Intermountain GIS Conference

This study investigated trends in aspen (Populus tremuloides) extent and distribution in southeast Idaho to inform targeted management decisions for Bureau of Land Management (BLM) project partners seeking to promote aspen stand health. Remotely sensed Landsat imagery combined with aerial imagery, topographic layers, and in situ observations were used to train a probabilistic decision forest model to model aspen at three scales: 1) a focused study area (FSA) scale, 2) a watershed basin scale, and 3) targeted regions of interest where active management has been conducted. Climatic datasets were used to interpret model results. Historic wildfire locations were used to better understand the study area’s disturbance regime. Model results suggest aspen has declined in extent across the FSA by approximately 50,000 acres (32%) between 2004 (163,356 acres) and 2025 (112,320 acres). Watershed basin analysis shows spatial variability with some basins exhibiting stable aspen extents while others show declines. Personal communications with land managers indicate the model overestimated aspen extent. Various interacting factors may be driving aspen decline including (1) lack of disturbance and infrequent fires affecting aspen in the northern section of the FSA, (2) rising Tmin, Tmax, growing degree days, and frost-free days causing prolonged periods of stress –especially during drought years-- leaving them susceptible to secondary disturbance factors like pests, pathogens, and increasing competition pressure with conifers. Even when considering model uncertainties, aspen are most likely experiencing a decline across eastern Idaho. Further research, monitoring, and management activities to promote aspen habitat is merited