Effects of White-Tailed Deer Herbivory on Forest Gap Dynamics in a Wildlife Preserve, Pennsylvania, USA

Many forests perpetuate themselves through a cycle of overstory tree mortality, canopy gap formation, new tree establishment and growth, and eventual gap closure. At high population densities, white-tailed deer (Odocoileus virginianus Zimmerman) could inhibit gap closure by consuming small trees. We compared forest gap dynamics in a private wildlife preserve, where deer population management is prohibited, and an ecologically-similar forest, where hunting is permitted. Counts of deer fecal pellet groups were 6-100 times greater in the wildlife preserve, indicating more intense deer herbivory. Overstory tree species composition, stand basal area, and the density of trees 2 20 cm dbh (diameter at breast height, 130 cm) were similar. However, the density of trees 30 cm tall-4.9 cm dbh was 36 times less at the wildlife preserve, or 240 times less if we only considered the tree taxa capable of joining the forest overstory. Canopy gap fraction was 41% greater at the preserve even though the density of large, dead gapmaker trees was 37% less, and these gapmakers were more decomposed, indicating that the canopy gaps were older. The prevalence of antler rubs, forest floor vegetation, or vines did not explain the differences in the densities of small trees or the gap cycles at the two sites. The findings suggest that gap closure has been inhibited at the wildlife preserve and raise the possibility that deforestation is occurring there gradually, from the bottom up. This article was written by Brian S. Pedersen and Angela M. Wallis for the Natural Areas Journal.

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