Sustainability of Rangeland Pastoralism—a Case Study from the West Australian Arid Zone using Stochastic Optimal Control Theory

Optimal economic policies with respect to stocking rate and season of grazing for an arid chenopod pasture type were derived for various starting states under a stochastic optimal control framework. Optimal policies were determined using decision criteria which involved either no discounting of future returns or a discount rate of 6%, and were further evaluated by analysing their long-run economic and ecological consequences. All optimal policies involved either year-long set stocking or destocking. Policies involving seasonal grazing or variable stocking rates were not economically viable at the specified cost levels. Optimal stocking rates increase with the level of forage biomass and the density of adult plants, but decrease with the level of either young or old seedlings when these provide an opportunity for regeneration of degraded range. Without discounting, pastoral use of this vegetation type can be both economically and ecologically sustainable. Long-run vegetation dynamics under this criterion are similar to those expected in an ungrazed community. However, land which is severely degraded is, for all practical purposes, not recoverable either by privately optimal grazing management or by complete removal of grazing. Discounting of future returns results in a more exploitative set of grazing policies and reduces opportunities for regeneration of degraded land. Pastoralism under this criterion is not ecologically sustainable although it is economically viable. The role of such analyses in pastoral management decision-making, and the implications of the results for policy with respect to administration of public rangelands, are briefly discussed.