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Effect of paper birch density on the performance of interior douglas-fir when grown in mixture in the… Baleshta, Karen Eileen 2003

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EFFECT OF PAPER BIRCH DENSITY ON THE PERFORMANCE OF INTERIOR DOUGLAS-FIR WHEN GROWN IN MIXTURE IN THE SOUTHERN INTERIOR OF BRITISH COLUMBIA by KAREN EILEEN BALESHTA B.N.R.S., The University College of the Cariboo, 1998 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE 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 April 2003 © Karen Eileen Baleshta, 2003 In presenting this thesis in partial fulfillment 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 ^G/l&^'C Scxe)\Jce5 The University of British Columbia Vancouver, Canada Date APrUL. JI003 ABSTRACT The objective of this study was to examine the effects of Betula papyrifera Marsh, (paper birch) density treatments on the productivity of Pseudotsuga menziesii var. glauca (Beissn.) Franco (interior Douglas-fir) saplings when the two species are grown in mixture in the ICHmw3 and IDFmw2 variants in the southern interior of British Columbia. Four study sites were selected in May 1999 in 10- to 15-year-old interior Douglas-fir plantations in the Adams Lake drainage, approximately 100 kilometers (km) northeast of Kamloops. Five paper birch (Ep) density treatments (0, 400, 1111, 4444 stems per hectare and control) were replicated four times in a randomized complete block design, where site location was used as the blocking factor. The effects of the paper birch density treatments on the performance of interior Douglas-fir were determined by comparing individual tree and environmental response variables. Interior Douglas-fir survival was high and there were no significant differences in mortality among treatments two-years following the initiation of the paper birch density treatments. Interior Douglas-fir mortality due to Armillaria ostoyae tended to be lower in the control (no thinning) versus the four thinned treatments combined, but the differences among treatments were not significant (P=0.2114). In this study, mean diameter increment of interior Douglas-fir was higher in the treatments where the broadleaf component was completely removed, heavily thinned and lightly thinned (e.g. 0 Ep, 400 Ep and 4444 Ep, respectively) compared with the control two years after the density treatments were implemented. On average, interior Douglas-fir in the lightly thinned treatment (4444 Ep) tended to be the tallest with the largest stem diameter, crown diameter, stem volume and canopy volume. Interior Douglas-fir height:diameter ratio tended to decrease in all treatments, with significant differences occurring among treatments in 2001 (P=0.0333). The ii control had a higher height:diameter ratio than (a) the four other thinning treatments combined, and (b) the treatment where the broadleaf component was completely removed (0 Ep)(P=0.0046 and P=0.0169, respectively). Mean net photo synthetic rate and mean stomatal conductance of the interior Douglas-fir measured in 2001, and mean foliar nitrogen concentration measured in 2000, were not significantly different among treatments (P=0.8157, P=0.8020 and P=0.8994, respectively). Mean specific leaf area of the interior Douglas-fir sampled in 2000 increased with increasing paper birch density and decreasing light availability (P=0.0018). Mean light transmittance measured in 2000 yielded differences among treatments (PO.0001), with the trend from highest to lowest as follows: 0 Ep > 400 Ep > 1111 Ep > 4444 Ep > control. Soil moisture content did not differ among treatments in 2000 (P=0.3922), but it did in 2001 (P=0.0086). In 2001, the lowest mean soil moisture content was in the control (10.12% ± 2.18%), whereas the 0 Ep treatment, where the broadleaf component was completely removed, had the highest (17.23% ± 3.31%). In this study, paper birch survival was high, averaging between 98% and 99%. Substantial main stem breakage (at 1.54 - 2.40 meter height) by moose occurred in the heavily thinned treatment (400 Ep)(excluding Burton Creek), whereas little occurred in the other treatments between 1999 and 2001, but differences among treatments were not significant (P=0.1889). The mean relative diameter growth rate of the dominant paper birch (tallest 250 stems per hectare) increased with decreasing birch density (P=0.0005). Mean diameter increment also tended to increase with decreasing birch density, although the treatment rankings were not systematic (P=0.0213). The trends in interior Douglas-fir growth across treatments in this study tend to support other studies showing that moderate densities of paper birch can be retained without i i i detrimentally affecting interior Douglas-fir performance. While preliminary, these results provide valuable information toward identifying density regimes that are indicative of healthy conifer/broadleaf mixed-stands. iv TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS v LIST OF TABLES viii LIST OF FIGURES xi ACKNOWLEDGEMENTS xv DEDICATION xix CHAPTER 1 INTRODUCTION 1 1.1 Ecology of Mixed Stands 2 1.2 Silviculture Practices in Young Mixed Stands 4 1.3 Role of Paper Birch in Mixed Stands 6 1.4 Competition in Young Mixed Stands 8 CHAPTER 2 METHODS 11 2.1 Study Sites 11 2.2 Treatments and Experimental Design 17 2.3 Measurements 24 2.3.1 Individual Tree Response Variables: Interior Douglas-fir 24 2.3.1.1 Growth 24 2.3.1.2 Net Photosynthetic Rate and Stomatal Conductance 25 2.3.1.3 Foliar Nitrogen Concentration 29 2.3.1.4 Incidence of Armillaria ostoyae 30 2.3.1.5 Survival 30 2.3.2 Individual Tree Response Variables: Paper Birch 30 2.3.2.1 Growth 30 2.3.2.2 Net Photosynthetic Rate and Stomatal Conductance 31 2.3.3 Environmental Response Variables 33 2.3.3.1 Light Availability 33 2.3.3.2 Soil Moisture Content 34 2.4 Statistical Analyses 35 v CHAPTER 3 RESULTS 40 3.1 Interior Douglas-fir Performance 40 3.1.1 Survival 40 3.1.2 Growth 41 3.1.3 Net Photosynthetic Rate and Stomatal Conductance 47 3.1.4 Specific Leaf Area 48 3.1.5 Foliar Nitrogen Concentration 51 3.2 Paper Birch Performance 51 3.2.1 Survival 51 3.2.2 Growth 52 3.3 Dominant Paper Birch Performance 59 3.3.1 Growth 59 3.3.2 Net Photosynthetic Rate and Stomatal Conductance 64 3.3.3 Foliar Nitrogen Concentration 64 3.4 Environmental Conditions 64 3.4.1 Light Availability 64 3.4.2 Soil Moisture Content 66 CHAPTER 4 DISCUSSION 67 4.1 Growth Response of Interior Douglas-fir 67 4.2 Survival Response of Interior Douglas-fir 70 4.3 Physiological Response of Interior Douglas-fir 73 4.4 Resource Availability to Interior Douglas-fir 76 4.4.1 Light A vailability 76 4.4.2 So il Moisture A vailab ility 78 4.4.3 Soil Nutrients 80 4.5 Paper Birch Responses to Treatments 81 4.5.1 Growth 81 4.5.2 Survival - Moose Damage 82 4.6 Conclusions and Management Implications 83 4.6.1 Concluding Statement About Results 83 4.6.2 Management Implications 84 4.6.3 Future Directions for the Study 87 4.6.4 Future Directions for Mixture Silviculture Research 89 LITERATURE CITED 91 APPENDIX: CUT-BRANCH TECHNIQUE TEST 101 vi 6.1 Introduction 101 6.2 Materials and Methods 103 6.2.1 Study Area and Experiment Details 103 6.2.2 Leaf Gas Exchange Measurements 104 6.2.3 Statistical Analyses 105 6.3 Results 106 6.3.1 Net Photosynthetic Rate 106 6.3.2 Stomatal Conductance 110 6.4 Discussion 115 6.5 Literature Cited for Appendix 117 v i i LIST OF TABLES Table 2-1. Site characteristics of each study site in 1999 15 Table 2-2. Pre-treatment species, density and diameter characteristics of each study site 16 Table 2-3. Formulae used to calculate various growth increment variables 26 Table 2-4. The time it took to collect and measure leaf gas exchange of randomly selected interior Douglas-fir branches at each site 28 Table 2-5. Analysis of variance table for interior Douglas-fir individual tree and environment response variables 36 Table 2-6. Analysis of variance table for paper birch individual tree response variables 38 Table 3-1. Means, standard error of the treatment means (S.E.) and P-values of interior Douglas-fir growth variables stem diameter, height and crown diameter in 1999, 2000 and 2001 41 Table 3-2. Means, standard error of the treatment means (S.E.) and P-values of interior Douglas-fir growth variables heightdiameter ratio, height to live crown, stem volume and canopy volume in 1999, 2000 and 2001. Treatment means are significantly different at a=0.05 42 Table 3-3. Means and P-values of planned contrasts that compare interior Douglas-fir stem diameter, height and heightdiameter ratio among treatments for the years 2000 and 2001. Contrast means are significantly different at a=0.05 45 Table 3-4. Means, standard error of the treatment mean (S.E.; n=4) and P-values of interior Douglas-fir diameter increment, relative diameter growth rate, height increment and relative height growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two-year period) 46 Table 3-5. Means, standard error of the treatment means (S.E.), and P-values for net photosynthetic rate (pmol CO2 m"2 s"1) and stomatal conductance (mmol H2O m"2 s"1) of randomly selected interior Douglas-fir within 3.0 - 6.0 cm stem diameter in the paper birch thinning treatments in late-August/early September 2001 48 Table 3-6. Means and P-values of planned contrasts that compare interior Douglas-fir diameter increment, relative diameter growth rate, height increment and relative height growth rate among treatments between 1999 and 2001 (two-year period). Contrast means are significantly different at a=0.05 49 Table 3-7. Means and P-values of planned contrasts that compare interior Douglas-fir diameter increment, relative diameter growth rate, height increment and relative height growth rate among treatments between 1999 and 2000 (one-year period). Contrast means are significantly different at a=0.05 50 v i i i Table 3-8. Means, standard error of the treatment means (S.E.) and P-values of paper birch growth variables stem diameter, height and crown diameter in 1999, 2000 and 2001. Treatment means with different letters are significantly different (a=0.05) 53 Table 3-9. Means, standard error of the treatment means (S.E.) and P-values of paper birch growth variables height:diameter ratio, height-to-live crown, stem volume and canopy volume in 1999, 2000 and 2001. Treatment means with different letters are significantly different (a=0.05) 54 Table 3-10. Means, standard error of the treatment means (S.E.) and P-values of paper birch diameter increment and relative diameter growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two year period). Treatment means with different letters are significantly different (a=0.05) 55 Table 3-11. Means, standard error of the treatment means (S.E.) and P-values of paper birch height increment and relative height growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two year period). Treatment means with different letters are significantly different (a=0.05) 56 Table 3-12. Means and P-values (a=0.05) of planned contrasts that compare paper birch height-to-live crown (m) and crown diameter (m) in the paper birch density treatments for the years 1999, 2000 and 2001 57 Table 3-13. Means and P-values of planned contrasts that compare paper birch diameter increment (cm), relative diameter growth rate (cm cm"1), height increment (m) and relative height growth rate (mm"1) between 1999 and 2001 (two-year period) among treatments. Contrast means are significantly different at a=0.05 58 Table 3-14. Means, standard error of the treatment means (S.E.) and P-values of dominant paper birch (largest 250 stems ha"1) growth variables stem diameter, height and crown diameter in 1999, 2000 and 2001. Treatment means with different letters are significantly different (a=0.05) 60 Table 3-15. Means, standard error of the treatment means (S.E.) and P-values of dominant paper birch (largest 250 stems ha"1) growth variables height:diameter ratio, height-to-live crown, stem volume and canopy volume in 1999, 2000 and 2001. Treatment means with different letters are significantly different (a=0.05) 61 Table 3-16. Means, standard error of the treatment means (S.E.) and P-values of dominant paper birch diameter increment, relative diameter growth rate, height increment and relative height growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two-year period). Treatment means with different letters are significantly different within years (a=0.05) 62 Table 3-17. Means and P-values (a=0.05) of planned contrasts that compare dominant paper birch diameter increment (cm), relative diameter growth rate (cm cm"1), height increment (m) and relative height growth rate (m m"1) between 1999 and 2001 (two-year period) among treatments 63 i x Table 3-18. Statistical summary of paired t-test results testing differences between hemispherical canopy photograph means (HCP) and handheld light sensor (HLS) means within each treatment, excluding the 0 Ep L I S T O F F I G U R E S Figure 2-1. Location of the study sites: Gold Creek 1 and 2 (GC1 & GC2), Momich River (MR) and Burton Creek (BC) 12 Figure 2-2. Photograph of the Gold Creek 1 site with treatment area outlined in white. Photo credit: Kent Watson 13 Figure 2-3. Photograph of the Gold Creek 2 site with treatment area outlined in white. Photo credit: Kent Watson 13 Figure 2-4. Photograph of the Burton Creek site with treatment area outlined in white. Photo credit: Kent Watson 14 Figure 2-5. Photograph of the Momich River site with treatment area outlined in white. Photo credit: Kent Watson 14 Figure 2-6. Paper birch density treatments at Gold Creek 1 (shaded) and Gold Creek 2 18 Figure 2-7. Paper birch density treatments at Momich River (MR) 18 Figure 2-8. Paper birch density treatments at Burton Creek. "A-Pr", "B-Pr" and "C-Pr" mark the location of another unrelated experiment 19 Figure 2-9. The 0 Ep treatment prior to brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 20 Figure 2-10. The 0 Ep treatment three months after brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 20 Figure 2-11. The 400 Ep treatment prior to brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 21 Figure 2-12. The 400 Ep treatment three months after brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 21 Figure 2-13. The 1111 Ep treatment prior to brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 22 Figure 2-14. The 1111 Ep treatment three months after brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 22 Figure 2-15. The 4444 Ep treatment prior to brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 23 Figure 2-16. The 4444 Ep treatment three months after brushing at the Gold Creek 2 site. Photo credit: Tanya Luszcz 23 Figure 2-17. The control treatment at the Gold Creek 2 site. Photo credit: Tanya Luszcz 24 x i Figure 3-1. Mortality due to Armillaria ostoyae of interior Douglas-fir in the paper birch density treatments in 2001. Arcsine transformation (Kozak 1998) was used to produce normality. The treatment means are the arcsine transformed values and standard error of the treatment means (error bars). The standard error of the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and MSE is the mean square error 40 Figure 3-2. Mean stem diameter (cm) and standard error of the treatment mean bars of the interior Douglas-fir trees for each treatment for the years 1999, 2000 and 2001. Treatment means with different letters are significantly different (a = 0.05). The standard error of the treatment mean is + (square root (MSE)/square root (n)), where n = 4 and MSE is the mean square error 43 Figure 3-3. Interior Douglas-fir heightdiameter ratio transformed (Base e log) means in the various treatments in 1999, 2000 and 2001. Treatment means with different letters are significantly different in 2001 (a = 0.05). In 1999 and 2000, there were no differences among treatments 44 Figure 3-4. Mean diameter increment (cm) and standard error of the treatment mean bars of interior Douglas-fir in the density treatments in 2000 and 2001. Treatment means with different letters are significantly different (a = 0.05). The standard error of the treatment mean is ± square root (MSE) / square root (n), where n = 4 46 Figure 3-5. Effect of paper birch density treatments on interior Douglas-fir specific leaf area (cm2 g"1) and standard error of the treatment mean bars in 2000 and 2001. Treatment means with different letters are significantly different (a = 0.05). The standard error of the treatment mean is + square root (MSE) / square root (n), where n = 4 and MSE is the mean square error 51 Figure 3-6. Percentage of main stem breakage of paper birch (Ep) caused by moose browsing in the density treatments in 2001. Arcsine transformation (Kozak 1998) was used to produce normality. The treatment means are the arcsine transformed values and standard error of the treatment means (error bars). The standard error of the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and MSE is the mean square error 52 Figure 3-7. Mean percent photosynthetic photon flux density (PPFD) at 1.3 meters above the forest floor in the paper birch density treatments in July and August 2000. Two methods of measuring PPFD were compared: (a) hemispherical canopy photographs (HCP), and (b) a handheld light sensor (HLS). Treatment means with different letters are significantly different within a method (a=0.05). The standard error of the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and MSE is the mean square error. Note: Handheld light sensor measurements were not collected in the 0 Ep treatments 65 Figure 3-8. Mean soil moisture (H2O) content in the paper birch density treatments in 2000 and 2001. Natural logarithm transformation was used to produce normality. The treatment means are the natural logarithm transformed values and standard error of the treatment means (error bars). The standard error of the treatment mean is ± x i i (square root (MSE)/square root (n)), where n = 4 and MSE is the mean square error calculated using the natural logarithm transformed values. Treatment means with different letters are significantly different (a=0.05) 66 Figure 6-1. Comparison of the net photosynthetic rate (pmol CO2 m"2 s"1) of attached branch measurements versus the first cut branch measurement on each sampled interior Douglas-fir (Fdi) 107 Figure 6-2. Comparison of the net photosynthetic rate (pmol CO2 m"2 s"1) of interior Douglas-fir (Fdi) attached branches versus the mean cut branch measurements. The mean cut branch measurement represents the average of the measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after each of the five branches were harvested 107 Figure 6-3. Comparison of the net photosynthetic rate (pmol CO2 m"2 s"1) of interior Douglas-fir (Fdi) attached branch versus the mean cut branch measurements. The mean cut branch measurement represents the average of the measurements taken between 09:30 and 11:50 hours on the same day to correspond with the time frame that leaf gas exchange measurements would take place when using the cut-branch technique in the field 108 Figure 6-4. Net photosynthetic rate (pmol CO2 m" s" ) of interior Douglas-fir (Fdi) attached branch (open diamond) and cut branches (closed diamonds) for samples (a) Fdi #1, (b) Fdi #2, and (c) Fdi #3 109 Figure 6-5. Net photosynthetic rate (pmol CO2 m"2 s"1) of interior Douglas-fir (Fdi) attached branch (open diamond) and cut branches (closed diamonds) for samples (d) Fdi #4, and (e) Fdi #5 110 Figure 6-6. Comparison of the stomatal conductance (mmol H2O m"2 s"1) of attached branch versus first cut branch measurement on each sampled interior Douglas-fir (Fdi). .111 Figure 6-7. Comparison of the stomatal conductance (mmol H2O m"2 s"1) of interior Douglas-fir (Fdi) attached branches versus the mean cut branch measurements. The mean cut branch measurement represents the average of the measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after each of the five branches were harvested 112 Figure 6-8. Comparison of the stomatal conductance (mmol H2O m"2 s"1) of interior Douglas-fir (Fdi) attached branches versus the mean cut branch measurements. The mean cut branch measurement represents the average of the measurements taken between 09:30 and 11:50 hours on the same day to correspond with the time frame that leaf gas exchange measurements would take place when using the cut-branch technique in the field 112 Figure 6-9. Stomatal conductance (mmol H2O m"2 s"1) of interior Douglas-fir (Fdi) attached branch (open diamond) and cut branches (closed diamonds) for samples (a) Fdi #1, and (b) Fdi #2 113 Xlll Figure 6-10. Stomatal conductance (mmol H2O m"2 s"1) of interior Douglas-fir (Fdi) attached branch (open diamond) and cut branches (closed diamonds) for samples (c) Fdi #3, (d) Fdi #4, and (e) Fdi #5 114 xiv A C K N O W L E D G E M E N T S M.Sc. Committee, Non-departmental Examiner and Chairperson of the Thesis Defense Examination: • Suzanne W. Simard, Ph.D., R.P.F., Associate Professor, Department of Forest Sciences, Faculty of Forestry, University of British Columbia - for agreeing to take me on as a graduate student and for being my research supervisor; for providing outstanding support and encouragement and the freedom to learn. • Robert D. Guy, Ph.D., Professor, Department of Forest Sciences, Faculty of Forestry, University of British Columbia - for taking me on as a graduate student and for being my academic supervisor and chair of the supervisory committee; for assisting me with measuring leaf area and specific leaf area of needles gathered for photosynthesis measurements in 2000 and 2001; for providing support, encouragement and excellent assistance. • Christopher P. Chanway, Ph.D., Professor, Department of Forest Sciences, Faculty of Forestry, University of British Columbia - for agreeing to be a committee member and for providing support, encouragement and excellent assistance. • Peter L. Marshall, Ph.D., R.P.F., Associate Dean, Undergraduate Studies, Professor, Department of Forest Resources Management, Faculty of Forestry, University of British Columbia - for agreeing to be the non-departmental examiner for my thesis defense. • Bruce C. Larson, Ph.D., Professor, Department of Forest Sciences, Faculty of Forestry, University of British Columbia - for agreeing to preside as chairperson over my thesis defense. Research Funding Contributors: • British Columbia Ministry of Forests, Kamloops Forest Region, Research Department -for funding and supporting this study. • Lana Kurz, R.P.F., Silviculture Forester, INTERFOR, Adams Lake Lumber Division -for accepting my Master's project and agreeing to be my industry collaborator; also for helping me select prospective research sites and offering your expertise. • Science Council of British Columbia - for providing me with a GREAT scholarship, which contributed greatly to pursuing the Master's research. • Forestry Innovation Investment - for providing funding to (a) complete my Master's thesis, and (b) co-author and submit a journal article to Forest Ecology and Management outlining the ecological impact of the paper birch density treatments on the performance of interior Douglas-fir. xv My Husband: • Doug Baleshta - for his constant encouragement and support of my project; for the unselfish assistance at 3:30 am when the truck needed to be loaded with photosynthesis gear, ladders; for dinners and screening my phone calls! I couldn't have completed this thesis without you! Individuals Who Contributed To The Research (in alphabetical order): • Tammy Anderson - for helping me (on a very, very hot day in August 1998 when the air conditioning in my vehicle decided to pack it in!) to look for potential research sites within INTERFOR's operating area. • Arthur and Suzanne, Adams Lake Adventures - for giving me a break on accommodation and for providing such a lovely setting to return to from fieldwork. • Basil and Betty Baleshta - for the loan of the pruning pole and extension used to harvest the paper birch and interior Douglas-fir branches for leaf gas exchange measurements; for the use of your travel trailer in 2000, which we kept at the Adams Lake Adventures northeast end of Adams Lake and was our "home-away-from-home" when gathering measurements at the Burton Creek and Momich River sites during the field season; for your endless encouragement. • Ian Cameron, J.S. Thrower & Associates Ltd. - for your insight and expertise into mixed-species stand dynamics; for introducing me to the SAS programming language; for your encouragement and interest in my study. • Andrew Cant - for your help tagging trees at Burton Creek (1999), and collecting paper birch leaf gas exchange data at Burton Creek (1999) (my second try because the weather turned cloudy, cool and rainy on my first attempt to gather the data). • Merle Collinge, B.C. Ministry of Forests, Kamloops Forest District - for taking the time to meet with me to locate potential research sites on the