Does white-tailed deer density affect tree stocking in forests of the Eastern United States?

Background White-tailed deer (Odocoileus virginianus) have increased during the past century in the USA. Greater deer densities may reduce tree regeneration, leading to forests that are understocked, where growing space is not filled completely by trees. Despite deer pressure, a major transition in eastern forests has resulted in increased tree densities. Methods To reconcile conflicting trends, we applied generalized linear mixed models to compare deer densities during 1982 and then 1996 to tree stocking after about 30 years and 15 years of potential reductions of small trees by deer, for the entire eastern US and 11 ecological provinces. We also compiled deer browse preferences and compared preferred browse with trends in tree species composition from historical (1620-1900) and current tree surveys. Results The forested area of the eastern US, including a prairie ecological province, was equally well-stocked (52%) and understocked (48%) during 2011-2017 tree surveys. For 1982 deer densities, 38% of area had deer densities > 5.8 deer/km(2) and for 1996, 66% of area had deer densities > 5.8 deer/km(2). Deer densities and tree stocking were not related significantly for the entire eastern US. Deer may reduce tree stocking in the Laurentian Mixed Forest; however, this province had both lower deer densities and greater tree stocking than other provinces. Furthermore, major tree species trends did not match tree browse preferences. Conclusions Rather than too few trees, too many trees is an ecological problem where historical open oak and pine forests had herbaceous understories, and currently, trees have captured growing space. We attribute other drivers than deer to explain this transition.