MS Thesis Defense: Brianna Ingram, The Role of Spartina patens on U.S Atlantic Dunes: A Review, Examples from the North Carolina Coast, and Implications for Dune Building and Recovery

Abstract: Coastal foredunes, which arise from feedbacks between sediment transport and vegetation, protect coastal habitats and coastal development from storm impacts. The rate of dune growth and dune shape are influenced by the morphology of the dune-building grasses that give rise to them, because grass morphology determines the amount and location of sand capture. In this study, I focus on better understanding the role of Spartina patens, a species of beach and dune grass once considered to stabilize sediments and keep elevation low, but recently shown to be a moderate dune builder. I conducted a review of the natural history of S. patens along with an analysis of a longitudinal data set of co-collected topography and vegetation from the North Carolina coast to test a new hypothesis regarding the role of S. patens on beaches and dunes following storms. I found that S. patens occupies higher elevations than reported by earlier studies, likely a reflection of the broader range of beach and dune elevations encompassed in my data set compared to earlier studies that focused on S. patens in overwash areas due to its prevalence there. Consistent with earlier studies, I found a higher occurrence of S. patens on islands and transects that were more recently overwashed, likely due to the high salinity tolerance of this grass. How recently transects had been overwashed, along with dune elevation, are good predictors of where S. patens will be found: On younger/lower dunes S. patens is found primarily on the dune toe/face and heel, and on older/higher dunes S. patens is found almost exclusively on the heel. Based on my findings, I propose a new conceptual model in which S. patens, where present, plays an important role in initiating and speeding up the dune building process in its early stages. If this new conceptual model is correct, S. patens may provide value in restoration efforts that seek to accelerate the growth of natural dunes following overwash.