Southwestern Forests Burn Only a Fraction as Often as They Once Did. But When They Do, the Consequences are Severe

BY SETH MENSING  |  University Communications Manager

 

New research highlights how modern fires compare to those of the past

• New research from scientists at Western Colorado University, the U.S. Forest Service, and others shows that since 1985, wildfires in the Western United States have burned on average every 59 years. Prior to colonization, those same forests averaged a fire every 11 years.
• When wildfires do occur, their impacts are far more severe. Nearly half of all modern fires burn severely enough to kill trees at sites where trees have historically survived low- to medium-severity wildfires for centuries.
• The research underscores the critical role that prescribed burns and managed wildfires play in restoring the natural resilience of dry conifer forests.

 

With devastating wildfires and mass evacuations making the news with alarming frequency, it’s often assumed that Western forests are burning hotter and more often than they used to. However, new research contrasting historical tree-ring records and modern satellite imagery challenges part of that assumption.

Scientists at the National Park Service, the U.S. Forest Service, Western Colorado University, and others used tree-ring data from more than 400 sites in New Mexico and Arizona forests, demonstrating the extent to which recent fire activity from 1985-2020 is unprecedented compared with the historical record spanning 1700-1880.

 

Understanding the Fire Deficit

In the paper titled Contemporary Fires are Less Frequent but More Severe in Dry Conifer Forests of the Southwestern United States, the researchers show that wildfires burned forested sites on average every 11 years between 1700 and 1880. This was followed by the near complete loss of fire for over a century associated with Euro-American colonization, disruption of Indigenous land stewardship, and other land use changes, producing what is known as a fire deficit. While recent decades have been marked by a rapid escalation in fire activity, fire is still less than a quarter as frequent since 1985 as it was historically, now burning forested sites every 59 years.

When wildfires do occur, however, their impacts are far more severe. Nearly half of all modern fires are burning severely enough to kill trees at sites where trees historically survived dozens of low- to medium-severity wildfires for centuries. These hotter fires have prompted experts to advocate for a change in how we manage fire-prone landscapes.

 

Advocating for Prescribed Fires

Emma McClure, the paper’s lead author and an alumnus of Western Colorado University, hopes the research will provide even more evidence that the right kind of fire, burning under the right conditions, is an essential component of healthy conifer forests in the American Southwest. It’s the latest effort by researchers trying to communicate this apparent paradox.

“Our research adds to the chorus of voices suggesting that to prevent bad fires, we need to restore fire-resilient forests on our terms during more favorable conditions,” McClure said. “Perhaps by alleviating the fire deficit through actions such as prescribed fire, we can help reduce anomalously high severity wildfire.”

 

The Role of Managed Wildfires

In the paper, published in the journal Nature Communications Earth & Environment, the authors describe using tree ring data, satellite data, and field measurements to conclude that wildfires are occurring far less often than they have historically been in Arizona and New Mexico forests, but their severity has increased significantly as a result.

The researchers’ findings underscore the critical role that prescribed burns and managed wildfires play in restoring the natural resilience of dry conifer forests. They suggest that the expanded use of low-severity fire practices would not only mitigate the risk of severe fires but also bring fire regimes and forests closer to historical patterns.

According to the paper, “Intentional and informed management strategies are essential to protecting communities and improving forest resilience, particularly in forest ecosystems with markedly altered structure, function, and disturbance regimes.”

 

 

Photo Credit: Courtesy