A better world for bryophytes? A rare and overlooked case of positive community-wide effects of browsing by overabundant deer (original) (raw)

ECOLOGICAL IMPACTS OF DEER OVERABUNDANCE

Annual Review of Ecology, Evolution, and Systematics, 2004

Key Words browsing, Cervidae, forest regeneration, herbivory, plant-herbivore interactions ■ Abstract Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. In forests, sustained overbrowsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession to shift future overstory composition. Many of these simplified alternative states appear to be stable and difficult to reverse. Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer on ecosystems.

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

In many ecosystems, browsing of large mammals can aff ect plant species compositions. However, much less is known about potential above-and below-ground trophic interactions of large browsing mammals. Th is study focused on the direct and indirect eff ects of browsing on trophic and abiotic interactions within forest ecosystems. To quantify above-and belowground cascade eff ects, 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 eff ects on forest food webs. Deer exclusion directly altered woody species composition and signifi cantly increased shrub and sapling density. Above-ground cascade eff ects include greater leaf litter accumulation and higher arthropod density and biomass within the exclosures. Below-ground indirect eff ects include signifi cant decrease in soil nutrients, and higher arbuscular mycorrhizal fungal inoculum potential in the exclosures. Because ecosystems have fi nite 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 eff ects demonstrated largely unidirectional negative responses suggesting that high deer density has reduced the biodiversity of the forest community.