Drought blamed for Colo. tree die-off

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WASHINGTON, Feb. 11 (UPI) -- A recent widespread die-off of Colorado aspen trees is a direct result of damage caused by a drought 10 years ago, scientists say.

A team led by the Carnegie Institution's Department of Global Ecology, writing in the journal Global Change Biology, estimate the die-off has affected as much as 17 percent of Colorado aspen forests.

In 2002, the drought subjected the trees to the most extreme growing season water stress of the past century, they said.

While the drought did not kill the trees directly it damaged their ability to provide water to their leaves, the researchers said, leading to a decline in growth and increased mortality in the decade since the drought.

An ongoing decrease in precipitation, combined with high summer temperatures, has seen the die-off accelerate in recent years, the researchers said.

"Since there is a very strong upward trend in Colorado summer temperatures, they could link tree death to climate change," Carnegie researcher Chris Field said.

Aspens are particularly susceptible because they use shallow soil moisture, which evaporates quickly with increased temperatures during the summer drought of 2002, researchers said.

The type of climate-change hot summer drought experienced in 2002 occurred again in 2012, they said, which could indicate more tree die-offs are in the pipeline.