Global Conservation Issues

Tree mortality and climate change in a Highland Rim karst swamp: Sinking Pond, Coffee County, Tennessee

William Wolfe

Friday, October 17, 2008 - 4:00-4:30

Increased precipitation since 1970 has suppressed regeneration of overcup oak (Quercus lyrata Walt.) in Sinking Pond, a 35-hectare seasonally-flooded compound sinkhole near Manchester, Tennessee. A hydrologic accounting model, based on daily rainfall and temperature records covering the period January 1854 through September 2005, shows increases in ponding frequency and duration throughout Sinking Pond after 1970. This increase in ponding frequency and duration coincides with the local suppression of tree regeneration and corresponds to increases in regional streamflow and precipitation throughout the eastern United States. In a representative 2.3-hectare area of Sinking Pond, overcup oak saplings and young adults were found only in shallow (wet-season water depth less than 0.5 meter) sites, even though overcup oak seedlings and mature trees were concentrated in deep (water depth greater than 1 meter) sites. Analysis of tree rings from a 10-percent sample of mature overcup oaks in the same 2.3 hectare area shows an even distribution of tree ages across ponding-depth classes from the 1850s through 1970, abruptly followed by complete suppression of recruitment in deep and intermediate (water depth between 0.5 meter and 1 meter) areas after 1970. Trees younger than 30 years were concentrated in a small area with shallow ponding depth. The mechanism seedling mortality is prolonged inundation during at least 2 of the first 5 years after germination.

Keywords: KARST, CLIMATE CHANGE, TREE MORTALITY, FORESTED WETLANDS, QUERCUS LYRATA