Gregory J. Pec
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Cascading effects of insect outbreak on plant and fungal community structure and function by Gregory J. Pec A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ecology Biological Sciences University of Alberta © Gregory J. Pec, 2016 Abstract Western North American landscapes are rapidly being transformed by forest die- off caused by mountain pine beetle with implications for plant and soil communities. The mechanisms that drive changes in plant and soil community structure and function, particularly for understory vegetation and the highly prevalent ectomycorrhizal fungi in pine forests, are complex and intertwined. In this thesis, I use a recent bark beetle outbreak in lodgepole pine (Pinus contorta) forests of western Canada to disentangle the relative importance of beetle- induced tree mortality from changes in environmental conditions following tree death, and in turn, its effects on: (1) understory plant community diversity and productivity, (2) the richness and composition of soil fungal communities, (3) the spatial structuring of ectomycorrhizal and saprotrophic fungal communities, and (4) the functional importance of ectomycorrhizal fungal networks on tree seedling establishment. My results indicate that both deterministic and stochastic processes structure plant and soil fungal communities following landscape-level insect outbreak and reflect both the independent and shared roles tree mortality, soil chemistry, and spatial distance play in regulating both these communities. My results also demonstrate that ectomycorrhizal fungal networks seemed to not be degraded with stand level tree mortality, with access to these networks improving both the growth and nutrition of tree seedlings. Taken together, this thesis demonstrates the far-reaching effects of biotic disturbance and emphasizes the interconnectedness between understory vegetation, trees, soils, and soil fungi. ii Preface A version of Chapter 2 of this thesis has been published as Pec G.J., J. Karst, A.N. Sywenky, P.W. Cigan, N. Erbilgin, S.W. Simard, and J.F. Cahill, Jr., “Rapid increases in forest understory diversity and productivity following a mountain pine beetle (Dendroctonus ponderosae) outbreak in pine forests,” PLoS ONE 10(4): e0124691. G.J.P., J.K., N.E., S.W.S., and J.F.C. conceived and designed the research. G.J.P., A.N.S., and P.W.C. conducted the fieldwork. G.J.P. analyzed the data. G.J.P. prepared the manuscript. G.J.P., J.K., N.E., S.W.S., and J.F.C. contributed to manuscript edits. A version of Chapter 3 of this thesis has been accepted for publication as Pec G.J., J. Karst, D.L. Taylor, P.W. Cigan, N. Erbilgin, J.E.K. Cooke, S.W. Simard, and J.F. Cahill, Jr., “Changes in soil fungal community structure driven by a decline in ectomycorrhizal fungi following a mountain pine beetle outbreak,” New Phytologist. G.J.P., J.K., N.E., J.E.K.C., S.W.S., and J.F.C. conceived and designed the research. G.J.P. and P.W.C. conducted the fieldwork. G.J.P., J.K., and D.L.T. analyzed the data. G.J.P. prepared the manuscript. G.J.P., J.K., D.L.T., N.E., J.E.K.C., S.W.S., and J.F.C. contributed to manuscript edits. iii Acknowledgements First and foremost I would like to thank my supervisors, Drs. James (JC) Cahill and Suzanne Simard. I could not have asked for better mentors and appreciate the guidance and the freedom given toward achieving my goals. Thank you for your unwavering support through my highs and lows both professionally and personally over these past years. I would also like to thank my other supervisory committee member, Dr. Nadir Erbilgin, for his guidance, support, and time. I am forever grateful and indebted to Dr. Justine Karst for all her encouragement, guidance, patience, and time. You all have been an inspiration in the completion of this research. I am grateful to past and present members of the Cahill Lab for their friendship, encouragement and support. I would also like to thank Drs. Janice Cooke, Ronald Treu (Athabasca University) and D. Lee Taylor (University of New Mexico), the many field and lab assistants as well as the Molecular Biological Sciences Unit (MBSU) and the Natural Resources Analytics Laboratory (NRAL) for providing the support needed to accomplish this body of work. Last but not least, I would like to thank my family for their unwavering support. I owe a special word of thanks to my wife, Maryam, for her endless love and encouragement. Much of the research presented within this thesis was made possible by a Natural Sciences and Engineering Research Council of Canada (NSERC) Strategic Grant awarded to Drs. James Cahill, Suzanne Simard, Nadir Erbilgin and Janice Cooke, and an NSERC Discovery Grant awarded to James Cahill. My PhD was supported by a University of Alberta doctoral recruitment scholarship, graduate research and teaching assistantship as well as an iv Alberta Conservation Association (ACA) grant in biodiversity awarded to Dr. James Cahill and myself. v Table of Contents Chapter 1: General Introduction ............................................................................................... 1 1.1 The Boreal Forest ............................................................................................................................... 2 1.1.1 Lodgepole Pine Dominant Forests ...................................................................................................... 3 1.2 Disturbance .......................................................................................................................................... 4 1.2.1 Mountain Pine Beetle Outbreak ........................................................................................................... 6 1.2.2 Forest Regeneration ................................................................................................................................. 7 1.3 Soil Fungi ............................................................................................................................................... 9 1.3.1 Mycorrhizal fungi ..................................................................................................................................... 10 1.3.2 Mycorrhizal networks ............................................................................................................................ 11 1.4 Spatial Scale ....................................................................................................................................... 12 1.5 Overview of Thesis .......................................................................................................................... 14 Chapter 2: Rapid increases in forest understory diversity and productivity following a mountain beetle (Dendroctonus ponderosae) outbreak in pine forests ............................................................................................................................................................. 16 2.1 Introduction ...................................................................................................................................... 16 2.2 Methods ............................................................................................................................................... 18 2.2.1 Study Area ................................................................................................................................................... 18 2.2.2 Plant Survey ............................................................................................................................................... 18 2.2.3 Data Analysis .............................................................................................................................................. 20 2.3 Results ................................................................................................................................................. 22 2.4 Discussion .......................................................................................................................................... 25 2.4.1 Effects of tree mortality and resource availability on understory plant communities ..................................................................................................................................................................................... 26 2.4.2 Mountain pine beetle outbreaks versus fire and harvesting ................................................. 27 2.5 Conclusion .......................................................................................................................................... 29 Chapter 3: Change in soil fungal community structure driven by a decline in ectomycorrhizal fungi following a mountain pine beetle outbreak ........................... 42 3.1 Introduction ...................................................................................................................................... 42 3.2 Materials and Methods .................................................................................................................. 45 3.2.1 Study area.................................................................................................................................................... 45 3.2.2 Sampling and molecular characterization of fungi .................................................................... 48 3.2.3 Statistical analysis ...................................................................................................................................