Climate-induced catastrophic shifts in pastoralism systems managed under the maximum sustainable yield model

The effects of the foreseen change in precipitation and temperature on dynamic grazing systems that are managed under the hypothesis of the maximum sustainable yield (MSY) are assessed. The standard Gordon Schaefer approach that relates the rate of above-ground vegetation production to biomass consumption by herbivores is adopted to simulate the grazing system. In order to account for future climate variability, the model is modified using principles from water balance hydrology, thus introducing vegetation growth limitations due to climatic aridity. The model is applied for an equilibrium established under the much criticized MSY hypothesis that assumes the optimum herbivore density for maximum biomass removal. Sensitivity analysis results indicate that as climate changes towards a warmer and drier future, the probability of a low ecological stability grazing system to collapse increases, especially in arid environments where water is a limited resource. Such sudden shifts that lead to undesirable stable states of arid ecosystems are investigated by the CASCADE EU project.