Aspen Overstory Recruitment in Northern Yellowstone National Park During the Last 200 Years

Using a monograph provided by Warren (1926) and two sets of aspen increment cores collected in 1997 and 1998, we analyzed aspen overstory recruitment in Yellowstone National Park (YNP) over the past 200 years. We found that successful aspen overstory recruitment occurred on the northern range of YNP from the middle to late 1700s until the 1920s, after which it essentially ceased. We hypothesized why the browsing influence of Rocky Mountain elk (Cervus elaphus) may be different now than it was historically. At a landscape scale, elk hunting outside YNP may be a significant factor changing elk foraging behavior. At a finer scale, elk foraging patterns and behavior due to predation risk may have been altered with the removal of the gray wolf (Canis lupus) from YNP in the early 1900s. Wolves may positively influence aspen overstory recruitment through a trophic cascades effect by reducing elk populations and decreasing herbivory on aspen by modifying elk foraging patterns and behavior.