Aspen Decline PNAS Study

Dying aspen on Mancos-Dolores Ranger District, San Juan National Forest in 2006. Photo by Phil Kemp, US Forest Service, Mancos-Dolores District.

There have been many stories about this but this one I could find easily:

Drought May Be Causing Aspen Tree Die-Off
Trees Developing Embolisms, Researchers Say
Deb Stanley, 7NEWS Producer

DENVER — A mysterious malady has killed off nearly one-fifth of Colorado’s aspens. But forest ecologists have struggled to explain the widespread die-off, known as Sudden Aspen Decline.

The Aspen Daily News reports that a new study from researchers at Stanford University and the University of Utah may provide a breakthrough in understanding the decline and how it kills trees.

The research found that aspens have essentially dehydrated due to a drought that took hold of Colorado from 2000 to 2004. In a delayed reaction to the drought, the systems that carry water through aspen stands broke down.

“If they can’t transport water, they’re kind of screwed,” said Duncan Smith of the University of Utah, who worked on Anderegg’s project and co-authored a paper on it released this month in the Proceedings of the National Academy of Sciences

Researchers pruned dying aspens and studied them in the lab, and listened to their inner workings with microphones as they died.

“Just as there are a number of ways people can die and you can’t always pinpoint it, it’s the same with trees,” said Stanford Ph.D. candidate William Anderegg, who led the research.

Researchers found that in response to drought, the trees were developing embolisms — much like common human blood vessel blockages — which hampered their ability to move water.

In trees affected by the decline, an average of 70 percent of the vascular system was blocked. That’s up from an average of 17 percent in healthy aspens. The trees, researchers found, fought against dehydration for a few years after the drought but lost and eventually died.

The researchers concluded that drought caused widespread failure of water transport systems in the trees.

Their conclusion is a foreboding sign for Aspen’s signature trees in the age of global warming.

Anderegg’s team studied climate records in 51 different aspen-filled areas in Western Colorado from 1900 to 2009. The period from 2000 to 2004 marked the most severe drought in the entire period.

“For aspens, hot temperatures tend to be really stressful,” Anderegg said. “Climate change and global warming will be a real problem for aspen trees anywhere.”

Here’s a link to the article.

My favorite quote is in the text

Physiological mechanisms provide a foundation to understand, predict, and model threshold events that may dominate certain ecosystem responses to climate change and allows us to better project the uncertain future of forest ecosystems in a warming climate. Although more research is needed to better incorporate drought-induced vegetation mortality into models, our results provide insight into the processes that occur during drought stress.

In fact, I have always said that if you want to model how organisms will respond to the environment, it’s good to understand their physiology and genetics. To project the future of ecosystems, though, seems like you would have to know the physiology and genetics of lots of species, and their interactions… which are good to know anyway.

More info on SAD can be found on the Aspen Delineation webpage here.

1 thought on “Aspen Decline PNAS Study”

  1. WESTERN ASPEN ALLIANCE is a joint venture between Utah State University’s College of Natural Resources, USDI Bureau of Land Management, and the USDA Forest Service Rocky Mountain Research Station and National Forest Systems, whose purpose is to facilitate and coordinate research issues related to quaking aspen communities of the west. The Western Aspen Alliance will facilitate cooperative research and disseminate state-of-the-science aspen information to interested managers, researchers, the public, and other entities.


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