White-tailed deer alter a wide array of forest community components: Effects on arbuscular mycorrhizae, vascular plants, animals, and more

Background/Question/Methods

White-tailed deer (Odocoileus virginianus) have become increasingly abundant in eastern U.S. forests over the last fifty years and are often described as keystone species or ecosystem engineers for their role in structuring forest communities. Despite their abundance and clear effects on individual aspects of understory forest communities, the sum of their direct and indirect effects on forests remains largely unknown. In addition, the majority of studies in the U.S. have a strong geographic bias; most have been done in northern states dominated by hemlock-maple forests. It is unclear how well results of these studies translate to hardwood forests that lack evergreen species that can provide winter food. I have constructed a series of fifteen deer exclosures with paired control plots in a forest that has high densities of deer.  I measured a wide array of plants and animals in control and deer-excluded plots with an effort to understand the interactions between different community components and how they may be altered by high deer abundance. I have collected data on soil nutrients and compaction, arbuscular mycorrhizal abundance and inoculation potential, abundance and size of herbaceous and woody plants, and abundance of salamanders, mice, ticks, and earthworms.

Results/Conclusions

I found significant changes in forest communities after only a single year of deer fencing, and these effects persisted and often increased in strength over time.  Herbaceous species were taller and had greater percent cover inside the fences after a single year of fencing.  After multiple years of fencing, there was an increase in the number of flowers produced. Fenced plots also had higher recruitment of tree seedlings and faster growth of mature trees.  The soil inside the exclosures was less compacted than the unfenced controls and had higher activity of arbuscular mycorrhizal fungi.  We are exploring how interactions among arbuscular mycorrhizae and herbaceous and woody plants may be altered by high deer abundance.  There were also significant indirect effects of deer on other animal species.  Mice, ticks, and salamanders were more abundant inside deer exclosures during summer, possibly due to more moderate environmental conditions created by the dense vegetation.  These results indicate that high densities of deer have a dramatic effect on the structure of forest communities and have strong implications for deer management and preservation of biodiversity.