Wolves and Elk Shape Aspen Forests
The deep-green coniferous forests lining the valley bottoms of Jasper National Park arise from people manipulating wolves, elk and wildfire over the past century. Whether young aspen trees grow to maturity depends upon the dynamics of wolf and elk populations. Exterminating wolves from the Canadian Rockies park has unexpectedly eliminated young aspen.
Scientists from Oregon State University have learned from the age structure of Jasper's aspen stands that there were extensive periods since 1900 when no aspen saplings survived. Aspen regeneration was plentiful during the early 1900s after over-hunting removed elk and wolves from the region. Forest fires also helped maintain large areas of aspen, willow and shrubs.
The situation changed after 1920 when 90 elk from Yellowstone Park were transplanted to Jasper, and wolves gradually moved back into the valleys. That's also the time when fire fighters began promptly snuffing out wildfires, enabling spruce and pine to replace the deciduous vegetation.
The wolf population grew to around 50 animals until the 1940s when a program of poisoning and shooting nearly extirpated wolves from the park for a second time. Without their main predator, elk flourished, to the point where during winters they browsed every young aspen within reach.
In the groves examined by researchers, no trembling aspen suckers lived long enough during this period to mature.
The aspen recruitment failure lasted 28 years in a relatively remote region of the park. After the control policy was abandoned, wolves began denning there again in the mid-1960s. Predation, along with other influences, kept the wintering elk herds in check. Once elk became less common, the aspen started successfully regenerating.
The dynamics of wildlife and trees played out differently a few kilometres east of Jasper townsite. Since the 1950s, no young aspen near Highway 16 have survived. The area continues to be heavily browsed by elk herds. The ungulates appear to take refuge here because the presence of people keeps wolves away.
An absence of regenerating aspen is cause for concern because it signals the decline of the most diverse ecosystem in Jasper Park. Many birds and mammals benefit from the berries and seeds produced by the exceptionally rich array of shrubs and other plants associated only with aspen-dominated stands. And without aspen forests, elk would find winters more difficult.
R.L. Beschta and W.J. Ripple. 2007. Wolves, elk, and aspen in the winter range of Jasper National Park, Canada. Canadian Journal of Forest Research. 37(10): 1873-1885.