Study shows Sierra trees dying at alarming rate as climate warms

SACRAMENTO, Calif.—Conifer trees in the Sierra Nevada are dying at nearly double the rate as they were two decades ago, stressed by hotter temperatures and lower precipitation, according to a study to be presented later this week.

The 400-mile-long range has endured dry spells in the past, but its trees now are more likely to die during such periods because they are struggling with the effects of a new challenge—global warming.

"What surprised us are how sensitive these trees are to short-term changes in climate," said Phillip van Mantgem, an ecologist with the U.S. Geological Survey and the report's author. "That was kind of a shock."

Geological Survey researchers will present their findings Friday at a meeting of the Ecological Society of America in San Jose. They say their report is the first of its kind, coming after researchers spent 22 years examining coniferous trees in Yosemite and Sequoia national parks.

While some trees have grown faster in other parts of the U.S., the USGS researchers found the opposite to be true in the Sierra.

The study, begun in 1983, examined 21,338 trees in a variety of forests—ponderosa pine-mixed conifer, white fir-mixed conifer, red fir, Jeffrey pine and subalpine.

During the study period, the average mortality rate increased every year by about 3 percent, leading to a near doubling of the rate by the end of the period.
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