Influence of Soils and Parent Materials on Grasslands of the Wichita Mountains Wildlife Refuge, Oklahoma

The basal area and relative composition of the grassland communities of the Wichita Mountains Wildlife Refuge were determined by the point—contact method. Basal area varies from 13 to 16% in communities with a considerable amount exposed rock, from 18 to 20% on tall grass sites, and to a maximum of 27% on the shallow—soiled short—grass areas. Based on relative abundance of the most frequent species there are nine distinct grassland faciations on six soil types and four geological formations. If topography is considered further delineations raise the total to eleven. Several of the areas support the same major dominants but there are often significant differences in abundance. Andropogon scoparius makes up 24 to 48% of the stand in eight of the eleven faciations, Andropogon gerardi provides 10 to 40% in ten types and Bouteloua hirsuta composes 11 to 35% in four types. These species are the major dominants from the 50 grass species, 4 genera of sedges, and 64 species of forbs in the sample. Forbs such as Coreopsis tinctoria, Vernonia baldwinii, Crysopsis villosa, Liatris punctata, and Gaillardia pulchella are valuable seasonal indicators of soil types although the most abundant forb, Ambrosia psilostachya, is not. Definite correlations exist between soil types and vegetation and between geological formations and vegetation. The correlation of vegetation with a combination of soil type and geological formation is better than with soil type alone.