Deer are intricately connected to the habitat in which they live, relying on habitat resources for food, water, and cover. Yet as herbivores feeding on a wide variety of herbaceous and woody plants, deer are capable of dramatically altering the structure and composition of their forest habitat. Accordingly, deer impacts on forest ecosystems are an important consideration for managing deer populations throughout New York. The extent of deer impacts on forests reflects the relationship of deer abundance and forage availability, whereby as forage availability increases the impact of deer on forest resources decreases (Marquis et al. 1992).

In areas with abundant food resources, deer impacts may be slight even at moderate to high densities. Yet in areas with limited food resources, even low density deer populations may negatively impact forest condition and have cascading effects on other wildlife species. By selectively feeding on the highest quality and most palatable forage available, excessive deer browsing can result in mortality or reduced growth of young plants and prohibit successful regeneration of preferred forage species. Highly preferred herbaceous and woody plants may be suppressed, and the forest may slowly transition toward less palatable and browse-tolerant vegetation (Horsley et al. 2003). This reduces the ability of a forest to replace itself and creates conditions that favor exotic and invasive species (Baiser et al. 2008). Areas heavily impacted by deer are typified by clear browse lines, lacking much of the understory vegetation up to the height deer can reach.

Such changes to forest structure and composition not only reduce the value of the habitat for deer but can substantially reduce the habitat suitability for many other wildlife species resulting in local declines in biodiversity. Loss of understory vegetation from excessive deer browse has been linked to reduced diversity and abundance of forest-breeding birds (deCalesta 1994, McShea and Rappole 1994), and deer may affect trophic interactions between small mammals and birds, through direct competition for mast resources, particularly in years of low mast production (McShea 2000).

In New York, deer impacts on forest ecosystems are most apparent in areas where deer populations are unmanaged or hunting activity is severely constrained (e.g., parks and suburban green spaces), but detrimental deer impacts are also evident across a range of deer densities and forest habitats. Foresters practicing in New York estimated that forest regeneration, in stands opened up for regeneration, was moderately or highly successful only 30% of the time. They identified deer browsing and interfering vegetation as the primary causes of the problem (Connelly et al. 2010). Lack of interest or unwillingness of landowners to implement timber stand improvement or other measures to control less desirable tree species was also cited as a contributing factor to poor regeneration success.