Preventing wildfires: Effectiveness of fuel treatment in forests

 
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The scale and frequency of wildfires in the American West has accelerated in recent years. This trend is expected to continue as climate change and droughts exacerbate the conditions that enable such fires, according to the U.S. Forest Service. Since 2000 the amount and costs of fire-suppression efforts have been rising significantly, and now total in the billions of dollars annually.

A 2011 study by the U.S. Forest Service, “Review of Fuel Treatment Effectiveness in Forests and Rangelands and a Case Study from the 2007 Megafires in Central Idaho,” examines various practices used to manage areas in the “wildland-urban interface,” where fires are mostly likely to affect human life.

The study surveys a variety of past research reports, focusing on forest “fuel treatments,” which typically entail thinning vegetation through cutting, prescribed burning, and the use of animal grazing. The goal is to reduce the intensity of wildfires, limit risk to humans and increase the resiliency of ecosystems. But these programs are expensive, their effectiveness is subject to debate, and the science of forest-fire management continues to evolve.

The study’s findings include:

  • Analysis of the 2007 Central Idaho megafire confirms what previous scientific literature had hypothesized, that the most effective treatment was mechanical thinning of trees and brush followed by a controlled surface fire.
  • Prescribed burn treatments alone are more limited in their effectiveness, and the benefits diminish over time: “It is difficult to kill most medium-sized trees and many small trees by fire alone. Multiple rounds of prescribed fire are more effective … than single entry treatments.”
  • Animal grazing was found to be an effective technique: “The removal of biomass during grazing (particularly heavy grazing) reduces fine fuels and decreases risk of fire occurrence and spread.”
  • There appears to be no “magic formula” for all forest area types: “While thinning from below is a common treatment and thresholds in tree density, crown base height, crown bulk density, tree spacing, and other fuel composition descriptors exist for a given stand, there is no general prescription that will work in all or even most stands.”
  • More research is required on the question of whether fuel treatments might actually increase the likelihood of intense fires in certain environments. It is “certainly possible for fuel treatments to increase fine fuel temperature and create a micro-climate that favors increased winds and lower relative humidity.”
  • A 2009 study found that treatments often fell outside the wildland-urban interface (WUI). The National Fire Plan mandates that 50% of treatments be within the WUI, but the study found that, of 44,000 fuel treatments in the western United States, only 3% were within a WUI and only 8% within 2.5 km of the WUI.
  • Some past scholarship has concluded incorrectly that expensive fuel treatment programs are not worth their cost, having only “a mean probability of 2.0% to 7.9% of being encountered by moderate or high severity fire within 20 years following treatment.” However, there is strong evidence that fuel treatments indeed mitigate fire effects.

Tags: California, disasters, water, global warming

Last updated: July 7, 2011

 

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Citation: Hudak, Andrew, T.; et al. "Review of Fuel Treatment Effectiveness in Forests and Rangelands and a Case Study from the 2007 Megafires in Central Idaho", U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, 2011, PDF.