Tuesday, August 4, 2009: 9:50 AM
Blrm A, Albuquerque Convention Center
Background/Question/Methods Recent theoretical models and some empirical observations suggest that rising variance may provide an early warning of incipient regime shifts, but studies to date overwhelmingly emphasize lentic ecosystems undergoing transitions between oligotrophic and eutrophic conditions. Here we evaluate the utility of variance as an indicator of impending regime shift in two distinct wetland ecosystems where state transitions are governed by biogeomorphic feedbacks. In aridland streams, channel stabilization by dense vegetation allows persistence of wetlands during massive flash floods. Data from a two year field study of these systems are re-analyzed to determine whether systems with greater spatial variance of vegetation biomass are more susceptible to catastrophic erosion. In the peatlands of the Florida Everglades, interactions among hydrologic regime, plant community structure, and carbon balance maintain distinct soil elevation modes with associated vegetation communities (ridges and sloughs). Soil elevation probability density functions (pdfs) along a spatial gradient of hydrologic modification in the Everglades are evaluated to determine whether increased variance within these communities precedes losses of soil elevation bimodality.
Results/Conclusions In arid streams, wetlands with greater spatial variance in vegetation biomass experienced greater losses of vegetation cover and were more likely to undergo channel scour and re-organization, suggesting that occurrence of small patches with lower flood resistance influenced resilience at the whole-ecosystem scale. In the Florida Everglades, soil elevation bimodality persisted in sites subject to moderate changes in hydroperiod and inundation depth, but was lost in sites where hydrologic change was more dramatic. However, regardless of the direction of hydrologic modification, moderately disturbed sites exhibit greater variance within soil elevation modes than either conserved sites or sites where bi-modality was lost. These studies support the use of variance as an indicator of future regime shifts in biogeomorphic systems. Further, these findings suggest that variance can be predictive of regime shifts in systems characterized by press or pulse disturbances.
Results/Conclusions In arid streams, wetlands with greater spatial variance in vegetation biomass experienced greater losses of vegetation cover and were more likely to undergo channel scour and re-organization, suggesting that occurrence of small patches with lower flood resistance influenced resilience at the whole-ecosystem scale. In the Florida Everglades, soil elevation bimodality persisted in sites subject to moderate changes in hydroperiod and inundation depth, but was lost in sites where hydrologic change was more dramatic. However, regardless of the direction of hydrologic modification, moderately disturbed sites exhibit greater variance within soil elevation modes than either conserved sites or sites where bi-modality was lost. These studies support the use of variance as an indicator of future regime shifts in biogeomorphic systems. Further, these findings suggest that variance can be predictive of regime shifts in systems characterized by press or pulse disturbances.