district office database (August 19, 1998), and for contacting Mei-Ching Tsoi (Victoria) to see if she could search the MOF database in Victoria for possible sites in the Kamloops, Nelson, Clearwater, Salmon Arm and Vernon forest districts. • Derek Donaldson - for the loan of your 10-foot orchard ladder to reach and harvest paper birch branches with intact leaves from the upper 1/5th of the canopy used to measure leaf gas exchange. • Nancy Flood, M.Sc, Department of Biological Sciences, Faculty of Science, University College of the Cariboo - for your valuable assistance with my query regarding Analysis of Covariance. • J.D. Fournier Consulting brushing crew: Doug Fournier, Erik Anogrson, Oscar Pettersson and Martin Guenther - Thank you for the great work brushing the Burton Creek site (July 23/99). x v i Clyde Fuoco - for your enthusiastic support and help collecting Site Index and height measurements at Burton Creek in 2001. Kirsten Hannam - for helping me to find the Gold Creek site and Momich River site in August 1998 after searching numerous potential sites in the following forest districts: Kamloops, Clearwater, Salmon Arm, and Vernon; for helping me collect growth measurements and interior Douglas-fir foliage for nitrogen analysis; for her terrific encouragement. Steve Haourt - for your help collecting year 2001 growth measurements, performing the cut-branch technique test (August 2001), and collecting soil samples from beneath interior Douglas-fir sampled for leaf gas exchange measurements. Corinna Hoodicoff- for your help collecting paper birch leaf gas exchange data at Gold Creek #1, #2, Momich and Burton (1999). INTERFOR brushing crew: Roger Berglund, John Sheldon Jr., Doug King, James Gibbons, Kirk Fraser, and Mike Duplisse - Thank you for a job well done! (July 1999). John Karakatsoulis, Department of Natural Resource Science, University College of the Cariboo, Kamloops, B.C. - for your encouragement of pursuing my Masters, and your help in the field when I needed assistance measuring light availability at Gold Creek. Simon M. Landhausser, Ph.D., Research Assistant Professor, Department of Renewable Resources, Faculty of Agriculture, Forestry and Home Economics, University of Alberta - for your insights on using the cut-branch technique to collect interior Douglas-fir branches to measure leaf gas exchange. Tanya Luszcz - for assisting me in setting up the treatments at the four replicates (i.e. ribbon treatment areas, select paper birch trees to leave in the 400, 1111 and 4444 treatments, supervise brushing of treatment areas and to tag each tree); for taking photographs of the treatments pre- and post-treatment. Karen Mackinnon - for your unconditional support and encouragement, and for helping me collect hemispherical canopy photographs and leaf gas exchange data in 2000. Jean Mather, R.P.F., Skyline Forestry Consultants Ltd. - for your help searching for potential research sites in 1998, for performing the pre-treatment stem diameter tally and collecting the 1999 growth measurements; for your commitment to precision, accuracy and enjoyment of fieldwork. Hadrian Merler, Regional Pathologist, Kamloops Forest Region - for your time and expertise regarding root disease in the southern interior of British Columbia. Al K. Mitchell, Research Scientist, Tree Physiology, Forestry Canada, Pacific Forestry Centre, Victoria, BC - for your insights on measuring net photosynthesis of interior Douglas-fir. x v i i Martin and Rose Nichol - for your unconditional support and encouragement, your insights into research, and your help collecting year 2000 growth measurements at the Gold Creek site. Terry Pape - for your help collecting 2000 growth measurements and the leaf gas exchange measurements. Shane Rollans, Ph.D., Department of Mathematics and Statistics, School of Advanced Technologies and Mathematics, University College of the Cariboo - for your keen interest in my research and invaluable help with statistics. Mei-Ching Tsoi, Silviculture Information Analyst, B.C. Ministry of Forests, Forestry Division, Forest Practices Branch, Silviculture Practices Section - for your time sourcing potential research sites. Bernie Warren - for helping Doug and Basil make the roads more drivable! Kent Watson - for taking the aerial photographs of my research sites prior to implementing the density treatments (July 6, 1999). Jim Wright, B.C. Ministry of Forests, Salmon Arm Forest District - for meeting with me and suggesting possible research sites within the forest district. Amber Yourk - for your help when I needed an extra hand collecting the 1999 growth measurements. Ed Yourk, Assistant to Jean Mather - for your help performing the pre-treatment stem diameter tally and collecting the 1999 growth measurements; it was a pleasure to work with you, Jean and Amber. Barb Zimonick, Research Technician, B.C. Ministry of Forests, Kamloops Forest Region - for your help (a) supervising the brushing crew on the first day of brushing the replicates, (b) tagging the trees in Gold Creek 2, (c) collecting handheld light sensor measurements and hemispherical canopy photographs (d) laying out reflective ribbon at the sites to aid in attempting to collect pre-dawn xylem water potential measurements, (e) collecting mid-day xylem water potential measurements at Burton Creek (unfortunately it rained), (f) collecting Site Index measurements, (g) performing the cut-branch technique test (August 2001) and (h) gathering year 2001 growth measurements. Thank you for your immense support, at the office and in the field, and for your encouragement to my project and me. And last, my friends and family, if I haven't mentioned you earlier, for your unwavering support and encouragement! Thanks! xviii DEDICATION I dedicate this thesis to my mother, The late G. Evelyn Stevenson (1913 - 1982) and To my mother's sister "Aunt Dot" (Mrs. Dorothy Warner). (1923 - ) I have been blessed! xix Chapter 1 Introduction Within the broader scope of forest stand management this study fits under the umbrella of forest vegetation management, which has been referred to "the practice of efficiently channeling limited site resources into usable forest products rather than into noncommercial plant species" (Walstad and Gjerstad 1984 cited in Walstad and Kuch 1987). Competitive relationships between usable forest products (i.e. crop trees, such as conifers) and adjacent noncommercial plant species (i.e. vegetation such as grasses, shrubs and broadleaves) can occur in response to accessing potentially limited environmental resources, such as light, water, or nutrients (i.e. exploitative competition) (Bravo et al. 2001). In young conifer plantations, without outside intervention (e.g. manual cutting or herbicide application to control unwanted vegetation) interspecific competition persists, particularly for light on mesic sites, favoring the faster-growing early-seral species. In the past, forest vegetation management has been based on the agricultural model of weed control, such as intensive site preparation and application of fertilizers to increase growth and yield of crop trees, and in particular, the application of herbicide to control the growth of non-crop vegetation. Strong social pressure worldwide against the use of herbicide forced the forest industry to rethink their vegetation management strategies and investigate other ecological alternatives (Wagner 1993). Walstad and Kuch (1987) identified that science-based knowledge was lacking for silviculture practitioners regarding the time frames over which interspecific competition becomes detrimental to the physiology of planted conifers leading to economic losses. Studies since then are providing valuable information to forest managers about economic and ecological density thresholds in conifer/broadleaf stands (Simard 1990; Wagner and Thompson 1998; Simard and Sachs 2002). It is within this context that this study attempts to advance prior knowledge concerning broadleaf 1 ecological density thresholds that support productive conifer/broadleaf stands, focusing on interior Douglas-fir and paper birch, in the southern interior of British Columbia. 1.1 Ecology of Mixed Stands The highly productive Interior Cedar-Hemlock (ICH) and Interior Douglas-fir (IDF) wet-belt forests of southern interior British Columbia (B.C.) are distinguished by a mosaic of early serai conifer/broadleaf mixed stands, mid- to late-successional stands, and climax stands (Meidinger and Pojar 1991). On areas that have had large-scale disturbances, like wildfire or clearcut logging, pioneer broadleaf species such as paper birch (Betula papyrifera Marsh.), and to a lesser degree, trembling aspen (Populus tremuloides Michx.) and black cottonwood (Populus balsamifera ssp. trichocarpa (T.& G.) Brayshaw) will establish, either by seeding-in or basal sprouting, within five to ten years (Ketcheson et al. 1991; Simard and Vyse 1992; Peterson et al. 1997a). Also, early serai conifers, such as interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), western white pine (Pinus monticola Dougl. ex D. Don in Lamb), lodgepole pine {Pinus contorta Dougl. ex. Loud.), and western larch (Larix occidentalis Nutt.) will regenerate from seed on these sites, forming even-aged mixedwood stands of complex vertical and spatial structure (Johnson et al. 1990; Ketcheson et al. 1991; Simard and Vyse 1994). As these stands develop, the short-lived broadleaf species gradually die out giving way to mid- and late-successional conifer-dominated stands with understory shade-tolerant western red cedar (Thujaplicata Donn ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg). In climax stands, dominated by western red cedar and western hemlock, small-scale disturbances such as root disease pockets, create canopy openings for paper birch to regenerate either on exposed mineral soil when fallen trees are uprooted or on the decaying wood of trees (Safford et al. 1990; Meidinger and Pojar 1991; Morrison et al. 1991). 2 Paper birch is the "most widely distributed broadleaf species" in the southern interior wet-belt zones and plays a prominent role in young mixed-species stand development following large-scale disturbances (Peterson et al. 1997a). Birch, which is shade-intolerant, will rapidly colonize exposed sites, tolerating a wide range of microclimate conditions (e.g. from rock crevices and sandy slopes to swamp boundaries), but grows best on mesic sites with well-drained sandy loam or silty-textured soils (Peterson et al. 1997a). Localized paper birch densities can range between 1,000 - 60,000 stems per hectare (stems ha"1) up to 10-years following a disturbance, depending on disturbance type and degree (Simard and Vyse 1992). Their ability to establish at high densities and grow rapidly has been shown, in the short term, to inhibit growth and survival of white spruce (Picea glauca (Moench) Voss) and interior Douglas-fir by reducing availability to resources, particularly light (Gregory 1966; Simard 1990). It also helps birch to maintain prominence in mixed-stands as the stands mature (Safford et al. 1990). However, it is this competitive edge, particularly in newly reforested conifer stands, that has historically labeled paper birch and other broadleaved trees as "weed species" by the forest industry (B.C. Min. For. 1995b). Armillaria ostoyae (Romagn.) Herink and Phellinus weirii (Murr.) Gilbn., are two common root diseases found in the ICH and IDF zones in the southern interior of B.C. (Morrison et al. 1991). Of the two, A. ostoyae appears to be the principal cause of planted conifer mortality in young plantations because of the fungus' ability to produce rhizomorphs, "root-like structures initiated on the food base" (i.e. on the tree stumps), that grow and come in contact with the roots of susceptible seedlings growing nearby, such as interior Douglas-fir. In contrast, Phellinus root disease does not produce rhizomorphs and must rely on the roots of susceptible trees growing nearby and possibly coming in contact with the fungus to initiate infection (Morrison et al. 1988; Morrison et al. 1991). Where soil conditions and terrain slope are suitable, harvested sites can be 3 prepared for planting by excavating stumps to reduce rhizomorph production and inoculum loads of A. ostoyae (Morrison et al. 1991; B.C. Min. For. 1995a). While removal of the stumps facilitates reducing the inoculum available that could potentially infect planted conifer seedlings through root contact, the exposed mineral soil provides an ideal substrate for broadleaves to regenerate (Safford et al. 1990; Morrison et al. 1991) and can reduce soil productivity on some sensitive sites (Smith and Wass 1991; Davis and Wells 1994). 1.2 Silviculture Practices in Young Mixed Stands Forestry is one of the most important economic activities in the ICH and IDF forests of southern interior British Columbia (Ketcheson et al. 1991; Hope et al. 1991). Intrinsically, logging activity has concentrated on the extraction of commercial species, particularly interior Douglas-fir which can account for up to 50% of the tree species milled.1 The standard method of removing these species has been clearcut logging (B.C. Min. For. 1997). In an attempt to increase the economic value obtained from timber extraction and reforestation, some of British Columbia's forest policies recommend planting one or two commercially valuable conifer species, such as interior Douglas-fir and lodgepole pine. Site preparation, planting and vegetation management are primary silviculture activities that are carried out by resource managers to ensure successful regeneration of harvested forests. Broadcast operational brushing has commonly been conducted to improve conifer production on backlog NSR (Not Satisfactorily Restocked) plantations (between 1984 and 1987). Brushing has also been performed on current conifer plantations, usually within 10 years after harvest, to minimize competing vegetation (post-1987) (B.C. Min. For. 1998). This reforestation practice is supported by the free growing requirement policy in the Forest Practices Code of British 1 L . W i l l , Forest Renewal Silviculturist, International Forest Products Limi ted ( I N T E R F O R ) - A d a m s Lake Lumber Divis ion , pers. comm., January 1998. 4 Columbia Act (1995), which legislates that crop trees (i.e. conifers) be unimpeded by competition from plants, shrubs or other trees within a specified time following plantation establishment (B.C. Min. For. 2000). Regeneration success is generally evaluated using criteria that include minimal stocking of acceptable tree species that are growing free of competing vegetation. Determination of the "free-growing" condition is based on maximum allowable levels (i.e. thresholds) of interspecific competition from herb, shrub and broadleaf vegetation. For example, broadleaf trees are considered unacceptable competition if they exceed specific stand densities and relative heights in British Columbia's interior forests (B.C. Min. For. 2000). These guidelines have been supported by research that demonstrated survival and growth of interior Douglas-fir, pine or spruce can be jeopardized when growing under vigorous, high density stands of paper birch (Gregory 1966; Andersson 1985; Simard and Hannam 2000). Studies have demonstrated that maximum conifer growth commonly occurs in the absence of competing vegetation (e.g. Kimmins and Comeau 1990; Wagner and Radosevich 1991). Following removal of broadleaf species, it is likely that increased availability of light and soil moisture, particularly on mesic or drier sites, enhances the growth of interior Douglas-fir (Simard 1990; Hermann and Lavender 1990). Removing broadleaf species like paper birch, from mixed-stands, for high conifer production goals may have negative long-term repercussions (Perry 1994). Several studies indicate that single-species stands are more susceptible than mixed-species stands to insect outbreak (e.g. Stiell and Berry 1985; Alfaro et al. 1994, Shore and Safranyik 1992; Taylor et al. 1994), pathogen infestations (e.g. Morrison et al. 1991), moose browsing (Simard and Heineman 1996b), and frost damage (Andersson 1985; Stathers 1989). Susceptibility to A. ostoyae, which extends as far north as Williams Lake, British Columbia, and is found in the ICH, IDF, Montane 5 Spruce (MS), Engelmann-Spruce Subalpine Fir (ESSF) and Sub-Boreal Spruce (SBS) zones, is highest among interior Douglas-fir, Abies spp., and Picea spp. (Morrison et al. 1991). Average mortality rates among planted susceptible conifer species are 0.1 - 0.2 % per year (Morrison et al. 1988). In a study in the ICH zone, interior Douglas-fir and lodgepole pine mortality due to Armillaria ostoyae was 2 to 3 times higher in treatments in which all paper birch were manually cut or girdled, as compared to the control (Simard et al. 2001). 1.3 Role of Paper Birch in Mixed Stands Paper birch trees are thought to play an important role in nutrient cycling (through rapid rates of foliage and root biomass growth) and maintaining long-term productivity on wet-belt sites (Sachs and Comeau 1996). Studies have found that the nitrogen (N), magnesium (Mg) and calcium (Ca) concentrations were higher in paper birch tissues than in neighboring conifers, which are thought to contribute to the nutrient cycle and site productivity (Simard and Vyse 1994; Wang et al. 1996). Binkley and Giardina (1998), however, question the observations put forth in studies that support the important influence of broadleaves in nutrient cycling citing the lack of similar results produced in "common garden experiments". Paper birch also provides important habitat for wildlife. For example, birch is an important source of browse and cover to deer and moose, and during the winter, birch is a reasonably significant browse for mountain goat, mule deer, Rocky Mountain elk, and caribou (Miquelle 1983; Schwartz et al. 1988; Peterson et al. 1997a). Mature trees provide habitat for cavity-nesting bird species, such as woodpeckers and owls (Cannings et al. 1987; Machmer et al. 1995; Peterson et al. 1997a). French et al. (1986) found that mixed-species conifer/broadleaf stands, with their structural diversity, have a major positive influence on the enhancement of species richness of bird populations by providing a variety of habitat. 6 Recent studies indicate there may be a benefit to conifer species, such as interior Douglas-fir, from mycorrhizal fungi linkage with paper birch. Jones et al. (1997) showed that diversity of the ectomycorrhizal community on two-year-old interior Douglas-fir root systems was higher when it was grown in mixture with paper birch than when grown in pure stands. They suggested that this increased diversity resulted from ready inoculation of interior Douglas-fir roots by colonized paper birch roots because of a readily available carbon supply (from birch roots), and from favorable modification of the soil, both chemically and biologically, by the presence of paper birch. Simard et al. (1997) also showed interior Douglas-fir seedlings that had access to the root systems of overstory paper birch and interior Douglas-fir trees, were host to a greater richness and diversity of ectomycorrhizal fungi than seedlings that were grown in isolation. Seedlings with higher diversity of ectomycorrhizae exhibited greater net photosynthetic rate and greater height growth than those grown in isolation of mature trees. The results of Jones et al. (1997) and Simard et al. (1997) suggest that maintenance of a diversity of tree species following logging, either through planting mixtures or leaving residuals, results in higher ectomycorrhizal diversity and potentially greater seedling productivity than does single-species management. In addition to the ecological benefits of retaining a component of paper birch on conifer plantations there is the potential financial gain of utilizing birch as a secondary timber source. The wood of birch is high quality and can be used for dimensional lumber, veneer logs and furniture (Peterson et al. 1997a). In Finland, silver birch (Betulapendula) has been successfully regenerated in mixture with Norway spruce (Picea abies (L.) Karsten) or Scotch pine (Pinus sylvestris L.). Mielikainen (1985) found that the optimum proportion of birch in mixture with Norway spruce or Scotch pine is between 25 - 50%, when the main objective was to maximize total volume of the mixed-stand. Also, when spruce and birch were grown in mixture, where the 7 birch component was 25%, "the yield of sawtimber was almost 10% higher than in pure stands of spruce" (Mielikainen 1996). On a smaller scale, tapping of paper birch in the spring to obtain sap for making syrup and other confectionaries is a young but growing cottage industry in Alaska and British Columbia (Smith 2001; Kahiltna 2002). 1.4 Competition in Young Mixed Stands Studies have identified a range of densities over which paper birch minimally affects the performance of interior Douglas-fir (when the two species are grown in mixture) allowing options for mixed-species management. In a neighborhood study of competition between interior Douglas-fir and paper birch, Simard (1990) used linear regression to show that interior Douglas-fir maintained near-normal diameter growth rates at paper birch densities of 2100 stems ha"1 on medium quality sites and 340 stems ha"1 on high quality sites. In a more recent study, Simard and Sachs (2002, submitted) used a "ceiling function" to examine competition thresholds and found that interior Douglas-fir maintained good diameter growth rate in the neighborhood of 4000 stems ha"1 where all paper birch were included and 2500 stems ha"1 where only taller birch were included. Under the current British Columbia free growing guidelines, broadleaf species may be established or retained to fulfill specific silvicultural obligations, such as (a) for "short-rotation interim crop to manage for root rot centers", (b) "to provide a nurse crop", (c) "to promote nutrient cycling", and (d) "to meet other resource objectives such as biodiversity or wildlife habitat". However, the stocking level of broadleaf trees must not "unacceptably" affect the conifer crop tree growth. Presently, a maximum of 600 stems ha"1 of paper birch may be retained on a mixed-species site if the prescription warrants it (B.C. Min. For. 2000). 8 This study examined the effects of paper birch density on the performance of interior Douglas-fir when the two species are grown in mixture in the ICHmw3 and IDFmw2 variants in the southern interior of British Columbia. It represents the next step in identifying stand density and composition conditions that are indicative of healthy conifer/broadleaf mixed-stands (i.e. tests the thresholds identified by Simard and Sachs (2002, submitted)). This study takes an experimental approach toward identifying broadleaf density thresholds by manipulating a range of paper birch densities and examining conifer and birch responses to them. The research will benefit operational forestry by (a) providing information for the development of mixedwood (e.g. management of both coniferous and broadleaf species on the same site (B.C. Min. For. 2000)) stocking standards in British Columbia, (b) providing information on mixture management techniques that can help mitigate spread of Armillaria root disease, and (c) helping identify management options for the ICH and IDF wet-belt forests that maintain biodiversity values similar to the unmanaged landscape. Finally, it will contribute information toward identifying free growing standards that encourage sustainable forest management. The primary objectives and working hypotheses of this thesis are as follows: 1. To examine the effect of paper birch density on the performance of interior Douglas-fir saplings when the two species are grown in mixture in the ICHmw3 and IDFmw2 variants in the southern interior of British Columbia. Hoi: The density of paper birch has no effect on the performance of interior Douglas-fir. 2. To examine the effect of reducing paper birch density on survival of interior Douglas-fir saplings when the two species are grown in mixture in the ICHmw3 and IDFmw2 variants in the southern interior of British Columbia. H 0 2 : Reducing the density of paper birch has no effect on the survival of interior Douglas-fir saplings. 