coastal Douglas-fir at the coastal site and interior Douglas-fir at the interior sites. Bars represent mean 1 SE of mean. Data were from the one-seedling-per-pot treatment without any competition 44 Figure 4.2. Seasonal growth patterns of mean foliage biomass (a, b) and shoot biomass (c, d) per plant of paper birch and coastal Douglas-fir at the coastal site and interior Douglas-fir at the interior sites. Bars represent ±1 SE of mean. Data were from the one-seedling-per-pot treatment without any competition 46 Figure 4.3. Seasonal growth patterns of mean root (a, b) and total biomass (c, d) per plant of paper birch and coastal Douglas-fir at the coastal site and interior Douglas-fir at the interior sites. Bars represent ±1 SE of mean. Data were from the one-seedling-per-pot treatment without any competition 47 Figure 4.4. Seasonal growth patterns of mean rootshoot ratio of paper birch (b) and Douglas-fir (a) at the coastal and interior sites. Bars represent ±1 SE of mean. Data were from the one-seedling-per-pot treatment without any competition 49 Figure 4.5. Seasonal allocation patterns of biomass between foliage, shoot and roots for Douglas-fir (a and b) and paper birch (c and d) at the coastal and interior xi sites. Data were from the one-seedling-per-pot treatment without any competition 50 Figure 4.6. Total biomass (left panel) and foliage biomass (right panel) per plant of paper birch (a, b), coastal Douglas-fir (c, d) and interior Douglas-fir (e, f) grown in pure culture at different densities. Bars represent ± 1 SE of mean 55 Figure. 4.7. Shoot biomass (left panel) and root biomass (right panel) per plant of paper birch (a, b), coastal Douglas-fir (c, d) and interior Douglas-fir (e, f) grown in pure culture at different densities at different sites. Bars represent ± 1 SE of mean 56 Figure 4.8. Total biomass per plant of coastal Douglas-fir (a), interior Douglas-fir (b) mixed with paper birch, and paper birch mixed with coastal Douglas-fir (c) and interior Douglas-fir (d) at different densities. Bars represent ± 1 SE of mean 59 Figure 4.9. Foliage biomass per plant of coastal Douglas-fir (a), interior Douglas-fir (b) mixed with paper birch, and paper birch mixed with coastal Douglas-fir (c) and interior Douglas-fir (d) at different densities. Bars represent + 1 SE of mean 60 Figure 4.10. Relationships between foliage and total biomass per plant of paper birch (P) and coastal Douglas-fir (C) and interior Douglas-fir (I) at the two research sites. Regression equations and significance are presented in Table 4. 6 62 Figure 4.11. The relationships between target (Douglas-fir) biomass and neighbor (paper birch) biomass in two different environments (coast and interior). Lines are shown only for significant regressions (p<0.05). Dashed line indicates a 1:1 relationship. The data were from mixed cultures at 2, 4, and 6 seedlings per pot 65 Figure 5.1. Relative growth rate (RGR) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown either individually or in competition with each other at the coastal and interior sites. Bars represent ± 1 SE of mean 74 Figure 5.2. Relative growth rate (RGR) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown either individually or in competition with each other at the coastal and interior sites. Bars represent + 1 SE of mean 75 Figure 5.3. Relationships between RGR and density (plants per pot) for paper birch and Douglas-fir grown in pure and mixed cultures at the two sites. Panels a and b reflect intra-specific competition, and panels c and d reflect inter-specific competition. Data were from the August harvest, 1994 80 Figure 5.4. Relationships between leaf weight ratio (LWR) and leaf area ratio (LAR) of paper birch and Douglas-fir at the coastal (a and c) and interior sites (b andd) 81 Figure 6.1. Yield of total biomass per pot from the replacement series: for paper birch (PB) mixed with coastal Douglas-fir (C-DF) (a and b) and with interior Douglas-fir (I-DF) (c and d) at the two sites 98 Figure 6.2. Three-dimensional plot of the combined effects of paper birch and Douglas-fir densities on the reciprocal of total biomass per seedling of C-DF (a and c), and I-DF (b and d) at the two sites 102 Figure 6.3. Three-dimensional plot of the combined effects of paper birch and Douglas-fir densities on the reciprocal of total biomass per seedling of paper birch mixed with C-DF (a and b), and I-DF (c and d) at the two sites 103 Figure. 7.1. Comparison of paper birch and Douglas-fir height growth at the coastal and interior sites in British Columbia 115 Figure 7.2. Comparison of functional plots of paper birch and Douglas-fir height growth at the coastal and interior sites in British Columbia 117 Figure 7.3. Relationships between estimated height and measured height for paper birch and Douglas-fir at the coastal and interior sites. The 1:1 ratio line represents a perfect fit 119 Figure 7.4. Plots of residuals against the estimated height for paper birch and Douglas-fir at two sites 120 X l l l Acknowledgments I am mostly grateful to my supervisor, Professor J. P. (Hamish) Kimmins for recruiting me to the Department of Forest Sciences at UBC, his excellent guidance and his broad and up-to-date knowledge which led me to the topic of my thesis. I would also like to thank my committee members: Drs. Robert Guy, Peter Jolliffe, Peter Marshall, and Cindy Prescott for guidance on different aspects of my research at UBC. I wish to sincerely acknowledge all colleagues at Ponderosa B for providing me with help as well as a pleasant atmosphere, especially to Daniel Mailly for many thought provoking discussions and Min Tsze for analyzing the plant samples and other help. The project was funded by the Hardwood TAC, Ministry of Forests, British Columbia. I would like to thank Dr. Suzzane Simard in Kamloops Forest Region, Ministry of Forests, for her support in the field work and UBC Research Forest for providing the coastal research site. 1 Chapter 1. Introduction There is little experience in the management of "mixedwood" forests (forests of both deciduous and coniferous species) in the U. S. Pacific Northwest and British Columbia. Interest in changing from monoculture plantation management to mixedwood management in order to maintain biological diversity and other values is very recent, but it is increasing rapidly as public interest in forests and the environment grows. However, without adequate knowledge of how inter- and intra-specific competition affects the growth and development of trees, and of how competition should be managed, the many potential benefits of practicing mixedwood management, where it matches the local ecology, will not be realized. In the absence of experience, quantitative descriptions of the competitive interactions between Douglas-fir {Pseudotsuga menziesii (Mirb.) Franco) and paper birch {Betula papyrifera Marsh.) or other deciduous species are a prerequisite for the successful management of mixedwood stands of these species. These interactions should cover the effects of plant density, resource availability and climatic factors on competition. This study examined the apparent variation in competitive relationships between Douglas-fir and paper birch in two different biogeoclimatic subzones and explored the causes and consequences of this variation. This was done through a combination of descriptive field studies and field experimental studies of the dynamics of Douglas-fir and paper birch mixtures in the two biogeoclimatic subzones. Forest ecosystems in British Columbia vary along a regional climatic gradient from the coast to the interior. In the coastal region, conifers such as Douglas-fir, western hemlock {Tsuga heterophylla (Raf.) Sarg), western redcedar {Thuja plicata Don ex D.) and grand fir {Abies grandis (Dougl.) Lindl.) or amabilis fir {Abies amabilis (Dougl. ex Loud.) Forbs) are the dominant species. Deciduous species such as red alder {Alnus rubra Bong.), bigleaf maple {Acer macrophyllum Pursh) and paper birch are less 2 abundant and are generally confined to specialized habitats or disturbed areas (Meidinger and Pojar 1991). Red alder becomes more widely distributed after disturbance because of its ability to fix atmospheric nitrogen and colonize soil low in nitrogen and organic matter (Binkley 1982). In the interior of British Columbia, paper birch is abundant in disturbed areas such as clearcuts or following fire, where it often forms pure stands, but it is also commonly scattered throughout mature second growth coniferous stands. In the coastal region, very few pure paper birch stands are found and it is rarely found in mature coniferous stands. Waring and Franklin (1979) discussed the dominance of conifers in the Pacific Northwest coastal region, and why they are distributed across such a wide range of habitats. They suggested three factors as the determinants of coniferous dominance in this region: (1) the potential for active net photosynthesis by evergreen conifers outside the deciduous species leafy season; (2) water stress limitations on net photosynthesis during the growing season; and (3) the high nutrient use efficiency of conifers (Hicks and Chabot 1985). This thesis explores these concepts to evaluate whether non-growing-season photosynthesis by the evergreen Douglas-fir is a sufficient explanation for the apparent difference in its ability to compete with the deciduous paper birch between coastal and interior B. C. forest ecosystems. It also examines some other possible determinants of the regional difference in competition between these species. 1.1 Ecophysiological characteristics of evergreen and deciduous species The length of the net active photosynthetic period is probably a key factor affecting the competitive relationships between deciduous and evergreen species in the coastal region. However, there are additional important differences between these two life forms which are important for their growth and competition. Evergreen stands have at least twice as much leaf area as deciduous stands on the same site (Schulze 1982; Jarvis and Leverenz, 1983), and sometimes four to five times as much (Waring et al. 3 1978). The leaf area ratio (LAR), foliage N and photosynthetic rates in evergreens are comparatively low due to their low specific leaf area (Chabot & Hicks 1982, Margolis et al. 1995) and long leaf life-span (Reich et al. 1992, Reich et al. 1995). In addition, the turnover of mineral nutrients (Monk 1966; Small 1972,1973; Reader 1978) is generally lower in evergreen than in deciduous species. Conifers have a pattern of nutrient utilization different from that of most deciduous species; they have less than half the annual nutrient uptake requirement of most deciduous species because they retain numerous age classes of foliage and thus have lower nutrient demands for foliage replacement. In the Alaskan tundra, evergreen shrubs occupy the least fertile soils, and forbs and deciduous shrubs occupy the most fertile sites (Webber 1978; Miller 1982, Woodward 1995). Similar patterns have been observed in temperate ecosystems (Larcher 1980) and have been explained on the basis of greater growth response of deciduous species to higher nutrient supply (Chapin 1980, Havranek and Tranquillini 1995) as a result of higher potentials for nutrient absorption, photosynthesis (Small 1972, Stenberg et al. 1995) and growth (Grime & Hunt 1975, Graumlich and Brubaker 1995). The advantage of evergreens on infertile soils may reflect slow growth and associated low nutrient demand (Grime & Hunt 1975), more effective resorption of nutrients from senescing leaves or greater photosynthesis per unit of nutrient (Small 1972). However, other studies have found no difference in photosynthesis per unit of nutrient (Chapin et al. 1980; Field & Mooney 1986). Deciduous species generally have higher photosynthetic capacities than evergreen species and require higher photon flux densities before photosynthesis in individual leaves becomes light saturated (Mooney & Gulmon 1982; Schulze 1982). Deciduous shrubs completed accumulation of biomass, nitrogen (N) and phosphorus (P) in new leaves and current year's twigs by midsummer in Arctic Alaska, whereas these processes continued through the growing season in comparable tissues of evergreen 4 shrubs (Chapin and Shaver 1989). Simulations indicate that the evergreen species can produce canopies with greater annual production than the deciduous species with low N or water availability; the converse is true at higher levels of resource supply (Hollinger 1992). Lechowicz and Ives (1989) compared gas exchange of 2-year-old Acer saccharum and Fraxinus americana in the field. Fraxinus had a shorter period of foliage retention than Acer, but it compensated for this constraint by maintaining higher gas exchange than Acer. Hollinger (1992) studied how leaf and canopy level differences interact in determining total canopy productivity. He found that maximum rates of carbon gain and transpiration were higher in leaves of a deciduous oak than in a co-occurring evergreen oak. However, the evergreen oak partially compensated for the lower photosynthetic capacity of leaves by its longer canopy duration. Young (1985) reported that within a forest understory, sympatric deciduous and evergreen species differed in crown architecture, light interception, and stomatal conductance patterns. Takenaka (1986) compared the photosynthetic properties of deciduous Quercus serrata and evergreen Quercus myrsinaefolia and found that the evergreen oak could utilize the favorable light environment on the forest floor in deciduous stands during the winter. Leaf construction and maintenance costs are always higher in evergreen than in deciduous species. Coexisting deciduous and evergreen species in tropical dry forests differ greatly in their energy investment for leaf construction and maintenance as well as in benefits (Sobrado 1991). 1.2 Competition between species in mixed stands A central question in plant ecology concerns the extent to which competition is important in structuring natural plant communities. Competition occurs when adjacent plants are forced to share the limited resources in a restricted area (Tilman 1988). Plants that arrive first and deplete resources may be considered superior competitors if this 5 prevents later-arriving plants from reaching their maximum potential productivity (Grime 1979). Cole and Newton (1986) studied growth of Douglas-fir seedlings under three competition conditions: Douglas-fir only, Douglas-fir plus grass, and Douglas-fir plus red alder. On the basis of measurements of water stress, light interception, and foliar nutrient concentrations, they concluded that initial reduction in Douglas-fir growth in the presence of other species is largely due to increased moisture stress; light competition became important only as stands aged and crown closure occurred. Shainsky and Radosevich (1992a) assessed mechanisms of interactions between Douglas-fir and red alder in experimentally manipulated stands. They found that when the two species were established at the same time on a relatively fertile site at high density, competition for soil moisture and light were dominant mechanisms underlying the growth of these species in mixtures. Douglas-fir was more sensitive than red alder to light limitation and significantly increased leaf area and biomass production in response to increased light level. 1.3 Competitive ability of competing species Competitive ability is a measure of the ability of one species to obtain limiting resources when grown in mixture with another species, compared with its ability to utilize those resources when grown in pure stands (Snaydon 1991). Competitive ability is usually measured by comparing the biomass yield of the species in mixtures with that in pure stands. Competitive ability of species is an important determinant of community pattern (Gaudet and Keddy 1988). Individual competitive ability can be compared between species in three distinct ways: in their competitive effect, competitive response or ability to avoid being suppressed (Goldberg and Landa 1991). Most studies have examined relative competitive ability under only one set of environmental conditions. Goldberg and Barton (1992) reviewed 101 different competition studies during the 1979-88 period; 6 only seven of them tested sitexcompetition interaction at the individual plant level. Gaudet and Keddy (1988) found size-related traits were the most important measurements of competitive ability, with biomass being the best predictor of competitive ability across 44 species of wetland plants. The competitive ability of an individual plant is determined by three main categories of plant attributes: 1). the ability to deny resources to neighbors; 2). the ability to tolerate being denied resources by neighbors; and 3). the ability to maximize fecundity when denied resources by neighbors (Aarssen 1992). The three attributes may be affected by genetic and environmental variations. Therefore, the competitive ability of a species may change as a function of the environment. This allows for the possibility that relative competitive ability of two species may reverse along a resource gradient, such as climate. Latham (1992) reported a change in the competitive hierarchy of plant species with resource variation. A reversal in relative competitive abilities (as measured by the relative crowding coefficient) of two species, Eriophorum vaginatum and E. scheuchzeri, was found to be a function of nutrient availability (McGraw and Chapin 1989). A correlation between the competitive ability of a species and its photosynthetic performance would be expected on the assumption that the more CG*2 a plant assimilates (thereby increasing its biomass), the greater its competitive advantage. 1.4 Research questions Paper birch is the major competitor of the commercially important Douglas-fir in the Interior Cedar-Hemlock (ICH) biogeoclimatic zone. Forest operations such as spraying and girdling have been employed in the past to control the competition from paper birch sprouts following clearcutting (Simard and Vyse 1992). In contrast, paper birch does not seem to pose a competition problem in Douglas-fir plantations in the Coastal Western Hemlock (CWH) zone. The general question posed here is whether this is because of climatic impacts on the competitive relationship between the two species or 7 whether other mechanisms (such as frequency of disturbance and differences in pathogens) might be involved. There have been few studies of the effects of climate on photosynthetic rate, biomass allocation and relative growth of evergreen and deciduous species, or on competitive abilities of the two tree life forms. From the available literature, it is not possible to answer the following questions: 1. does change in climate affect the seasonal photosynthetic patterns of paper birch and Douglas-fir differently ? 2. does Douglas-fir achieve significant photosynthesis before paper birch leafs out and after paper birch leaf senescence, and how does this vary in different climates ? 3. is Douglas-fir more competitive than paper birch in the coastal climate and vice versa in the interior climate ? 4. what are the differences in water use efficiency (WUE), and nitrogen use efficiency (NUE) between paper birch and Douglas-fir and how do these efficiencies vary between these two biogeoclimatic subzones ? 1.5 The rationale for the study Mixedwood management is rapidly gaining favor because of concerns over the possible relationships between tree species diversity and nutrient cycling, other measures of biological diversity and ecosystem sustainability, and because in some zones and on some site-types, mixed tree species forests may exhibit greater ecosystem resilience in the face of predicted global climate change than single tree species forests. However, to successfully manage a mixed Douglas-fir and paper birch stand so that the productivity of Douglas-fir is not compromised by competition with the birch, a clear understanding of their competitive interactions is necessary. Climatic change may potentially affect the competitive relationships between species. General circulation models predict that temperature will increase by 1.5-4.5 °C in much of interior North America in response to a doubling of atmospheric C O 2 (Mitchell et al. 1990). To predict the effects of such a 8 temperature change on vegetation, it is necessary to investigate the competitive relationship between deciduous and evergreen conifers in different climatic zones. Most studies of competition have been based on growth responses examined at the end of the growing season or experiment. Few have attempted to quantify the response of a species to gradients of competition or the response through the growing season. 1.6 Objectives and hypotheses The overall objective of this research was to test whether an evergreen species (Douglas-fir) on the coast can utilize the longer period available for non-growing season photosynthesis, and will therefore compete more effectively with a deciduous species (paper birch) than in the interior region where the more continental climate restricts non-growing season photosynthesis of conifers. The general hypothesis examined in this thesis is that Douglas-fir is more competitive than paper birch on the coast but that this relationship is reversed in the interior, and that mechanisms of interaction between Douglas-fir and paper birch can be interpreted from patterns of photosynthesis, biomass allocation and relative growth rate. The specific objectives and companion alternative hypotheses were: 1. To quantify seasonal patterns of photosynthetic rates of paper birch and Douglas-fir in the two biogeoclimatic subzones (Chapter 3). H A : Douglas-fir photosynthesizes year round on the coast but not in the interior. During the growing season, paper birch has a higher net photosynthetic rate than Douglas-fir at both coastal and interior sites. 2. To determine the WUE and NUE of paper birch and Douglas-fir (Chapter 3). H A : Paper birch and Douglas-fir differ in WUE and NUE in the different biogeoclimatic subzones, and this is correlated with their achieved growth rate and competitive abilities. 3. To quantify the phenological patterns of leaf development, growth and biomass allocation of paper birch and Douglas-fir in the two biogeoclimatic subzones (Chapter 4). 9 H A : The patterns of leaf area development and relative growth rates of both paper birch and Douglas-fir are different in the two biogeoclimatic subzones. 4. To determine seasonal patterns in relative growth rates ( R G R ) of paper birch and Douglas-fir in the two biogeoclimatic subzones (Chapter 5). H A : R G R S of paper birch and Douglas-fir are related to the species competitive abilities. 5. To assess competitive abilities of paper birch and Douglas-fir in the two biogeoclimatic subzones (Chapter 6). H A : Competitive abilities of the two species change when climate changes. 6. To determine height growth patterns of mature trees of paper birch and Douglas-fir in the two biogeoclimatic subzones (Chapter 7). H A : Paper birch and Douglas-fir have different height growth patterns between the two biogeoclimatic subzones. This difference is related to the species competitive abilities. The study was composed of two major parts: 1). a factorial pot experiment to define ecophysiological processes and growth performance of Douglas-fir and paper birch in the two different biogeoclimatic subzones; and 2). stem analysis to describe height growth patterns of mature forest stands of the two species in the two different biogeoclimatic subzones. 10 Chapter 2. Study sites and ecology of the species 2.1 The study sites To address the questions and achieve the objectives listed in Chapter 1, a comparative study was conducted on paper birch and Douglas-fir in both coastal and interior climatic regions. Two study sites were established: one in the Interior Cedar-Hemlock zone near Kamloops (referred to as the "interior" site) and the other in the Coastal Western Hemlock zone at the Malcolm Knapp Research Forest, Haney, British Columbia (referred to as the "coastal" site). These represent typical interior and coastal climates that occur within the range of natural Douglas-fir and paper birch combinations. The interior site is located at the northern end of Adams lake within the Moist Warm ICH biogeoclimatic subzone ICHmw (Lloyd et al. 1990) at approximately 700 meters elevation. The site is flat with a Humo-Ferric Podzol soil. The climate is generally continental, with long, relatively cold winters and short, hot summers. The frost free season is shorter and diurnal fluctuations of temperature are much larger than at the coastal site. Much of the precipitation is as winter snow. Mean annual precipitation is significantly lower in the ICH than in most of the Coastal Western Hemlock zone (CWH). However, the greater snow pack and snow melt in the ICH than in the CWH contributes considerably to the early summer hydrologic regime in the former, thereby minimizing summer moisture deficits. The climatic data in 1994 from the interior site were recorded by Suzanne Simard for a birch-conifer mixture experiment about 300 m away from my research site (Table 2.1). The coastal study site is located at the southern end of the Malcolm Research Forest within the Dry Maritime CWH biogeoclimatic subzone (CWHdm), close to the Research Forest's weather station at an elevation of 143 m. The climate of the coastal site is characterized by mild temperatures year round with frequent cloudiness, a narrower seasonal temperature range than the ICHmw site, wet, mild winters and warm, relatively dry summers, a long frost free season, and a narrow diurnal fluctuation of temperature. 11 The CWH is, on average, the rainiest biogeoclimatic zone in British Columbia, but the CWHdm subzone and the CWH site are close to the drier end of the CWH range (Meidinger and Pojar 1991). Precipitation at the coastal site, mostly as rain, is concentrated in the winter months. The mean annual precipitation is 2140 mm with 600 mm falling between April and September. Mean temperatures of the coldest and warmest months are 1.4 and 16.8 °C (Klinka and Krajina 1986), respectively. Table 2.1 Monthly climatic data from the two research sites. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Interior Site (northern Adams Lake) Tc -4.8 -2.1 0.9 5.3 13.2 16.4 20.3 18.5 14.7 5.6 0.5 -2.7 7.4 T30 -6.6 -2.3 0.7 6.4 12.5 15.9 18.4 17.6 12.8 6.9 0.7 -3.8 6.6 Pc 114.6 90.2 76.4 59.4 57.8 61.5 42.7 50.4 60.8 88.7 79.7 147.2 929.4 P30 122.0 89.8 88.2 59.1 52.5 64.8 56.8 42.3 58.5 83.9 84.9 143.8 946.6 Coastal site (UBC Research Forest) Tc 5.8 3.7 7.4 10.5 13.3 14.2 18.5 18.0 16.1 9.8 3.5 3.3 10.3 T30 1.4 3.9 5.2 8.3 11.9 14.4 16.8 16.7 14.3 9.9 5.2 2.8 9.2 Pc 234.5 297.4 124.1 136.4 63.2 156.8 23.0 40.7 139.8 194.5 340.0 363.7 2114.1 P30 228.8 182.5 156.1 115.0 83.6 82.7 57.1 66.5 106.1 167.0 223.3 179.9 1738.6 Note: Tc: daily mean temperature for 1994 and T30: daily mean temperature for 30 years average; Pc: precipitation for 1994 and P30: precipitation of 30 years average (Environment Canada 1982). There was no permanent climate station near the interior site, but the climate in Revelstoke is believed to be similar (D. Lloyd, Kamloops Forest Region, BC Ministry of 12 Forests, personal communication). Therefore, the 30-year average climatic data for the interior site were from Revelstoke weather station. The climate (temperature and precipitation) during the study appears to have been representative of the "normal" climatic regimes for the two research sites, respectively. 2.2 Ecology of the species The species chosen for this study were: the evergreen conifer Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and the deciduous broadleaf paper birch {Betula papyrifera Marsh.). Two variants of Douglas-fir were used, P. menziesii (Mirb.) Franco var. menziesii (coastal Douglas-fir) and P. menziesii var. glauca (Beissn.) Franco (interior Douglas-fir). 2.2.1. Paper birch Paper birch is found throughout British Columbia but is sporadic on the outer coast, absent in the Queen Charlotte Islands, and found only on the southeastern portion of Vancouver Island (Calder and Taylor 1968; Massie et al. 1994). Paper birch is common in most low- to medium-elevation biogeoclimatic zones in the Interior. It is abundant and reaches its greatest productivity in the ICH zone, which occurs in the warm, moist valleys of the south-eastern interior of British Columbia, but it also grows well in transitional climates, such as in the Coast/Interior ecotone and between the dry and wet belts in the southern Interior. It rapidly invades these interior sites following disturbances that expose mineral soil, such as clearcutting. Such sites are also invaded by, or replanted with, Douglas-fir. Paper birch occurs on a variety of parent materials and on soil textures ranging from gravely sands to loam and organic soils. It is most abundant on rolling upland terrain or on alluvial sites, but it is also found on open slopes, rock slides, bogs and swamp margins. Best growth occurs on well drained sandy or silty soils or on soils 13 derived from limestone (Marchant and Sherlock 1984; Safford et al. 1990). The exceptionally wide geographic distribution of paper birch in British Columbia is a result of several factors: its ability to be a prominent species on sites of poor quality where other tree species have difficulty becoming established; its ability to regenerate on sites after fire and harvesting disturbances; a high resistance to growing-season frost; and, an ability to begin early season growth. Although paper birch is considered to be an aggressive species in the central and southeastern interior, its present distribution and abundance on the coast is too scattered for it to be a significant competitor for conifers. In the wetter ICH subzones of the Kamloops Forest Region, paper birch usually does not pose problems for regeneration establishment, but may affect growth and survival in subsequent decades (Massie et al. 1994). Recent work by Simard (1990) indicates that low densities of paper birch growing with Douglas-fir may have positive effects on the latter by limiting the spread of Armillaria root rot disease. 