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Wildfire resistance found in aspen tree populations

A new study from Colorado State University, Western Colorado University and the U.S. Forest Service found evidence that stands of aspen trees could resist wildfires by slowing a fire's advance or changing its course.

The researchers found that even modest increases in aspen cover dramatically reduced the rate at which fires spread. Their findings suggest that aspen forests can act as natural firebreaks, which is valuable information for land managers and agencies.

"Where managers can encourage aspen over conifers, they may represent a more desirable fuel treatment in some forest types than traditional thinning or shaded firebreaks because of the aesthetic value and wildlife habitat aspen provide," said Camille Stevens-Rumann, study principal investigator and interim director of the Colorado Forest Restoration Institute at CSU.

The study, July 7 in Ecological Applications, analyzed 20 years of fire behavior across more than 300 wildfires in the Four Corners region.

Key findings include:

• Fires in areas with vegetation composed of at least 25% aspen spread at about a third the rate of fires in forests with less than 10% aspen trees.
• Aspen was more abundant at the edges of fires, where fires stopped, than in burn interiors, indicating that aspen not only slow a fire but also stop it or change its course.

According to the study, it has long been understood that aspen is more resistant to burning because of higher moisture content in an aspen stand's foliage and understory, high branches and chemical differences that reduce flammability. However, prior to the team's research, the extent to which aspen slows or stops the advance of a fire relative to conifer forests hadn't been quantified.

The team found that differences in spread persisted even under extreme fire weather conditions, which are expected to become more common in a warmer, drier future.

"My hope is that this research can help inform fire and fuels management focused on the propagation of aspen through prescribed fire," said Matt Harris, lead author and a recent graduate from Western's Clark School of Environment and Sustainability. "In some settings, aspen might even be planted around communities to form green fuel breaks for fire protection."

The research relied on fire and vegetation data developed and maintained by federal agencies.

"This research is a direct result of long-term federal investment in understanding wildfire and forest dynamics," said Jonathan Coop, a professor of environment and sustainability at Western's Clark School and a co-author of the study.

"The wildfire challenges we face in the western U.S. continue to grow every year, and we require good science to inform solutions to protect communities and sustain the ecosystem functions we depend on, from water to timber."