9 3. To examine the effect of paper birch density on resource availability to interior Douglas-fir saplings when the two species are grown in mixture in the ICHmw3 and IDFmw2 variants in the southern interior of British Columbia. H03: The density of paper birch has no effect on availability of resources to interior Douglas-fir saplings. This thesis consists of the following components: (a) Chapters 1-4, deal with the main focus of this study, (b) Literature Cited, and (c) Appendix - Cut Branch Technique Test. Chapter 1 - Introduction, briefly provides background to this study. Chapter 2 -Methods, describes the field study and statistical analyses that compares the effects of paper birch density on (a) performance of interior Douglas-fir, (b) survival of interior Douglas-fir, and (c) resource availability to interior Douglas-fir when the two species are grown in mixture between 1999 and 2001. Chapter 3 - Results, summarizes the findings of the field study, including the effect of the paper birch density treatments on the dominant paper birch growth. Chapter 4 - Discussion, examines the (a) growth, survival and physiological response of the interior Douglas-fir to the paper birch density treatments, (b) resource availability to interior Douglas-fir, and (c) paper birch response to the density treatments. It also consists of conclusions and management implications drawn from this study, future directions for the study and for mixture silviculture research. Appendix - Cut Branch Technique Test, discusses the test that was performed in August 2001 to examine if leaf gas exchange of interior Douglas-fir differs between an attached branch measurement and a cut branch over different time periods. This test was performed to examine the reliability of the cut-branch technique at collecting interior Douglas-fir leaf gas exchange measurements. 10 Chapter 2 Methods 2.1 Study Sites The study area is situated in the ICHmw3 and IDFmw2 variant in the Kamloops Forest Region, British Columbia, Canada. The ICHmw3 variant has a continental climate distinguished by cool, wet winters and warm, moderately dry summers. Climax stands of western hemlock and western redcedar are interspersed with successional stands, commonly composed of interior Douglas-fir, paper birch, lodgepole pine and trembling aspen. Mean annual precipitation ranges from 431 - 874 mm and average annual snowfall is 252 cm. Mean annual temperature ranges from 3.7 - 6.9 C and mean growing season temperature is 13.8 C. The IDFmw2 is situated below the ICHmw3 and is warmer and drier with cool winters, moderate snowfall and warm, dry summers. Climax stands can be comprised of either pure stands of interior Douglas-fir or a mixture of interior Douglas-fir and western redcedar. Successional stands will include interior Douglas-fir, lodgepole pine (generally at higher elevations within the variant), paper birch and trembling aspen. Mean annual precipitation ranges from 487 - 551 mm and average annual snowfall is 171 cm. Mean annual temperature ranges from 4.2 - 7.6 C and mean growing season temperature ranges from 14.5 - 16.3 C (Lloyd et al. 1990). Four study sites were selected in May 1999 based on the following criteria: (1) mesic ICH or IDF sites, (2) uniform physiography, (3) minimum density of 7,000 stems ha"1 of paper birch, and (4) adequate area for five-0.25 hectare treatment plots. The sites are situated in 10- to 15-year-old Douglas-fir plantations in the Kamloops and Clearwater forest districts within the operating area of International Forest Products Limited (INFERFOR) - Adams Lake Forest Division (Figure 2-1). The four sites are Gold Creek 1 (GC1), Gold Creek 2 (GC2), Burton Creek (BC) and Momich River (MR) (Figures 2-2 to 2-5). Very few even-aged interior Douglas-fir plantations in the ICH and IDF wet-belt had sufficient paper birch stems because the majority 11 of the areas had been previously brushed (i.e. release of conifers by removing the broadleaf stems). Therefore, two replicates, GC1 and GC2, are located on the same cutblock because the two replicates are sufficiently distinct (i.e. slope position and paper birch density). GC1 is located on the upper slope with approximately 11,000 stems ha"1 of paper birch. GC2 is situated on the lower slope with approximately 19,500 stems ha"1 of paper birch. Table 2-1 outlines the site characteristics of each study site. Figure 2-1. Locat ion o f the study sites: G o l d C r e e k 1 and 2 ( G C 1 & G C 2 ) , M o m i c h R i v e r ( M R ) and B u r t o n C r e e k ( B C ) . 12 Figure 2-2. Photograph of the Gold Creek 1 site with treatment area outlined in white. Photo credit: Kent Watson. Figure 2-3. Photograph of the Gold Creek 2 site with treatment area outlined in white. Photo credit: Kent Watson. 13 Figure 2-4. Photograph of the Bur ton C r e e k site w i th treatment area out l ined in white. Photo credi t : K e n t Watson All four sites had been clearcut logged, mechanically site prepared and slash burned, and then planted with interior Douglas-fir (Fdi) seedlings (1+0 plug styro blocks (PSB)). In all stands, there was a naturally occurring, even-aged (< 20 years age difference) broadleaf component that was dominated by paper birch, with secondary densities of trembling aspen, black cottonwood (Populus balsamifera ssp. trichocarpa (T.& G.) Brayshaw), Rocky Mountain maple (Acer glabrum Torr.) and willow (Salix spp.) (Table 2-2). The paper birch density was relatively uniform with 7,000 stems ha"1 or greater on three of the four sites. On the Burton Creek site, the combined densities of paper birch and trembling aspen exceeded 7,000 stems ha"1. T a b l e 2-1. Site characteristics o f each study site in 1999. Study sites Characterist ics G o l d Creek 1 G o l d Creek 2 M o m i c h River Burton Creek Forest District Kamloops Kamloops Clearwater Clearwater Lat . /Long. 51 :00 :00N 51 :00 :00N 51 :20 :00N 51:31:00 N Longitude 119:35:00 W 119:35:00 W 119:15:00 W 119:35:00 W Opening Number 82L093-203 82L093-203 82M034-8241 82M053-8062 Site History 1 ' L1985 L1985 L1985 L I 982 M ( B ) 1987 M ( B ) 1987 B1987 B1983 PI988 (Fdi) P1988 (Fdi) PI988 (Fdi) PI985 (Fdi) B E C Variant IDFmw2 IDFmw2 ICHmw3 ! C H m w 3 Interior Douglas-fir density (stems ha"1) 1,387 1,538 1,109 724 Initial paper birch density (stems ha"1) 10,976 19,407 14,327 7,311* Site Index ( m ) § 29.36 31.17 26.92 21.78 Elevation (m) 940 890 550 900 Slope (%) 30 30 40 35 Aspect W W N N E Soi l Texture S i L S i L S i L S i L t L (year) = year logged; M(B)(year) = year the site was mechanically prepared and slash burned; P(year)(sp.) = year seedlings planted (where species planted is Interior Douglas-fir (Fdi)). X combined densities o f paper birch (5000 stems ha"1), black cottonwood (840 stems ha"1) and trembling aspen (1471 stems ha"1) § site index (SI) calculated using Thrower & Goudie (1992) equation where SI = potential tree height (m) at 50 years breast height age. Breast height age = number o f years the tree has been growing since it attained a height o f 1.3 m above the ground measured on the uphill side o f the stem 15 T a b l e 2-2. Pre-treatment species, density and diameter characteristics o f each study site. Density M e a n stem Stem diameter Study site Species (stems ha"1) diameter (cm) range (cm) G o l d Acer glabrum Torr. 64 0.8 0 . 2 - 2 . 5 C r e e k 1 Be tula papyrifera Marsh. 10976 1.7 0.1 - 12.0 Picea engelmannii x glauca (Moench) Voss 4 1.1 0 . 5 - 1 . 7 Pinus contorta Dougl . ex Loud . 122 4.2 1 .1-8 .4 Pinus monticola Dougl . ex D .Don in Lamb. 4 0.7 0 . 7 - 0 . 7 Pinus ponderosa Dougl . ex Laws. & Laws. 2 1.1 1.1 - 1.1 Populus balsamifera ssp. trichocarpa (T. & G.) Brayshaw 258 1.6 0.1 - 11.3 Populus tremuloides M i c h x . 287 2.0 0.1 - 6 . 5 Pseudotsuga menziesii var. glauca (Beissn.) Franco 1387 3.3 0 . 1 - 8 . 3 Salix spp. 411 1.1 0 . 1 - 3 . 3 Thuja plicata Donn ex D . Don in Lamb. 89 2.9 0 . 2 - 1 2 . 1 G o l d Acer glabrum Torr. 2331 0.9 0.1 - 5 . 4 C r e e k 2 Alnus sinuata (Reg.) Rydb. 118 0.9 0 . 1 - 2 . 7 Be tula papyrifera Marsh. 19407 1.3 0 . 1 - 8 . 5 Picea engelmannii x glauca (Moench) Voss 7 1.0 0 . 5 - 1 . 3 Pinus contorta Dougl . ex Loud . 67 3.8 0 . 8 - 9 . 6 Pinus monticola Dougl . ex D.Don in Lamb. 11 2.1 0 . 6 - 3 . 9 Populus balsamifera ssp. trichocarpa (T. & G.) Brayshaw 387 1.0 0.1 - 6 . 0 Populus tremuloides M i c h x . 447 1.3 0.1 - 6 . 8 Prunus pensylvanica 2 0.6 0 . 6 - 0 . 6 Pseudotsuga menziesii var. glauca (Beissn.) Franco 1538 3.7 0.1 - 10.2 Salix spp. 1027 1.3 0 . 1 - 3 . 7 Thuja plicata Donn ex D . Don in Lamb. 100 1.5 0 . 2 - 8 . 5 M o m i c h Acer glabrum Torr. 167 1.6 0 . 1 - 5 . 3 R i v e r Alnus sinuata (Reg.) Rydb. 62 1.2 0 . 2 - 3 . 5 Betulapapyrifera Marsh. 14327 1.4 0.1 - 12.0 Pinus contorta Dougl . ex Loud. 20 3.1 0 . 6 - 6 . 2 Pinus monticola Dougl . ex D .Don in Lamb. 16 1.7 0 . 6 - 4 . 2 Populus balsamifera ssp. trichocarpa (T. & G.) Brayshaw 198 1.2 0 . 1 - 4 . 7 Populus tremuloides M i c h x . 24 1.6 0 . 4 - 4 . 0 Prunus pensylvanica 351 1.0 0 . 1 - 3 . 8 Pseudotsuga menziesii var. glauca (Beissn.) Franco 1109 4.2 0 . 1 - 8 . 6 Salix spp. 973 1.4 0 . 1 - 6 . 0 Thuja plicata Donn ex D . Don in Lamb. 756 0.7 0 . 1 - 6 . 9 Tsuga heterophylla (Raf.) Sarg. 204 0.6 0 . 1 - 2 . 2 B u r t o n Abies lasiocarpa (Hook.) Nutt. 11 0.9 0 . 5 - 1 . 6 C r e e k Acer glabrum Torr. 53 1.8 0 . 2 - 5 . 7 Alnus sinuata (Reg.) Rydb. 260 1.2 0 . 2 - 3 . 9 Betula papyrifera Marsh. 5000 2.7 0.1 - 13.5 Picea engelmannii x glauca (Moench) Voss 44 1.0 0 . 5 - 2 . 0 Pinus contorta Dougl . ex Loud. 33 4.4 0 . 4 - 8 . 6 Pinus monticola Dougl . ex D . D o n in Lamb. 140 2.4 0 . 5 - 1 0 . 3 Populus balsamifera ssp. Trichocarpa (T. & G.) Brayshaw 840 3.0 0 . 2 - 1 3 . 9 Populus tremuloides M i c h x . 1471 4.5 0 . 2 - 1 2 . 5 Prunus pensylvanica 13 1.8 0 . 5 - 3 . 0 Pseudotsuga menziesii var. glauca (Beissn.) Franco 724 3.4 0 . 3 - 1 0 . 4 Salix spp. 107 2.2 0 . 1 - 7 . 8 Thuja plicata Donn ex D . Don in Lamb. 87 1.3 0 . 1 - 5 . 6 Tsuga heterophylla (Raf.) Sarg. 44 0.9 0 . 2 - 2 . 3 t stem diameter was measured at 1.3 meters from the high side o f the base o f the stem. 16 2.2 Treatments and Experimental Design Five density treatments were replicated four times in a randomized complete block design, where site location was used as the blocking factor. Five density treatments representing a gradient in paper birch density were applied as follows: 1 * 1 9 1. 0 stems ha" paper birch/1,190 stems ha" interior Douglas-fir" - removal of all broadleaf tree species and all conifer tree species except interior Douglas-fir. 2. 400 stems ha"1 paper birch/1,190 stems ha"1 interior Douglas-fir - 5.0 meter spacing between remaining paper birch and removal of all conifer tree species except interior Douglas-fir. 3. 1111 stems ha"1 paper birch/1,190 stems ha"1 interior Douglas-fir - 3.0 meter spacing between remaining paper birch and removal of all conifer tree species except interior Douglas-fir. 4. 4444 stems ha"1 paper birch/1,190 stems ha"1 interior Douglas-fir - 1.5 meter spacing between remaining paper birch and removal of all conifer tree species except interior Douglas-fir. 5. 7,000+ stem ha"1 paper birch/1,190 stems ha"1 interior Douglas-fir (Control) - the broadleaf and conifer component in the treatment plot were not altered. The treatment plots measured 0.25 hectares, and included a central 0.09-hectare measurement plot with a 10-meter surrounding buffer. The paper birch treatments were randomly assigned to the five treatment plots within each block (Figures 2-6 to 2-8). 1190 stems ha"1 is the average number o f interior Douglas-fir across the four sites. Actual stems ha"1 at each site are: G o l d Creek 1 =1387, G o l d Creek 2 = 1538, M o m i c h River = 1109, and Burton Creek = 724. 17 Figure 2-6. Paper b i rch density treatments at G o l d C r e e k 1 (shaded) and G o l d C r e e k 2. M o m i c h R i v e r F igure 2-7. Paper b i rch density treatments at M o m i c h R i v e r ( M R ) . 18 Figure 2-8. Paper birch density treatments at Burton C r e e k . " A - P r " , " B - P r " and " C - P r " m a r k the location of another unrelated experiment. Paper birch trees were selected and marked prior to thinning. Selection criteria for the paper birch were: (1) dominant or co-dominant crown class; (2) uniform spacing relative to other paper birch; (3) single, straight, healthy stem; and (4) seed-origin. Stem diameter (measured at 1.3 meters from the high side of the base of the stem) and species were identified for all trees within the measurement plots in June 1999, prior to implementing the density treatments. The paper birch density treatments were applied in early July 1999. After thinning, the remaining interior Douglas-fir and paper birch trees within the measurement plots were identified with pre-numbered aluminum tags. Figures 2-9 to 2-17 illustrate the treatments pre-thinning and post-thinning at Gold Creek 2 study site. 19 Figure 2-10. The 0 E p treatment three months after b rush ing at the G o l d C r e e k 2 site. Photo credi t : T a n y a Luszcz . 20 Figure 2-11. T h e 400 E p treatment pr ior to brushing at the G o l d C r e e k 2 site. Photo credit: T a n y a Luszcz . Figure 2-12. T h e 400 E p treatment three months after brushing at the G o l d C r e e k 2 site. Photo credit: T a n y a Luszcz . 21 Figure 2-13. T h e 1111 E p treatment pr ior to brushing at the G o l d C r e e k 2 site. Photo credit: T a n y a Luszcz. F igure 2-14. T h e 1111 E p treatment three months after brushing at the G o l d C r e e k 2 site. Photo credit: T a n y a Luszcz . 22 Figure 2-15. The 4444 E p treatment p r i o r to brush ing at the G o l d C r e e k 2 site. Photo credit : T a n y a Luszcz . Figure 2-17. T h e control treatment at the G o l d C r e e k 2 site. Photo credit: T a n y a Luszcz. 2.3 Measurements The effect of the paper birch density treatments on the productivity of interior Douglas-fir was determined by comparing the following groups of response variables: 1) tree (a) interior Douglas-fir and, (b) paper birch, and 2) environmental. 2.3.1 Individual Tree Response Variables: Interior Douglas-fir 2.3.1.1 Growth Growth variables were measured in September 1999, September 2000 and August/September 2001. They included: stem diameter ( ± 0.1 cm), height (± 0.05 m in 1999 and 2000; ±0.1 m in 2001), crown diameter (± 0.01 m), height to base of live crown ( ± 0.01 m), incidence of A. ostoyae root disease and other damaging agents, and survival. 2 4 Stem diameter was measured at 1.3 meters from the high side of the base of the stem using a dial caliper. To ensure an accurate measurement of stem diameter at the same height and location on individual Douglas-fir trees each year, a horizontal line of white paint (Aervoe tree & log paint) was sprayed on the stem in 1999 to mark the location that the measurement was taken during the 1999 field season. Height was measured using a height pole from the high side of the base of the stem to the top of the leader in 1999 and 2000. In the case of multiple leaders, the height was measured to the highest leader. In 2001, height was measured using a Vertex III hypsometer and transponder (Haglof, Sweden). Height to base of live crown was measured from the high side of the base of the stem to the lowest live whorl on the stem. The lowest live whorl contained two or more live branches, with continuous live whorls above it. Crown diameter was the average of two perpendicular measurements at the widest part of the live crown. Based on these measurements, the following were calculated for the 2000 and 2001 analyses: (a) height:diameter ratio, (b) stem volume (m3), canopy volume (m3), diameter increment (cm), relative diameter growth rate (cm cm"1), height increment (m) and relative height growth rate (m m"1). See Table 2-3 for formulae used to calculate these variables. 2.3.1.2 Net Photosynthetic Rate and Stomatal Conductance Five randomly selected interior Douglas-fir trees in the 3.0 - 6.0 cm stem diameter class from each treatment at each site were measured in the year 2000. These trees represent the average-sized interior Douglas-fir trees across all treatments. Net photosynthetic rate and stomatal conductance measurements were taken once in late-August/early-September over a four-day period (one site per day). The cut-branch technique (see Dang et al. 1997) was used due to the rugged terrain and the height of the interior Douglas-fir. One healthy branch from the top third whorl of each sampled tree was randomly selected and cut about 10 cm from the main stem. The branch stem 25 T a b l e 2-3. Formulae used to calculate various growth increment variables. F o r m u l a n u m b e r F o r m u l a [I] Height:diameter ratio = (height (m) * 100) / stem diameter (cm) [2] Stem volumetm3)1^ = 7i * (stem diameter (cmVlOOl2 * height-1.3(m)) + n * (stem diameter (cmVlOO)2 * 1.0(m) 4 3 4 [3] Canopy volume^3)''" = (height (ml - height to base of live crown (m)) * n * (crown diameter (m) / 2)2 3 [4] One-year diameter increment (cm) = year 2000 stem diameter (cm) - year 1999 stem diameter (cm) [5] Two-year diameter increment (cm) = year 2001 stem diameter (cm) - year 1999 stem diameter (cm) [6] One-year relative diameter growth rate (cm cm"1) = year 2000 stem diameter (cm) - year 1999 stem diameter (cm) year 1999 stem diameter (cm) [7] Two-year relative diameter growth rate (cm cm"1) = year 2001 stem diameter (cm) - year 1999 stem diameter (cm) year 1999 stem diameter (cm) [8] One-year height increment (m) = year 2000 height (m) - year 1999 height (m) [9] Two-year height increment (m) = year 2001 height (m) - year 1999 height (m) [ 10] One-year relative height growth rate (m m"1) = year 2000 height (m) - year 1999 height (m) year 1999 height (m) [II] Two-year relative height growth rate (m m"1) = year 2001 height (m) - year 1999 height (m) year 1999 height (m) t using the formula for a cone (representing stem volume from top height to 1.3 meters from the base) plus the formula for a cylinder (representing the stem volume from 1.3 meters from the base to 0.3 meters from the base, excluding the stump). X using the formula for a cone (Mawson et al. 1976) 26 was immediately recut under water at least 5. cm from the end, with the cut surface submerged and the foliage kept above the water. While the cut surface was still submerged, the stem was placed in a vial of creek water. The level of the water in the vials was monitored throughout the collection procedure to ensure the cut surfaces were constantly submerged. The collection procedure took place between 08:00 and 11:00 hours. The cut branches were carried from treatment to treatment during the collection process, and care was taken to keep the branches upright and under minimal stress. Leaf gas exchange measurements took place between 12:00 and 15:00 hours on the same day at the site using a portable open CIRAS-1 differential CO2/H2O infra-red gas analyzer system and a narrow-leaf Parkinson leaf cuvette (PP Systems, Haverhill, MA, USA). Branches were randomly selected and measurements were made on one lateral shoot bearing fully expanded current year's foliage. The inlet CO2 concentration was set at 400 ppm, which was slightly above ambient (~ 350 ppm), and the inlet H2O concentration was set at 0% of ambient. Since the exact leaf area of the needles in the cuvette for each sample was not known, a fixed area of 10.0 cm2 was programmed into the CIRAS-1. To maintain a steady source of light, a 75-watt high-pressure sodium lamp was used to saturate the leaf cuvette (>1000 //mol m" s" PPFD 2 1 and <1600 //mol m"z s" PPFD). The needles were placed in the cuvette in a manner that reduced self-shading. Once the CO2 concentration within the cuvette had stabilized, internal CO2 2 1 concentration (ppm), photosynthesis rate (pmol CO2 m" s"), stomatal conductance (mmol H2O 2 1 2 1 m" s" ), and transpiration rate (mmol H2O m" s") were simultaneously recorded, and the data stored in the CIRAS-1. After the measurements were completed, the needles were removed from the cuvette chamber and placed in individually labeled GLAD® Zipper plastic storage bags (17.8 cm x 20.3 cm). They were then stored in a freezer until February 2001, when the leaf area was determined 27 using a LI-COR 3100 area meter. The leaves were then freeze-dried (Labconco Lyph-Lock 6) and weighed on a balance to determine leaf weight. Specific leaf area (cm2 g"1) of the interior Douglas-fir needles was calculated as the ratio of leaf area to corresponding leaf dry weight. Net photosynthetic rate and stomatal conductance were recalculated based on the actual leaf area of the samples. The collection of the sampled branches and the measurement timeframe were modified in 2001 in order to reduce the time lag between cutting the branch and taking the measurement. This was achieved by randomly sampling three interior Douglas-fir trees in the 3.0 - 6.0 cm stem diameter class, rather than five. Measurements were taken once in early-September over a four-day period (one site per day). As in 2000, the cut-branch technique was used to collect the samples. Collection of the samples began as soon as the sun illuminated the site and measurement of randomly selected branches ended before 12:00 noon as outlined in Table 2-4. T a b l e 2-4. T h e time it took to collect and measure leaf gas exchange o f randomly selected interior Douglas-f ir branches at each site. Site Col lect ion time (hr:min) Measurement time (hr:min) G o l d C r e e k 1 G o l d C r e e k 2 M o m i c h River B u r t o n C r e e k 08:20-9:35 08:30-9:45 07:00-09:00 07:45-09:15 10:00-11:40 10:00-11:49 09:45- 11:16 09:30- 11:07 Throughout the measurement time-period the cut branches were stored upright in the sunlight and the level of the water in the vials was monitored to ensure the cut surfaces were constantly submerged. Branches were randomly selected and measurements were made on one lateral shoot bearing fully expanded current year's foliage. Leaf gas exchange measurements were collected using a portable open CIRAS-1 differential CO2/H2O infra-red gas analyzer system and a narrow-leaf Parkinson leaf cuvette. As in 2000, the CIRAS-1 inlet C O 2 28 concentration was set at 400 ppm, and since the exact leaf area of the samples was unknown, a fixed value of 10.0 cm was programmed. The inlet H2O concentration was set at 70% of ambient. The measurements took place under saturating light (>1000 //mol m"2 s"1 PPFD). To maintain a steady source of light, a 75-watt high-pressure sodium lamp was used to saturate the leaf cuvette (>1200 //mol m"2 s"1 PPFD and <1600 //mol m"2 s"1 PPFD). Dry bulb and wet bulb temperatures (°C) were taken at the beginning of the measurement process and at the end using an aspirated hygrometer (Casella London Limited, London, England), and relative humidity (%) was calculated. As in the year 2000, the needles were removed from the cuvette chamber and placed in individually labeled plastic storage bags. They were stored in a freezer until early-December, when the leaf area and leaf dry weight was determined as per 2000. Specific leaf 2 1 area (cm g" ) was calculated as per 2000. Photosynthetic rate and stomatal conductance were recalculated based on the actual leaf area of the samples. 2.3.1.3 Foliar Nitrogen Concentration In September 2000, a minimum of 25 grams of current-year foliage from two lateral branches from the uppermost Vi to lA of the live crown (disregarding the top three whorls) were collected from seven randomly selected Douglas-fir in the 3.0 - 6.0 cm stem diameter class in each treatment (Ballard and Carter 1985). The samples were placed in individually labeled GLAD® Zipper plastic storage bags at the site, transported to Kamloops, and transferred to labeled brown paper bags. The samples were air-dried and sent to Pacific Soil Analysis Inc., Richmond, BC for analysis of percent (%) nitrogen concentration. Foliar nitrogen analysis was not conducted in the year 2001 field season due to funding limitations. 29 2.3.1.4 Incidence ofArmillaria ostoyae Incidence of A. ostoyae on individual interior Douglas-fir was observed at the same time growth measurements were collected each year. Interior Douglas-fir that displayed symptoms of A. ostoyae, such as chlorotic (or red), stunted and sparse foliage or production of numerous cones, were noted, according to Morrison et al. (1991). Additionally, interior Douglas-fir that exhibited signs of the root disease, such as basal resinosis on the bark surface, and/or clusters of A. ostoyae mushroom fruiting bodies on or near the stem of live saplings, or creamy, white mycelial fans in the bark of the lower stem, were recorded (Morrison et al. 1991). 2.3.1.5 Survival Observations of interior Douglas-fir mortality were recorded at the same time that growth measurements were collected each year. Where possible, mortality cause was recorded (e.g. A. ostoyae). 