Vegetation controls on coastal foredune size: Field and remote sensing evidence
Coastal foredunes (the most seaward dunes on a beach) which provide protection for marshes, bays, and human infrastructure against elevated water levels, form and become stabilized via a feedback between sand transport and perennial dune grasses. A recent model of these processes suggests that the seaward limit of the growth of dune-building plants on the beach controls the location and ultimate height of a foredune, yet this critical parameter is poorly studied. We report the results of a field experiment conducted on the Virginia Eastern Shore in the mid-Atlantic Bight, USA, in which we planted 120 transplants, 40 of three different dune plant species (Uniola paniculata, Ammophila breviligulata, and Spartina patens), from the water line to the top of the foredune. We measured plant growth and topographic changes throughout the 2014 and 2015 growing seasons to investigate species-specific plant growth as a function of elevation and distance to the mean high water line. Additionally, we conducted remote sensing analyses to investigate the relationship between vegetation type and dune morphology on islands in Massachusetts, Virginia, North Carolina, South Carolina, and Georgia.
During the 2014 growing season, we saw no correlation between distance from the shoreline and plant growth for individual species and all species combined. However, we found that plants transplanted in low elevations grew larger than those planted at higher elevations, potentially because of groundwater effects. We anticipate the 2015 data collection effort will either confirm or expand on these results. Initial results from ongoing remote sensing work indicate that foredune height is related to the seaward limit of vegetation growth and that foredune height distributions are not uniform along the East Coast. These ongoing projects will allow us to more fully understand role of the dune grass community in influencing dune topography.