for the 2003 North American Forest Ecology Workshop,
for old-growth forest structure in northern hardwood forests: experimental test
of a new silvicultural system
S. Keeton, Ph.D.
of Natural Resources
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.