Impacts of white-tailed deer on regional patterns of forest tree recruitment

White-tailed deer (Odocoileus virginianus) had substantial cumulative impacts on patterns of forest tree recruitment across most of northern Wisconsin between 1983 and 2013. The diagram shows the path model used to trace direct and cumulative effects of deer on patterns of sapling recruitment in Acer rubrum, Acer saccharum, and Populus tremuloides over this interval. Deer densities refer to 10-year average estimates from Wisconsin DNR’s Sex-Age-Kill model as customized for each of 48 Deer Management Units in northern Wisconsin. Saplings refers to the logged sums of 2.5–5cm DBH sapling numbers in these species as tallied over matching 10-year intervals from U.S. Forest Service FIA survey data on tree numbers and growth within 13,105 plots in this region. See Fig. 7 and Table 5. Image of deer used with permission by the Integration and Application Network, Univ. of Maryland Center for Environmental Science (ian.umces.edu/imagelibrary/). [Display omitted] •Trees deer prefer to eat have failed to regenerate over the past 30years.•The mean, mode, and skew of sapling numbers in USFS FIA data reveal deer impacts.•Regeneration of less palatable trees declines in direct response to deer density.•Regeneration failures have already shifted forest composition and diversity. Local, short- to medium-term studies make clear that white-tailed deer can greatly suppress tree growth and survival in palatable tree species. To assess how deer have broadly affected patterns of tree recruitment across northern Wisconsin, we analyzed recruitment success in 11 common trees species that vary in palatability across 13,105 USFS - FIA plots sampled between 1983 and 2013. We also examined how recruitment in these species covaried with estimated deer densities here. Saplings of five palatable species were scarce relative to less palatable species and showed highly skewed distributions. Scarcity and skew provide reliable signals of deer impacts even when deer have severely reduced recruitment and/or no reliable deer density data are available. Deer densities ranged from 2.3 to 23 deer per km2 over a 30year period. Sapling numbers in two maples (Acer) and aspen (Populus) with intermediate palatability declined sharply in apparent response to higher deer density. Path analysis also reveals that deer act to cumulatively depress sapling recruitment in these species over successive decades. Together, these approaches show that deer have strongly depressed sapling recruitment in all taxa excep