Plant community structure in a freshwater tidal wetland

Abstract

The vascular plant community in a freshwater tidal wetland on the lower Connecticut River was studied in 2000. The effects of abiotic conditions on density and species density of plants in 70 samples, each 0.25 m2 in area, were characterized. Sixty species were recorded. The mean species density was highest in shallow water because the number of emergent species in the community was far greater than the number of submerged species, which occurred with higher frequency in deeper water. Plant density had a bimodal distribution because of the different responses of emergent and submerged plants to water depth and was lowest in shallow water, where physiological stress, physical disturbance, and possibly herbivory are suspected of being limiting. Ordination and regression analyses found that water depth and the amount of organic matter and nitrogen in the sediment had the greatest effect on wetland plant density, although other variables also were influential. Abundance of emergent and submerged species differed in their responses to ammonium and nitrate levels. Overall species density was most strongly correlated with water depth. Several plant associations, including associations of submerged and emergent species, were identified, based on shared affinities for environmental conditions.