HUMAN AND ENVIRONMENTAL-INFLUENCES ON FOREST COMPOSITION OF A TENNESSEE LOESS BLUFF

Prior investigations of forests on Mississippi River loess bluffs sugg est that their composition is regionally distinct, attributing mesophy tic species abundance to atypical physical conditions or Pleistocene h istory. Owing to the widespread anthropogenic impacts on this landscap e, this study examines the relative importance of human and natural fa ctors influencing bluff forest composition. Within the mosaic of forme r agricultural fields and uncleared areas on the Third Chickasaw Bluff of southwestern Tennessee, 10 transects were placed along the gradien t from bottomlands to ridgetops, stratified by former land use. Ordina tion indicates that the greatest compositional distinction exists betw een bottomlands and upland positions. Treated separately, the uplands are organized along two primary dimensions: the first distinguishes fo rmerly cleared ridgetops from all other habitats, the second represent s a moisture gradient. Three species groups respond differently to the se upland conditions: (1) recently disturbed sites favor sweetgum/tuli p poplar; (2) sites likely to have been disturbed in the more distant past are oak dominated; (3) mesophytic species prefer undisturbed habi tats. The disturbance-related characteristics of each habitat, rather than their direct environmental controls, are a major determinant of b luff composition. The ubiquity of anthropogenic disturbance throughout the region gives rise to the seeming uniqueness of the atypical bluff sites that escaped disturbance.