Sustainability of agroecosystems in semi-arid grasslands: simulated management of woody vegetation in the Rio Grande Plains of southern Texas and northeastern Mexico

Abstract

We describe a model that simulates use of chemical treatments, mechanical treatments (roller chopping and root plowing), and fire to manage woody vegetation in the Rio Grande Plains of southern Texas and northeastern Mexico. The model consists of two submodels representing dynamics of woody and herbaceous vegetation, respectively. Percent canopy cover of woody vegetation changes as the result of application of management schemes. Aboveground biomass of herbaceous vegetation changes as the result of differences in rates of net primary production, senescence, decomposition, and losses due to grazing and fire. The model is represented as a compartment model based on difference equations with a time step of 1 month. Model predictions of changes in canopy cover of woody vegetation, number of acres required to support a cow, and net production of herbaceous vegetation following application of each of the four treatments are similar to typical 25-year post-treatment response curves for the Rio Grande Plains. Simulation results suggest that the period of opportunity for effective use of fire to manage woody vegetation and sustain production of herbaceous vegetation is longest following root plowing, intermediate following use of chemicals, and shortest following roller chopping. In each case, the efficacy of fire in reducing canopy cover of woody vegetation diminishes rapidly as percent canopy cover increases from roughly 30–50%.