Evaluation of silvicultural treatments and biomass use for reducing fire hazard in western states
Several analyses have shown that fire hazard is a concern for substantial areas of forestland, shrubland, grassland, and range in the western United States. In response, broadscale management strategies, such as the National Fire Plan, established actions to reduce the threat of undesirable fire. Available budgets are insufficient to pay for vegetative management on all acres where fire threat is considered unacceptable. The purpose of this report is to begin to identify locations in the west where fire hazard reduction treatments have a potential to “pay for themselves” at a scale and over a long enough time to make investment in additional forest product processing infrastructure a realistic option. The resulting revenues from these activities could presumably subsidize treatment for other locations. Accordingly, we concentrate on areas where wood removed during fire hazard reduction treatments has the potential to support a forest products infrastructure. Areas for treatment were selected by the criterion where either torching or crowning is likely during wildfires when wind speeds are below 25 mph. We considered thinning treatments designed to result in either evenaged or uneven-aged stand conditions. If there are ecological limitations on basal area that is allowed to be removed and there is a need to obtain a certain amount of merchantable wood volume to help cover costs, then uneven-aged treatments appear more likely to achieve one of our hazard reduction targets. Thinning to maintain an uneven-aged structure could be more controversial because it removes larger trees, although the revenue from such treatment covers harvest costs more frequently than does revenue from thinning to maintain an even-aged structure. The removal of large trees by uneven-aged thinning may be reduced by supplementary treatments to increase torching index rather than thinning to reach a high crowning index. Treatments analyzed would treat 7.2 to 18.0 million acres, including 0.8 to 1.2 million acres of wildland urban interface area, and would provide 169 to 640 million oven-dry tons of woody biomass (e.g., main stem, tops, and limbs). About 55% of biomass would be from sawlogs. Sixty to 70% of acres to be treated are in California, Idaho, and Montana. To prepare an example estimate of annual harvest amount for the 12 selected western states, we assume acres needing treatment are divided into two parts of equal area. For half the acres, an uneven-aged treatment would be applied if at least 300 ft3 of merchantable wood is removed; for the other half, an even-aged treatment would be applied if at least 300 ft3 of merchantable wood is removed. Under this scenario, treatment of 0.5 million acres/year would generate 14.6 million oven-dry tons of biomass per year or about 29% of the current level of roundwood removals for the selected states.