Arizona scientists: Tree-rings link wildfires to natural suppression
While some researchers are trying to improve fire suppression techniques, others are attempting to understand what the history of wildfires can teach.
Using the tree-ring record of forest fire history, University of Arizona scientists have compiled statistics on when, where, and how often fire has burned forests in the U.S. Southwest and northwestern Mexico.
Their findings teach a sobering lesson about huge wildfires like the recent Rodeo-Chediski fire that burned nearly a half-million acres of the Apache-Sitgreaves National Forests in Arizona.
“The tree-ring record clearly shows us that the vast majority of events were frequent, low-intensity surface or ground fires,” said Don Falk, Laboratory of Tree Ring Research and Department of Ecology and Evolutionary Biology, University of Arizona.
These smaller fires consumed the fine annually produced grass and needle fuels, as well as small tree seedlings, but mature overstory trees typically survived with little ill effect. There is almost no evidence for the catastrophic fires that we are experiencing now, he said.
“These enormous wildfires are the direct result of human changes to the forest system that have been going on for a century,” Falk said.
The extreme high-intensity canopy fires of recent years are atypical in many Southwestern forests. Such fires endanger the lives of firefighters, as well as cause extreme damage to wildlife, soils, watershed, homes and communities.
“It's irrational from both an ecological perspective and in terms of society's interests, to perpetuate forest management practices that have created these disaster-prone forest conditions,” Falk said. “Fire is the keystone process in Southwestern forests, and hence the key to restoring and maintaining healthy forest conditions.”
Falk said the most important goal must be to return frequent, low-intensity fires to the landscape. However, after nearly a century of fire exclusion, the first burn must be conducted carefully so as not to damage old trees, healthy soils, wildlife and water quality. This often will mean thinning out the smaller diameter trees.
“Repeat burning on the order of the natural fire interval of 5-10 years per 100 acres should be programmed into all of our land management,” he said. Ultimately, the goal must be to return the forest to the point where naturally-occurring fires can be allowed to burn themselves out.”
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