Nearly all ecosystems are subject to periodic disturbances by natural events, such as flood, fire, drought, and insect infestation (Vogl 1980). When such perturbations are extreme, ecosystems of immense complexity undergo rapid transformation to systems of remarkable simplicity that are characterized by a scarcity of life forms and few or no symbiotic interactions. However, this transformation sets the stage for recovery, which allows the ecosystem to adapt to changing environments (Holling 1986). In healthy systems, therefore, these perturbations are seldom more than a temporary setback, and recovery is generally rapid (Odum 1969). By contrast to natural disturbances, anthropogenic stress is not a revitalizing agent, but a debilitating one. Stressed ecosystems do not recover; rather, further degradation may follow. Indeed, Odum et al. (1979) defined stress as a debilitating agent and perturbation (subsidy) as potentially beneficial.