Native desert grassland plant species declines and accelerated erosion in the Paint Gap Hills of southwest Texas

Abstract

Due to the hotter droughts occurring with climate change, grasslands of southwestern deserts and southern plains in the United States are predicted to increasingly lose cover of native plant species, be invaded by nonnative species, and have accelerated soil erosion. We evaluated these predictions for desert grasslands in the Paint Gap Hills of Big Bend National Park, Texas. We used data from 10 monitoring transects established in 1981 and surveyed vegetation composition, canopy cover, and soil surface elevations in 1981, 1983, 1995, and 2014. Four longer and hotter droughts occurred between 1985 and 2014. We found that by 2014 canopy covers of two dominant native warm-season perennial grasses, Bouteloua curtipendula and Bouteloua ramosa, were reduced to near zero, and the cover of many native shrubs and subshrubs had notably declined. By 2014 two nonnative perennial grasses, Eragrostis lehmanniana and Pennisetum ciliare, had invaded, and their expansion could have long-term ecological consequences. Soil surfaces changed from accumulating sediments at a rate of 0.7 mm/year for 1983–1995 to eroding at −1.6 mm/year for 1995–2014. These soil and vegetation changes support predictions of major declines in native desert grasslands and emphasize their vulnerability to climate change.