New Study Questions Effectiveness of Forest Thinning to Reduce Wildfire Risk

Santa Fe, NM - A new study "has revealed a startling lack of scientific information to guide forest managers in selecting effective fuel treatments to reduce wildfire risk" according to Henry Carey, principal investigator of the research.

The study, entitled, "Modifying Wildfire Behavior - the Effectiveness of Fuel Treatments" covered more than 250 of the most current scientific studies that evaluate methods for treating hazardous fuels in western forests. The study was prepared by the Southwest Community Forestry Research Center of the Forest Trust

"The literature shows that factors other than tree density, such as surface vegetation and the distance from the ground to the tree crown, play a profound role in the spread of fire" Mr. Carey said. "The specifics of how thinning treatments are to be used and their relative effectiveness in changing wildfire behavior are not supported by a significant consensus of scientific research at this point in time." By contrast, Mr. Carey found that "substantial evidence supports the effectiveness of prescribed fire as a fuel treatment."

The study also surveyed the scientific literature to evaluate recent suggestions by policy makers that commercial logging can be used to treat forest fuels. "We found that the proposal that commercial logging can reduce the incidence of canopy fire was untested in the scientific literature. Commercial logging, with its focus on large diameter trees, does not remove the ladder fuels that contribute to fire spread," said Mr. Carey.

The Southwest Community Forestry Research Center works with rural communities to investigate forestry-related issues. The report can be downloaded from <http://www.theforesttrust.org/>. For more information visit the Center's website at www.theforesttrust.org/research.

Executive Summary of MODIFYING WILDFIRE BEHAVIOR - THE EFFECTIVENESS OF FUEL TREATMENTS

By Henry H. Carey and Martha Schumann

This paper assesses existing research on the effectiveness of hazardous fuel reduction in changing wildfire behavior. Over two years, we reviewed more than 250 papers that evaluated three types of fuel treatment in relation to fire behavior in western forests - prescribed fire, mechanical thinning, and a combination of thinning and burning. We also surveyed the literature to evaluate recent suggestions by policy makers that commercial logging can be used to treat dense forest fuels.

This assessment focused on ponderosa pine - a "fire adapted" forest type where periodic, low-intensity fires were the ecological norm in presettlement times. Nonetheless, studies in other forest types were reviewed if the research provided useful information on the relationship between fuel treatments and fire behavior.

Findings:

* Although the assertion is frequently made that simply reducing tree density can reduce wildfire hazard, the scientific literature provides tenuous support for this hypothesis.

* The literature leaves little doubt, however, that fuel treatments can modify fire behavior. Thus, factors other than tree density, such as the distance from the ground to the base of the tree crown, surface vegetation and dead materials play a key role. Research has not yet fully developed the relationship among these factors in changing fire behavior.

* The specifics of how treatments are to be carried out and the relative effectiveness of alternative prescriptions in changing wildfire behavior are not supported by a significant consensus of scientific research at this point in time.

* Substantial evidence supports the effectiveness of prescribed fire, a treatment that addresses all of the factors mentioned above. Significantly, several empirical studies demonstrated the effectiveness of prescribed fire in altering wildfire behavior.

* By contrast, we found a limited number of papers on the effects of mechanical thinning alone on wildfire behavior. The most extensive research involved mathematical simulation of the impact of mechanical thinning on wildfire behavior. However, the results of this research are highly variable.

* A more limited number of studies addressed the effectiveness of a combination of thinning and burning in moderating wildfire behavior. The impacts varied, depending on the treatment of thinning slash prior to burning. Again, crown base height appeared as important a factor as tree density. The research community is still building a scientific basis for this combination of treatments.

* The proposal that commercial logging can reduce the incidence of canopy fire was untested in the scientific literature. Commercial logging focuses on large diameter trees and does not address crown base height - the branches, seedlings and saplings which contribute so significantly to the "ladder effect" in wildfire behavior.

* Much of the research on the effectiveness of fuel treatments uses dramatically different methodology, making a comparison of results difficult. To provide a basis for analysis, we structured our review of the literature into four general groupings: observations, case studies, simulation models and empirical studies. Empirical studies provide the strongest basis for evaluating treatments whereas personal observations are the least reliable.

* We found the fewest studies in the most reliable class - empirical research. We found the greatest number of studies in the least reliable class of research - reports of personal observation. Several other reviews of the literature confirm this finding, stating that the evidence of the efficacy of fuel treatment for reducing wildfire damage is largely anecdotal.

* The results of simulation studies are highly variable, in terms of such factors as fire spread, intensity and the occurrence of spotting and crowning.

* Scientists recognize that large scale prescribed burning and mechanical thinning are still experimental and may yet reveal unanticipated effects on biodiversity, wildlife populations and ecosystem function.

Recommendations:

* Systematic field research, in combination with synthesis from existing knowledge, is needed to provide a sound scientific basis for evaluating and designing fuel reduction treatments.

* The notion that mechanical thinning, or a combination of thinning and prescribed fire, reduces the incidence of catastrophic fire should be viewed as a working hypothesis. Specific combinations of treatments need to be tested through experimentation using site- and weather-specific data.

* Priority should be given to locating fuel treatments in areas that include a well-constructed, experimentally driven design, so that agencies can optimize their ability to learn, providing a higher return on future investment.

* In 2000, our nation embarked on an emergency $1.6 billion program to reduce fuels on millions of acres. The Western Governors Association calls for sustaining this level of investment over the next ten years. Based on the findings of this paper, a comparable investment must also be made in primary and applied research to provide a credible scientific basis for the design, implementation and evaluation of alternative treatments.