Yellow Aspen leaves hang on to a tree limb during the autumn, near Buena Vista, Colorado. 

(AP Photo/Nathan Bilow)

Brilliant red and yellow aspen trees have become emblematic of Colorado’s fall foliage. But in recent years, scientists have noticed a decline in the trees—most notably in southwestern Colorado.

Drought is the prime contributor to aspen trees' death. Most recently, a Carnegie-led team of scientists looked more closely at the relationship. Key to the study is how the lack of water damages the vascular system in aspens, which transports water throughout the tree. 

Listen to the sound of aspen tree decline

“You can think of it as a tree heart attack. The tiny air bubbles shoot in and embolize inside the tree’s circulation system that pumps water,” said Princeton  University  researcher  William Anderegg, who co-wrote the study.

For the first time, Anderegg and others established the threshold for the lethal amount of vascular damage for aspens. The understanding helped the team create predictions for how future climate patterns could affect them. 

If there's a high increase in greenhouse gas emissions in the 2050s, large fractions of aspen forests in southwest Colorado could die and not regenerate. But the lower emissions scenarios did not always lead to widespread deaths.

“One really key finding of this is that the clock is ticking on these forests. A lot of control rests in our hands," said Anderegg.

"If we act to address climate change early, we can prevent and avoid some of the massive die offs that seem to be coming down the pipeline,” he said.

The findings were published in Nature Geoscience.