Prepared in cooperation with the U.S. Air Force, Arnold Air Force Base and the University of the South Tree-Regeneration and Mortality Patterns and Hydrologic Change in a Forested Karst Wetland—Sinking Pond, Arnold Air Force Base, Tennessee Water-Resources Investigations Report 03-4217 U.S. Department of the Interior U.S. Geological Survey Cover photographs: Left photograph is overcup oak in Sinking Pond under drained conditions, courtesy of K.C. Fitch, Arnold Engineering Development Center, 2001. Right photograph is overcup oak in Sinking Pond under flooded conditions. Tree-Regeneration and Mortality Patterns and Hydrologic Change in a Forested Karst Wetland—Sinking Pond, Arnold Air Force Base, Tennessee By William J. Wolfe, Jonathan P. Evans, Sarah McCarthy, W. Scott Gain, and Bradley A. Bryan Prepared in cooperation with the U.S. Air Force, Arnold Air Force Base and the University of the South Water-Resources Investigations Report 03-4217 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, Director U.S. Geological Survey, Reston, Virginia: 2004 For sale by U.S. Geological Survey, Information Services Box 25286, Denver Federal Center Denver, CO 80225 For more information about the USGS and its products: Telephone: 1-888-ASK-USGS World Wide Web: http://www.usgs.gov/ Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Wolfe, W.J., Evans, J.P., McCarthy, Sarah, Gain, W.S., and Bryan, B.A., 2004, Tree-regeneration and mortality patterns and hydrologic change in a forested karst wetland—Sinking Pond, Arnold Air Force Base, Tennessee: U.S. Geological Survey Water-Resources Investigations Report 03-4217, 53 p. iii Contents Abstract .......................................................................................................................................................... 1 Introduction ................................................................................................................................................... 1 Purpose and Scope ............................................................................................................................. 3 Previous Studies .................................................................................................................................. 3 Description of Study Area ........................................................................................................................... 3 Karst Hydrology and Geomorphology .............................................................................................. 5 Hydrogeology ....................................................................................................................................... 5 Soils ................................................................................................................................................... 6 Climate ................................................................................................................................................... 6 Vegetation ............................................................................................................................................ 6 Tree-Regeneration and Mortality Patterns .............................................................................................. 7 Overcup Oak Population Dynamics in Sinking Pond, 1997-2001 .................................................. 7 Seedling Establishment and Recruitment .............................................................................. 8 Adult Mortality ............................................................................................................................ 9 Spatial Patterns of Tree-Size Classes and Ponding Depth ........................................................ 10 Adults ........................................................................................................................................ 11 Small Adults and Saplings ....................................................................................................... 11 Seedlings .................................................................................................................................... 15 Age Distribution of Adult Overcup Oaks ........................................................................................ 15 Botanical Evidence for Hydrologic Change ................................................................................. 19 Hydrologic Change in Sinking Pond, 1854-2002 ..................................................................................... 20 Hydrologic Modeling ......................................................................................................................... 22 Model Input Data ...................................................................................................................... 22 Model Structure ........................................................................................................................ 23 Definition of Parameters .......................................................................................................... 24 Model Equations ....................................................................................................................... 25 Calibration and Verification .................................................................................................... 29 Simulated Hydrologic Record of Sinking Pond, 1854-2002 ......................................................... 30 Ecological Effects of Hydrologic Change in Sinking Pond .................................................................. 33 Hydrologic Constraints on Overcup Oak Recruitment and Survival ......................................... 33 Future Ecological Conditions in Sinking Pond .............................................................................. 36 Conclusion: Management and Scientific Implications of Hydrologic and Ecological Change in Sinking Pond ........................................................................................... 37 Acknowledgments ...................................................................................................................................... 38 References ................................................................................................................................................... 38 Appendix A. Flora of Sinking Pond. .......................................................................................................... 43 Appendix B. Evaluating Effects of Local Human Activity on the Hydrology of Sinking Pond ....... 47 Glossary ........................................................................................................................................................ 53 iv Figures 1. Map showing major physiographic regions of Tennessee and locations of The Barrens, Arnold Air Force Base, and study area ............................................................ 2 2. Map showing location of Sinking Pond, adjacent drainage basins, monitored wells, and surface-water stations ............................................................................................ 4 3. Hydrograph showing water-surface elevations in Sinking Pond and adjacent well 355 for the period October 1, 1992, through February 12, 1995 .................................... 5 4. Graph showing normal annual precipitation at Tullahoma, Tennessee, 1960-2000 .......... 7 5. Photographs of areas in the interior and along the margins of Sinking Pond .................. 8 6. Graph showing aggregate mortality of adult overcup oaks by ponding depth and size class, assessed annually in 55 circular plots in Sinking Pond, 1998-2001 ............... 11 7. Map showing distribution of overcup oak by ponding-depth class and life-history state in a 2.3-hectare area of Sinking Pond ...................................................... 12 8. Graph showing size-class distribution of adult overcup oak in a 2.3-hectare area of Sinking Pond by ponding-depth class. ................................................ 13 9. Map showing distribution of sweetgum by ponding-depth class and life-history state in a 2.3-hectare area of Sinking Pond ...................................................... 14 10. Graph showing size-class distribution of adult sweetgum in a 2.3-hectare area of Sinking Pond by ponding-depth class. ................................................ 15 11. Map showing distribution of willow oak by ponding-depth class and life-history state in a 2.3-hectare area of Sinking Pond .............................................. 16 12-16. Graphs showing: 12. Size-class distribution of adult willow oak in a 2.3-hectare area of Sinking Pond by ponding-depth class. ............................................................................ 17 13. Size-class distribution of adult river birch in a 2.3-hectare area of Sinking Pond by ponding-depth class. ............................................................................ 17 14. Frequency distributions of tree diameters at 1.5 meters above land surface and elevation for adult