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Congressional Research Service

CRS Report RL30755
Forest Fire / Wildfire Protection

Historical Background
Concerns and Problems
Fuel Management
Fire Control
Wildfire Effects
Roles and Responsibilities
Current Issues

CRS Report RS21544 Wildfire Protection Funding

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Order Code RL30755

CRS Report for Congress
Received through the CRS Web

Forest Fire/Wildfire Protection

Updated February 14, 2005

Fuel Management

Fuel management is a collection of activities intended to reduce the threat of significant damages by wildfires. The FS began its fuel management program in the 1960s. By the late 1970s, earlier agency policies of aggressive suppression of all wildfires had been modified, in recognition of the enormous cost of organizing to achieve this goal and of the ecological benefits that can result from some fires. These understandings have in particular led to an expanded prescribed burning program.

The relatively recent recognition of historically unnatural fuel loads from dead trees, dense understories of trees and other vegetation, and non-native species has spurred a renewed interest in fuel management activities. The presumption is that lower fuel loads and a lack of fuel ladders will reduce the extent of wildfires, the damages they cause, and the cost of controlling them. Numerous on-the-ground examples support this belief. However, little empirical research has documented this logical presumption. As noted in one research study: “scant information exists on fuel treatment efficacy for reducing wildfire severity.”26 This study also found that “fuel treatments moderate extreme fire behavior within treated areas, at least in” frequent fire ecosystems. Others have found different results elsewhere; one study reported “no evidence that prescribed burning in these [southern California] brushlands provides any resource benefit ... in this crown-fire ecosystem.” [27] A recent summary of wildfire research reported that prescribed burning generally reduced fire severity, that mechanical fuel reduction did not consistently reduce fire severity, and that little research has examined the potential impacts of mechanical fuel reduction with prescribed burning or of commercial logging. [28]

Before examining fuel management tools, a brief description of fuels may be helpful. [29] Wildfires are typically spread by fine fuels [30] — pine needles, leaves, grass, etc. — both on the surface and in the tree crowns (in a stand-replacement crown fire); these are known as 1-hour time lag fuels, because they dry out (lose two-thirds of their moisture content) in about an hour. Small fuels, known as 10-hour time lag fuels, are woody twigs and branches, up to 1 inch in diameter; these fuels also help spread wildfires because they ignite and burn quickly. Larger fuels — particularly the 1000-hour time lag fuels (more than 3 inches in diameter) — may contribute to the intensity and thus to the damage fires cause, but contribute little to the rate of spread, because they are slow to ignite. One researcher noted that only 5% of large tree stems and 10% of tree branches were consumed in high intensity fires, while 100% of the foliage and 75% of the understory vegetation were consumed. [31] Finally, ladders of fine and small fuels between the surface and the tree crowns can spread surface fires into the canopy, thus turning a surface fire into a stand-replacement fire.

Prescribed Burning.

Fire has been used as a tool for a long time. [32] Native Americans lit fires for various purposes, such as to reduce brush and stimulate grass growth. Settlers used fires to clear woody debris in creating agricultural fields. In forestry, in large part because of severe wildfires in logging debris in the Northeast and Lake States more than a century ago, fire has been used to eliminate logging debris, by burning brush piles and by prescribed burning harvested sites to prepare them for reforestation. [33]

Prescribed burning has been used increasingly over the past 40 years to reduce fuel loads on federal lands. FS prescribed burning has exceeded 1.2 million acres annually since FY1998, except for FY2000, when the severe fire season limited prescribed burning to 772,000 acres; as recently as FY1995, the prescribed burning acreage was less than 500,000 acres annually. (Comparable data on BLM prescribed burning are not published.) However, more than half of FS prescribed burning is in the FS Southern Region, and thus prescribed burning in the intermountain west is still at relatively modest levels.

Typically, areas to be burned are identified in agency plans, and fire lines (essentially dirt paths) are created around the perimeter. The fires are lit when the weather conditions permit (i.e., when the burning prescription is fulfilled) — when the humidity is low enough to get the fuels to burn, but not when the humidity is so low or wind speed so high that the burning cannot be contained. (This, of course, presumes accurate knowledge of existing and expected weather and wind conditions, as well as sufficient fire control crews with adequate training on the site.) When the fire reaches the perimeter limits, the crews “mop up” the burn area to assure that no hot embers remain to start a wildfire after everyone is gone.

