• Return to the previous page

Impact of Deer Browsing on Forest Growth
by Collin Law
Fall 2004

This summer, Hannah Roth and I studied the effects of deer browsing on forest regeneration in Black Rock Forest.  Browsing by a variety of mammals, predominantly the white-tailed deer, Odocoileus virginianus, has been shown in numerous studies to inhibit tree regeneration and to alter the nature of forest regrowth patterns.  The deer herd in the northeastern United States has expanded tremendously in the absence of natural predators (such as the coyote), reaching 35-40 per square mile in Black Rock, well over the 15 per square mile known to be detrimental to forest regeneration.

In 1988, Forest staff constructed an exclosure, a fenced area that deer cannot enter, along Hall Road near Sutherland Pond.  Both dead and living trees were cleared.  A large area that was clear-cut in 1971 serves as an approximate control.  The plots are directly adjacent, topographically identical, and have been subject to similar forest management practices for the past 75 years.  The important difference is that the unexclosed 1971 clear-cut was cleared 17 years before the 1988 exclosure.

For a 1999 study, three 0.01-acre plots were established in the 1988 exclosure (called exclosure-in), and part of the fencing was removed to create an additional study area with three more plots (called exclosure-out).  Hannah and I established six new plots in the 1971 clear-cut area this summer.  In each of these randomly positioned plots, we identified and measured the trees and surveyed vegetation by species and coverage.

Our most significant finding comes from comparisons between the exclosure plots and the 1971 clear-cut area.  The clear-cut area has never been protected from deer browsing.  Over the past 33 years, not a single tree has reached even one inch in diameter.  While both the exclosure-in and exclosure-out plots have grown into lively birch stands with some other hardwood species, the adjacent 1971 clear-cut area has grown into a dense, treeless blueberry patch.  (A predominantly birch stand is an indicator of healthy regeneration because birches are “early-to-intermediate” species in ecological succession, typical trees that recolonize cleared areas.) These data strongly support the hypothesis that deer browsing is effectively inhibiting forest regrowth in Black Rock Forest.

Collin Law is a senior in Ecology, Evolution, and Environmental Biology at Columbia University, and Hannah Roth is a junior in Urban Studies at Barnard College.  They learned about the Forest internship through the Center for Environmental Research and Conservation; their research was supervised by Dr. William Schuster, with assistance from John Brady, Matthew Munson, and Rob Carson (a Columbia graduate student).