2.3.2 Individual Tree Response Variables: Paper Birch 2.3.2A Growth Growth variables were measured in September 1999, September 2000, and August/September 2001 and included: stem diameter (± 0.1 cm), height (± 0.05 m in 1999 and 2000; ±0.1 m in 2001), crown diameter (± 0.01 m), height to base of live crown (+ 0.01 m), damaging agents and survival. Based on these measurements, the following were calculated for 2000 and 2001 analyses: (a) height:diameter ratio (see Formula [1]), (b) stem volume (m3) (see Formula [2]), canopy volume (m3), diameter increment (cm) (see Formulae [4] and [5]), relative diameter growth rate (cm cm"1) (see Formulae [6] and [7]), height increment (m) (see Formulae [8] and [9]) and relative height growth rate (m m"1) (see Formulae [10] and [11]. The formula 30 for canopy volume (m3) was as follows: [12] Canopy volume 3 (m 3 ) = (height (m) - height to base o f live crown (m)) x Tt x (crown diameter (m) / 2)2 2 Growth variables were measured on all paper birch in the 400 Ep and 1111 Ep treatments. Due to the very high number of birch trees in the 4444 Ep treatment and the control, however, 10 trees were randomly selected from five stem diameter classes in each treatment at each site that represented the range of the stem diameter measurements. Stem diameter was measured at 1.3 meters from the high side of the base of the stem using a dial caliper for small diameter trees (~ < 4.0 cm), and a diameter tape for large diameter trees. To ensure an accurate measurement of stem diameter at the same height and location on the paper birch trees each year, a horizontal line of white paint (Aervoe tree & log paint) was sprayed on the stem in 1999 to mark the location that the measurement was taken during the 1999 field season. Height was measured using a height pole from the high side of the base of the stem to the top of the canopy in 1999 and 2000. In 2001, height was measured using a Vertex III hypsometer and transponder (Haglof, Sweden). Height to base of live crown was measured from the base of the stem to the lowest live branch, excluding sprouts. Crown diameter was the average of two perpendicular measurements at the widest part of the live crown. 2.3.2.2 Net Photosynthetic Rate and Stomatal Conductance Five dominant paper birch trees were randomly selected from each treatment at each site for measurement. Net photosynthetic rate and stomatal conductance measurements were taken once in early-September, 1999, over a four-day period (one site per day). Leaf gas exchange 3 U s i n g the f o r m u l a for a pa rabo lo id to determine canopy v o l u m e ( m 3 ) ( M a w s o n et a l . 1976). 31 measurements for paper birch were not repeated in the 2000 and 2001 field seasons due to lack of funding. Due to the rugged terrain and the height of the paper birch trees, the cut-branch technique was used to measure net photosynthetic rate and stomatal conductance. A randomly selected healthy branch was cut from the top of the crown using a pruning pole (with extension) from each of the paper birch sampled. The branch stem was immediately recut under water, at least 5 cm from the end, with the cut surface submerged and the foliage kept above the water. While the cut surface was still submerged, the stem was placed in a vial of creek water. The level of the water in the vials was monitored throughout the collection procedure to ensure the cut surfaces were constantly submerged. The sampled branches were carried from treatment to treatment in a large, plastic garbage can during the collection process, and care was taken to keep the branches upright and the foliage in the sunlight. The collection procedure took place between 08:00 and 11:00 hours. Leaf gas exchange measurements took place between 12:00 and 15:00 hours on the same day at the site with a portable open CIRAS-1 differential CO2/H2O infra-red gas analyzer system and a broadleaf Parkinson leaf cuvette, which has a known area of 2.5 cm2 (PP Systems, Haverhill, MA, USA). The inlet C0 2 concentration was set at 360 ppm and the inlet H20 concentration was 70% of ambient. The measurements took place under saturating light (>1000 2 1 //mol m" s" PPFD). The cut branches were randomly selected for measurement and three fully developed attached leaves were randomly sampled and measured from each branch. The mean value of the three leaves per tree represented the individual tree measurement. The leaves that were measured, and the balance of the healthy leaves on the sampled branch, were harvested for nitrogen analysis. 3 2 2.3.2.3 Foliar Nitrogen Concentration All paper birch leaves from the branches sampled for photosynthesis and stomatal conductance were collected, air-dried and sent to Pacific Soil Analysis Inc., Richmond, BC for analysis of percent (%) nitrogen concentration. 2.3.2.4 Survival Paper birch mortality was recorded at the same time growth measurements were collected each year. Where possible, mortality cause was determined. Birch trees that were heavily browsed (e.g. broken stems at a height of at least 2.0 m from the ground) but still alive were noted. 2.3.3 Environmental Response Variables Environmental response variables included (1) light transmittance, and (2) soil moisture. 2.3.3.1 Light Availability Transmittance, the ratio of the photosynthetic photon flux density (PPFD) (waveband 400 -700 nm) incident on the interior Douglas-fir trees to total incoming PPFD, was measured using two direct methods: (a) handheld light sensor (Linear PAR Ceptometer, model PAR-80, Decagon Devices, Inc., Pullman, WA), and (b) fisheye (hemispherical) photographs. Two consecutive north-south measurements and east-west measurements were collected at a height of 1.3 meters at the outside edge of the crown of randomly selected interior Douglas-fir using the handheld light sensor. The average of the four measurements was calculated (Qj) for each interior Douglas-fir sampled. The open-sky light intensity measurements (Q0) were recorded at 10-minute intervals using the same handheld light sensor. To reduce variability in incident light intensity, measurements were taken on uniformly sunny days between 10:00 and 33 14:00 hours in July 2000 (Gendron et al. 1998). Formula [13] was used to calculate percent light transmittance for each sampled tree. [13] Percent light transmittance (%) = (Qj / Q0) * 100 One hemispherical canopy photograph was taken at ten randomly selected points within each treatment at each site under mainly overcast skies in August 2000. On partly overcast days photographs were taken when cloud cover blocked the sun from view. The photographs were taken with a tripod-mounted Minolta X700 camera equipped with a Minolta 7.5 mm circular image fisheye lens and Kodak Gold 400 ASA print film. The camera was positioned with the top to the north on the tripod at 1.3-meter height above the ground. Percent light transmittance (%) for each sample point was calculated using the Gap Light Analyzer imaging software (Frazer etal. 1999). 2.3.3.2 Soil Moisture Content Mineral soil was collected in labeled aluminum tins from a depth of 15-cm, after the overlying humus layer was removed, at 50.0 cm from the base of the sampled interior Douglas-fir trees, where the fine roots would access soil water (Hermann and Lavender 1990). Soil moisture samples were collected from the base of trees randomly selected for leaf gas exchange measurements (i.e. the morning of the same day leaf gas exchange measurements were taken at each site). Lids were secured on each tin using electrician tape to minimize any possible moisture loss. The samples were refrigerated upon return from the site, and analyzed within one or two days. The soil samples and tins were weighed to the nearest 0.1-gram using a Denver Instrument XP-3000 scale at the Kamloops Forest Region lab. After the initial weighing, the soil samples were uncovered (each lid positioned on the bottom of the tin) and placed in an oven at 34 105 °C for 72 hours (Fisher Scientific Isotemp® Oven, Model 655F). After drying, the tins (including the soil and the lids) were weighed. The soil was then removed from the tins and the tins (and lids) were weighed. Formula [14] was used to determine the percent soil moisture for each sample: [14] Percent soil moisture content (%) = (soil weight before drying (e) - tin weighttg")") - ("soil weight after drying (g) - tin weight (gV) * 100 (soil weight before drying (g) - tin weight (g)) 2.4 Statistical Analyses The linear model on which the analyses of individual tree and environmental response variables was based is as follows: Yjj = p + Pi + Tj + Sjj Where Yjj represents the total observations, i= l,...n(# of blocks) (n = 4), j = 1,... k (# of treatments) (k = 5 for interior Douglas-fir response variables); (k = 5 for environmental response variables); (k = 4 for paper birch response variables), p represents the overall mean of the observations, Pi represents the added effect representative of the z'th block (location effect), Xj represents the effect of the jth treatment (treatment effect), and 8ij represents the experimental error associated with the unit on the y'th treatment in the z'th block. 35 Data were analyzed using the SAS statistical package (SAS Institute Inc., Cary, N.C.). Descriptive statistics and boxplots were examined for each data set to ensure there were no outlying data points, and that the mean and standard deviation were appropriate. Descriptive statistics, histograms and probability plots were examined for each data set to screen for normality. Data transformations were used when data points were not normally distributed (i.e. where skewness and kurtosis were not zero (Tabachnick and Fidell 1989)). The transformations were tested for normality before applying them to the data set and afterward. One-way analysis of variance was used to test for pre-treatment differences in interior Douglas-fir stem diameter among the density treatments. Subsequently, one-way analysis of variance was used to test treatment differences in (a) interior Douglas-fir individual tree response variables, and (b) environmental response variables (Table 2.5). Means were considered different at a significance level of a = 0.05. Where differences were found, treatment means were separated using the Waller and Duncan Bayes Least Significant Difference procedure (Duncan 1975). The standard error of the treatment mean was calculated as Sy.j = V M S E E / n where M S E E = Mean Square Error (i.e. SSEE / df EE) and n = number of blocks (Kozak 1998). T a b l e 2-5. Analys is o f variance table for interior Douglas-fir individual tree a n d environment response variables. Source o f variat ion Degrees of F r e e d o m (df) SS M S Components o f variance B l o c k (replicate) n - 1 = 3 S S B M S B k a B 2 Treatment k - 1 = 4 SSTR M S T R a E E 2 + n a T R 2 Exper imenta l E r r o r (n - l ) (k - l )= 12 S S E E M S E E _ 2 CTEE T o t a l n k - 1 = 19 S S J O T Block (random): F 0.os (i), [ n - i , ( n - o ( k - i ) ] critical Treatments ( f ixed) : F 0.05 o>,[k-i,(n-o(k-i)] critical 3 6 Planned contrasts were used to compare different treatment combinations of interior Douglas-fir growth variables. The planned contrasts were: 1. Is interior Douglas-fir growth different where no thinning occurs (control) versus all thinning treatments combined (0 Ep, 400 Ep, 1111 Ep, 4444 Ep)? 2. Is interior Douglas-fir growth different where there is complete removal of broadleaf species (0 Ep) versus partial removal (400 Ep, 1111 Ep, 4444 Ep)? 3. Is interior Douglas-fir growth different where there is complete removal of broadleaf species (0 Ep) versus none (control)? 4. Is interior Douglas-fir growth different where there is light thinning (4444 Ep) versus heavy thinning (400 Ep and 1111 Ep)? 5. Is interior Douglas-fir growth different where there is complete removal of broadleaf species (0 Ep) versus light thinning (4444 Ep)? 6. Is interior Douglas-fir growth different where there is complete removal of broadleaf species (0 Ep) versus moderate thinning (1111 Ep)? 7. Is interior Douglas-fir growth different where there is complete removal of broadleaf species (0 Ep) versus heavy thinning (400 Ep)? One-way analysis of variance detected pre-treatment differences among paper birch stem diameter treatment means (P < 0.05). Consequently, the Pearson correlation coefficient (r) was used to measure the linear relationship between the paper birch pre-treatment stem diameter and the growth variables measured in years 1999 to 2001. Pre-treatment stem diameter was highly correlated with 1999 to 2001 stem diameter, height, crown diameter and stem volume (r >0.85, PO.0001). To adjust for the effects of paper birch pre-treatment stem diameter, analysis of covariance was used to analyze these growth variables using pre-treatment stem diameter as the 37 covariate. Analysis of variance was used to test for differences between treatment means for the remaining growth variables (Table 2-6). Analysis of covariance was also used to test for differences between treatment means of dominant paper birch trees. Dominant paper birch trees were defined as the largest 250 trees ha"1 based on stem diameter. This was equivalent to the largest 23 trees in each treatment plot (250 trees ha"1 x 0.09 ha"1 treatment plots = 22.5 trees), which were observed and analyzed throughout the three-year measurement period. Dominant paper birch were analyzed in order to remove any size effects introduced by the act of thinning, and also to analyze those birch canopy trees most likely to dominant the future stand. T a b l e 2-6. Analys is o f variance table for paper b irch individual tree response variables. Source o f variat ion Degrees o f F r e e d o m (df) SS M S Components o f variance B l o c k (replicate) n - 1 = 3 S S B M S B k a B 2 Treatment k - 1 =3 SSTR M S T R 2 , 2 a E E + naTR Exper imenta l E r r o r (n - l ) (k - l ) = 9 SSEE M S E E CTEE2 T o t a l n k - 1 = 15 SSTOT Block (random): F 0 . 0 5 (i), [n-i, (n-i)(k-i)] critical Treatments (f ixed): F 0os (i), [k-i, (n-i)(k-i)] critical Pearson correlation coefficient (r) was used to measure the linear relationship between 2 1 2 1 net photosynthetic rate (pmol CO2 m" s" ) and stomatal conductance (mmol H2O m" s" ) of the dominant paper birch leaves sampled from the density treatments (excluding 0 Ep) at the four study sites in 1999, two months post-treatment. Planned contrasts were used to compare different treatment combinations of overall paper birch and dominant paper birch growth variables as follows: 38 1. Does paper birch growth differ where no thinning occurs (control) versus where thinning occurs (400 Ep, 1111 Ep, 4444 Ep)? 2. Does paper birch growth differ where there is light thinning (4444 Ep) versus moderate thinning (1111 Ep)? 3. Does paper birch growth differ where there is moderate thinning (1111 Ep) versus heavy thinning (400 Ep)? 4. Does paper birch growth differ where there is light thinning (4444 Ep) versus heavy thinning (400 Ep)? 5. Does paper birch growth differ where no thinning occurs (control) versus moderate thinning (1111 Ep)? 6. Does paper birch growth differ where no thinning occurs (control) versus light thinning (4444 Ep)? 7. Does paper birch growth differ where no thinning occurs (control) versus heavy thinning (400 Ep)? 39 Chapter 3 Results 3.1 Interior Douglas-fir Performance 3.1.1 Survival Interior Douglas-fir survival was high (>97%) and there were no significant differences in mortality due to all causes combined (i.e. stem breakage due to snow press and death due to Armillaria ostaoyae) among treatments two-years following the initiation of the paper birch density treatments (P=0.6566). While not significantly different, planned contrasts showed that interior Douglas-fir mortality due to Armillaria ostoyae tended to be lower in the control (no thinning) versus the four thinned treatments combined (P=0.2114) (Figure 3-1). These analyses were conducted using the arcsine transformation, where Y j * = (sin"1 * (square root of Yjj)), which was applied to normalize the survival data. 0.160 0.140 0.120 0.100 0.080 0.060 0.040 1 0.020 0.000 -0.020 -0.040 OEp a I 400 Ep l l l l E p Treatment 4444 Ep a I Control Figure 3-1. Morta l i ty due to Armillaria ostoyae o f interior Douglas-fir in the paper b irch density treatments in 2001. Arcs ine transformation ( K o z a k 1998) was used to produce normality . T h e treatment means are the arcsine transformed values and s tandard error o f the treatment means (error bars). T h e standard error o f the treatment mean is + (square root ( M S E ) / s q u a r e root (n)), where n = 4 and M S E is the mean square error . 40 3.1.2 Growth There were no significant differences in interior Douglas-fir mean stem diameter, height, height:diameter ratio, height-to-live crown, crown diameter, stem volume or canopy volume among treatments in 1999 (immediately after the paper birch density treatments were established), 2000 and 2001 (with the exception of height:diameter ratio)(Table 3-1 and 3-2). Overall mean values in 1999 were 3.89 cm, 3.86 m, 119, 0.35 m, 1.84 m, 0.00234 m3 and 4.06 m , respectively. Overall mean values in 2000 were 4.66 cm, 4.29 m, 104, 0.47 m, 1.96 m, 0.00364 m and 5.02 m , respectively. Overall mean values in 2001 were 5.4 cm, 4.7 m, 98, 0.48 m, 2.12 m, 0.00530 m3 and 6.60 m3, respectively. T a b l e 3-1. Means , s tandard e r r o r o f the treatment means (S.E.) and P-values of interior Douglas-fir growth variables stem diameter, height and crown diameter in 1999,2000 and 2001. Y e a r : Treatment Stem diameter (cm) Height (m) C r o w n diameter (m) 1999: 0 3.7 3.72 1.75 400 4.1 3.87 1.90 1111 3.6 3.69 1.77 4444 4.5 4.31 1.99 Control 3.6 3.69 1.79 S . E . 1 0.39 0.25 0.12 P-value 0.4831 0.4009 0.6054 2000: 0 4.6 4.11 1.88 400 4.9 4.31 2.00 1111 4.3 4.05 1.87 4444 5.2 4.79 2.13 Control 4.3 4.19 1.90 S . E . t 0.43 0.30 0.13 P-value 0.4900 0.4623 0.5471 2001: 0 5.3 4.6 2.05 400 5.7 4.3 2.18 1111 5.0 4.6 2.04 4444 6.0 5.4 2.29 Control 4.9 4.7 2.03 S . E . 1 ' 0.47 0.4 0.13 P-value 0.4449 0.4867 0.5811 | standard error of the treatment means is + square root ( M S E ) / square root (n), where n = 4. 41 Tab le 3-2. Means , s tandard e r r o r o f the treatment means (S.E.) and P-values of in ter ior Douglas- f i r growth var iables height :d iameter rat io, height to l ive c rown , stem vo lume and canopy volume in 1999,2000 and 2001. Treatment means are s igni f icant ly dif ferent at a=0.05. Height- to- l ive Height :d iameter rat io c rown (m) Stem vo lume (m ) C a n o p y volume (m ) Y e a r : Un t rans- T r a n s - Unt rans- T rans - Unt rans- T rans - Unt rans- T rans -Treatment fo rmed formed fo rmed formed formed formed formed fo rm e d + 1999: 0 125 0.12748 0.36 -1.2013 0.00308 1.003088 3.84 1 4 1 x 1 0 6 400 107 0.02284 0.30 -1.4073 0.00324 1.003258 4.17 745 x 10 6 1111 129 0.15668 0.36 -1.1703 0.00276 1.002763 3.78 60 x 10 6 4444 105 0.01591 0.37 -1.1077 0.00396 1.003976 4.82 l x 10 6 Control 128 0.14483 0.36 -1.1989 0.00275 1.002760 3.69 52 x I0 6 S . E . 1 0.06569 0.1193 0.000605 335 x 10 6 P-value 0.4053 § 0.4972 § 0.61731' 0.5192" 2000: 0 104 -0.01288 0.52 -0.74335 0.00492 1.004944 4.84 0.8956 400 94 -0.08326 0.46 -0.87731 0.00500 1.005024 5.07 1.2379 1111 107 0.02154 0.46 -0.86706 0.00409 1.004109 4.49 0.9472 4444 97 -0.05161 0.47 -0.85613 0.00583 1.005860 6.06 1.5074 Control 117 0.08281 0.45 -0.90051 0.00413 1.004150 4.66 1.0175 S . E . 1 0.04700 0.05659 0.000909 0.2444 P-value 0.1768 § 0.3719 § 0.6482" 0.4150 § 2001: 0 95 -0.07793 b 0.50 0.00712 1.007171 6.47 1.2351 400 91 -0.12224 b 0.44 0.00715 1.007198 6.65 1.5561 1111 99 -0.03067ab 0.48 0.00588 1.005910 5.98 1.2688 4444 94 -0.08010 b 0.50 0.00818 1.008237 7.84 1.7836 Control 113 0.06402 a 0.48 0.00577 1.005806 6.05 1.2850 S . E . 1 0.03674 0.02 0.001247 0.2405 P-value 0.0333 § 0.3080 0.6299'I 0.4563 § t Analysis o f variance was performed on transformed data, where the data was not normally distributed. J Standard error o f the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and M S E is mean square error. § P-value based on natural log transformed data. || P-value based on exponential transformed data. Interior Douglas-fir in the lightly thinned treatment (4444 Ep), while not significantly different, tended, on average over the three-year measurement period, to be the tallest with the largest stem diameter, crown diameter, stem volume and canopy volume (Table 3-1 and Table 3-2, Figure 3-2). Conversely, the moderately thinned treatment (1111 Ep), while not significantly different, tended, on average, to have the lowest canopy volume in 2000 and 2001, although it wasn't the case in 1999 (Table 3-2). 42 7.0 a H O Ep • 400 Ep • 1111 Ep • 4444 Ep • Control 1999 2000 2001 Year F igure 3-2. M e a n stem diameter (cm) and standard e r r o r of the treatment mean bars of the interior Douglas-fir trees for each treatment for the years 1999, 2000 and 2001. Treatment means with different letters are significantly different ( a = 0.05). T h e s tandard error of the treatment mean is ± (square root ( M S E ) / s q u a r e root (n)), where n = 4 and M S E is the mean square error . Height:diameter ratio in 2001 of interior Douglas-fir was significantly different among the paper birch density treatments (Table 3-2, P=0.0333). Planned contrasts also revealed that height:diameter ratio was significantly higher (16%) in the control versus the four other density treatments combined in 2001(Contrast 1, Table 3-3, P=0.0046). Complete removal of the broadleaf trees (0 Ep) resulted in a 16% lower height:diameter ratio when compared to the control (Contrast 3, Table 3-3, P=0.0169). When the study was initiated in 1999, the height:diameter ratios of the interior Douglas-fir in all the treatments were greater than 100:1 (Figure 3-3). Over the three-year measurement period the interior Douglas-fir height:diameter ratio decreased in all treatments. The trend among treatments in percentage reductions in height:diameter ratio occurred between 1999 and 2000, and tended to range from 17% to 8% as follows: 0 Ep = 1111 Ep > 400 Ep > Control > 4444 Ep. Between 2000 and 2001 the percentage decreases tended to range from 9% to 3% as 43 follows: 0 Ep > 1111 Ep > 400 Ep = 4444 Ep = Control. The total reduction from 1999 to 2001 tended to be as follows: 0 Ep (24%) > 1111 Ep (23%) > 400 Ep (15%) > Control (12%) > 4444 Ep(10%). Y r 1 9 9 9 Y r 2000 Y e a r Y r 2 0 0 1 •0 Ep — O — 4 0 0 Ep — A — 1111 Ep —X- -4444 Ep - - © - - Control Figure 3-3. Interior Douglas-fir height:diameter ratio transformed (Base e log) means in the various treatments in 1999, 2000 and 2001. Treatment means with different letters are significantly different in 2001 ( a = 0.05). In 1999 and 2000, there were no differences among treatments. Any level of thinning improved mean diameter increment over the control between 1999 and 2001, and complete paper birch removal (0 Ep) was of comparable benefit as heavy (400 Ep) and light (4444 Ep) thinning (Figure 3-4, P=0.0449). Mean diameter increment did not increase following moderate thinning (1111 Ep). There were no significant differences in mean relative diameter growth rate, mean height increment or mean relative height growth rate among treatments (Table 3-4). 44 B cu £ ca a -Si a c = a c — si "3 £ C5 •gl "3 -= •o E SB of cu cu s SB E cu v: -I En ?I .2 S ° B u a « w g c .= = ** B . M CA r 2 £ B * e v> •- s TJ S - -B E = — S in — c s § "3 E 5! 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JJ S w ' cu to "5 "5 ~3 "5 ~a :ter ( 0 o mov mov S5 O •* mov mov mov 00 CJ CJ o CJ CJ E _C5 o c r-; — CJ oo — CJ m vi > SO ^. CJ CN •— CJ m to Os o c H 5J -r EX ^* CJ «n -r QJ -r tern < CN £. CS JS vi > r i O -r mpl > o s mpl vs tN O in UJ crt > CS CN SO o_ E vi > OC O O CJ E cn > CS o OC "a. E vi > •00 o> SO tern < J o cn cn o SO SO o sO so m CN o sO CN c sO SO o SO m as >• Z •<t o U o U -r d d U -t d y - f d U -r cs> JS r -5 9 CJ S •T— CS — CJ vi 2 r» > cj * • CJ '42 S S c o E i A a U U < n . U U < £ u u < o : E o A o A 'JO =0 _c Is KJ 3 cs C E o — cj -r. CS J S CJ _5 cs > • Year 2000 • Year 2001 0 Ep 400 Ep 1111 Ep Treatment 4444 Ep Control Figure 3-4. M e a n diameter increment (cm) and standard error o f the treatment mean bars o f interior Douglas-f ir in the density treatments in 2000 and 2001. Treatment means with different letters are significantly different ( a = 0.05). T h e s tandard e r r o r o f the treatment mean is ± square root ( M S E ) / square root (n), where n = 4. T a b l e 3-4. Means , s tandard e r r o r o f the treatment mean (S .E . ; n=4) and P-values o f interior Douglas-fir diameter increment, relative diameter growth rate, height increment and relative height growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two-year period). M e a n diameter M e a n relative diameter M e a n height M e a n relative height increment (cm) growth rate ( cm c m ' ) increment (m) growth rate (m m"1) Y e a r : Untrans- Untrans- T r a n s - Untrans- Untrans- T r a n s -Treatment formed formed formed formed formed formed 1^ 1999 -2000 : 0 0.85 0.29 0.50937 0.42 0.11 400 0.82 0.24 0.47101 0.44 0.11 1111 0.69 0.26 0.47691 0.39 0.10 4444 0.76 0.19 0.42214 0.50 0.12 Control 0.63 0.20 0.41955 0.50 0.13 S.E. 1 0.053 0.02612 0.05 0.01 P-value 0.0768 0.1346 § 0.3799 0.1379 1 9 9 9 - 2 0 0 1 : 0 1.60 a 0.56 0.71411 0.9 0.24 0.46770 400 1.61 a 0.46 0.65570 0.9 0.24 0.48240 n i l 1.37 ab 0.52 0.68054 0.9 0.24 0.46730 4444 1.49 a 0.37 0.59872 1.1 0.36 0.49904 Control 1.22 b 0.39 0.59875 1.0 0.27 0.50597 S.E* 0.087 0.03438 0.10 0.01754 P-value 0.0407 0.1312 § 0.4516 0.4359 § t Analysis of variance was performed on transformed data, where the data was not normally distributed. J Standard error of the treatment mean is ± (square root (MSE) / square root (n)), where n = 4 and MSE is mean square error. § P-value based on square root transformed data. 46 Planned contrasts were more sensitive than the Waller and Duncan Bayes LSD procedure at distinguishing interior Douglas-fir growth differences. Two-year mean diameter increment was 24% lower in the control than in the other four thinning treatments combined (Contrast 1,Table 3-6, P=0.0102). Also, complete removal of the broadleaf trees (0 Ep) resulted in a 24% higher mean diameter increment than in the control (Contrast 3, Table 3-6, P=0.0093). One-year mean diameter increment was 19% lower in the control than in the other treatments combined (Contrast 1, Table 3-7, P=0.0243), and 25% lower in the single treatment where all broadleaf trees were removed (Contrast 3, Table 3-7, P=0.0251). Planned contrasts detected treatment differences in mean relative diameter growth rate over a two-year period. Complete removal of the broadleaf trees (0 Ep) resulted in a 30% and 32% higher mean relative diameter growth rate compared to the control and the lightly thinned (4444 Ep) treatments, respectively (Contrast 3, Table 3-6, P=0.0352; Contrast 5, Table 3-6, P=0.0352, respectively). Planned contrasts detected treatment differences in mean relative height growth rate over a one-year period (1999 to 2000) but not the two-year period. Over the one-year period, the control had a (i) 17% higher mean relative height growth rate than the four other treatments combined (Contrast 1, Table 3-7, P=0.0171), and (ii) 19% higher mean relative height growth rate than in the treatment where all broadleaf trees were removed (0 Ep) (Contrast 3, Table 3-7, P=0.0354). 