Vegetation of a 25-Year Exclosure on the Edwards Plateau, Texas

An evaluation was made of current species composition, production and 25-year vegetation trends within an exclosure on the Texas A&M University Agricultural Research Station at Sonora, Texas. Community composition was variable and most species responded individually to soil variables, particularly soil depth and degree and kind of stoniness. Common curlymesquite (Hilaria belangeri) was the most characteristic and widespread species of the area. Communities dominated by Texas cupgrass (Eriochloa sericea), on soils greater than 25 cm in depth, produced 4,330, 2,235, and 504 kg/ha in June and August 1972 and January 1973, respectively. Wright threeawn (Aristida wrightii) dominated communities with soil depths of 15 cm, produced 1,318, 1,349, and 413 kg/ha for the same dates; and hairy tridens (Erioneuron pilosum) sites with soil depths of 10 cm yielded 970, 1,456, and 84 kg/ha. Vegetation change over the past 25 years has been primarily adjustment in relative dominance of species rather than addition or loss of species. Following establishment of the exclosure some species adjusted to previous grazing history, and thereafter primary changes followed precipitation variation.