Ecological effects of fire on Texas wintergrass (Stipa leucotricha) communities

Abstract

Texas wintergrass (Stipa leucotricha Trin. & Rupr.) is an erect, tufted, cool-season, perennial which is an important component in plant communities of central and northcentral Texas. Experiments were conducted in the northern Edwards Plateau and southern Rolling Plains to determine the effects of season of burning and clipping on plant density, point frequency, basal area, reproductive vigor, and standing crop of Texas wintergrass. Texas wintergrass responded similarly to burning and clipping. The response of Texas wintergrass to burning was a function of fire intensity, growing conditions following burning, and post-burn competitive interactions with other plant species. Neither burning nor clipping significantly affected density, basal area or the number of reproductive culms of Texas wintergrass plants in dense homogeneous stands. Burning in January or March reduced Texas wintergrass point frequency, for one year and burning, regardless of season, reduced standing crops for one year. When annual, cool-season grasses were abundant, Texas wintergrass density, point frequency, and standing crop tended to increase following burning, apparently a result of reduced competition from annual plants. These increases were greater following fall burning and less pronounced following spring burning. Cool-season, annual grasses and forbs were usually killed if burned during the growing season. However, seed reserves in the soil and/or subsequent seed immigration into burned areas appeared to be sufficient to reestablish or even increase annual plant populations the second year following burning. Warm-season, perennial grasses were generally benefitted by burning in the spring and damaged by burning in fall. Soil water contents were reduced for 2 to 6 months following burning, and again when the subsequent crop of cool-season grasses and forbs began growth. Soil water reductions were greatest following March burns. Reductions in soil water contents were greater at 15 to 30 cm and 30 to 45 cm depths than at 0 to 15 cm. Post-burn soil temperatures were increased for most of the first year following burning. Burning had no significant effect on soil pH, organic matter, nitrate, phosphate, calcium, or magnesium. Contribution of ash to the soil appears to be unimportant in the ecology of Texas wintergrass communities compared to direct effects of the fire and subsequent changes in micro-environments.