Complexity and variation in the effects of low-severity fires on forest biota

Short, Karen C. , Ph.D., May 2003 Organismal Biology and Ecology Complexity and variation in the effects of low-severity fires on forest biota. (206 pp.) Advisor: Richard L. Hutto The ecological effects of fire are varied and complex, yet the effects of even the most commonly applied fire treatments in the United States have been documented in ways that necessarily mask complexity and hide much of the variation effected by nominally similar bums. Reliance upon information gleaned from case studies of a narrow range of fire effects within a limited focal area to develop fire-management strategies for a wide domain of interest is especially evident in the American Southwest. Despite ardent speculation on both the acute and chronic influences of prescribed burning on populations of southwestern forest biota, including birds and arthropods, actual responses have seldom been quantified, and have never been quantified in ways that convey reliability. Here, I provide the first estimates of short-term responses of a wide range of arthropods to low-severity, fall bums in southwestern ponderosa pine forests. I characterize these effects functionally, by grouping all insects, arachnids, and myriapods according to thengeneral ecological roles within the forest community, and quasi-experimentally, by capitalizing on three nominally similar prescribed fires set within widely separated stands of comparable forest. I show that arthropods of southwestern ponderosa pine forest are keenly sensitive to even the most outwardly benign fire treatments, and that similar fires can effect disparate responses from a number of taxa. Birds that depend heavily on the forest understory for food, cover, or both, are commonly assumed to be sensitive to prescribed bums. I show that the reproductive success of a ground-nesting, ground-foraging, insectivorous bird the Yellow-eyed Junco can indeed be compromised by low-severity, autumn fire in southwestern ponderosa pine forest. I attribute this effect to changes in availability of preferred nesting microhabitat. If all fires were to affect junco demography in a similar fashion, the chronic influence (i.e., historic recurrence) of disturbance alone could set bounds to populations of these birds. I show, however, that different prescribed bums can affect key resources in different ways, such that fire's influence on junco populations may differ considerably among treatments. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS This research is the product of considerable time and effort devoted by many people, to all of whom I am deeply indebted. First and foremost, I am grateful to Steve Russell at for taking me under his wing while I was an undergraduate at the University of Arizona and encouraging me to pursue graduate study in ecology. I also thank Bill Mannan for encouragement and assistance during the inception of this project, Tom Huels and Jerram Brown, for giving me my first taste of laboratory and field work in ornithology, and, of course, Richard Hutto, for accepting me into his laboratory as a graduate student at The University of Montana and for guidance through the most recent years of my academic career. In the fall of 1996 my interest in fire ecology was piqued as I watched the woods bum in Saguaro National Park. I was a seasonal Biological Science Technician, hired by the park to conduct breeding bird surveys, but assisting at the time with a prescribed bum in ponderosa pine forest atop Mica Mountain. This experience spurred my initial ideas for this research, work that would capitalize upon prescribed bums to further our understanding of the ecological role of fire in Southwestern ponderosa pine forests. It was also work that, from the outset, I knew would not be possible without tremendous logistical assistance from the park. For their unwavering support over the many years that followed, I am so very grateful to past and present staff at Saguaro National Park including Natasha Kline, Meg Weesner, Kathy Schon, Rick Anderson, Rob Martin, Pat Haddad, Chuck Scott, Paula Natsiatka, Don Swann, Bob Lineback, Doug Morris, Frank Walker, Bill Dabney, Jim Williams, Todd Nelson, and Denise Jupinko. The initial funding for this undertaking was provided by Southwest Parks and iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Monuments Association (SPMA). In subsequent years, generous support came from the Canon National Parks Science Scholars Program, the Grand Canyon Association, The University of Montana Graduate School, and again from SPMA. With these funds, I was able to expand the scope of my research, adding study sites in Walnut Canyon National Monument and Grand Canyon National Park. I am indebted to Kathy Schon, Tom Ferrell, Ken Kerr, and Tonja Opperman for making it possible for me to work in conjunc­ tion with planned bums in these additional areas. As the project grew, so did my network of administrative support. I thank Raneid Patrick, Patricia Bristol, Patricia Hoy, Gary Machlis, Sandy Watson, Natasha Kline, Meg Weesner, Della Snyder, Jeri DeYoung, Don Christian, Patty McIntyre, and Sean Boushie for their help in this regard. I owe my sanity to a veritable army of field and laboratory assistants, who not only made this work possible but enjoyable. Thanks to Phillip Meza, Rob Klotz, James Borgmeyer, Jill Rubio, Nathan and Suzanne (Suki) Christy, Michael Olker, Jennifer Mi­ lan, Chris Butler, Angela and Chuck Barclay, Tiffany Stromberg, Alicia Michaels, Janet Gorrell, Tony Robatzek, Heather Tone, Sjana Taylor, Steffen Oppel, and Nate Schweber for their time and effort in the field. Thanks to Adam Ehmer, Molly White, Seth Schaub, Jesse Thompson, Mitch Willett, Brandon Henley, and Nathan Jensen for help sorting, identifying, and counting hundreds of thousands (! ) of critters in the lab. I am grateful that my interest in fire ecology led me to the graduate program at The University of Montana. I have benefited tremendously from interactions with both faculty and graduate students in the Division of Biological Sciences and the School of Forestry, among others. In particular, I would like to thank my graduate committee iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tom Martin, Doug Emlen, Dave Patterson, Mark Lindberg, and Diana Six — for their commitment to my academic development. Erick Greene and John Graham have also generously given their time to help refine this study. I am especially grateful for having been surrounded by an amazing cohort of graduate students. In particular, Kathryn War­ ner, Christina von der Ohe, Brett Walker, Charles Eldermire, Chris Templeton, Amy Cilimburg, Hugh Powell, Christina Ramsted, Dalit Ucitel, and Craig Stafford were sources of much-needed advice and diversion. Finally, I owe so much to my parents for supporting me through this and all of my endeavors, from day one; to Kathy Schon and Mark Briggs for providing a such a won­ derful home-away-from-home in Tucson for four summers; and to Garth Whitson for a wealth of inspiration, support, and patience throughout these past years. Thank you. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Page Abstract. ii Acknowledgements. iii List of tables. viii List of figures. x Preface.1 Literature Cited. 7 Chapter 1: Challenges and opportunities in the study of prescribed fires: an evaluation of fire experiments conducted in the conterminous U.S., 1950-2002.9 Introduction. 10 Methods. 12 Results. 14 Discussion. 32 Literature Cited. 41 Chapter 2: Responses of arthropods to prescribed autumn fires in southwestern ponderosa pine forests: a quasi-experimental, functional approach.49 Introduction. 50 Methods. 52 Results.70 Discussion. 93 Literature Cited. 120