Ecological wild cards of Arizona’s Wallow wildfire

Is a specific person to blame for recent wildfires? While Arizona’s Wallow Fire fuels finger pointing, it takes more than a campfire to fuel the destructive wildfire raging across southeastern Arizona. A perfect storm of local ecology, climate and human management decisions have combined to set the stage for the largest wildland fire in Arizona’s history. The Wallow Fire that began on May 8 still rages through the largest ponderosa pine forest on the continent. Pinus ponderosa forests cover the higher mesas and mountains of the Colorado plateau on which the northeastern half of the state of Arizona sits. Forest fires are common in ponderosa forests: Typical ponderosa forest climate includes a spring dry season accompanied by increasing air temperatures, low humidity and consistent winds; conditions conducive to frequent early-summer fires. Before people started suppressing ponderosa forest fires, they burned about every 2-12 years. These were mostly low-intensity ground fires that destroyed small trees and shrubs. This process actually helped to return nutrients to the soil. Mature pines with their thick bark could withstand these small fires, which effectively removed fuel that might have fed larger, more destructive crown fires—fires like Wallow that burn from treetop to treetop. Then in 1886, the United States government kick-started federal forest fire policy in the newly-created National Parks. Lacking the ecological research to understand the important role of fire in these forests, the US Federal Government embarked on nearly a century of poor fire management policies. From 1886 to the 1960s, with few exceptions, federal forest fire policy was dominated by fire suppression, according to a comprehensive overview of US Federal Fire policy published in Ecological Applications in 2005. While the first prescribed burn program started in 1968, it was not until 1995 that federal fire policy was altered to “recognize and embrace the role of fire as an essential ecological process.” During the long period of fire suppression, some forests missed 8 to 10 fire rotations. These rotations had previously created a landscape of “majestic, open stands with rich grasses and occasional shrubs beneath,” as described by early explorers of the western US. Today the landscape is transformed into a dense forest with thickly arranged trees and an accumulation of litter and shrubs. “Where we once had 10 to 25 trees per acre [in western forests],” said Wally Covington, a professor of forest ecology at Northern Arizona University and executive director of NAU’s Ecological Restoration Institute, “we now have hundreds.” While crown fires occurred in ponderosa forests before EuroAmerican settlement, according to a 2003 Ecological Monographs article, crown fires of such intensity as the Wallow fire seem to be a modern...

Read More