Fluctuations in Biotic Communities, V. Aspection in a Mixed-Grass Prairie in Central Oklahoma

As representative of the south-central mixed-grass prairies a large cattle range in McClain county, Oklahoma (R. 4 W., T. 8 N., sec. 12), near the University of Oklahoma was selected and a study made of the ecology of its plants and animals. A consideration of the affiliations of the community found here with the remainder of the mixed-grass prairie community is included in a separate study dealing with the ecology of the entire grassland biome (Carpenter, 1939a). The area studied in Oklahoma, known locally as Johnson's Pasture, has been somewhat overgrazed in the past, and burnings in the spring have been frequent. Grazing and fire have contributed to severe gulleying in the ravines and according to local reports the general appearance of the ravines which cut into the upland has been greatly changed by grazing with a resulting invasion of trees and shrubs which were not present in their present-day abundance 50 years ago. Elsewhere an account of succession in these ravines has been given (Carpenter, 1937). It is apparent that the instability of the tension zone has been enhanced by increased grazing pressure with a disproportionate increase in erosion. Erosion in the upland, except in the vicinity of the heads of the ravines, has been confined to sheet erosion. The upland is dominated by mixed-prairie grasses for the most part and the aspect,is typically that of prairie. The local distribution of the dominant grasses and the seasonal plants of the serotinal aspect has been described by Carpenter (1939b).