2.2.2. Douglas-fir Douglas-fir is one of the world's most important and valuable timber trees. It was discovered on Vancouver Island in British Columbia, and was initially known as Oregon pine. It was first recorded by a European, Archibald Menzies in 1793, a Scottish physician and naturalist, but was named for David Douglas, the Scottish botanist who studied the tree in 1825 (Harlow and Harrar 1950). Menzies finally got his due, however, when the species' scientific name was changed to Pseudotsuga menziesii in the mid 1900s. Two variants of the species are recognized. 2.2.2.1 Coastal Douglas-fir On the coast, Douglas-fir is a serai species, except on extremely dry sites. It seems to compete most successfully in areas of relatively low summer precipitation. 14 Periodic recurrence of catastrophic wildfires created vast, almost pure stands of coastal Douglas-fir forest. In the absence of fire, successful regeneration of Douglas-fir on moist and fertile sites in the commercial range of Douglas-fir on the coast depends on vegetation management because many associated plant species on these sites have growth rates much higher than that of juvenile coastal Douglas-fir. Seedlings of coastal Douglas-fir in this region normally survive best when the seeds germinate on moist mineral soil, but it will tolerate a light litter layer (Hermann and Lavender 1990). 2.2.2.2. Interior Douglas-fir In the interior of British Columbia, Douglas-fir is an extremely important commercial tree species in the southern half of the province. Of all the biogeoclimatic zones in the southern Interior, this species reaches its greatest productivity in the Interior Cedar-Hemlock (ICH) zone. On mesic sites, for example, site index at 100 years ranges from 31 to 35 m in the ICH zone compared with only 23 to 29 m in the drier Interior Douglas-fir (IDF) zone (Lloyd et al. 1990). Generally, interior Douglas-fir grows at relatively higher altitudes at comparable latitudes than the coastal variety. In the Interior, Douglas-fir may be considered as a serai species in moist habitats and a climax component in the warmer, drier areas. In such areas, competing vegetation may promote the establishment of interior Douglas-fir seedlings by reducing temperature stress, but may inhibit seedling growth by competing for moisture (Hermann and Lavender 1990). 15 Chapter 3. Seasonal physiology of Douglas-fir and paper birch seedlings 3.1 Introduction Although shoot and cambial growth of Douglas-fir is dormant in winter in the Pacific Northwest, photosynthesis continues. Emmingham and Waring (1977) suggested that up to 50% of annual carbon assimilation by temperate conifers growing in coastal western North America occurs during the period from October to May. In contrast, photosynthesis by Douglas-fir in the interior region of British Columbia is limited by the cold and long winter. In northern Sweden, 20% of the seasonal photosynthetic production by evergreen species was reported to be during the early and late parts of the growing season, during which time the deciduous species were leafless (Karlsson 1985a, b, and 1989). Nutrient uptake and storage are possible for conifers during much of the relatively warm, wet fall, winter and early spring months of the west coast of Canada and the northwestern United States (Emmingham and Waring 1977). Deciduous species such as paper birch are at a disadvantage in competing with conifers in much of the Pacific Northwestern forests. Their photosynthesis is limited to the growing season when evaporative demand may be high and water is often limiting because of the dry summer (Waring and Franklin 1979). The length of the potential growth period may therefore differ between paper birch with annual broadleaves and Douglas-fir with perennial needle leaves by more than just the differences in leaf area duration; evergreens have a potentially longer season in this climatic region during which they can assimilate C O 2 and grow (Chabot and Hicks 1982). Evergreens have been found to start assimilating earlier than deciduous species in the spring, to continue later in the autumn (Karlsson 1985a) and to accumulate carbohydrates in foliage and roots during the first part of the vegetative period for later translocation to the emerging shoot (Karlsson 1985b). The apparent competitive advantage of Douglas-fir over paper birch in coastal B. C. may not occur in the interior of the province, where a cold winter and 16 relatively moist summer in the interior wet belt is associated with highly competitive paper birch growth. Among woody plants, evergreen conifers usually show lower rates of net photosynthesis and growth than do deciduous broadleaved species (Krueger and Ruth 1969). The question often arises whether differences in the rate of net photosynthesis between conifers and deciduous species are related to their competitive abilities. Physiological responses of plants are useful precursory indicators of competitive stress and provide insight into the mechanisms of adaptation to competition. By studying seasonal patterns of photosynthesis, water relations and related parameters of paper birch and Douglas-fir, the research reported here sought to provide fundamental information on the responses and adaptations of the two species to coast and interior environments. Seasonal patterns of photosynthetic capacity were determined in a field pot experiment as a prelude to more extensive investigations of environmental effects on photosynthetic and growth performance of the two species in natural stands. The determination of seasonal patterns of photosynthetic capacity of these two species provides insight into the evolution of temporal patterns of photosynthetic capacity among species of different growth form. Low soil temperatures reduce moisture availability and nutrient cycling (Chapin 1983), which in turn determines the performance of tree seedlings. Low soil temperatures are thought to be more limiting to plant growth than air temperatures, and to strongly influence tree distribution (Larsen 1989). Soil temperature is strongly related to net annual aboveground tree production and the annual tree requirement for N, P, K, Ca and Mg (Van Cleve et al. 1983). Landhausser et al. (1995) reported that paper birch had greater ecophysiological responses (e.g., net assimilation) to increased soil temperature than Picea mariana. The objective of the experiment reported in this chapter was to examine the seasonal variation in leaf photosynthesis of paper birch and Douglas-fir in the two 17 different biogeoclimatic subzones. The information is then used to test whether Douglas-fir can utilize the longer potential period of photosynthesis for growth and carbon assimilation, and to identify the significance of the difference to the competitive relationship between paper birch and Douglas-fir in the two different biogeoclimatic subzones. 3.2 Methods 3.2.1 Research sites The two research installations in which all the physiological measurements were made in two different biogeoclimatic subzones are described in Chapter 2. The climatic characteristics of the sites are presented in Figure 2.1. The coastal research site used for the pot experiment was located inside a fenced area on flat ground. The interior site was located in a recent clearcut. The site was mechanically prepared, destumped and all the slash removed. 3.2.2 Experimental design A 5x4x2 factorial pot experiment (five different combinations of the two species and two variants of coastal and interior Douglas-fir, four densities and two biogeoclimatic subzones) with completely randomized layout of the pots was conducted at each of the two sites (Table 3.1). Each treatment was replicated three times. A total of 3402 seedlings were planted in 972 pots on each site during July 10 and 15 in 1993. Four-month-old seedlings of Douglas-fir and paper birch were obtained from Sldmikin nursery, Surrey nursery and Pacific Regeneration Technology Inc. in Vernon, British Columbia. The seeds of coastal Douglas-fir were from the sunshine coast just northwest of Vancouver. Seeds of interior Douglas-fir were obtained from the Kamloops area and for paper birch from Salmon Arm. These seed sources are within the same geographical provenance as the experimental sites. Before planting, all seedlings were graded for 18 uniformity. Similar initial sizes of seedlings were sought to ensure that any differences found among species in competitive ability were attributable to species differences rather than to initial transplant size differences. Experimental seedlings were planted in pots (21.5 cm in diameter) buried in the ground to avoid rapid soil temperature change. The pots were filled with commercial potting soil and were laid out 1 m apart to avoid mutual shading among the pots (Figure 3.1). No fertilizer was added to the pots. The buried pots provided a uniform edaphic environment. Sites were kept free of other vegetation competition by regular hand weeding. Two weeks after planting, any dead seedlings were replaced. No measurements were made in the first growing season. Table 3.1. The 5x4x2 factorial experiment design Species combination BGC Density Monoculture Mixture subzones seedlings/pot PB C-DF I-DF PB+C-DF PB+I-DF CWFfdm 1 X X X . * -2 X X X X X 4 X X X X x 6 X X X X x ICHmw 1 X X X - -2 X X X X X 4 X X X X X 6 X X X X X Note: PB: paper birch; C-DF: coastal variety of Douglas-fir; I-DF: interior variety of Douglas-fir * Statistically this is a missing cell, but biologically it is an impossibility. 19 Figure 3.1. Random layout of the pot experiment and field condition at UBC Research Forest site. The same layout was used at the interior site. 20 Field photosynthetic measurements at the coastal site were made monthly in 1994 on the two Douglas-fir variants and on paper birch when there were leaves. At the interior site, measurements on the two variant of Douglas-fir were limited to April to September period because of the snow coverage; birch leaves were measured monthly when they were available. The photosynthesis measurements were only made on monoculture, one-seedling-per-pot treatments. 3.2.3 Net photosynthetic rates Three seedlings of each species and variety were randomly selected for photosynthetic measurements. Five measurements of gas exchange were made on each selected seedling on each measurement date to obtain an average estimate of photosynthetic rates of the seedlings. For paper birch, the fifth leaf from the tip was chosen for the measurement because it was considered fully mature. For Douglas-fir, the measurement was made in the middle of the current year twigs, but excluding any buds. All physiological measurements were made in the field on clear sunny days between 12:00 noon and 14:00 h. In total 9 seedlings were chosen and 45 measurements of gas exchange were made on one day. The average for each species or variety (n=15) was taken as the monthly mean photosynthetic rate for that species. Net photosynthesis (A) and stomatal conductance (gs) were determined using a portable C O 2 gas analyzer (LI-COR 6200 Portable Photosynthesis System, Lincoln, Nebraska). Along with gas exchange, air temperature, ambient CO2, relative humidity, and photosynthetically active radiation (PAR) were also measured and recorded. 3.2.4 Specific leaf area (SLA) and total leaf area After gas exchange measurement, leaves for paper birch and twigs for Douglas-fir were clipped and put into plastic bags for later leaf area and dry weight measurement in the laboratory. Leaf area (one side) of each sample was measured using a LI-COR 3100 21 area meter (LI-COR Portable Area Meter, LI-3100, Lincoln, Nebraska). The leaf area meter was calibrated by passing a known-area calibration disc through the machine. The foliage samples were then dried at 70°C until the mass stabilized. Dry mass was determined to the nearest milligram. Average specific leaf area (SLA, leaf area per unit of leaf biomass, cm^ g-1) was determined for each species. 3.2.5 Water use efficiency (WUE) and nitrogen use efficiency (NUE) WUE and NUE were calculated using the data from the measurement made in August. Leaf samples after SLA measurement were analyzed for total nitrogen by an autoanalyzer using the micro-Kjedahl method (Kedrowski 1983). NUE was calculated in two different ways: 1) as the net photosynthesis (A) per unit of leaf nitrogen (photosynthetic NUE; Sobrado 1991), and 2) as total tree biomass per unit of foliage nitrogen content (biomass NUE, Sheriff et al. 1995). WUE for paper birch and Douglas-fir was calculated as the ratio of net photosynthesis (A) to stomatal conductance (gs) because it represents a more consistent estimate of the relative WUE than does the ratio of A (net photosynthesis) to E (transpiration rate) (Meinzer et al. 1990). 3.2.6 Soil temperature and soil moisture Soil temperature was continuously monitored at a depth of 10 cm in selected pots using temperature probes constructed from 24 gauge copper-constant thermocouple wire. The temperature probes were connected to a CR-10 Campbell Scientific multi-purpose data logger (Campbell Scientific, Inc.). Soil moisture content was measured using gypsum soil moisture blocks. At each site, six moisture blocks (Type GB-1 Gypsum Soil Blocks, Hoskin Scientific Ltd.) were buried 10 cm deep in the selected pots. The moisture blocks were also connected to the data logger. Soil thermocouples and moisture blocks were scanned every 5 minutes and the data were condensed to daily averages and then to monthly averages. 22 3.2.7. Statistical analysis The significance of differences between the two species and variants for means of variables measured at the two sites were analyzed by ANOVA using the MGLH procedure in the SYSTAT statistical package (Wilkinson 1996). Significance was set at a= 0.05. If significant differences were detected among the levels of a factor, then a multiple comparison procedure (Tukey Test) was used. Individual means were compared by a least significant difference test, based on student's -^distribution (Sokal and Rohlf 1995). Regression analysis was conducted on the A over gs and leaf area over leaf weight relationships for paper birch and Douglas-fir in the two different biogeoclimatic subzones. 3.3 Results 3.3.1 Seasonal soil temperature and soil moisture During the winter, the lowest mean soil temperature (10 cm deep in the pot) at the interior site was -0.1 °C in December. In contrast, the lowest soil temperature at the coastal site (4.0°C) occurred in February (Table 3.2). The relatively high winter soil temperature (in comparison to air temperature) at the interior site was because of snow cover. The low heat conductivity of snow inhibits the penetration of subfreezing air temperatures into the soil at the interior site, and early snowfall (before the soil is frozen) can result in unfrozen soil throughout the winter. Because soil temperature in winter at the interior site was very similar to that at the coastal site (Table 3.2), the winter respiration of the root system of Douglas-fir may be similar at both sites. The highest soil temperatures (in July) at both sites were similar: 20.3 and 21.1°C for the interior site and coastal site, respectively. Warmer soil temperature has been reported to increase the photosynthetic rate of paper birch (Lawrence and Oechel 1983). There were about three months of water shortage at both sites (June, July and August, Table 3.2). The severe 23 water stress was caused partially by the use of commercial top soil with a coarse texture and good drainage. This illustrates the need to control, or at least monitor, the soil temperature and moisture in any pot- or container-grown experiment where these variables could differ significantly from natural field conditions. Table 3.2 Monthly mean soil water potential and temperature on the two study sites in 1994. Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Soil temperature (°C) ICH 0.5 0.3 0.7 8.4 13.5 16.6 20.3 19.8 15.9 9.2 2.6 -0.1 CWH 5.9 4.0 6.6 13.1 15.8 17.2 21.1 20.4 17.0 11.4 4.9 5.0 Soil moisture (bar) ICH -0.38 -0.37 -0.37 -0.73 -0.74 ws ws ws -0.37 -0.56 -0.39 -0.39 CWH -0.36 -0.40 -0.37 -0.32 -0.36 ws ws ws -0.62 -0.37 -0.39 -0.44 Note: ws= water stress i.e. water potential was too low to be measured by the Gypsum Block. 3.3.2 Seasonal patterns of leaf photosynthesis Seasonal changes of mean mid-day photosynthetic rates of paper birch, and coastal and interior Douglas-fir at the interior and coastal sites are illustrated in Figure 3.2. Photosynthesis of paper birch started one month earlier (in April) at the coastal site than at the interior site (in May) because of the earlier bud break in the former. Paper birch stopped photosynthesis at the same time (in October) at both the interior and coastal sites. Therefore, it had a one-month longer photosynthetic period at the coastal site than at the interior site. 24 o 1 1 i i 1 1 1 1 i i i i .. 0 1 2 3 4 5 6 7 8 9 10 11 12 Month Figure 3.2. Mean mid-day seasonal photosynthetic rates of paper birch and Douglas-fir (I-DF for the interior site and C-DF for the coastal site) in the two different biogeoclimatic subzones. Bars indicate ± 1 standard error of mean (n=25). Data were from the one-seedling-per-pot treatment. Photosynthesis was not measured on DF when the seedling were covered with snow. 25 No leaves of paper birch were available for photosynthetic measurement in October at either site. In contrast, Douglas-fir at the coastal site continued photosynthesis year round. At the interior site, Douglas-fir started to photosynthesize in April and stopped in October (Figure 3.2); during the period from October to April, all the seedlings at the interior site were covered by snow. Consequently, no photosynthetic measurements were made during this period (Figure 3.2). However, larger Douglas-fir, with canopies above the snow, probably did achieve some photosynthesis during the October to April period. The seasonal patterns of photosynthetic rates of interior and coastal Douglas-fir variant were very similar when grown at the same site (Figure 3.2). The only significant differences (Mest, p<0.05) between the monthly means of photosynthetic rates for interior and coastal Douglas-fir occurred in July, August and September at the coastal site (Figure 3.2b), and in April, May and June at the interior site (Figure 3.2a). Climate had a significant effect on photosynthetic rates of both species and variants (Table 3.3), but a comparison using Tukey test revealed no significant difference in photosynthetic rates (p = 0.348) between interior and coastal Douglas-fir at either site. There was a significant (p<0.001) difference between photosynthetic rates of paper birch and Douglas-fir. At both sites, paper birch had a much higher photosynthetic rate per unit leaf area than Douglas-fir. The maximum photosynthetic rate for paper birch was observed in May at the interior site and in August at the coastal site. At the coastal site, the photosynthetic rate of paper birch was the lowest in June and second lowest in July (Figure 3.2b). This reduction in photosynthetic rate corresponded with low soil moisture in these months (Table 3.2). 26 Table 3.3. Analysis of variance for photosynthetic rates (A, prnol nr 2 s"1), stomatal conductance (gs, mol nr 2 s_l), water use efficiency (WUE) and nitrogen use efficiency (NUE) of Douglas-fir and paper birch at the coastal and interior sites. Data were from the one seedling-per pot treatment. Variables Source df MS F P A Climate 1 394.61 59.288 0.000*** Species 2 799.81 46.645 0.000*** CxS 2 7.62 1.145 0.000*** error 84 6.66 Ss Climate 1 0.33 129.082 0.000*** Species 2 0.13 51.526 0.000*** CxS 2 0.01 5.225 0.007** Error 84 0.002 WUE Climate 1 282.98 19.192 0.000*** Species 2 379.72 25.753 0.000*** CxS 2 104.10 7.060 0.001** Error 84 144.45 NUE Climate 1 20.16 6.340 0.000*** Species 2 825.97 259.526 0.000*** CxS 2 8.87 2.792 0.065 Error 84 3.18 Note: C: climate; S: species and variant. 27 3.3.3 NUE and WUE Both climate (coastal and interior) and species had a significant effect on photosynthetic NUE (Table 3.3). No significant interaction between climate and species (p =0.065) on NUE was detected by ANOVA. In this study, photosynthetic NUE based on instantaneous photosynthetic measurements was significantly (p<0.05) greater in paper birch than in Douglas-fir at both sites (Figure 3.3a). However, the nitrogen that Douglas-fir contains in its needles may contribute more to carbon gain during its lifetime than the nitrogen contained in paper birch leaves, depending on the climate. When NUE was calculated based on total biomass per unit of foliage nitrogen, Douglas-fir had higher NUE than paper birch at the interior site but not at the coastal site (Figure 3.3b). Significant differences (p<0.05) in WUE were detected for both tree species and variants between the coastal and interior sites (Table 3.3 and Figure 3.3c). However, there was no significant difference in WUE between coastal and interior Douglas-fir (p = 0.441). However, both coastal and interior Douglas-fir had slightly higher WUEs at the coastal site (Figure 3.3c). 3.3.4 Specific leaf area (SLA) The SLA data were measured from the one-seedling-per-pot treatment in August 1994 when the leaves and needles were considered fully mature. No seasonal changes of SLA were studied. The samples were collected immediately after photosynthetic measurement. The average SLA was 46. 5 cm^ g-1 for Douglas-fir and 204.4 cm^ g-1 for paper birch. There were significant linear relationships (p<0.001) between leaf dry weight (g) and leaf area (cm^ ) for paper birch and Douglas-fir (Figure 3.4). The coefficients of determination were 0.98 for both species. However, as leaf weight increased, leaf area increased faster for paper birch (y=0.04 x) than for Douglas-fir (y=0.019x). 28 Z 1 " o o" 2 10 o s 3 . P J g 5 a 2? 0 o +. o J3 PH • Coastal site • Interior site C-DF I-DF 500 C-DF I-DF 100 X o o o s U Figure 3.3. (a) photosynthetic NUE; (b) NUE based on the yield as total biomass per unit of foliage nitrogen; and (c) WUE of paper birch, coastal and interior Douglas-fir at two different sites. Bars represent mean ± 1 SE (n=15). Data were from the one seedling per pot treatment. Figure. 3.4. The relationships between leaf area (cm^ ) and leaf dry weight (g) of paper birch (a) and Douglas-fir (b). Data were from the one seedling per pot treatment. 30 3.4. Discussion 3.4.1 Soil temperature and soil moisture Air and soil temperatures are related and the latter is the hmiting factor for tree growth for much of the winter in climates in which air temperature becomes high enough for photosynthesis during the winter. In the Rocky Mountains, time of bud flushing of conifers below the tree-line has been shown to correspond more closely to soil temperature than to air temperature (Hansen-Bristow 1986). The soil temperature and moisture (10 cm deep in the pots) regimes for the coastal and interior sites (Table 3.2) observed in my study were different from those reported in other studies (Emmingham and Waring 1977; Waring and Franklin 1979; Gholz 1982, and Runyon et al. 1994) for Oregon and Washington. The winter temperatures and summer water stress were not as different between my interior and coastal site as between coastal and interior sites in Oregon and Washington States. Summer water stress at my coastal site was relatively less severe than on coastal Oregon compared with my interior site (Table 3.2). This was partially attributed to the drainage properties of the commercial potting soil that was used. A water stress of -0.57 MPa was reported by Harrington (1994); and Shainsky and Radosevich (1992a, b) to limit the growth of Douglas-fir. In a comparative study of the effects of winter temperatures on photosynthetic capacity, Douglas-fir had threshold temperature values of -1 to -2 °C for initial photosynthetic depression (Quehl 1985). Mean daily minimum temperature of the coldest month at the coastal site was -1.2 °C (Figure 2.1) and data from my study showed that soil temperature was above this Douglas-fir threshold. Therefore, at the coastal site, Douglas-fir seedlings were able to photosynthesize during the winter, thus utilizing solar energy over part of the year that is unavailable to paper birch seedlings. Winter photosynthesis may explain the ability of some evergreen species such as Douglas-fir, western hemlock and western red cedar to survive and grow quite large beneath deciduous overstories at coastal sites in B. C. and the Pacific Northwest. However, 31 decreasing air temperature and light intensity in autumn resulted in decreased gas exchange rates. At the interior site, during mild and clear days in winter, photosynthesis should be possible as long as needles and stems are not frozen (Havranek and Tranquillini 1995). However, in my study no winter measurements were taken as the seedlings were snow-covered. Applying a simulation model to data from a wide variety of environments in western North America, Emmingham (1982) concluded that many coniferous trees growing in mild winter climates probably accumulate a major proportion of their annual carbon uptake during the fall, winter and spring. 3.4.2 Photosynthesis and stomatal conductance Total daily photosynthetic production is determined not only by net photosynthetic rate but also by the shape of the diurnal patterns of photosynthesis and the duration of the photoperiod. Douglas-fir had relatively low photosynthetic rate compared with that of paper birch at both sites (Figure 3.2a, b). However, it photosynthesized at the coastal site throughout the winter when paper birch had no leaves, whereas the photosynthetic period at the interior site was similar for both Douglas-fir and paper birch (see section 3.3.2). Therefore, Douglas-fir at the coastal site is in a better position in terms of its carbon budget compared with Douglas-fir at the interior site. It can be summarized that through the continued production of photosynthate during this part of the year when shoot growth has ceased, Douglas-fir at the coastal site accumulated carbohydrate reserves that may be of importance for the spring shoot growth flush as well as for current (winter) and later (spring) fine root production (See Chapter 4 concerning root biomass production). Photosynthetic rate (A) and stomatal conductance (gs) of paper birch and Douglas-fir were positively and linearly correlated (P<0.05) at the May measurements in this study at both the interior and coastal sites (Figure 3.5). Coefficients of determination for A regressed on gs were 0.72 and 0.66 for interior and coastal sites, respectively. This 32 relationship changed from the interior site to the coastal site. At the same level of g s there was higher A at the coastal site than at the interior site. In both coastal and interior climates, paper birch had higher photosynthetic rates at the same level of stomatal conductance than Douglas-fir (Figure 3.5). These data do not necessarily imply that g s is the primary factor regulating photosynthesis (Farquhar and Sharkey 1982), although stomatal aperture certainly does have an effect on CO2 diffusion into the leaf mesophyll, and, therefore, on photosynthesis. Rather, these correlations indicate that the same factors controlling stomatal conductance (in this study soil moisture and vapor pressure deficit), also control photosynthesis. Shulze and Hall (1982) presented highly significant linear regression between C O 2 photosynthetic rates and concurrent stomatal conductance. These regressions were relatively constant for individual plants of the same species, but varied between plants of different species. They concluded that in natural environments the range of gs varied so that it matches the photosynthetic capacity of leaves, this capacity being determined by the long-term effects of several environmental and plant factors. Stomatal closure of Douglas-fir was nearly complete when plant water potential was -2.5 MPa (Harrington et al. 1994). Plants adjust their stomata to the prevailing conditions in a manner that enables them to achieve a high water use efficiency while at the same time maintaining a relatively high photosynthetic rate. Stomatal conductance of most species is influenced most strongly by relative humidity during winter and spring and by pre-dawn plant water potential, which is strongly influenced by soil water potential (Harrington et al. 1994). Low humidity and high vapor pressure deficits can directly reduce stomatal apertures in many plants (Grantz 1990). 33 Figure 3.5. The relationships between photosynthetic rate (A) and stomatal conductance (gs) of paper birch (P) and Douglas-fir (D) based on data measured in May 3 and 19„ 1995 at the two different sites. 34 In general, the leaves of deciduous tree species have the potential for higher photosynthetic rates than those of evergreens, particularly when the comparison is made on the basis of leaf dry weight. In terms of carbon uptake per unit of leaf surface area, the difference is less, but is sometimes still apparent (Waring and Schlesinger 1985). The results from my study supported this conclusion. Comparisons of carbon fixation per unit of leaf dry weight and per unit of leaf area are made in Chapter 5. 