Drivers, dynamics and consequences of non-linear change in coastal barrier systems

The Virginia Coast Reserve (VCR) is a heterogeneous landscape comprising mainland watersheds, tidal marshes, mudflats, shallow coastal bays, and barrier islands. Transitions between ecosystems can be abrupt with threshold responses to external drivers.  We have developed models that show inherent bistability in the intertidal and subtidal parts of the landscape, i.e., that there are two alternative stable configurations (states) that are induced by biotic-abiotic feedbacks, and have observed patterns in barrier island vegetation and island morphology that are consistent with bistable dynamics. These state transitions have important consequences for landscape change and ecosystem services. The central hypothesis of VCR VI is that ecosystem changes on the coastal barrier landscape in response to long-term drivers are primarily the result of complex non-linear dynamics based on the existence of alternative stable states and threshold responses. Our research is organized around three synthetic themes:  (1) Mechanisms of long-term change; (2) Ecosystem connectivity; and (3) Interacting drivers, scales and feedbacks.  We ask the questions related to these themes: (1) What are the mechanisms of non-linear state change in coastal barrier landscapes in response to environmental drivers? Are there specific thresholds for ecosystem state change and leading indicators of proximity to that threshold? (2) To what extent does connectivity of adjacent ecosystems via sediment fluxes affect responses to environmental change? Is there evidence of subsidies via organism fluxes between adjacent habitats that influence key ecosystem processes, services and states? (3) How will ecosystem resilience and state dynamics vary in response to climate drivers across the landscape? How will changes in land use affect subtidal and intertidal ecosystems, and how will these drivers affect the resilience of ecosystems to climate change?