Effects of abundant white-tailed deer on vegetation, animals, mycorrhizal fungi, and soils

Abstract

The last several decades have seen dramatic increases in ungulate populations worldwide, and white-tailed deer in the eastern United States currently exist at unprecedented densities in many areas. Numerous studies have demonstrated the effects of high densities of white-tailed deer on forest communities. However, few studies have simultaneously examined the effects of deer on multiple components of forest communities across trophic levels. Here, we simultaneously examine effects of excluding white-tailed deer on responses of woody and herbaceous vegetation, terrestrial and subterranean animals, mycorrhizal fungi, and soil characteristics. This study was conducted in a forest preserve with high deer densities in the central hardwoods region of the Midwestern US, using a series of replicated deer exclosures (15×15m) and adjacent unfenced controls that ranged in age from two to seven years. Despite significant tree recruitment inside exclosures, we recorded no native tree seedling recruitment in control plots. In addition, the growth rate of existing tree seedlings was significantly greater in exclosures than in controls, and the growth rate of invasive shrubs was approximately 30 times higher inside exclosures. Exclosures also had increased height, species diversity, and abundance of spring plants, and increased vegetation density in summer. We also found differences in terrestrial animals with higher densities of white-footed mice (Peromyscus leucopus) and dog ticks (Dermacentor variabilis) inside deer exclosures. However, there were no differences in salamanders or earthworms. Soil inside exclosures was significantly less compacted than in control plots despite the short period of deer exclusion, but there were no significant differences in soil nutrients or arbuscular mycorrhizal fungi. These results indicate that there are strong effects of high deer densities on all classes of understory vegetation and indirect effects on animals and soils. However, most belowground effects were nonsignificant, suggesting that responses of belowground communities to deer exclusion are weaker or slower to develop than aboveground effects.