3.4.3 Photosynthesis, N U E and W U E Nitrogen plays a central role in plant metabolism, not only as a constituent of the chlorophyll molecule, but also as a key component of Rubisco enzyme necessary for photosynthetic, respiratory, and growth processes. Knowledge of how plants use resources is basic to an understanding of the biology of ecosystems and of competition between species. Efficiency of use of resources has traditionally been determined by calculating ratios of productivity per unit of resource. When we obtain values for NUE and WUE of a species, we are often interested in the importance of differences between species or of the magnitude of NUE and WUE in relation to growth and survival. At the small scale of a leaf, photosynthetic NUE and WUE are calculated from gas exchange data collected from individual leaves, such as in this study. These data are often expressed as rates with a time step of 20 seconds. NUE of foliage (flux of C O 2 / g foliar nitrogen) (e. g., Sheriff 1992) is useful for comparing different species or treatments in short-term experiments. As with NUE, instantaneous gas exchange based WUE is usually determined only when conditions are suitable for carbon assimilation. It ignores water loss at other times; for example, at night when there is no photosynthesis. In some deciduous trees, photosynthetic rates can be increased by up to five-fold with higher levels of available nitrogen. Photosynthesis by conifers, on the other hand, is less responsive to variation in leaf nitrogen content, with rates usually increasing by less than 25% upon fertilization 35 (Brix 1981 and 1983). Deciduous forest trees nearly always have higher foliar N concentrations than coniferous tree species for a given climate (Yin 1993). Paper birch had significantly higher photosynthetic NUE than Douglas-fir at both sites (Figure 3.3b). However, Douglas-fir had higher biomass-based NUE (Figure 3.3a). Therefore, leaf longevity is important to definitions of NUE, because it seems likely that slower leaf turnover may be a response, possibly the most important response in evolutionary time, to low nutrient availability (Reich et al. 1992). At the leaf level, NUE can be determined either for total leaf content of nitrogen or for that portion of the nitrogen involved in carbon assimilation. Values of NUE may be different when expressed over the life of a leaf than when expressed on an instantaneous basis (Rundel 1982). The importance of this can be seen from comparison of two leaves. One such as Douglas-fir is long-lived, retains its nutrients for a long time, and has a small photosynthetic NUE; the other such as paper birch has a large photosynthetic NUE and is short-lived. Ecologically, climatic factors should better control the amount of carbon fixed per unit nitrogen than C fixation in general, which may be limited by N availability. Most comparisons of NUEs of different species that are only based on data for aboveground biomass may produce erroneous results. In this study, the results are consistent with the working hypothesis. Photosynthetic NUE of Douglas-fir in this study ranged from 1.74 to 4.98, which is within the range found in the literature (Pons et al. 1993). Within a species, NUE may be compromised as WUE increases in response to reduced water availability (Gutierrez and Meinzer 1994; Harrington et al. 1995a and b). Intrinsic WUE (ratio of assimilation to conductance) increases as water availability decreases (Harrington et al. 1995). In a fertilization experiment on Picea abies, N addition increased intrinsic WUE in a dry year but not in wet years, suggesting that the effect was that of increased LAI leading to more rapid depletion of soil water and thus stomatal closure rather than increased photosynthetic capacity (Hogberg et al. 1993). Instantaneous WUE and photosynthetic rate have been reported to be negatively 36 correlated across species (Field et al. 1983) and across treatments in Larrea tridentata (Lajtha and Whitford 1989). There is probably a negative relation between leaf area reduction and water deficit. Furthermore the decrease of leaf area growth rate (or foliage biomass) in response to summer drought (Table 3.1) seems to support the argument of Poole and Miller (1975) that the main response of shrubs to drought is to change leaf area index rather than physiological processes. Paper birch dropped some of its leaves in response to summer water stress at the coastal site. 3.4.4 Photosynthesis and SLA SLA links mass- and area-based expressions of leaf traits (Field and Mooney 1986). Significant positive relationships (p<0.05) between leaf nitrogen content per unit weight and SLA were observed for 12 tropical tree species by Reich and Walters (1994). Foliage N content per unit leaf weight increased with increasing SLA (i.e. was greater in "thinner" leaves). This was largely due to the tendency of older leaves to accumulate carbon, and thus have lower SLA and N content per unit weight than younger leaves (Reich et al. 1992). The importance of specific leaf area (SLA) is evident when the same investment of the two species in leaf mass in one year is considered. Thus, the much higher leaf area of Douglas-fir easily compensates for a lower annual carbon balance per unit of leaf mass, so that the plant with lower photosynthetic capacity actually gained more carbon. 3.5 Conclusions The results from these ecophysiological measurements on paper birch and Douglas-fir in the two different biogeoclimatic subzones partly support the hypotheses proposed in Chapter 1. Changes in climate might have affected the seasonal 37 photosynthetic patterns of paper birch and Douglas-fir differently. The following conclusions were drawn from the study. 1. Douglas-fir continued photosynthesis year round at the coastal site but only photosynthesized for seven months at the interior site. During winter it was assumed that Douglas-fir had no photosynthesis under deep snow cover. Paper birch had active photosynthesis for only six months at the coastal site and five months at the interior site. 2. Douglas-fir had higher photosynthetic NUE and WUE values at the coastal site than at the interior site. However it had higher biomass-based NUE at the interior site. 38 Chapter 4. Growth and biomass allocation of Douglas-fir and paper birch seedlings 4.1 Introduction Photosynthetic rates represent the instantaneous carbon fixation of a leaf. However, growth and competitive ability of a plant depend ultimately on its integrated lifetime carbon balance, which is associated with construction and maintenance costs. Biomass is a very good indicator of long-term photosynthetic efficiency, because it reflects the production of dry matter over long periods of time and integrates the effects of varying environmental factors (Grime 1979, Wilson and Keddy 1986). Intra- and inter-specific competition is better measured by biomass than by photosynthetic rate or yield of any plant part, because dry matter allocation within the plant varies with the competitive stress. The importance of interactions within and between species in forest ecosystems of the Pacific Northwest is well documented (Harper 1977, Walstad and Kuch 1987), especially for interactions between Douglas-fir and red alder (Shainsky and Radosevich 1992a, b). Studies examining the effects of stand density on tree performance in pure stands (Borman and Gordon 1984, Smith 1986) and in mixed stands (Puettmann et al. 1992, Shainsky and Radosevich 1991) indicate that increasing stand density generally has negative effect on tree size. Whole-plant responses to resource limitation are often described by patterns of biomass allocation to different organs (e.g., Chapin 1980; Bloom et al. 1985; Tilman 1988). The mass of an organ may be a good proxy for the cost of its construction, but mass alone is not always indicative of an organ's capacity to acquire resources. Beyond mass, the physical arrangement of roots and their physiological capacity for uptake determine the capacity for water and nutrient uptake from the soil. The spatial placement of organs in relation to resource supply determines the potential 'functional' value of biomass allocation. 39 A plant is dependent upon its root system for survival and productivity. The importance of roots has long been recognized by plant scientists, whose understanding has nonetheless been limited by the difficulties associated with the study of this organ. A large total plant root length has been associated with increased competitive ability due to the potential for increased uptake of nutrients and water. Plant root systems and their functions must be understood before competitive interactions between plants can be fully understood. Photosynthate allocation in trees must provide for stem and root extension to take advantage of available light, moisture, and nutrients, as well as for the growth necessary for structural support. When growing in competition with other plants, trees must have sufficient height extension and foliage production to avoid photosynthetic deficiency, and sufficient growth in root structure to provide mechanical support and to compete for resources. Little is known about resource allocation to roots in young stands, and even less is known about the effects of silvicultural practice (i.e., spacing and hardwood competition) on root development. Many phenotypic traits of plants change dramatically over the course of plant growth and development, a phenomenon referred to as ontogenetic drift by Evans (1972). For example, while total biomass in different plant parts, such as leaves, stem and roots, clearly increases in concert with overall growth, the proportional distribution of biomass among these parts is rarely constant for extended periods of time. Walters et al. (1993a, b) found that ontogenetic drift did affect morphology of paper birch. Few studies have quantitatively defined the effects of both intra- and inter-specific competition between Douglas-fir and paper birch, primarily because of a lack of controlled experiments with appropriate designs. Most studies on intra- and inter-specific competition in forest ecosystems have focused on aboveground competition. Roots are the least studied component of trees, even though a significant amount of carbon is allocated belowground. Newton and Cole (1991) showed that increasing the density of 40 Douglas-fir reduced both shoot and root biomass of Douglas-fir and that a constant root/shoot ratio was maintained at all densities and on all trees, except those suppressed to the point of imminent mortality. Three factors were hypothesized to strongly influence annual growth of Douglas-fir and paper birch: species specific potential growth, climate, and intra- and inter-specific competition. Potential growth is defined as growth in the absence of intra- and inter-specific competition. Climate is an integrated environmental factor. Intra-specific competition was examined by comparing biomass in different densities with that from one-seedling-per-pot pure culture. Inter-specific competition was defined as the biomass change between pure and mixed cultures at the same density level. The research objectives of the study were: 1) to quantify the phenological patterns of leaf area development, growth and biomass allocation of paper birch and Douglas-fir seedlings in the two biogeoclimatic subzones; 2) to compare treatment means of seedling growth and biomass production in the two different biogeoclimatic subzones; and 3) to test whether climate resulted in different intra- and inter-specific competitive abilities of Douglas-fir and paper birch seedlings in terms of height and basal diameter growth and biomass allocation. These objectives were achieved by sequential harvesting of seedlings over the period of the study. 4.2 Material and methods 4.2.1 Plant material and experimental design The species used and the experimental design in this study have been described in detail in Chapter 3. 4.2.2 Seedling measurements Before planting, 30 seedlings of each species were randomly selected and measured for their initial heights and basal diameters, and mass (dry weight at 70°C for 41 48 hrs) of stem, root and foliage in order to get the mean "zero" time values. Foliage nitrogen concentrations of five randomly selected seedlings were analyzed. Table 4.1 presents the characteristics of the planted seedlings at the start of the experiment. Seedlings were harvested and measured once every month during the growing season (May to October, 1994). A total of five sets of harvests and measurements were performed in one growing season. Three pots were randomly selected from each species-density-climate combination at each sampling date. Table 4.1 Characteristics of the seedlings of paper birch, coastal Douglas-fir and interior Douglas-fir at the start of the experiment. Based on 30 randomly selected seedlings. Character Paper birch Coastal Douglas-fir Interior Douglas-fir Height (cm) 31.5±0.89 14.5+0.32 16.3±0.32 Caliper (mm) 6.110.11 1.8±0.04 2.110.03 Foliage (g) 1.2±0.08 0.6±0.03 0.5±0.02 Shoot (g) 1.6±0.06 0.2±0.01 0.210.01 Root (g) 2.4±0.13 0.4±0.02 0.510.02 R/S ratio 0.8±0.04 0.5+0.02 0.710.02 Total biomass (g) 5.2±0.18 1.2±0.05 1.210.05 Foliage N (%) 2.5±0.13 0.9+D.16 1.010.05 After planting in pots and burying the pots, all the seedlings were marked on the stem at the same position. At each harvesting time the sampled pots were then excavated, the seedlings were carefully removed and measured for biomass of foliage, stem, branches and roots. Stem diameter at the mark was measured to the nearest 0.1 mm with a digital micrometer. Height from the mark to tip of the dominant meristem was 42 measured to the nearest mm with a steel ruler. Roots were carefully hand-washed in a series of trays of clean water in order to remove adhering soil and preserve broken fine roots. Each of these biomass components was oven-dried at 70°C for 48 hours and then weighed to the nearest O.Olg. To assess allocation patterns, the proportion of total biomass allocated to roots, foliage and stems was calculated. Allocation to leaves was assessed by calculating leaf area ratio (LAR: leaf area per unit of total biomass, cm"2 g " 1), and leaf weight ratio (LWR: leaf biomass per unit of total biomass). LAR and LWR are discussed in Chapter 5. 4.2.3 Statistical analysis Three-way factorial ANOVA (Zar 1984) was conducted on all growth and biomass parameters to test the effects of climate, species, and density, and their two- and three-way interactions. The MGLH procedures in SYSTAT (Wilkinson et al. 1996) were used on seedling means of height, basal diameter, biomass of foliage, stem and root and root/shoot ratio. The following is the model form for this design: Y = p + C i + S j+D k + (C*S) i j + (C*D) i k+ (S + Djfc+CC + S+Dfcjk + Eijk where Y is the observed mean \1 is the overall mean Cj represents the effect of climate (coastal, interior) Sj represents the effect of species and variant (paper birch, coastal and interior Douglas-fir) D^ represents the effect of densities (1, 2, 4 and 6 seedlings per pot) (C * S)ij, (C * D)^ and (S * D)^ and (C * S* D)^ represent the interactions between corresponding factors. £jjk is the random error 43 Significance was set at oc= 0.05. If significant differences were detected among the levels of a factor, then a multiple comparison procedure (Tukey Test) was used. In addition, to determine the statistical significance of species effects, separate analyses of ANOVA were performed for each harvest, and for pure and mixed cultures. To test the hypothesis that competition alters the allometric relationships of plants, allometric relationships between root and shoot biomass, and between height and basal diameter were examined using regression analysis and individual seedling observations. The basic form of each equation was In (Y) = a + b ln(X) where b represents the allometric coefficient for the relationship between Y and X. For each species, regression coefficients among the four (for pure culture) and three (for mixed culture) densities were compared using Tukey multiple comparison tests (Zar 1984). 4.3 Results 4.3.1 Seasonal growth patterns without intra- and inter-specific competition In this section, all the results and analyses were based on the one-seedling-per-pot treatment. This allows analysis of differences in growth patterns between the species and variants at the two different sites without inter- and intra-species competition. The potential growth rate was defined as growth that occurs in the absence of competition, and is thus largely a function of climate and the morphology of the species. 4.3.1.1 Height and basal diameter growth Figure 4.1 displays the means and standard errors of the means (n=3) of height (a and b) and basal diameter (c and d) for paper birch and Douglas-fir at each harvest time at 44 120 100 80 60 h 40 20 n 1 1 r Douglas-fir • C o a s t a l s i t e • I n t e r i o r s i t e L M M I S t a r t M a y J a n e J u l y A u g S e p t S t a r t M a y J u n e J u l y A u g S e p t S t a r t M a y J u n e J u l y A u g S e p t M o n t h 20 I S 10 d Douglas-fir S t a r t M a y J u n e J u l y A u g S e p t M o n t h Figure 4.1. Seasonal growth patterns of mean height (a, b) and basal diameter (c, d) of paper birch and coastal Douglas-fir at the coastal site and interior Douglas-fir at the interior site. Bars represent mean ± 1 SE. Data were from the one-seedling-per-pot treatment without any competition. Start refers to summer 1993. 45 the two sites. Douglas-fir seedlings were significantly (p<0.05) taller at the coastal site than at the interior site only in May and June (Figure 4.1b). However, in August and September, the height of paper birch at the interior site exceeded that at the coastal site (Figure 4.1 a). No significant difference in height of Douglas-fir between the two sites was detected in August (Figure 4.1b). Douglas-fir had a greater basal diameter and height at the coastal site than at the interior site (Figure 4.1b, d). Compared with paper birch, height and basal diameter growth of Douglas-fir was relatively slow at both sites. 4.3.1.2. Biomass production Foliage biomass per plant of both paper birch and Douglas-fir changed throughout the growing season between coastal and interior sites (Figure 4.2 a, b). However, Douglas-fir constantly had higher foliage biomass at the coastal site than at the interior site throughout the growing season (Figure 4.2 b). At the coastal site, paper birch lost most of its leaves in early September (Figure 4.2a). Leaf canopy duration in paper birch was 20 days less at the coastal site than at the interior site. Douglas-fir at the coastal site had the lowest foliage biomass in July. This coincided with summer water stress at the coastal site (see Table 3.2 and Figure 2.1). Shoot biomass (always included branches) per plant of paper birch increased significantly from May to September at both sites (Figure 4.2c); from May to August, it was higher at the coastal site, but the order was reversed in September. This was caused by early leaf fall of paper birch at the coastal site. Douglas-fir had significantly (p<0.05) greater shoot biomass at the coastal site than at the interior site (Figure 4.2d) but it increased slowly at both sites. Root biomass per plant of paper birch increased significantly with age from May to August at the coastal site (Figure 4.3a). Interestingly, root biomass of paper birch declined significantly in September at the 46 25 20 15 10 n 1 1 r Douglas-fir • Coastal site • Interior site • n 1*1 . i 1 i 1 Start May June July Aug Sep Start May June July Aug Sep Start May June July Aug Sep Month Start May June July Aug Sep Month Figure 4.2. Seasonal growth patterns of mean foliage biomass (a, b) and shoot biomass (c, d) per plant of paper birch and coastal Douglas-fir at the coastal site and interior Douglas-fir at the interior site. Bars represent mean ± 1 SE. Data were from the one-seedling-per-pot treatment without any competition. 47 25 20 15 10 5 h 1 1 1 r b Douglas-fir • C o a s t a l s i t e • I n t e r i o r s i t e S t a r t M a y J u n e J u l y A u g S e p S t a r t M a y J u n e J u l y A u g S e p 55 „ 44 a I 33 22 11 "i 1 r c Paper birch S t a r t M a y J u n e J u l y A u g S e p M o n t h S t a r t M a y J u n e J u l y A u g S e p M o n t h Figure 4.3. Seasonal growth patterns of mean root (a, b) and total biomass (c, d) per plant of paper birch and coastal Douglas-fir at the coastal site and interior Douglas-fir at the interior site. Bars represent mean ± 1 SE. Data were from the one-seedling-per-pot treatment without any competition. 48 coastal site (Figure 4.3a) as paper birch lost most of its leaves in September (Figure 4.2a). In contrast Douglas-fir root biomass per plant did not increase with age significantly except in September at the coastal site (Figure 4.3b). Douglas-fir had larger root biomass at the coastal site than at the interior site. Total biomass per plant of paper birch increased significantly with age except in September at the coastal site where paper birch lost its leaves earlier (Figure 4.3c). There were significant differences in total biomass per plant for Douglas-fir at the two sites (Figure 4.3d). 4.3.1.3. Biomass allocation Root/shoot ratios of paper birch declined from May to August and increased in September at the interior site, and varied throughout the growing season at the coastal site (Figure 4.4b). A similar seasonal pattern was found for Douglas-fir root/shoot ratio (Figure 4.4a). Both paper birch and Douglas-fir had significantly (p<0.05) larger root/shoot ratios at the interior site at the beginning of growing season (May). As Douglas-fir grew, allocation of biomass to foliage decreased slightly as root biomass increased at the coastal site (Figure 4.5a). At the interior site, Douglas-fir allocated less biomass to foliage and root at the end of growing season (Figure 4.5b). Allocation to foliage biomass of paper birch decreased rapidly towards the end of growing season at the coastal site (Figure 4.5c). The percentage of paper birch root biomass increased slightly at the beginning of the growing season and then dropped to the lowest level in July except for paper birch at the coastal site (Figure 4.5c). This might have been caused by water stress in July and the dying of fine roots. Paper birch had a relatively constant shoot biomass allocation throughout the growing season at the interior site (Figure 4.5d). 49 Figure 4.4. Seasonal growth patterns of mean root/shoot ratio of paper birch (b) and Douglas-fir (a) at the coastal and the interior sites. Bars represent mean + 1 SE. Data were from the one-seedling-per-pot treatment without any competition. 50 Coastal site Paper birch Interior site S F o l i a g e • S h o o t H R o o t s M o n t h M o n t h Figure 4.5. Seasonal allocation patterns of biomass between foliage, shoot and roots for Douglas-fir (a and b) and paper birch (c and d) at the coastal and interior sites. Data were from the one-seedling-per-pot treatment without any competition. 51 4.3.2 Climatic and density effects on biomass production in pure culture Data on biomass of foliage, shoot, and root, and on root/shoot ratios at the time of the August 1994 harvest are presented in Table 4.2 for interior and coastal sites. Data from the other harvest dates are presented in Appendix I. In general, both paper birch and Douglas-fir growing in pure culture had greater total biomass, and foliage, shoot and root biomass at the coastal site than at the interior site except foliage biomass for paper birch and shoot biomass for interior Douglas-fir (Table 4.2). Analysis of variance revealed that climate (interior vs. coastal), species and density had significantly (p<0.001) influenced all measured growth and biomass parameters (Table 4.3) of Douglas-fir and paper birch seedlings. Significant species effects on all the parameters measured occurred at all harvest dates (see the ANOVA tables in Appendix II). The climate xspecies interaction had significant (p<0.001) effects on foliage, shoot and root biomass, and the root/shoot ratio. This reflects the effects on growth of transplanting interior and coastal Douglas-fir outside their natural climatic regions. Only height was significantly affected by the climate x density interaction (see Appendix II). No significant effect was detected by the climate x density and the climate x species x density interactions on most other measured parameters except root/shoot ratio (Table 4.3). 52 Table 4.2. Foliage, shoot and root biomass (mean±SE, g per plant) and root/shoot ratios of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in pure cultures at four densities at the interior and coastal sites harvested in August, 1994. Density PB C-DF I-DF C-Site I-Site C-Site I-Site C-Site I-Site Foliage 1 8.30±2.63 9.05±0.26 5.76±2.61 2.90±0.29 4.45+0.50 2.9010.29 2 6.42±2.38 5.03±0.74 4.9211.05 1.73±0.14 3.74+0.40 1.73±0.14 4 3.37±0.36 2.57±0.22 8.00±0.87 2.19±0.15 3.19±0.41 2.19±0.15 6 2.5110.48 7.29+4.58 5.94±0.45 1.54±0.09 3.43+0.89 1.54+0.10 Shoot 1 15.89+3.79 12.22+0.64 4.23±2.10 3.21+0.18 3.18+0.15 3.21+0.12 2 12.19±3.09 6.6210.82 4.5610.66 1.6710.21 2.7410.55 1.6710.21 4 7.6010.69 4.7010.37 5.6110.51 2.1210.14 2.6710.39 2.1310.14 6 8.2010.77 4.9810.44 4.2610.24 1.3010.09 2.9110.53 1.30+0.09 Root 1 18.2614.72 11.2310.84 4.3410.28 2.7110.24 3.2410.22 2.7110.24 2 12.4712.48 7.5110.61 3.2510.38 2.4210.15 3.4410.77 2.4210.15 4 7.8410.70 5.1910.43 5.3510.57 2.7110.16 2.4710.35 2.7110.16 (j 6.3610.92 3.7510.27 2.9810.29 2.0210.10 2.0210.41 2.0210.10 R/S 1 0.7510.01 0.5310.02 0.6010.18 0.6110.01 0.4310.06 0.6110.01 2 0.7410.11 0.6810.07 0.3710.05 0.7210.03 0.52+0.07 0.7210.03 4 0.7310.04 0.7210.04 0.4110.04 0.6410.03 0.4210.03 0.64+0.03 6 0.5910.03 0.7810.03 0.3010.05 0.7310.04 0.3410.04 0.7310.04 Total 1 42.4519.93 32.4911.56 14.3414.95 9.8210.61 10.8610.60 9.8210.61 2 31.0817.62 19.1511.95 12.7511.91 8.8310.44 9.15+1.66 5.83+0.44 4 18.8211.61 12.4610.87 18.9611.87 7.0210.40 8.3311.10 7.0210.40 6 17.0712.00 11.77+0.89 13.5510.77 4.8610.24 8.3710.04 4.8610.24 53 Table 4.3. F-values from the three-way ANOVA of plant biomass variables in pure culture in the competition experiment. The data are from the August harvest, 1994 . Source of variance FoliageShoot Root Root/shoot Pure culture (n =70) Climate 44.154*** 52.745*** 33.548*** 23.863*** Species 16.810*** 153.002*** 150.402*** 10.915*** Density 10.878*** 13.769*** 25.769*** 3.324* Climate x species 15.253*** 7.486*** 13.823*** 22.821*** Climate x density 0.794 0.452 0.922 5.023 Species x density 9.148*** 9.530*** 13.823*** 3.455** Climate x species x density 1.314 0.952 1.525 2.855* *P<0.05, **P<0.01, ***P<0.001. Total biomass, foliage, shoot and root biomass, and root/shoot ratios per plant varied significantly with intra-specific competition (density effect) and climate for both species (Table 4.3, Figure 4.6 and Figure 4.7). However, no significant (p>0.05) differences in total biomass and foliage biomass per plant were detected (Figure 4.6a, b) for paper birch at the highest density (6 seedlings per pot) between the two sites (i.e. the two climates). Total biomass and foliage biomass per plant for paper birch grown in pure culture decreased as density (plants per pot) increased (Figure 4.6a, b), indicating that intra-specific competition was occurring above a density of 1 seedling per pot. No significant differences in foliage biomass per plant of paper birch between four and six seedlings per pot at the interior site were found (Figure 4.6b). At the interior site, paper birch had larger foliage biomass per plant than Douglas-fir in all treatments (Fig 4.16b). 54 Both coastal and interior Douglas-fir showed little intra-species competition, especially at the coastal site (Figure 4.6c-f). Total biomass and foliage biomass of coastal and interior Douglas-fir did not significantly(p>0.05) decrease as density increased (Figure 4.6 c, d and e, f), especially for interior Douglas-fir at the interior site (Figure 4.6f). However, coastal Douglas-fir had much larger total biomass and foliage biomass (Figure 4.1 c, d) at the coastal site than at the interior site. There were no significant differences among different densities in foliage biomass per plant of coastal and interior Douglas-fir at the interior site (Figure 4.6 d and f). Similar patterns were found for shoot and root biomass of coastal and interior Douglas-fir in pure culture at the two sites (Figure 4.7). Root biomass increased at the 2-seedlings-per-pot density for interior Douglas-fir at the coastal site (Figure 4.7f) and shoot biomass decreased significantly at the interior site as density increased (Figure 4.7e). Root/shoot ratios of paper birch increased as density increased at the interior site but decreased at the coastal site (Table 4.2). Root/shoot ratios of coastal Douglas-fir at the interior site ranged from 0.61 to 0.73 with an average of 0.68±0.06 across all densities. Increasing density tended to result in an increase in root/shoot ratio of interior Douglas-fir at the interior site. In contrast, coastal Douglas-fir had relatively small rool/shoot ratios at the coastal site with an average of 0.42±0.13. Increasing density tended to decrease the root/shoot ratio of Douglas-fir at the coastal site (Table 4.2). The same pattern was found for paper birch. The root/shoot ratio of paper birch increased from 0.53 to 0.78 as density increased from 1 seedling to 6 seedlings per pot (Table 4.2) at the interior site. In contrast, the root/shoot ratios of paper birch decreased as density increased at the coastal site. This indicates that there was likely more aboveground competition at the coastal site and more belowground competition at the interior site. 55 Figure 4.6. Total biomass (left panel) and foliage biomass (right panel) per plant of paper birch (a, b), coastal Douglas-fir (c, d) and interior Douglas-fir (e, f) grown in pure culture at different densities. Bars represent ± 1 SE. Data are from the August, 1994 harvest. 56 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Density (plants per pot) Density (plants pet pot) Figure. 4.7. Shoot biomass (left panel) and root biomass (right panel) per plant of paper birch (a, b), coastal Douglas-fir (c, d) and interior Douglas-fir (e, f) grown in pure culture at different densities at different sites. Bars represent ± 1 SE. Data are from the August, 1994 harvest. 