Tree Growth and Mortality in a Southern Appalachian Deciduous Forest Following Extended Wet and Dry Periods

We inventoried two 1-ha plots on opposing watersheds (WS2–WS-S, WS18–WS-N) three times (1983, 1989, 1998) over a 16-year period to contrast how differing precipitation (P) regimes affect tree mortality. From 1983 to 1989, annual precipitation averaged 16.5% less than the 64-year mean; from 1989 to 1998, it averaged 12.2% above the mean. In 1989 and 1998, standing crop biomass, aboveground net primary productivity, mortality rates and species composition were determined. In 1989, following the dry period, the highest mortality for canopy tree species was in Carya spp. and Quercus velutina in both watersheds. Following the wet period in 1998, mortality was highest in Cornus florida in both watersheds, presumably due to the Anthracnose fungus; however, net change in stem density due to ingrowth was positive for this species in the WS-S watershed (þ34%) and negative in the WS-N watershed ( 18%). Estimated ANPP for WS-S was 10 and 1,076 kg ha 1 yr 1 for the periods 1983–89 and 1989–98, respectively. In contrast, ANPP on WS-N was 679 and 93 kg ha 1 yr 1 for the same periods. Differences in ANPP are due to higher rates of mortality on WS-N compared with WS-S. In this study, species specific rates of mortality varied by watershed, and were likely due to microclimate-related increased susceptibility at the species level to certain proximal causes.