Use of Prescribed Fire to Reduce Wildfire Potential1

Fires were a part of our wildlands prehistorically. Prescribed burning reduces fire hazard and potential fire behavior primarily by reducing fuel quantity and continuity. Fuel continuity should be considered on the micro scale within stands, the midscale among, and the macro-scale among watersheds or entire forests. Prescribed fire is only one of the tools which can be used to reduce fire hazard, but it can be effective at all scales. Fire has been a part of many ecosystems, playing a large role in shaping them and leading to the adaptations of many plants and animals to different fire regimes. Without fires, many of the vegetative types and the associated fauna have changed drastically. The type may have become susceptible to changes from biotic or abiotic agents, and may lose its desirable characteristics for many years. Removal of fire from many of our forest and range types has led to change in species composition and accumulation of excessive biomass; it has set the stage for high-intensity, high-fuelconsumption, stand-removal fires. The purpose of this paper is to discuss the use of prescribed fire to reduce the potential for such fires. It should be noted that prescribed fires generally also accomplish other land management goals. These include maintenance of stand composition, increase in water quantity and quality, reduction of insect or disease damage, Presented at the Symposium on Fire and Watershed Management, October 2629,1988. Sacramento, CA. Professor of Forestry, University of California, Berkeley, CA; Assistant Professor of Range Science, Oregon State University, Corvallis, OR; Research Chemist, Pacific Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Bend, OR. and increase in esthetic and recreation value. Few prescribed fires could accomplish all of these objectives, but most, when well planned and executed, could accomplish several of them. Today, with our limited operating dollars, multi-objective prescribed fires are the rule rather than the exception. Prescribed fire is only one way to reduce wildfire potential. Fuels management, which is that branch of fire management dealing with the fuels, begins with vegetation management. Thus, the right vegetation in the right place is the first step in reducing wildfire potential. Biological, chemical, manual, and mechanical means may be used in conjunction with fire to modify fuels. The total job of managing fuels fuels management is the art or practice of controlling the flammability and resistance to control of wildland fuels through the means described above in support of land management objectives (Lyon 1984). Reduction of wildfire potential is best described in terms of modifying potential fire behavior. In turn, fire behavior is influenced by the three elements of the fire behavior triangle-­ fuels, weather, and topography. Of the three, the only one we can easily and directly affect is fuel, the biomass, or more specifically, the phytomass. We will first describe the basic properties of fuels which are important to fire behavior and then look at what prescribed fires can do to fuels, and how this reduces the potential for large wildfires and increases our ability to control them. BASIC CHARACTERISTICS OF FUELS Fuels can be described by six basic characteristics, and these character­ istics (Martin and others 1979) are chemistry, particle and density, moisture content, compactness, con­ tinuity, and quantity. Only the last two, continuity and quantity, are discussed in this paper, as they are most affected by prescribed burning. USDA Forest Service Gen. Tech. Rep. PSW-109. 1989 17