Ridges are natural elevated landforms found adjacent to bayous and distributaries throughout Louisiana’s coast that provide ecosystem services by mitigating erosion and storm surge, as well as providing habitat for plant species vulnerable to inundation. Anthropogenic changes to hydrology in Louisiana have disrupted the natural processes of overbank flooding and sediment deposition that form ridges. Existing ridges have degraded in response to the factors driving local land loss, including canal dredging, subsidence, and sea level rise. Louisiana’s coast has some of the highest rates of relative sea level rise in the world, making it a suitable model for predicting coastal changes globally. Over the past two decades, ridge restoration has become a favored technique in Louisiana’s coastal planning. Restored ridges are typically built from dredged sediment, either from neighboring areas or navigation canals, meaning soil characteristics are highly dependent on the dredging location.Ridge-associated communities are understudied, and the ridge-to-water elevation gradient provides a unique opportunity to examine how coastal vegetation communities may shift with rising sea levels. This study documents the vegetation communities on the slope and adjacent marsh of 8 coastal ridges of different along the coast of south-central Louisiana and determines the drivers of community composition across elevation and salinity gradients. The natural and man-made ridges range in age from ~1,000 to 5 years old.We established four transects at each ridge site, starting at the ridge slope and extending outward to open water or uniform low marsh, for a total of 402 0.25m2 subplots. Subplots were sampled for species composition, percent cover, average height, and soil characteristics, and neighboring subplots were averaged to derive plot-level data. Additionally, Real-Time Kinematic positioning is used to accurately measure elevations in all subplots. Initial results derived from non-metric multidimensional scaling (NMDS) paired with Spearman's correlation indicate that changes in community composition are significantly correlated with variations in elevation (ρ = 0.49), soil bulk density (ρ = 0.58), and soil moisture (ρ = -0.54). Ongoing soil core processing will produce plot-specific data for soil salinity, carbon, and pH. With the completed dataset, a predictive model will be developed using a classification and regression tree to assess how marsh communities will change with different sea level rise scenarios. As more ridge restoration projects are undertaken, the results from this study will allow for more effective and resilient ridges to be built and planted.
