We examine salinity, ground water depth, and water uptake of common plant species in coastal upland communities: buttonwood hammocks, hardwood hammocks, and buttonwood prairies of Everglades National Park. We show that the elevation gradient is gentle with a mean gradient of 0.12 m North American Vertical Datum of 1988 from buttonwood prairie to hardwood hammocks, but the species composition and canopy cover among communities are different. Plant communities differ significantly in groundwater salinity. Hardwood hammocks have brackish groundwater [14–27 parts per thousand (PPT)], buttonwood hammocks have brackish to saline groundwater (23–35 PPT), and buttonwood prairies have saline groundwater (30–44 PPT). The depth to water table is greater for plants in hardwood and buttonwood hammocks than in buttonwood prairies, which makes the freshwater recharge capacity of vadose zone larger in hammocks than in buttonwood prairies. The majority of species accessed water from deep soil (5–30 cm) and groundwater in dry season and switched to using shallow soil water (0–5 cm) in wet season. Exception to this pattern is herbaceous Chromolaena frustrata, endemic to buttonwood hammocks of South Florida, which accessed shallow soil water in dry season and deep soil water in wet season. Our study assesses susceptibility of coastal upland species to sea level rise (SLR)-driven changes in water table and salinity; the results of which can be incorporated into planning for adaptation to SLR.