Thursday, August 5, 2010: 1:30 PM
320, David L Lawrence Convention Center
James B. Heffernan, Nicholas School of the Environment, Duke University, Durham, NC, Danielle L. Watts, School of Natural Resources and Environment, University of Florida, Gainesville, FL and Matthew J. Cohen, School of Forest Resources and Conservation, University of Florida, Gainesville, FL
Background/Question/Methods Regular, self-organized patterning has been observed in a wide range of ecosystems and is attributed to the interaction of positive local and negative distal feedbacks. One such system is the Florida Everglades, which were historically dominated by a mosaic of high elevation ridges supporting productive emergent communities and lower elevation sloughs inhabited by floating and submerged plants. Interactions among hydroperiod, plant community composition (and therefore productivity), and respiration have long been hypothesized to produce and maintain the local elevation differences via their effects on peat accreation; however, mechanisms capable of producing the elongated, flow-oriented patterning of the ridge-slough mosaic habitats are less clear. In this study we evaluate a simple model in which peat accretion is coupled to hydrologic conditions, and in which hydrologic conditions in one patch are coupled to adjacent patches via their reciprocal effects on discharge through flow-perpendicular cross-sections. Results/Conclusions Analytical solutions of our model demonstrate that under a reasonably wide range of conditions, the necessity of maintaining some minimum discharge competence can produce distal negative feedbacks between patches. In effect, differential peat accretion between two patches displaces flow onto (and thus increases water depth in) the more slowly-accreting patch, creating conditions less favorable to rapid peat accretion due to threshold responses of productivity to inundation depth and duration. Importantly, these feedbacks act anisotropically, with greater effects between adjacent than downstream patches. This 'self-organizing canal' model thus represents a plausible mechanism of pattern formation even in the absence of sediment transport feedbacks recently suggested to produce ridge-slough patterning. Over a more limited, but highly probable, set of conditions, the self-organizing canal model produces global bi-stability between patterned and unpatterned configurations, suggesting the potential for catastrophic transitions in landscape structure. Also notable is that the model predicts divergence of ridge and slough elevations with increasing water levels, consistent with recent observations of the responses of microtopographic patterns to anthropogenic modification of Everglades hydrology.
