Abstract - Hardwood Tree Decline Following Large Carnivore Loss on the Great Plains, USA

In order to investigate long-term food web linkages and trophic cascades, we conducted a retrospective analysis of large carnivores, wild and domestic ungulates, human settlement, and hardwood trees from the late 1800s to the present at Wind Cave National Park in southwestern South Dakota. We measured diameters of all cottonwood (Populus spp) and bur oak (Quercus macrocarpa) trees withing a large portion of the Park to assess long-term patterns of recruitment (growth of sprouts or seedlings into tall saplings or trees). Increment cores from a subset of these trees were used to determine tree age and to develop relationships between age and diameter. Resulting age structure indicated a lack of cottonweed and bur oak recruitment for more than a centurey, beginning in the 1880s and continuing to the present. This is attributable to high levels of browsing, initially by livestock and subsequently by wild ungulates, in the absence of large carnivores. Conversely, we found that hardwood trees had recruited to areas protected from browsing, such as inside fenced exclosures and within a small browsing refuge. Results indicate that Great Plains ecosystems may have been profoundly altered by mounting levels of ungulate herbivory following the removal of large carnivores.