Sand supply and dune grass species density affect foredune shape along the US Central Atlantic Coast

Abstract

Coastal foredunes form via biophysical feedbacks between sand accretion and burial‐tolerant vegetation and can protect coastlines from hazards such as extreme storms and sea level rise. Predicting how coastal dunes, and the services they provide, will change in the future requires an understanding of the relative roles of the physical and ecological processes that shape their structure and function. Here we assess the relative roles of sand supply, beach morphology, and vegetation in determining foredune morphology, and its change, along a 300‐km stretch of the US Central Atlantic coast. In particular, we used the spatial variability inherent in beaches and dunes of this region to determine the relative importance of shoreline change rate (SCR; a proxy for sand supply to the beach), beach morphology, and grass density of four widespread dune grasses (Uniola paniculata, Ammophila breviligulata, Panicum amarum, and Spartina patens) to foredune morphology metrics (height, width, and aspect ratio) along the North Carolina Outer Banks barrier islands. Foredune morphology and change metrics are correlated with three main factors: multidecadal SCR (1997–2016), beach slope, and dune grass density and species identity. Multidecadal SCR and beach width explained the most variation in, and were positively correlated with, foredune height and width, and were negatively correlated with foredune aspect ratio (height divided by width). In addition, grass density and changes in grass density contributed significantly to foredune morphology change. We found a positive relationship between change in A. breviligulata density and foredune width, which aligns with previous studies on the US Atlantic and Pacific Northwest coasts. Our results demonstrate the interactive roles of beach sand supply and dune grass functional morphology in dune building processes on highly vulnerable coastlines.

Exploring Ecological, Morphological, and Environmental Controls on Coastal Foredune Evolution at Annual Scales Using a Process-Based Model

“…Coastal foredunes of the northern Outer Banks are dominated by grasses, lianas, shrubs, and forbs, though our modeling framework focuses on dune grasses. The dominant grass species are distributed across the dune profile in both monocultural and mixed patches, and include Uniola paniculata, Panicum amarum, Ammophila breviligulata, and Spartina patens, all of which demonstrate efficient sediment capture and positive growth responses to burial [44].…”

Drivers of dune formation control ecosystem function and response to disturbance in a barrier island system

“…In addition to sediment accretion interactions with grasses, dune building is controlled by large scale geophysical factors that influence sediment availability and abundance 7,9,40 . Even among islands that are geographically close to one another, the abundance and movement of sediment has an influence on island processes 10 and www.nature.com/scientificreports/ response to disturbance.…”