Tree Encroachment of A Sawgrass (Cladlum jamaicense) Marsh within an Increasingly Urbanized Ecosystem

Fire suppression and altered water drainage often change community structure and species composition in human-dominated ecosystems. We describe the decline of sawgrass marshes between 1940 and 2002, and assess the current condition of remnant marshes within the MacKay Tract, an isolated wetland embedded within rapidly developing eastern Orlando, Florida. We tested the correlation between live sawgrass and presence of adult hardwood trees and seedlings (primarily red maple, Acer rubrum) and describe vegetation in plots with different levels of tree encroachment. Total area occupied by open sawgrass in the MacKay Tract has declined dramatically the last 60 years, in 2006, open sawgrass comprised only 12% of the area covered in 1940. Tree basal cover was negatively associated with live sawgrass and positively related to red maple seedling density, but not associated with dead sawgrass tussocks. Sawgrass was positively correlated with the second axis of a non-metric multidimensional scaling ordination on understory plant assemblage, while red maple seedlings and several species associated with disturbed areas were significantly negatively cot-related with this axis. Another nine plant species were positively correlated with the first axis, while Osmunda cinnamomea (cinnamon fern) was negatively associated with it. We suggest that woody species are continuing to colonize what is left of the sawgrass marsh. Without intervention (e.g., restoring hydrologic flow and fire), the sawgrass (Cladium jamaicense Crantz) area within the marsh will continue being replaced by woody and exotic species