Vegetation Change in Salt Marshes of Cape Cod National Seashore (Massachusetts, USA) Between 1984 and 2013

Vegetation patterns in salt marshes are largely based on elevation in relation to tidal flooding. In New England salt marshes, vegetation is distinctly zoned into species that occur in the high marsh (elevations above mean high tide) vs. those that reside in the low marsh (elevations below mean high tide). The extent and distribution of these species is responsive to changes in hydrology, particularly sea level rise. In this study, six salt marshes within Cape Cod National Seashore (CCNS) were analyzed using a GIS-based mapping approach that utilized aerial images from 1984 and 2013. The results indicate that there have been highly variable amounts of change among marshes. There have been substantial losses of high marsh vegetation (> 190 acres in total), while low marsh vegetation has exhibited large gains in some marshes and relatively minor losses in others with a total net gain of > 131 acres. Because sea level rise appears to be outpacing vertical accretion, higher water levels in the near future could result in large vegetation shifts, which would translate to significant changes in marsh structure and function.