ABSTRACT Title of Dissertation: DISTURBANCE by FIRE
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ABSTRACT Title of Dissertation: DISTURBANCE BY FIRE AND ITS ROLE IN THE POPULATION BIOLOGY AND DISTRIBUTION OF A RARE TEMPERATE FOREST HERB Norman A. Bourg, Doctor of Philosophy, 2006 Dissertation directed by: Professor Douglas E. Gill Department of Biology This research comprises a comprehensive investigation of the role and effects of disturbance by fire on the population biology of turkeybeard ( Xerophyllum asphodeloides : Melanthiaceae) a rare forest herb of the Appalachian Mo untains. I first employ a long term monitoring dataset from a primary study population to examine demography and flowering patterns. The effects of forest disturbance on survival, fruit and seed production in this population are next investigated by eval uating the outcome of a controlled, fire and canopy alteration ‘pulse’ experiment. The pollination biology of X. asphodeloides in the context of the above habitat manipulation is then determined from hand pollination experiments over three flowering seaso ns. Lastly, the role of fire and other environmental variables in the distribution of X. asphodeloides populations at the landscape scale is assessed via the construction, cross -validation, and ground -truthing of a classification tree and geographic infor mation system (GIS) –based predictive habitat model for the mountains of northwestern Virginia, U.S.A. The major results demonstrate that X. asphodeloides is one of the few definitively fire -adapted forest understory herbs in the eastern United States. This is due to a number of factors, including high survival and rapid resprouting after burning, fire -induced mass flowering, significantly enhanced fruit and seed production in burnt and canopy -altered habitat, and greatly increased seed production in pla nts with larger floral displays. Additionally, support is found for characterizing X. asphodeloides as a primarily outcrossing species with what is highly likely to be a “leaky” self -incompatibility system. Populations typically exhibit low flowering lev els in undisturbed forest which in combination with their self -incompatibility subjects them to Allee effects due to pollinator limitation in most years. Disturbance by fire results in release from these limiting factors by inducing mass flowering, alteri ng the forest habitat and increasing pollinator activity, thus facilitating outcrossing and seed set. Finally, fire frequency, elevation, slope and forest type are indicated as the main explanantory variables for predicting suitable habitat in the classif ication tree/GIS model. This model correctly classifies 74% of known turkeybeard presence areas and 90% of known absence areas, and results in the discovery of eight new occupied habitat patches during ground -truthing exercises. Results of this research project are valuable not only for the conservation and management of X. asphodeloides , but also make a major contribution to the understanding of disturbance regimes in Appalachian forests and have important implications for improving ecologically based ma nagement efforts of these lands. DISTURBANCE BY FIRE AND ITS ROLE IN THE POPULATION BIOLOGY AND DISTRIBUTION OF A RARE TEMPERATE FOREST HERB by Norman A. Bourg Dissertation submitted to the Faculty of the Graduate School of the Univer sity of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2006 Advisory Committee: Professor Douglas E. Gill, Chair Professor Michele R. Dudash Professor David W. Inouye Dr. William J. McShea Professor Joseph Sullivan ©Copyright by Norman A. Bourg 2006 Dedication This work is dedicated to my parents, Norman W. and Mary L. ‘Babe’ Bourg, for their unwavering support, love and encouragement over the years, and to the memory of my maternal grandparents, Dominic and Mary V. Battistone, who first instilled in me an appreciation of plants and a love for nature. They each have my eternal gratitude. ii Acknowledgements Funding for this research was p rovided by a National Fish & Wildlife Foundation General Conservation Challenge Grant to W.J. McShea, N.A. Bourg and D.E. Gill, a Smithsonian Institution (SI) Pre -doctoral Fellowship to N.A. Bourg, the NSF Research Training Grant in the Biology of Small Po pulations at the University of Maryland – College Park (UMCP), the UMCP Graduate School, and USDA -Forest Service cost -share agreement #08 -97 -08 -11 for the Orchid Hill Ecosystem Management Project (OHEMP) . I would like to thank the members of my doctora l committee, in particular Doug Gill for his mentoring, friendship, careful and thorough editorial skills, and service as my major advisor over the years. A similar special thanks is due to Bill McShea for being my primary sponsor on my SI fellowship and for providing