TREE HEALTH DECLINE AND PHRAGMITES AUSTRALIS DENSITY IN RESPONSE TO INCREASING SOIL SALINITY IN A TRANSITIONING TIDAL LANDSCAPE ON THE DELMARVA PENINSULA

Sea level rise (SLR) is driving the inland migration of coastal ecosystems, with significant consequences for tidal forests and salt marshes. This research explores the controls on ecosystem migration and ghost forest development at five sites in the Chesapeake and Delaware Bay watersheds, regions experiencing some of the highest rates of relative SLR in the world. From 2020-2024, we monitored tree health, vegetation communities (with a focus on Phragmites australis), and soil characteristics along marsh-forest gradients. Our results show a clear "frontier of salinization," a zone of steep salinity change that correlates with tree mortality and the stands of P. australis. Topography, canopy cover, and P. australis all interact with salinity to control the location and direction of the frontier. Plot composition changes most rapidly around the frontier, indicating the beginnings of forest retreat. These results illustrate how topography, canopy cover, and salinity appear to cooperatively control the rate and direction of ecosystem migration. P. australis was primarily used as a spatial indicator given its transition zone niche. Coastal ecosystems respond in complex ways to SLR and these data highlight the need to consider multiple interacting factors when predicting future landscape transformations.