The influence of forested hillside seeps on local biodiversity is not well known in the glaciated northeastern USA. We documented the physical and vegetative characteristics of fifteen forested seeps and adjacent uplands to determine their contribution to local biodiversity and to improve existing regional seep classification methods. We determined the uniqueness of plant species using the Indicator Value Method, a method that combines individual species' relative abundance with its relative frequency of occurrence to produce a score (0–100%) based on the ability of that species to be associated within a defined group. We used nonmetric multidimensional scaling (NMDS) to address species-site relationships. Hardwood seeps were always located on slopes from 8–12° and were between 5 and 800 m2 in area. Conifer seeps were also located on similar slopes, but were typically larger (900 to 3600 m2) and within areas of lower topography or ‘benches’ on a hillslope. Herbaceous layer diversity (H′) was highest in hardwood seeps, highlighting their contribution to local biodiversity in headwater catchments. We found nine indicator species for hardwood seeps (α = 0.01), of which the highest scores belonged to Chrysosplenium americanum Schwein. ex Hook. (Indicator value = 83%), Viola cucullata Ait. (82%), and Circea alpina L. (77%). We found 11 indicator species in conifer seeps, with Osmunda cinnamomea L. having the highest score (83%). The NMDS ordination suggests that differences among hardwood and conifer seeps were correlated primarily to overstory composition. However, within site differences suggest a response to species diversity (H′ and J), percent bryophyte cover, and site hydrology. The indicator species identified here correspond with those from other New England states. However, further refinement of existing northeastern natural community classifications is necessary to reflect the unique understory composition. Although none of the species found was rare, the species present in these communities augment local and regional biodiversity. The results of this assessment provide further evidence that small, forested seeps support distinct vegetation communities within forested ecosystems.
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Vol. 136 • No. 4