Long term persistence of aspen in snowdrift-dependent ecosystems

Quaking aspen (Populus tremuloides) forests throughout the western United States have
experienced significant mortality in recent decades, much of which has been influenced by
climate variability, especially drought. In the western portion of its range, where most precipitation arrives during winter as snowfall and summers are dry, snowdrifts that persist into the growing season provide soil moisture recharge that sustain many aspen groves that are important locations of biodiversity within the landscape. There is growing concern that reduced
snowpack due to climate change may reduce the long-term persistence and productivity of aspen communities in these regions. In this study, we evaluated the potential for climate change and drought to reduce or eliminate isolated aspen communities in southwestern Idaho. We used a landscape simulation model integrated with inputs from an empirically derived biogeochemical
model of growth, and a species distribution model of regeneration to forecast how changes in
climate, declining snowpack, and competition with a conifer species is likely to affect aspen
occupancy over the next 85-years. We found that simulated reductions in snowpack depth (and
associated increases in climatic water deficit) caused a reduction in aspen persistence; aspen
occupancy was reduced under all high emissions climate scenarios. Douglas-fir (Pseudotsuga
menziesii) occupancy also declined under all future climates. Aspen regeneration declined over
the course of all simulations, with an ensemble ratio of mortality/establishment increasing over
the course of both low and high emissions climate scenarios. Climate-induced mortality of aspen
clones increased in frequency under all climate scenarios and, under the most severe emissions
scenarios, contributed to a substantial decline of aspen cover. Our research suggests that
snowbanks will be an important determinant of long-term persistence of aspen under changing climate in the region.