Description:    Coastal vegetation of South Florida typically comprises salinity-tolerant mangroves bordering salinity-intolerant hardwood hammocks and fresh water marshes. Two primary ecological factors appear to influence the maintenance of mangrove/hammock ecotones against changes that might occur due to disturbances. One of these is a gradient in one or more environmental factors. The other is the action of positive feedback mechanisms, in which each vegetation community influences its local environment to favor itself, reinforcing the boundary between communities. The relative contributions of these two factors, however, can be hard to discern. A spatially explicit individual-based model of vegetation, coupled with a model of soil hydrology and salinity dynamics is presented here to simulate mangrove/hammock ecotones in the coastal margin habitats of South Florida. The model simulation results indicate that an environmental gradient of salinity, caused by tidal flux, is the key factor separating vegetation communities, while positive feedback involving the different interaction of each vegetation type with the vadose zone salinity increases the sharpness of boundaries, and maintains the ecological resilience of mangrove/hammock ecotones against small disturbances. Investigation of effects of precipitation on positive feedback indicates that the dry season, with its low precipitation, is the period of strongest positive feedback. Content Type Journal Article Category Research Article Pages 1-11 DOI 10.1007/s10980-011-9689-9 Authors Jiang Jiang, Department of Biology, University of Miami, Coral Gables, FL 33124, USA Donald L. DeAngelis, Department of Biology, University of Miami, Coral Gables, FL 33124, USA Thomas J. Smith, U. S. Geological Survey, Southeast Ecological Science Center, 600 Fourth Street South, St. Petersburg, FL 33701, USA Su Yean Teh, School of Mathematical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Hock-Lye Koh, Disaster Research Nexus, School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia Journal Landscape Ecology Online ISSN 1572-9761 Print ISSN 0921-2973