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The Effects of Native Conifer Encroachment and Importance Of THE EFFECTS OF NATIVE CONIFER ENCROACHMENT AND IMPORTANCE OF HIGH-SEVERITY WILDFIRE IN FIRE-EXCLUDED CALIFORNIA BLACK OAK ECOSYSTEMS OF NORTHERN CALIFORNIA by Matthew I. Cocking A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Masters of Science In Natural Resources: Forestry November, 2011 THE EFFECTS OF NATIVE CONIFER ENCROACHMENT AND IMPORTANCE OF HIGH-SEVERITY WILDFIRE IN FIRE-EXCLUDED CALIFORNIA BLACK OAK ECOSYSTEMS OF NORTHERN CALIFORNIA By Matthew I. Cocking Approved by Master’s Thesis Committee: J. Morgan Varner, Major Professor Date E. Knapp, Committee Member Date R. Sherriff, Committee Member Date Coordinator, Natural Resources Graduate Program Date Natural Resources Graduate Program Number Jena’ Burges, Vice Provost Date ABSTRACT The absence of fire in many oak woodlands that historically experienced frequent fire has resulted in invasion and subsequent overtopping of oaks by fast-growing conifers. Little is known about the effects of these structural and compositional changes occurring in California black oak ( Quercus kelloggii ) woodlands. This study addresses two broad questions: 1) How will conifer-encroached California black oaks respond to re- introduced fire in areas that have gone unburned for many decades? And 2) what actions can forest managers take toward California black oak woodland restoration and maintenance over time? Tree competition around individual California black oaks, tree age, and California black oak post-fire responses were investigated in Klamath and Lassen National Forests in northern California. Plots were established around focal oaks where attributes of neighboring encroaching trees, tree regeneration, and fire effects were measured. At both sites woodland overstory was heavily dominated by relatively fire- intolerant conifers, particularly Douglas-fir ( Pseudotsuga menziesii ) and white fir ( Abies concolor ). At the Klamath site, trees that pierced California black oak crowns were younger than paired oaks. The probability of California black oak mortality from fire was correlated with neighboring Douglas-fir height, indicating a compromising effect of encroachment on oak survival. At the Lassen site 90% of killed California black oak stems sprouted following fire. Oak recovery was strongest in severely burned areas ; linear modeling revealed significant negative relationships between overstory tree survival and both California black oak sprout height and basal area. A conceptual model iii for the formation and persistence of these specific stand structures is proposed in which fire severity and encroachment pressure affect compositional change over time. Unless specific management actions are taken to protect California black oak woodlands, many encroached stands may be converted to conifer forest. iv ACKNOWLEDGEMENTS This research was funded by the United States Department of Agriculture Pacific Southwest Research Station. Many people contributed in various ways to the culmination of this project. My major advisor, Dr. Morgan Varner, was elemental to my success as a graduate researcher and his ability to provide unwavering inspiration, support, and friendship has kept me motivated and excited to work, and has greatly enriched my overall experience. Both my committee members, Dr. Rosemary Sherriff and Dr. Eric Knapp, were integral to this project, providing resources, academic guidance, and encouragement. Also, I would like to extend special thanks to Dr. Robert VanKirk for his expertise and exceptional patience. Others who helped in the field and during the writing process include but are not necessarily limited to: Ramona Butz, Max Creasy, Eamon Engber, Howard Kuljian, Dean Matheson, John Mola, Brandon Namm, Erin Rentz, Caroline Sulivan, Barry Kearns, Kaci Worth, Juan A delaFuente, Larry Fox, Adam Dresser, Justin Crotteau, Erin Banwell, and Frank Lake. Lastly, I would like to thank my parents, whose love, support, encouragement, and inspiration is unquantifiable. v TABLE OF CONTENTS ABSTRACT ........................................................................................................................ v ACKNOWLEDGEMENTS ................................................................................................ v TABLE OF CONTENTS ................................................................................................... vi LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ............................................................................................................ x LIST OF APPENDICES .................................................................................................. xiii CHAPTER 1: Effects of Douglas-fir Encroachment on California Black Oak Resilience to Wildfire in the Klamath Mountains ................................................ 1 1. INTRODUCTION .......................................................................................................... 1 2. METHODS ..................................................................................................................... 7 2.1 Site Description ............................................................................................. 7 2.2 Field Sampling ............................................................................................ 10 2.3 Data Analysis .............................................................................................. 15 3. RESULTS ...................................................................................................................... 19 3.1 Neighboring Competition ........................................................................... 19 3.2 Fire Effects .................................................................................................. 27 4. DISCUSSION ............................................................................................................... 32 5. REFERENCES ............................................................................................................. 39 CHAPTER 2: Long-term Effects of Varying Fire Severity on Stand Structure in a Mixed Conifer and California Black Oak Ecosystem ........................................ 45 1. INTRODUCTION ........................................................................................................ 45 2. METHODS ................................................................................................................... 49 vi 2.1 Site Description ........................................................................................... 49 2.2 Field Sampling ............................................................................................ 50 2.3 Data Analysis .............................................................................................. 53 3. RESULTS ...................................................................................................................... 57 3.1 Pre- and Post-Fire Composition .................................................................. 57 3.2 Post-Wildfire Tree Mortality and Stand Effects .......................................... 61 3.3 Regeneration Ten Years Post-Wildfire ........................................................ 63 4. DISCUSSION ............................................................................................................... 72 5. REFERENCES ............................................................................................................. 81 APPENDICIES ................................................................................................................. 87 vii LIST OF TABLES Table Page 1 Mean and standard error (SE) for density, basal area (BA), dbh, and height of trees within 10 m of focal California black oaks at the Dillon Mountain, Siskiyou County, California, 2010 research site (2010). The total trees tagged for each species (N) is relative to 800 tagged trees and the frequency (freq) is the proportion out of the 25 plots in which each species occurred..................................................................................................................20 2 Canopy composition and test statistics for the Dillon Mountain study site (Siskiyou County, California, 2010): Higher χ2 values contribute more to test significance. .....................................................................................................22 3 Values obtained for piercing and overtopping trees (Dillon Mountain, Siskiyou County, California, 2010): SE designates standa rd error; N is the total number of individuals measured. ...................................................................23 4 Distribution of pith presence for cored pairs of trees (Dillon Mountain, Siskiyou County, California, 2010): N pairs indicates the number of pairs of piercer and pierced oak where both cores had a pith date (both piths), only the piercing tree core possessed a pith date (piercer pith), or the piercing tree did not possess a pith date (no piercer pith). Numbers in brackets are confidence intervals for the age difference shown in years; t and p-values indicate results of one-sided, paired t-tests. ......................................26 5 Post-fire tree mortality and basal area reduction in plots at the Dillon Mountain site (Siskiyou County, California, 2010): “Above ground” refers to all stems killed above ground-level while “complete”
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