Georgia Southern University Digital Commons@Georgia Southern Electronic Theses and Dissertations Graduate Studies, Jack N. Averitt College of Fall 2005 Beaver (Castor Canadensis) Impacts on Herbaceous and Woody Vegetation in Southeastern Georgia Jessica R. Brzyski Follow this and additional works at: https://digitalcommons.georgiasouthern.edu/etd Recommended Citation Brzyski, Jessica R., "Beaver (Castor Canadensis) Impacts on Herbaceous and Woody Vegetation in Southeastern Georgia" (2005). Electronic Theses and Dissertations. 707. https://digitalcommons.georgiasouthern.edu/etd/707 This thesis (open access) is brought to you for free and open access by the Graduate Studies, Jack N. Averitt College of at Digital Commons@Georgia Southern. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of Digital Commons@Georgia Southern. For more information, please contact [email protected]. BEAVER (CASTOR CANADENSIS) IMPACTS ON HERBACEOUS AND WOODY VEGETATION IN SOUTHEASTERN GEORGIA by JESSICA R. BRZYSKI (Under the direction of Bruce A. Schulte) ABSTRACT North American beavers are considered ecosystem engineers. Their activities can quickly and drastically alter habitat properties and perhaps permit highly aggressive colonizing plants, notably non-native species, to invade and potentially dominate. This study examined if beavers in southeastern Georgia have an effect on the terrestrial plant community. Sampling areas included beaver modified (N=9) and nearby but relatively non-impacted riparian habitat (N=9) in a matched pairs design. Vegetation surveys were performed in spring and summer. Species richness was calculated for herbs, vines, woody seedlings, and woody vegetation. Richness of herbaceous vegetation was higher at distances closer to shore while richness of large woody vegetation increased with distance from shore. Woody vegetation also was more abundant in beaver sites. Composition was not different between the two site types. The presence of exotic species was rare and did not differ by site type. This study provides evidence that beavers may play an important role in determining the vegetative structure of their community. Index words: Castor canadensis, beaver, herbaceous, vegetation, exotics, ecosystem engineers, non-native BEAVER (CASTOR CANADENSIS) IMPACTS ON HERBACEOUS AND WOODY VEGETATION IN SOUTHEASTERN GEORGIA by JESSICA R. BRZYSKI B.S., State University of New York College of Environmental Science and Forestry, 2001 A Thesis Submitted to the Graduate Faculty of Georgia Southern University in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE STATESBORO, GEORGIA 2005 2 © 2005 Jessica R. Brzyski All Rights Reserved 3 BEAVER (CASTOR CANADENSIS) IMPACTS ON HERBACEOUS AND WOODY VEGETATION IN SOUTHEASTERN GEORGIA by JESSICA R. BRZYSKI Major Professor: Bruce A. Schulte Committee: Lissa M. Leege Lorne M. Wolfe Miche1le L. Zjhra Electronic Version Approved: October, 2005 4 ACKNOWLEDGEMENTS I want to thank my major professor, Dr. Bruce Schulte, for his support, guidance, and advice throughout this project. With his help I was able to create my own research study and receive outside grants to fund this project. Furthermore, I would like to thank my committee members, Dr. Lissa Leege, Dr. Lorne Wolfe, and Dr. Michelle Zjhra, for their advice and support, whether it was discussing methods, invasions, PhD programs, or just plain botanizing. For the funding of this project, I would like to thank Sigma Xi Research Grant, and Georgia Southern Graduate Research Fund. I would like to thank Dr. Donald Drapalik for all of his help identifying specimens from the field, as well as teaching me how to properly preserve them. It is with his help that I was able to complete my thesis research. Thanks to undergraduates, Matt McBride and Matt Hinman, for help in data collection, dodging snakes, and brushing off fire ants. I would like to thank the Department of Natural Resources, specifically Richard Tanner, for his help in finding beaver sites and contacting landowners. Of landowners, I would like to specially thank the Mathews brothers whom define the meaning of the phrase “Southern hospitality”. Lastly, I want to thank my family for all of their love and support. Thank you for teaching me to take pride in all of my hard work, for listening to my worries, and for driving 1800 miles roundtrip to see me whenever I needed my family fix. I could do none of this without my parents and brother by my side. 5 TABLE OF CONTENTS Page ACKNOWLEDGEMENTS……………………………………………………………….5 LIST OF TABLES………………………………………………………………………...7 LIST OF FIGURES………………………………………………………………………..8 CHAPTER 1. INTRODUCTION………………………………………………………………. 