Constraints on understory vegetation communities of tidal freshwater swamps: a reciprocal transplant experiment1

Abstract Plant community composition may be limited by propagule availability, environmental constraints, or both. In the Nanticoke River watershed in Maryland and Delaware, herbaceous communities of tidal freshwater swamps in upstream areas are less diverse than in downstream areas. To test factors constraining plant community composition, a reciprocal transplant study was conducted between an upstream site with lower diversity, Broad Creek, and a downstream site with higher diversity, Deep Creek. Species composition, height, biomass, and below-canopy PAR were measured in sections of soil with rooted vegetation (sods) assigned to one of three treatments arranged in a randomized block design: transplant (excavated and moved between sites), disturbed control (excavated and replaced in same location), or undisturbed control (no excavation). Data were also collected on soil seed bank composition, hydrology, and salinity. Vegetation measures in sods transplanted from Deep to Broad Creek were not significantly...