57 4.3.3. Climate and density effects on biomass production in mixed culture Foliage, root and total biomass per plant of paper birch decreased with increasing density in all the treatments (Table 4.4). In contrast, there were no clear decreasing patterns in any biomass parameters for Douglas-fir as density increased. Total biomass per plant of both coastal and interior Douglas-fir was significantly (p<0.001) higher at the coastal site than at the interior site (Figure 4.8a, b). Total biomass of paper birch decreased significantly from 2 seedlings per pot (i.e. 1 PB + 1 DF) to 4 seedlings per pot (i.e. 2 PB + 2 DF) at the coastal site (Figure 4.8 c, d). Paper birch had significantly less total biomass per plant as density and competition with Douglas-fir at the coastal site increased (Figure 4.8c and d). Foliage biomass per plant of coastal Douglas-fir was highest (5.6 g) at the density of 4 seedlings per pot at the coastal site (Table 4.4 and Figure 4.9 a) and decreased as the density increased to 6 seedlings per pot (i.e. 3 PB + 3 C-DF). Foliage biomass per plant of interior Douglas-fir decreased steadily with increasing density at the coastal site, but varied little at the interior site (Figure 4.9 b). Paper birch had lower foliage biomass per plant at the coastal site than at the interior site when competing with both Douglas-fir variants at higher densities (Figure 4.9 c, d). As in the pure cultures, ANOVA revealed no significant climate x density and climate x species x density interactions on all parameters measured (Table 4.5). Species and density interaction had significant effects on all the biomass parameters for the August harvest except the root/shoot ratio in the mixed culture (see Appendix II). Climate had a significant (p<0.01) effect on shoot biomass and the root/shoot ratio. No significant difference in the root/shoot ratio between species was detected in the ANOVA. Significant differences were found in the root/shoot ratios between species at the coastal site (Table 4.4) giving a significant (p<0.01) climate x species two-way interaction for the root/shoot ratio. This indicates that climate had altered the allocation patterns of these species, and that severe belowground inter-specific root competition 58 between paper birch and Douglas-fir occurred at the coastal site. The effects of increasing density from two to six seedlings per pot were not significant (p<0.05) on height and basal diameter growth (Appendix II). Table 4.4. Foliage, shoot, root and total biomass (mean±SE, g per plant), and root/shoot ratios of paper birch (PB), and coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in mixed culture at three densities at the interior and coastal sites harvested in August, 1994. Density PB C-DF I-DF C-site I-site C-site I-site C-site I-site Foliage 2 7.86±1.67 4.91±2.70 4.93±0.89 1.88+0.23 2.91±0.68 1.09±0.13 4 3.15+0.87 4.25+0.36 5.61±0.99 1.22+0.14 2.53±0.30 1.38+0.17 6 2.99+0.32 3.32±0.44 3.59+.0.48 1.28±0.08 2.36+0.49 1.06+0.13 Sh00t 2 15.23+2.56 8.48+0.63 2.54±1.14 1.16±0.17 1.81+0.12 1.29±0.11 4 7.49+1.35 7.05+0.74 2.82±0.39 1.00±0.15 1.20±0.22 1.32+0.22 6 9.12±1.30 4.47+0.47 2.35+0.15 0.96+0.04 1.13±0.21 0.74±0.08 Root 2 15.57±2.85 10.11+0.65 3.40+0.93 2.11±0.26 2.15+0.45 1.69±0.16 4 7.23+1.67 7.79±0.95 2.59+0.37 1.5710.09 1.80+0.32 1.77±0.21 6 7.07+0.65 6.29±0.43 2.14±0.18 1.50±0.14 1.56+0.23 1.57±0.24 R/S 2 0.68+0.07 0.85+0.19 0.46+0.01 0.70±0.02 0.46±0.04 0.71±0.04 4 0.81+0.02 0.6810.02 0.31±0.03 0.74+0.06 0.40+0.03 0.67±0.04 6 0.84±0.20 0.85+0.06 0.33+0.02 0.66+0.03 0.41+0.06 0.86±0.09 Total 2 38.66±6.81 23.51±2.73 10.87±2.95 5.15+0.63 6.87+1.19 4.08±0.36 4 17.79±2.78 19.10±1.99 11.02±1.69 3.97+0.32 6.25+0.78 4.46±0.57 6 19.34+2.65 14.07+1.17 8.08+1.12 3.74±0.25 6.01±0.89 3.37±0.40 Note: density 2= IDF +1PB; density 4= 2 DF +2 PB and density 6= 3 DF + 3 PB 59 1 2 3 4 Coastal DF density (plants per pot) 1 2 3 4 Interior DF density (plants per pot) Figure 4.8. Total biomass per plant at different densities of (a) coastal Douglas-fir, and (b) interior Douglas-fir mixed with paper birch; of paper birch mixed with (c) coastal Douglas-fir and (d) interior Douglas-fir. Bars represent ± 1 SE. Data are from the August, 1994 harvest. 60 10 ,59 u A oo 4 .S o Coastal D F 10 a 00 o tin Interior D F Interior site coastal site 1 2 3 4 Coastal DF density (plants per pot) 0 1 2 3 4 Interior DF density (plants per pot) Figure 4.9. Foliage biomass per plant at different densities of (a) coastal Douglas-fir, (b) interior Douglas-fir mixed with paper birch; of paper birch mixed with (c) coastal Douglas-fir and (d) interior Douglas-fir. Bars represent + 1 SE. Data are from the August, 1994 harvest. 61 Table 4.5. F-values from three-way ANOVAs of plant biomass variables in mixed culture in the competition experiment. The data were from the harvest in August, 1994. Source of variance FoliageShoot Root Root/shoot Mixed culture (n=211) Climate 0.755 5.490*** 3.680 7.749** Species 4.337** 82.378*** 109.998*** 2.340 Density 2.730* 4.176** 11.156*** 0.010 Climate x species 3.173* 0.651 0.718 6.652** Climate x density 1.608 0.330 2.184 0.726 Species x density 3.347* 5.832** 8.742*** 1.068 Climate x species x density 1.900 0.796 1.700 0.155 *P<0.05, **P<0.01, ***P<0.001. 4.3.4. Relationships between foliage and total biomass, and root and shoot biomass Regression analyses revealed no significant differences between different densities in relationships between foliage and total biomass per seedling, basal diameter and height, and root and shoot biomass (data not presented). Therefore, data from different density treatments were pooled to develop regression equations between these variables within each species for the coastal and interior sites, respectively. On both research sites, significant relationships between foliage and total biomass per seedling were observed within each species (Figure 4.10). It is clear that the difference in total biomass per unit of foliage biomass between paper birch and Douglas-fir was greater at the interior site than at the coastal site. This suggests that the competitive effect caused by Douglas-fir on paper birch at the coastal site was greater than at the interior site. Similar relationships were found for basal diameter and height, and root and shoot biomass (Table 4.6). A two tailed Mest revealed significant differences in intercept and slope between the two sites for the three relationships (p<0.05). 62 15 Interior site ~ 10 4 6 8 10 Foliage biomass (g) Figure 4.10. Relationships between total biomass and foliage biomass per plant of paper birch (P) and coastal Douglas-fir (C) and interior Douglas-fir (I) at the two research sites. Regression equations and significance levels are presented in Table 4. 6. 63 Table 4.6. Linear regression relationships between total biomass (Tb) and foliage biomass (Fb), height (Ht) and basal diameter (Bd), and root biomass (Rt) and shoot biomass (St) for paper birch (PB) and Douglas-fir (DF) growing at two different sites. Dependent Independent Species Site variable variable Intercept Slope r2 P PB c* Tb Fb 7.979 3.527 0.85 0.000 I Tb Fb 6.183 2.577 0.71 0.000 C Ht Bd 12.682 5.318 0.33 0.000 I Ht Bd 0.963 6.194 0.56 0.000 C Rt St 0.658 0.621 0.77 0.000 I Rt St 1.807 0.455 0.59 0.000 DF c* Tb Fb 1.658 2.045 0.93 0.000 I Tb Fb 0.392 2.945 0.88 0.000 C Ht Bd 12.336 3.457 0.32 0.000 I Ht Bd 9.678 4.642 0.38 0.000 C Rt St 0.826 0.269 0.53 0.000 I Rt St 0.614 0.475 0.73 0.000 * C represents the coastal site and I the interior site. 64 Regression models were also constructed relating Douglas-fir growth performance at the two different sites in response to paper birch biomass at the same densities (Figure 4.11). Following Turkington et al. (1993), it was assumed that the coefficient of determination (r2) of the regression is a measure of the competitive interactions between paper birch and Douglas-fir. Comparisons of slopes between sites for each species were performed where the slopes were significantly (p<0.05) different from 0 (Figure 4.11a, b and d). Regression coefficients, measures of the competitive effects of paper birch on Douglas-fir, were significantly different between coastal and interior sites (p<0.05, t-Test). The competitive effects of a neighbor species (paper birch) on a target species (Douglas-fir) could be ascertained from the slopes of the regressions of the size (e.g., biomass) of the target Douglas-fir on the amount of biomass of neighbors (paper birch). Douglas-fir biomass increased significantly with increasing neighbor paper birch biomass, especially for coastal Douglas-fir at the coastal site (Figure 4.1 la). Differences in slopes between the two sites within species were large relative to differences between species. 4.4 Discussion 4.4.1 Competition, growth and biomass production Compared with paper birch, height and basal diameter growth of Douglas-fir was relatively slow (Figure 4.1). This was because Douglas-fir allocated most of its biomass to roots and foliage in the early growing season. At the coastal site, paper birch lost most of its leaves in early September (Figure 4.2a). This was partially due to summer drought and partially to insect damage by the birch leafminer (Fenusa pusilla Lepeletier) observed in the field. No data were collected on damage by the birch leaf miner. 65 r2=0.241. SEE=1.425 Z « 10 20 30 Biomass (g/plant) 15 40 S 1 0 a o 5 5 —I ; r / / / / / / r2=0.331, SEE=0.715 y=2.758+0.064x / 10 20 30 Biomass (g/plant) 40 Paper birch Figure 4.11. The relationships between target (Douglas-fir) biomass and neighbor (paper birch) biomass in two different environments (coast and interior). Dashed line indicates a 1:1 relationship. The data were from mixed cultures at 2, 4, and 6 seedlings per pot. 66 Simultaneously varying conifer and hardwood ratios and their densities under controlled field conditions resulted in quantifiable changes in biomass production per tree of Douglas-fir and paper birch. Increased total biomass and foliage biomass of coastal Douglas-fir at the density of 4 seedlings per pot in the mixed culture at the coastal site (Figure 4.8a and Figure 4.9a) may reflect the relatively sheltered conditions for Douglas-fir under the paper birch canopy. Average height in August of paper birch was 57.9 cm and only 27.0 cm for Douglas-fir which was less than Douglas-fir height in pure culture (See Appendix I). The sheltering of Douglas-fir by paper birch thus appeared to have a positive effect. This was also shown by the fact that density had no significant (p<0.05) effect on Douglas-fir height growth. Inter-specific competition interacted with intra-specific competition to influence tree biomass production, as indicated by the significance of the interaction terms in the ANOVA (Table 4.3). In Figure 4.11 it was shown that the presence of paper birch benefited Douglas-fir the most at the coastal site. In other words, paper birch had less negative impact on Douglas-fir through competition at the coastal site. Therefore we may infer that at the coastal site, it may not be necessary to eliminate all paper birch where it occurs in a Douglas-fir plantation. 4.4.2 Competition and above- and below-ground biomass allocation There are two preconditions that must exist before root competition can occur: (1) there must be overlap of uptake zones for nutrients and water between the roots of neighboring plants, and (2) there must be insufficient nutrients and moisture available from the whole root system to support unrestricted growth of all plants (i.e., nutrient limitation). In this experiment, the wide array of growing conditions produced by the gradient in densities (seedlings per pot) caused great variation in soil moisture and nutrient regimes. The different soil moisture and nutrient regimes would have resulted in changes of carbon allocation to above- and below-ground biomass of the competing 67 seedlings. In the pure cultures, paper birch, coastal and interior Douglas-fir decreased their root/shoot ratios as density increased at the coastal site, but increased their root/shoot ratios at the interior site (Table 4.2). This indicates that there was more below-ground intra-specific competition for these species at the interior site than at the coastal site. In the mixed culture, no significant difference (p<0.05) was found in root/shoot ratios between coastal and interior sites for paper birch (Table 4.4). In contrast, both coastal and interior Douglas-fir had significantly smaller root/shoot ratios at the coastal site than at the interior site. This indicates that Douglas-fir experienced less below-ground competition from paper birch at the coastal site than at the interior site. The results from this study agree with that of Newton and Cole (1991). They reported an increased root/shoot ratio where trees were severely suppressed. Gedroc et al (1996) and Aerts et al. (1991) reported that high-nutrient-grown plants had lower root/shoot ratios than low-nutrient-grown plants. However, Tesch et al. (1993) reported that competition from sclerophyllous shrub sprouts reduced Douglas-fir seedling growth but did not alter its root/shoot ratios. The very small change in root/shoot ratio through the whole growing season for both paper birch and Douglas-fir at both sites (Figure 4.4 a, b) is similar to results observed by Newton and Cole (1991) for Douglas-fir on wetter sites in Oregon. Both the root/shoot ratios (Table 4.4) and the allometric equation slope coefficients (Table 4.6) indicated that seedlings under all levels of competition favored root biomass growth during the growing season. This reflects the low level of aboveground competition for light since the experimental pots were laid out 1 m apart; there was no mutual shading among the pots. Unfortunately, the effects of available light, soil moisture and soil nutrients could not be separated from those of climate in this study. The phenology of the species indicates that all parts do not grow simultaneously; rather, the growth of various parts is phased separately (e.g., roots, leaves and shoot). The argument has been made that time separation of growth phases is due in part to the 68 limitation of the building material and that priority is given at any time to the current most critical growth phase (Mooney 1983; Bloom et al. 1985; Chapin et al. 1990). This study demonstrated temporal differences in the resource allocation patterns to the various structural plant components (Table 4.3; Table 4.4 and Figure 4.1-4.5). Allocating more carbon to leaves may result in an enhancement of the photosynthetic apparatus under low light conditions. This enhancement may be minimal if nitrogen and other nutrients are unavailable for sufficient production of rubisco and other photosynthetic components (Tissue etal. 1993). Plant traits are ultimately based on allocation. A plant that allocates more carbon to the production of stem has less to allocate to roots, leaves and seeds. Thus, a change in the morphology, physiology or behavior of a plant that increases its fitness in response to one suite of environmental constraints should have a cost that decreases its fitness under other conditions. 4.5 Conclusions Growth and biomass production are the ultimate indicators of long-term photosynthetic efficiency. Competitive ability of a species is related to its ability to grow. Climate significantly affected growth, biomass production and allocation of paper birch and Douglas-fir, and, therefore, their competitive abilities in this study. Conclusions drawn based on the results of this Chapter are as follows: In the one-seedling-per-pot treatment with no intra- and inter-specific competition 1. Douglas-fir had significantly larger basal diameter and height at the coastal site than at the interior site throughout the growing season. In contrast, paper birch were taller in the early part of the growing season at the coastal site. No significant difference in basal diameter was found for paper birch between the coastal and interior sites. 69 2. Douglas-fir had significantly larger foliage, root, shoot and total biomass per plant at the coastal site than at the interior site. However, it had a lower root/shoot ratio at the coastal site. The opposite was true for paper birch. With infra-specific competition 3. Paper birch decreased its foliage, shoot, root and total biomass significantly with increasing density. A strong intra-specific competition was detected for paper birch at both sites. 4. Douglas-fir experienced less intra-specific competition at both sites. With intra- and inter-specific competition 5. Douglas-fir had greater negative effects on paper birch in terms of growth and biomass production at the coastal site than at the interior site. In contrast, paper birch had greater negative effect on Douglas-fir at the interior site than at the coastal site. 6. Douglas-fir had a lower root/shoot ratio when competing with paper birch at the coastal site than at the interior site. 70 Chapter 5 Growth analysis of paper birch and Douglas-fir seedlings at the coastal and interior sites 5.1 Introduction The growth of a plant is an expression of interactions among its physiological processes and the environment. Plant productivity is expressed in several ways. The simplest is the size of a plant (e.g., biomass, basal area, or height as described in Chapter 4). Remeasurement of plant size over time allows determination of growth rates. However, in all plants, and particularly in perennial plants, growth rate is strongly related to plant size, and treatment effects are often obscured by the variability in size of individual plants. Comparison of the growth of plants of different sizes is facilitated by the use of relative growth rate (RGR) (Hunt 1982). RGR analysis helps to explain differences in plant growth, either between species growing under the same environmental conditions, or within a species grown in different environments. Growth analysis provides a method of integrating the physiological responses of plants growing under different environmental conditions over time. Thus, it provides a powerful tool for evaluating the early growth of planted seedlings. Plant growth analysis is well developed in the fields of agriculture and botany where the majority of species are annual, biennial, or short-lived perennials (Evans 1972, Hunt 1982). Growth analysis has been a useful technique in the study of these plants because it bridges between the empirical and the mechanistic approaches to modeling growth and development. The procedure involves collecting primary data on leaf area and plant component dry weights from periodic harvests of sample plants. In this study, height and basal diameter of the sample plants were also measured periodically. Growth analysis has been less widely applied to forest stands or trees, owing to the problems of tree size and life span. However, the few studies that have made use of growth analysis have provided insight into mechanisms of response to fertilization and thinning (Brix 71 1983, Pothier and Margolis 1991), competition between Douglas-fir and hardwood species (Tesch etal. 1993, Shainsky and Radosevich 1992a), and plantation establishment (Margolis and Brand 1990, Brand 1991). Walters et al. (1993a, 1993b) reported the relative growth rate of paper birch seedlings in relation to physiological and morphological traits, and light conditions. It was found that for paper birch in moderately low light (8% of full light) growth was correlated only with allocation to leaves. Thus, allocation to leaves could be more important than leaf photosynthetic rate as a source of variation in low light growth rate. In this study, deciduous paper birch and evergreen Douglas-fir were grown in a pot experiment replicated in two different biogeoclimatic subzones: CWH and ICH in British Columbia. A detailed growth analysis was carried out in order to identify the key processes and structures responsible for the differences in seedling growth rate between the two sites. The wide range of RGR exhibited by these two species also permitted general relationships to be drawn between RGR and various components of growth. The objective of this study was to explore in greater detail relationships between RGR and plant traits by asking: (1) How are RGR and its physiological and morphological determinants influenced by competition and climate? (2) Are relationships between RGR and linked plant traits consistent within and across the environmental gradients? 5.2. Material and methods 5.2.1. Experimental design and measurements The data analyzed in this Chapter were from the sequential biomass harvests. Therefore, the experimental design, growth and biomass measurements were the same as described in sections 3.2.2. and 4.2.1. 72 5.2.2. Data analysis Standard parameters of growth analysis were used to analyze the growth of different species and treatments. RGR was determined by functional growth analysis (Hunt 1982) of means of monthly measurements for each species by using the equation RGR = '"^Ij^1 > where W2 and W\ are the end and beginning dry weight, respectively, T2 and T\ are the days after planting at the end and beginning of the calculation period. Cubic polynomial curves were fitted for all treatment combinations and a common intercept (initial biomass, see Table 4.1) was specified for both species and the Douglas-fir variant to describe the response curves of means of total plant dry weight, foliage, shoot, root weight, root/shoot ratio, height and basal diameter growth over time (days after planting). Data were transformed prior to the analysis by taking the natural logarithm of the original values. Allocation patterns were assessed by calculating the other growth indices such as leaf area ratio (LAR, leaf area per unit total plant biomass, m 2 g-1), leaf weight ratio (LWR, leaf weight per unit total plant biomass, g g_i) and root weight ratio (RWR, root weight per unit total plant biomass, g g"1) determined on a per plant basis according to the following formulae: LAR=LA/W, LWR=LW/W, RWR=Rw/W where, L A is leaf area, L w is leaf weight, W is dry weight of a whole plant, and Rw is root weight. The net assimilation rate (NAR, g m" 1 day'l) is defined as the rate of increase in plant weight per unit leaf area (Lambers and Poorter 1992). Thus NAR was calculated as: NAR=RGR/LAR. 5.3 Results 5.3.1 Seasonal changes of RGR RGRs of both paper birch and Douglas-fir varied through the growing season (Figure 5.1 and 5.2). At the coastal site Douglas-fir had significantly higher RGR values 73 in every month than paper birch did in either no-competition or with-competition cultures (Figure 5.1a and b). In contrast, at the interior site paper birch had higher RGR values when competing with Douglas-fir (Figure 5. Id) except in May and June. In the no-competition culture, RGR of Douglas-fir was greater that those of paper birch except in September (Figure 5.1 c). Furthermore, in order to compare RGR values of the same species at the two different sites. Figure 5.2 shows that paper birch had greater RGR values at the coastal site than at the interior site except in September when there was no competition from Douglas-fir (Figure 5.2a). However, when competing with Douglas-fir, paper birch had greater RGR values at the interior site than at the coastal site except in May (Figure 5.2b). As noted above, Douglas-fir had significantly greater RGR values than paper birch throughout the growing season at the coastal site in either the no-competition or competition cultures (Figure 5.2 c and d). 74 Pure culture 0.010 ~~i 1 1 r Coastal site 0.008 h •° 0.006 O 0.004 ai 0.002 0.000 • C-DF • PB f t Mixed culture May June July Aug Sept 0.010 0.008 0.006 0.004 0.002 0.000 1 1 Coastal site a C-DF • PB rh rh i May June July Aug Sept 0.010 0.008 •° 0.006 O 0.004 0.002 0.000 Interior site • I-DF • PB T 1 May June July Aug Sept Month 0.010 0.008 0.006 0.004 0.002 h 0.000 May June July Aug Sept Month Figure 5.1. Relative growth rate (RGR) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown either individually or in competition (PB+DF) with each other at the coastal and interior sites. Bars represent ±1 SE of mean. 75 Pure culture Mixed culture 0.010 0.008 0.006 O 0.004 ai 0.002 0.000 ~i 1 r Paper birch • Coastal site • Interior site May June July Aug Sept 0.010 0.008 0.006 0.004 0.002 0.000 Paper birch • Coastal site • Interior site rh J May June July Aug Sept 0.010 0.008 •° 0.006 00 .2? O 0.004 0.002 0.000 i r ~i r Douglas-fir • Coastal • Interior rh May June July Aug Sept Month 0.010 0.008 0.006 0.004 0.002 0.000 Douglas-fir • Coastal • Interior rh May June July Aug Sept Month Figure 5.2. Relative growth rate (RGR) of paper birch (PB) and coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown either individually or in competition (PB+DF) with each other at the coastal and interior sites. This figure presents the same data as in Figure 5.1, but graphed by species rather than by site. Bars represent ±1 SE of mean. 76 5.3.2 Effects of climate, species and density on growth indices To compare the interactive effects of density and climate on growth indices of paper birch, coastal and interior Douglas-fir, Tables 5.1 and 5.2 show changes of RGR, LAR, LWR and RWR of paper birch, interior and coastal Douglas-fir grown in pure and mixed cultures, respectively, in the two biogeoclimatic subzones. RGR and LAR for paper birch decreased faster as density increased than for Douglas-fir. This suggested that growth of paper birch is more sensitive to intra-specific competition than Douglas-fir. The two species were markedly different in LAR and LWR in mixed cultures on the two sites. Paper birch had a much larger LAR than Douglas-fir in both pure and mixed cultures (Tables 5.1 and 5.2). This was mainly caused by its larger SLA (Figure 3.5). In contrast, Douglas-fir had a much larger LWR than paper birch. ANOVA revealed the same significance patterns of effects of climate, species and density on all growth parameters for both pure culture and mixed cultures (Table 5.3). Except for the non-significant effect of density on LAR and LWR in both cultures, and on RWR in the mixed culture, climate, species and density had significant (/xO.001) effects on RGR, LAR, LWR and RWR. There was a significant (p<0.001) climate and species interaction for all measured growth parameters. The parallel trends in RGR with density (Figure 5.3) show that there was no significant interaction between climate and density in either pure or mixed cultures except for paper birch in the mixed culture (Figure 5.3c). It is also clear from Figure 5.3 (a and c) that RGR of paper birch declined less from the coastal site to the interior site, especially in the mixed culture, than Douglas-fir, which reduced its RGR very significantly from the coastal site to the interior site (Figure 5.3d). This may indicate that Douglas-fir is more sensitive to differences in climate than paper birch. Paper birch had a greater RWR at the coastal site than at the interior site. This reflects the greater allocation of biomass to its root system by paper birch at the coastal site during early growth. Both coastal DF and interior DF had larger LAR, LWR and 77 RWR value at the coastal site than at the interior site, for both pure and mixed cultures (Tables 5.1 and 5.2). Table 5.1. Relative growth rate (RGR), leaf area ratio (LAR), leaf weight ratio (LWR) and root weight ratio (RWR) (mean±SE) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in pure cultures at four densities at the interior and coastal sites harvested in August, 1994. Density PB C-DF I-DF C-site I-site C-site I-site C-site I-site RGR 1 5.56±0.72 5.0110.13 6.4910.87 5.7410.17 5.8410.15 5.1510.24 xlO-3 2 4.6110.61 3.4910.30 6.3310.37 4.2810.22 5.4910.43 4.9910.24 4 3.4510.34 2.3210.19 7.3910.31 4.7910.15 4.9610.32 4.42+0.15 6 2.9410.33 2.1210.19 6.5510.18 3.7710.13 4.7910.64 3.6510.14 LAR 1 38.3716.00 57.0712.07 17.4211.83 13.6810.68 18.9511.23 13.5911.15 2 39.3014.89 52.6613.59 17.3411.45 13.9310.72 17.9910.95 13.9410.54 4 36.5512.69 42.7612.81 19.1911.12 14.4310.56 17.9410.53 15.4310.46 6 27.5612.72 56.6417.76 20.06+0.84 14.6810.46 17.6711.64 14.5810.42 LWR 1 0.1910.03 0.2810.01 0.3810.04 0.2910.02 0.4110.03 0.2910.03 2 0.1910.02 0.2610.02 0.3710.04 0.3010.02 0.3910.01 0.3010.01 4 0.1810.01 0.2110.01 0.4110.02 0.3110.01 0.3910.01 0.3310.01 6 0.1410.01 0.2810.04 0.4310.02 0.3210.01 0.3810.03 0.3110.01 RWR 1 0.4310.00 0.3510.01 0.3610.08 0.3210.00 0.3010.03 0.3710.02 2 0.4210.03 0.4010.02 0.2710.03 0.4210.01 0.34+0.03 0.3710.01 4 0.4210.01 0.4210.01 0.2910.02 0.3910.01 0.3010.02 0.3710.01 6 0.3710.01 0.3210.01 0.2210.02 0.4210.01 0.2510.02 0.4210.01 78 Table 5.2. Relative growth rate (RGR), leaf area ratio (LAR), leaf weight ratio (LWR) and root weight ratio (RWR) (mean±SE) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in mixed culture at four densities at the interior and coastal sites harvested in August, 1994. Density PB mixed with C-DF PB C-DF C-site I-site C-site I-site RGR 2 5.40±0.51 4.46ifl.58 5.84±0.69 3.9510.32 xlO-3 4 3.17±0.49 3.43±0.24 5.9810.38 3.1010.22 6 2.87±0.47 2.76±0.20 4.9810.41 3.0710.17 LAR 2 41.06±1.72 24.99±3.46 22.0411.79 16.9710.73 4 32.46±1.88 47.45±3.51 23.4610.60 14.8610.56 6 31.12±1.30 54.06±2.86 22.3511.15 15.9310.31 LWR 2 0.20±0.01 0.12+0.06 0.4710.04 0.3710.02 4 0.16±0.03 0.32+0.02 0.5010.01 0.3210.01 6 0.15±0.03 0.26±0.01 0.4110.05 0.3410.01 RWR 2 0.40±0.02 0.47±0.06 0.3110.00 0.4110.01 4 0.42+0.04 0.42±0.03 0.2410.02 0.4110.02 6 0.44±0.03 0.38±0.01 0.2310.02 0.4010.01 PB mixed with I-DF PB I-DF C-site I-site C-site I-site RGR 2 4.83±0.31 4.10+0.31 4.5110.46 3.1410.25 xlO"3 4 3.30+0.43 3.30+0.36 4.2310.33 3.5010.26 6 1.07±0.64 2.65±0.24 3.9710.58 2.4810.36 LAR 2 48.44±5.74 28.96±1.72 19.3210.54 12.4610.88 4 35.77±1.89 45.98±1.93 18.9110.72 14.3710.47 6 33.97±0.54 46.87±3.78 17.6510.62 14.7310.66 LWR 2 0.24±0.03 0.19±0.08 0.4210.04 0.27+D.02 4 0.18±X).01 0.26±0.01 0.4110.02 0.3110.01 6 0.19±0.03 0.23±0.02 0.3910.03 0.3210.01 RWR 2 0.42±0.00 0.45±0.07 0.3110.02 0.4210.02 4 0.41±0.02 0.41±0.01 0.2810.02 0.4010.01 6 0.43±0.04 0.45±0.02 0.3210.03 0.4510.03 79 Table 5.3. F-values from three-way ANOVAs of parameters from plant growth analysis in the competition experiment. The data were from the August harvest. Source of variance RGR LAR LWR RWR Pure culture (n =70) Climate 72.388*** 4.561* 12.700*** 35.193*** Species 65.741*** 234.988*** 105.026*** 12.798*** Density 22.552*** 0.764 0.036 5.029** Climate x species 8.058*** 31.451*** 36.711*** 26.667*** Climate x density 1.557 1.995 0.463 6.118*** Species x density 5.677*** 1.883 1.931 2.321** Climate x species x density 0.894 2.741 1.838 3.262** Mixed culture (n=211) Climate 15.757*** 0.348 11.985*** 54.011*** Species 7.415*** 49.955*** 34.143*** 3.528* Density 35.364*** 1.608 1.604 2.863 Climate x species 21.621*** 7.607*** 23.066*** 13.766*** Climate x density 1.846 1.129 1.477 9.818*** Species x density 7 273*** 2.161 2.217 1.759 Climate x species x density 0.962 1.136 0.997 1.078 *P<0.05, **P<0.01, ***p<0.001. Competition depressed RGR in both paper birch and Douglas-fir. However, this effect was more pronounced in Douglas-fir than in paper birch, especially at the interior site in both pure and mixed cultures (Figure 5.3b and d). In contrast, paper birch showed a strong density response in RGR. Its RGR decreased significantly with density (Figure 5.3a and c), especially in the pure culture. This indicates that paper birch is more sensitive than Douglas-fir to intra-specific competition. This is consistent with the results found in Chapter 4. The ability of Douglas-fir to at least partially overcome the difference of seedling initial size (Table 4.1) between paper birch and Douglas-fir is reflected in their relative growth rates (RGR). Douglas-fir always had higher RGR at the 80 coastal site than at the interior site (Figure 5.1c, d), especially when it grew in competition with paper birch. o.oio 0.008 5 0.006 3) Hi 0.004 O Bi 0.002 0.000 i r Pure culture 0.010 a Paper birch Interior site Coast site _l L_ 0.008 0.006 0.004 0.002 0.000 b i i Douglas- fir - Interior site Coast site -i . -i i 0.010 0.008 Hi 0.004 O 0.002 0.000 Paper birch Mixed culture o.oio Interior site Coast site 2 4 6 Density (plants per pot) 0.008 0.006 0.004 0.002 0.000 d Douglas-fir Interior site Coast site l - - „ 2 4 6 Density (plants per pot) Figure 5.3. Relationships between RGR and density (plants per pot) for paper birch and Douglas-fir grown in pure and mixed cultures at the two sites. Panels a and b reflect intra-specific competition, and panels c and d reflect inter-specific competition. Data were from the August harvest. 