3.1.3 Net Photosynthetic Rate and Stomatal Conductance The paper birch density treatments did not significantly affect the mean net photosynthetic rate of interior Douglas-fir foliage sampled in late-August/early-September 2001 (Table 3-5). The treatment in which all broadleaf trees were removed (0 Ep) tended to have the 47 9 1 lowest mean net photosynthetic rate (8.312 pmol CO2 m" s"), whereas interior Douglas-fir in the moderately thinned treatment (1111 Ep) tended to have the highest rate (9.418 pmol CO2 m"2 s"1). Likewise, there was no significant difference in mean stomatal conductance among treatments in 2001 (Table 3-5). The control tended to have the lowest mean stomatal conductance (62.17 mmol H2O m"2 s~l) and 4444 Ep tended to have the highest (91.00 mmol H2O m"2 s-1). T a b l e 3-5. Means , s tandard e r r o r of the treatment means (S.E.) , and P-values for net photosynthetic rate (umol C 0 2 m"2 s'1) and stomatal conductance (mmol H 2 0 m~2 s"1) o f randomly selected interior Douglas-f ir within 3.0 - 6.0 c m stem diameter in the paper b irch thinning treatments in late-August/early September 2001. Net photosynthetic rate Stomatal conductance (p.mol C Q 2 m 2 s'') (mmol H 2 Q m 2 s ') Treatment Untransformed Untrans formed Trans formed^ 0 Ep 8.312 79.07 4.0648 400 Ep 8.511 75.57 3.9244 1111 Ep 9.418 72.71 3.8955 4444 Ep 9.398 91.00 4.2393 Control 8.898 62.17 3.9956 S . E . * 0.812 0.2156 P r > F 0.8157 0.8020 § f Analysis o f variance was performed on transformed data, where the data was not normally distributed. J Standard error o f the treatment mean is + (square root ( M S E ) / square root (n)), where n = 4 and M S E is mean square error. § P-value based on natural log transformed data. 5. / . 4 Specific Leaf Area Mean specific leaf area of the interior Douglas-fir increased significantly with increasing paper birch density in 2000 (Figure 3-5, P=0.0018). By contrast, there were no significant differences among treatments in 2001. Mean specific leaf area of interior Douglas-fir was 55% lower in 2001 (26.31 cm2 g"1) than in 2000 (58.56 cm2 g"1). The difference was due to the smaller mean leaf area in 2001 (13.61 ± 0.36 cm2) versus 2000 (29.69 ± 0.88 cm2) but corresponding identical weight (0.52 ± 0.02 g). 48 it £ it i. u * © o a II * « 1 -2 S 5 B | | OS ^ 2 5 E I •3 "5 w '•C a _« s S- VI ~r B a u 1 a 2 1 s i I § I w .2 o •o "C «- 2 "3D >-> 1 e a 2 H .S e s cs os e. os £ 2 8 = a g 0 I 1 S B 2 o E •a 2 2 " B OS S B * £ 0 cs CO gj s a - ^ 1 2 B OS W ^ 2 -B B OS 68 «J c w 1 * so s ii •S 1 3 2 B u > it 2 E 3= .£ £ i- a *- B I s 53 £ i- a | E i s o U CN •* CN oo SO CN ro r- ro m ro i t rsj CN r-i CN CN CN o o o d d d d co cn CO cn CO cn CO > Os > — > OS > > > ro > SO CN >/o i/o OO so CN I/O o I/O r~ •3-r- OS ro S© ro I/O 00 ro ro ro 00 ro SO CN —' rsj V CN — CN CN CN CN CN as CN u-i o d o o o o d o d d d d d d KO o^ O _ CN w — O c£ tu o ^ o o Q. > UJ o o » w ro DO O c c o c o DO c J= > * * CN O ( N c <L) o^ W £ o 4 os i n • * o o oZ tu a . tu o E > I/O C3 ' Q. n. tu C3 > o Os O U i s ro O oo SO CN —• d CO in S £ B C O O u u >- V. ° < y > u I I O i-U < o OS OS p t-" oo OS —' d — d d .90 vs. .3188 .09 vs. ,1330 .90 vs. 1807 90 vs. 8216 90 vs. 7830 o o ~- o o o o o o o s ° oo r i d « J 3 *> o o c a . ca > o E u o d CN CN 1) — i i B8 a . > E o o so U -c C3 1) o c o U _ n > u a s i 1 § « A o o ft -a c CO ft U J o o ** , O S o > ro r~ CN CO —< O d ro o [A > CN tu ^ f> W IT) O ft U J CO > o ft U J CO a> CN SO OS OS rr Os —' d Os 1> — J§ »5 _ & > SO £ o r~ O so ro U - ' d ro CN ft ro m KO o — d d ft tu CO > o I -C ro V C CO > a> CO 5 2 35 Jsj 2 cn "S3 S > •a s —1 QJ to — M cn ft > E O o so O -c -E to « cn ^ ** ai "S3 g « J ta. 1 ft J - -as A B E § b M « O C cn S SO > (j *• 19 33 §s s g s & E Os I/O d > OS CN ft W l I/O U J W l CN 0 d d o cn ft U J CO > o E _ dj _ S cn' _ s- * S E o 00 O SO Os U - d o , u u < o . u j < D : u u < a : u o < ._ _ ta. 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UJ ca > O IS cj d J ? cn-n. > o U T in oc — d d E •3 CJ c/i CN d CN d m O s o_ oo UJ ~" o o CN ro d d UJ CJ o 1 cn' _ g- > CN E T CN o oo O S U d d ea S2 cj g "-T1 CCJ ,J-i CJ CA E i A o • Ts b 3, § § es j^  K ia « < cu U cj CJ -j3 S i u. s C U < ou o I/O Oct 3 CT cn C O -O cj cn cd JB cj _3 CO > I CU -f-2000 2001 Y e a r • 0 Ep • 400 Ep • 1111 Ep 0 4444 Ep • Control Figure 3-5. Effect o f paper b irch density treatments on interior Douglas-f ir specific leaf area ( c m 2 g"1) and standard error o f the treatment mean bars in 2000 and 2001. Treatment means with different letters are significantly different ( a = 0.05). T h e standard e r r o r of the treatment mean is ± square root ( M S E ) / square root (n), where n = 4 and M S E is the mean square error . 3.1.5 Foliar Nitrogen Concentration Interior Douglas-fir foliar nitrogen (N) concentration (%) did not differ significantly among treatments in September 2000 (P=0.8994). The overall mean foliar nitrogen concentration was 1.27 ± 0.04%, which is similar to foliar N concentrations found in other studies assessing sapling Douglas-fir foliage (e.g. Bauerle et al. 1999). 3.2 Paper Birch Performance 3.2.1 Survival Paper birch survival was high, averaging between 98% and 99%. There were no trends in mortality among treatments, and causes of mortality were either unknown, or due to breakage at the base of the stem, moose browsing or trampling. 51 Paper birch had a high percentage of main stem breakage due to moose browsing between 1.54 meters and 2.40 meters from the ground in the heavily thinned treatments (400 Ep) compared with the other remaining treatments (Figure 3.6, P=0.1889). This occurred primarily at the Gold Creek 1 and Gold Creek 2 sites, and secondarily at the Burton Creek site. There was no main stem breakage due to moose browsing at the Momich River site. Main stem breakage was not significantly different because of high variability in moose use among sites. 0.4 n 0.35 09 0.3 -tern 0.25 -Wl C 0.2 -it e 0.15 -— 0.1 -e. _ a 0.05 -_= u o -< -0.05 --0.1 400 Ep 1111 Ep 4444 Ep Treatment C o n t r o l Figure 3 -6 . Percentage of main stem breakage o f paper b irch (Ep) caused by moose browsing in the density treatments in 2001. Arcs ine transformation ( K o z a k 1998) was used to produce normality . T h e treatment means are the arcsine transformed values and standard e r r o r o f the treatment means (error bars). T h e standard e r r o r o f the treatment mean is + (square root ( M S E ) / s q u a r e root (n)), where n = 4 and M S E is the mean square error . 3.2.2 Growth Application of the paper birch density treatments resulted in a significant difference in mean diameter, height and stem volume among the four birch-containing treatments (i.e. excluding 0 Ep) in 1999 (Tables 3-8 and 3-9; P=0.0293, P=0.0219 and P=0261, respectively). The smaller size of paper birch remaining in the 400 Ep resulted from appropriately spaced small 52 birch to achieve an even spatial distribution. In 2000, trends were similar to 1999 for these growth variables, with smaller sized paper birch trees in the 400 Ep as compared to the other treatments. However, in 2001, there were no significant differences in mean diameter, height or stem volume among treatments (P>0.05) indicating that faster growth rates in the lower density treatments had allowed those trees to catch up to the paper birch in the higher density treatments. Table 3-8. Means , s tandard e r ro r o f the treatment means (S.E.) and P-values of paper b i r ch growth variables stem diameter, height and c rown diameter in 1999, 2000 and 2001. Treatment means wi th different letters are significantly different (a=0.05). Stem diameter Height C r o w n diameter Y e a r : Unt rans- Trans - Untrans- Trans - Untrans- Trans -Treatment formed (cm) formed formed (m) formed formed (m) formed^ 1999: 400 2.88 0.9029 b 4.58 1.4626 b 1.28 0.1652 1111 3.48 1.0540 ab 5.44 1.6160a 1.48 0.3029 4444 3.97 1.1376 a 5.70 1.6466 a 1.53 0.3287 Control 3.93 1.0696 ab 5.62 1.6140a 1.51 0.2604 S.E* 0.0537 0.0353 0.0577 P-value 0 .0293 8 0.0219 s 0.2825 § 2000: 400 3.54 1.0966 b 5.08 b 1.47 0.2947 ab 1111 4.07 1.2181 ab 5.89 a 1.63 0.3937 ab 4444 4.49 1.2736 a 6.08 a 1.71 0.4272 a Control 4.29 1.1541 ab 6.07 a 1.53 0.2743 b S . E . 1 0.0491 0.18 0.0427 P-value 0.0391 § 0.0098 0.0849 § 2001: 400 4.02 1.2211 5.27 1.5551 1.71 0.4392 1111 4.60 1.3518 6.38 1.7738 1.92 0.5675 4444 4.94 1.3560 6.55 1.7844 1.97 0.5882 Control 4.61 1.2334 6.49 1.7549 1.80 0.4292 S.E.* 0.0569 0.0526 0.0509 P-value 0.0865 § 0.0759 § 0.1537 § t Analysis o f Covariance on untransformed and transformed data (where the data were not normally distributed) for growth variables (i) Stem diameter, (ii) Height and, (iii) C rown diameter, using pretreatment stem diameter means as the Covariate. X Standard error o f the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and M S E is mean square error. § P-value based on natural log transformed data. 53 Table 3-9. Means , s tandard e r ro r o f the treatment means (S.E.) and P-values o f paper b i rch growth variables height:diameter ratio, height-to-live c rown , stem volume and canopy volume in 1999,2000 and 2001. Treatment means wi th different letters are significantly different (a=0.05). Height :d iameter Height-to-l ive ratio c r o w n ( m ) f Stem volume (m3)+ C a n o p y volume (m 3 ) Y e a r : Unt rans- Trans - Untrans- T r a n s - Untrans- Trans - Unt rans- Trans -Treatment formed formed formed formed formed formed formed formed 1999: 400 181 0.5597 1.31 0.1759 0.00237 -6.9382 b 3.25 0.4955 1111 184 0.5620 1.68 0.4119 0.00394 -6.5196 ab 5.16 0.8701 4444 177 0.5089 1.59 0.3819 0.00569 -6.3261 a 6.02 0.9693 Control II 191 0.5444 1.60 0.3089 0.00581 -6.4812 a 6.17 0.7750 S .E.H 0.0331 0.0640 0.1316 0.1996 P-value 0.6618 1 0.1089 1 0.0254 1 0.4187 1 2000: 400 161 0.4494 1.34 b 0.00350 -6.4933 b 5.02 0.8549 1111 165 0.4672 1.73 a 0.00550 -6.1402 ab 6.93 1.1462 4444 160 0.4270 1.66 a 0.00751 -6.0098 a 8.27 1.2244 Control II 185 0.5301 1.81 a 0.00730 -6.2584 ab 7.27 0.8447 S . E J 0.0353 0.09 0.1202 0.1809 P-value 0.2616 1 0.0248 0.0358 1 0.3711 1 2001: 400 144 0.3204 1.37 0.2224 b 0.00478 -6.2360 7.36 1.1317 1111 158 0.4175 1.78 0.4732 a 0.00730 -5.8085 10.03 1.6026 4444 156 0.3985 1.69 0.4393 a 0.00930 -5.7242 11.27 1.6703 Control || 185 0.5215 1.94 0.5350 a 0.00872 -6.0467 10.27 1.2335 S .E." 0.0482 0.0501 0.1426 0.1978 P-value 0.0910 1 0.0086 1 1 0.0885 1 1 0.2139 1 1 t Analysis o f Variance was performed on transformed and untransformed data (where the data were not normally distributed) for this growth variable. X Analysis o f Covariance on transformed data was performed for growth variable, Stem volume (m 3 ) , using pretreatment stem diameter means as the Covariate. § Analysis o f Variance was performed on transformed data, unless otherwise noted, where the data was not normally distributed. || Standard error o f the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and M S E is mean square error. | P-value based on natural log transformed data. Height-to-live crown was significantly lower in the 400 Ep treatment compared to the other treatments in 2000 and 2001, indicating that lower branches were being retained in the more open canopy conditions (Table 3-9, P=0.0248 and P=0.0086, respectively). Significant differences in one-year mean diameter increment, relative diameter growth rate and relative height growth rate occurred among treatments (Tables 3-10 and 3-11, P=0.0374, 54 P=0.0001, and P=0.0012, respectively). Growth rates increased significantly with decreasing paper birch density. After two years, mean diameter increment and relative diameter growth rate continued to increase with decreasing birch density (Table 3-10; P=0.0309 and pO.OOOl, respectively), whereas relative height growth rate no longer varied among treatments as it did for the one-year period (Table 3-11). T a b l e 3-10. Means , s tandard error of the treatment means (S .E. ) and P-values of paper b i rch diameter increment and relative diameter growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two year period). Treatment means with different letters are significantly different (a=0.05). M e a n relative diameter M e a n diameter increment growth rate Y e a r : Treatment Untransformed (cm) T r a n s f o r m e d Untrans formed (cm cm"2) Trans formed^ 1 9 9 9 - 2 0 0 0 : 400 0.57 0.7270 a 0.22 0.4543 a 1111 0.55 0.7073 a 0.18 0.4074 b 4444 0.52 0.6702 ab 0.15 0.3634 c Control 0.38 0.5390 b 0.11 0.2878 d S . E . 1 0.0406 0.0144 P-value 0.0374 § 0.0001 § 1 9 9 9 - 2 0 0 1 : 400 1.06 0.9854 a 0.39 0.6116 a 1111 1.05 0.9888 a 0.34 0.5675 a 4444 0.96 0.0332 b 0.28 0.5127 b Control 0.67 0.7449 c 0.19 0.3978 c S . E . * 0.0531 0.0180 P-value 0.0309 § <0.0001 § t Analysis o f Variance was performed on transformed data (where the untransformed data were not normally distributed). X Standard error o f the treatment mean is ± (square root ( M S E ) / square root (n)), where n = 4 and M S E is mean square error. § P-value based on square root transformed data. 55 Table 3-11. Means , s tandard e r ro r o f the treatment means ( S . E . ) and P-values o f paper b i rch height increment and relative height growth rate between 1999 - 2000 (one-year period) and 1999 - 2001 (two year period). Treatment means w i t h different letters are significantly different (a=0.05). M e a n relative height M e a n height increment growth rate Y e a r : Treatment Unt ransformed (m) Transformed Unt ransformed (m m"2) Transformed 1 9 9 9 - 2 0 0 0 : 400 0.44 0.6188 0.22 0.2928 a 1111 0.42 0.5992 0.18 0.2608 b 4444 0.41 0.5749 0.15 0.2414 c Control 0.46 0.6170 0.11 0.2520 b S . E . 1 0.0204 0.0058 P-value 0.4379 § 0.0012 § 1 9 9 9 - 2 0 0 1 : 400 0.76 0.16 1111 0.90 0.17 4444 0.85 0.15 Control 0.86 0.15 S.E.* 0.05 0.01 P-value 0.3361 0.7422 t Analysis o f Variance was performed on untransformed and transformed data (where the untransformed data were not normally distributed). J Standard error o f the treatment mean is ± (square root ( M S E ) / square root (n)), where n = 4 and M S E is mean square error. § P-value based on square root transformed data. Planned contrasts found that the control had a significantly higher (17%) height-to-live crown in 2001 than the three thinning treatments combined (400 Ep, 1111 Ep and 4444 Ep) indicating that lower branches were self-pruning in the more closed canopy (Contrast 1, Table 3-12, P=0.0283). Compared with the control, any level of thinning (light, medium or heavy) improved mean diameter increment and relative diameter growth rate (Contrast 1, Table 3-13, P=0.0053 and pO.OOOl, respectively). Relative diameter growth rate in the heaviest thinned treatment (400 Ep) was significantly faster (28%) than in lightest thinned treatment (4444 Ep)(Contrast 4, Table 3-13, P=0.0037). 56 tu s. es a, & tu E -3 3 es o tu > •-tu Se-es CS a E o tu es — cn cn es . - _ s © 2 ° * 5 s « c e cs © ° CSV C5N m ess © — © II 5, *> cu CU 2 ol 5 2 1 s 5 » es g g -5 es cu tu tl — = ' cu r o -a i i J S J S tu « .= S- JS tu tu E .2 •5 s •* o ~ co oc 00 o> -r r i o — — a> vs. c- vs. m vs O so vs o o CS • — i m cn m OC p» CD rz? 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S A c 2 £ Cj -B ca - 60 CD £ u 2 2 o u -a CD u. g 8 t, o O (X U U 00 — oo o Os SO SO r-o Os c n 00 SO r-d d d d d d d .86 vs. .6977 .85 vs. .5458 .90 vs. .0913 85 vs. ,2384 86 vs. 6211 86 vs. 9104 86 vs. 2013 o o o o © © o o o o o o o © oo m m oo r o i n r o Os OS r o 00 ON r o r o r o r o C N r o d d © d d d CO cn CO CO CO cn > o > 00 > > o > i n > O r o as oo so r o o o OO m r o •— 00 © oo p oo o oo p C N o r o '— C N © CL ' • © CL ' • o — d d d d d d © tu © V tu <=> d C L © V tu o o o fe E O o i q 'E B cn O so Z d ca CD X B, si A g e t, o o £ u u B ca A CD / x E P o S ffi U U S cu oo i n ca tx cn E O -a CD cn ca X) CD ca > 3.3 Dominant Paper Birch Performance 3.3.1 Growth In 1999 and 2000, there were significant differences in mean stem diameter, height, crown diameter, stem volume, canopy volume and height:diameter ratio of the dominant paper birch (largest 250 stems ha"1) (Tables 3-14 and 3-15). Trees in the heavily thinned treatment (400 Ep) were smaller and had higher height:diameter ratio than those in the moderately (1111 Ep) and lightly thinned treatments (4444 Ep) and the control. In 2001, treatment effects on mean stem diameter, height, crown diameter, stem volume and canopy volume persisted, with the inclusion of height-to-live crown (Tables 3-14 and 3-15). Mean diameter increment and mean relative diameter growth rate were significantly affected by the density treatments from 1999 to 2001 (Table 3-16, P=0.0213 and P=0.0005, respectively). Any level of thinning (light, moderate or heavy) improved mean diameter increment and relative diameter growth rate of dominant paper birch over those in the control (Contrast 1, Table 3-17, P=0.0095 and P=0.0004, respectively). The moderately thinned treatment (1111 Ep) had a 37% greater mean diameter increment than the control (Contrast 5, Table 3-17, P=0.0031), and the heaviest thinned treatment (400 Ep) had a 116% higher relative diameter growth rate than the control (Contrast 7, Table 3-17, P<0.0001). Mean height increment of dominant paper birch was significantly lower in the heavily thinned treatment (400 Ep) than in the moderately thinned treatment (Contrast 3, Table 3-17, P=0.0179), or the control (Contrast 7, Table 3-17, P=0.0397). 59 Table 3-14. Means , s tandard e r ro r o f the treatment means (S.E.) and P-values of dominant paper b i r ch (largest 250 stems ha"1) growth variables stem diameter, height and c rown diameter in 1999, 2000 and 2001. Treatment means wi th different letters are significantly different (a=0.05). Stem diameter Height C r o w n diameter Y e a r : Unt rans- Trans - Untrans- Trans - Untrans- T r a n s -Treatment formed (cm) formed formed (m) formed formed (m) f o r m e d + 1999: 400 3.63 1.8610 b 5.31 b 1.50 0.3491 b 1111 6.10 2.4419 a 7.78 a 2.16 0.7244 a 4444 6.10 2.4393 a 7.57 a 2.02 0.6755 a Control 6.12 2.4433 a 7.60 a 2.07 0.6982 a S . E . : 0.0476 0.16 0.0543 P-value 0.0014 § 0.0007 0.0328" 2000: 400 4.33 1.3859 b 5.82 b 1.70 0.4690 b 1111 6.95 1.8960 a 8.37 a 2.39 0.8224 a 4444 6.85 1.8794 a 8 .14a 2.28 0.7884 a Control 6.69 1.8554 a 8.19 a 2.12 0.7140 a S.E.* 0.0478 0.17 0.0422 P-value 0.00501' 0.0011 0.0267" 2001: 400 4.94 2.1806 b 6.02 1.96 1111 7.74 2.7566 a 8.92 2.73 4444 7.45 2.7015 a 8.66 2.56 Control 7.15 2.6466 a 8.71 2.50 S . E . 1 0.0503 0.18 0.08 P-value 0.0064 § 0.0004 0.0188 t Analysis o f Covariance was performed on untransformed or transformed data (where the untransformed data were not normally distributed) for growth variables (i) Stem diameter (cm), (ii) Height (m) and, (iii) Crown diameter (m). Covariate is pretreatment paper birch stem diameter (cm) means using natural log transformation to produce normality. J Standard error o f the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and M S E is mean square error. § P-value based on square root transformed data || P-value based on natural log transformed data. 60 T a b l e 3-15. Means , s tandard e r r o r o f the treatment means (S.E.) an d P-values of dominant paper b irch (largest 250 stems ha"1) growth variables height:diameter ratio, height-to-live crown, stem volume and canopy volume in 1999,2000 and 2001. Treatment means with different letters are significantly different (a=0.05). Height:diameter Height-to-live ratio crown (m) Stem volume ( m 3 ) f C a n o p y volume (m 3 ) Y e a r : Untrans- T r a n s - Untrans- T r a n s - I n trans- T r a n s - Untrans- T r a n s -Treatment formed formed formed formed formed formed formed formed* 1999: 400 157 a 1.37 0.00352 -6.2295 b 4.66 1.0809 b 1111 132 b 1.85 0.01091 -4.7899 a 13.20 2.2625 a 4444 129 b 1.71 0.01112 -4.8234 a 10.94 2.1370 a Control 127 b 1.64 0.01129 -4.8100 a 11.51 2.2088 a S . E . S 4 0.14 0.1187 0.1668 P-value 0.0015 0.1643 0.00131' 0.0020" 2000: 400 143 a 1.40 1.1598 b 0.00516 -5.7846 b 6.84 1.4362 b n i l 124 b 1.89 1.3301 a 0.01506 -4.4650 a 17.55 2.5465 a 4444 122 b 1.82 1.3315 a 0.01458 -4.5227 a 15.13 2.4444 a Control 126 b 1.87 1.3163 a 0.01414 -4.5665 a 13.60 2.2976 a S . E . § 4 0.0446 0.1134 0.1564 P-value 0.0128 0.0630 1 0.0031" 0.0027" 2001: 400 132 1.43 1.1697 b 0.00705 -5.5088 b 9.90 2.7419 b m i 118 1.95 1.3506 a 0.01937 -4.1854 a 23.53 4.5722 a 4444 119 1.84 1.3364 a 0.01785 -4.2945 a 20.06 4.2431 a Control 125 2.08 1.3981 a 0.01681 -4.3726 a 19.02 4.0956 a S . E . 8 3 0.0454 0.1172 0.2374 P-value 0.0584 0.02891 1 0.0042" 0.00191 1 t Analysis o f Covariance was performed on transformed data for growth variable, Stem volume (m 3 ) , using pretreatment stem diameter means as the Covariate. { Analysis o f Variance was performed on untransformed or transformed data (where the data were not normally distributed) for growth variables: (i) Height:diameter ratio, (ii) Height-to-live crown (m) and (iii) Canopy volume (m 3 ). § Standard error o f the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and M S E is mean square error. I P-value based on natural log transformed data. I P-value based on square root transformed data. 61 Tab le 3-16. Means , s tandard e r ro r o f the treatment means (S .E.) and P-values of dominant paper b i r ch d iameter increment, relat ive d iameter growth rate, height increment and relative height growth rate between 1999 - 2000 (one-year per iod) and 1999 - 2001 (two-year per iod). Treatment means wi th dif ferent letters are signi f icant ly di f ferent w i th in years (a=0.05). M e a n d iameter M e a n relative d iameter M e a n height M e a n relat ive increment growth rate increment height growth rate Unt rans- T r a n s - Unt rans- T r a n s - Un t rans - Un t rans -Y e a r : formed formed formed formed formed fo rmed Treatment (cm) (cm cm" 2) (m) (m m 2 ) 1 9 9 9 - 2 0 0 0 : 400 0.70 0.8194 0.210 -1.6347 a 0.53 0.104 a 1111 0.85 0.9050 0.143 -1.9988 b 0.60 0.077 b 4444 0.75 0.8462 0.130 -2.1424 b 0.57 0.077 b Control 0.57 0.7184 0.100 -2.3950 c 0.59 0.080 b S . E . 1 0.0438 0.0688 0.05 0.007 P-value 0.0786" 0.0002 § 0.7642 0.0486 1 9 9 9 - 2 0 0 1 : 400 1.32 1.1210 ab 0.391 -1.0164 a 0.93 0.170 1111 1.64 1.2663 a 0.279 -1.3129 b 1.15 0.150 4444 1.34 1.1424 ab 0.236 -1.5251 b 1.09 0.147 Control 1.03 0.9959 b 0.181 -1 .8126c 1.11 0.149 S . E . 1 0.0477 0.0822 0.06 0.010 P-value 0.0213" 0.0005 § 0.0738 0.3886 t Analysis o f Variance was performed on untransformed or transformed data (where the data were not normally distributed). t Standard error o f the treatment mean is ± (square root (MSE)/square root (n)), where n = 4 and M S E is mean square error. § P-value based on natural log transformed data. || P-value based on square root transformed data. 62 E £ E DC w •ss a JS cs « <-> JS " H m st 1 £ OS ox ox E 1- u ** s E 3 | 53 CU •— SI E > JS © SO O o o o o m m r- r- m T f r-» —i <—1 »—< i—i —i d d d d d d d cn" c/i cn" cn cn cn cn > T f > 00 > o > IS > o > m > m Os m r- o o Qs Os oo Os 00 Os I—• 00 — m o T f cn TT cn TT r- TT — m — oo CN —-> — Os OO — © d d d d d d d d d d d d d SO o cn cn CN — OS — cn —' d W T f T f T f Q. 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Stomatal conductance of dominant paper birch also did not differ among treatments in 1999. The average rate was 275.16 ± 27.87. 