Historic Wildfires in Arizona: New Research Challenges Perceptions
Arizona’s infamous Wallow Fire, which ravaged over half-a-million acres in 2011, has long been considered a significant event in the state’s wildfire history. However, recent research by Chris Guiterman and colleagues at the Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, suggests this fire might not be as exceptional as once believed.
The team conducted an extensive study by examining tree rings around the Wallow Fire’s burn area to trace wildfire occurrences over several centuries. According to Guiterman, “So we could estimate the acreage of fires in each year from 1650 right on to 2023. The Wallow Fire is one of the largest. It’s exceptional. It’s quite large, but we found three other years that had fires that were at least as big, and potentially larger than the Wallow Fire was.” This revelation indicates that there were historical fires of similar or greater magnitude.
In addition to these monumental fires, the researchers uncovered evidence of numerous low-intensity fires that historically swept through approximately 200,000 acres at a time. This pattern of frequent, less intense burning was abruptly halted by a century of aggressive fire suppression policies by the federal government starting in the 1900s.
Guiterman explains, “The really predominant pattern is that these extensive wildfires were burning quite commonly every 20 years in that landscape, and that has been completely missing since 1900.” Unlike the catastrophic blazes of today, these past fires remained largely ground-based, consuming grasses and smaller vegetation.
As modern land managers seek to restore ponderosa pine forests using prescribed fires, the research emphasizes that one-time burns are insufficient. Guiterman states, “Historically, we did have some pretty extensive burning, and we could have that extensive burning fairly frequently. It was really a central process in this forest. Just like rain, just like oxygen, the forest needs to burn and have that fire in there to kind of keep everything going.”
This study challenges the notion that current megafires are unprecedented, suggesting instead that such events were once as regular as monsoon rains in the Southwest. The findings carry significant implications for how forest restoration and fire management strategies might evolve to more closely mimic historical fire patterns.
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