EFFECTS OF PRESCRIBED FIRE, INVASIVE SPECIES, AND GEOGRAPHIC DISTRIBUTION PATTERNS ON GRANITE ROCK OUTCROP PLANT COMMUNITIES IN THE GEORGIA PIEDMONT by MELISSA CASPARY (Under the Direction of JAMES AFFOLTER) ABSTRACT The granite rock outcrops of the southeastern United States are a unique assemblage of island-like habitats that support many endemic and rare species in their unique plant communities. The flora associated with the ecotone for many of these outcrops has shifted over time. Fire suppression, exotic plant invasion, and anthropogenic impacts are creating a dense understory environment of high competition and low light levels that discourage establishment and persistence of native outcrop flora. This research project includes two small-scale field studies and a broader landscape-level assessment of disturbance effects on species diversity and composition in the ecotone of rock outcrop environments. Prescribed burns were applied to the ecotone plant community of two rock outcrops in the Piedmont of Georgia. Two other outcrop sites were chosen to assess community response to removal of invasives in the ecotone. Occurrence of vegetation classes and species richness were measured along random stratified belt transects. Hemispherical photographs, soil nutrients, and soil depth were used to monitor changes initiated by the prescribed burn. Neither fire, nor removal of invasives had a significant effect on vegetation class occurrence, including invasive and rare plant occurrence, or species richness. A site-specific evaluation, including the consideration for disturbance history and potential rare species’ response, would be necessary to determine whether prescribed fire should be an appropriate management tool on rock outcrop ecotones. Data for tree canopy, impervious surface, and landcover produced by the University of Georgia Natural Resources Spatial Analysis Laboratory were used to observe a 33-year snapshot of landcover change surrounding Georgia outcrops. Predictive models of species geographic distributions were used to determine the key environmental variables that determine local and regional species patterns. Landcover trends reveal increasing urban development and deforestation in all areas that were analyzed. Impervious surface surrounding rock outcrops significantly increased from 1991 to 2005. Rare plant occurrence increased with latitude and outcrop spatial complexity and did not appear to be tied to outcrop size or isolation. Geology, population density, and outcrop shape complexity were predictive of quarrying. These models may be applied to specific habitats to assist in identifying threats and informing conservation decisions. INDEX WORDS: granite rock outcrop, ecotone, endemic species, Piedmont, invasion, prescribed fire, species diversity, rare plant, spatial distribution, plant community EFFECTS OF PRESCRIBED FIRE, INVASIVE SPECIES, AND GEOGRAPHIC DISTRIBUTION PATTERNS ON GRANITE ROCK OUTCROP PLANT COMMUNITIES IN THE GEORGIA PIEDMONT by MELISSA CASPARY BS, Lehigh University, 2000 BA, Lehigh University, 2000 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2011 © 2011 Melissa Caspary All Rights Reserved EFFECTS OF PRESCRIBED FIRE, INVASIVE SPECIES, AND GEOGRAPHIC DISTRIBUTION PATTERNS ON GRANITE ROCK OUTCROP PLANT COMMUNITIES IN THE GEORGIA PIEDMONT by MELISSA CASPARY Major Professor: James Affolter Committee: Ron Carroll Dov Sax Rebecca Sharitz Robert Wyatt Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2011 DEDICATION To my family who have inspired me to grow. iv ACKNOWLEDGEMENTS I would like to acknowledge my major professor, Dr. James Affolter, for his steadfast support and patience. I would also like to acknowledge the members of my committee, Dr. Ron Carroll, Dr. Dov Sax, Dr. Rebecca Sharitz and Dr. Robert Wyatt, for sharing their time and the wealth of their experience. I am grateful to Dr. Donald Shure of Emory University for his guidance and time on my advising committee. I am indebted to my colleagues in the Research and Conservation Lab, Heather Alley, Jennifer Ceska, and Linda Chafin, for their companionship and infectious love of plants. I am so grateful to the entire staff of the State Botanical Garden for making me feel like a part of their family. I would like to thank the State Botanical Garden Research and Conservation Volunteers for their weekly assistance, privet clearing, and years of friendship. I would like to express my gratitude to Kim Love-Myers, with the Statistical Consulting Center in the Department of Statistics at the University of Georgia, for her continual willingness to field my questions. I would like to thank James Rickard and Pete Pattavina at the U.S. Fish and Wildlife Service Georgia Ecological Services Field Office for their humor and commitment to support my love affair with rock outcrop plant communities. I would like to thank Malcolm Hodges and Erick Brown with The Nature Conservancy for their expertise in lighting fires and willingness to humor me. I would like to acknowledge Shan Cammack, Chris Canalos, Lisa Kruse, Dr. Mincy Moffet, and Tom Patrick with the Department of Natural Resources, Nongame Conservation Section, for their guidance in setting up this research. I want to thank James Allison for his advice in developing the v project. I am grateful to Hugh and Carol Nourse for their willingness to teach me about outcrop flora and share their beautiful photographs. I am indebted to the Garden Club of America for the Catherine H. Beattie Fellowship, the Native Plant Society for the Marie Mellinger Grant and the Georgia Botanical Society for a Field Botany Grant. I want to thank Jennifer Bartmess for countless hours of fieldwork and companionship. Finally, I would like to express my most sincere appreciation to husband Mark, my brother Scott, and my sister Alye for taking care of Ethan and Sam so I could do field work. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS.................................................................................................v LIST OF TABLES...............................................................................................................x LIST OF FIGURES .......................................................................................................... xii CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW .........................................1 Introduction..................................................................................................1 Rock Exposures in North America ..............................................................2 Rock Outcrops of the Georgia Piedmont.....................................................4 Granite Outcrops as Centers of Endemism..................................................9 Threats to Rock Outcrops of the Georgia Piedmont..................................12 The Role of Invasion and Fire in Rock Outcrops ......................................13 Exploring the Ecotone of Granite Outcrop Systems..................................15 Research Objectives...................................................................................19 Literature Cited..........................................................................................21 2 THE INFLUENCE OF FIRE ON TWO GRANITE ROCK OUTCROP ECOTONES IN THE PIEDMONT OF THE SOUTHEASTERN UNITED STATES...........................................................................................................37 Abstract......................................................................................................37 Introduction................................................................................................38 vii Methods......................................................................................................42 Results........................................................................................................47 Discussion..................................................................................................50 Literature Cited..........................................................................................57 3 EXOTIC INVASION OF TWO GRANITE ROCK OUTCROP ECOTONES IN THE PIEDMONT OF THE SOUTHEASTERN UNITED STATES ........79 Abstract......................................................................................................79 Introduction................................................................................................79 Methods......................................................................................................84 Results........................................................................................................88 Discussion..................................................................................................91 Literature Cited..........................................................................................96 4 USING SPATIAL ANALYSIS TO PREDICT HABITAT THREATS AND RARE SPECIES OCCURRENCE IN GRANITE ROCK OUTCROPS.......115 Abstract....................................................................................................115 Introduction..............................................................................................116 Methods....................................................................................................119 Results......................................................................................................121