10 2. METHODS a. Study Area…………………………………………….………………….18 b. Data Collection………………………………………………………….. 20 c. Statistical Analyses……………………………………………………… 22 3. RESULTS……………………………………………………………………….. 24 4. DISCUSSION……………………………………………………………………30 REFERENCES………………………………………………………………………….. 40 APPENDICES 1. Directions and Descriptions of Study Sites………………………………………65 2. Species Area Curve………………………………………………….…………...104 3. List of Plant Vouchers Collected at Study Sites……………………………....…113 6 LIST OF TABLES Page Table 1: An example of a split-plot design for richness of herbaceous vegetation……………………………………………………………………45 Table 2: Wetland classification of herbaceous and woody vegetation as per U.S. Fish & Wildlife Service (1988)………………………………………...46 Table 3: Principle Components Analysis of large woody vegetation of beaver- modified and control sites in Bulloch County, Georgia……………………. 47 7 LIST OF FIGURES Page Figure 1: Map of study sites in Bulloch County, Georgia……………………………. 48 Figure 2: Diagram of vegetation survey method………………………………………49 Figure 3: Average herbaceous vegetation richness measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………… 50 Figure 4: Average woody richness in 1 m2 plots measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………………. 51 Figure 5: Average woody richness in 25 m2 plots measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………………. 52 Figure 6: Average vine richness measured at four distances from shore in beaver- modified (n=9) and control sites (n=9)……………………………………...53 Figure 7: Average herbaceous vegetation abundance measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………………. 54 Figure 8: Average abundance for herbaceous vegetation when the outlier sites (2 beaver and 1 control) were removed from analysis…………………………55 Figure 9: Average woody abundance in 1 m2 plots measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………………. 56 Figure 10: Average large woody vegetation abundance measured in 25 m2 plots at four distances from shore in beaver-modified (n=9) and control sites (n=9)…….57 Figure 11: Diversity of herbaceous vegetation measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)…………………………. 58 Figure 12: Diversity for small woody vegetation measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………………. 59 Figure 13: Diversity of large woody vegetation measured at four distances from shore in beaver-modified (n=9) and control sites (n=9)……………………. 60 Figure 14: The relative abundance of all large woody vegetation measured in 25 m2 plots for beaver-modified (n=9) and control (n=9) sites…………………… 61 Figure 15: Principle Components Analysis performed on large woody vegetation with site type the grouping variable………………………………………... 62 8 Figure 16: Canopy cover measurements for matched beaver-modified and control sites (n=9) measured at 10 m from the water’s edge………………………. 63 Figure 17: The number of exotic plant species, herbaceous and woody, per site for beaver-modified and control (n=9)………………………………………….64 9 CHAPTER 1 INTRODUCTION Plant communities change over time through a process termed ecological succession, which includes altering species composition or the structure of a community (Cowles, 1910; Clements, 1916; Clements, 1936). Ecological changes through time can be classified as allogenic or autogenic (Barbour et al., 1999). Allogenic changes are caused by external forces not affected by biotic factors. The changes are the result of the physical environment, for example, when the temperature decreases as elevation increases. Autogenic changes are the direct result of a biotic influence in the community. These changes can be inhibitory to other organisms, such as when tree roots uptake water and nutrients from the soil, potentially reducing the ability of nearby vegetation to grow. Autogenic changes also can be facilitative, such as when organisms benefit from nitrogen fixers in the soil. The focus of this study was on autogenic changes, specifically those caused by the North American beaver (Castor canadensis). Beavers were once abundant and widely distributed throughout North America. Population numbers were estimated at 60-400 million, occupying the majority of waterways in North America, from as far north as the arctic tundra to the deserts of northern Mexico (Jenkins & Busher, 1979). As a consequence of unregulated trapping and habitat loss, beaver populations declined drastically and only small populations existed east of the Mississippi River by 1850 (Johnson & Chance, 1974). In Georgia, beaver were virtually eliminated, so a restoration program began in the 1940’s and lasted approximately