( of the Proceedings of the National Acad...)Underlying cause of massive pinyon pine die-off revealed

of the Proceedings of the National Academy of Sciences. A complete list of authors and their affiliations is at the end of this release. Los Alamos National Laboratory (LANL), the National Science Foundation, the U.S. Forest Service, the U.S. Geological Survey, NASA and the National Institutes of Health funded the research.

Ecologists want to learn more about long-term changes in ecosystems that occur in response to climatic and other environmental variation.

So in 1987, researchers established a study site in the pinyon-juniper woodland zone at LANL. Roughly every two weeks, Breshears and his colleagues measured soil moisture on the 100-by-150 meter plot (about three times the size of a football field). Temperature and precipitation data were recorded at a nearby site. In 1992, the team began tracking tree mortality.

"I could see the plot from my office window," said Breshears, who used to work at LANL. When the recent drought hit, the scientists were well-positioned to compare how the vegetation fared before and during the drought.

Initially the trees managed, but in 2002 the pinyon pines began to die. By the end of 2003, more than 90 percent of the pinyons on the plot were dead. Breshears said, "I would see the trees go from vibrant green to pale, gasping green to pale brown to dropping all their needles."

Pinyon pines all over the Southwest were doing the same thing.

U.S. Forest Service's aerial surveys of the region's pinyon-juniper woodlands in 2002 and 2003 revealed significant tree die-off covering more than 4,600 square miles (12,000 square km).

The effect was so dramatic it could be detected by satellite.

Rich and his colleagues at LANL and the University of Kansas analyzed satellite images of the region's pinyon-juniper woodlands for the years 1989 through 2003 using a measure of vegetation greenness known as Normalized Difference Vegetation Index (NDVI). The weekly composite images came from
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Source:University of Arizona

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