Effects of range management on the lower Rio Grande watershed

The SPUR-91 model was used to simulate the effect of alternate stock densities on properties of the lower Rio Grande watershed. The output data was then used as input data into an income maximizing model to measure economic effects of alternate management on two representative ranches in Texas and Mexico. Each ranch had a management choice defined over four stocking densities combined with two alternate deer leasing systems. Deer lease income was inversely related to cattle density. Each management choice had a different outcome on firm revenue, and runoff and sediment mean and standard deviations. The economic model recorded the watershed data related to the management choice that maximized ranch incomes under nine scenarios. SPUR-91 results showed greatest runoff under heavy stocking (7.9 cm year−1) and least under light stocking (7.1 cm year−1). Sediments and soil evaporation showed similar correlations. Plant transpiration had an inverse correlation, and deep percolation was non-existent. Nine scenarios were generated with the economic model: (1) no deer leasing, (2–5) alternate deer lease prices, (6) a base, present condition, (7–8) imposed runoff limits with and without deer leasing, and (9) imposed runoff increases.