Drought's Impact on Forests Causes Trees to Store Less Greenhouse Gases

It turns out that drought may have more of an impact on forests than we thought. Scientists have found that living trees take an average of two to four years to recover and resume normal growth rates after droughts end.

"This really matters because in the future droughts are expected to increase in frequency and severity due to climate change," said William R.L. Anderegg, one of the researchers, in a news release. "Some forests could be in a race to recover before the next drought strikes."

Trees in forests play a huge role in buffering the impact of human-induced climate change by removing massive amounts of carbon dioxide emissions from the atmosphere and incorporating the carbon into woody tissues. The finding that drought stress sets back tree growth for years means that Earth's forests are capable of storing less carbon than climate models have predicted.

"If forests are not as good at taking up carbon dioxide, this means climate change would speed up," said Anderegg, one of the researchers.

So how did the researchers find the rate of recovery after drought? They measured the recovery of tree stem growth after severe droughts since 1948 at more than 1,300 forest sites around the Earth using records from the International Tree Ring Data bank.

On average, trunk growth took two to four years to return to normal. In fact, growth was about 9 percent slower than expected during the first year of recovery, and remained 5 percent slower in the second year. Long-lasting effects of drought were most prevalent in dry ecosystems, and among pines and tree species with low hydraulic safety margins.

"In most of our current models of ecosystems and climate, drought effects on forests switch on and off like a light," said Anderegg. "When drought conditions go away, the models assume a forest's recovery is complete and close to immediate. That's not how the real world works."

The findings are published in the journal Science.

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