Scale and frequency of natural disturbances in the northeastern US: implications for early successional forest habitats and regional age distributions

Abstract

Recent declines in the amount of habitat suitable for early successional wildlife in the northeastern US have prompted public land managers to consider establishing minimum levels of young forest, based on the natural range of variation, in order to maintain viable populations of these species. In this paper, we review evidence on the frequency, severity, and scale of natural disturbances in four major forest regions of the northeastern US. Using six independent lines of evidence, we examined the influence of natural disturbances in presettlement and modern times. In situations where estimates of annual disturbance rates were available, we estimated the regional age distribution of forest stands based on the assumption of random spatial pattern of disturbance. Available evidence suggests a gradient of generally decreasing disturbance frequency from coastal regions to the interior uplands and mountains. The proportion of the presettlement landscape in seedling–sapling forest habitat (1–15 years old) ranged from 1 to 3% in northern hardwood forests ( Fagus– Betula– Acer– Tsuga) of the interior uplands to possibly >10% in coastal pine–oak ( Pinus– Quercus) barrens. Within a region, variability in the amount of young forest is not well known, but upper slopes and ridges generally had the highest disturbance frequency and severity. Comparison of line transect data of the presettlement land surveys with modern plot surveys suggests that present-day amounts of young forests in northern hardwood and spruce–hardwood forests in some regions may be several times higher than in presettlement times. In coastal oak forests and pine–oak barrens, the amount of young forests and open woodlands may be less because of reduced fire frequency.