PHYSIOGRAPHIC POSITION, DISTURBANCE AND SPECIES COMPOSITION IN NORTH-CAROLINA COASTAL-PLAIN FORESTS

Relations among physiographic heterogeneity, disturbance and temporal change in forest composition were analyzed on 765 forest stands in the southern coastal plain of North Carolina. Physiographic position strongly restricted the species composition of forest stands, though broad overlap of some physiographic classes was noted. Forest stands in different physiographic positions experienced significantly different disturbance regimes. Temporal dynamics were represented as displacement vectors in an ordination space. The distance and direction of displacement over time were analyzed to determine the impact of disturbance on vegetation composition. After removing the effects of physiographic position and initial state of the vegetation, three general pathways were identified. Wildfire, insect and harvest disturbance types induce stand dynamics that are directionally opposite to undisturbed stands' developmental trends. Prescribed burning induced compositional dynamics unlike those observed for any other disturbance types, while other disturbance types, including weather, disease and non-harvest cutting, do not substantially differ from undisturbed stands in the overall direction of their displacement in the ordination space. Only harvesting and prescribed fires induce displacements in the ordination space that are very much different in magnitude from undisturbed stands.