Wolves, Elk, and Aspen in the Winter Range of Jasper National Park, Canada
We undertook a retrospective study of aspen age structure in the winter range of Jasper National Park to assess potential trophic cascades in wolf-elk-aspen systems. We compiled historical wolf (Canis lupus Linnaeus,1758) and elk (Cervus elaphus Linnaeus, 1758) population date and, in 2005, sampled 42 trembling aspen (populus tremuloides Michx.) stands within the Palisades site along the Athabasca Valley near Jasper townsite and another 30 stands within the Willow Creek site in a relatively remote portion of the park. Results indicated that the aspen recruitment (suckers or seedlings growing into tall saplings and trees) occurred at both sites in the early 1900s but decreased in the 1940s as elk numbers were reaching a maximum. Wolves were largely eliminated from the park in the mid-1900s, and aspen recruitment during that time ceased at both sites, apparently because of heavy browsing by elk. With recovery of wolf populations in the late 1960s and increasing predation risk, elk use of the Willow Creek site declined, and aspen recruitment resumed. However, at the Palisades site, an area of relatively low predation risk due to human use and developments, renewed aspen recruitment has not occurred. Results indicate that historical wolf or ungulate control programs and human developments influenced trophic cascades involving wolves, elk, and aspen in these winter ranges.