Plant Community Response to Post-Wildfire Management Activities in Interior Douglas-Fir Forests of Southern BC
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Plant Community Response to Post-wildfire Management Activities in Interior Douglas-Fir Forests of Southern BC by Scott T. Black B.Sc. (Hons.) The University of Victoria, 2004 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate Studies (Botany) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) October 2009 © Scott T. Black, 2009 Abstract Post-wildfire disturbances such as salvage logging and seeding of agronomic species occur over large parts of the forested land base in British Columbia. However, there is surprisingly little research on the effects of these management practices on plant community composition and species diversity. The future of plant and animal biodiversity will depend increasingly on regional floras surviving in highly managed and disturbed environments. I examined vascular and nonvascular plant community responses four years after wildfire and post-wildfire management practices in interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests following two separate 2003 wildfires near Kamloops, BC, Canada. Wildfire sites with all combinations of seeding and salvage logging disturbance were selected in similar post-wildfire environments. Analysis at the plot (400m2, n=104) and stand (400-1200m2, n=42) scales suggested that post-wildfire disturbance had a significant negative effect on native species richness and reduced the frequency of some shrub and shade tolerance species including Ceanothus sanguineus and Prosartes hookeri. As well, multivariate analysis showed evidence for altered post-wildfire community composition and structure mainly due to increased dominance of exotic and graminoid species. These negative effects were most apparent in wildfire sites that were both seeded and salvaged-logged. Sustainable forest management requires a thorough understanding of the cumulative impacts of post-wildfire management practices on understory vegetation and ecosystem processes. The results of this study can aid resource managers by helping them incorporate the effects of natural and anthropogenic disturbance into future post-wildfire management activities. ii Table of Contents ABSTRACT ................................................................................................................................................................ ii TABLE OF CONTENTS .......................................................................................................................................... iii LIST OF TABLES ......................................................................................................................................................iv LIST OF FIGURES ..................................................................................................................................................... v ACKNOWLEDGEMENTS ..................................................................................................................................... vii CHAPTER 1 INTRODUCTION ................................................................................................................................ 1 1.1 Review of Concepts and History of Succession and Disturbance ................................................................. 2 1.2 Disturbance and Invasive Species ................................................................................................................. 8 1.3 Natural History of Interior Douglas-fir Forests ........................................................................................... 9 1.4 Disturbance History and Post-fire Communities of Dry Douglas-fir Forests ............................................. 11 1.5 Similar Studies ............................................................................................................................................ 14 CHAPTER 2 METHODS ......................................................................................................................................... 17 2.1 Study Area ................................................................................................................................................... 17 2.2 Study Design ............................................................................................................................................... 17 2.3 Data Analysis .............................................................................................................................................. 20 2.4 Community Composition Analysis .............................................................................................................. 22 CHAPTER 3 RESULTS ........................................................................................................................................... 25 3.1 Patterns of Species Composition ................................................................................................................. 25 3.2 Patterns of Species Richness ....................................................................................................................... 29 3.3 Environmental Characteristics ................................................................................................................... 33 3.4 Tree Seedling Regeneration ........................................................................................................................ 35 CHAPTER 4 DISCUSSION ..................................................................................................................................... 36 4.1 Project Limitations ...................................................................................................................................... 37 4.2 Effects of Post-wildfire Grass Seeding Disturbance on Douglas-fir Plant Communities ........................... 40 4.3 Effects of Post-wildfire Salvage Logging Disturbance on Douglas-fir Plant Communities........................ 44 4.4 Combined Effects of Seeding and Salvage Logging .................................................................................... 50 CHAPTER 5 CONCLUSIONS ................................................................................................................................ 56 TABLES ..................................................................................................................................................................... 58 FIGURES ................................................................................................................................................................... 76 LITERATURE CITED ........................................................................................................................................... 100 APPENDIX I ............................................................................................................................................................ 115 APPENDIX II .......................................................................................................................................................... 118 iii List of Tables Table 1. Sampling summary for McLure and McGillivray fire areas, 2007....................................... 59 Table 2. Species mixtures for seeding application in McClure and McGillivray post‐fire areas showing proposed density and proportion of species for each seed mix............................. 60 Table 3. Proportion of plots occupied by individual species in each site type. Bold values indicate top 20 most common species for that site type (N = native, E = exotic, Agro = seeded agronomic species) ............................................................................................................... 56 Table 4. Summary of understory species attributes and trait groups ( 1 = coniferous tree, 2 = broad‐leaved tree, 3 = evergreen shrub, 4 = deciduous shrub, 6 = graminoid, 7 = forb, 9 = moss, 10 = hepatic, 11 = lichen, 12 = dwarf woody plant, A = annual, B = biennial, P = perennial, I = introduced, Iv = invasive, Av = avoider ‐ fire sensitive species, In = invader ‐ highly dispersive, ruderal species, Ev = evader ‐ long lived species with propagules stored in the soil or canopy and germinate post‐fire, En = endurer ‐ sprouts from above or below ground structures post‐fire, C = common >33%, O = occasional 10‐33%, U = uncommon <10% of plots). .................................................................................... 61 Table 5. Results of multi‐response permutation procedures (MRPP) to detect differences in total species composition among treatments. ........................................................................................ 68 Table 6. Indicator species for each site type (treatment). Only species with an indicator value greater than 20 and a p-value less than 0.05 are shown (A= seeded agronomic species, E = exotic species, Iv = invasive species)......................................................................................... 69 Table 7. Summary of select biotic and abiotic characteristics of the McLure and McGillivray fires and the four site types by plot. (WF= wildfire only, WFSE = seeded wildfire, WFSA = salvage logged wildfire, WFSESA = seeded and salvaged wildfire, SA = all salvage logged sites, SE = all grass seeded) ................................................................................ 70 iv List of Figures Figure 1. Map of the two study areas showing plot locations in the McClure (A) and McGillivray