Newspaper article The Christian Science Monitor

Can Forests Rebound from Severe Drought?

Newspaper article The Christian Science Monitor

Can Forests Rebound from Severe Drought?

Article excerpt

It's no surprise that droughts can severely weaken forests. But what happens when the drought ends?

Traditionally, climate models have operated under the assumption that forests bounce back quickly from periods of extreme stress. But new research, published Thursday in the journal Science, suggests that trees may take years to resume normal growth after a period of drought.

"It's probably not too surprising that trees don't seem to recover from severe drought immediately," lead author William Anderegg told the Monitor. "A large body of plant physiological research has studied drought stress and damage, and repair of that damage is rarely observed as perfect or immediate."

He added, "What surprised us was how widespread and pervasive this delayed recovery from drought was."

Dr. Anderegg, who studies climate change at Princeton University, found that living trees took an average of two to four years to recover post-drought. There was just one exception: California and Mediterranean regions actually grew faster after a drought.

"We don't have a clear answer as to why this was," Anderegg says. "One possibility is that these regions tended to be dominated by oak forests, and we found that oaks tended to recover relatively quickly."

Or maybe the droughts killed off some trees entirely, he theorizes, so the surviving trees had more light and nutrients available. "Without more detailed studies, we won't know for sure," he says.

Each year, forests take in about a quarter of all human carbon dioxide emissions. By absorbing CO2 and cycling oxygen back into the atmosphere, trees slow the progression of climate change. But Anderegg and colleagues found that trees take in significantly less carbon during and after drought.

"Forests are on average still taking up carbon," Anderegg says, but that could change. …

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