Prescribed burning is widely used for fuel management because it reduces biomass (the fuels) to ashes (minerals). It is particularly effective at reducing the smaller fuels, especially in the arid west where deterioration by decomposers (insects, fungi, etc.) is often very slow. In fact, it is the only human treatment that directly reduces the fine and small fuels that are important in spreading wildfires. However, prescribed fires are not particularly effective at reducing larger-diameter fuels or thinning stands to desired densities and diameters. [34]

There are several limitations in using prescribed fire. The most obvious is that prescribed fires can be risky — fire is not a controlled tool; rather, it is a self-sustaining chemical reaction that, once ignited, continues until the fuel supply is exhausted. [35] Fire control (for both wildfires and prescribed fires) thus focuses on removing the continuous fuel supply by creating a fire line dug down to mineral soil. The line must be wide enough to prevent the spread of fire by radiation (i.e., the heat from the flames must decline sufficiently across the space that the biomass outside the fire line does not reach combustion temperature, about 550° F). Minor variations in wind and in fuel loads adjacent to the fire line can lead to fires jumping the fire line, causing the fire to escape from control. Winds can also lift burning embers across fire lines, causing spot fires outside the fire line which can grow into major wildfires under certain conditions (such as occurred near Los Alamos, NM, in May 2000). Even when general weather conditions — temperature, humidity, and especially winds — are within the limits identified for prescribed fires, localized variations in the site (e.g., slope, aspect, [36] and fuel load) and in weather (e.g., humidity and wind) can be problematic. Thus, prescribed fires inherently carry some degree of risk, especially in ecosystems adapted to stand-replacement fires and in areas where the understory and undergrowth have created fuel ladders.

Another concern is that prescribed fires generate substantial quantities of smoke — air pollution with high concentrations of carbon monoxide, hydrocarbons, and especially particulates that degrade visibility. Some assert that prescribed fires merely shift the timing of air pollution from wildfires. Others note that smoke from pre-industrial wildland fires was at least three times more than from current levels from prescribed burning and wildfire. [37] The Clean Air Act requires regulations to preserve air quality, and regulations governing particulate emissions and regional haze have been of concern to land managers who want to expand prescribed burning programs. Previous proposed legislation (e.g., H.R. 236, 106th Congress) would have exempted Forest Service prescribed burning from air quality regulations for 10 years, to demonstrate that an aggressive prescribed burning program will reduce total particulate emissions from prescribed burning and wildfires. However, owners and operators of other particulate emitters (e.g., diesel vehicles and fossil fuel power plants) generally object to such exemptions, arguing that their emissions would likely be regulated more stringently, even though wildland fires are one of the largest sources of particulates. [38]

Salvage and Other Timber Harvesting.

Another tool commonly proposed for fuel treatment is traditional timber harvesting, including salvaging dead and dying trees before they rot or succumb to disease, commercially thinning dense stands, etc.

In areas where the forest health problems include large numbers of dead and dying trees, a shift toward an inappropriate or undesirable tree species mix, or a dense understory of commercially usable trees, timber harvesting can be used to improve forest health and remove woody biomass from the forest. Nonetheless, some interest groups object to using salvage and other timber harvests to improve forest health. [39]

Timber generally may only be removed from federal forests under timber sale contracts. Newly authorized stewardship goods-for-services contracts allow timber sales and forest management services, such as fuel reduction, to be combined in one contract, essentially as a trade of goods (timber) for services (fuel reduction); this form of contracting is discussed below, under “Other Fuel Management Tools.” Because timber sale contracts have to be bought and goods-for-services contracts must generate value to provide services, the contracts generally must include the removal of merchantable trees. Critics argue that the need for merchantable products could compromise reducing fuel loads or achieving desired forest conditions.

Timber harvests remove heavy fuels that contribute to fire intensity, and can break fuel ladders, but the remaining limbs and tree tops (“slash”) substantially increase fuel loads on the ground and get in the way of controlling future fires, at least in the short term, until the slash is removed or disposed of through burning. “Slash is a fire hazard mainly because it represents an unusually large volume of fuel distributed in such a way that it is a dangerous impediment in the construction of fire lines” (i.e., in suppressing fires). [40]

If logging slash is treated, as has long been a standard practice following timber harvesting, the increased fire danger from higher fuel loads that follow timber harvesting can be ameliorated. Various slash treatments are used to reduce the fire hazard, including lop-and-scatter, pile-and-burn, and chipping. [41] Lop-and-scatter consists of cutting the tops and limbs so that they lie close to the ground, thereby hastening decomposition and possibly preparing the material for broadcast burning (essentially, prescribed burning of the timber harvest site). Pile-and-burn is exactly that, piling the slash (by hand or more typically by bulldozer) and burning the piles when conditions are appropriate (dry enough, but not too dry, and with little or no wind). Chipping is feeding the slash through a chipper, a machine that reduces the slash to particles about the size of a silver dollar. and scattering the chips to allow them to decompose. Thorough slash disposal can significantly reduce fuel loads, particularly on sites with large amounts of noncommercial biomass (e.g., undergrowth and unusable tree species) and if combined with some type of prescribed burning. However, data on the actual extent of various slash disposal methods and on needed slash disposal appear to be available only for a few areas.

