Trees Vulnerable to "Heart Attack" in a Warming Climate

Apr 21, 2016

Aspen trees killed by drought stress
Credit William Anderegg

Hot and dry weather is the norm for much of the Intermountain West and a fact of life for the plants and animals that live there. However, a warming climate may be pushing some iconic tree species to the breaking point.

 

Drought induced tree mortality is the subject of a new study published in the Proceedings of the National Academy of Sciences. Recent extreme heat and drought events have led to massive tree die-offs in forests across the globe, and scientists want to know why.

Findings of the study suggest that under heat stress many trees succumb to something like a tree heart attack. William Anderegg, Ph.D., an assistant professor in biology at the University of Utah and the study’s lead author, explained it this way.

 

“Quite literally, trees have millions of these tiny straws that go down and through their roots, into the soil, and up to their leaves, and all the water in these pipes is under tension. What happens during this embolism process is that as trees are pulling harder and harder on this water in the soil, to get it up to their leaves, the tensions get too high and tiny air bubbles shoot in and start blocking these pipes that move water. The broader analogy of a heart attack for a tree is fairly accurate.”

 

Dead ponderosa pine tree
Credit William Anderegg

Not all trees are equally susceptible to the formation of these embolisms, however, which puts some tree species at greater risk during heat and drought events. For instance, the iconic pale-barked quaking aspen, beloved of so many Westerners is not particularly well-suited for dealing with these embolisms and is therefore at a higher risk. In the face of steadily increasing temperatures brought on by climate change, Western forests may look very different in the coming decades as less drought resilient trees die off and are replaced by their hardier cousins.

 

“It’s going to get hotter in the West, and we’re in for probably more frequent and more severe droughts. And so our forests are going to be increasingly stressed and at risk of mortality. We’ve seen the beginning signs of this from these hot droughts, and I think these are really the canary in the coal mine; just the tip of the iceberg. Climate change is really going to be this great reshuffling event. It’s going to shuffle which species can survive and there’s going to be a lot of change in our landscapes and our ecosystems in the coming decades driven by climate change.”