81 Coastal site 0.010 0.008 •° 0.006 DO .5? O 0.004 0.002 0.000 c Cog * ca<r c c7c c & >» p p 1 z P . 0 10 20 30 40 50 60 70 Leaf Area Ratio 0.010 0.008 0.006 0.004 0.002 0.000 Interior site i r b 1 1 1 1 P=PB C=C-DF I=I-DF !& P j p p r P P r p P P P S i P P P P P P P P P 1> D P P p P » ' £ 1 1 P I T i i i i 0 10 20 30 40 50 60 70 Leaf Area Ratio 0.010 0.008 0.006 O 0.004 0.002 0.000 r2=0.59 SEE=0.001 c p^O.OOl c c c E c 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Leaf Weight Ratio 0.010 0.008 0.006 0.004 0.002 0.000 r2=0.19 SEE=0.001 p^O.OOl 0.0 0.1 0.2 0.3 0.4 Leaf Weight Ratio 0.5 0.6 Figure 5.4. Relationships between leaf weight ratio (LWR) and leaf area ratio (LAR) of paper birch and Douglas-fir at the coastal (a and c) and interior sites (b and d). The regression lines in panel c and d are fitted to the entire data set. 82 No significant linear relationships were detected between LAR and RGR of paper birch and Douglas-fir at the two sites (Figure 5.4 a and b). However, RGR was significantly related to LWR at both sites (Figure 5.4 c and d). The range of variation in LAR (Figure 5.4a) was much wider for paper birch at the coastal site (11.3-55.3) than at the interior site. On the other hand, the LAR was greater for Douglas-fir at the coastal site than at the interior site. LAR and specific leaf area (SLA, see section 3.3.4) are two morphological parameters that differ most between deciduous trees and conifers. SLA, which is an indication of how leaf dry matter is expended, is systematically higher in deciduous trees than in conifers. LAR, which is an index of the leafiness of the plant, is the product of SLA and LWR. Douglas-fir had much larger LWR (0.19-0.54) at the coastal site than at the interior site (0.21-0.38) (Figure 5.4b). 5.4. Discussion In general, there is a problem with direct application of growth analysis to trees. Because of the continuous accumulation of non-productive tissue, the annual increment of a tree's growth becomes a diminishing proportion of its total weight. The relative growth rates (RGR) of mature trees become very small, less sensitive to treatment and inversely related to the amount of accumulated biomass. However, among the options available, RGR, especially when applied to developmentally similar material, is the most robust growth analysis technique. In this study, the growth analysis was carried out on data from one growing season starting with three month-old seedlings. The RGRs of both paper birch and Douglas-fir responded to the treatments significantly. In an experiment using the classical methods of growth analysis, it is impossible to obtain estimates of the true within-sample variability of the various mean rates calculated over a time interval: typically relative growth rate and unit leaf rate (RGR and ULR). This is because the computation of a mean rate necessitates dry weight data acquired from two points in time (harvests) which implies a destruction of the plants 83 taken at each harvest; therefore, separate samples of plants are required at each harvest. Because of this independence of the samples at each harvest, the classical methods of growth analysis assume, either directly or indirectly depending on the method of calculation involved, that there is no correlation between the two samples. While statistically correct, this leads to large variances of the computed rates which may not conform to biological reality (Causton 1994). From this study, it is clear that RGR of the seedlings varied across different harvests. These variances were caused to some extent by sampling different individuals at different harvests. 5.4.1. Differences between species The initial differences in RGR between Douglas-fir and paper birch (Figure 5.1) were due to the different initial sizes of seedlings of the two species, even though the seeds were sown at the same time. The ability of individually grown Douglas-fir to rapidly increase in size relative to paper birch, thereby overcoming the difference in initial size, was due to a combination of factors. Early in the experiment Douglas-fir had both a higher LAR and LWR than paper birch (Table 4.1). These two factors accounted for the higher initial relative growth rate of Douglas-fir. 5.4.2. Individual versus competitively grown seedlings Competition (both intra- and inter-specific) caused a reduction in the RGR of both species (Figure 5.3 and Table 5.1 and 5.2), but the growth of paper birch was generally depressed more than that of Douglas-fir at the coastal site. The reason for the decrease in growth rate with competition appears to be differences in LAR and LWR at the two sites (Figure 5.4). From Figure 5.4 it can be seen that Douglas-fir had a larger LAR and LWR at the coastal site than at the interior site. The reverse was true for paper birch. There was substantial leaf overlap among neighboring plants within the competition pots. Douglas-fir, which has a lower light saturation point, was less affected than paper birch. 84 Also, the greater height at which paper birch held its leaf area than did Douglas-fir would tend to enhance the ability of paper birch to compete with Douglas-fir for light. Paper birch had much larger LAR than Douglas-fir. This competitive effect was more significant at the interior site. 5.4.3 RGR and biomass allocation RGR was positively correlated (p<0.05) with LWR at both sites and across all density treatments (Figure 5.4c and d). Strong positive relationships between RGR and LAR, RGR and LWR were also found by Poorter et al. (1990) for 24 herbaceous monocot and dicot species, Gamier (1992) for seven annual/perennial pairs of grasses, and Walters et al. (1993a, b) for paper birch. A possible explanation for this is that increasing LAR can result from both greater LWR and SLA. If SLA is positively related to photosynthetic rate, as was found across an assemblage of species from various ecosystems (Reich et al. 1992) then photosynthesis should covary positively with LAR. Therefore, LAR and SLA are positively associated with growth. In this experiment, the agents of variation in plant traits related to RGR were climate, species and density. Yet in nature, variation in the allocation of biomass or RGR may commonly occur in response to variation in the balance between the availability of several resources (e.g., moisture, nutrients, light) and in response to several stress factors. It is possible that a high RGR is particularly advantageous early in a seedling's life for pioneer species so that they can quickly pre-empty space and resources from slower establishing later successional species. Small differences in RGR may have large effects on early survival. Growth rate is determined by rates of photosynthesis and by allocation of fixed carbon to leaves versus allocation to non-photosynthetic tissues (e.g., branches, stems and roots). Poorter et al. (1990) found that, relative to changes in photosynthesis, small increases in biomass allocation to non-photosynthetic tissues profoundly decreased 85 growth rate. In a growth analysis of 24 species from infertile habitats, which were grown under optimal conditions of light and moisture supply, Poorter and Remkes (1990) showed that the inherent differences in RGR were not due to differences in net assimilation rate per unit leaf area (NAR), but to differences in the ratio of total leaf area to total plant weight (e.g., LAR). Changes in forest ecosystems are commonly evaluated by analyzing changes in productivity. Leaf area is the site where carbon dioxide and light uptake and water loss occur. This critical surface functions as the aboveground interface between a tree and its environment. Productivity of forest stands is dependent on leaf area because leaves are the primary organs of photosynthesis. The most important characteristics of forest stands are their leaf area index and leaf area density. These determine the amount of radiation that will be absorbed by the stand, and hence are closely related to the amount of C O 2 taken up in photosynthesis. 5.5. Conclusions 1. RGR of paper birch and Douglas-fir decreased as density increased on both coastal and interior sites. 2. Douglas-fir had greater RGR at the coastal site than at the interior site. In contrast, paper birch had greater RGR at the interior site. , 3. The reduction in RGR for Douglas-fir from the coastal site to the interior site was greater than the reduction for paper birch. 4. The higher RGR of Douglas-fir at the coastal site was mainly attributed to the higher LAR and LWR. A similar relationship was found for paper birch at the interior site. 86 Chapter 6. Competition between Douglas-fir and paper birch 6.1 Introduction Many studies have quantified the responses of Douglas-fir to competition from various hardwood, shrub, and herbaceous species (Cole and Newton 1986,1987; Newton and Cole 1991; Harrington and Tappeiner 1991; Harrington et al. 1995a and b; Tesch et al. 1993; Shainsky and Radosevich 1992a, b). However, tree responses to competition can be difficult to predict because they vary with climate, site characteristics, vegetation abundance and proximity, and species composition. Predicting tree responses over a range of biological and environmental conditions requires an improved understanding of competitive processes. Differences among the competitive abilities of plant species are frequently invoked as factors controlling the distribution and composition of natural vegetation (Grime 1979, Keddy 1990, Tilman 1990). For plants, the existence of some degree of competition in most ecological situations is widely recognized, because all plants require light, water, and nutrients. When plants grow together they shade their neighbors and /or have somewhat overlapping root systems that draw from common, often limiting nutrient and water resources. This is especially significant for forest stands composed of a single tree species. In a mixedwood forest, such as Douglas-fir and paper birch, competition between species may be alleviated through different phenological, morphological and physiological characteristics (i.e. niche separation). The competitive ability of a species may change as a function of the environment. This view allows for the possibility that relative competitive abilities of two species may reverse along an environmental gradient. To test whether competitive abilities are constant (Grime 1979) or vary among environments (Tilman 1988), it may be necessary to make comparisons among species and environments using plants with similar distribution ranges. It is instructive to take two species and by analysis of their behavior 87 when grown together in two different biogeoclimatic subzones, to ascribe the success of one over another to a particular morphological feature, a particular pattern of life cycle, or a physiological trait. It is also often interesting and important to know about the time sequence of the events in a competitive interaction. The many competing ideas about plant competition challenge ecologists to show not only whether competition is occurring in the field, but whether it has any significance at all in shaping plant community structure. Before the effects of competition on plant community structure can be related to the competitive ability of certain species, competitive ability must be quantitatively determined. The many experimental designs that have been developed to study plant competition have a variety of strengths and limitations (Cousens 1991). Several have been used to quantify competition gradients in early successional forest stands (e.g., Cole and Newton's [1986,1987] study of intra- and inter-specific competition between Douglas-fir and red alder). The experimental design most commonly used to investigate plant competition in two species mixtures is the replacement series, in which the total density of plants is kept constant whilst the relative frequencies of the two species are varied (de Wit 1960). The interference effects of one species on another can be assessed by comparing yields in mixtures with those in pure stands. While the design has been employed mostly in studies of field crops, it has also been used in studies of competition between different tree species (Shainsky and Radosevich 1986; Fredericksen et al. 1993). However, the design has been criticized (Jolliffe et al. 1984; Firbank and Watkinson 1985; Snaydon 1991) primarily because the relative yields of the replacement series are dependent on the initial planting density chosen, and because differences in initial size of the two species may bias results. In contrast, Hamilton (1994) concluded that the replacement series design gives useful information on competition. The problems with this approach may be minimized if the density chosen is high enough or the duration of the experiment is long enough to reach the range of constant final yield. 88 The term "interference" is used to describe various interactions among plants. Interference may have negative effects on plants, as in resource competition or allelopathy, or it may have positive effects, such as beneficial microclimate modification or nitrogen fixation. Better quantification of the effect of interference and an understanding of interference mechanisms is likely to lead to a greater ability to manage mixedwood forests. Knowledge of how interference occurs in forest stands will be essential for the development of silvicultural systems to manage the mixed-species forests, such as a Douglas-fir-paper birch mixedwood. Several current theories about population and community ecology make predictions as to how the "intensity" of competition will change in different environments, such as along gradients in resource availability (e.g., Grime 1979, Tilman 1988, Keddy 1990). Testing such theories requires that intensity of competition be quantified in a manner that will allow comparisons among different species or environmental conditions. In this chapter absolute and relative competition intensities were calculated for paper birch and Douglas-fir and compared across the two different biogeoclimatic subzones. The objectives of this study were: (1) to estimate the relative yields and assess the level of competition and relative competitive abilities of Douglas-fir and paper birch in the two different biogeoclimatic subzones and (2) to investigate the nature of competitive mechanisms and other interference interactions which determine the early growth and development of pure and mixed stands of these two species. 6.2 Materials and Methods 6.2.1 Plant materials and study sites Seedlings of paper birch, coastal and interior Douglas-fir were used in the experiment. Basic information about these seedlings was presented in Table 4.1. The two research sites were described in detail in Chapter 2. 89 6.2.2 Competition experimental design The two competition experiments were carried out in two different biogeoclimatic subzones (at the coastal and interior sites) described below, respectively. 6.2.2.1. Sequential harvest competition experiment Level of competition and relative competitive ability of the two species were examined using data from the pot experiment (see Chapters 4 and 5). Field collected seeds of each species were germinated and grown in the nursery (Pacific Regeneration Technology Inc., Vernon). In pure cultures, seedlings were planted at three densities (two, four and six seedlings per pot), while in mixtures seedlings were grown at the same densities with a 1:1 ratio of the two species and variant. For a detailed description of the experimental design, see Chapter 3 (Table 3.1). 6.2.2.2. Replacement series A replacement series experiment was conducted to compare with the sequential harvesting study of the relative competitive abilities of Douglas-fir and paper birch. Two separate replacement series, paper birch vs. coastal Douglas-fir and paper birch vs. interior Douglas-fir, were established on the two research sites described in Chapter 2. The replacement series, developed by de Wit (1960), is one of several experimental designs used to study competition between two species. The experiment design and densities (seedlings per pot) of each species were as follows: The replacement series (1) . Paper birch 6 5 4 3 2 1 0 CoastalDF 0 1 2 3 4 5 6 (2) . Paper birch 6 5 4 3 2 1 0 InteriorDF 0 1 2 3 4 5 6 The numbers represent seedlings per pot in each treatment. Each treatment was replicated three times. The seedlings were harvested in August 1995. Seedling 90 measurement and biomass determinations were made following the procedures described in Chapter 4. This experimental design created a gradient of soil resource variation (soil moisture and soil nutrient availability) by growing different numbers of seedlings in the same size pot filled with the same soil. With these resource variations we should detect variations in the performance ranking of species for measures linked to competitive ability. In other words, differences in species performance ranking across resource gradients may translate into different competitive abilities among species. 6.2.3. Resource complementarity The relative yield total (RYT), first defined by de Wit (1960), has been used almost universally as a measure of the extent to which species of a mixture compete for common limiting resources. From the average total biomass (foliage, shoot and root) data of each species in each pot (Table 4.2), the total number of individuals in each pot and the ratio of each species in the pot, the relative yield per plant (RYP) and relative yield total (RYT) were calculated as follows (Fowler 1982). If p equals the initial proportion of species i, and q equals the proportion of species j, and p + q =1 in a mixture of the two species, then, given a constant total density, RYP i j =Y i j / / ? Y i i [1] R Y P ^ W J J [2] RYT values were calculated by the expression: RYT = pRYPij + ^RYPji = ( Y ^ ) + (Yji/Yjj) [3] where Yjj and Yy are the yields per pot (or per unit area) of species i and j when grown in pure stands, respectively, and Yjj and Yjj are the yields of the species when grown in mixtures with each other. An RYT > 1 indicates niche differentiation with respect to the yield measure, such that the yield in mixture exceeds the average yield of each species 91 growing alone. RYT = 1 indicates use of the same resources (or no inter-specific competition occurring). RYT < 1 implies a mutually antagonistic relationship between the two species. The results were examined for fit to one of the three possible outcomes or "models" of competition between the two species to determine whether the outcome of competition varies with density and climate. To determine whether the yield of the mixture was greater than the mean of the two monocultures, the relative yield of the mixture (RYM) was calculated in a 50:50 mixture (Wilson 1988) using the total biomass data in Table 4.2 and Table 4.4. RYM = (Yjj + Y j i)/(Y i i +Yjj)*0.5 [4] 6.2.4. Competitive ability One of the most common indices of competitive ability is the relative crowding coefficient (RCC), first used by de Wit (1960); however, as de Wit did not clearly define the index, at least two forms of the index now exist. The definition used here is that of Harper (1977): RCCij = (Y i j/Y i i)/(Y j i/Y j j) [5] where RCQj is the relative crowding coefficient of species i, when grown with species j, and all other symbols are as in the above equations. If the two species in a mixture have equal competitive abilities, the RCC of each will be 1.0; if species i is more competitive than species j, then its RCC will be greater than 1.0 and tending towards infinity, while if the competitive ability of species i is less than that of species j, its RCC will be less than 1.0 and tending towards zero. As a result, the index is asymmetrical about 1.0, causing difficulties in both statistical analysis and biological interpretation. This problem can be solved if the index is transformed logarithmically so that values of the index are symmetrical about zero; a positive value would then indicate that species i is more competitive than species j, while a negative value would indicate that species j is more competitive than species i. The transformed RCC was calculated for each species and 92 each climate separately to determine whether competitive abilities of paper birch and Douglas-fir reverse from coastal to interior climates. 6.2.5. Intra- and inter-specific competition A reciprocal yield regression analysis procedure (Spitters 1983, Rejmanek et al. 1989) was used to create equations that described the relationships between biomass production and Douglas-fir and paper birch densities. The equations developed to describe intra- and inter-specific competition for Douglas-fir and paper birch on a per plant basis were: DF: yi-Uai + biiXi + bijXj [6] PB: yj-Uaj + bjjXjfbjiXi [7] where yj~l and yj'l are the inverse weight of Douglas-fir and paper birch in grams per seedling, respectively; aj and aj are the theoretical biomass (intercept of the regression line) of Douglas-fir and paper birch grown without competition in grams per seedling; b[[ is the coefficient for intra-specific competition or the effects of Douglas-fir on itself; bjj is the coefficient for inter-specific competition indicating the effect that paper birch had on Douglas-fir biomass production in the mixture, bjj is the coefficient for inter-specific competition indicating the effect that Douglas-fir had on paper birch biomass production in the mixture. Xj and Xj are the Douglas-fir and paper birch densities in seedlings per pot, respectively. Two separate sets of the equations were developed for ICHmw and CWHdm subzones. The coefficients of these equations were then compared. Significance of difference between two partial regression coefficients b[[ and bjj, and between bjj and bjj in equation [6] and [7] was tested using t-test described by Zar (1984). Three types of question were considered in these two equations. One deals with how the two species compete with each other regardless of within species (intra-species) competition. The null hypothesis is that they do not compete, so that bjj = 0. The second deals with how they differ in patterns of resource acquisition. The null 93 hypothesis is that they do not differ, so that bjj = b[[. The third deals with the effect of different climatic regimes on competitive relationships between Douglas-fir and paper birch. The null hypothesis is that the relationships are the same, so that bjjc = bjjj. Relative competitiveness of Douglas-fir and paper birch (RC f^ and RCpD) and an index for niche differentiation (NDI) was calculated using the following equation (Spitters 1983) RC d f=b i i/b i j [8] and RCpb = by/bji [9] NDI = R C d f xRCpb [10] An NDI value less than one indicates that a niche differentiation did not occur and that the species competed for the same resources. 6.2.6. Competition intensity Two measures of competition intensity were calculated: absolute competition intensity (ACI) and relative competition intensity (RCI). ACI was determined as: ACI = Pm 0no " ^mix [11] where Pm 0no represents the performance of a plant in monoculture (e. g., expressed as total biomass produced) and P m i x represents the performance of a plant in mixture. RCI is simply calculated as (Grace 1995, Miller 1996 and Twolan-Strutt and Keddy 1996) RCI = (Pm0no " Pmix V Pmono [121. The first measure (ACI) expresses the absolute reduction in biomass production due to competitive effects, while the second measure (RCI) expresses the corresponding reduction standardized by biomass production of plants growing in the absence of competitive effects. 94 6.2.7. Statistical analysis Multiple regression models were constructed relating Douglas-fir performance (total biomass per plant) to paper birch densities (seedlings per pot) in the mixtures. The individual replicates of reverse yield (yl) were used. Regression coefficients, measures of competitive effects of paper birch on Douglas-fir, were compared statistically between two climatic regions using the MANOVA procedure in SYSTAT (Wilkinson et al. 1996). The competitive effects of a neighbor species (paper birch) on a target species (Douglas-fir) can be ascertained from the slope of these regression equations of total biomass of the target (Douglas-fir) on the amount of neighbor (paper birch). A two-tailed student's t test was used to determine if mean total competition intensity was different in the two different biogeoclimatic subzones. Data from both coastal and interior sites were then used in regression analysis to determine whether there was a relationship between standing crop (total biomass) and competition intensity. Simple linear regression was used to test for an effect of standing crop on competition intensity. All statistical analyses were repeated for each species separately to determine whether the two different species yield similar results. The per-gram effect of paper birch on Douglas-fir performance was examined by regressing Douglas-fir biomass and growth rate on paper birch biomass. The slope of this relationship is a measure of the per-gram effect of neighbors on the growth rate of Douglas-fir (the intensity of competition), which the r 2 value is the proportion of variation in growth rate that can be accounted for by the neighbor paper birch. Preliminary data inspection suggested that Douglas-fir biomass varied non-linearly with paper birch biomass, and both variables were therefore logi o-transformed. It was determined whether the intensity of competition on a per-gram basis varied between the two sites by testing whether the regression slopes for each species varied from the coastal site to interior site (Tukey test). 95 6.3. Results 6.3.1 Inter-specific competition from the mixture experiment In this study, the mixture experiment could be used as a special case of de Wit (1960) replacement series in combination with the pure cultures. In Table 6.1 the values of relative yield per plant (RYP), relative yield total (RYT) as well as relative yield of the mixture (RYM) for the mixture experiment are presented. The RYP represents the average yield of an individual in a mixed culture in relation to the yield of an individual of the same species in a pure culture at the same density (Fowler 1982). In the case of both coastal and interior Douglas-fir, RYP was <1 at all three densities at both coastal and interior sites (Table 6.1). This implies that individuals of paper birch had a greater effect on individuals of Douglas-fir (inter-specific competition) than individuals of Douglas-fir had on themselves (intra-specific competition). In the case of paper birch, RYP varied across three densities and the two sites. However, paper birch had larger RYP values at the interior site than at the coastal site. RYP of paper birch was >1 when it was grown at the interior site and at densities of 2 and 6 seedlings per pot than at the coastal site. This implies that individuals of paper birch had a greater effect on themselves (intra-specific competition) than individuals of Douglas-fir had on paper birch at the interior site. RYT represents the sum of the proportional changes in yield which occurred in the mixtures (Fowler 1982) and measures the degree to which the two components of a two-species mixture make demands on the same resources (Taylor and Aarssen 1990). RYT values were >1 at the interior site except at the low density mixture with interior Douglas-fir (Table 6.1). Values of RYM were larger than 1 except for high densities (6 seedlings per pot) at the interior site. This indicates that paper birch and Douglas-fir mixtures have a higher yield than pure cultures of each species. 