Other Fuel Management Tools.

The other principal tool for fuel management is mechanical treatment of the fuels. [42] One common method is precommercial thinning — cutting down many of the small (less than 4 1/2-inch diameter) trees that have little or no current market value. Other treatments include pruning and mechanical release of seedlings (principally by cutting down or mowing competing vegetation). Mechanical treatments are often effective at eliminating fuel ladders, but as with timber cutting, do not reduce the fine fuels on the sites without additional treatment (e.g., without prescribed burning). Mechanical fuel treatments alone tend to increase fine fuels and sometimes larger fuels on the ground in the short term, until the slash has been treated.

Some critics have suggested using traditionally unused biomass, such as slash and thinning debris, in new industrial ways, such as using the wood for paper or particleboard or burning the biomass to generate electricity. [43] Research has indicated that harvesting small diameter timber may be economically feasible, [44] and one study reported net revenues of $624 per acre for comprehensive fuel reduction treatments in Montana that included removal and sale of merchantable wood. [45] However, thus far, collecting and hauling chipped slash and other biomass for products or energy have apparently not been seen as economically viable by timber purchasers, given that such woody materials are currently left on the harvest sites. [46]

Another possibility is to significantly change the traditional approach to timber sales. Stewardship contracting, in various forms, has been tested in various national forests. [47] Sometimes, the stewardship contract (payment and performance) is based on the condition of the stand after the treatment, rather than on the volume harvested; this is also known as end-results contracting. A variation on this theme, which has been discussed sporadically for more than 30 years, is to separate the forest treatment from the sale of the wood. The most common form is essentially to use commercial timber to pay for other treatments; that is, the contractor removes the specified commercial timber and is required to perform other activities, such as precommercial thinning of a specified area. Because of the implicit trade of timber for other activities, this is often called goods-for-services stewardship contracting. FS and BLM goods-for-services stewardship contracting was authorized through FY2013 in the FY2003 Continuing Appropriations Resolution (P.L. 108-7). Some observers believe that such alternative approaches could lead to development of an industry based on small diameter wood, and thus significantly reduce the cost of fuel management. Others fear that this could create an industry that cannot be sustained after the current excess biomass has been removed or that would need continuing subsidies.

Fuel Management Funding.

Direct federal funding for prescribed burning and other fuel treatments (typically called hazardous fuels or fuel management) is part of FS and BLM appropriations for Wildfire Management. (See CRS Report RS21544, Wildfire Protection Funding.) Appropriations for fuel reduction have risen from less than $100 million in FY1999 to more than $400 million since FY2003.

Funds appropriated for other purposes can also provide fuel treatment benefits. As noted above, salvage and other commercial timber sales can be used to reduce fuels in some circumstances. Various accounts, both annually appropriated and permanently appropriated mandatory spending, provide funding reforestation, timber stand improvement, and other activities. Reforestation actually increases fuels, but timber stand improvement includes precommercial thinning, pruning, and other mechanical vegetative treatments included in “Other Fuel Management Tools” (see above), as well as herbicide use and other treatments that do not reduce fuels.

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26 Philip N. Omi and Erik J. Martinson, Effects of Fuels Treatment on Wildfire Severity: Final Report, submitted to the Joint Fire Science Program Governing Board (Ft. Collins, CO: Colorado State Univ., Western Forest Fire Research Center, Mar. 25, 2002), p. i.

27 Jon E. Keeley, “Fire Management of California Shrubland Landscapes,” Environmental Management, v. 29, no. 3 (2002): 395-408.

28 Henry Carey and Martha Schumann, Modifying WildFire Behavior — The Effectiveness of Fuel Treatments: The Status of Out Knowledge, Southwest Region Working Paper 2 (Santa Fe, NM: National Community Forestry Center, April 2003).

