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

We describe a model that simulates use of chemical treatments, mechanical t reatments (roller chopping and root plowing), and fire to manage woody vege tation in the Rio Grande Plains of southern Texas and northeastern Mexico. The model consists of two submodels representing dynamics of woody and herb aceous vegetation, respectively. Percent canopy cover of woody vegetation c hanges as the result of application of management schemes. Aboveground biom ass of herbaceous vegetation changes as the result of differences in rates of net primary production, senescence, decomposition, and losses due to gra zing and fire. The model is represented as a compartment model based on dif ference 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 r esponse curves for the Rio Grande Plains. Simulation results suggest that t he period of opportunity for effective use of fire to manage woody vegetati on and sustain production of herbaceous vegetation is longest following roo t plowing, intermediate following use of chemicals, and shortest following roller chopping. In each case, the efficacy of fire in reducing canopy cove r of woody vegetation diminishes rapidly as percent canopy cover increases from roughly 30-50%. (C) 1999 Elsevier Science B.V. All rights reserved.