Complex interactions shaping aspen dynamics in the Greater Yellowstone Ecosystem

Loss of aspen (Populus tremuloides) has generated concern for aspen persistence across much of the western United States. However, most studies of aspen change have been at local scales and our understanding of aspen dynamics at broader scales is limited. At local scales, aspen loss has been attributed to fire exclusion, ungulate herbivory, and climate change. Understanding the links between biophysical setting and aspen presence, growth, and dynamics is necessary to develop a large-scale perspective on aspen dynamics. Specific objectives of this research were to (1) map aspen distribution and abundance across the Greater Yellowstone Ecosystem (GYE), (2) measure aspen change in the GYE over the past 50 years (3) determine if aspen loss occurs in particular biophysical settings and (4) investigate the links between biophysical setting and aspen presence, growth, and change in canopy cover. We found that aspen is rare in the GYE, occupying 1.4% of the region. We found an average of 10% aspen loss overall, much lower than that suggested by smaller-scale studies. Aspen loss corresponded with biophysical settings with the lowest aspen growth rates, where aspen was most abundant. The highest aspen growth rates were at the margins of its current distribution, so most aspen occur in biophysical settings less favorable to their growth.