Interactions Between Physical Template and Self-organization Shape Plant Dynamics in a Stream Ecosystem

Both internal feedbacks and preexisting heterogeneity of a physical template can produce biological patchiness in ecosystems. The relative importance of the two drivers might change over time, in response to changes in the external environment. This is especially relevant for ecosystems experiencing high environmental variability. We investigated the interaction between these two drivers—internal feedbacks and template heterogeneity (represented by variation in water permanence in this study)—using 9-year data on macrophyte (wetland) patch distribution collected from Sycamore Creek, a desert stream in Arizona, USA. Sycamore Creek is highly variable both in space and in time due to its flashy hydrograph. We used a lattice simulation model that considered both the spatial heterogeneity of the geomorphic template and the influence of local positive feedbacks on plant growth. We showed that the relative strengths of local feedbacks and the template effect varied with the hydrological condition in a given year. Overall, the effect of template heterogeneity increased in wetter and more frequently flooded years and the effect of internal positive feedback decreased. Averaging over the 9-year study period, the effect of local feedbacks on wetland distribution and abundance in Sycamore Creek was about twice that of template heterogeneity. In the driest years, it reached up to ~ 12 times. Our study suggested that compared to catastrophic floods, severe droughts—the type of hydrological change projected to become more frequent for the region under a changing climate—have a stronger legacy effect on the biotic community in subsequent years.