Monday, November 13, 2006 - 1:30 PM

Changes in Carbon and Nutrient Pools in Forests of Walker Branch Watershed, 1972 - 2004.

Dale W. Johnson, Natural Resources and Environmental Science, Fleischmann Ag, MS 370, Univ of Nevada, Reno, Reno, NV 89557, Donald E. Todd, Environmental Sciences Division, Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, TN 37830, and Carl Trettin, USDA Forest Serv South Research Station, 2730 Savannah Hwy, Charleston, SC 29414.

Soils, litter and vegetation were sampled in selected plots on Walker Branch Watershed, Tennessee four times over a period of 32 years. The same individual was responsible for each sampling (D.E. Todd) and samples from previous years were re-analyzed in order to minimize sampling and laboratory bias and to maximize quality assurance. Changes in soil and litter pools over time were not uni-directional and patterns observed in previous samplings  were often reversed in 2004. For example, the observed declines in soil C and N pools observed between 1982 and 1993 in several plots (Johnson and Todd, 1990; Trettin et al., 1999) were reversed in the 2004 sampling. On the other hand, declines in surface soil exchangeable Ca2+ and Mg2+ continued throughout the sampling periods in most cases, and could be attributed mostly to vegetation uptake in this aggrading forest ecosystem. Litter C and nutrient pools showed as much as 50% variation over the sampling period with no obvious overall trends across plots or time. With rare exception, however, C and nutrient pools in aboveground vegetation continued a general trend of accumulation over time, with some fluctuations due to insect and disease outbreaks that caused species shifts. We conclude that the changes in forest floor and soil pools in these ecosystems are much greater than expected and much less consistent than expected over both space and time.