Plant Community Structure and Temporal Variability in a Channelized Subtropical Floodplain

Abstract

Species composition, cover, diversity, and temporal dynamics of the three main plant communities in the channelized Kissimmee River floodplain were evaluated to provide a baseline for tracking the success of an ongoing restoration project. Much of the drained floodplain supports an upland herbaceous community with cover dominated by the planted pasture grasses Paspalum notatum and Axonopus fissifolius. Mesophytic woody communities are comprised primarily of Myrica cerifera, Baccharis halimifolia, Ludwigia peruviana, and understory ferns, while Sagittaria lancifolia, Pontederia cordata, and Panicum hemitomon are dominant species in remnant wetland communities. Community composition and the associated gradient of weighted averages of wetland indicator species reflect prevailing hydroperiods and land uses on the drained floodplain. Managed hydrologic regimes have promoted temporal stability, with seasonal variability of plant community characteristics limited to a decline in live plant cover and species richness during winter months. Lower live vegetation cover during winter resulted from senescence of dominant herbaceous species, while the winter decline in species richness was due primarily to sampling error resulting from seasonal phenology of taxonomic characteristics and obscured growth of rare or diminutive species. The limited variability of plant community characteristics in the channelized floodplain reduces the potential for confounding uncertainty in evaluating successful restoration. Results indicate that functional assessment of plant community characteristics in this subtropical floodplain is most accurately measured in spring and summer.