Changes in Composition of the Mixed Mesophytic Forest: Effects of Succession and Disturbance

Abstract

This study investigated the hypothesis that air pollution is causing mortality of the larger overstory trees, which results in a shift in species composition. To determine if the theorized shifts in species composition have occurred, this study compared historical changes in forest composition as described by Braun (1940) with more recent changes as quantified by the Forest Inventory Analysis (FIA) program of the USDA Forest Service. FIA estimated recent composition changes using records of live, dead, and cut trees from 5,404 randomly sampled plots. Analyses suggest that the forest overstory consisted mostly of late-successional species in the 1940s and early- and mid-successional species in the 1980s. Thus, differences were most likely due to disturbances (insects and diseases, fire, weather, pollution) that killed trees, which allowed pioneer species to occupy openings. Forest succession may account for the 6 percent of dead trees in the 1980s since the percentages of dead trees were significantly greater among early-successional species. Percentages and spatial gradients of dead trees of species tolerant to air pollutants were similar to dead trees of intolerant species. Most of the 4 percent of all trees cut in the 1980s were not late-successional species, which may have favored successional trends.

Citation

Steinman, Jim. 1999. Changes in Composition of the Mixed Mesophytic Forest: Effects of Succession and Disturbance. USDA Forest Service NA-TP-04-99 Northeastern Area