Impacts on Ecosystems

The abundance and distribution range of white-tailed deer in North America (Tilghman, 1989; Conover, 1997; Waller and Alverson, 1997; Rooney, 2001; Côté et al., 2004), together with other cervid species worldwide (Akashi and Nakashizuka, 1999; Cooke and Farrell, 2001; Martin and Baltzinger, 2002; Darimont et al., 2005), have been increasing rapidly over the last few decades. The situation is particularly alarming in areas where there are no natural predators or where predators have been extirpated (Horsley et al., 2003; Potvin et al., 2003). Overabundant white-tailed deer populations have led to major impacts on preferred plant species (Rooney, 2001; Côté et al., 2004), affecting competitive interactions between plants and favoring some species over others (Huntly, 1991; Côté et al., 2004). Overbrowsing by deer has modied forest succession in many ecosystems, from temperate deciduous forests to boreal forests (Alverson and Waller, 1997; Healy et al., 1997; Horsley et al., 2003; Potvin et al., 2003). Because of the nature of their impact on ecosystems, white-tailed deer have been referred to as ecosystem engineers (Côté et al., 2004; Baiser et al., 2008). By modifying vegetation structure in various habitats, whitetailed deer at high population densities can have numerous direct and indirect effects on other organisms (Huntly, 1991; Rooney and Waller, 2003), such as small mammals (McShea, 2000), birds (deCalesta, 1994; McShea and Rappole, 2000), and invertebrates (Barrett and Stiling, 2007, see also Allombert et al., 2005b). Given that white-tailed deer population numbers are still increasing in North America, mainly due to improved habitat conditions, decreasing hunting pressure, and milder climate, impacts on

Overview of Causes of High Deer Densities ......................................................................................... 380 History of Deer Impacts on Ecosystems ................................................................................................ 380 Impacts on Vegetation ............................................................................................................................ 381

Nutrient Cycling and Energy Transfer .............................................................................................. 381 Forest Understory .............................................................................................................................. 382

Preferred Plants ............................................................................................................................ 382 Nonpreferred Plants ..................................................................................................................... 383 Invasive Species ........................................................................................................................... 383

Tree Regeneration ............................................................................................................................. 384 Forest Succession ......................................................................................................................... 384

Hard Mast Seeds ............................................................................................................................... 385 Impacts on Other Animals ..................................................................................................................... 386

Invertebrates ...................................................................................................................................... 386 Avian Communities .......................................................................................................................... 387 Small Mammals ................................................................................................................................ 387 Other Mast Consumers ..................................................................................................................... 387

Impacts of Disease Transmission ........................................................................................................... 388 Impacts of Management to Increase or Maintain Deer Densities .......................................................... 389 Conclusion ............................................................................................................................................. 390 Acknowledgments .................................................................................................................................. 391 References .............................................................................................................................................. 391

ecosystems are likely to become increasingly frequent. This chapter addresses and discusses the impacts of overabundant white-tailed deer populations on ecosystems, from individual responses of organisms to community level processes.