Drought Damage Will Cause Widespread Forest Death by 2050

It is well known that climate change is causing all sorts of extreme weather, and may lead to events such as 35-year-or-longer "megadroughts" that will be the worst we've seen in 1,000 years. Now researchers are giving us another glimpse into the future, saying that drought damage will likely cause widespread forest death by the 2050s as a result of climate change.

A team lead by the Carnegie Institution describes in the journal Nature Geoscience how tree mortality can radically transform ecosystems, affect biodiversity, harm local economies, and pose fire risks, and even further increase global warming.

"A forest die-off over a large area like the Amazon Basin, could have a major impact on Earth's system as a whole," researcher Joseph Berry explained in a statement.

On one hand, rising concentrations of carbon dioxide (CO2) can benefit trees and help them use water more efficiently. On the other hand, rising temperatures and resulting droughts from climate change can cause many forest trees to die off. The latter is what occurred during the 2000-2003 drought in the American southwest, which triggered a widespread die-off of about 17 percent of aspen forests around the region - including most of Colorado, as well as parts of the western United States and Canada.

Most current models of forests under climate change cannot predict when or where forests might die from temperature and drought stress. So the Carnegie-led team of scientists developed a new modeling tool to explain how and where trembling aspen forests died as a result of this drought.

They focused on the physiology of how drought kills trees, and found that it's based on damage to the individual trees' ability to transport water under water-stressed conditions - referred to as the vascular system. Until now, the threshold at which drought conditions start to degrade an aspen's water-transporting vascular system were previously unknown. But using data from forests in southwest Colorado, the researchers were able to identify this threshold and incorporate it into their new modeling tool.

They used this newfound information to predict drought-induced forest mortality in the future. What they realized was that if greenhouse gas emissions continue to rise, the threshold for widespread drought-induced vascular damage would eventually be crossed.

This, in turn, will lead to widespread tree deaths on average across climate model projections in the 2050s.

"Finding the thresholds in plant physiology after which climate stress causes tree mortality will allow us to resolve uncertainty over the fate of forest ecosystems in a changing climate," said lead author William Anderegg. "But most importantly, a lot rides on human decisions to slow climate change. The clock is ticking on the future of these forests."

Unfortunately, with the world's 2 degrees climate goal being "utterly inadequate," according to a recent report, the likelihood that we will save the world's forests in the future seems bleak.

California is already experiencing the worst drought in a millennium, and the Southwestern United States will likely see megadroughts that last 30 years or more down the line. Right now plants including forests are ill-prepared for dealing with droughts - more so than scientists thought. That's bad news, considering that forests are central to many of the planet's chemistry and energy cycles, and play an important role in human life on the planet.

But as researchers work to help plants tolerate future droughts, there is still hope that global forests will manage to survive.

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