Post-Hurricane Sandy Vegetation Recovery in the Presence of a Hyper-abundant Deer Population

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The Challenge: The primary dune along barrier island beaches protects leeward vegetation from tidal fluctuation, salt spray and storm surge.  However, storm surges like those experienced during Hurricane Sandy can obliterate the primary dune, transporting sand inland and burying existing vegetation.  The dune rebuilds naturally as recovering vegetation traps wind-blown and waterborne sand.  The rate at which the primary dune rebuilds is determined largely by abiotic factors affecting transport of sand.  In the presence of a hyper-abundant deer population, the biotic impacts of grazing, browsing and trampling might also affect vegetation and dune recovery.

The Science: Using high-resolution aerial imagery and field sampling, we are reconstructing vegetation recovery trajectories in nine over wash fans in a protected natural area of Fire Island National Seashore.  We sampled vegetation development during three periods of the growing season over the last two years.  We used georeferenced, nadir photography and computer-assisted image analysis to record foliar cover for all plant species re-colonizing over wash fans.  We also placed wildlife trail cameras in each over wash fan to estimate local deer abundance.  We are currently developing statistical models that examine the relative influences of site productivity (NDVI), spatial location, local deer abundance and vulnerability to erosion as key determinants of vegetation recovery. 

The Future: Despite the devastation and human suffering caused by Hurricane Sandy, its landfall provides a fortuitous opportunity to study vegetation recovery and barrier island resilience/vulnerability.  Comparable storm impacts have not been experienced on Fire Island for at least 200 years.  In the time since, the white-tailed deer population has irrupted island-wide and imposes serious vegetation management challenges in other natural zones.  Barrier island ecosystems are inherently dynamic due to the strong physical forcing caused by wind and wave.  This is the first study to quantify the relative contribution of both abiotic and biotic stressors on vegetation recovery and hence, barrier island stability.