Subcontinental-scale patterns of large-ungulate herbivory and synoptic review of restoration management implications for midwestern and northeastern forests

Browse of forest understory vegetation by deer and other large ungulates alters ecosystem processes, making it difficult to regenerate forest land in herbivory-stressed areas. Seventy years ago, Aldo Leopold identified problem areas in the United States where overpopulation of white-tailed deer (Odocoileus virginianus) was likely to lead to overbrowsing of nutritive plants. Species of plants with little or no nutritive value would thereby gain a competitive advantage. Recent measurements of browse impacts on regionwide forest inventory plots in the midwestern and northeastern United States provide the opportunity to review the work of Leopold and others. A visualization of the probability of browse impact levels that warrant consideration during regeneration planning is presented for comparison to historical maps. Currently, 59 percent of the 182.4 million acres of forest land inventoried in the Midwest and Northeast was estimated to have moderate or high browse impacts. The Mid-Atlantic region had the highest proportion of forest land with moderate or high browse impacts (79 percent). The oak/hickory (Quercus/Carya) and maple/beech/birch (Acer/Fagus/Betula) forest-type groups each had percentages of forest land with moderate or high impacts above the regional average, 69 percent and 65 percent, respectively. The problem areas described by Leopold and others persist and new areas have emerged in the Central/Plains, Mid-Atlantic, and New England States. The study findings confirm three realities of forest regeneration management for forests under herbivory stress in the Midwest and Northeast: 1) The scope and persistence of large-ungulate herbivory has long-term wide-ranging implications for regeneration management; 2) less palatable tree species will continue to have a competitive advantage during the regeneration phase and are likely to be different species from the current canopy dominants; and 3) successful regeneration management of these forests requires more emphasis on ungulate-compatible prescriptions, novel approaches, and adaptive science.