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Ungulate exclusion accentuates increases in woody species richness and abundance with canopy gap creation in a temperate hardwood forest

Sabo, Autumn E., Forrester, Jodi A., Burton, Julia I., Jones, Phillip D., Mladenoff, David J., Kruger, Eric L.
Forest ecology and management 2019 v.433 pp. 386-395
Odocoileus virginianus, canopy gaps, deer, environmental factors, hardwood forests, overstory, plant communities, population density, saplings, seedlings, shade tolerance, shrubs, soil water content, species richness, understory, wildlife management, woody plants, Wisconsin
Forest biodiversity is declining due to a wide variety of anthropogenic factors. Forest and wildlife management can be part of the problem or part of the solution. Our objective was to examine the influence of white-tailed deer exclusion on the response of understory communities to a gradient in overstory disturbance. We expected that greater overstory disturbance would act synergistically with deer exclusion to increase understory species richness and abundance. In northern Wisconsin, USA, we monitored changes in understory vegetation in a temperate hardwood forest following four overstory treatments (no-harvest controls and three gap sizes) and two deer treatments (deer access or exclosure). By the seventh year following gap creation, understory species richness and the abundance of multiple species groups had increased, especially when deer were excluded. Effects were most pronounced in larger gaps, particularly among saplings of less shade-tolerant tree species. The tree seedling community responded similarly, but less strongly, to treatments. In contrast, change in the short-stature shrub and herbaceous community seven years following gap and deer treatments was limited and species-specific. Environmental conditions at the groundlayer, such as light availability and soil moisture content, rarely differed by treatment in our study. Increased density of understory vegetation at seven years post-treatment may have negated early pulses in resource availability resulting from gap creation. Gap creation alone increased species richness and abundance of woody taxa, whereas deer exclusion alone had little effect on the understory community. When treatments were applied in combination, we saw the greatest change in the plant community. Our study provides evidence that, when accompanied by a reduction in deer population density, relatively intense overstory disturbance (e.g., group-selection harvest) may be an effective management strategy for restoring forest heterogeneity.