Collaborative Research:The Role of Ecomorphodynamic Feedbacks in Barrier Island Response to Climate Change

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Climate-change-induced sea level rise and increases in storm intensity will affect barrier islands worldwide. The traditional view of barrier island evolution considers only changes in environmental conditions (such as sea level rise, changes in storms) and physical processes (such as the transport of sand), and predicts that barrier islands will respond to climate change gradually. However, recent work suggests that biological factors involving vegetation and interactions, or feedbacks, between vegetation and physical processes are also important in shaping islands and determining how they will respond to changing conditions in the future. For example, anticipated climate-change induced shifts in the geographic ranges of dune-building grasses may increase the vulnerability of islands to storms by changing the shape and height of protective dunes. And, just as interactions between vegetation and physical processes can build dunes (via sand trapping by dune-building grasses) they can also hinder, and even prevent, dune-building by maintaining areas of low elevation. Such feedbacks may cause gradual changes in environmental conditions to produce rapid changes in barrier island evolution, which would make human adaptation difficult. This project will allow us to better understand the processes that are important in determining how barrier islands will change in the future and the conditions under which the important processes and interactions will likely lead to rapid, rather than gradual changes in island behavior. This project will test a hypothesis that ecomorphodynamic feedbacks have the potential to amplify the effects of climate change on barrier island evolution, causing a nonlinear response to gradual changes in forcing, i.e., tipping points at which barrier islands rapidly convert from a high-relief, stable, ecologically diverse state to a low-relief, rapidly migrating, ecologically homogenous state. Through integrated numerical modeling and ecological experiments in the undeveloped barrier system of the Virginia Coast Reserve (VCR) LTER this project will address critical questions including: How do vegetation and physical processes interact in the formation and evolution of barrier island topography? How do overwash events affect topographic recovery and colonization of vegetation following storms? What is the role of ecomorphodynamic feedbacks in topographic recovery following storms? What combinations of factors lead to tipping points in the transition between high-relief and low-relief states as a result of nonlinearities in the ecomorphodynamic system? How are ecomorphodynamic feedbacks altered by climate change and what is the role of feedbacks in the transition between states?