access to his intern, equipment, and scientific resources at the SI National Zoological Park – Conservation and Research Center (CRC). Michele Dudash and David Inouye provided valuable training in plant population biology, mating and breedin g systems, and pollination biology. Joe Sullivan kindly and efficiently served as the Dean’s Representative for my defense. I thank Terry Slater, Ecosystem Management Officer for the Dry River Ranger District of the GWNF, and Steve Croy, GWNF Ecologist , for their important assistance with the field experiment portion of this research. Drs. Chris Wemmer and John Rappole provided administrative support and permission to work at the CRC during my SI fellowship tenure. Dr. Peter Leimgruber and Melissa Son ger provided access and guidance at the SI - CRC Conservation GIS lab. Dr. Mary C. Christman offered beneficial statistical and CART modeling input. Dr. W. John Kress and Ms. Ida Lopez of the SI National Museum of Natural History - Department of Botany p rovided additional employment support and professional advice for which I am very grateful. I thank Kevin Koy for his advice on model preparation and Lyndon Estes for his assistance with ground -truthing. Kari Veblen, Carrie O’Brien, Wrenn Martin, Jenny G agnon, Dan Kelly, Dan Guertin, Julian Bock and other interns from the CRC as well as Connie Bennett, Chad Brassil, Annie Bush, Jen Greene, Alex Eilts, Suja Joseph, Ryan Lesh, Brendan Carroll, Long Nguyen, Rina Aviram, and Jen Obadia of UMCP provided valuab le assistance and camaraderie in the laboratory and/or field. I would also like to thank my friends for their support and companionship during my graduate studies, especially Deb Rowan, Thad DuBois, Vinita Gowda, Mike Leigh, Gary Dodge, Pete Blank, Mar got Bass, Rina Aviram, Mariana Panuncio, Nathan Martin, Tina Han, Daniella Schweizer, Francisca Saavedra, and Brian Williams. Last but in no way least, I extend a heartfelt thanks to the many members of my family, most importantly my parents and my sister s Geri, Michelle, and Allison, for their encouragement and all that they have done for me during my graduate studies. iii Table of Contents Dedication ……………………………………………………………………………….ii Acknowledgments ……………………………………………………………………...iii Table of Contents ……………………………………………………………………….iv List of Tables ....................................................................................................................v List of Figures .......................................................................... ......................................vii Chapter 1 : Disturbance by Fire in the Appalachians and Its Effects on Demography and Reproduction in Turkeybeard ( Xerophyllum asphodeloides ) (L.) Nutt., a Rare Forest Herb …………………………………………………………………………….....1 Abstract ..................................................................................................................2 Introduction ……………………………………………………………………....3 Study Sites and Methods ………………………………………………………..16 Results …………………………………………………………………… ……..22 Discussion ……………………………………………………………………....55 Literature Cited ………………………………………………………………....71 Chapter 2 : Pollination Biology of Turkeybeard ( Xerophyllum asphodeloides ) (L.) Nutt. (Melanthiaceae) in the Context of Fire in the Appalachian Mountains of Virginia, U.S.A. ………………………………………………………………………....86 Abstract ……………………………………………………………………….....87 Introduction ……………………………………………………………………...88 Methods ……………………………………………………………………….....91 Results …………………………………………………………………………...99 Discussion ………………………… …………………………………………...106 Literature Cited ………………………………………………………………...114 Chapter 3 : Classification Tree and GIS -based Predictive Habitat Modeling for a Rare Fire -adapted Temperate Forest Herb ……………………………………………..119 Abstract ……………………………………………………………………….. .120 Introduction ………………………………………………………………….....121 Study Area and Methods …………………………………………………….....126 Results ……………………………………………………………………….....137 Discussion ……………………………………………………………………...146 Literature Cited ………………………………………………………………...153 Complete B ibliography ………………………………………………………………...160 iv List of Tables Chapter 1 Table 1. Areal extent, plant densities, and population size estimates for 25 surveyed populations of X. asphodeloides ............................................................ 30 Table 2. A) Summary ANCOVA table for the effects of treatment and isolation on fruit production in 115 single inflorescence plants in the experimental response years of 1998 and 1999 at the Orchid Hill study site, and B) paired treatment comparison s ............................................................36 Table 3. A) Summary ANCOVA table for the effects of treatment and isolation on seed production in 115 single inflorescence plants in the experimental response years of 1998 and 1999 at th e Orchid Hill study