Alternative stable states in inherently unstable systems.

Alternative stable states are nontransitory states within which communities can exist. However, even highly dynamic communities can be viewed within the framework of stable-state theory if an appropriate "ecologically relevant" time scale is identified. The ecologically relevant time scale for dynamic systems needs to conform to the amount of time needed for a system's community to complete an entire cycle through its normal range of variation. For some systems, the ecologically relevant period can be relatively short (eg, tidal systems), for others it can be decadal (eg, prairie wetlands). We explore the concept of alternative stable states in unstable systems using the highly dynamic wetland ecosystems of North America's Prairie Pothole Region. The communities in these wetland ecosystems transition through multiple states in response to decadal-long climate oscillations that cyclically influence ponded-water depth, permanence, and chemistry. The perspective gained by considering dynamic systems in the context of stable-state theory allows for an increased understanding of how these systems respond to changing drivers that can push them past tipping points into alternative states. Incorporation of concepts inherent to stable-state theory has been suggested as a key scientific element upon which to base sustainable environmental management.