Dr. Steven Pennings studies the factors that structure plant communities in salt marshes, mangroves and coastal prairies. Coastal wetlands are relatively simple systems that contain strong gradients in physical stress (notably waterlogging of soils, and salinity). As a result, they are ideal systems for experimentally studying how physical stress, disturbance and biological interactions combine to create pattern in plant communities. Mangroves are a major habitat type at low latitudes on the East and Gulf Coasts of the U.S. The distribution limit of mangroves is set by winter freezing. With recent warmer winters, mangroves are expanding to higher latitudes. Pennings is interested in how the switch from marsh to mangrove will affect wetland function, and especially the services (coastal protection, support of fisheries, eco-tourism) that people depend on.