Vegetation Controls on the Maximum Size of Coastal Dunes and the Role of Biophysical Interactions in Determining Dune/Island State Laura J. Moore and Orencio Duran Duran and Moore (2013) recently extended the model of Hermann et al. (2008) to create an aeolian eco-morphodynamic model (the Coastal Dune Model, CDM), which resolves the coevolution of topography and vegetation in response to both physical and ecological factors to simulate the formation of coastal foredunes. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. Model results suggest that the distance from the shoreline that dune-building vegetation becomes established is the primary factor controlling the maximum size of foredunes. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward thus leading to larger foredunes, suggesting that plants play a more active role in modifying their habitat and altering coastal vulnerability than previously thought. Extending the model of Duran and Moore (2013) to include dune erosion by storm events (Duran and Moore, 2015) we find island response to be intrinsically bistable and controlled by previously unrecognized dynamics: the competing, and quantifiable, effects of storm erosion, sea-level rise, and the aeolian and biological processes that drive dune recovery. When the biophysical processes driving dune recovery dominate, islands tend to be high in elevation and vulnerability to storms is minimized. Alternatively, when the effects of storms dominates, islands may become trapped in a perpetual state of low elevation and maximum vulnerability to storms, even when storms are mild. When sea-level rise dominates, islands become unstable and face possible disintegration. These findings are supported by data from the Virginia Barrier Islands, USA and provide a broader context for considering island response to climate change and the likelihood of potentially abrupt transitions in island state. In a current effort we are collaborating with U.S. and international partners to merge the Coastal Dune Model with XBeach (a modelling approach to dune erosion, overwashing and breaching; Roelvink et al., 2009) and AeoLiS (which simulates the influence of supply-limiting factors on aeolian transport initially developed by De Vries et al. 2014). In addressing both subaqueous and subaerial sediment transport and erosion during storms as well as inter-storm evolution of subaerial topography, the resulting coupled model will allow, for the first time, process-based simulation of event- and decadal-scale co-evolution of nearshore, beach and dune systems.