96 Table 6.1 The relative yield of mixture (RYM), relative yield per plant (RYP), relative yield total (RYT) and relative crowding coefficient (RCC) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) from the mixed culture at the two different sites. Density RYP RYT RYM RCC Coastal Interior Coastal Interior Coastal Interior Coastal Interior site site site site site site site site PB:C-DF PB 1:1 1.24 1.45 1.05 1.17 1.13 1.32 1.46 1.64 2:2 0.95 1.48 0.76 1.01 0.76 1.14 1.63 2.75 3:3 0.91 1.13 0.87 1.68 0.89 C-DF 0.87 1.90 1.18 1:1 0.85 0.88 0.69 0.61 2:2 0.58 0.54 0.62 0.36 3:3 0.60 0.77 0.85 0.53 PB:I-DF PB 1:1 0.99 1.23 0.84 0.86 0.90 1.01 1.43 2.43 2:2 0.98 1.53 0.87 1.13 0.91 1.26 1.30 2.11 3:3 0.73 0.88 0.863 0.78 0.64 I-DF 0.83 0.79 0.79 1:1 0.69 0.53 0.70 0.41 2:2 0.75 0.73 0.77 0.47 3:3 0.92 0.68 1.27 0.77 97 A paired two-sample f-test (Zar 1984) revealed that paper birch had significantly (t=4A2,p= 0.007) larger RCC values at the interior site than at the coastal site (Table 6.1). This indicates that paper birch is more competitive at the interior site than at the coastal site. In contrast, Douglas-fir had significantly (t=5.32, ^ =0.001) larger RCC values at the coastal site than at the interior site, indicating a reversal in competitive ability of Douglas-fir from the coastal site to the interior site. 6.3.2 Inter-specific competition from the replacement series Competitive relationships are indicated in replacement diagrams when the curve is concave for one species and convex for the other. When two species compete for hmiting resources, the RY of each differs from the expected RY. RYT diagrams for total biomass per pot (Figure 6.1) showed that competitive abilities of paper birch and Douglas-fir reversed for the two research sites. At the coastal site, the RY of coastal Douglas-fir reached its expected RY (dashed line) as indicated by the shape of the curves in replacement series diagrams (Figure 6.1a). In contrast, its RY was lower than the expected RY (Figure 6.1b) at the interior site. In comparison with Douglas-fir, paper birch (dotted line) had higher RY than expected at the interior site but not at the coastal site (Figure 6.1 a, b). For interior Douglas-fir and paper birch mixture, similar patterns were found (Figure 6.1 c, d). In general Figure 6.1 indicates that Douglas-fir is the superior competitor at the coastal site, and vice versa for paper birch. This reversal was shown by the change in the relative crowding coefficients (RCC) for paper birch with respect to Douglas-fir with increasing environmental stress (Table 6.2). Total biomass per pot of paper birch in pure cultures declined from 98.8 g (Figure 6.1a) at the coastal site to 73.2 g at the interior site (Figure 6.1b), a 26% reduction. On the other hand, total biomass per pot of coastal Douglas-fir declined from 79.2 g per pot at the coastal site to 35.3 g per pot, a 45% reduction. 98 Figure 6.1. Yield of total biomass (Total) per pot from the replacement series: for paper birch (PB) mixed with coastal Douglas-fir (C-DF) (a and b) and with interior Douglas-fir (I-DF) (c and d) at the two sites. 99 Table 6.2. Relative yield per plant (RYP), relative yield total (RYT), relative crowding coefficient (RCC) of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) from the replacement experiment at the two sites. ^ Density Species RYP RYT RCC PB:C-DF Coastal Interior Coastal Interior Coastal Interior site site . site site site site 1:5 PB 1.94 1.97 2.96 2.72 1.89 2.64 2:4 1.05 1.29 1.89 2.02 1.25 1.78 3:3 1.11 1.21 2.07 1.88 1.15 1.81 4:2 1.27 1.62 2.15 2.17 1.44 1.62 5:1 0.97 1.29 1.75 1.83 1.24 2.39 1:5 C-DF 1.02 0.74 0.53 0.38 2:4 0.84 0.73 0.80 0.56 3:3 0.96 0.67 0.87 0.55 4:2 0.88 0.55 0.70 0.62 5:1 0.78 0.54 0.80 0.42 PBT-DF 1:5 PB 1.56 1.62 2.39 2.52 1.89 1.79 2:4 1.25 1.12 2.01 1.91 1.66 1.41 3:3 1.09 1.34 1.81 2.17 1.51 1.62 4:2 1.29 1.07 1.87 1.87 2.21 1.33 5:1 0.90 1.00 1.72 1.85 1.10 1.17 1:5 I-DF 0.83 0.90 0.53 0.56 2:4 0.76 0.79 0.60 0.71 3:3 0.72 0.83 0.66 0.62 4:2 0.58 0.80 0.45 0.75 5:1 0.82 0.85 0.91 0.85 100 In Table 6.2 the values of relative yield per plant (RYP) represent the average yield of an individual in a mixed culture in relation to the yield of an individual of the same species in a pure culture at the same density. In the case of Douglas-fir, RYP was <1 at both the interior and coastal sites except for PB:C-DF ratio 1:5 at the coastal site. However, the paired sample Mest showed a significant (f=3.24, /?=0.007) difference in RYP between the two sites (p<0.001). This implies that individuals of paper birch have a greater effect on individuals of Douglas-fir than they have on themselves (intra-specific competition). In the case of paper birch, RYP was >1 at both sites (Table 6.2). However, it had a larger mean RYP at the interior site (1.35) than at the coastal site (1.24). This indicates that individuals of paper birch have a greater effect on themselves (intra-specific competition) than individuals of Douglas-fir have on paper birch (inter-specific competition). Paper birch was more sensitive to both its own canopy and root competition than to competition by Douglas-fir. This may suggest that a paper birch and Douglas-fir mixed stand would be a good option to reduce competition between species. These relationships are presented graphically in Figure 6.1. The RYT (Table 6.2) represents the sum of the proportional changes in yield which occur in the mixed culture and measures the degree to which two components of a mixture make demands on the same resource units. RYT values were all larger than 1 implying that the two species make demands on significantly different resources and that a degree of niche differentiation occurs. Relative yield total values >1 seldom occur in agricultural crops, except where a nitrogen-fixing legume is one of the components (Trenbath 1974). Fowler (1982), however, predicted that RYT values >1 should be relatively common in natural communities, because the species have developed together in an evolutionary pathway. 101 6.3.3 Reciprocal yield analysis The regression coefficients in all equations for paper birch were greater than those for coastal and interior Douglas-fir, indicating that the yield of an isolated paper birch seedling was greater than that of an isolated Douglas-fir seedling. This agreed with the results in Chapter 4 (Figure 4.1). The regression plane of each graph represents the expected values derived from the experimental results. Partial regression coefficients in the equations for coastal and interior Douglas-fir at both sites were significantly different (bjj vs. bjj and bjj vs. bjj; p<0.001). Ratios of these regression coefficients indicate that one paper birch was approximately equivalent to 1.54 coastal Douglas-fir plants (0.0137/0.0089 in Figure 6.2 a), as measured by effects on coastal Douglas-fir biomass at the coastal site. Conversely, one paper birch was approximately equivalent to 3.11 coastal Douglas-fir plants when competing at the interior site (0.0442/0.0142, Figure 6.2b). As paper birch density increased, biomass of both coastal and interior Douglas-fir decreased more significantly at the interior site (Figure 6.2b and d) than at the coastal site (Figure 6.2a and c). This is in agreement with the mixture result (Figure 4.6 and Figure 4.7). Similar relationships were found between paper birch and both Douglas-fir variants. Both Douglas-fir variants had relatively small effects on paper birch reciprocal yield (Figure 6.3 and Table 6.3). Table 6.3. Reverse yield model fit statistics for paper birch and Douglas-fir at the coastal and interior sites. The fitted 3-D response surfaces were presented in Figures 6.2 and 6.3. Note that SP, P, E and SE represent species, parameter, estimate and standard error, respectively. Site SP P E SE SP P E SE CWH PB a 0.0201 0.0140 CDF a 0.0255 0.0084 b 0.0094 0.0025 b 0.0089 0.0054 c 0.0033 0.0021 c 0.0137 0.0099 ICH PB a 0.0182 0.0105 IDF a 0.0767 0.0157 b 0.0125 0.0021 b 0.0200 0.0032 c 0.0076 0.0024 c 0.0356 0.0283 102 Coastal site Interior site a. y~'=0.0255+0.0089*CDF+0.0137*PB b. y~'=0.1011+0.0142*CDF+0.0442*PB Figure 6.2. Three-dimensional plot of the combined effects of paper birch and Douglas-fir densities on the reciprocal of total biomass per seedling of C-DF (a and b), and I-DF (c and d) at the two sites. Figure 6.3. Three-dimensional plot of the combined effects of paper birch and Douglas-fir densities on the reciprocal of total biomass per seedling of paper birch mixed with C-DF (a and b), and I-DF (c and d) at the two sites. 104 6.3.4. Competition intensity For Douglas-fir, both absolute competition intensity (ACI) and relative competition intensity (RCI) were significantly (p<0.05) different between the coastal and interior sites except for RCI at 6 seedlings (p=0.065) per pot (Table 6.3). In general, both paper birch and Douglas-fir had smaller ACI and RCI at the interior site than at the coastal site. This indicates that competition intensity increased with site productivity. ACI and RCI increased generally as density increased. The negative values of ACI and RCI indicate that intra-species competition was larger than inter-specific competition. Therefore, there was an ecological niche differentiation between paper birch and Douglas-fir. If the data across all densities were pooled, a paired-sample Mest showed that there were significant differences in ACI and RCI between coastal and interior sites for paper birch (f=-2.486, /?=0.019) and Douglas-fir (r=-0.224,/?=0.008). Table 6.3 Mean competition intensity at the coastal and interior sites for paper birch and Douglas-fir, and the statistical comparison of means between the two sites. Competition intensity Density Coastal Interior? df P Paper birch ACI 2 -7.57 -8.62 -0.29 15 0.079 4 -2.27 -6.01 -1.49 30 0.021 6 1.03 1.50 0.26 45 0.009 RCI 2 -0.24 -0.45 0.79 15 0.045 4 -1.33 -0.48 -1.73 30 0.012 6 0.05 0.09 -0.45 45 0.007 Douglas-fir ACI 2 4.03 1.88 1.34 15 0.002 4 7.94 1.08 -4.17 30 0.000 6 5.47 1.60 -2.40 45 0.004 RCI 2 0.15 0.49 1.31 15 0.025 4 0.42 0.27 -1.92 30 0.009 6 0.40 0.32 -0.47 45 0.065 105 6.4 Discussion Two views prevail on the role of competition in structuring plant communities along productivity gradients, and they predict different patterns of competition. The first view states that there is an increase in total competition (above- and belowground competition) as productivity increases. The relative importance of belowground to aboveground competition is constant as productivity increases (Grime 1979). The second view states that there is an increase in aboveground competition and a decrease in belowground competition as productivity increases, resulting in a decrease in the relative importance of below- to aboveground competition intensity and no net change in the total amount of competition (Tilman 1988). Although this study did not specifically determine below- and aboveground competition between paper birch and Douglas-fir at the two sites, it was shown through biomass allocation patterns (Figure 4.5) that both species allocated more total biomass to their roots at the interior site (Figure 4.5 b and d). This may indicate that at the interior site aboveground competition is less intense than below-ground competition between paper birch and Douglas-fir. Competition from paper birch strongly influenced Douglas-fir growth at the interior site. This is consistent with other studies where increases in Douglas-fir growth were achieved through the control of hardwood competition in the southern interior of BC (Simard 1990, Simard and Vyse 1992). In contrast, paper birch is not a severe competitor for Douglas-fir in most coastal forest ecosystems. Silvicultural practices are aimed mainly at control of competition from red alder (Cole and Newton 1986, 1987, Newton and Cole 1991) and other hardwoods (Tesch et al. 1993). A principal effect of hardwood and shrub competition in southwestern Oregon is to limit Douglas-fir bud production through reducing soil water availability, because light is not a limiting factor in this area (Harrington and Tappeiner 1991). Therefore, competition from hardwoods significantly reduced Douglas-fir shoot length. At the interior site, where seedlings of both paper birch and Douglas-fir grew more slowly than 106 their counterparts at the coastal site, the competitive effects might not be detectable in the low densities for the short period of the experiment. Paper birch was more affected by its intra-specific competition than by inter-specific competition from Douglas-fir. It is important to keep in mind that the environment plays an important role in the interaction between species by determining the intensity of competition as well as the direction of competitive dominance. The results from this study show that the competitive responses of each species are influenced by experimental sources of variation. Climate is the main factor affecting competitive intensity (Table 6.3). Also, relative crowding coefficients (RCC) of paper birch and Douglas-fir reversed from coastal to interior sites (Table 6.1). RCC can be a useful index (de Wit 1960) for measuring the relative competitive ability of a deciduous species (usually a weed species in agriculture) with respect to the conifer (crop). However, many researchers have found that RCC changes with different total densities (Firbank and Watkinson 1985, Connolly 1986, 1987). Connolly (1986) has pointed out that substitutive designs are essentially one-dimensional, and that various ratios are all points on the same line of a two-dimensional system. Recently, some plant biologists have questioned the limitation of partial additive and replacement series models (Jolliffe et al. 1984, Firbank and Watkinson 1985, Rejmanek et al. 1989). One better alternative model is the reciprocal yield (inverse linear) model of plant competition. The reciprocal model has been proposed to overcome the limitations of other methods of analysis such as replacement series. This type of model uses multiple linear regression in which the densities of the competing species are the independent variables and the reciprocals of the average per plant yield are the dependent variable, such as equations 6 and 7 and the models in Figures 6.2 and 6.3. In comparison with the replacement series model (Figure 6.1), reciprocal yield models allow the competitive ability of each species to be quantified by parameters that do not vary with total stand density. The results from this study demonstrated the advantages of the 107 reciprocal yield model. The parameters of bjj and bjj in equations 6 and 7 are a measures of how efficient the plant is with respect to resource utilization i.e., competitive ability. According to Spitters (1983), if the intensity of inter-specific competition was much less than the intensity of intra-specific competition (in the case of paper birch, Figure 6.3), the two plants competed for different resources, or for the same resources but in a different ways. I explored the application of reciprocal yield models, previously employed mainly in annual plants, to examine the yield-density relationships of the competing conifer and hardwood. In addition, the unique design of this study was to focus on the climatic effect on intra- and inter-specific competitive relationships. The design used in this study facilitated the development of predictive equations that quantify the discrete effects of intra- and inter-specific competition. 6.5 Conclusions 1. Paper birch had greater relative yield per plant (RYP) and RCC at the interior site than at the coastal site. 2. Douglas-fir had RYP<1 at both sites and a smaller RCC at the interior site than at the coastal site. This indicates that Douglas-fir and paper birch reversed their competitive abilities between the two biogeoclimatic subzones; i.e. paper is more competitive at the interior site and Douglas-fir at the coastal site. 108 Chapter 7. Height growth patterns of Douglas-fir and paper birch in two different biogeoclimatic subzones in B. C. 7.1. Introduction Douglas-fir and paper birch are two important tree species in the interior cedar-hemlock (ICH) zone in B.C. Mixedwood stands of these two species are a significant component of the forest landscape of this zone. Paper birch is a serai hardwood species which frequently dominates harvested sites in the wetter subzones of the ICH. Its reproductive success on cutover areas can be attributed to rapid and prolific establishment of seedlings on burned or mechanically disturbed areas, and vigorous sprouting from damaged or cut stumps (Haeussler and Coates 1986). In the ICH zone, where conifer growth is usually not limited by moisture or nutrient availability, competition between Douglas-fir and paper birch appears to be driven primarily by light (Simard 1990). Competition between these two species for light is very important in their stand dynamics because both species are relatively light-demanding, shade intolerant species (Haeussler et al. 1990). Therefore, height growth is a key factor determining the outcome of light competition. The rapid juvenile height growth of paper birch (especially from sprouts) gives the species an early competitive advantage over Douglas-fir (Simard and Vyse 1992). Many previous studies of height growth of Douglas-fir have been devoted to the development of site index equations (King 1966; Curtis etal. 1974; Cochran, 1979). In such equations, development of tree height is expressed as a function of age and site productivity, where site productivity is indexed by height attained by some dominant and or codominant component of the stand at some reference age (usually at age 50). Monserud (1984,1985) reported a study on height growth of inland (interior) Douglas-fir and then compared site index and height growth curves for different climates in the Pacific Northwest. He concluded that the indirect synoptic measures of climate, soil moisture and soil nutrients were good predictors of Douglas-fir site index over a large 109 area and provide useful estimates of the direct measures. However, very few studies have linked height growth patterns with the competitive relationship between paper birch and Douglas-fir, and the effects of climate on the height growth-competitive ability relationship. Ritchie and Hann (1986) presented a predictive 5-year height growth model as a nonlinear function of potential height growth, crown ratio and height of the subject tree. The 5-year height growth was related to tree position and crown competition factor. The height growth pattern of Douglas-fir changes gradually from one geographic region to another; the greater the distance between regions, the greater the difference in the pattern of height growth. Coastal Douglas-fir attains the greatest height increments between 20 and 30 years of age but retains the ability to maintain a fairly rapid rate of height growth over a long period (Hermann and Lavender 1990). Douglas-fir in high-elevation forests in the Oregon-Washington Cascade Range can continue height growth at a reasonable rate for more than 200 years (Curtis et al. 1974). Height growth of the terminal shoot is influenced by growing conditions in three periods: the season the bud is formed, the non-growing season (storage), and the period of elongation following bud burst. Consequently, height growth is the average of influences of long-term climatic conditions and is not affected by short-term weather fluctuations so much as diameter is. Photosynthate allocation to height growth by light-demanding species is given priority over diameter growth. Consequently, for many species a tree's height growth is relatively independent of its degree of crowding and amount of foliage, except at extremely high stand stocking densities and narrow tree spacing. It is necessary to investigate and quantify height growth patterns so that the appropriate silvicultural plans and management regimes can be developed for both increasing timber production and complying with non-timber value management requirements. To test the impact of regional climate on height growth patterns and competitive relationship between paper birch and Douglas-fir, this study compared 110 sample stands (on zonal sites) across the widest possible climatic range within the geographical distribution of paper birch and Douglas-fir. It was observed from the field that Douglas-fir has a very dense crown structure and much higher foliage biomass on coastal sites (Waring and Franklin 1979), compared with its counterpart (interior Douglas-fir) in the interior. It was hypothesized that height of Douglas-fir exceeds height of paper birch at an earlier age at the coastal site than at the interior site, and that this contributes to the competitive exclusion of paper birch from coastal forests dominated by coastal Douglas-fir at a much earlier stage relative to the interior forests dominated by interior Douglas-fir. The objectives of this study were: (1) to determine height growth patterns of paper birch and Douglas-fir; (2) to compare height growth patterns of the two species between the two different biogeoclimatic subzones; and (3) to test the above hypothesis. 7.2. Methods 7.2.1 Study sites Two sites were selected for sampling trees for stem analysis. One site, at the UBC Malcolm Knapp Research Forest representing a coastal climate, was located about 2 km away from the pot experiment site described in Chapter 3. It was logged in 1932 and regenerated naturally into an even-aged, well stocked stand dominated by Douglas-fir, western hemlock, and western red cedar. Very few paper birch trees remained in this stand in 1994, scattered among the coniferous trees. The other site, representing the interior climate of the ICFfmw subzone, was located at the northern end of Adams Lake, adjacent to the interior pot experiment site. The stand was about 80 years old in a fire-origin second growth forest. The major tree species were interior Douglas-fir, western red cedar and paper birch. Il l 7.2.2 Sample trees and stem analysis Ten pairs of Douglas-fir and paper birch trees were selected from each site. The paired sample trees were chosen within 5 to 10 meters from each other in order to avoid microsite variations. In total, 40 trees were felled and discs were taken from each tree at the stem base (0.0 m height), at 1.3 m, and at 2 m intervals thereafter, up to the growing tip of the tree. Annual rings were counted after sanding the discs. The ring counts were converted into actual tree age at each section point, the age at the base being considered as year zero. Height-over-age data obtained from stem analyses can be biased if the height at which stem age measurement is taken as the tree height for the corresponding tree age, because of the presence of a 'hidden tip' above the sample point (Carmean, 1972). Dyer and Bailey (1987) compared six published algorithms for estimating the true height within a section and concluded that Carmean's (1972) method was the best. Carmean's method is based on two assumptions. First, annual height growth is assumed to be constant for each year for which height growth is wholly or partially contained within the section. Second, it is assumed that, on the average, a sample stem disc for age measurement will occur in the middle of a year's height growth. This is expressed mathematically as: Hij = hi + (hi+1-hi)/[2(ri - r i + 1)] + (j-l)(hi+1-hi)/(ri-ri+1) (7.1) where rj is the number of growth rings at the ith crosscut; hj is the height at the ith crosscut and Hjj is the estimated total tree height at age tjj. The raw stem analysis data were adjusted using Carmean's algorithm to calculate tree height corresponding to the tree age at each crosscut. Plots of height-versus-age were examined for each tree. These curves were carefully checked for indications of early suppression in height growth or of top breakage or dieback. However, it was impossible to find any suppression-free paper birch trees in the 50-year-old Douglas-fir stand at the coastal site. All paper birch trees from the coastal site were severely suppressed. 112 7.2.3 Model development Richards (1959) derived the following sigmoidal function based on Von Bertalanffy's quantitative laws about organisms: y = a(l- e"bt)c (7.2) where y is the total living biomass, t is time, a is the asymptote, b is the rate parameter, and c is the shape parameter. Equation 7.2 is most commonly known as the Chapman-Richards function in forestry. It has been shown on numerous occasions to be very flexible and has been used extensively in growth and yield studies for describing height-age, diameter-age, basal area-age, and volume-age relationships (Burkhart and Tennent 1977; Clutter et al. 1983; Somers and Farrar 1991; Wang etal. 1994). Arney (1985) also adopted the basic Chapman-Richards function for modeling coastal Douglas-fir diameter increment. The height-prediction model was fitted using nonlinear least squares regression (Wilkinson 1996). The Quasi-Newton iterative method was applied in model fitting. If unequal error variance was evident from analysis of residuals, weighted regression was applied to achieve uniform error variance. An average height growth curve was fitted to the stem analysis data from individual sample trees from each site using the Chapman- Richards function. H = a[(l- exp(-bA)]c (7.3) where H is height (m), A is base height age, a, b and c are parameters described in equation 7.2. 7.3. Results At the coastal site, average heights of paper birch and Douglas-fir were 28.9±2.3 m and 28.7±2.8 m at average ages of 47.8 and 50.6 years, respectively (Table 7.1). After examining the age structure of paper birch and Douglas-fir at the coastal site, tree #1 for paper birch and tree #6 for Douglas-fir were deleted from the data set because of their relatively young ages. At the interior site, all sampled trees came from the same cohort. 113 Mean heights were 23.8±2.5 m and 30.5±5.5m for paper birch and Douglas-fir, respectively, at an age of 79 years (Table 7.1). Table 7.1. Characteristics of sample trees of Douglas-fir and paper birch at the two sites. Coastal site Interior site Tree No. Age (yr) DBH(cm) Ht(m) Tree No. Age (yr) DBH (cm) Ht(m) Paper birch 1 26 21.0 27.1 1 80 22.5 23.0 2 43 24.0 28.7 2 84 26.0 24.7 3 49 27.5 30.1 3 77 30.7 29.5 4 41 28.0 27.4 4 78 27.3 23.1 5 46 21.5 25.7 5 80 21.0 26.0 6 42 18.8 27.1 6 81 25.0 23.3 7 53 22.5 32.4 7 80 16.0 23.9 8 70 57.6 32.3 8 70 13.5 20.3 9 57 23.7 28.1 9 78 15.5 21.7 10 51 19.0 29.7 10 83 17.5 22.4 Mean 47.8 26.36 28.9 Mean 79.1 21.5 23.8 Dougl as-fir 1 56 21.5 28.8 1 79 32.4 28.3 2 57 22.4 29.5 2 77 27.0 29.3 3 51 22.0 29.1 3 85 35.2 39.2 4 49 27.4 33.1 4 83 34.5 39.2 5 51 23.5 27.7 5 85 25.0 31.6 6 30 17.6 22.7 6 72 18.7 21.6 7 45 22.5 29.8 7 79 25.5 28.2 8 52 30.0 30.7 8 73 18.5 21.2 9 59 23.4 29.5 9 80 27.5 26.1 10 56 29.5 26.1 10 76 29.7 30.2 Mean 50.6 23.9 28.7 Mean 78.9 27.4 30.5 Adjusted heights calculated from equation 7.1 versus age and the fitted curves are plotted in Figure 7.1 for each species at the two sites. Results for the final fits of the equation 7.3 are presented in Table 7.2. Asymptotic standard errors, 95% confidence interval, and R 2 values are presented. The R 2 values range from 0.864 to 0.927 (Table 7.2), indicating good agreement between the data and fitted values. 114 To facilitate comparisons of height growth patterns of Douglas-fir and paper birch at the two different sites, their height-over-age curves were plotted together by site in Figure 7.2. At both sites, paper birch had more rapid early height growth than Douglas-fir, but Douglas-fir continued to grow at a relatively high rate and eventually overtook the height of paper birch. However, there was a significant difference in the timing of the change in relative height dominance (Figure 7.2 a, b). At the coastal site, height of Douglas-fir exceeded height of paper birch at about 25 years after stand establishment (Figure 7.2a). In contrast, the height of Douglas-fir did not exceed that of paper birch at the interior site until about 48 years (Figure 7.2b). At the coastal site, as Douglas-fir grew up around paper birch and competition for light increased, the height growth of paper birch continued to followed the trend of Douglas-fir height growth. This could be explained by the fact that the few remaining paper birch trees occupied small gaps in the Douglas-fir canopy. In 1993, paper birch trees in these canopy gaps had a mean crown depth of less than 5 meters; most were in poor condition and were in the process of being eliminated as a result of overtopping and shading by Douglas-fir. In contrast, there was a greater difference in heights of paper birch and Douglas-fir during the first 45 years before Douglas-fir took over paper birch in height at the interior site (Figure 7.2b). This resulted in a severe competition from paper birch on Douglas-fir at the interior site. 115 Figure. 7.1. Comparison of paper birch and Douglas-fir height growth at the coastal and interior sites in British Columbia. 116 Table 7.2. Height growth model fitting statistics for paper birch (PB) and Douglas-fir (DF) at the coastal and interior sites, respectively. Site Species Parameter Estimate ASE 1 Lower2 Upper R 2 Coastal PB a 52.419 5.735 41.09 63.75 0.896 b 0.013 0.003 0.01 0.02 c 0.896 0.056 0.79 1.01 DF a 41.020 3.691 33.73 48.31 0.925 b 0.031 0.006 0.02 0.04 - c 1.483 0.160 1.17 1.80 Interior PB a 36.664 4.716 27.31 45.98 0.864 b 0.019 0.004 0.01 0.02 c 0.888 0.081 0.73 1.05 DF a 38.770 2.210 34.41 43.13 0.927 b 0.029 0.004 0.02 0.04 c 1.800 0.181 1.44 2.16 Note: 1. ASE: Asymptotic standard error. 2. 95% confidence interval. 117 b. Interior site 0 10 20 30 40 50 60 70 80 Age (yr) Figure. 7.2. Comparison of functional plots of paper birch and Douglas-fir height growth at the coastal and interior sites in British Columbia. 