Vascular flora of beaver wetlands in western Massachusetts

The composition and structure of vegetation in beaver wetlands located in Franklin and Hampshire Counties of western Massachusetts were studied from 1980 to 1995. A flora of 231 vascular plants was recorded within fifteen selected field sites including seven new county records and one state-listed species (Ophioglossum vulgatum var pseudopodum), Relatively few species (5.6% of the total flora) were introduced. Factors contributing to high vascular plant diversity included 1) steep hydrological gradients created by beaver dams; 2) spatial heterogeneity caused by beaver artifacts, human structures and geological features; and 3) temporal heterogeneity resulting from beaver activity and hydrological fluctuations. While beaver activity has helped maintain regional vascular plant diversity in western Massachusetts since the reestablishment of beaver populations in the 1920s, current increases in beaver densities may pose a threat to later successional wetland species.