Deer have a documented impact on the regeneration of trees and herbs, and interact with other forest processes. Impact is a function of deer density and landscape forage availability. At any given density impact is affected by the amount of landscape forage available. Deer impact refers to the ability of deer to influence tree seedling numbers, species composition, and seedling height growth. They do this by selectively browsing on understory vegetation. In areas with high deer impact the number of seedlings is reduced, the species composition is often shifted to less valuable (palatable) species, and the surviving seedlings are generally smaller. This relates directly to research findings indicating that when deer population numbers exceed what the land is able to support they can have a severe impact on the ability of the forest to regenerate itself.
Forage availability relates directly to the ability of the land to carry a specific population of healthy deer. When forage is less abundant, deer eliminate preferred forage species and spread their foraging out across many more non-preferred species. Many more plant species are browsed, and preferred plant species are much reduced in abundance or are completely eliminated. In regions where the habitat has been severely depleted from decades of over-browsing, deer can still have a high impact on the forest even with relatively few deer per square mile.
Indicators of high deer impact include obvious browse lines; evidence of severe browsing on species that are not preferred such as American beech, striped maple, and black cherry; and understories dominated by species that deer avoid such as hayscented fern, striped maple, American beech, hophornbeam, mountain laurel, blueberry, and spicebush. In areas with high deer impact we often see these species dominating the forest floor. Many of us in Pennsylvania do not know what forest understories would look like with low deer impact, we have never seen that throughout our lifetimes! The real concern is that even if deer densities are lowered are these altered plant communities semi-permanent? They may be.
I will leave you with a quote from Dr. Gary Alt, retired PA Game Commission, "If this is not corrected it threatens our entire forest ecosystem, the health of our deer herd, and even the future of hunting as we know it." Please tune in to the webinar.