Repeat droughts may cause permanent damage to forests: scientists

ROME (Thomson Reuters Foundation) - Trees and their environment need as long as two years to recover from drought in some places, and if a second dry spell hits before then, it may cause permanent damage to the landscape, researchers said on Wednesday.

With climate change expected to bring more frequent and intense droughts, the implications for areas that do not have time to bounce back fully could be severe, the researchers said in a paper to be published in Nature journal this week.

“That could have a double whammy effect,” said co-author William Anderegg, assistant professor of biology at the University of Utah. “A second drought could be harder on an ecosystem and have the potential to push it off a cliff.”

In practice, that means affected areas could eventually turn from lush forest to a land of grass and shrubs.

Boreal forests in northern parts of Europe, Russia and Canada can take up to two years to recover from drought, partly because they do not have a wide variety of plants, Anderegg told the Thomson Reuters Foundation.

Forests in the tropics of South America and Southeast Asia have also taken the same amount of time to rebound.

“That’s worrisome because those regions store the largest chunks of carbon in ecosystems across the globe,” Anderegg said.

Forests help tackle climate change by sucking carbon out of the air, reducing levels of planet-warming carbon dioxide, the main greenhouse gas. But when trees die, most of the carbon they have absorbed is released back into the atmosphere.

The Amazon rainforest suffered a double drought in the first decade of this century when dry spells, both of a once-in-a-100-years severity, hit the region.

“Satellites showed that forests hadn’t recovered from the 2005 drought by the time the 2010 drought struck,” Anderegg said.

Other regions need less than six months to recover, the scientists found using global satellite data.

Temperatures and rainfall levels after a drought - as well as fire, disease and tree deaths during a drought, and the severity and length of a drought - affect how quickly an ecosystem recovers, the researchers said.

Rain brings relief, but it does not immediately solve the problems caused by drought, Anderegg said.