Overabundant white-tailed deer (Odocoileus virginianus) and nitrogen inputs to forest patches in a multiple-use landscape

Background/Question/Methods In the Eastern United States, white-tailed deer (Odocoileus virginianus) have become overabundant in many multiple-use landscapes where they regularly feed on agricultural crops and utilize forest stands during the daylight for concealment, rumination, social interactions, etc.  Seagle (2003; Oikos 103:230-234) hypothesized that this scenario placed overabundant deer in a position to effect a net flux of nutrients (up to 30-40 kg N / ha, depending on deer density and landscape structure) from fertilized agricultural fields into forest ecosystems, where these nutrient subsidies could influence detrital food webs and nutrient cycling.  Experimental studies were used to examine the effect of deer urine nitrogen on the detrital food web.  Twelve months of field collections of deer fecal pellets and stochiometric calculation of potential nitrogen input were carried out for 100 randomly chosen forest patches within a multiple-use landscape to examine the variation in deer nitrogen input to forests and thus variation in possible food web effects.

Results/Conclusions At hypothesized application rates, forest floor detritivore (collembolan) populations increased up to 180%.  However, addition of deer nitrogen tended to decrease (-2.5%) invertebrate predators of collembola, specifically total spider populations, so that collembola population increases likely resulted from both bottom-up stimulation from fertilization and decreased top-down control.  At the landscape scale, results suggest that a high degree of deer nitrogen input to the forest floor, probably resulting from variation in landscape structure/composition, directly impacts the degree of trophic impacts, thus leading to greater variation in forest floor ecosystem processes.