A species effect on storm erosion: invasive sedge stabilized dunes more than native grass during Hurricane Sandy.
Abstract
Vegetation and biogeomorphology are highly coupled in beach dune systems, but plant species effects on abating storm erosion are largely unexplored. We quantified coastal dune erosion from Hurricane Sandy (October 2012) as a function of pre-storm system characteristics - dune height, beach width and dominant vegetation stabilizing dunes (native Ammophila breviligulata or invasive Carex kobomugi) at Island Beach State Park, New Jersey, USA. We assessed dune erosion using a combination of pre- and post-Sandy aerial image spatial analyses in ArcGIS and GPS field mapping. Our two erosion metrics are novel, macroscale 2D surface area changes and Dune Crest Transgression, the later of which is measured at the microscale (1 m-1) and analysed using a mixed model incorporating spatial autocorrelation. We document a species-specific effect on collision erosion. Although C. kobomugi reduces native diversity and abundance, it may be beneficial for coastal protection, as dunes fronted and stabilized by C. kobomugi suffered less erosion than those dominated by A. breviligulata under the same abiotic conditions. Dune height and beach width were equal for species prior to the storm and therefore do not account for or confound differences in erosion. Similarly, traditional calculations of erosion with volumetric loss confer these results. Synthesis and applications. This is the first study to show a species effect on coastal dune erosion. Native Ammophila breviligulata stabilized dune stretches suffered more erosion from Hurricane Sandy than complimentary invasive Carex kobomugi stretches, contradicting anecdotal reports that foredunes stabilized by a shorter statured species are more prone to erosion. This study highlights the importance of vegetation for dune stability and management using two novel metrics for erosion. Our erosion metrics are related to volumetric loss, can be monitored and calculated by managers with or without remote sensing, and can be applied to other systems. Discussions on coastal management of dunes as habitats and protective buffers must include vegetation and the results of this study suggest that not all species are equal with regard to their ability to combat storm erosion. Multidisciplinary studies with applied implications will grow increasingly important as storms continue to grow more frequent, severe and unpredictable with climate change.