Preferred Habitat for Coastal Shrub Establishment Across a Barrier Island Landscape

Barrier islands occur along the Eastern Coast of North America and buffer mainland coasts from major oceanic storms. Landscape characteristics and vegetation profiles of these islands are constantly changing in response to varying environmental drivers, especially salinity, shoreline erosion and accretion. Relationships between shrubs and other native flora can affect the island landscapes and resiliencies against storms. Hog island is a barrier island along the Eastern Shore of Virginia and is within the Virginia Coast Reserve NSF funded Long-Term Ecological Research (VCR/LTER) site. As such, Hog Island has a well-documented history of changes in landscapes and ecosystems. Northern and southern portions of Hog Island differ, with the northern part, low elevation marsh and grassy swales transition to shrub thickets while the southern portion has been primarily grassland habitat. Over the last 20 years, shrubs, Morella cerifera and Baccharis halimifolia, have been encroaching towards the southern part of the island. These species are dispersed by birds and wind, respectively, and mostly in a random fashion. This study is quantifying the spatial variations in environmental variables for Hog Island to both characterize habitat where seedlings and smaller shrubs currently exist. These variables include distance to shoreline, elevation, depth to groundwater, soil salinity, and vegetation profiles of each area. Where shrubs are currently established, location in relation to the ocean and dunes was an important factor in the success of shrub seedling survival. As shrubs encroach into the southern grasslands and densities increase, that region may shift to a community dominated by woody species, potentially leading to changes in landscape structure. The knowledge gained 8 from this study will be used by scientists at the VCR/LTER to help understand the long term effects of shrub encroachment on barrier islands.