A Migratory Ungulate Facilitates Cross-Boundary Nitrogen Transport in Forested Landscapes

Forest ungulates impact ecosystems in a number of ways. Most studies have focused on consumptive effects that may cascade to other components of the ecosystem, and tend to be motivated by harvest management or the mitigation of undesired effects on vegetation. In this study, we demonstrate that white-tailed deer (Odocoileus virginianus), a common forest ungulate in eastern North America, may directly increase availability and heterogeneity of nitrogen due to excretion of nitrogenous wastes. We conducted fecal pellet counts in 39 winter cover habitat patches, ranging in area from 0.04 to 59.6 ha, each spring for eight consecutive years. Pellet counts were used to develop allometric models of annual deer-associated nitrogen inputs at both whole-stand and fine (<10 m²) spatial scales. Deer-associated nitrogen estimates were in the range of 1-4 kg[N] ha^-1 in persistently used patches when estimated at the stand scale. Fine-scale estimates in areas of consistent aggregation were equivalent to up to 20 kg[N] ha^-1. These areas, such as bedding sites and trails, experienced greater N inputs compared to the surrounding forest matrix. Annual deer use and associated nitrogen inputs were highly variable over space, and spatial patterns in use were consistent over time at both stand and fine spatial scales. Deer-associated nitrogen likely represents a cross-boundary nitrogen flux into patches of conifer cover because deer accumulate nutrients in other habitat types during the warm season, and lose body mass during winter. Nitrogen hotspots and heterogeneity derived from the nitrogenous wastes of forest ungulates may be a generally overlooked phenomenon in forest ecology, with impacts varying according to ecological context.