Stress, disturbance and change in rangeland ecosystems

Ecological systems and the organisms which comprise them have evolved with and are a product of various stresses, perturbations, and disturbance regimes. However, in human-influenced systems, new disturbances and stresses may be introduced and the frequency, intensity and spatial extent of natural disturbances altered. Natural and anthropogenic disturbances invariably co-occur, so it becomes difficult to ascertain which may be the proximate cause of ecosystem change. It is likely that their effects are compounded by synergistic interactions. In some cases, anthropogenic disturbance may alter the susceptibility of organisms, populations and communities to natural disturbances. In other cases, anthropogenic activities may initiate positive feedbacks that produce rapid, unexpected changes in ecosystem structure and function. These changes may be stabilized by new ecosystem processes, making them irreversible over time frames relevant to management.