Spatial and Temporal Patterns of Tree Encroachment Into a Southern Appalachian Grass/Heath Bald Using Tree Rings

Abstract

Craggy Gardens, a Southern Appalachian grass/heath bald in western North Carolina, is experiencing Quercus rubra L. encroachment on the western slope. Grass balds provide habitat for a number of rare and endemic species and have been ranked by The Nature Conservancy as G1 (Critically Imperiled Globally). We used belt transects and dendroecological analysis to reconstruct Quercus rubra establishment and recruitment over the past 245 years. Tree-ring records from 128 trees yielded distinct spatial and temporal patterns of encroachment that appear to be explained in large part by historical land use. Grazing by European livestock suppressed tree establishment, and its cessation in the early 1930s facilitated tree establishment and recruitment. Reduced rates of tree encroachment after the 1960s appear to be linked to shading of the understory upon canopy closure after the initial surge of establishment. Tree encroachment declined significantly after 1980, and was followed by the initiation of an ecological restoration project aimed at maintaining the grass bald at Craggy Gardens to preserve rare and endangered species and scenic appeal. Active management has reintroduced a strong human influence on the successional development of the bald.