Effects of Twenty Years of Deer Exclusion on Woody Vegetation at Three Life-History Stages in a Mid-Atlantic Temperate Deciduous Forest

Chronic browsing by Odocoileus virginianus (White-tailed Deer) has potential to alter the life history of trees within Mid-Atlantic forests, including seedling size and abundance in the short term to overstory composition in the long term. Most studies quantify the effects of deer browse using small plots (<1 ha) and short time frames (<10 years), which may misrepresent larger-scale and longer-term impacts. We maintained a 4-ha deer exclusion plot for 20 years in a mesic northern Virginia temperate deciduous forest to examine the impacts of browsing on forest trees at multiple life-history stages. We compared the abundance and species composition, as well as seedling height, of woody stems across the seedling, small-sapling, and large-sapling size classes inside the deer exclosure and within an adjacent reference area. There were no significant differences in seedling abundance or community composition, but seedling height was on average 2.25 times greater in the exclosure than the reference plot. Small-sapling (1–5 cm DBH) stem count was 4.1 times greater inside the exclosure, with all species more abundant in the exclosure except Asimina triloba (Pawpaw) and Carya tomentosa (Mockernut Hickory). Differences were smaller in the large-sapling size class (5–10 cm DBH), with relative total large-sapling stem count only 1.25 times greater in the exclosure. Browsing pressure appeared to influence the composition and size structure of smaller stems in the past 20 years, but has had little effect on larger stems. While the lack of replication limited the scope of inference of our study, our findings suggest that natural delays in mature tree recruitment in a closed-canopy forest may mask the full impact of deer herbivory for decades.