Sudden Aspen Decline (SAD)

Aspen forests in some areas of Colorado and neighboring states have experienced widespread, severe, rapid branch dieback and crown thinning leading to mortality. Aerial surveys in 2008 indicated that about 553,000 acres of aspen were affected in Colorado (~17% of the cover type), and neighboring areas of Wyoming are affected as well. Evidence suggests that it is a decline disease incited by acute, warm drought. Predisposing factors include low elevation, south and southwest aspects, droughty soils, open stands, and physiological maturity. Contributing factors, which kill the stressed trees, include Cytospora canker, two bark beetle species, poplar borer, and bronze poplar borer. For more information:

• Our SAD FAQs has basic information that may be of most interest to the public and media (3.2 MB, updated February 2011).
• Effects and etiology of sudden aspen decline in southwestern Colorado. Report in the Forest Ecology and Management.
• A scientific journal article in Forest Ecology and Management describes our initial findings and conclusions (1.1 MB).
• A preprint of a more concise article with some additional technical information (409 KB).