Considering the Different Roles of Ammophila breviligulata and Spartina patens in Coastal Foredune Formation and Growth

Abstract:

Coastal foredunes arise from interactions between vegetation and aeolian sand transport. Two of the most important grasses that influence dune growth and formation along the barrier islands of the U.S. mid-Atlantic coast are Ammophila breviligulata and Spartina patens. Variations in topography, distance to the shoreline and the associated biotic and abiotic stressors (e.g., salt spray, sand burial, soil chemistry, and competition from other plants) affect the survival of both species. Additionally, differences between the grasses in response to these stressors may directly control foredune morphology. Although a relationship between the cross-shore vegetation limit and maximum dune height has been developed (Durán and Moore 2013) we do not yet quantitatively understand how each grass affects dune formation and shape. We carried out a field experiment on Hog Island, VA and complementary model experiments to address gaps in our understanding of species control on vegetated foredunes.

We transplanted 120 plants of each species along two cross-shore transects (from foredune crest to the shoreline) to investigate the effects of topography and distance to the shoreline on vegetation growth. Throughout the growing season, we monitored the longest leaf of each transplant, the frontal and basal area of each transplant, and elevation at each transplant site to quantify vegetative growth and aeolian accretion along the each transect. We used these data to improve the coastal dune model presented by Durán and Moore (2013) so that it includes two grasses which more closely represent the growth characteristics of A. breviligulata and S. patens, specifically, rather than a generic dune-building grass species. These additions allow us to conduct simulations of dune development under varying initial abundances of morphologically important species, ranging from a dune populated only with A. breviligulata to one populated only with S. patens. Results from this coupled field and model experiment can be used to quantitatively understand the role of dune-building species on coastal foredune morphology.