3.3.3 Foliar Nitrogen Concentration The density treatments had no effect on mean foliar nitrogen (N) concentration (%) of the dominant paper birch sampled in 1999, two months post-treatment. The mean foliar N concentration ranged from 1.72% to 1.83%). 3.4 Environmental Conditions 3.4.1 Light Availability The methods used to measure percentage of photosynthetic photon flux density (PPFD) under the canopy clearly illustrated the positive relationship between canopy openness and the percentage of light transmitted to 1.3 meters above the forest floor. Complete removal of the broadleaf trees (0 Ep) received the highest percentage of incident light for the hemispherical canopy photograph technique (HCP), and the control (no thinning) received the lowest percentage (PO.0001 and P<0.0001, for HCP and handheld light sensor (HLS) technique, respectively) (Figure 3-8). The hemispherical canopy photograph technique consistently yielded higher averages than the handheld light sensor (Figure 3-8). The hemispherical photographs were taken at randomly selected points within each treatment and some photographs were therefore not shaded by nearby interior Douglas-fir. The handheld light sensor readings were taken at the outside 64 edge of the crown of randomly selected interior Douglas-fir and were subject to shading by the sampled Douglas-fir. 0 Ep 400 Ep 1111 Ep 4444 Ep Control Treatment Figure 3 -7 . M e a n percent photosynthet ic photon f lux density ( P P F D ) at 1.3 meters above the forest f loor in the paper b i r ch density treatments in J u l y and Augus t 2000. T w o methods o f measur ing P P F D were compared : (a) hemispher ica l canopy photographs ( H C P ) , and (b) a handheld l ight sensor ( H L S ) . T rea tment means wi th di f ferent letters are signi f icant ly di f ferent w i th in a method (a=0.05). The s tandard e r ro r o f the treatment mean is ± (square root ( M S E ) / s q u a r e root (n)), where n = 4 and M S E is the mean square er ror . Note: Handhe ld l ight sensor measurements were not collected in the 0 E p treatments. Excluding the 0 Ep treatment, which was not measured using the handheld light sensor due to cloudy weather, a paired t-test (n=40; t-critical = 2.021) comparing the treatment means found there were statistical differences between the two measurement techniques in each treatment (Table 3-18). Tab le 3-18. Stat ist ical s u m m a r y o f pai red t-test results testing differences between hemispher ica l canopy photograph means ( H C P ) and handheld l ight sensor ( H L S ) means w i th in each treatment, exc lud ing the 0 E p . S tandard E r r o r of the Treatment M e a n Dif ference Va r i ance S tandard Deviat ion M e a n Dif ference t-statistic P r > |t| 400 E p 13.66 402.00 20.05 3.17 4.31 0.0001 1111 E p 13.42 428.06 20.69 3.27 4.10 0.0002 4444 E p 15.58 400.22 20.01 3.16 4.93 <0.0001 C o n t r o l 17.31 562.40 23.72 3.75 4.62 <0.0001 65 3.4.2 Soil Moisture Content Soil moisture content did not differ among treatments in 2000 (P=0.3922). In 2001, by contrast, soil moisture decreased with increasing density of paper birch (Figure 3-9, P=0.0086). The lowest mean soil moisture content was in the control (10.12% ± 2.18%), whereas the 0 Ep (where all broadleaf component was removed) had the highest (17.23% ± 3.31%). 2000 2001 Year Figure 3-8. M e a n soi l moisture ( H 2 0 ) content in the paper b i rch density treatments in 2000 and 2001. Na tu ra l logar i thm t ransformat ion was used to produce normal i ty . The treatment means are the natura l logar i thm t ransformed values and s tandard e r ro r of the treatment means (er ror bars) . The s tandard e r ro r of the treatment mean is ± (square root ( M S E ) / s q u a r e root (n)), where n = 4 and M S E is the mean square e r ro r calculated using the natura l logar i thm t ransformed values. Treatment means wi th di f ferent letters are s igni f icant ly di f ferent (rx=0.05). 66 Chapter 4 Discussion Despite the short period of time between applying the treatments in 1999, and gathering and analyzing the tree growth and environmental response data in 2001, the results indicate that the interior Douglas-fir are responding in growth, survival and physiology to the paper birch density treatments. Changes in resource availability, light and water, were also evident, particularly in 2001. 4.1 Growth Response of Interior Douglas-fir Mean diameter increment of interior Douglas-fir was higher in the treatments where the broadleaf component was completely removed, heavily thinned and lightly thinned (e.g. 0 Ep, 400 Ep and 4444 Ep, respectively) compared with the control two years after the density treatments were implemented. With the exception of the lightly thinned (4444 Ep) treatment, this is consistent with previous studies that showed increased Douglas-fir stem diameter with decreasing broadleaf density (Simard 1990; Shainsky and Radosevich 1992). On average, interior Douglas-fir in the lightly thinned treatment (4444 Ep) were tallest with the largest stem diameter, crown diameter, stem volume and canopy volume. There was a pretreatment tendency for the interior Douglas-fir in the 4444 Ep treatments to be larger and this effect was expressed throughout the study period. By contrast, mean diameter increment of the interior Douglas-fir in the moderately thinned treatment (1111 Ep) was similar to those in the control. By chance, the saplings in the 1111 Ep treatments appeared more suppressed prior to treatment as indicated by their spindlier growth form and lower canopy volume. However, the mean relative diameter growth rate of interior Douglas-fir in the 1111 Ep treatment tended to be higher than in the 4444 Ep treatment over the two-year period. If this trend continues, mean diameter increment of the 67 saplings in 1111 Ep should surpass those in 4444 Ep in time. Mean height increment of interior Douglas-fir over the two-year study period was not significantly affected by the birch density treatments. This supports the findings of previous studies showing that height is less sensitive to changes in competitive stress (e.g., the density treatments) and will lag behind stem diameter responses to the treatments (Lanner 1985; Lanini and Radosevich 1986; Wagner and Radosevich 1991; Simard and Heineman 1996a; Harrington and Tappeiner 1997; Simard et al. 2001). Interior Douglas-fir is one of many species in which the current year's shoot growth is determined by (a) the previous year's bud formation, and (b) the current year's environmental conditions before bud formation (Oliver and Larson 1996; Guy 1999). Therefore, 1999 height and crown diameter measurements would reflect (a) environmental conditions in 1998 prior to bud formation, and (b) environmental conditions in 1999 pre-treatment and post-treatment (less than one-month period). In contrast, individual tree stem diameter growth is a function of the current year's environmental growing conditions (e.g. soil moisture, soil nutrients, light transmittance) and is more sensitive to initial treatment applications (Lanner 1985; Wagner and Radosevich 1991). For these reasons, interior Douglas-fir stem diameter growth would be more affected than height by the change in resource availability due to the implementation of the paper birch density treatments. Another important reason for no height response is that previous studies have shown that height is only affected by extremes in competition levels (Bell et al. 2000; Simard and Hannam 2000). This suggests that the tree densities in the control, in this study, were not high enough to affect interior Douglas-fir height. Heightdiameter ratio is a measure of how well the crown foliage has produced and allocated carbon to primary and secondary tree growth (e.g. stem elongation and cambium growth) (Smith et al. 1997). When this study was initiated in 1999, the heightdiameter ratios of 68 the interior Douglas-fir in all the treatments were greater than 100:1, which Cremer et al. (1982) would describe as "high height:diameter ratio" and the trees as "spindly". This was probably due to overtopping broadleaf trees decreasing light availability to the interior Douglas-fir (Williams et al. 1999). Other studies have described how the relationship of height to diameter changes in response to reductions in available light caused by overtopping vegetation (Brix 1981; Howard and Newton 1984; Pearson et al. 1984; Brand 1986). High heightdiameter ratios have been observed in studies examining competitive interactions between overtopping vegetation and plantation conifer seedling growth (Lanner 1985; Simard 1990). Over the three-year measurement period, interior Douglas-fir height:diameter ratio tended to decrease in all treatments, with significant differences occurring among treatments in 2001. The control had a higher height:diameter ratio than (a) the four other thinning treatments combined, and (b) the treatment where the broadleaf component was completely removed (0 Ep). The heightdiameter ratio did not systematically decrease with decreasing paper birch stem density, as shown in previous studies, but the ratio did decrease each year in each treatment. "Shock effect" has been observed among released trees a few years after thinning in some studies, where height growth decreased and upper canopy branch elongation decreased (Staebler 1956; Reukema 1964). In this study, interior Douglas-fir did not experience decreased height growth over the two-year study period. Upper canopy branch elongation was not measured. I did observe in September 1999 (three months after initiating the density treatments), however, that the current year needles on the majority of the interior Douglas-fir in the 0 Ep, 400 Ep and 1111 Ep treatments had turned brown, possibly due to photooxidation of the leaf surface catalyzed by ultraviolet (UV) radiation in sunlight (L'Hirondelle and Binder 2002). This suggests that trees were stressed by the thinning treatments, but not enough to manifest as height growth depression. Needle browning was not observed in 2000 or 2001. 69 4.2 Survival Response of Interior Douglas-fir In this study, the incidence of Armillaria root disease tended to be higher in the brushed treatments than in the control, supporting previous research in the ICH in which interior Douglas-fir mortality due to Armillaria ostoyae increased following manual cutting of neighboring paper birch (Woods 1994; Simard and Heineman 1996b). Woods (1994) compared the effect of brushing (manual cutting) versus no brushing on infection patterns in 25-year-old interior Douglas-fir plantations that had similar stump basal area (m2/ha) Armillaria root disease infection. The brushed stand had 53% more plots with infected trees than the non-brushed stand. Woods (1994) also found that interior Douglas-fir mortality increased at a higher rate in the brushed plantation than the non-brushed plantation. Simard and Heineman (1996b) found that 7-year-old interior Douglas-fir seedling mortality due to Armillaria root disease on an ICHmw2 site near Salmon Arm, B.C., was 15% three-years following manual cutting of neighboring paper birch, compared to 3 - 5% mortality in the control and chemical treatments. Armillaria root disease mortality nine-years following manual cutting and chemical treatments was 20 - 23% versus 15% mortality in the control. In another study, Simard et al. (2001) found that five-year lodgepole pine sapling mortality due to A. ostoyae was over four times higher in treatments where paper birch had been manually cut (9%) than where it had not (2%). In this study, there are several possible mechanisms that may explain the response of A. ostoyae to manual cutting of paper birch. First, A. ostoyae was present on the sites prior to treatment initiation, which is consistent with other studies that have found a moderate to high occurrence of A. ostoyae in the ICH and IDF wet-belt forests (Morrison et al. 1991; Cruickshank et al. 1997). Armillaria ostoyae is considered a "high hazard" throughout the ICHmw and IDFmw subzones in British Columbia (B.C. Min. For. 1995a). In this study, single, dead interior Douglas-fir saplings scattered within each treatment showed signs of the root disease, most 70 notably the presence of white mycelial fans under the bark of the stem below the root collar (Morrison et al. 1991). By removing all or a portion of the broadleaf trees (along with other natural regeneration) in the thinned treatments, the size of the food base for pathogenic Armillaria root disease increased. Armillaria ostoyae can swiftly colonized the stumps and root systems of cut or killed hosts, utilizing them as a food source (Morrison et al. 1991). Armillaria then had a higher "inoculum potential", defined as the "fungus' energy of growth available to infect a new host"; the new hosts in this study were the root systems of neighboring paper birch and interior Douglas-fir (Garrett 1960, cited in Morrison et al. 1991). Second, prior to initiating the thinning treatments, the root systems of some paper birch were host to A. ostoyae, based on the occurrence of mushroom fruiting bodies surrounding the base of cut stems of paper birch in September 2000 (Morrison et al. 1991)(Figure 4-1). Paper birch trees less than 15-years-old appear resistant to Armillaria infection, after which they are tolerant, but not immune, to the fungus' attack (Morrison et al. 1991). The root systems of species less susceptible to Armillaria root disease, like paper birch, are thought to act as a barrier to the spread of A. ostoyae to susceptible conifer root systems by blocking root contact with the fungus (Morrison et al. 1988; Morrison and Mallett 1996). Alternatively, root contacts between paper birch and interior Douglas-fir established before the density treatments were implemented may have acted as corridors for A. ostoyae, increasing the potential of the fungus to colonize the root systems of neighboring interior Douglas-fir (Morrison et al. 1991). Third, studies have found that the larger, faster growing susceptible conifers in low density, thinned stands (e.g. 300 stems ha"1) tend to be infected more readily by A. ostoyae because the root systems of these trees are more extensive, and therefore more likely to come in contact with adjacent root systems infected by the fungus (Rosso and Hansen 1998). In this study, interior Douglas-fir relative diameter growth rate was greater in the 0 Ep treatment 71 Figure 4-1. M u s h r o o m fruit ing bodies of Armillaria ostoyae on paper birch stumps at the M o m i c h R iver site in the 400 E p that were cut in 1999 when paper b irch density treatments were implemented. (Photo credit: K a r e n Baleshta). ( c o m p l e t e r e m o v a l o f b r o a d l e a f t rees) t h a n i n the 4 4 4 4 E p t rea tmen t ( l i g h t l y t h i n n e d ) a n d the c o n t r o l ( n o t h i n n i n g ) . C o r r e s p o n d i n g l y , i n t e r i o r D o u g l a s - f i r m o r t a l i t y d u e t o A. ostoyae t e n d e d to be l o w e r i n the 4 4 4 4 E p a n d the c o n t r o l , a n d h i g h e s t i n t he 0 E p t rea tmen t . F o u r t h , m i x e d - s p e c i e s s t a n d s o f i n t e r i o r D o u g l a s - f i r a n d p a p e r b i r c h h a v e b e e n f o u n d to h a v e f o u r t i m e s h i g h e r p o p u l a t i o n s o f Pseudomonas fluorescens, a p l a n t - g r o w t h p r o m o t i n g r h i z o b a c t e r i u m w i t h s t ra i ns a n t a g o n i s t i c to A. ostoyae in vitro, t h a n p u r e s t a n d s o f D o u g l a s - f i r ( D e L o n g et a l . 2002). D e l o n g et a l . (2002) f o u n d that p o p u l a t i o n s o f P. fluorescens w e r e p o s i t i v e l y c o r r e l a t e d w i t h b a s a l a r e a o f p a p e r b i r c h i n m i x e d s t a n d s , a n d n e g a t i v e l y c o r r e l a t e d w i t h that o f D o u g l a s - f i r . I n t h i s s t u d y , r e d u c t i o n s i n p a p e r b i r c h d e n s i t y f o l l o w i n g t h i n n i n g m a y h a v e n e g a t i v e l y a f f e c t e d the b e l o w g r o u n d m i c r o b i a l c o m m u n i t y , i n c r e a s i n g s t a n d s u s c e p t i b i l i t y to Armillaria r o o t d i s e a s e . T h i s s u p p o r t s p r e v i o u s s t u d i e s s h o w i n g r e d u c e d i n c i d e n c e o f Armillaria r o o t d i s e a s e , a n d r e d u c e d c o n i f e r m o r t a l i t y d u e to A. ostoyae, i n m i x e d -72 species stands compared to pure species stands (Morrison et al. 1988; Woods 1994; Gerlach et al. 1997). 4.3 Physiological Response of Interior Douglas-fir Mean net photosynthetic rate of interior Douglas-fir cut branches sampled in 2001 was not significantly different among treatments. Rates were within the values for evergreen conifers (Larcher 1980, cited in Guy 1999; Salisbury and Ross 1985). The lack of treatment effect suggests that physiological responses of interior Douglas-fir were delayed or highly variable or, more likely, that there was an artifact introduced in the measurements. The cut-branch technique was used in this study to facilitate sampling of tall trees under uniform conditions, but the procedure may have yielded results unrepresentative of treatment conditions for the following reasons. Light was not a limiting factor for each cut-branch sample. However, the treatment-to-treatment variation in light conditions may not be adequately represented using the steady-state light source. For instance, branches collected from the moderately thinned (1111 Ep), lightly thinned (4444 Ep) and control treatments, which are subject to increased shading by adjacent overtopping paper birch, may actually have lower photosynthetic rates while attached to the stem under natural light conditions. Tests performed on interior Douglas-fir within the 0 Ep treatment buffer suggested that placing the cut branches in the full sunlight during the measurement period would not significantly alter the maximum photosynthetic rate of the leaves on the cut branches as compared to attached branches. In a separate test (see Appendix: Cut-branch Technique Test) conducted on August 09, 2001, net photosynthetic rate of attached interior Douglas-fir branches did not differ from (a) the first cut-branch measurement taken immediately after harvesting each attached branch, (b) the mean cut-branch measurements taken between 1 hour 30 minutes and 73 3 hours 25 minutes after harvesting each attached branch, and (c) the mean cut-branch measurements taken between 09:30 and 11:50 hours. It is unknown, however, whether this relationship also existed in the remaining treatments. Performing the same test on interior Douglas-fir in the remaining paper birch density treatments would have addressed this concern. Second, water was not a limiting factor for the interior Douglas-fir cut-branch samples. The level of the water in the vials was monitored during the collection process and the measurement period to ensure the cut surfaces were constantly submerged to maintain the negative hydrostatic pressure (i.e. tension) in the xylem column, thereby eliminating the internal water deficit of the cut branch so that leaf gas exchange measurements could be taken (Kozlowski 1971). In contrast, the mean soil moisture content in 2001 of the sampled interior Douglas-fir, which ranged from 17.23% to 10.12% and tended to decrease with increasing birch density (0 Ep > 400 Ep > 1111 Ep > 4444 Ep > Control), was potentially a limiting factor to photosynthesis (Brady 1990). These trees were likely experiencing internal water deficits within this range. If the leaf gas exchange of the attached branches had been measured, the maximum net photosynthetic rate may not have been attained. Xylem water potential (y/) measurements taken pre-dawn and midday of same sampled interior Douglas-fir would have provided an insight into the "water status" of the trees in each treatment. Well-watered trees whose water potential is between -0.2 to -0.6 megapascals (MPa), given adequate available light and CO2, would photosynthesize. Lower (more negative) water potential measurements would translate into increased water stress for the trees, inhibiting photosynthesis (Kozlowski 1971). Therefore, leaf gas exchange of cut branches of interior Douglas-fir experiencing mid-day water stress may not reflect the physiological response of the trees from the treatment, or treatments, in their natural environment. I tried to gather pre-dawn xylem water potential measurements, however it was physically impossible to move around the plots in the middle of the night due to the rugged terrain. 74 Foliar nitrogen (N) concentration did not differ significantly among treatments in September 2000. The overall mean foliar N concentration was 1.27%, which is similar to other studies of Douglas-fir saplings (e.g. Bauerle et al. 1999). Foliar N is directly correlated with net photosynthetic rate (Wang et al. 1995), and the stability of foliar N in this study may partly account for the weak interior Douglas-fir photosynthesis response to the birch density reduction treatments. In this study, the specific leaf area (cm g") of the interior Douglas-fir sampled in 2000 significantly increased with increasing paper birch density and decreasing light availability. This is consistent with other studies where specific leaf area was strongly negatively correlated with light availability in the stand (Tucker and Emmingham 1977; Tucker et al. 1987; Klinka et al. 1992; Chen et al. 1996). Under low light conditions plants will increase specific leaf area and allocate more carbon to shoots (i.e. large leaf surfaces) for increased light absorption efficiency (Boardman 1977, cited in Man and Lieffers 1997). In 2001, the overall mean specific leaf area of the interior Douglas-fir sampled across the treatments was 55% lower than in 2000 (26.31 cm2 g"1 in 2001 versus 58.56 cm2 g"1 in 2000). The difference was due to the smaller mean leaf area of the needles collected in 2001 (13.61 cm 1 2 1 2 1 2 1 g" ± 0.36 cm g" ) versus 2000 (29.69 cm g" ± 0.88 cm g"), not due to changes in average leaf weight, which was identical in 2000 and 2001 (0.52 g ± 0.02 g). To better utilize available light, Cole and Newton (1986) found that five-year-old coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) seedlings had higher specific leaf area and a greater proportion of shade needles when planted into high densities of over-topping red alder (Alnus rubra Bong.), compared with treatments where it was planted into high-density of Douglas-fir only, or into Douglas-fir - grass treatments. Chen et al. (1996) also found that under decreasing light availability the specific leaf area of interior Douglas-fir saplings increased allowing the saplings to be more efficient in capturing available light in low-light environments. 75 The ability of interior Douglas-fir to adapt to a changed environment, such as that caused by a decrease in paper birch density, is a function of "phenotypic plasticity" (Guy 1999). Studies comparing the ability of shade-tolerant and shade-intolerant conifers to adapt to changing understory light environments have found that shade-tolerant conifers were able to make greater crown morphological changes (greater plasticity) along a light gradient compared with shade-intolerant conifers (Carter and Klinka 1992; O'Connell and Kelty 1994; Chen et al. 1996). Interior Douglas-fir, for example, allocated more biomass to above-ground growth in low light conditions compared to high light conditions, whereas shade-intolerant ponderosa pine did not exhibit any plasticity in biomass allocation (Chen et al. 1996). In this study, interior Douglas-fir exhibited plasticity by decreasing specific leaf area in response to increasing light availability with increasing paper birch thinning. Interestingly, in 2001, the mean specific leaf area of interior Douglas-fir also declined in the control, but not as much as in the other treatments. This may be explained by the increase in interior Douglas-fir height relative to neighboring paper birch, resulting in more available light incident on the top three whorls of the saplings, which is where the samples were harvested. 