Alternative stable states in inherently unstable systems

Abstract

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. K E Y W O R D Salternate stable states, community change, dynamic systems, ecological theory, prairiepothole wetlands, state shifts

Dynamic of Dominant Plant Communities in Kettle Holes (Northeast Germany) during a Five-Year Period of Extreme Weather Conditions

“…We suggest that terrestrial phases of kettle holes could also be regarded as alternative stable states, because if we assume irreversible succession the "dark diversity" will not reappear, resulting in irreversible changes to community composition. Hence, we agree with Mushet et al [15] that alternative stable states exist for highly dynamic systems, not only for changes in the horizontal hydrological axis, but also in the vertical rainwater axis. We hypothesize that many central European kettle holes, especially from the storage type, will shift towards more advanced succession stages after "appropriate ecological time scales" of drought conditions with less extreme wet years.…”

“…The realization that kettle holes and comparable small wetland types develop towards irreversible wood dominated climax stages, shows that the "wetland continuum concept" developed on the basis of pothole research [24,25] is not fully transferable to all kinds of small wetland ecosystems. As Mushet et al [15] pointed out, the "wetland continuum concept" incorporates the prairie-marsh cycle [9] at the vertical rainwater axis, with lake marsh during deluge and dry-marsh during drought, as two end-points that could be considered as stable systems and with the regenerating-marsh and degenerating-marsh as alternative stable or transitory states [15]. Alternatively, Mushet et al [15] postulate that all predictable phases described by van der Valk and Davis [9] are the "stable state" of the highly dynamic potholes and need to be viewed over longer time scales.…”

“…As Mushet et al [15] pointed out, the "wetland continuum concept" incorporates the prairie-marsh cycle [9] at the vertical rainwater axis, with lake marsh during deluge and dry-marsh during drought, as two end-points that could be considered as stable systems and with the regenerating-marsh and degenerating-marsh as alternative stable or transitory states [15]. Alternatively, Mushet et al [15] postulate that all predictable phases described by van der Valk and Davis [9] are the "stable state" of the highly dynamic potholes and need to be viewed over longer time scales. This idea becomes particularly clear when highlighting seedbanks in the concept, which are a component of the diversity described as "dark diversity" or "sleeping" diversity within one stable state (see 15 and references therein).…”

“…This idea becomes particularly clear when highlighting seedbanks in the concept, which are a component of the diversity described as "dark diversity" or "sleeping" diversity within one stable state (see 15 and references therein). Instead of the rainwater axis, shifts along the hydrological axis of the "wetland continuum concept", which describes the influence of groundwater on wetland hydrology, are considered to be alternative stable states [15]. Within these alternative stable states, all phases of the prairie-marsh cycle occur and are assumed to be reversible.…”

“…This, in turn, affects biodiversity, productivity and biogeochemical processes of small wetlands [10][11][12][13]. Thus, differences in oscillating water levels-due to natural meteorological variability or climate change-directly affect the vegetation dynamics of small wetlands and may shift them to alternative stable states [14][15][16]. Hence, a prediction of changes in the functioning of small wetland ecosystems requires a good understanding of oscillating water levels and their effect on wet-dry cycles of vegetation and their interactions.…”