Research suggests aspen could be on rebound

We last reported on the mysterious ailment plaguing Western aspen trees, known as "sudden aspen decline," in October 2009. A year later, the decline appears to have stabilized. "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," Kirk Johnson of The New York Times reports. A research paper from James Worrall, a forest pathologist for the U.S. Forest Service, published in the journal Forest Ecology and Management, points to a sudden severe drought and heat wave early in the decade as the likely cause of S.A.D. (NYT photo by Benjamin Rasmussen)

"Wetter, cooler seasons since then — more to the aspen’s liking — have halted SAD’s spread," Johnson writes. "Although the aspen is the most widely distributed tree species in North America, the die-off struck mostly in the Southwest, where the drought beginning in 2002 was most severe. And lower elevations were affected more than upper ones, which tend to be cooler and wetter." Dan Binkley, a professor of forest ecology at Colorado State University, explained, "It [weather] was a really large stressor to the trees, and that made them more susceptible to other things — there’s pretty good comfort among scientists that that was what was going on."

The new research isn't all good news: "It has shown how profoundly vulnerable aspen are to environmental events outside their niche," Johnson writes. "In keeping with their delicate image, they do not like sudden weather shifts." Long-term climate projections for wider, more severe weather fluctuations could be a bad predictor for aspen. "It’s the extremes of variation that gets the aspen — not the average," Worrall told Johnson. (Read more)