Short-term understory plant community responses to timber-harvesting intensity on non-industrial private forestlands in Pennsylvania
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abstract
Understanding harvesting impacts on non-industrial private forestlands is important, since they represent 75% of all commercial forestlands in the State of Pennsylvania, as well as a large percentage of most of the eastern United States. This study measured species composition, richness, and diversity of herb- and shrub-layer plant communities on a total of 40 nonindustrial private forest stands in northeastern Pennsylvania. These northern hardwood and oak-hickory stands had been recently harvested at different intensities. Remaining basal area was used as an indicator of harvest intensity. Species richness and diversity were not significantly related to basal area for summer or vernal herb understory plant communities for either forest type, although there was some evidence of a weak negative relationship between plant species richness and remaining basal area on more intensively harvested northern hardwood stands. Summer plant-species richness and diversity were related to percent litter cover and percent slope on northern hardwood stands, and percent Vaccinium cover and percent slope on oak-hickory stands. Ground- and shrub-layer cover significantly increased with increasing harvest intensity. Species composition of vernal herb communities did not vary in stands with differing amounts of basal area. Species composition of summer forest-floor communities differed with amount of basal area remaining, but only for northern hardwood stands. Shade-intolerant ruderal species dominated northern hardwood stands with low basal area, while more shade-tolerant plants dominated northern hardwood stands with high basal area. Summer plant understories of northern hardwood stands were generally dominated by feta and/or Rubus spp. (blackberry and raspberry), while oak-hickory stands were dominated by Vaccinium (blueberry) species. Litter cover, Vaccinium cover, fern cover, total ground cover, and forest type were significant variables related to species composition of vernal herb communities. Based on these results, forest landowners in this region should not expect significant short-term changes in vernal herbaceous or summer understory plant richness or diversity on their lands, regardless of the intensity of logging. However, short-term changes in vegetation structure (increased growth of forest-floor and shrub layers) should be expected for both oak-hickory and northern hardwood stands and a slight shift in species composition should be anticipated with intensive harvesting of northern hardwood stands.