4.4 Resource Availability to Interior Douglas-fir 4.4.1 Light A vailability Light is considered to be one of the most important resources for plant growth (Cannell and Grace 1993; Gendron et al. 1998). Paper birch competes with interior Douglas-fir by overtopping it and reducing light availability, particularly on moist, productive sites (Comeau et al. 1998; Simard and Sachs 2002, submitted). In low light environments, interior Douglas-fir, a moderately shade-tolerant species (Hermann and Lavender 1990), allocates more photosynthate to lateral branch growth than to terminal leader growth in order to capture more light (Oliver and 76 Larson 1996; Chen et al. 1996; Williams et al. 1999). In this study, interior Douglas-fir mean diameter increment increased with increasing light availability (and decreasing paper birch density), agreeing with other studies that examined thinning responses in mixed ICH stands (Comeau et al. 1998; Simard and Hannam 2000; Simard et al. 2001). One exception was in the moderately thinned treatment (1111 Ep), where diameter increment of interior Douglas-fir responded similarly to saplings in the control despite having approximately 50% higher light transmittance. Mean relative diameter growth rate in the moderately thinned treatment tended to be higher than in the control and lightly thinned treatment (4444 Ep), however, suggesting that interior Douglas-fir was responding to increased light availability, despite initially being suppressed when the treatments were initiated in 1999. Several techniques have been used by researchers to evaluate light conditions beneath the forest canopy (Canham et al. 1990; Chazdon 1992; Comeau et al. 1993; Oberbauer et al. 1993; Rich et al. 1993; Brown and Parker 1994; Easter and Spies 1994; Messier and Puttonen 1995; Chen 1997; Comeau et al. 1998; Gendron et al. 1998). They include: (a) the use of photodiodes connected to dataloggers that measure PPFD continuously over the growing season, (b) handheld light sensors that provide instantaneous below- and above-canopy measurements, (c) hemispherical canopy photographs, and (d) instantaneous diffuse non-interceptance (DIFN) using the LAI-2000 Plant Canopy Analyzer. In this study, understory (1.3 meters above the ground) PPFD was measured using (a) hemispherical canopy photographs, and (b) a handheld light sensor (ceptometer). Hemispherical canopy photographs taken on homogeneous overcast days capture diffuse light (e.g. from all parts of the sky) incident above and below the canopy, which is uniform in space and time (Anderson 1964; Reifsnyder et al. 1971; Oke 1987; Messier and Puttonen 1995; Parent and Messier 1996; Williams et al. 1999). Ceptometer measurements collected on a uniformly sunny day capture diffuse light and direct light (e.g. from the full sun 77 and light reflected off vegetation), which can be comparatively variable (Anderson 1970; Hutchison and Matt 1976; Canham et al. 1990; Messier and Puttonen 1995; Gendron et al. 1998). This variability can be reduced if ceptometer measurements are collected between 10:00 and 14:00 under uniformly sunny skies in July and August, when the sun is directly overhead, thereby minimizing the influence of self-shading, canopy structure (e.g. foliage distribution, canopy height and quantity of stems or branches of neighboring broadleaf or conifer saplings) or gap size during that time period (Gendron et al. 1998). Other researchers recommend that quick and accurate instantaneous measurements of %PPFD can be obtained by taking above- and below-canopy measurements simultaneously. This would be achieved by using a PPFD sensor linked to a data logger to record above-canopy measurements, and a handheld light sensor to record below-canopy measurements. The sky must be homogenously overcast, and the sun must not be visible, thereby allowing for the recording of diffuse light. When these conditions are met, instantaneous measurements could be collected at anytime during the day and would adequately estimate mean daily %PPFD under the forest canopy (Messier and Puttonen 1995; Parent and Messier 1996). The hemispherical canopy photograph technique tended to yield consistently higher average percentages of PPFD than the handheld light sensor, probably because the photographs were taken at randomly selected points and were not subject to shading by nearby interior Douglas-fir. By contrast, the handheld light sensor readings were taken at the outside edge of the crown of randomly selected interior Douglas-fir and some were subject to self-shading by the sampled interior Douglas-fir. 4.4.2 Soil Moisture A vailability Soil moisture content in September 2001 significantly decreased with increasing paper 78 birch density, reflecting the increased demand and faster depletion rate of soil water due to higher evapotranspiration in the higher density treatments. In this study, competition for soil moisture with increasing paper birch density may have contributed to the lower mean diameter increment of the interior Douglas-fir in the control. This is consistent with Shainsky and Radosevich (1992) who found that increasing red alder densities resulted in reduced soil moisture and decreased relative growth rates of Douglas-fir seedlings. Although the interior Douglas-fir in the moderately thinned treatment (1111 Ep) had a lower stem diameter increment when compared to the lightly thinned treatment (4444 Ep), the two treatments had similar soil moisture content, on average. The growth difference is probably a reflection of the pretreatment growth differences of the saplings in which the interior Douglas-fir in the moderately thinned treatment (1111 Ep) were by chance more suppressed. In the ICH wet-belt zone, soil moisture is not usually considered a limiting resource during the majority of the growing season for interior Douglas-fir. One reason is that there is ample growing season precipitation in the zone (mean: 305 mm; range: 194 to 461 mm) (Lloyd et al. 1990), and another is that interior Douglas-fir is moderately drought tolerant because most lateral roots and fine roots (<0.5 cm) are located in the upper 20 cm of the soil (Hermann and Lavender 1990). Where treatment differences exist, however, they should be more evident in late summer due to soil surface evaporation and leaf surface transpiration. That was the case in this study, where soil moisture treatment values declined well below those considered adequate (20-30%) for good plant growth (Brady 1990). While the measurements provided a snapshot of soil moisture content during the dry period of the summer, they did not provide a clear picture of soil moisture availability to the stand throughout the growing season. 79 4.4.3 Soil Nutrients In this study, available soil nitrogen (ammonium (NH/) and nitrate (NO3')), generally the most limiting nutrient to plant growth (Killman 1994), was not measured because of insufficient time during the field seasons. Based on the uniformity in the interior Douglas-fir foliar N concentrations across treatments in 2001, however, soil nitrogen availability may have been unaffected by treatment between 1999 and 2001. At the time this study was initiated, the uniformly high density of paper birch and the uniform spacing of the interior Douglas-fir probably resulted in homogeneous soil nitrogen capital across treatments. Short-term changes in birch density probably were insufficient to affect the large nitrogen capital characteristic of ICH sites (Wang et al. 1996), although changes in microclimatic conditions may have been sufficient to improve N availability (Forge and Simard 2001). Examining mean nitrogen concentration in the interior Douglas-fir foliage in 2000 may not reflect changes in soil nitrogen uptake across the treatments, however. Gymnosperms generally reduce most available nitrogen in their roots whereas angiosperms reduce it in their leaves (Guy 1999). Paper birch foliar N concentrations may therefore better reflect soil N availability, but unfortunately it was measured only in 1999, a few months after the treatments were applied. Tree species nitrogen reduction patterns may help explain why mean foliar nitrogen concentration of paper birch is consistently higher than that of interior Douglas-fir (Simard et al. 1997; Thomas and Prescott 2000). I expect that nitrogen availability will increase with increasing paper birch thinning intensity in time because (a) fewer trees are accessing these resources, (b) more solar radiation is reaching the forest floor, resulting in higher soil temperatures and better conditions for N mineralization, and (c) soil moisture content is increasing, improving conditions for N cycling through the soil foodweb (Carcamo et al. 2001). 80 4.5 Paper Birch Responses to Treatments 4.5.1 Growth Analyzing the dominant paper birch trees (tallest 250 stems ha"1) allowed me to examine those birch trees most likely to dominate the future broadleaf stand. It also helped remove any size effects that may have been introduced by the act of thinning. Because thinning was applied using tree size as well as spacing criteria, however, trees of all canopy classes were removed, with an emphasis on thinning from below. As a result of this mixed approach, dominant birch trees in the heavily thinned treatment (400 Ep) were smaller than those in the remaining treatments before and after thinning was applied. Despite the smaller initial size of the birch in the 400 Ep treatment, mean relative diameter growth rate increased with decreasing birch density. This growth response is probably due to (a) increased photosynthetically active radiation under the canopy, and (b) increased soil moisture availability with increased thinning intensity, and is consistent with the findings of other studies (Roberge 1988; Wang et al. 1995; Peterson et al. 1997b). Mean height-to-live crown was the lowest in the heavily thinned treatment (400 Ep), compared to the birch in the control in 2001, indicating that lower branches were being retained in the more open canopy conditions created by thinning. Mean diameter increment of the dominant paper birch also tended to increase with decreasing birch density, although the treatment rankings were not systematic. This result generally agrees with Simard et al. (2003, submitted) who found five years after thinning that mean diameter increment of dominant and co-dominant paper birch increased with increased paper birch thinning intensity. In contrast, mean height and mean height increment were not affected by the paper birch density treatments, in this study, during 1999 to 2001, agreeing with other longer-term, thinning studies that quantify the insensitivity of height to density (Graham 1998; Simard and Hannam 2000; Simard et al. 2003). 81 "Thinning shock", expressed as a reduction in relative growth rate and net photosynthetic rate (Harrington and Reukema 1983, cited in Wang et al. 1995), was not evident among thinned birch in this study, which is similar to the findings of Wang et al. (1995), but contrasts with Pothier and Margolis (1991, cited in Wang et al. 1995). Timing of thinning was cited as a factor in Wang et al.'s (1995) study, which took place in the month of June, allowing the birch to "acclimate to the increased light conditions" before measurements were collected the next growing season. In this study, the paper birch density treatments were also implemented in June, but leaf gas exchange measurements were taken in September of the same year, so insufficient time between thinning and measuring could explain why thinning shock was not detected. The photosynthetic capacity of the dominant paper birch sampled in this study were within the typical maximum values for net photosynthetic rate, ranging from 8.75 to 11.90 pmol CO2 m"2 s"1 (Larcher 1980, cited in Guy 1999). Although not significant, dominant birch in the heavily thinned treatment (400 Ep) tended to have the highest mean net photosynthetic rate compared with the other treatments, corresponding with the findings of Wang et al. (1995). In this study, the physiological measurements were collected two months after the paper birch density treatments were brushed, so an inadequate amount of time may have passed to observe a significant physiological response to the changed environment. 4.5.2 Survival - Moose Damage Considerable main stem breakage (at 1.54 - 2.40 meter height) by moose occurred in the heavily thinned treatment (400 Ep) (excluding Burton Creek), whereas little occurred in the other treatments between 1999 and 2001. This appears to be related to the increased moose access in the lower density treatment, and has been reported in other birch thinning studies (Simard and Heineman 1996b; Karlsson and Albrektson 2001; Simard et al. 2003). Moose bend the stems to 82 reach browse in winter, resulting in frequent breakage of the main stem (Peterson et al. 1997a). Main stem breakage was not different among treatments because of high variability in moose use among sites. 4.6 Conclusions and Management Implications 4.6.1 Concluding Statement About Results This master's thesis examined the effects of paper birch density on the (a) performance of interior Douglas-fir, (b) survival of interior Douglas-fir and, (c) resource availability to interior Douglas-fir when the two species are grown in mixture in the BC interior wet-belt between 1999 and 2001. It builds on existing knowledge of early stand dynamics and treatments in the serai forests of the interior wet belt (Simard 1990). It also builds on the research of Simard and Sachs (2002, submitted), who found that competition thresholds for interior Douglas-fir averaged 4000 stems ha"1 where all paper birch were included and 2500 stems ha"1 where taller birch could be retained without considerable diameter growth loss to associated conifers. This research project is the next step in improving the accuracy of the paper birch density thresholds and identifying stand composition conditions that are indicative of healthy interior Douglas-fir/paper birch mixtures. In doing so, the study aims to benefit operational forestry by (a) providing information for the development of mixedwood stocking standards in British Columbia, (b) providing information of mixture management techniques that can help mitigate spread of Armillaria root disease, (c) helping identify management options for the ICH and IDF wet-belt forests that maintain biodiversity values similar to the unmanaged landscape, and (d) contributing information toward identification of free growing standards that encourage sustainable forest management. The results of this study suggest that any density reduction of paper birch below and 83 including 4444 stems ha"1 benefited the interior Douglas-fir growth performance. These benefits to growth will likely increase with time, particularly in the lower paper birch density treatments, as longer-term competition studies generally found that conifer survival and growth are enhanced with decreasing paper birch density (Comeau et al. 1999; Simard et al. 2001). To minimize the spread of Armillaria ostoyae, the results suggest that no brushing (control) would be the best alternative. However, if the interior Douglas-fir growth is suppressed, then minimal brushing to release suppressed trees would increase growth, yet minimize mortality (see Figure 3-1 and 3-4). Further assessment of this will be needed to strengthen the short-term findings. Resource availability, light and soil moisture, in the low (400 Ep), medium (1111 Ep) and high (4444 Ep) density paper birch treatments appear to have been sufficient for favorable growth of the interior Douglas-fir during the two-year study period. In time, this study will contribute valuable information toward finding a balance between improved interior Douglas-fir growth response and increased Armillaria root disease as thinning intensity increases on these ICH and IDF wet-belt sites. In addition to examining conifer productivity, this study also investigated thinning effects on paper birch productivity. Currently, the vast broadleaf resources in mixed stands are underutilized (e.g. less than 10% of province-wide potential (Comeau et al. 1999)), and are not included in the annual allowable cut (AAC)(B.C. Min. For. 2002). The results from this study indicate that maintenance of 4444 stems ha"1 of dominant paper birch has not been detrimental to the performance of the birch, at this stage of growth. 4.6.2 Management Implications These results are applicable to the productivity, environmental stewardship and silviculture management of the highly productive ICH and IDF wet-belt forests in British 8 4 Columbia. Considering the short-term nature of the results, I propose that the following management regime is appropriate for management of mixedwood stand for sawlog production of conifers and broadleaf trees. This regime is based on results from this study, the literature, and personal observations of management in mixed stands of varying ages in the interior wet-belt. a. 5- to 15-Years Post-Establishment: In this age range, paper birch may be thinned to below 4444 stems ha"1 in adequately stocked interior Douglas-fir plantations (e.g. approximately 1,200 stems ha"1). On Armillaria root disease-free sites, thinning paper birch to as low as 400 stems ha"1 would likely benefit the interior Douglas-fir by providing more growing space and resources, while retaining a component of paper birch for biodiversity values. Single, straight-stem dominant or co-dominant paper birch trees should be retained, with half the paper birch height as living crown. Where multi-stem clumps are present, rather than single stem birch, birch can be selected to leave based on the recommendations outlined in Peterson et al. (1997a) and observations in this study. b. 10- to 20-Years Pre-Harvest (of Paper Birch): Commercial thinning of paper birch may take place at this time, if the dominant birch height has reached 13-15 meters, as is performed in Finland (Mielikainen 1996), thereby providing an earlier financial return from the mixed stand. Healthy interior Douglas-fir should be released and, paper birch retained where active root disease centres exist (Morrision et al. 1991). Further thinning of paper birch past 35 years of age may be unproductive (Robertson et al. 1991). c. Year 60 - 80: Paper birch may be harvested when average stand stem diameter at breast height is 25.0 - 30.0 cm, where a proportion is reserved as seed trees for future regeneration (Cameron 1996; Mielikainen 1996). d. 80- 140 Years: Harvest interior Douglas-fir for production forestry. This time frame 85 can vary depending on social and stand management objectives (e.g. maintenance of stand for old-growth), as well as the conditions of the stand and the surrounding forest landscape. This proposed management regime is aimed toward releasing competitively stressed interior Douglas-fir while maintaining an adequate density of paper birch that may help mitigate the spread of A. ostoyae through the stand, resulting in improved growth performance and lower interior Douglas-fir mortality (Morrison et al. 1991). In addition, this management regime may (a) enhance habitat for wildlife and bird management, and ecosystem productivity, (b) provide a more aesthetically pleasing landscape in keeping with visual quality objectives and, (c) maintain the potential for harvesting a future crop of paper birch. It would result in a higher capital investment (e.g. planning and treatment costs) that may be partly reimbursed by revenue generated from the intermediate harvests of paper birch as the stand matures (Peterson et al. 1997a), and long-term revenue from increased stem volume due to reduced conifer mortality. If the paper birch were initially thinned to 1111- or 4444-stems ha"1, this management regime would not meet free growing standards with respect to (a) the current allowable countable broadleaf component, or (b) the current maximum time period for a free growing stand to be established (B.C. Min. For. 2000). The free growing standards recognize the importance of establishing or retaining broadleaf trees within a stand to meet silvicultural objectives, such as a "short-rotation interim crop to manage for root rot centers" or "to meet other resource objectives such as biodiversity or wildlife habitat". However, free growing stands allow only 600 broadleaf 1 2 stems ha" (i.e., three trees in a 50 m plot) where the primary crop tree is interior Douglas-fir. In addition, the interior Douglas-fir trees in these stands must meet the required minimum height (e.g. 125% and 150% of the paper birch height within a 1 meter radius in the ICH and IDF sites, respectively) within approximately 15 years post-harvesting, a condition unlikely to be met in this scenario. 86 In this study, results to-date do not indicate that maintaining 400 stems ha"1 (e.g. two stems in a 50 m plot) of dominant paper birch would be detrimental to the performance of interior Douglas-fir in the short-term. Therefore, it would be possible to achieve free growing status 15 years following harvesting for the stands at these sites if the stands were thinned to 400 - 600 stems ha"1. The main disadvantages of this approach are the loss of a potential commercial paper birch harvest as well as lowered stocking of interior Douglas-fir caused by Armillaria root disease. Longer-term observation of these study sites will provide a clearer understanding of the role the paper birch densities play in the spread of Armillaria. Finally, the early results of this study suggest that selective manual brushing treatments can be applied to release competitively stressed interior Douglas-fir on recently harvested wet-belt sites. The method of thinning (e.g. manual cutting versus cut stump-glyphosate) broadleaf species, however, may affect spread of Armillaria root disease as well as the performance of the interior Douglas-fir over time. Simard et al. (2001) found that the cut stump-glyphosate thinning methods resulted in (a) lower root disease incidence, (b) lower broadleaf sprouting heights, and (c) larger growth responses among interior Douglas-fir five-years after thinning, compared to manual cutting. 4.6.3 Future Directions for the Study This study provides the groundwork for continued assessment of the effect of paper birch thinning on the performance of interior Douglas-fir in ICH and IDF wet-belt forests. It also provides the foundation for further analysis of how the dominant paper birch responds in mixedwood stands. The next step in this research should be to collect survival and growth measurements in August/September, 2004, and 2009 (five- and ten-years after treatment initiation, respectively) to monitor (a) the performance of the interior Douglas-fir and paper 87 birch, and (b) the incidence of Armillaria root disease in each treatment. Collection of survival and growth measurements could be performed every 10 years thereafter, as funding permits. Analysis and reporting of the five- and ten-year measurement periods should be conducted, peer-reviewed and presented to silviculture foresters to ensure the most recent scientifically-based results are available for management of mixedwood stands. Longer-term investigation will further strengthen the findings and help provide scientific and ecological bases for management of conifer/broadleaf mixtures. Ideally, these measurement periods should be continued for the full-rotation to provide growth and stand development information for maturing mixedwood stands. However, the treatment plots may be too small to adequately monitor long term growth and yield, and too close together to avoid treatment edge effects in the measurement plot area. This study also provides an opportunity for researchers to assess the effect of the paper birch density treatments on the incidence of A. ostoyae on the interior Douglas-fir in these wet-belt forests. Trees that were alive in 1999, but have subsequently died due to infection by Armillaria root disease, are recorded. Therefore, stem mapping of the treatments in 2003/2004 would allow tracking of active and inactive disease centers over time based on aboveground symptoms. More in-depth analysis of the resource availability (e.g. light, soil moisture and soil nutrients) to both interior Douglas-fir and paper birch could also be performed to improve our understanding of interspecific competition mechanisms. A better understanding of mechanisms would lead to improved management regimes over a broader range of sites than those included in this study. For instance, Wang et al. (1996) recommended management of paper birch thinning intensities on young forest plantations so that nutrient input from the birch leaves, branches, and bark will benefit the remaining stand over time. This study provides an opportunity for 88 researchers to examine treatment effects on rates of nitrogen availability and their effects on long-term productivity. Finally, the study sites provide opportunities for researchers to observe the effect of the paper birch density treatments on interior Douglas-fir plantations on other biota, such as the soil microbial community and wildlife (e.g. small mammals, birds, ungulates). 