Riparian Vegetation Survey of Four Small Streams in Northwestern Pennsylvania

Abstract

The species composition and richness of the summer riparian vegeta? tion of four small streams in the nonglaciated Allegheny Plateau of northwestern Pennsylvania (Forest, Warren and McKean Counties) were examined. The arboreal stratum (stems > 2.5 cm dbh) of the four streams consisted of twenty species with Fagus grandifolia, Betula alleghaniensis, and Tsuga canadensis dominant (mean number of arboreal species across sites = 9.8 + 0.9 SE). Ninety-nine species were recorded from the ground-layer stratum (all vascular plants < 2 m tall) of the four streams with forbs as the dominant growth form. Four species, Dryopteris intermedia, Maianthemum canadense, Pilea pumila, and Viola blanda, were common to the ground-layer vegetation associated with all streams. Species of upland affinity were more prevalent in the riparian vegetation across streams than werewetland species. Several of the plant species recorded are indicators of rich and/or subacid to circumneutral soils, an edaphic medium of limited occurrence in the region. Mean ground-layer species richness and cover differed significantly among streams and ranged from 3.7 to 10.5 species/m2 (mean number of species/m2 across sites = 7.9 ? 1.5 SE) and 8.3 to 43.0% (mean percent cover across sites = 30.4 + 7.7 SE), respectively. Similarity in ground-layer species composition among streams ranged from 33.3 to 54.1% (mean similarity across sites = 38.9 ? 3.7% SE ). Although compositionally distinct, the small stream riparian flora documented by this study compares favorably in richness to other riparian habitats in northwestern Pennsylvania.