Landscape Patterns of Forb Pannes Across a Northern New England Salt Marsh

Most salt marshes are dominated by graminoids, but patches dominated by a diverse assemblage of perennial forbs, known as forb pannes, occur on marshes in north temperate areas. These pannes and their associated species diversity appear to be highly responsive to anthropogenic change, including climate warming. We mapped all of the forb pannes on a salt marsh in Wells, Maine in order to 1) determine if geospatial features were related to panne location and species composition, and 2) record a baseline to compare with future responses to anthropogenic change. Forb pannes occupied approximately 5% of the high marsh surface, with sizes ranging from 7 m2 to 5000 m2. Pannes themselves were clustered at river/creek edges and near pools. Within pannes, species diversity was highest away from pools and the river mouth, and relative abundance of Plantago maritima was related to spatial variables. These results suggest that forb panne distribution and community structure are influenced by spatial variables and reinforce the notion that forb pannes may be used to track salt marsh responses to global change.