Aspen (Populus tremuloides) forests are keystone ecosystems in the western United States that supply economic and social benefits, including drawing tourists, serving as potential fire breaks, improving local economies, and providing habitat and forage for wildlife and livestock. However, in many areas these forests are at risk from climate change and past land use. This vulnerability is especially true for lower-elevation aspen, where the effects of drought and browsing animals are often more severe and can threaten aspen forest health and long-term persistence. In the northern Great Basin, lower-elevation aspen stands often occur as small, isolated patches within sagebrush-dominated landscapes. Sagebrush shrublands are increasingly being transformed into grasslands that are composed of exotic, fire-prone, nonnative plant species (such as cheatgrass [Bromus tectorum]). Although aspen is a fire-adapted species, if fire is too frequent at low elevations it could negatively affect aspen survival, especially when combined with impacts from invasive plants, worsening droughts, or other stressors such as insects and disease. The intent of this research is to identify aspen stands using multispectral imagery from Landsat 8, Sentinel-2, and Planet satellites to complement field sampling and ecological modeling. This research also compares aspen stand conditions derived from field measurements and remotely sensed data, using indices such as the Normalized Difference Moisture Index (NDMI). In previous research, information on plant moisture trajectories revealed forest areas that were resistant (positive trend), persistent (no trend), and vulnerable (negative trend) to drought-related stressors, providing resource managers with long-term perspectives on forest dynamics that can inform treatment options or monitoring efforts. The anticipated outcome of this research is a regional assessment of where and under what conditions lower-elevation aspen are most vulnerable to a potential decline in forest health. The resulting tools and information will have direct and timely uses for land managers working to conserve aspen forests in the Great Basin and surrounding regions.
A characteristic mixed-age aspen (Populus tremuloides) stand beginning to turn as seasons change in the northern Great Basin, Idaho. Photo credit: Doug Shinneman (U.S. Geological Survey).
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