29 See Arthur A. Brown and Kenneth P. Davis, “Chapter 4: Forest Fuels,” Forest Fire Control and Use (New York, NY: McGraw-Hill Book Co., 1973), pp. 79-110.

30 Robert E. Martin and Arthur P. Brackebusch, “Fire Hazard and Conflagration Prevention,” Environmental Effects of Forest Residues Management in the Pacific Northwest: A State-of-Knowledge Compendium (Owen P. Cramer, ed.), Gen. Tech. Rept. PNW-24 (Portland, OR: USDA Forest Service, 1974).

31 Agee, Fire Ecology of PNW Forests, p. 42. It is also important to recognize that the percentage of biomass in 1-hour, 10-hour, 100-hour, and 1000-hour fuels depends largely on tree diameter, with the percentage in large fuels increasing as diameter increases.

32 Historical evidence indicates that current levels of burning through prescribed burns and wildfires represent levels perhaps 10%-30% of pre-industrial burning levels from natural and Native-set fires. See Bill Leenhouts, “Assessment of Biomass Burning in the Conterminous United States,” Conservation Ecology 2(1), 1998, at [http://www.]. (Hereafter referred to as Leenhouts, “Assessment of Biomass Burning.”)

33 David M. Smith, The Practice of Silviculture, 7th ed. (New York, NY: John Wiley & Sons, 1962), pp. 317-321.

34 See Arthur A. Brown and Kenneth P. Davis, Forest Fire Control and Use, 2nd Ed. (New York, NY: McGraw-Hill Book Co., 1973), pp. 560-572.

35 Fire can also be halted by eliminating the supply of oxygen, as occurs when fire retardant (“slurry”) is spread on forest fires from airplanes (“slurry bombers”). However, reducing oxygen supply usually can only occur in a limited area, because of the cost to spread the fire retardant.

36 Aspect is the term used for the direction which the slope is facing; in the northern hemisphere, south-facing slopes (south aspects) get more radiant energy from the sun than north aspects, and thus are inherently warmer and drier, and hence are at greater risk of more intense wildfires.

37 Leenhouts, “Assessment of Biomass Burning.”

38 See, for example, U.S. House, Committee on Resources, Hearing on the Use of Fire as a Management Tool and Its Risks and Benefits for Forest Health and Air Quality, Sept. 30, 1997 (Washington, DC: GPO, 1997), Serial No. 105-45, 141 p.

39 Timber harvesting has a variety of proponents and opponents for reasons beyond fuel management. Some interests object to timber harvesting on a variety of grounds, including the poor financial performance of Forest Service timber sales and the degradation of water quality and certain wildlife habitats that follows some timber harvesting. Others defend timber sales for the employment and income provided in isolated, resource-dependent communities as well as for increasing water yields and available habitat for other wildlife species. The arguments supporting and opposing timber harvests generally have often been raised in discussions about fire protection, but are not reproduced in this report. See CRS Report 95-364 ENR, Salvage Timber Sales and Forest Health.

40 Smith, The Practice of Silviculture, p. 312.

41 Smith, The Practice of Silviculture, pp. 312-317.

42 Chemical treatments (herbicides) are also used in forestry, mostly on unwanted vegetation, but they are not included here as a fuel treatment tool, because they are used primarily to kill live biomass rather than to reduce biomass levels on a site. Biological treatments (e.g., using goats to eat the small diameter material) are feasible, but are rarely used.

43 Robert Nelson, Univ. of Maryland, cited in: Rocky Barker, “Wildfires Creating Odd Bedfellows,” The Idaho Statesman (Aug. 14, 2000): 1A, 7A.

44 Henry Spelter, Ron Wang, and Peter Ince, Economic Feasibility of Products From Inland West Small Diameter Timber, FPL-GTR-92 (Madison, WI: USDA Forest Service, May 1996), 17 p.

45 Carl E. Fieldler, Charles E. Keegan, Todd A. Morgan, and Christopher W. Woodall, “Fire Hazard and Potential Treatment Effectiveness: A Statewide Assessment in Montana,” Journal of Forestry, v. 101, no. 2 (March 2003), p. 7

46 Research documenting the economics of slash use (in contrast to small diameter trees) is lacking. However, this seems a reasonable conclusion, given that the slash is left on the site by the timber purchaser (who could remove and sell the material) and that the agencies and various interest groups have been trying to develop alternatives to the traditional contracts (e.g., stewardship contracts) to remove thinning slash and other biomass fuels.

47 See CRS Report RS20985, Stewardship Contracting for Federal Forests, by Ross W. Gorte.

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