The Trembling Aspen Is in Trouble
A new study shows that droughts will cause massive die offs of the trembling aspen, a pillar of North American forests, by mid-century, unless we take action on climate change today.
KATE WHEELING
Growing up in Western Colorado, William Anderegg has fond memories of countless hiking, fishing, and camping trips in the Rockies. But when he returned as an adult, he found a changed landscape. “A lot of these forests, just within my lifetime, had really died off,” says Anderegg, a post-doc at Princeton University.
While decades of research have given scientists a pretty good understanding of how trees grow, we still don’t really know much about how they die. “We don’t have a very good monitoring network of tree mortality, but the pieces of the puzzle that we can see don’t look very good” Anderegg says. Tree deaths have hit North America particularly hard, affecting multiple forest types and tens of millions of acres. Widespread deaths of trembling aspen, the most widely distributed tree species across North America, have “stretched from Arizona to Alberta, and seem to have been entirely triggered by drought and climate change,” he says.
As the climate warms and droughts become more frequent and severe, predicting how trees will respond to the stress becomes ever more important. Trees take in water from the soil around their roots, and try to hold on to it against the pull of gravity and transpiration, like competing ends of a spring; as drought progresses, the soil gets drier, the atmosphere gets hotter, and the spring is pulled tighter and tighter. In a new study published today in Nature Geoscience, Anderegg and his colleagues measured water flow in tree branches to find the threshold at which water flow was reduced enough that aspen trees would succumb to drought. Using this threshold, they made predictions about past mortality events and found that they matched observations about 75 percent of the time.
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http://www.psmag.com/nature-and-technology/the-trembling-aspen-is-in-trouble
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