Stand dynamics of an Appalachian old-growth forest during a severe drought episode

Abstract

We analyzed data from 19 0.1 ha permanent plots of an old-growth cove forest in Walker Cove Research Natural Area (North Carolina), in order to understand the process affecting old-growth forest dynamics. During the study period (1979–1994) every stem with DBH larger than 5 cm was identified to species level and DBH was measured every 5 years. Between 1984 and 1989 censuses, a severe drought occurred in the forest. In the studied period, basal area proportions among dominant tree species changed: Acer saccharum and Aesculus flava showed significant increases, whereas Tilia americana and Fagus grandifolia decreased. Recruitment increased significantly during the study period. Mortality had a maximum during drought, having an U-shaped pattern as a function of diameter for T. americana and F. grandifolia and an L-shaped pattern for A. saccharum and A. flava. Diameter growth was negatively related to mortality, and was a stronger predictor of mortality than DBH. Surprisingly, diameter growth was highest during the drought. This pattern was constant among the dominant species, but varied considerably across the different size classes, with growth increases in the smaller size classes, but growth reduction for the largest size class.