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Aspen trees near Monarch Pass, CO, September 2018  |  Credit: Frani Halperin, H2O Media, Ltd.

Fading Fast? Colorado's Iconic Aspen Trees Will Likely Decline with Climate Change

Tourists in Colorado's high country might want to snap a lot of pictures while they can. Researchers predict that climate change will reduce the number of aspens that make fall color in the Rocky Mountains so captivating.

By Frani Halperin, Executive Producer
Published: 18 Sep 2020 | © H2O Media, Ltd.

In Colorado, nothing says fall like a drive in the high country to see the bright orange and yellow leaves of the aspen trees shimmering against a crisp, blue sky. People flock to the mountains not only to see the vibrant colors, but they can hear them, too.

“When the wind blows, they kind of rattle or shake. So it's sort of a multisensory experience,” says Dr. Jelena Vukomanovic, assistant professor in the North Carolina State University Department of Parks, Recreation, and Tourism Management.

Vukomanovic and her team of researchers just released a study looking at how the iconic trees in the Colorado landscape will fare in a warming world. Unfortunately for aspens, the future is already here.

The researchers used computer modeling to predict how the distribution of native quaking aspen (Populus tremuloides) will change amid rising temperatures over the next 100 years by analyzing whether trees would be seen along three popular routes people drive when the leaves are turning—Cache la Poudre, Trail Ridge Road, and the Peak-to-Peak Highway.

Vukomanovic told H2O Radio that scientists are already starting to see declines in aspen trees in recent years because of more drought and warming temperatures but that climatologists aren’t sure that, as the Colorado climate warms, if it will be drier or wetter. Vukomanovic says it’s not clear if the Front Range will “go with the Southwest or the Northwest in terms of changes.” For that reason, she modeled three scenarios: if climate does not change from historical conditions observed from 1980 to 2010; under a 4-degree temperature increase with 15 percent less precipitation; and with a 4-degree decline and 15 percent more precipitation.

NC State News explains that overall, they found that aspen are expected to decline in all three climate scenarios. In the two warmer scenarios, the losses were more than two times greater overall, and aspen loss was even greater in the visible areas from the scenic byways. And, even if current conditions continue, there would be declines in the trees. At elevations between 6500 to 9000 feet where aspen are most abundant, they saw consistent decreases across all three scenarios. At the highest elevations above 9000 feet they saw lower declines, and they think that means the trees will shift to higher elevations as warming occurs.

Vukomanovic predicts a slightly better outcome for the trees, if the future is wetter in Colorado. But heat is the biggest factor in driving the trees to higher elevations in the mountains. That might mean fewer people will see them when driving on popular roads because they'll be less accessible. Communities that rely on tourism along those routes will suffer as the aspen disappear. The researchers saw some estimates as high as $20 billion that the aspens contribute to the economy, which will be threatened.

The authors wanted to show how a warming world will affect environments but in a less dramatic way than hurricanes or wildfires. Most people experience aspens by driving through these landscapes, Vukomanovic said, "It’s the kind of human dimension where you have to kind of see it to believe it sometimes. It's going to impact all aspects of our life, even something like taking a drive to see fall foliage.”

For Coloradans, aspens are part of the state’s identity and give residents a sense of place. In a warming world with the trees forced to higher and cooler regions, instead of driving a convertible to see them, you might need a pair of hiking boots.

The study was published online in Ecosystem Services. 💧