Ecosystem Dynamics in Central Appalachian Riparian Forests Affected by Hemlock Woolly Adelgid
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Ecosystem dynamics in Central Appalachian riparian forests affected by hemlock woolly adelgid DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Katherine Lee Martin Graduate Program in Environment and Natural Resources The Ohio State University 2012 Dissertation Committee: Dr. P. Charles Goebel, Advisor Dr. John Cardina Dr. Peter S. Curtis Dr. Ronald L. Hendrick Copyrighted by Katherine Lee Martin 2012 Abstract In an era of rapid ecological change due to loss of biodiversity, climate change, and altered nutrient dynamics, predicting ecosystem dynamics and maintaining ecosystem services provided by complex natural ecosystems is an increasing concern. Novel disturbances, including those caused by invasive insects, provide an unfortunate opportunity to test the applicability of ecological theories to practical problems. One such case study is the loss of eastern hemlock (Tsuga canadensis, hemlock) from much of eastern North America due to the invasive pest hemlock woolly adelgid (Adelges tsugae; HWA). Foundation species such as hemlock are abundant and define the ecosystem processes of a community through a small number of strong interactions. As these interactions are lost, ecosystems are predicted to transition rapidly and develop distinctly different energy exchanges, nutrient cycles, and compositions that define a new community state. Much of the understanding of such transitions is conceptual. To advance the understanding of the function of foundation species and transitions to alternate community states when a foundation species is lost, my dissertation examines vegetation community composition and ecosystem function in 38 hemlock-dominated riparian forests across the central Appalachians. On the unglaciated Allegheny Plateau in Ohio, uninvaded forests provide baseline data on hemlock as a foundation species. iii Across West Virginia and Virginia, sites impacted by HWA for 9-32 years were selected as a chronosequence to compare changes in compostion and function. Hemlock forests exhibit low species richness, and thus have low resiliency. In uninvaded forests of Ohio, hemlock dominates the vegetation, although other species are structured by environmental gradients. Structural equation modeling indicates hemlock has a negative influence on vegetation species richness, light availability and productivity. Thus, a likely future HWA arrival will result in a complete reorganization of these ecosystems, but impacts will differ across environmental gradients. Data from sites impacted by HWA 9-32 years in West Virginia and Virginia indicate all hemlock forests will likely be impacted. Although mortality is initially slowed at higher elevations and on steeper slopes with northerly aspects, eventually, the duration of HWA invasion is the most important driver of mortality and ecosystem change. As decline progress, hemlock remains dominant in sites impacted for decades, although compositions are shifting and diverging across overstory hemlock decline classes. Some species, including the native evergreen shrub rhododendron (Rhododendron maximum) and other evergreen species including red spruce (Picea rubens), may be particularly influential during community reorganization. Environmental gradients, including elevation and soil characteristics, are also important ecologial drivers. Among overstory hemlock decline categories, resource availability and nutrient cycling are accelerating, but this varies with environmental context. This research supports broad patterns in compositional and functional shifts found in other regions, but also highlights the complexity of the loss of hemlock as a foundation iv species. As a model system, hemlock provides and example where resilience and atlternate state theories apply, but require some expansion for complex systems dominated by long-lived species. This indicates restoration and management will be more efficient when adapted based on the environmental context and component species. v For everyone that supported me on this journey, for the resilience of the Appalachians, and for eastern hemlock. vi Acknowledgments This dissertation research was supported by funding from an Ohio Agricultural Research and Development Center (OARDC) SEEDS graduate grant as well as The Charles E. Thorne Memorial Associateship, the OARDC Director’s Associateship, the College of Food, Agriculture & Environmental Science Fellowship, and National Science Foundation GK-12 Graduate Fellowship (Grant 0638669). Data collection assistance was provided by Tom Macy, Lara Kobelt, Cody Clifton, Stephen Rist, and Jack Martin. In particular, Tom, Lara, and Jack maintained positive attitudes during unexpected