Species Loss Over Sixty-Six Years in the Ground-Layer Vegetation of Heart's Content, an Old-Growth Forest in Pennsylvania, USA

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In 1929, baseline vegetation data were collected in Heart's Content Scenic Area, an old-growth, 50-ha hemlock-northern hardwood tract within the Allegheny National Forest in northwestern Pennsylvania, USA. In 1995, we resampled the ground layer to document the extent of changes in the herb and shrub vegetation in this tract since 1929. We recorded changes in herb and shrub species frequency, abundance, richness, and evenness between 1929 and 1995. Numerous species present in 1929 were absent in 1995: 33 species (80%) were missing from the hemlock-beech stand, and 16 species (59%) were missing from the hemlock stand. More species were missing than were new in the hemlock-beech (sign test, p<0.0001) and in the hemlock stand (sign test, p=0.0001), and more species declined in abundance than increased (sign test p<0.000 1) in the hemlock-beech stand. In both stands, species with relative abundance values of <1% in 1929 were more likely than more abundant species to be missing in 1995. Evenness of herbaceous species declined in the hemlock-beech stand but increased in the hemlock stand. High species richness at the quadrat scale was negatively associated with high densities of hay-scented fern (Dennstaedtia punctilobula Michx.). The number of families represented declined from 27 in 1929 to 10 in 1995 (sign test, p=0.001). We attribute declines in species richness to the direct and indirect effects of herbivory by white-tailed deer. We suggest that this tract can and should be restored using a management strategy that includes building a deer exclosure around the entire tract, reducing fern abundance, and reintroducing extirpated species.

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