Composition, Classification and Species Response Patterns of Remnant Tallgrass Prairies in Texas

Abstract

Thirty-five remnant upland grasslands within the Blackland, San Antonio, Fayette and Upper Coastal prairies were sampled for species frequency, foliage cover and richness. PCA ordination and cluster analysis were used to ordinate and classify these communities. The majority of these grasslands are dominated by Schizachyrium scoparium with Sorghastrum nutans the second most important species. Andropogon gerardii and Bouteloua curtipendula increase in importance with increasing soil clay content, organic matter and pH and decreasing total annual precipitation. Paspalum plicatulum becomes an important secondary species in communities over acid Alfisols in the Fayette Prairie and acid Alfisols and Vertisols of the Upper Coastal Prairie. High precipitation ( > 90 cm) areas over Alfisols at the northern end of the Blackland Prairie support a unique grassland dominated by Sporobolus silveanus with Carex meadii as an important secondary species. In this same area on Vertisols communities are found that are dominated by Tripsacum dactyloides and Panicum virgatum. Species respond independently and continuously along soil and climatic gradients except where locally sharp transitions occur between Alfisols and Vertisols. Species diversity did not vary significantly among communities. Soil pH was positively correlated with species richness, which was related to slightly higher richness of stands on Alfisols whici. have low pH, and slightly higher richness of Coastal Prairie stands which also have generally lower pH values. INTRODUCTION The Blackland, Fort Worth, San Antonio, Fayette and Upper Coastal prairies occupy a N-S strip comprising approximately 8 million ha within E central Texas (Godfrey et al., 1973) (Fig. 1). Native vegetation of these grasslands has largely been destroyed by cultivation, overgrazing and urbanization. Although several authors have described these prairies (Dyksterhuis, 1946; Launchbaugh, 1955; Collins et al., 1975; Butler, 1979; Diamond, 1983; Smeins and Diamond, 1983), no attempt has been made to compare patterns of community composition and species diversity among them. The Upper Coastal Prairie has traditionally been separated from other Texas prairies (Tharp, 1926; Gould, 1975), but lack of quantitative data makes an evaluation of the degree of relationship among the Coastal Prairie and other Texas prairies impossible. This study provides quantitative data on vegetation and soils of uplands within the Blackland, Fayette, San Antonio and Upper Coastal prairies. These data allow detailed analysis of Texas grasslands to: (1) determine relationships among communities; (2) evaluate species-to-species and species-to-environment relationships; (3) clarify classification, and (4) evaluate patterns in species diversity. STUDY AREA Location and extent. -The grasslands studied are located in a N-S strip approximately 300 km wide and 100 km long in E and central Texas (Fig. 1). To the N the Blackland Prairie borders on the Red River, whereas to the S the Coastal Prairie grades into the Gulf Coast marshes. The eastern border is defined by the Post Oak Savannah, while the western border is defined by the western Cross Timbers in the N, the Edwards Pla-