Demographic patterns and disturbance responses of understory vegetation in a managed forest of southern New England: Implications for sustainable forestry and biodiversity maintenance

Current interest in sustainable forestry is generating a need for an increased understanding of the effects of forest management practices on floristic diversity patterns. For U.S. forests, it is the herbaceous understory plants as a group that must be better understood physiologically and demographically if forest managers are to successfully maintain or increase biological diversity within vegetative communities. This dissertation describes a study that (1) investigates understory floristic patterns in a southern New England mixed-hardwood forest and (2) tests the ability of understory plants to adapt to full sun conditions that would accompany canopy removing disturbances.; Data collected in 1996 and 2004 from 400 plots at The Yale-Myers Forest, Eastford, CT, USA was used in an observational study to relate stand characteristics to understory plant diversity. Species richness was significantly influenced by forest cover type and followed the decreasing trend of regenerating > hardwood > hardwood-pine > pine > mixed > hardwood-hemlock > hemlock. Slope position was also related to richness, valley > midslope > ridge, and valley sites contained the greatest number of indicator species. Overstory basal area of Tsuga canadensis showed a higher order influence than topography, and mediated the effects of slope position on both understory species richness and composition. Changes in overstory basal area between the two sampling periods had little effect on species diversity.; A controlled experiment tested the ability of Aralia nudicaulis, Maianthemum canadense, and Arisaema triphyllum to respond to full sun conditions at different times in leaf development. Plants were moved from shaded to open sites in the winter before emergence (developmental plasticity), and in the summer after leaves had matured (rapid acclimation). Artificial edge treatments were used to provide afternoon shade for some groups of plants. Plants that developed in full sun conditions were able to adjust morphological, anatomical, and physiological traits to take advantage of the new light environment. Mature plants showed major stress responses indicating limited ability to acclimate to high light, although edge treatments improved the acclimation response.; Results of these studies are discussed in the context of sustainable forest management and the maintenance of floristic diversity.