118 Residual analyses based on the preliminary nonlinear least squares fit were performed to detect possible model inadequacies. Estimated height was plotted against measured height (Figure 7.3). Simple regressions between estimated height and measured height showed that the height-age models provided a good fit for the tree height data. These models accounted for much of the total variation in measured height (between 86.4 and 92.7%) with standard errors of estimate (SEE) of <3.0m. Figure 7.4 shows the plot of residuals against the estimated height for paper birch and Douglas-fir at the two sites, respectively. The plots displayed a homogenous band centered on zero, indicating the height prediction models were appropriately identified and fitted. 119 Measured height (m) Measured height (m) Figure 7.3. Relationships between estimated height and measured height for paper birch and Douglas-fir at the coastal and interior sites. The 1:1 ratio line represents a perfect fit. 120 P •a Coastal 10 Paper birch • «•. • • • . • • • • • • • • • • -10 10 20 30 40 50 60 Age (yr) 70 80 9 •a Interior 10 -10 i 1 r Paper birch • • • •••••• • m < 0 10 20 30 40 50 60 70 80 Age (yr) 10 3 CO U Pi Douglas-fir -5 -10 10 20 30 40 50 Age (yr) 60 70 80 30 40 50 Age (yr) 60 70 80 Figure 7.4. Plots of residuals against the estimated height for Douglas-fir and paper birch at the two sites. 121 7.4. Discussion The height prediction model (equation 7.3) provides individual tree height predictions for two important tree species for interior British Columbia. It is apparent from the statistics in Table 7.2 that the model fits well for both Douglas-fir and paper birch from the two sites. The percentages of height variation explained by tree age are high: 89.6 to 86.4 % for paper birch and 92.5 to 92.7% for Douglas-fir at the coastal and interior sites, respectively (Table 7.2). Because of the mathematical properties of the sigmoidal base function, all curves produced by the models (Figure 7.2) have biologically reasonable shapes that closely mimic real biological growth patterns. This results in accurate height predictions within the range of observed data. The height prediction models reflect some commonly held beliefs about height growth patterns in mixed paper birch and Douglas-fir forests. Height growth of Douglas-fir is determinate (or fixed); it is characterized by a single, short burst of shoot growth. In contrast, paper birch is associated with indeterminate (or free) shoot growth, characterized by continuous shoot growth over most of the growing season. Paper birch is a shade intolerant species and Douglas-fir is intermediate in shade tolerance. Paper birch responds to shading by growing taller to capture enough light to survive and grow. This may explain the height growth curve of paper birch at the coastal site (Figure 7.2a). Competition in mixed stands of Douglas-fir and paper birch is influenced by the different natural growth rhythms of the species that strongly influence the competition for light, as suggested by Simard (1990), and Simard and Vyse (1992). Whether a tree can survive a given physical environment depends on the species' physiological characteristics and the characteristics of the environment. Whether a tree can compete successfully depends on the attributes of the species, its competitors, and the environment. Paper birch is more dominant (or abundant) in the ICH zone not because it grows best there, but in part because it can outcompete Douglas-fir in height growth there over the first 45 years post-disturbance (Figure 7.2b). A tree's competitive vigor varies 122 within its ecological niche. It may rarely be able to compete within parts of its fundamental niche; where a species is actually found is in its realized niche, The realized niche is flexible and depends on the species with which it grows on each site. At the coastal site, paper birch was overtopped by Douglas-fir at about 25 years after establishment (Figure 7.2a). In combination with the much dense crown structure and higher LAI of Douglas-fir at the coastal site than at the interior site, this reduces the light available to the paper birch in mixed stands much more on the coast than in the interior. The prolonged growing activity in late fall and winter photosynthesis by Douglas-fir also contributes to its success in height growth over paper birch at the coastal site. There are two ways to test if a nonlinear regression is the best fit: residual analysis and statistical validation. Residual analysis showed that estimation errors from all height-age models were within 5 m (Figure 7.4) and the standard errors of estimate (SEE) were 2.87 m and 2.67 m for paper birch (Figure 7.3a, b), and 2.49 m and 2.59 m for Douglas-fir (figure 7.3c, d) at the coastal and interior sites, respectively. Statistical validation of the fitted height-age models is impossible in this study because the validation data should be collected in the same way as the model development data and those data should be different (independent) from the data used to develop these models (Nigh and Sit 1996). In this study, the data set used for height growth analysis was relatively small. Therefore, it was not practical to divide the data set into two groups, using one group to develop the height-age models and the other to validate the models. The results from this study support the proposed hypothesis that height of Douglas-fir exceeds height of paper birch at an earlier age at the coastal site than at the interior site. However, it does not mean that once this happens paper birch will die out quickly. In fact, a few paper birch trees survive for a relatively long period (40 years after the height curves crossover) in a Douglas-fir stand at the coastal site. The almost parallel height growth curves (Figure 7.2a) reflect this phenomenon. 123 Site index studies normally sample only dominant and codominant trees to build height growth curves. Furthermore, in many height-age models for site index prediction, age is breast height age, (i.e., the number of years the trees have been growing since they reached breast height). Using breast-height age reduces variation in height growth caused by non-site factors (Monserud 1984) such as vegetation competition. To study this early competition effect on height growth, it was necessary to determine tree age from the base of the sampled trees. It was also necessary to sample suppressed trees in this study. Therefore, the data and the models presented in this Chapter should not be used to compare with any height growth or site index predictions. The results were used only for the purpose of evaluating how important height growth patterns are to the competitive ability of each species and stand dynamics at each site. 7.5 Conclusions 1. Simulated height growth patterns of paper birch and Douglas-fir were different in the two biogeoclimatic subzones. At the coastal site, height growth of Douglas-fir exceeded that of paper birch at the age of 25-30 years. At the interior site, this process happened at about 45-50 years after stand establishment. 2. There was a height difference between paper birch and Douglas-fir before Douglas-fir height exceeded paper birch height at the interior site but not at the coastal site. This indicates that it may be necessary to control paper birch in order to improve height growth of Douglas-fir at the interior site. It is not as important to control paper birch at the coastal site. In summary, the results support the hypothesis that paper birch is more competitive at the interior site and Douglas-fir at the coastal site. 124 Chapter 8. General Discussion and Conclusions 8.1 Comparison of plant traits The central question of this dissertation was why do paper birch and Douglas-fir coexist as mixedwood forests in the interior cedar-hemlock (ICH) biogeoclimatic zone, but not in the coastal western hemlock(CWH) zone, where paper birch is a relatively uncommon serai species. The answer to the question is important in order to predict what impact climatic change will have on B. C.'s forest vegetation. It also has practical significance for mixedwood stand management, and vegetation management. There are many possible explanations for the difference in paper birch occurrence and persistence in the two biogeoclimatic subzones. Waring and Franklin (1979) proposed the hypothesis that winter photosynthesis by conifers and summer photosynthetic depression by drought at the coastal site is the main reason why conifers dominate the forest landscape of the Pacific Northwest. The study presented in Chapter 3 tested this hypothesis and concluded that Douglas-fir seedlings continued photosynthesis all-year-round at the coastal site but only photosynthesized for seven months at the interior site. Although photosynthesis of saplings and mature trees was not measured, the results support Waring and Franklin's hypothesis. In addition, I proposed that the following differences in performance of paper birch and Douglas-fir at the coastal and interior sites contribute to the explanation of the differences in performance of the two species in the two biogeoclimatic subzones: (1) difference in growth, biomass allocation and phenology (Chapter 4); (2) difference in RGR (Chapter 5); (3) difference in competitive ability (Chapter 6); and (4) difference in height growth patterns (Chapter 7). Table 8.1 summarizes information concerning all the differences in paper birch and Douglas-fir at the two sites. 125 Table 8.1 Comparison of characteristics of paper birch and Douglas-fir grown at the two different sites (coastal and interior) summarizing information presented in the thesis. Characteristics Paper birch Douglas-fir Coastal Interior Coastal Interior Physiology Photosynthesis/leaf area lower higher lower higher Photosynthetic NUE higher lower lower higher Biomass based NUE higher lower lower higher Photosynthetic WUE higher lower higher lower Morphology, growth and biomass allocation Leaf area ratio lower higher higher lower Leaf weight ratio lower higher higher lower Root weight ratio similar similar lower higher Root shoot ratio similar similar lower higher RGR smaller larger larger smaller Height growth slower faster faster slower Competitive ability lower higher higher lower 126 Comparisons of the plant traits at the two sites (Table 8.1) will help us understand the differences in competitive abilities of Douglas-fir and paper birch in the two biogeoclimatic subzones. The results of seasonal photosynthesis patterns from Chapter 3 show that based on instantaneous measures of photosynthesis on sunny days Douglas-fir had over 43% of its annual net photosynthesis during October to April when paper birch had no leaves at the coastal site. This estimate may be too high because it does not adequately account for day-length, sun angle and temperature condition in the winter. In contrast, Douglas-fir had only 10% of its annual net photosynthesis during the same period at the interior site. In spite of the shortcomings of the methods used to determine these estimates, they indicate that winter photosynthesis by Douglas-fir contributed significantly to its higher competitive ability at the coastal site. Douglas-fir had lower NUE and higher WUE at the coastal site than at the interior site. In contrast, paper birch had significantly higher WUE and NUE at the coastal site than at the interior site. These NUE and WUE patterns show the opposite trend to the inferred pattern of competitive ability, suggesting that they are not closely related to the differential performance of paper birch in the two sites. Growth rate varied significantly with climate, providing an additional basis for the variation in competitive interactions between paper birch and Douglas-fir between the two climates. Paper birch had a lower RGR at the coastal site than at the interior site, and vice versa for Douglas-fir. This association between species growth potential (RGR) and the quality of its natural habitat raises two questions. First, how are the differences in RGR between paper birch and Douglas-fir brought about? And, second, what ecological advantage is conferred by their different RGR in different climatic zones? These two questions are in fact closely related. A plant is a complex of organs with contrasting functions and subject to conflicting demands. A low or high RGR may either be the basis for, or a by-product of, adaptation to a certain set of environmental conditions. 127 Numerous plant characteristics contribute to a plant's RGR in its natural habitat, e.g. SLA, LAR, LWR and RWR. Gamier (1992) reported a significant positive relationship between SLA and RGR among 14 annuals and perennials. Walters et al. (1993a) found positive relationships among four northern hardwood species. Poorter (1989) arrived at the conclusion that LAR was the predominant factor explaining the inherent variation in RGR after a review of 45 literature sources. Differences in LAR can be due to variation in LWR or in SLA. Some authors have found a negative correlation between LWR and RGR (Hunt et al., 1987, Shipley and Peters 1990). In this study, the results agree with the literature: paper birch had a larger SLA and Douglas-fir had a smaller SLA. Paper birch had a larger LAR and low RWR at the interior site, and, therefore, a larger RGR than at the coastal site (Table 8.1). The opposite held true for Douglas-fir. Unfortunately, seasonal patterns of variation in SLA of the species were not measured in this study. Respiration provides the driving force for three major energy-requiring processes: maintenance, growth and ion uptake. Walters et al. (1993b) found positive relationships between RGR and leaf, stem and root respiration rates. I did not measure respiration rate. Comparison of respiration rates of paper birch and Douglas-fir at the two sites should be a main focus for future study to provide a better evaluation of the contribution by winter photosynthesis of Douglas-fir to its higher relative competitive ability at the coastal site. Although height growth patterns of mature trees of paper birch and Douglas-fir were compared between the two different sites (Chapter 7), most of the results of this study were from the short-term pot experiments. This leads to two questions requiring further attention: (1) are the two species distributions and abundance in the field better predicted from knowledge of competitive effects or competitive response, and (2) which plant traits are correlated with higher relative competitive effects and higher relative competitive response? 128 One feature of my results complicates the analysis: both growth rate and allocation patterns changed with time even over the short period of this experiment. How much can we infer from this short-term study of seedlings ? Although the recruitment stage is important in many vegetation types, working only with seedlings may well overemphasize the recruitment phase interactions which may be different from the adult phase interactions, because at the seedling stage the leaves have not yet differentiated into the different sizes and morphologies which typify more mature forest vegetation. 8.2 The role of disturbances in sustaining paper birch-Douglas-fir mixtures This study focused on physiological, morphological and growth characteristics as explanations for the variation in competitive abilities of paper birch and Douglas-fir at one site in each of the two biogeoclimatic subzones. However, disturbance and successional processes may be equally important. Paper birch is a shade intolerant, early serai or pioneer species. Where there is an adequate seed source it rapidly colonizes areas deforested by fire, insect outbreaks or logging. In parts of the local forest it can also play a role in late serai stages when it invades gaps caused by the breakup of spruce and balsam fir climax stands. In the long-term absence of fires it can persist through several cycles of breakeups because of its greater longevity J. P. Kimmins, Forest Ecologist, UBC, personal communication). Where it existed in the pre-disturbance forest, it sprouts vigorously from stumps following stand replacing disturbance.. However, its ultimate maximum height is less than that of Douglas-fir (Hermann and Lavender 1990, Haeussler et al. 1990) and it would, therefore, be expected that it would be absent from mid and late serai stands in the study areas. This is true on the coast, but it is a common component of early and mid serai stages in the interior ICH zone. While this is explained in part by the processes explored in this thesis, it is probably that these act in concert with disturbance processes. 129 There is a fundamental difference in the natural disturbance regime between the coast and the interior. On the coast, fire is either uncommon, or occurs on relatively long cycles of 200 to 450 years (Oliver and Larson 1996). In comparison, fire cycles are much shorter in the interior. The higher fire frequency in the interior creates regeneration opportunities for paper birch while there is still a substantial component of birch in the stand, providing a seed rain and "bud" bank (stump sprouts) for prompt recolonization. The longer fire cycles on the coast results in very few birch surviving between major stand replacing disturbance events. Bark beetle and defoliator outbreaks in the ICH zone are a major cause of gap formation or stand replacement, whereas they are much less important on the coast. Root rot diseases have recently been recognized as an additional major force in Douglas-fir stand development in the interior of B. C. They may result in a slow change in species composition, mainly from conifers to hardwoods (van der Kamp 1993), and contribute to the canopy gaps found in the climatically dry-belt of the southern interior. These gaps are rapidly colonized by paper birch where there is a seed rain and bud bank. In the interior wet-belt areas of B. C , brushing operations which remove competing hardwood species from Douglas-fir plantations are also thought to increase the risk of infection of crop trees by root rot (Vyse et al. 1990). The root rot disease caused by Armillaria ostoyae (Romagnesi) Herink is responsible for a large part of 3.8 x 10^  m 3 annual loss of coniferous tree volume to root disease in the southern interior of British Columbia (Morrison et al. 1991). In comparison, root rots are less dominant as a disturbance process in unmanaged coastal forests, and with the relative scarcity of paper birch seed and stumps, where root rot openings occur, paper birch has not been an important colonizer in unmanaged forests. Root rot pathogens cause growth loss and mortality throughout a rotation. Damage is most serious in the ICH biogeoclimatic zone (Peet et al. 1996). Paper birch resprouts from its stumps is more resistant to root rot diseases. Holah et al. (1993) 130 studied the effects of a native forest pathogen, Phellinus weirii, on Douglas-fir forest composition in western Oregon. They studied whether the presence of P. weirii in the old growth Douglas-fir communities of the Cascade Mountains and Coast Ranges of Oregon had an effect on forest composition. They found that the long-term presence of laminated root rot caused by P. weirii in old-growth and mature Douglas-fir stands of the Pacific Northwest can significantly impact community composition. Development of root-disease gaps may influence understory patterns during early succession following harvest (Ingersol et al. 1996). The persistence of paper birch in mixture with Douglas-fir in the ICH zone and not on the coast is thus probably the interaction between the physiological, resource allocation and growth rate adaptations of the two species, and the frequency, extent and intensity of allogenic and biogenic disturbance factors that create "safe sites" (appropriate seedbeds, microclimate and freedom from competition) while there is still a seed rain or bud bank to facilitate colonization by paper birch. Differences in foliage diseases, winter respiration and paper birch insects between the two biogeoclimatic subzones undoubtedly also contribute to the overall determination of the competitive differences in the two environments. As timber harvesting shortens the length of the disturbance cycle in coastal forests, there should be an increase in the abundance of paper birch in these forests, if this interpretation of the role of disturbance is correct. However, the results of this thesis suggest that this should not result in silvicultural problems for the growth of Douglas-fir on the coast that have been documented in the interior. The complexity of the determination of the stability and persistence of paper birch-Douglas-fir mixtures requires the use of appropriate ecosystem simulation models. Such models are ultimately the most useful short-term method of testing successional theories such as the different role of paper birch in the two biogeoclimatic subzones examined in this thesis. In the long run, these issues should be investigated in long-term 131 field experiments, but modeling is the best short-term approach to the problem. Modeling was beyond the scope of this thesis, but will be pursued as a component of my subsequent research into mixedwood ecology and management. 8.3 Limitations on the experimental design of the study Because of time and resource limitations this study has the classic experimental design flaw of pseudoreplication. Research sites were not replicated. With only one research site per subzone, it is impossible to separate the confounding effects of the climatic regime from the natural variation that occurs among sites. In addition, the study was carried out in two growing seasons. Therefore, the interpretation of the results and implications of the conclusions from this study should be limited to the subzones studied and just for the years when the research was carried out. However, to the extent that the climatic data suggest that the study years had "normal" climatic regime, and with the opinion of local ecologists that the study sites are climatically representative of the subzones where the study sites are located. It seems reasonable that the conclusion drawn could be considered as a working hypothesis until further research is done. The analysis of competition experiments is often obscured by the dependence of the outcome of the experiments on the starting conditions and the duration of the experiment (Spitters and Aerts 1983; Wilson 1988). The experimental design for this study was based on the designs used by de Wit (1960) and Shainsky and Radosevich (1992). The seedlings were grown outside under prevailing weather conditions. In my opinion this experimental design mimics the natural situation as closely as possible. Nevertheless, this experiment still suffers from the limitations of a pot experiment, notably from the limited rooting space and the relatively short duration of the experiment (two growing seasons) and as well as the commercial potting soil. There are a few caveats that should be considered when interpreting the results of this study. First, this was a short-term pot experiment with long-lived trees. Seedlings 132 were grown in what might be considered very small pots and there is quite a debate in the literature regarding the possibility that pot restriction of root growth can affect growth, allocation and physiological parameters (McConnaughay and Bazzaz 1991, Thomas and Strain 1991). In fact, there was severe root restriction, especially for the six seedlings-per-pot treatment. In this treatment, the relatively small pots intensified root competition. On the other hand, by using pots, a more accurate root biomass measurement was achieved. By changing seedling density (seedlings per pot), soil nutrient and moisture gradients were created, so the experimental results may reflect competition for soil resources as much or more than competition for light. Lastly, controlling resource availability to roots in an experiment of this size under field conditions is very difficult. Although data collected from the potted experimental seedlings may lack a direct quantitative comparability with the data set from stem analysis of adult trees, I feel that conclusions based on the combined results of the pot experiments and the stem analysis are stronger than those that could be drawn on the basis of either individual study. While the pot experiment can be faulted for its changed environmental conditions (pot root bounding effect), it certainly ehminated those problems presented in stem analysis such as competitive interactions, seedling history, etc. 8.4 Douglas-fir and paper birch mixedwood management Management of mixed stands requires quantitative understanding of the behavior of yield-density relationships and their underlying mechanisms. Complete control of associated hardwoods is difficult to achieve. Means for identifying thresholds of competing hardwoods such as paper birch, below which the cost of conifer yield-loss remains less than the cost of further vegetation control, are needed to evaluate and prescribe stand management strategies. While increasing the abundance of hardwoods usually causes negative effects on the growth of the desired crop tree species such as Douglas-fir (Simard 1990, Simard and Vyse 1992, Shainsky and Radosevich 1986), 133 potential positive effects by hardwoods on conifer crop tree growth and survival may also exist. The presence of hardwoods can protect conifers from drought-inducing radiation (Conard and Radosevich 1982), and can potentially serve as refugia of essential mycorrhizae (Perry et al. 1987, Borchers and Perry 1990). Mixtures of paper birch and Douglas-fir benefited both species. It has been suggested that paper birch can be used as a nurse crop to improve conifer establishment and growth. Simard (1990) reported that leaving a certain amount of paper birch trees mixed with Douglas-fir improves growth of Douglas-fir in the southern interior of B. C. In Scandinavia, the recommended proportion of birch is usually 25 to 50 % of basal area in a paper birch and Norway spruce mixed stand. Such proportions of birch do not constrain conifer growth and, because of the intra-species competition, birch grows better in mixed stands than in pure stands (Mielikainen 1996). The interaction between the effects of paper birch and Douglas-fir densities on seedling performance may reflect the interactive effects that competing seedlings have on each other: the effect that Douglas-fir had on paper birch influenced the way paper birch affected Douglas-fir. There is no a priori reason to assume that a plant grown in intimate proximity with its neighbors will respond to each independently. Limitations on one resource imposed by individuals of one species, such as the shading of the understory through light interception by the overstory, may interact with the limitations in another resource imposed by another species such as soil moisture depletion by the understory, to constrain growth of both species. In addition, species may exhibit differences in sensitivities to resource limitations as well as different abilities to use resources, and these characteristics may interact to influence the way two species compete. In conclusion, the reader is reminded that the conclusions of this thesis are based on results from a single study site in each of the two biogeoclimatic subzones. While it is believed that the two study sites are climatically representative of these subzones, and that the climatic conditions during the study were within the "normal" range of climatic 134 variation in these subzones, the conclusions must be considered as working hypothesis only until further research is able to test them more critically. 135 References Aarssen, L. W. 1992. Causes and consequences of variation in competitive ability in plant communities. J. Veg. Sci. 3:165-174. Aerts, R., Boot, R.G.A., and van der Aart, P. J. M. 1991. The relation between above-and belowground biomass allocation patterns and competitive ability. Oecologia 87:551-559. Arney, J. D. 1985. A modeling strategy for the growth projection of managed stands. Can. J. For. Res. 15:511-518. Binkley, J. W. 1982. Case studies of red alder and Sitka alder in Douglas-fir plantations: nitrogen fixation and ecosystem production. Ph. D. thesis, Oregon State University, Corvallis, OR. pp. 95. Bloom, A. J., Chapin, FS III, Mooney, H. A. 1985. Resource limitation in plants. An economic analogy. An. Rev. Ecol. Syst. 16:363-392. Borchers, S. L., and Perry, D. A. 1990. Growth and ectomycorrhiza formation of Douglas-fir seedlings grown in soils collected at different distances from pioneering hardwoods in southwest Oregon clear-cuts. Can. J. For. Res. 20:712-721. Borman, B. T. and Gordon, J. C. 1984. Stand density effects in young red alder plantations: productivity, photosynthate partitioning, and nitrogen fixation. Ecology 65:394-402. Brand, D. G. 1991. The establishment of boreal and sub-boreal conifer plantations: an integrated analysis of environmental conditions and seedling growth. For. Sci. 37:68-100. Brix, H. 1981. Effects of thinning and nitrogen fertilization on branch and foliage production in Douglas-fir Pseudotsuga menziesii. Can J. For. Res. 11:502-511. Brix, H. 1983. Effects of thinning and nitrogen fertilization on growth of Douglas-fir: relative contribution of foliage quantity and efficiency. Can. J. For. Re. 13:167-175. Burkhart, H. E. and Tennent, R. B. 1977. Site index equations for radiata pine in New Zealand. N. Z. J. For. Sci. 7:408-416. Calder, J. A. and R. L. Taylor. 1968. Flora of the Queen Charlotte Islands (I). Dept. Agric. Ottawa, Ont. Monogr. No. 4(1). 136 Carmean, W. H., 1972. Site index curves for upland oak in the Central States. For. Sci., 18: 109-120. Causton, D. R. 1994. Plant growth analysis: A note on the variability of unit leaf rate (net assimilation rate) within a sample. Ann. Bot. 74:513-518. Chabot, B. F. and Hicks, D. J. 1982. The ecology of leaf life spans. Ann. Rev. Ecol. Syst. 13:229-259. Chapin. F. S. HI. 1983. Adaptation of selected trees and grasses to low availability of phosphorus. Plant Soil 72:283-287. Chapin, F.S., UI and G.R. Shaver. 