Abstract for the 2003 North American Forest Ecology Workshop, Corvalis, Oregon

Managing for old-growth forest structure in northern hardwood forests: experimental test of a new silvicultural system

William S. Keeton, Ph.D.

School of Natural Resources

University of Vermont


Recent research on sustainable forestry in the northeastern U.S. has focused on “structure” or “disturbance-based” silviculture.  The as yet untested hypothesis is that these systems can sustain a broader array of biodiversity and ecosystem functions than conventional systems.  I am testing this hypothesis using an approach intended to promote old-growth structural characteristics.  The study is replicated at two research forests in Vermont.  Study areas are mature northern hardwood forests with minor shade-tolerant conifer components.  The experimental design consists of four treatment units (two manipulations and two controls) at each location.  Each unit is 2 ha in size.  Structural objectives include multi-layered canopies, elevated large snag and downed coarse woody debris (CWD) densities, variable horizontal density, and re-allocation of basal area to larger diameter classes.  The later objective is achieved using an unconventional marking guide based on a rotated sigmoid target diameter distribution, applied as a non-constant q-factor.  The marking guide is also derived from a target basal area (34 m2/ha.) and maximum diameter at breast height (90 cm) indicative of old-growth structure.  This results in residual stocking levels just above the B line.  Accelerated growth in larger trees is also promoted through crown release.  Prescriptions for enhancing snag and downed woody debris volume and density are based on stand potential and literature-derived targets.  On some units downed CWD is created by pulling trees over, rather than felling, to create pits and exposed root wads.  We have completed two years of pre-treatment data collection, permanent plot establishment, stem-mapping, and treatment implementation (January 2003).  Effects on overstory and understory vegetation, soils, invertebrates, and vertebrates will be assessed annually.  Collaborating researchers are assessing economic and operational tradeoffs.