GUNNISON, Colo. — Aspen trees, with their quivering, delicate foliage and the warm glow of color they spread across the high country of the Rocky Mountains this time of year, have an emotional appeal that their stolid, prickly evergreen cousins do not.
So tree lovers and scientists alike felt the impact when the aspen in the West started dying around 2004 — withering away in a broad band from here in southwest Colorado through the mountains of Utah, Arizona, and New Mexico and into Wyoming.
“There’s definitely something powerful about these trees,” said James Worrall, a forest pathologist for the United States Forest Service, gazing at a brilliant yellow swath of healthy aspen in a stand in the mountains here, about four hours southeast of Denver.
“It’s partly, I think, an emotional impression,” he said. “Partly a very real impression that the aspen is very important in our forests — hydrologically, biologically, to wildlife, every kind of way you can imagine.”
The good news is that the phenomenon known as sudden aspen decline, or SAD, appears to have stabilized, Dr. Worrall and other researchers say. Individual trees are still dying, since the process can take years to unfold, but many stands of trees are holding their ground against any new onset.