Constraints of seed bank species composition and water depth for restoring vegetation in the Florida Everglades, USA

The Rotenberger Wildlife Management Area (RWMA) is a northern Everglades marsh, in Florida, U.S.A., that will undergo hydrologic restoration to remedy an artificially shortened hydroperiod. In an effort to predict vegetation responses to the impending changes in hydrology, plant community development from the resident seed bank was observed in response to three different moisture regimes in March and September 1998. Percent cover, species densities, total seedling densities, and percentages of facultative, facultative-upland, and upland indicator species were significantly higher in moist than in saturated soils. Flooding inhibited the germination of all species except Typha domingensis (cattail), which emerged in the highest numbers from saturated soils in both assays. Lythrum alatum (purple loosestrife) was abundant in both saturated and moist conditions. The season of assay affected species densities and the communities. Percent facultative-wetland species increased in saturated soils in the March assay but not in September. In contrast, percent obligate hydrophytes were higher in saturated conditions only in the September assay. In general the assay communities bore little resemblance to vegetation in currently undisturbed or historic wetlands of the northern Everglades. Consequently the RWMA seed bank will contribute little to the development of a restored community. Moreover, rehydration may encourage the spread of undesirable hydrophytes such as T. domingensis. This study supports the contention that hydrologic restoration must be accompanied by some level of active vegetation management and that the reference condition cannot be attained passively.