Beyond the browse line: complex cascade effects mediated by white-tailed deer

In many ecosystems, browsing of large mammals can affect plant species compositions. However, much less is known about potential above- and below-ground trophic interactions of large browsing mammals. This study focused on the direct and indirect effects of browsing on trophic and abiotic interactions within forest ecosystems. To quantify above- and below-ground cascade effects, white-tailed deer have been excluded for over 18 years from three 4-ha plots, which were paired with same sized deer access plots. Our results demonstrate complex direct and indirect cascade effects on forest food webs. Deer exclusion directly altered woody species composition and significantly increased shrub and sapling density. Above-ground cascade effects include greater leaf litter accumulation and higher arthropod density and biomass within the exclosures. Below-ground indirect effects include significant decrease in soil nutrients, and higher arbuscular mycorrhizal fungal inoculum potential in the exclosures. Because ecosystems have finite resource availability, high deer density may imbalance the system by redirecting resources toward maintaining deer biomass at the expense of multiple trophic levels throughout the forest community. Both complex bottom up and top down trophic cascade effects demonstrated largely unidirectional negative responses suggesting that high deer density has reduced the biodiversity of the forest community.