Influence of inundation potential and forest overstory on the ground-layer vegetation of Allegheny Plateau riparian forests.

摘要

A study was conducted during 1993-94 in the nonglaciated Allegheny Plateau of northwestern Pennsylvania where ground-layer plant communities of headwater riparian forests are among the most species-rich of the region. The study was undertaken to investigate the influence of inundation potential (geomorphic surfaces with high, moderate or low probability of seasonal inundation) and forest overstory (stems >=2.5 cm dbh) characteristics (percent overstory cover, overstory basal area, overstory stem density and basal area) of eastern hemlock (Tsuga canadensis) on species richness, biomass and cover of the summer ground-layer (all vascular plants <=1 m tall) at 6 riparian sites. The study design used inundation as a class variable with sites or portionsof sites within each class as replicates. Mean total, forb and graminoid species richness and biomass were significantly greater on geomorphic surfaces of high inundation potential than for those of moderate and low inundation potential. Overstory cover,overstory stem density and basal area of T. canadensis were not correlated with ground-layer species richness, biomass and cover within inundation classes. Wetland species (obligate and facultative wetland species), chiefly forbs and graminoids, occurred most often on geomorphic surfaces of high inundation potential, while upland species, mainly tree seedlings, occurred principally on geomorphic surfaces of moderate and low inundation potential. Differences in species composition, richness, biomass andcover indicated that the ground-layer of Allegheny Plateau riparian forests was composed of a series of wetland and upland species guilds that replaced each other along the stream to mesic forest gradient.