A Comparison of Some Woody Upland and Riparian Plant Communities of the Southern Edwards Plateau

Abstract

Vegetation of the southern Edwards Plateau in northwestern Bexar County and northeastern Medina County, Texas, was analyzed using the point- centered-quarter method to determine major community relationships. Two geo- logically different areas were studied, including outcroppings of the Buda forma- tion and Quaternary deposits or creekbottoms. Although the total acreage occupied by the Quaternary deposits and intermittent creeks was small compared to the overall area studied, many species were found only in the creekbottoms. A total of 35 woody species was encountered; 49% were found only in riparian habitats, 14% were exclusively upland, and 37% were common. Dominants on the Buda formation were Mexican juniper (Juniperus ashei), live oak (Quercus fusiformis), and Texas persimmon (Diospyros texana), while Mexican juniper, cedar elm (Ulmus crassifolia), sycamore (Platanus occidentalis), and Texas persimmon were dominants in the creekbottoms. The number of species, total density and the sum of average dominance values were statistically different in the two communities. There were 30% more species in the creekbottoms and total density was almost three times greater on the Buda; however, the sum of the average dominance values was eight times greater in the creekbottoms. The Edwards Plateau region (Gould 1969) is located in west central Texas (Fig. 1). It is bounded rather sharply by the Balcones Escarp- ment on the east and south, grades gradually into the Rolling Plains and High Plains on the north, and the Trans-Pecos region on the west. Thorthwaite (1948) considers the eastern half as dry subhumid and the western half as semiarid. However, both are mesothermal. Rainfall varies from approximately 38 cm/yr in the west to approxi- mately 84 cm/yr in the east. with peaks occurring in the spring and fall. The soils are typically shallow and calcareous Tarrant-Brackett Association Soils for the upland sites with the deeper Venus-Frio-