Effect of herbivory on the nutritional value of six hardwood species for white-tailed deer in the Allegheny Forest

Herbivores alter plant quantity and quality through direct tissue consumption and indirectly via the structural and chemical allocational strategies plants deploy in response to herbivory. Here we examine how browsing by white-tailed deer Odocoileus virginianus alters nutritional quality of six regenerating hardwood species (red maple Acer rubrum, black cherry Prunus serotina, birch Betula spp., pin cherry Prunus pennsylvanica, white ash Fraxinus americana, and American beech Fagus grandifolia). Using an established, large-scale experiment that manipulated deer access to plots using fencing, we tested whether browsing altered the nutritional quality and biomass as well as nutritional capacity to support deer of six hardwood species in an early successional hardwood forest of Pennsylvania, United States. Pin cherry was the most nutritious of the six species with greater dry matter digestibility and digestible protein and lesser neutral detergent fiber. Areas exposed to browsing had less browse biomass of stems and leaves yet greater digestible protein; an effect driven by digestible protein of pin cherry. We found no effect of browsing on neutral detergent fiber or dry matter digestibility. Although deer browsing reduced biomass of the six hardwood species, it did not alter the nutritional capacity to support lactating females in the summer. Our results confirm that browsing limits tree regeneration and available browse and provide conservative conclusions on how deer can alter their diet quality.