Aspen, Elk, and Fire in the Rocky Mountain National Parks of North America

• Published in: Wildlife Society bulletin 1998-10, Vol.26 (3), p.449-462
• Main Authors: White, Clifford A., Olmsted, Charles E., Kay, Charles E.
• Format: Article
• Language: English
• Subjects: Browsing; Comparative studies; Ecosystems; Elks; Environmental monitoring; Forest ecology; Forest ecosystems; Herbivores; Humans; National parks; Special Feature: Ungulate Management in National Parks of Western North America; Trees; Wildlife ecology; Wildlife management; Wolves
• ISSN: 0091-7648; 1938-5463

Trembling aspen (Populus tremuloides) forests in the Rocky Mountains are an indicator of ecological conditions because they have maintained their presence for thousands of years through vegetative reproduction, and these communities have high biodiversity. Aspen can be tied to ecosystem condition through a 4-level trophic model that links humans, wolves (Canis lupus), elk (Cervus elaphus), and aspen through the processes of predation, herbivory, burning, and differential wildlife responses to humans. We used a comparative study of research literature and historic photographs to evaluate aspen change over time in 6 Rocky Mountain national parks in Canada and the United States: Jasper, Banff, Yoho, Kootenay, Yellowstone, and Rocky Mountain. Across all parks, aspen has consistent responses to increased browsing by ungulates and decreased frequency of fire. Although aspen was historically vigorous in all parks, today most stands are in decline. Trees are intermediate to mature in age (60-120 years old), and elk browse off new suckers before they reach 2 m in height. Fire, combined with browsing, has hindered regeneration of aspen. The exception to this pattern is northern Jasper National Park where elk densities appear to have been reduced by wolves in the 1970s, and aspen regenerated. We found a gradient of increasing human-caused ecosystem changes in Rocky Mountain national parks: (1) historic conditions with frequent fires and low elk density regulated by humans, wolves, and other predators (i.e., all parks); (2) current conditions of patches of high elk density, where wolves are displaced by human land use, within a matrix of moderate elk density, where wolves and other predators are present (i.e., Banff and Jasper national parks); (3) recent conditions inside parks, where wolves are absent, and very high elk density is regulated by competition for food (i.e., Yellowstone before 1995); and (4) potential future conditions, where increasing human land use around parks displaces carnivores and reduces hunting, and very high elk density occurs throughout landscapes. Aspen stands regenerate well in areas of low elk density and in some areas of moderate elk density; however, in areas of high and very high elk density, aspen does not regenerate to heights >2 m, and burning accelerates clone deterioration. Our recommendations to national park managers are to restore carnivores, use fire in areas of low elk density, and control human uses that displace carnivores.