4.6.4 Future Directions for Mixture Silviculture Research Further studies are needed to refine competition indices and paper birch thresholds for growth and survival of multi-species complex stands in the interior of British Columbia. Similar research examining the effects of aspen density on the performance of conifers is being conducted in northern British Columbia. Further assessment of the thinning methods, manual brushing versus cut-stump glyphosate, when applied to these varying broadleaf density treatments would be very informative, not only in examining the effect of the brushing methods on the performance of the target species, but also the effect of the methods on the incidence and spread of root disease through the stand. Finally, studies are needed to measure the effect of treatments on mixedwood stands as they relate to biodiversity, carbon sequestration, growth and yield, wildlife management, and wood quality. In the last decade, great strides have been made in setting up long-term research sites in the interior of British Columbia specifically to examine the mixedwood silviculture applications. The primary goal of this study was to determine the effect of paper birch density on the performance of interior Douglas-fir when the two are grown in mixture. By doing so, this study aimed to improve the accuracy of the paper birch density thresholds and ascertain the stand composition conditions that are indicative of healthy interior Douglas-fir/paper birch mixtures. The results of this study have provided, in the short term, evidence that modification of the free 89 growing standards for increasing the allowable broadleaf component on ICHmw3 and IDFmw2 variants should be considered. 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Various tree physiological responses can be tested, such as leaf gas exchange, foliar nitrogen concentration, and xylem water potential, either in the laboratory or in the field. For instance, leaf gas exchange measurements of fully expanded current-year leaves from seedlings, saplings and mature trees can be measured using a gas exchange system, from which net photosynthesis and stomatal conductance are calculated. Portable open gas exchange systems, such as the CIRAS-1 differential CO2/H2O infra-red gas analyzer system and a leaf cuvette (PP Systems, Haverhill, MA, USA) used in this study, are designed for field-use, as well as being functional in the lab. This equipment is very practical for measuring the leaf gas exchange of seedlings or saplings growing on level terrain. It is less functional for measuring leaf gas exchange of tall saplings and mature trees unless, for instance, scaffolding is constructed on the treatment plots to facilitate reaching the branches at various canopy levels (low-, mid- and upper-canopy)(e.g. Boreal Ecosystem-Atmosphere Study (BOREAS) in Manitoba, Canada (Sellers et al. 1995)). The use of a ladder to allow the researcher to reach various canopy heights to collect measurements using the portable open gas exchange system, while effective on level terrain where tree height is within the expansion capacity of the ladder, is less efficient if the terrain is rugged and the slope is not level. An alternative to collecting leaf gas exchange measurements of attached branches on tall saplings and mature trees has been to collect the measurements of detached branches, using a cut-branch technique (Dang et al. 1997). Cut-branch techniques have been used previously to 101 examine leaf gas exchange of Sitka spruce (e.g. Watts and Neilson 1978, and Beadle et al. 1979, 1981, cited in Dang et al. 1997). Dang et al. (1997) conducted two tests to "establish the limits of the cut-branch technique". The first test examined the differences in net photosynthesis and stomatal conductance between cut branches and attached (in situ) branches of three tree species: (1) 75-year-old black spruce (Picea mariana (Mill.) B.S.P.); (2) 58-year-old jack pine (Pinus banksiana Lamb.); and (3) 70- to 80-year-old aspen (Populus tremuloides Michx.) within the BOREAS Northern Study Area between Nelson House and Thompson, Manitoba, Canada (56° N, 99° W). They found "there were no significant differences (P>0.35) in net photosynthesis and stomatal conductance between the cut and in situ branches in any of the species". The second test examined the stability of net photosynthesis and stomatal conductance of cut branches, from the same stands of black spruce, jack pine and aspen, in the lab over a 14-hour time period to obtain response curves. With black spruce and jack pine, there were no significant changes in the hourly net photosynthesis or stomatal conductance during the 14-hour time period. With aspen, net photosynthesis was "stable for the first 10 hours and then started to decline". Based on the findings of Dang et al. (1997), I considered the possibility of using the cut-branch technique to collect and measure leaf gas exchange of branches (needles) from the upper canopy of randomly sampled interior Douglas-fir in each treatment. In this study, the reason for using the cut-branch technique, rather than measuring attached branches, was the difficulty associated with (a) moving from tree-to-tree within treatments over rugged and steep terrain, while carrying the portable gas exchange system with the cuvette and 10-foot tripod orchard ladder, (b) reaching the upper canopy (i.e. if the upper canopy tree height exceeded the ladder height), and (c) collecting measurements within a short enough time frame to eliminate sampling bias between the treatments. 102 While the findings of Dang et al. (1997) indicated that using the cut-branch technique could provide stable net photosynthesis and stomatal conductance measurements of the two conifer and one broadleaf species, the authors cautioned scaling the cut-branch data to represent a whole-tree response to the environmental conditions, because "the physiological performance of a given branch may also be influenced by the environmental conditions and physiological behavior of other branches on the same tree" (Whitehead et al. 1996, cited in Dang et al. 1997). Also, the time period between harvesting the cut branch and measuring the leaf gas exchange was less than 30 minutes. Therefore, the measurements "do not take into account acclimation of or damage to the foliage that occurs over a longer period of time" (Dang et al. 1997). The purpose of this test was as follows: (a) to examine if leaf gas exchange differs significantly (a = 0.05) when taking a measurement of foliage on a branch while it is attached to the interior Douglas-fir stem versus taking a measurement of interior Douglas-fir foliage on a branch after it has been detached from the tree using the cut-branch technique, and (b) to determine the time period in which the leaf gas exchange measurements of the foliage on the cut branch remain stable. 6.2 Materials and Methods 6.2.1 Study Area and Experiment Details The study was conducted on August 09, 2001 at the Gold Creek 1 site between 8:30 am and 4:15 pm. Four interior Douglas-fir saplings from the buffer of treatment 0 Ep were selected based on having uniformly healthy branches. A fifth interior Douglas-fir sapling was added to the sample when it was determined that leaf gas exchange measurements of five samples could be measured every 30 minutes. The interior Douglas-fir ranged in height from 2.5 m to 4.6 m, with stem diameter from 2.1 cm to 5.9 cm. 103 6.2.2 Leaf Gas Exchange Measurements Leaf gas exchange was measured using the portable open CIRAS-1 differential C O 2 / H 2 O infra-red gas analyzer system with a narrow-leaf Parkinson leaf cuvette (PP Systems, Haverhill, MA, USA). The CIRAS-1 inlet C0 2 concentration was set at 400 ppm and the inlet H20 concentration was set at 70% of ambient. The weather was clear, sunny and hot (temperature ranged from 25°C to 35°C). One lateral shoot bearing fully expanded current year's foliage was selected from a south-facing branch located on the third whorl from the top of each interior Douglas-fir. The foliage was measured in situ (on the attached branch). The location of the cuvette was marked on the branch with felt pen so all-subsequent measurements would take place at the same location after the branch was harvested. Immediately following the measurement of the attached branch, it was harvested (cut approximately 2 cm from the main stem). The cut branch was immediately recut under water at least 5 cm from the cut end, with the cut surface submerged and the foliage kept above the water. While the cut surface was still submerged the branch was placed in a vial of creek water and the leaf gas exchange of the cut branch was immediately measured. This process was repeated for the remaining four interior Douglas-fir. The first two measurements (attached and cut) of the first four interior Douglas-fir took place between 08:50 and 09:40, and the fifth interior Douglas-fir between 10:00 and 10:11, under saturating light (780 //mol m'2 s"1 < PPFD < 1440 //mol m"2 s"1). To maintain a steady source of light on the cut branches for subsequent measurements, as would be done if the cut-branch technique were applied in this study, a 75-watt high-pressure sodium lamp was used to saturate 9 1 9 1 the leaf cuvette (857 //mol m" s" < PPFD <1568 //mol m" s"). The needles were placed in the cuvette in a manner that reduced self-shading. Once the C O 2 concentration within the cuvette * * 2 1 had stabilized, internal C O 2 concentration (ppm), photosynthetic rate (//mol C O 2 m" s"), 104 2 1 2 1 stomatal conductance (mmol H2O m" s"), and transpiration rate (mmol H2O m" s") were simultaneously recorded and the data stored in the CIRAS-1. The leaf gas exchange measurement of each cut branch took an average of 5.75 minutes, ranging from three minutes to 13 minutes, of which two measurements took more than nine minutes each (12 minutes and 13 minutes, respectively). Between measurements the cut branches were stored in a manner that was similar to the environmental state of the branches on the respective interior Douglas-fir trees sampled, so in this case full sunlight. The level of the water in the vials was monitored throughout the day to ensure the cut surfaces were constantly submerged. The branches were measured every 31-33 minutes until 4:06 pm when the four batteries for the CIRAS-1 were depleted. After the last cut branch measurement of each sample was taken the foliage was removed from the branch and placed in individually labeled GLAD® Zipper plastic storage bags (17.8 cm x 20.3 cm). They were stored in the freezer until August 12, 2001, when the leaf area was determined. The leaf area (cm2) of each interior Douglas-fir foliage sample was measured by (a) capturing a JPEG image of the horizontally displayed (one side) needles using a Hewlett Packard® Scanjet 4300C flatbed scanner and, (b) analyzing the JPEG image to determine pixel count, which was converted to a standard unit (cm2) using Adobe® Photoshop® 3.0.5. Net photosynthetic rate and stomatal conductance for each interior Douglas-fir sample was recalculated based on the measured leaf area. 6.2.3 Statistical Analyses Paired t-tests4 (null hypothesis (H0): Udiff = 0; alternative hypothesis (Ha): Udiff ^ 0, where Udif f = H a - uc,) were used to determine differences between the individual interior Douglas-fir 4 S. Rollans, Ph.D. , Department o f Mathematics and Statistics, School o f Advanced Technologies and Mathematics, University College o f the Cariboo, pers. comm., June 2002. 105 attached branch calculations (pa) and the cut branch calculations (uc) of (a) net photosynthetic rate and (b) stomatal conductance as follows: Is there a significant difference between the individual attached branch measurements and the first cut-branch measurements? Is there a significant difference between the individual attached branch measurements and the cut-branch measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after harvesting each cut branch? This represents the time frame between harvesting the first cut branch sample and measuring the last randomly selected cut branch when using the cut-branch technique in the field. Is there a significant difference between the individual attached branch measurements and the cut-branch measurements taken between 09:30 and 11:50 hours? This corresponds with the time frame when the interior Douglas-fir leaf gas exchange measurements would be collected when the cut-branch technique is used in the field. 6.3 Results 6.3.1 Net Photosynthetic Rate The net photosynthetic rate of the attached branches did not differ significantly from the net photosynthetic rate of the first cut branch measurement taken immediately after harvesting each branch (n=5; t-statistic 2.29 < t-critical 2.78; Pr > |t|: 0.0841) (Figure 6-1). The net photosynthetic rate of the attached branch measurement did not differ from the mean cut-branch measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after harvesting each branch (n=5; t-statistic 1.63 < t-critical 2.78; Pr > |t|: 0.1782) (Figure 6-2). 106 v " 8.0 E 7.0 o U 6.0 I 5.0 ] t 4.0 -u 3.0 >> 2.0 ja i .u a I o.o • Attached branch • First cut branch Fdi #1 Fdi #2 Fdi #3 Tree number Fdi #4 Fdi #5 Figure 6-1. C o m p a r i s o n of the net photosynthetic rate (urnol C 0 2 m"2 s"') of attached branch measurements versus the first cut branch measurement on each sampled interior Douglas-fir (Fdi). 8.0 E 7.0 o Q 6.0 | 5'° ^ 3 4.0 * 2.0 o 1 1.0 c I o.o «> Attached branch • Mean cut branch Fdi # 1 Fdi #2 Fdi #3 Tree number Fdi #4 Fdi #5 Figure 6-2. C o m p a r i s o n o f the net photosynthetic rate (umol C 0 2 m"2 s"1) of interior Douglas-fir (Fdi) attached branches versus the mean cut branch measurements. T h e mean cut branch measurement represents the average of the measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after each o f the five branches were harvested. The net photosynthetic rate of the attached branch measurement did not differ from the mean net photosynthetic rate of the cut branch measurements taken between 09:30 and 11:50 hours ((n=5; t-statistic 2.18 < t-critical 2.78; Pr > |t|: 0.0942) (Figure 6-3). 107 o u £ sg 8.0 7.0 6.0 5.0 4.0 '•§ 3.0 = O J : D. 2.0 1.0 0.0 Fdi#l • Attached branch • Mean cut branch Fdi #2 Fdi #3 Fdi #4 Tree number Fdi #5 Figure 6-3. C o m p a r i s o n of the net photosynthetic rate (umol C 0 2 m"2 s"1) o f interior Douglas-fir (Fdi) attached branch versus the mean cut branch measurements. T h e mean cut branch measurement represents the average o f the measurements taken between 09:30 and 11:50 hours on the same day to correspond with the time frame that leaf gas exchange measurements would take place when using the cut-branch technique in the field. Figures 6-4 and 6-5 illustrate the individual net photosynthetic rate readings and the time when each reading was taken. The first cut-branch measurement, taken immediately after the attached branch measurement, showed an increase in net photosynthetic rate for each of the interior Douglas-fir, after which, the net photosynthetic rate fluctuations varied from tree-to-tree. Fdi #1, #2, #4 and #5 cut-branch readings remain fairly stable after harvesting until between 12:00 and 13:00 hours, when the readings of each branch, with the exception of #5, fluctuated more dramatically. The net photosynthetic rate of sample Fdi #5 fluctuated minimally, and appeared to stabilize as the day progressed. The greatest increase in the net photosynthetic rate of the first cut-branch reading immediately following the attached branch measurement occurred on Fdi #3 (-2.1 pmol C0 2 m"2 s"1 to -5.6 pmol C0 2 m~2 s"')(Figure 6-4c). Unlike the other four interior Douglas-fir trees sampled, the net photosynthetic rate of sample Fdi #3 steadily decreased after the 10:27 measurement and did not display the erratic fluctuations exhibited by samples Fdi #1, Fdi #2, and Fdi #4. 108 10.0 1 9.0 8.0 -7.0 -6.0 -5.0 -4.0 3.0 -2.0 1.0 0.0 10.0 E 9.0 CO: 8.0 (umol 7.0 -6.0 -rate 5.0 -4.0 tosyntht 3.0 2.0 Net phol 1.0 0.0 -8:55 9:06 9:48 10:18 10:47 11:19 11:49 12:22 12:55 13:29 14:10 14:43 15:33 9:12 9:18 9:57 10:24 10:50 11:24 11:55 12:26 13:03 13:35 14:17 14:53 15:41 9:26 9:33 10:01 10:27 10:53 11:27 12:00 12:32 13:07 13:56 14:21 14:59 15:49 Time (hrsrmin) net photosynthetic rate recorded Figure 6-4. Net photosynthetic rate (umol C0 2 m~2 s"1) o f interior Douglas-f ir (Fdi) attached branch (open diamond) a nd cut branches (closed diamonds) for samples (a) F d i #1, (b) F d i #2, and (c) F d i #3. 109 9:12 9:18 9:57 10:24 10:50 11:24 11:55 12:26 13:03 13:35 14:17 14:53 15:41 9:26 9:33 10:01 10:27 10:53 11:27 12:00 12:32 13:07 13:56 14:21 14:59 15:49 Time (hrs:min) net photosynthetic rate recorded Figure 6-5. Net photosynthetic rate (umol C 0 2 m"2 s ') of interior Douglas-fir (Fdi) attached branch (open diamond) and cut branches (closed diamonds) for samples (d) F d i #4, and (e) F d i #5. 6.3.2 Stomatal Conductance The stomatal conductance of the attached branches did not differ significantly from the stomatal conductance of the first cut branch measurement (n=5; t-statistic 1.20 < t-critical 2.78; Pr > |||: 0.2977)(Figure 6-6). However, the variance (s2diff) was large: 520.22 mmol H20 m"2 s"1. 110 200.0 C 180.0 E 160.0 O ET 140.0 o | 120.0 -| | 100.0 | 80.0 TJ © 60.0 1 40.0 2 20.0 H 0.0 Fdi #1 • Attached branch • First cut branch Fdi #2 Fdi #3 Tree number Fdi #4 Fdi #5 Figure 6-6. C o m p a r i s o n of the stomatal conductance (mmol H 2 0 m 2 s"') o f attached branch versus first cut branch measurement on each sampled interior Douglas-fir (Fdi) . The stomatal conductance of the attached branches did not significantly differ from the mean stomatal conductance of the cut branch measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after harvesting each branch (n=5; t-statistic 2.29 < t-critical 2.78; Pr > |t|: 0.0830)(Figure 6-7), although, the variance (s2difr) was very large: 3353.27 mmol H20 m"2 s"1. The stomatal conductance of the attached branches did not differ significantly from the mean stomatal conductance of the cut branch measurements taken between 09:30 and 11:50 hours (n=5; t-statistic 1.67 < t-critical 2.78; Pr > |t|: 0.1702)(Figure 6-8). Then again, the variance (s diff) was very large: 3852.68 mmol H20 m s . 200.0 180.0 160.0 140.0 120.0 100.0 80.0 60.0 40.0 20.0 0.0 • Attached branch • Mean cut branch Fdi # 1 Fdi #2 Fdi #3 Tree number Fdi #4 Fdi #5 Figure 6-7. C o m p a r i s o n of the stomatal conductance (mmol H 2 0 m"2 s"1) of interior Douglas-fir (Fdi) attached branches versus the mean cut branch measurements. T h e mean cut branch measurement represents the average of the measurements taken between 1 hour 30 minutes and 3 hours 25 minutes after each of the five branches were harvested. 200.0 180.0 160.0 140.0 120.0 100.0 80.0 60.0 40.0 20.0 H 0.0 • Attached branch • Mean cut branch Fdi #1 Fdi #2 Fdi #3 Tree number Fdi #4 Fdi #5 Figure 6-8. C o m p a r i s o n o f the stomatal conductance (mmol H 2 0 m"2 s"1) of interior Douglas-fir (Fdi) attached branches versus the mean cut branch measurements. T h e mean cut branch measurement represents the average of the measurements taken between 09:30 and 11:50 hours on the same day to correspond with the time frame that leaf gas exchange measurements would take place when using the cut-branch technique in the field. 112 Figures 6-9 and 6-10 illustrate the individual stomatal conductance calculation based on the leaf gas exchange measurement and the time when each measurement was taken. With the exception of sample Fdi #3, the stomatal conductance of the remaining four interior Douglas-fir increased after the attached branch was harvested and the first cut branch measurement was taken. Within one hour of harvesting each branch, the stomatal conductance measurements are below 40.0 mmol H2O m"2 s"1 and remain so until the end of the testing session. 200.0 1 '» 180.0 E C 3T "0 160.0 -140.0 (mm 120.0 = 100.0 -—. 80.0 condi 60.0 a — 40.0 Stom; 20.0 Stom; 0.0 -8:55 9:06 9:48 10:18 10:47 11:19 11:49 12:22 12:55 13:29 14:10 14:43 15:33 9:12 9:18 9:57 10:24 10:50 11:24 11:55 12:26 13:03 13:35 14:17 14:53 15:41 T i m e (h rs :m in ) s tomatal conductance recorded Figure 6-9. Stomatal conductance (mmol H 20 m"2 s"1) o f interior Douglas-fir (Fdi) attached branch (open diamond) and cut branches (closed diamonds) for samples (a) F d i #1, and (b) F d i #2. 113 9:26 9:33 10:01 10:27 10:53 11:27 12:00 12:32 13:07 13:56 14:21 14:59 15:49 _r 200.0 -, E 180.0 0 160.0 ar o 140.0 -E i 120.0 -n u gj 100.0 cv 80.0 = — c 60.0 0 s 40.0 -eg E 20.0 -c cn 0.0 .0 "V3 10:07 10:11 10:39 11:09 11:34 12:11 12:44 13:21 14:03 14:37 15:19 16:09 Time(hrs:min) stomatal conductance recorded Figure 6-10. Stomatal conductance (mmol H 2 0 m"2 s"1) o f interior Douglas-fir (Fdi) attached branch (ope diamond) and cut branches (closed diamonds) for samples (c) F d i #3, (d) F d i #4, and (e) F d i #5. 114 6.4 Discussion The net photosynthetic rate results, in this test, are similar to the findings by Dang et al. (1997). Using the cut-branch technique, Dang et al. (1997) found no significant differences in the net photosynthetic rate between attached branches and cut branches over a 2-hour time frame for mature black spruce, jack pine and aspen. In addition, Dang et al. (1997) found that under laboratory controlled environmental conditions the net photosynthetic rate of the cut branches of the spruce and jack pine remained stable for at least 14 hours, whereas the cut branches of the aspen began to lose stability after 10 hours. However, the n-value of this test is small (n=5) and improved confidence in the results would occur by modifying the experiment to increase the number of attached and cut branches measured. This will occur in the summer of 2003. In this test, the net photosynthetic rate of the cut branches destabilized approximately three hours after each branch was harvested. This may be a result of performing the experiment in the field, as opposed to in a laboratory where conditions such as air temperature inside the leaf cuvette could be controlled. Between 12:00 and 12:30 the leaf cuvette air temperature was 33.0° C to 33.6° C, after which the net photosynthetic rate of the cut branches either gradually reduced (e.g., samples Fdi #3 and #5) or destabilized (e.g. samples Fdi #1, #2, and #4) (Figures 6-4 and 6-5). Between 12:30 and the final measurement at 16:09, the leaf cuvette air temperature varied from a low of 31.7° C to a high of 36.2° C. In the lab, Dang et al. (1997) controlled the air temperature in the leaf cuvette, although the temperature range wasn't stated. Leaf gas exchange was not limited by the supply of water, as the cut surface of each branch was always submerged. However, the stomatal conductance results, in this test, differ from the Dang et al. (1997) study. Inexplicably, the stomata of the sampled interior Douglas-fir began closing within 30 minutes of the branch being harvested, yet the net photosynthetic rates increased. The n-value of this test is small (n=5) and improved confidence in the results would 115 occur by modifying the experiment to increase the number of attached and cut branches measured. Therefore, to improve the interior Douglas-fir physiological database, testing of the cut-branch technique under low light and high light environments will take place in July/August 2003. The challenge of collecting physiological measurements in the field is one of minimizing error associated with the technique used to gather these measurements. There appears to be a knowledge gap when it comes to having a reliable technique for gathering leaf gas exchange measurements, particularly if researchers want to examine the effect of silviculture treatments on the physiology of sapling- and mature-aged conifer and hardwood species in the rugged ICH and IDF wet-belt forests of southern British Columbia. The advantage of pursuing further experiments to test the cut-branch technique outlined in this study is to provide information toward honing the technique to increase confidence and identify its limitations. 116 6.5 Literature Cited for Appendix Beadle, C.L., P.G. Jarvis and R.E. Neilson. 1979. Leaf conductance as related to xylem water potential and carbon dioxide concentration in Sitka spruce. Physiol. Plant. 45: 158 - 166. Beadle, C.L., R.E. Neilson, P.G. Jarvis and H. Talbot. 1981. Photosynthesis as related to xylem water potential and carbon dioxide concentrations in Sitka spruce. Physiol. Plant. 52: 391 - 400. Dang, Q. -L. , H.A. Margolis, M.R. Coyea, M. Sy and G.J. Collate. 1997. Regulation of branch-level gas exchange of boreal trees: roles of shoot water potential and vapor pressure difference. Tree Physiology 17: 521 - 535. Sellers, P.J., F.G. Hall, H.A. Margolis, R. Kelly, D.D. Baldocchi, G.D. Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier and D.E. Wickland. 1995. The Boreal Ecosystem-Atmosphere Study (BOREAS): an overview and early results from the 1994 field year. Bull. Am. Meteorol. Soc. 76: 1549- 1577. Watts, W.R. and R. Neilson. 1978. Photosynthesis in Sitka spruce (Picea sitchensis (Bong.) Car.). VIII. Measurements of stomatal conductance and 1 4 C 0 2 uptake in controlled environments. J. Appl. Ecol. 15: 245 -255. Whitehead, D., N.J. Livingston, F.M. Kelliher, K.P. Hogan, S. Pepin, T.M. McSeveney and J.N. Byers. 1996. Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree. Plant Cell Environ. 19: 949 - 957. 117 

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