Does Ungulate Foraging Behavior in Forest Canopy Gaps Produce a Spatial Subsidy with Cascading Effects on Vegetation

Concentrated foraging in forest canopy gaps by large ungulates may produce a pulsed spatial resource subsidy with cascading effects on the composition and developmental trajectory of gap vegetation. To test this hypothesis, we investigated the influence of white-tailed deer (Odocoileus virginianus) use of 12 artificial canopy gaps in a hemlock-northern hardwood forest. Ground-layer vegetation was monitored and available reactive nitrogen was assayed using resin beads deployed under the snowpack (March‐April) and soon after snowmelt (May). Deer use of openings was consistent with the forage maturation hypothesis, with the greatest levels of use occurring in small gaps. Allometric relationships suggest that mean localized winter pulses of deer-excreted N may be on par and/or in excess of annual atmospheric N deposition in the region. Correspondingly, deer access plots contained significantly more reactive N than exclosure plots soon after snowmelt (P 0.036) in April. While the pulse was indistinguishable by May, our nonmetric multidimensional scaling ordination results suggest that plant community composition in exclosure and control plots reflects this pulsed gradient in N availability. Given the importance of canopy disturbances and gaps to the perpetuation of forest ecosystems, localized and/or heterogeneous impacts may be magnified as forests turn over.

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