Appalachian surprises. Advice and assistance with research permits was provided by John Perez, Dr. Thomas Schuler, Randy Beinlich, Merrick Smith, Wanda San Jule, Kent Karriker, Terry Slater, Edward Haverlack, Stephen Tanguay, David Glass and Sam Cowell. Research permits were provided by the United States Department of the Interior National Park Service (Gauley River National Recreation Area and New River Gorge National River), the United States Department of Agriculture National Forest Service (Monongahela National Forest, Fernow Experimental Forest, Washington and Jefferson National Forest), the West Virginia Department of Natural Resources (Carnifex Ferry State Battleground Park), and the Nature Conservancy Virginia Chapter (Warm Springs Preserve). I am very grateful to the consistent support and encouragement of my advisor, Dr. Charles Goebel who helped me develop and design all phases of this project and vii supported my development as an independent scientist. Drafts of my dissertation were improved by the generous consideration and helpful suggestions of my committee members, Drs. John Cardina, Peter Curtis, and Ron Hendrick. In the School of Environment & Natural Resources, Mary Cappocia, Amy Schmidt, Pat Patterson, Anthony Utz, and Bev Winner were wonderfully helpful. Rocky & Belynda Smiley were great personal and professional supporters and friends, particularly with MWGL-SER. This journey was supported by my dear family and friends, particularly my parents Jackie and Bunn Martin, and numerous wonderful people including, but not limited to: Julia Barton, Ray Ball, Sarah Becker, Sabrina Grossman, Jessica Fouke, Krista Jacobsen, Laura Kearns, Kay Kirkman, Jessica Rutledge, Shannan Reichenberg, and Rachel Schultz. viii Vita June 1997 .......................................................Hayfield Secondary School May 2001 .......................................................B.S. Biology, minor Computer Science, College of William & Mary December 2006 ..............................................M.S. Ecology, University of Georgia June 2007 to present ......................................Graduate Fellow, School of Environment & Natural Resources, The Ohio State University Publications Martin, K.L., D.M. Hix , and P.C. Goebel. 2011. Coupling of vegetation layers and environmental influences in a mature, second growth Central Hardwood forest ecosystem. Forest Ecology and Management 261: 720-729. Martin, K.L. and P.C. Goebel. 2011. Preparing for hemlock woolly adelgid in Ohio: communities associated with hemlock-dominated ravines of Ohio’s Unglaciated Allegheny Plateau. Proceedings, 17th Central Hardwood Forest Conference; 2010 April 5-7; Lexington, KY. USDA Forest Service General Technical Report. Refereed paper. Martin, K.L. and P.C. Goebel. 2010. Impacts of hemlock decline on successional pathways and ecosystem function at multiple spatial scales in forests of the central ix Appalachians, USA. Pp. 147-152, In: J.C. Azevedo, M. Feliciano, J. Castro and M.A. Pinto (Editors), Proceedings of the IUFRO Landscape Ecology International Conference, Sept. 21-27. Bragança, Portugal. Non-referred paper. Martin, K.L. and L.K. Kirkman. 2009. Management of ecological thresholds to re- establish disturbance-maintained herbaceous wetlands of the Southeastern USA. Journal of Applied Ecology 46: 906-914. Fields of Study Major Field: Environment and Natural Resources x Table of Contents Abstract .............................................................................................................................. iii Acknowledgments............................................................................................................. vii Vita ..................................................................................................................................... ix List of Tables ................................................................................................................... xiv List of Figures .................................................................................................................. xvi Chapter 1: Introduction ...................................................................................................... 1 Chapter 2: Resilience, alternate states, and biodiversity of eastern forests during rapid environmental change ....................................................................................................... 13 2.1 Abstract ................................................................................................................... 13 2.2 Introduction ............................................................................................................. 14 2.3 Resilience and alternate states ................................................................................