1989. Differences in growth and nutrient use among arctic plant growth forms. Funct. Ecol. 3:73-80. Chapin, F. S., HI. 1980. The mineral nutrition of wild plants. Ann. Rev. Ecol. Syst. 11:233-260. Chapin, F. S., UI, Johnson, D. A. and Mckendrick, J. D. 1980. Seasonal movement of nutrients in plants of different growth form in an Alaska tundra ecosystem: implications for herbivory. J. Ecol. 68:189-209. Chapin, F. S. HI, Schulze, E. D., Mooney, H. A. 1990. The ecology and economics of storage in plants. Annual Review of Ecology and Systematics 21:423-447. Clutter, J. L., Fortson, J. C , Piennar, L. V., Blister, G. H., and Baily, R. L. 1983. Timber Management- a Quantitative Approach. John Wiley & Sons, New York. Cochran, P. H. 1979. Site index and height growth curves for managed, even aged stands of Douglas-fir east of the Cascades in Oregon and Washington. U. S. For. Serv. Res. Pap.PNW-251. Cole, E. C. and Newton, M. 1986. Nutrient, moisture, and light relations in 5-year-old Douglas-fir plantations under variable competition. Can. J. For. Res. 16:727-732. Cole, E. C. and Newton, M. 1987. Fifth -year responses of Douglas-fir to crowding and nonconiferous competition. Can. J. For. Res. 17:181-186. Conard, S. D. and Radosevich, S. R. 1982. Growth responses of white fir to decreased shading and root competition by montane chaparral shrubs. For. Sci. 28:309-320. Connolly, J. 1986. On difficulties with replacement series methodology in mixture experiments. J. Applied Ecol. 23:125-137. 137 Connolly, J. 1987. On the use of response models in mixture experiments. Oecologia 72:95-103. Cousens, R. 1991. Aspects of design and interpretation of competition (interference) experiments. Weed Technol. 5:664-673. Curtis, R. O., Herman, F. R., DeMars, D. J. 1974. Height growth and site index for Douglas-fir in high-elevation forests of the Oregon-Washington Cascades. For. Sci. 20:307-316. Dyer, M. E. and Bailey, R. L. 1987. A test of six methods for estimating true heights from stem analysis data. For. Sci. 33:3-13. Emmingham, W.H. and R.H. Waring. 1977. An index of photosynthesis for comparing forest sites in western Oregon. Can. J. For. Res. 7:165-174. Emmingham, W. H. 1982. Ecological indexes as a means of evaluating climate, species distribution and primary production, pp. 45-67 In R. L. Edmonds (ed.), Analysis of Coniferous Forest Ecosystems in the Western United States. US/ IBP Ser. No. 14. Dowden, Huchison & Ross, Inc., Stroudsburg, Pennsylvania. Evans, G. C. 1972. The Quantitative Analysis of Plant Growth. Blackwell Scientific Publications, Oxford, 734 pp. Firbank, L. G. and Watkinson, A. R. 1985. On the analysis of competition within two-species mixtures of plants. J. App. Ecol. 22:503-517. Farquhar, G. D. and Sharkey, T. D. 1982. Stomatal conductance and photosynthesis. Annu. Rev. Plant Physiol. 33:317-345. Field, C , Merino, J. and Mooney, H. A. 1983. Compromises between water-use efficiency and nitrogen-use efficiency in five species of California evergreens. Oecologia 60:384-389. Field, C. and Mooney, H. A. 1986. The photosynthesis nitrogen relationship in wild plants, pp. 25-55. In T. J. Givinish (ed.), On the Economy of Plant Form and Function. Cambridge University Press, Cambridge. Fowler, N. 1982. Competition and coexistence in a North Carolina grassland. III. mixtures of component species. J. Ecol. 70: 77-92. Fredericksen, T. S., Zedaker, S. M., Smith, D. W. Seiler, J. R., and Kreh, R. E. 1993. Interference interactions in experimental pine-hardwood stands. Can. J. For. Res. 23: 2032-2043. 138 Gamier, E. 1992. Growth analysis of congeneric annual and perennial grass species. J. Ecol. 80:665-675. Gaudet, C. L. and P. A. Keddy, 1988. Predicting competitive ability from plant traits: a comparative approach. Nature 334:242-243. Gedroc, J. J., McConnaughay, K.D.M. and Coleman, J. S. 1996. Plasticity in root/shoot partitioning: optimal ontogenetic, or both? Funct. Ecol. 10:44-50. Gholz, H. L., 1982. Environmental limits on aboveground net primary production, leaf area, and biomass in vegetation zones of the Pacific Northwest. Ecology 63:469-481. Goldberg, D. E. and Landa, K. 1991. Competitive effect and response: hierarchies and correlated traits in the early stages of competition. J. Ecol. 79:1013-1030. Goldberg, D. E. and Barton, A. M. 1992. Pattern and consequences of inter specific competition in natural communities: a review of field experiments with plants. Am. Nat. 139:771-801. Grace, J. B. 1995. On the measurement of plant competition intensity. Ecology 76: 305-308. Grantz, D. A. 1990. Plant response to atmospheric humidity. Plant Cell Environ. 13: 667-679. Graumlich, L. J. and Brubaker, L. 1995. Long-term records and distribution of conifers: Integration of paleoecology and Physiological ecology. In: W. K. Smith and T. M. Hinckley, eds. Ecophysiology of Coniferous Forests, pp. 37-62, Academic Press, San Diego. Grime, J. P. 1979. Plant Strategies and Vegetation Progresses. John Wiley & Sons, New York, USA. Grime, J. P. and Hunt, R. 1975. Relative growth rate: its range and adaptive significance in a local flora. J. Ecol. 63.393-422. Gutierrez, M. V. and Meinzer, F. C. 1994. Carbon isotope discrimination and photosynthetic gas exchange in coffee hedgerows during canopy development. Aust. J. Plant Physiol. 21:207-219. Haeussler, S. and Coates, D. 1986. Autoecological characteristics of selected species that compete with conifers in British Columbia: a literature review. B. C. Min. For., Victoria, B. C , Land Manage. Report No. 33. 139 Haeussler, S., Coates, D. and Mather, J. 1990. Auto ecology of common plants in British Columbia: A literature review. B. C. Min. For., Victoria, B. C , FRDA Rep. 158. Hamilton, N. R. S. 1994. Replacement and additive designs for plant competition studies. J. of Appl. Ecol.. 31:599-603. Hansen-Bristow, K. 1986. influence of increasing elevation on growth characteristics at timberline. Can. J. Bot. 64:2517-2523. Harlow, W. H. and E. S. Harrar. 1950. Text Book of Dendrology. 3rd ed. McGraw-Hill Book Company, Inc., New York. 555 pp. Harper, J. L. 1977. Population Biology of Plants. Academic Press, London. 892 pp. Harrington, T. B., R. J. Pabst and J. C. Tappeiner n. 1994. Seasonal physiology of Douglas-fir saplings: Response to microclimate in stands of tan-oak or Pacific madrone. For. Sci. 40: 59-82. Harrington, T. B. and Tappeiner II, J. C. 1991. Competition affects shoot morphology, growth duration, and relative growth rates of Douglas-fir saplings. Can. J. For. Res. 21:474-481. Harrington, T. B., Wagner, R. G., Radosevich, S. R. arid Walstad, J. D. 1995a. Interspecific competition and herbicide injury influence 10-year responses of coastal Douglas-fir and associated vegetation to release treatments. For. Ecol. Manag. 76:55-67. Harrington, R. A., Fownes, J. H., Meinzer, F. C. and Scowcroft, P. G. 1995b. Forest growth along a rainfall gradient in Hawaii: Acacia koa stand structure, productivity, foliar nutrients, and water- and nutrient-use efficiencies. Oecologia 102:277-284. Havranek, W. and Tranquillini, W. 1995. Physiological processes during winter dormancy and their ecological significance. In: W. K. Smith and T. M. Hinckley (eds.), Ecophysiology of Coniferous Forest, pp. 95-124, Academic Press. San Diego. Hermann, R. K. and D. P. Lavender. 1990. Pseudotsuga menziesii (Mirb.) Franco, Douglas-fir. In R. M. Burns and B. H. Honkala (eds.), Silvics of North America. Volume 1. Conifers. Agriculture Handbook 654. USDA For. Serv., Washington, DC. Hicks, D. J. and B. F. Chabot. 1985. Deciduous forest, pp. 257-277 In Chabot, B. F. and H. A. Mooney (eds.), Physiological Ecology of North American Plant Communities. 140 Hogberg, P., Johannisson, C. and Hollgren, J. E. 1993. Studies of in the foliage reveal interactions between nutrients and water in forest fertilization experiments. Plant Soil 152:207-214. Holah, J. C , Wilson, M. V., and Hansen, E. M. 1993 Effects of a native forest pathogen, Phillinus weirii, on Douglas-fir forest composition in western Oregon. Can. J. For. Res. 23:2473-2480. Hollinger, D. Y. 1992. Leaf and simulated whole-canopy photosynthesis in two co-occurring tree species. Ecology 73:1-14. Hunt, R. 1982. Plant Growth Curves: The Functional Approach to Plant Growth Analysis. Edward Arnold, London. Hunt, R., Nicholis, A. O. and Fathy, S. A. 1987. Growth and root-shoot partitioning in eight British grasses. Oikos 50:53-59. Ingersol, C. A., Wilson, M. W. and Thies, W. G. 1996. Effects of Phellinus weirii gaps on early successional vegetation following timber harvest. Can. J. For. Res. 26:322-326. Jarvis, P.G. and J.W. Leverenz. 1983. Productivity of temperate, deciduous and evergreen forests, pp. 233-280. In Lange, O.L., et al. (eds.), Ecosystem processes: Mineral cycling, productivity and man's influence. Volume 12D. Physiological plant ecology. New series. Springer-Verlag. New York. Jolliffe, P. A., Minjas, A. N. and Runeckles, V. C. 1984. A reinterpretation of yield relationships in replacement series experiments. J. Appl. Ecol. 21:227-243. Karlsson, P.S. 1989 In situ photosynthetic performance of four coexisting dwarf shrubs in relation to light in a subarctic woodland. Funct. Ecol. 3:481-487. Karlsson, P. S. 1985a. Photosynthetic characteristics and leaf carbon economy of a deciduous and an evergreen dwarf shrub: Vaccinium uliginosum L. and V. vitisidaea L. Holarctic Ecology 8: 9-17. Karlsson, P. S. 1985b. Patterns of carbon allocation above ground in a deciduous {Vaccinium uliginosum) and an evergreen (Vaccinium vitisidaea) dwarf shrub. Physiol. Plant. 63: 1-7. Keddy, P. A. 1990. Competition hierarchies and centrifugal organization in plant communities, pp. 265-290, In: J. B. Grace and D. Tilman, (eds.) Perspectives on plant competition, Academic Press, San Diego, California, USA. 141 Kedrowski, R. A. 1983. Extraction and analysis of nitrogen, phosphorus and carbon fractions in plant material. J. Plant Nut. 6:989-1011. King, J. E., 1966. Site index curves for Douglas-fir in the Pacific Northwest. Weyerhauser Co., WA. Weyerhauser For. Pap.8, 49 pp. Klinka, K. and Krajina, V. J. 1986. Ecosystems of the university of British Columbia Research Forest, Haney, B. C , University of British Columbia, Vancouver, B. C. 123pp. Krueger, K.W. and R.H. Ruth. 1969. Comparative photosynthesis of red alder, Douglas-fir, Sitka spruce, and western hemlock seedlings. Can. J. Bot. 47:519-527. Lajtha, K. and Whitford, W. G. 1989. The effect of water and nitrogen amendments on photosynthesis, leaf demography, and resource-use efficiency in Larrea tridentata, a desert evergreen shrub. Oecologia 80:341-348. Lambers, H. and Poorter, H. 1992. Inherent variation in growth rate between higher plants: A search for physiological causes and consequences. ImBegon, M. and Fitter, A. F. (eds.), Advances in Ecological Research. Vol. 23, Academic Press, Harcourt Brace Jovanovich Publishers, London. Landhausser, S. M.; R. S. Wein and P. Lange. 1995. Gas exchange and growth of three arctic tree-line tree species under different soil temperature and drought preconditioning regimes. Can. J. Bot. 74:686-693. Larcher, W. 1980. Physiological Plant Ecology. Springer-Verlag, New York, USA. Larsen, J. A. 1989. The northern forest border in Canada and Alaska. Ecol. Study 70.35-47. Latham, R. E. 1992. Co-occurring tree species change rank in seedling performance with resource varied experimentally. Ecology 73:2129-2144. Lawrence, W. T. and W. C. Oechel. 1983. Effects of soil temperature on carbon exchange of taiga seedlings, n. Photosynthesis, respiration, and conductance. Can. J. For. Res. 13:850-859. Lechowicz, M.J. and N.E. Ives. 1989. Comparative ecology of drought response in hardwood trees: Acer saccharum versus Fraxinus americana. pp. 283-292. In: Kreeb, K.H., H. Richter and T.M. Hinckley (eds.), Structural and Functional Response to Environmental Stresses. SPB Academic Publishing by, The Hague, The Netherlands. 142 Lloyd, D.; Angove, K.; Hope, G. and Thompson, C. 1990. A Guide to Site Identification and Interpretation for the Kamloops Forest Region. Ministry of Forests, Victoria, B.C. Marchant, C. and J. Sherlock. 1984. A guide to selection and propagation of some native woody species for land rehabilitation in British Columbia. B. C. Min. For., Victoria, B. C. Res. Rep. RR84007-HQ. Margolis, H., Oren, R. Whitehead, D. and Kaufman, M. 1995. Leaf area dynamics of conifer forests. In: W. K. Smith and T. M. Hinckley, eds. Ecophysiology of Coniferous Forests, pp. 181-224, Academic Press, San Diego. Margolis, H. A., and Brand, D. G. 1990. An ecophysiological basis for understanding plantation establishment. Can. J. For. Res. 20:375-390. Massie, M. R.C., Peterson, E. B., Peterson, N. M., and Enns, K. A. 1994. An assessment of the strategic importance of the hardwood resource in British Columbia. B.C. Min. For., Victoria, B. C, FRDA Rep. 221. McConnaughay, K. D. M. and Bazzaz, F. A. 1991. Is physical space a soil resource ? Ecology 72:94-103. McGraw, J. B. and Chapin, F. S. in . 1989. Competitive ability and adaptation to fertile and infertile soils in two Eriophorum species. Ecology 70:736-749. Meidinger, D. and Pojar, J. 1991. Ecosystems of British Columbia, BC Ministry of Forests, Victoria, B. C. Meinzer, F.C, G. Goldstein and D.A. Grantz 1990. Carbon isotope discrimination in coffee genotypes grown under limited water supply. Plant Physiol. 92:130-135. Mielikainen, K. 1996. Approaches to managing birch-dominated mixed stands in Finland. In P. G. Comeau and K. D. Thomas (eds.). Silviculture of temperate and boreal broadleaf-conifer mixtures. Ministry of Forests, British Columbia, Victoria, B. C. Miller, P. C , 1982. Environmental and vegetation variation across a snow accumulation area in montane tundra in coastal Alaska. Holarctic Ecology 5:85-98. Miller, T. E. 1996. On quantifying the intensity of competition across gradients. Ecology 77:978-981. Mitchell, J.F.B., Manabe, S, Tokioka, T. and Meleshko, V. 1990. Equilibrium climate change, pp. 131-170. In: J. T. Houghton, G. J. Jenkins, J. J. Ephraums (eds.), Climate Change. Cambridge University Press. Cambridge. 143 Monk, C. D. 1966. An ecological significance of evergreenness. Ecology 47:504-505. Monserud, R. A. 1985. Comparison of Douglas-fir site index and height growth curves in the Pacific Northwest. Can. J. For. Res. 15: 673-679. Monserud, R. A. 1984. Height growth and site index curves for inland Douglas-fir based on stem analysis data and forest habitat type. For. Sci. 30:943-965. Mooney, H. A. and Gulmon, S. L. 1982. Constrains on leaf structure and function in reference to herbivory. Biosicence 32:198-206. Mooney, H. A. 1983. Carbon-gaining capacity and allocation patterns of Mediterranean-climate plants. In: Kruger FJ, Mitchell DT, Jarvis JUM, (eds.), Mediterranean-Type Ecosystems: The role of nutrients. Berlin: Springer-Verlag, Ecological Studies, 43:103-119. Morrison, D., Merler, H , and Norris. 1991. Detection, recognition and management of Armillaria and Phellinus root diseases in the southern interior of British Columbia. Research Branch, B. C. Ministry of Forests. Victoria. FRDARep. 179. Newton, M. and Cole, E. C. 1991. Root development in planted Douglas-fir under varying competitive stress. Can. J. For. Res. 21:25-31. Nigh, G. and Sit., V. 1996. Validation of forest height-age models. Can. J. For. Res. 26:810-818. Oliver, C. and Larson, B. C. 1996. Forest Stand Dynamics. Update edition, John Wiley & Sons, Inc., New York. Peet, F. G., Morrison, D. J., and Pellow, K. W. 1996. Rate of spread of Armillaria ostoyae in two Douglas-fir plantations in the southern interior of British Columbia. Can. J. For. Res. 26:148-151. Perry, D. A., Molina, R. and Amaranthus, M. P. 1987. Mycorrhizae, mycorrhizospheres, and reforestation: current knowledge and research needs. Can. J. For. Res. 17:929-940. Pons. T. L., Van der Werf, A., and Lambers, H. 1993. Photosynthetic nitrogen use efficiency of inherently slow- and fast-growing species: possible explanations for observed differences, pp. 51-67. In: Roy, J. and Gamier, E. (eds.), A Whole Plant Perspective on Carbon-Nitrogen Interactions. SPB Academic, The Hague. Poole, D. and Miller, P. C. 1975. Water relations of selected species of chaparral and coastal sage communities. Ecology 56:1118-1128. 144 Poorter, H. 1989. Interspecific variation in relative growth rate: On ecological causes and physiological consequences, pp. 45-68. In: H. Lambers, M. L. Cambridge, H. Konings and T. L. Pons (eds.), Causes and Consequences of Variation in Growth Rate and Productivity of Higher Plants. SPB Academic Publishing, The Hague. Poorter, H. and Remkes, C. 1990. Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate. Oecologia 83:553-559. Poorter, H., Remkes, C , and Lambers, H. 1990. Carbon and nitrogen economy of 24 wild species differing in relative growth rate. Plant Physiol. 94:621-627. Pothier, D. and Margolis, H. A., 1991. Analysis of growth and light interception of balsam fir and white birch saplings following pre commercial thinning. Ann. Sci. For., 48:123-132. Puettmann, K. J., Hibbs, D. E. and Hann, D. W. 1992. The dynamics of mixed stands of Alnus rubra and Pseudotsuga menziesihextension of size-density analysis to species mixture. J. Ecol. 80:449-458. Quehl, J. M. 1985. Comparative study of the winter photosynthetic potential of three evergreen conifers of the temperate zone {Pseudotsuga menziesii Mirb., Abies alba Mill, and Picea excelsa Link.). Ann. Sci. For. 42:23-38. Reader, R. J. 1978. Contribution of overwintering leaves to the growth of three broad-leafed evergreen shrubs belonging to the Ericaceae family. Can. J. Bot. 56:1248-1261. Reich, P. B., Koike, T., Go wer, S. T., and Schoettle, A. W. 1995. Causes and consequences of variation in conifer leaf life-span. In: W. K. Smith and T. M. Hinckley, eds. Ecophysiology of Coniferous Forests, pp. 225-254, Academic Press, San Diego. Reich, P. B. and Walters, M. B. 1994. Photosynthesis-nitrogen relations in Amazonian tree species. II. Variation in nitrogen vis-a-vis specific leaf area influences mass-and area-based expressions. Oecologia 97:73-81. Reich, P. B., Walters, M. B., and Ellsworth, D. S. 1992. Leaf life-span in relation to leaf, plant and stand characteristics among diverse ecosystems. Ecol. Monogr. 62:365-392. Rejmanek, M., Robinson, G. R, and Rejmankova, E. 1989. Weed-crop competition: Experimental designs and models for data analysis. Weed Science. 37:276-284. Richards, F. J. 1959. A flexible growth function for empirical use. J. Exp. Biol. 10:290-300. 145 Ritchie, M. W. and Hann, D. W. 1986. Development of a tree height growth model for Douglas-fir. For. Ecol. Manag. 15:135-145. Rundel, P. W. 1982. Nitrogen utilization efficiencies in Mediterranean-climate shrubs of California and Chile. Oecologia 55: 409-413 Runyon, J. Waring, R. Ff. Goward, S. N., Welles, J. M. 1994. Environmental limits on net primary production and light-use efficiency across the Oregon Transect. Ecol. Appl. 4:226-237. Safford, L. O., J. C. Bjorkbom, and J. C. Zasada. 1990. Betulapapyrifera Marsh, paper birch Betulaceae: birch family, pp. 158-171. In R. M. Burns and B. H. Honkala. (eds.), Silvics of North America. Vol. 2. Hardwoods. U. S. Dep. Agric. For. Serv. Washington, D. C. Agric. Handbook 654. Schulze, E. D. and Hall, A. E. 1982. Stomatal response, water lose and C O 2 assimilation rates of plants in contrasting environments, pp. 181-430. In O. L. Lange, P. S. Nobel, C. B. Osmond, and H. Ziegler, (eds.), Encyclopedia of plant physiology. New Ser. Vol. 12B. Physiological plant ecology n. Springer-Verlag, Berlin. Schulze, E. D. 1982. Plant life-forms and their carbon, water and nutrient relations, pp. 615-676. In O. L. Lange, P. S. Nobel, C. B. Osmond, and H. Ziegler, (eds.), Encyclopedia of Plant Physiology. New Ser. Vol. 12B. Physiological plant ecology II. Springer-Verlag, Berlin. Shainsky, L. J. and Radosevich, S. R. 1992a. Mechanisms of competition between Douglas-fir and red alder seedlings. Ecology 73:30-45. Shainsky, L. J. and Radosevich, S. R. 1992b. Analysis of yield-density relationships in experimental stands of Douglas-fir and red alder seedlings. For. Sci. 37:574-592. Shainsky, L. J. and Radosevich, S. R. 1991. Analysis of yield-density relationships in experimental stands of Douglas-fir and red alder seedlings. For. Sci. 37:574-592. Shainsky, L. J. and Radosevich, S. R. 1986. Growth and water relations of Pinus ponderosa in competitive regime with Arctostaphylos patula seedlings. J. Appl. Ecol. 23:957-966. Sheriff, H., Margolis, H. A., Kaufman, M. R. and Reich, P. B. 1995. Resource use efficiency. In: W. K. Smith and T. M. Hinckley, eds. Resource Physiology of Conifers, pp. 143-178, Academic Press, San Diego. 146 Sheriff, D. W., 1992. Nitrogen nutrition, growth and gas exchange of Eucalyptus camaldulensis and Eucalyptus globulus seedlings. Aust. J. Plant. Physiol. 19:637-652. Shipley, B. and Peters, R. H. 1990. A test of the Tifman model of plant strategies: Relative growth rate and biomass partitioning. Am. Nat. 136:139-153. Simard, S. W. and Vyse, A. 1992. Ecology and Management of Paper Birch and Black Cotton wood in Southern British Columbia. Land Management Report No. 75. B. C. Ministry of Forests, Victoria, B.C. Simard, S. 1990. A Retrospective Study of Competition between Paper Birch and Planted Douglas-fir. FRDA Rep. 147. B. C. Min. For. Victoria, B. C. Small, E. 1972. Photosynthetic rates in relation to nitrogen recycling as an adaptation to nutrient deficiency. Can. J. Bot. 50:2227-2233. Small, E. 1973. Xeromorphy in plants as an adaptation to nutrient deficiency. Can. J. Bot. 126:534-539. Smith, N. J. 1986. A model of stand allometry during the self-thinning process. Can. J. For. Res. 16:990-995. Snaydon, R. W. 1991. Replacement or additive designs for competitive studies? J. Appl. Ecol. 28:930-946. Sobrado, M.A. 1991. Cost-benefit relationships in deciduous and evergreen leaves of tropical dry forest species. Funct. Ecol. 5:608-616. Sokal, R. R. and Rohlf, F. J., 1995. Biometry. Third edition,W. H. Freeman and Company, New York. Somers, G. L., and Farrar, R. M. Jr. 1991. Biomathematical growth equations for natural longleaf pine stands. For. Sci. 37:227-244. Spitters, C. J. T. 1983. An alternative approach to analysis of mixed cropping experiments. I. Estimation of competition effects. Neth. J. Agric. Sci. 31:1-11. Stenberg, P., DeLucia, E. H., Schoettle, A. W. and Smolander, H. 1995. Photosynthetic light capture and processing from cell to canopy. In: W. K. Smith and T. M. Hinckley, eds. Resource Physiology of Conifers, pp. 3-38, Academic Press, San Diego. Takenaka, A. 1986. Comparative ecophysiology of two representative Quercus species appearing in different stages of succession. Ecol. Res. 1:129-140. 147 Tesch, S. D., Korpela, E. J., and Hobbs, S. D. 1993. Effects of sclerophyllous shrub competition on root and shoot development and biomass partitioning of Douglas-fir seedlings. Can. J. For. Res. 23:1415-1426. Thomas, R. B. and Strain, B. R. 1991. Root restriction as a factor in photosynthetic acclimation of cotton seedlings to elevated carbon dioxide. Plant Physiol. 96:627-634 Tilman, D. 1988. Plant strategies and the dynamics and structure of plant communities. Princeton University Press, Princeton, New Jersey, USA. Tissue, D. T., Thomas, R. B., Strain, B. R. 1993. Long term effects of elevated C O 2 and nutrients on photosynthesis and rubisco in loblolly pine seedlings. Plant Cell Environ. 16:859-865. Trenbath, B. R. 1974. Biomass productivity of mixtures. Adv. Agron. 26:177-210. Turkington, R., Klein, E. and Chan way, C. P. 1993. Influence effects of nutrients and disturbance: an experimental test of plant strategy theory. Ecology 74:863.878. Twolan-Strutt, L. and Keddy, P. A. 1996. Above- and belowground competition intensity in two contrasting wetland plant communities. Ecology 77:259-270. Van Cleve, K., Oliver, L., Schlentner, R., Viereck, L. A., and Dyrness, C. T. 1983 Productivity and nutrient cycling in taiga forest ecosystems. Can. J. For. Res. 13:747-766. Van der Kamp, B. J. 1993. Rate of spread of Armillaria ostoyae in the central interior of British Columbia. Can. J. For. Res. 23: 1239-1241. Vyse, A., R. A. Smith and B. G. Bondar 1990. Management of interior Douglas-fir stands in British Columbia: Past, present and future, pp. 177-186. In D. M. Baumgartner and J. E. Lotan (eds.), Proc. Interior Douglas-fir: The species and its management. Washington State University, Spokane, Washington, USA. Walstad, J. D. and Kuch, P. J. 1987. Forest Vegetation Management for Conifer Production. Wiley, New York. Walters, M. B., Kruger, E. L. and Reich, P. B. 1993a. Growth, biomass distribution and C O 2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance. Oecologia 94:7-16. Walters, M. B., Kruger, E. L. and Reich, P. B. 1993b. Relative growth rate in relation to physiological and morphological traits for northern hardwood tree seedlings: 148 species, light environment and ontogenetic considerations. Oeologia 96:219-231. Wang, G. G., Marshall, P. L. and Klinka, K. 1994. Height growth pattern of white spruce in relation to site quality. For. Ecol. Manage. 68:137-147. Waring, R. H.; Emmingham, W. H ; Gholz, H. L. and Grier, C. C. 1978. Variation in maximum leaf area of coniferous forests in Oregon and its ecological significance. For. Sci. 24:131-140. Waring, R.H. and J.F. Franklin. 1979. Evergreen coniferous forests of the Pacific Northwest Science 204:1380-1386. Waring, R. H. and Schlesinger, W. H. 1985. The carbon balance of trees. In: R. H. Waring and W. H. Schlesinger (eds.). Forest Ecosystems Concepts and Management, p. 7-37, Academic Press, Orlando, Florida. Webber, P. J. 1978. Spatial and temporal variation of the vegetation and its productivity, Barrow, Alaska, in L. L. Tieszen ed. Vegetation and production ecology of an Alaska arctic tundra, pp. 36-112. Springer-Verlag, Berlin. Wilkinson, L. 1996. SYSTAT: The System for Statistics. SYSTAT, Inc. Evanston, IL. Wilson, S. D. and Keddy, P. A. 1986. Measuring diffuse competition along an environmental gradient: results from a shorline plant community. Am. Nat. 127:862-869. Wilson, J. B. 1988. Shoot and root competition. J. Appl. Ecol. 25: 279-296. de Wit, C. T. 1960. On competition. Verslagen van landbouwkundige Onderzoekingen, 66:1-82. Woodward, F. I. 1995 Ecophysiological control of conifer distributions. In: W. K. Smith and T. M. Hinckley, eds. Ecophysiology of Coniferous Forests, pp. 79-94, Academic Press, San Diego. Yin, X. 1993. Variation in foliar nitrogen concentration by forest types and climatic gradients in North America. Can. J. For. Res. 23:1587-1602. Young, D.R. 1985. Crown architecture, light interception, and stomatal conductance patterns for sympatric deciduous and evergreen species in a forest understory. Can. J. Bot. 63:2425-2429. Zar, J. H. 1984. Biostatistical Analysis. Prentice Hall, NJ. ^ Os o S ° ^ +-! 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B B t3 OO a CD T J X a 0 0 S T J X OO CD oo d o CN in cn r- o cn d * * * Os O oo s T J X oo CD •lH CD CD OH oo X a U co Q CD „ „ u i-H rH CL, rH U U oo U o o d v QH * * o d v OH * * in O d v OH * 164 Appendix 3 Foliage, shoot and root biomass (mean±SE, g per plant) and root/shoot ratio of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in a replacement experiment at the interior site harvested in April, 1995. Ratio plant per pot Species FoliageShoot Root Root/shoot PB:C-DF Paper birch mixture with coastal DF 0:6 C-DF 1.98+0.06 1.6010.09 2.3110.07 0.6510.01 1:5 C-DF 1.5310.05 1.0510.06 1.8110.06 0.7110.01 2:4 C-DF 1.50±0.05 1.00+0.05 1.7710.05 0.7110.01 3:3 C-DF 1.38±0.06 0.8910.07 1.6410.07 0.7410.01 4:2 C-DF 1.16±0.08 0.6610.08 1.4010.09 0.7710.02 5:1 C-DF 1.14±0.16 0.6510.15 1.3810.18 0.7810.03 1:5 PB 5.2010.88 11.7012.17 7.1610.91 0.4410.02 2:4 PB 3.36±0.27 7.2610.52 5.1510.26 0.4910.01 3:3 PB 3.13±0.19 6.7410.44 4.8610.22 0.5010.01 4:2 PB 2.27±0.17 4.7510.38 3.7910.21 0.5510.01 5:1 PB 4.50+0.16 6.2110.36 4.9810.17 0.4710.01 6:0 PB 2.57+0.11 5.4410.26 4.1810.14 0.5310.01 PB:I-DF Paper birch mixture with interior DF 0:6 I-DF 1.79±0.05 1.3510.05 2.0910.06 0.6710.01 1:5 I-DF 1.63±0.08 1.1710.10 1.9210.09 0.7010.01 2:4 I-DF 1.46±0.08 0.9710.08 1.7310.09 0.7210.01 3:3 I-DF 1.52+0.09 1.0310.10 1.7910.10 0.7110.01 4:2 I-DF 1.47±0.06 0.9710.06 1.7410.07 0.7210.01 5:1 I-DF 1.55±0.14 1.0610.16 1.8310.15 0.7110.02 1:5 PB 4.24±0.41 8.4810.63 10.1110.65 0.8510.19 2:4 PB 2.90+0.36 7.05+0.74 7.7910.95 0.6810.02 3:3 PB 3.5010.27 4.4710.47 6.2910.43 0.8510.06 4:2 PB 2.7610.48 4.4710.47 6.2910.43 0.8510.06 5:1 PB 2.5710.20 4.4710.47 6.2910.43 0.8510.06 6:0 PB 2.5710.11 5.4410.26 4.1810.14 0.5310.01 165 Foliage, shoot and root biomass (meaniSE, g per plant) and root/shoot ratio of paper birch (PB), coastal Douglas-fir (C-DF) and interior Douglas-fir (I-DF) grown in a replacement experiment at the coastal site harvested in April, 1995. Ratio Species FoliageShoot Root Root/shoot plant per pot PB:C-DF Paper birch mixed with coastal DF 0:6 C-DF 5.72±0.28 4.3510.23 5.1310.23 0.3110.01 1:5 C-DF 5.70±0.42 4.4810.26 3.3110.25 0.3310.02 2:4 C-DF 6.64±0.28 3.4010.17 3.4510.22 0.3410.01 3:3 C-DF 5.53±0.48 1.2010.39 2.9910.40 0.2910.01 4:2 C-DF 5.12±0.47 3.8610.36 2.6410.36 0.2710.02 5:1 C-DF 4.57+0.78 3.4310.63 2.2510.56 0.7810.03 1:5 PB 2.62±0.33 7.4010.63 4.2410.45 0.5510.09 2:4 PB 3.60±0.48 6.9811.03 6.6311.13 0.6110.02 3:3 PB 3.8110.30 7.40+0.65 7.0610.71 0.6210.01 4:2 PB 4.23±0.56 8.3711.24 8.2311.43 0.6310.01 5:1 PB 3.38+0.44 6.44+0.95 6.1111.06 0.6010.02 6:0 PB 3.4710.26 6.6910.56 6.3110.61 0.6110.01 PB:I-DF Paper birch mixed with interior DF 0:6 I-DF 5.09+0.32 3.8610.26 2.6910.25 0.2910.00 1:5 I-DF 4.3410.40 3.2410.32 2.0710.28 0.2710.01 2:4 I-DF 4.01+0.17 2.9710.13 1.8110.11 0.26+0.01 3:3 I-DF 3.8510.26 2.8510.21 1.7210.18 0.2510.01 4:2 I-DF 3.1810.35 2.3210.28 1.3010.21 0.2310.01 5:1 I-DF 4.27+0.82 3.1910.65 2.0410.57 0.2610.03 1:5 PB 5.1710.49 10.3911.09 10.4611.26 0.6710.01 2:4 PB 4.2210.45 8.3110.99 8.0811.10 0.6410.02 3:3 PB 3.7510.37 7.2810.80 6.9510.89 0.6210.01 4:2 PB 4.3110.47 8.5311.05 8.3911.19 0.6410.01 5:1 PB 3.1610.27 6.0410.57 5.6210.60 0.6010.01 6:0 PB 3.4710.26 6.6910.56 6.3110.61 0.6110.01 

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