Hydrology effects on propagule bank expression and vegetation in six Carolina bays

Hydrology, which filters propagule bank expression, differs among Carolina bay wetlands. We examined the relationships among hydrology, recruitment from the propagule bank, and bay vegetation over one season in six herbaceous bays that differ in hydroperiod. Sediment cores were taken at distances from each bay center representing 10%, 25%, 50%, and 75% full water level and subjected to flooded, midsummer drawdown, or moist soil conditions in an outdoor mesocosm experiment. Vegetation from the cores was compared among hydrology treatments and with bay vegetation. In bay vegetation, species richness and dissimilarity, calculated among replicate plots at each distance, increased from flooded bay centers toward the margins, where water level fluctuated. Among bays, vegetation richness increased from more pond-like bays to the flashiest bay. Within bays, vegetation graded from obligate wetland species to a mixture of obligate and facultative species from center to margin. The flooding treatment promoted convergence on obligate wetland floating-leaved and emergent species, low species richness, and high community similarity of vegetation from the sediment cores. Our research supports the hypothesis that hydrology filters recruitment and species distribution in Carolina bays. The extent of inundated, fluctuating water, and exposed sediment areas can determine seasonal vegetation organization in such wetlands. Vegetation in wetlands with steep basins and stable hydrology is more likely zoned; dominant species show discontinuous distributions along the flooding gradient. In contrast, fluctuating hydrology in shallow basins results in unzoned vegetation, with more continuous species distributions from wetland center toward the margins.