What Climate Change Means for North America’s Most Widespread Tree

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Alder, aspen, birch, elm, maple and oak are some of the most popular trees in North America. But it might come as a surprise that aspen, with their iconic white bark and beautiful autumn colors, have the largest range of any tree on the continent – one that extends from Alaska to Mexico and Vancouver to Maine, including almost every elevation in between.

Image: Autumn Aspens, Mountains, and Evergreens
Autumn in the Canadian Rockies.
Public domain

Alder, aspen, birch, elm, maple and oak are some of the most popular trees in North America. But it might come as a surprise that aspen, with their iconic white bark and beautiful autumn colors, have the largest range of any tree on the continent – one that extends from Alaska to Mexico and Vancouver to Maine, including almost every elevation in between.

Many aspen colonies have survived major climatic changes during thousands of years on Earth. But, following severe drought during the last decade, many aspen stands in the Rocky Mountains underwent a dramatic die-off. Some low elevation populations suffered losses of up to 90 percent. Under projected climate-change, some models predict 40 percent or more of climatically-suitable habitat for aspen in the western United States could be lost by as early as 2060.

Aspen’s white bark is actually alive and capable of photosynthesis – an unusual adaptation that helps them grow under a wide range of conditions. Aspen also reproduce both sexually, like most trees, and clonally, forming extensive underground networks of roots. The underground networks help Aspen share water and nutrients from a single source and rebound quickly after a disturbance like fire or avalanche.

Aspen stands are important in the western U.S. because they provide critical habitat and increase species richness for animals like elk and songbirds. They are also economically and socially important, producing high quality forage for livestock and wildlife, as well as drawing tourists and improving local economies.

When stressed, aspen show surprising toughness and might be more resilient than scientists originally thought. A pair of researchers funded by the Department of the Interior Northwest Climate Science Center, Tim Link and Doug Shinneman, are working to better understanding the factors that effect aspen resilience.

Link, a hydrologist at the University of Idaho, is concerned with the impact of a climate-change induced shift from snow to rain on aspen growing in the northern Great Basin.  Less snow means fewer and smaller distributed snow drifts and, as a result, less reliable water availability for aspen in the spring and summer. How aspen respond to this shift is unknown and has important implications for managers.

Image: Reynolds Creek Experimental Watershed
Ben Soderquist, a Northwest Climate Science Center Fellow from the University of Idaho, works at the Reynolds Creek experimental watershed in Idaho.
Public domain

Meanwhile Shinneman, a fire ecologist with the U.S. Geological Survey, is interested in how climate change could lead to an increase in wildfires and the resulting impact on aspen stands.

“In parts of its range periodic fire may give aspen a competitive boost by knocking back conifers which would otherwise dominate the landscape,” said Shinneman. “In other areas, such as low elevation or drought-prone regions, more fire might hasten the decline of aspen.”

Understanding the details of aspen’s relationship to fire will help inform decisions such as whether or not to burn in order to maintain aspen groves – an important question for managers in places like northeastern Oregon where aspen groves provide critical habitat for elk.

After submitting independent proposals to the Northwest Climate Science Center (NW CSC) to study aspen, Link and Shinneman were invited to work together as co-PIs of a single project, given the similarity of their research questions. Despite its unusual inception, their collaboration has been a marked success, leading not only to a productive partnership among Link, Shinneman and NW CSC graduate fellow, Ben Soderquist, but also to additional research being carried out by other members of their teams, which include both university and government scientists.

“A really rewarding aspect of this project has been to hear from mangers about how much they value the work that we’re doing,” said Link. “And to have them help us spin our work into things that will be helpful to them.”

The aim is to help resource managers and landowners invest their efforts strategically so our Northwest landscapes will include aspen groves and the wildlife that they support for many decades to come.

The Northwest Climate Science Center is a federal-academic partnership established by the U.S. Department of the Interior to address the challenges presented by climate change in managing cultural and natural resources in the northwestern United States.

Learn More

Projecting Climate Change Effects on Aspen Distribution and Productivity in the Central and Northern Rockies by Coupling Hydrological and Landscape-disturbance Models.”

Image: Reynolds Creek Experimental Watershed
Aspen trees at the Reynolds Creek experimental watershed in Idaho.
Public domain