Changes in Structure, Pattern and Diversity Associated with Climax Forest Maturation in Piedmont, North Carolina

Abstract

During 1951 and 1952 the position and diameter were recorded for each tree on a 140 .times. 140 m plot of immature climax oak-hickory forest in the Duke Forest, Durham, North Carolina [USA]. To ascertain the changes in structure associated with climax forest maturation, this plot was remapped in 1974 and and the 2 maps compared. In general, tree density, particularly of overstory trees, decreased while total basal area increased from 1951-52 to 1974. The most notable changes were a 75% reduction in density of Carya spp. and a 230% increase in density of Acer rubrum. Many dominant species showed significant reduction of numbers in smaller size classes in 1974. Tree-by-tree analysis of mortality and recruitment revealed low rates of population recruitment and high mortality rates in these smaller size classes. Tree pattern, analyzed by quadrat and point-to-neighbor methods, was clumped in smaller size classes and random or regular in larger size classes on both maps. Total tree pattern shifted from random in 1951-52 to regular in 1974. This shift was the result of significantly higher mortality in the smaller size classes which had clumped distributions. Species diversity H'', decreased during this time; pattern diversity (Pielou, 1966) increased. Decreased species diversity resulted from diminished equitability, whereas increased pattern diversity was probably due to shifts in tree pattern.