Battered By Drought, Forests Lose Ability to Fend Off Climate Change

Forests play an important role as "carbon sinks" by absorbing and storing CO2 emissions, but a new study finds that that droughts--expected to become more frequent with climate change--deal that climate-buffering power a blow.

The findings, published this week in the journal Science, show that forests don't recover as quickly after a drought as had been previously thought, indicating a need to adjust climate models.

Researchers gathered tree ring data from over 1,300 sites across the globe to measure growth in periods after severe droughts that have occurred since 1948, and found that for the majority of the forests they studied, trees suffered years-long effects post-drought.

The researchers write: "We found pervasive and substantial 'legacy effects' of reduced growth and incomplete recovery for 1 to 4 years after severe drought."

They found that it took an average of 2 to 4 years for the trees to resume normal growth, with the first year growth happening about 9 percent more slowly than expected, and five percent more slowly the second. That's in contrast to previous ecosystem models that had assumed a quick recovery after drought.

"This really matters because in the future droughts are expected to increase in frequency and severity due to climate change," stated lead author William R.L. Anderegg, an assistant professor of biology at the University of Utah. "Some forests could be in a race to recover before the next drought strikes," he said.

What's the bottom line in terms of the impact on climate change?

Just looking at semi-arid ecosystems, these 'legacy effects' would mean 1.6 metric gigatons of carbon dioxide over a century. A press release for the study says that amount is roughly equal to one-fourth of the entire U.S. emissions in a year.

"If forests are not as good at taking up carbon dioxide, this means climate change would speed up," Anderegg stated.