Deer have been overabundant in many eastern deciduous forests since the 1930’s. Decades of overbrowsing by white-tailed deer (Odocoileus virginianus) have caused major declines in plant species abundance, richness, and diversity. Deer tolerant species such as ferns often become dominant in areas with high deer densities. Conversely, species preferred by deer, including many wildflowers and shrubs experience steep population declines, often becoming locally extirpated. If populations of species remain low and fragmented for long enough periods of time, it becomes difficult for the populations to rebound, even after many years. These are called “legacy effects” and can persist for decades even after reduction or absence of deer browsing. Here, we surveyed five fenced and paired control plots in the Allegheny National Forest, central Pennsylvania. This constitutes one of the longest running deer exclosure experiments in the northeastern US (22 years). We asked to what degree do communities recover following deer exclusion in terms of plant species abundance, richness, diversity, and community composition.
Results/Conclusions
Total plant cover and Shannon diversity did not differ between fence and control plots, even following approximately 20 years of deer exclusion. Species richness was significantly higher in control plots than fence plots, contrary to our predictions. Although total plant cover and diversity did not differ between deer treatments, ordination analyses revealed different community compositions between treatments. Total fern cover was 125% higher in control plots than in fenced plots. Total forb cover showed the opposite trend, with 113% higher cover in fenced plots than control plots. Similarly, cover by woody species was 67% higher within fenced plots. An indicator species analysis revealed that three species, Prunus serotina, Mitchella repens, and Trillium undulatum, were associated with fenced plots and only one species, Lysimachia quadrifolia, was associated with control plots. Indeed, Trillium undulatum, a species particularly sensitive to deer browsing pressure, was only found within fence plots and its abundance remains low. Our results reflect legacy effects that have persisted for two decades following deer exclusion.