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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

Concerns and Problems

Wildfires stir a primeval fear and fascination in most of us. Many have long been concerned about the loss of valuable timber to fire and about the effects of fire on soils, watersheds, water quality, and wildlife. In addition, the loss of houses and other structures adds to wildfire damages. Historically, wildfires were considered a major threat to people and houses primarily in the brushy hillsides of southern California. However, people have increasingly been building their houses and subdivisions in forests and other wildlands, and this expanding wildland-urban interface has increased the wildfire threat to people and houses. Also, a century of using wildlands and suppressing wildfires has significantly increased fuel loads and led to historically unnatural vegetative species and structures, and exacerbated wildfire threats. [15]

Wildland-Urban Interface (WUI).

The wildland-urban interface has been defined as the area “where combustible homes meet combustible vegetation.” [16] This interface includes a wide variety of situations, ranging from individual houses and isolated structures to subdivisions and rural communities surrounded by wildlands. While this situation has always existed to some extent, subdivisions in wildland settings appear to have grown significantly over the past two decades. Standard definitions of the interface have been developed by the federal agencies, [17] but have not been used to assess the changing situation.

One particular aspect is that the growth of the interface has also increased the roads into wildland settings. Increased road access has both benefits and costs for protecting resources and people from wildfires. Increased human access generally increases the frequency of wildfire ignitions — 88% of the fires from 1988-1997 were caused by humans, with only 12% caused by lightning. While human-caused fires can be catastrophic, they are typically in accessible areas, and thus can often be controlled more quickly; for example, only 48% of the acres burned from 1988-1997 were in human-caused fires. If the roads are mapped and marked (so that fire crews can find their way) and are sufficiently wide for fire-fighting equipment, increased access can allow for faster control efforts, and probably reduces the risk of a structure being burned. However, poorly marked or unmarked, narrow, twisting roads exist in some wildland subdivisions, in part because homeowners want to minimize non-local traffic in and through the subdivision. In such situations, the poor access may exacerbate the wildfire threat to homeowners.

Most observers agree that protecting homes and other structures in the interface is an appropriate goal for safeguarding the highest values at risk from wildfire. However, there are differences of opinion about how to best protect the WUI. FS research has indicated that the characteristics of the structures and their immediate surroundings are the primary determinants of whether a structure burns. In particular, non-flammable roofs and cleared vegetation for at least 10 meters (33 feet) and up to 40 meters (130 feet) around the structure is highly likely to protect the structure from wildfire, even when neighboring structures burn. [18]

Others, including sponsors of most wildfire protection bills, propose reducing fuels in a band surrounding communities in the WUI. Three types of communities in the interface have been identified: interface communities, intermix communities, and occluded communities. [19] Interface communities have a “clear line of demarcation between ... structures and wildland fuels,” generally with 3 or more structures per acre and shared municipal services, and typically with a population density of at least 250 people per square mile. Intermix communities are “where structures are scattered throughout a wildland area,” with fuels “continuous outside of and within the developed area,” and a range of densities of structures. Occluded communities are situations where structures surround and isolate a pocket (usually less than 1,000 acres) of wildland, like a large park. Many proposals for fuel reduction would authorize treatments typically within a half mile (sometimes a quarter mile) of interface or intermix communities.

Forest and Rangeland Health.

The increasing extent of wildfires in the national forests in the past two decades has been widely attributed to deteriorating forest and rangeland health, resulting at least in some cases directly from federal forest and rangeland management practices. Wildland ecological conditions in many areas, particularly in the intermountain west (the Rocky Mountains through the Cascades and Sierra Nevadas), have been altered by various activities. Beginning more than a century ago, livestock grazing affected ecosystems by reducing the amount of grass and changing the plant species mix in forests and on rangelands. This reduced the fine fuels that carried surface fires (allowed them to spread), encouraged trees to invade traditionally open grasslands and meadows, and allowed non-native species to become established, all of which, experts believe, induce less frequent but more intense wildfires. [20] In addition, first to support mining and railroad development and later to support the wood products industry, logging of the large pines that characterized many areas has led to regeneration of smaller, less fire-resistant trees in some areas. [21] Roads that provide access for logging, grazing, and recreation have also been implicated in spreading non-native species. [22]

The nature, extent, and severity of these forest and rangeland health problems vary widely, depending on the ecosystem and the history of the site. In rangelands, the problem is likely to be invasion by non-native species (e.g., cheat grass or spotted knapweed) or by shrubs and small trees (e.g., salt cedar or juniper). In some areas (e.g., western hemlock or inland Douglas-fir stands), the problem may be widespread dead trees due to drought and/or insect or disease infestations. In others (e.g., southern pines and western mixed conifers), the problem may be dense undergrowth of different plant species (e.g., palmetto in the south and firs in the west). In still others (e.g., Ponderosa pine stands) the problem is more likely to be stand stagnation (e.g., too many little green trees, because intra-species competition rarely kills Ponderosa pines).

One FS research report has categorized these health problems, for wildfire protection, by classifying ecosystems according to their historical fire regime. [23] The report describes five historical fire regimes:

I. ecosystems with low-severity, surface fires at least every 35 years (often called frequent fire ecosystems);

II. ecosystems with stand replacement fires (killing much of the standing vegetation) at least every 35 years;

III. ecosystems with mixed severity fires (both surface and stand replacement fires) at 35-100+ year intervals;

IV. ecosystems with stand replacement fires at 35-100+ year intervals; and

V. ecosystems with stand replacement fires at 200+ year intervals.

It is widely recognized that fire suppression has greatly exacerbated these ecological problems, at least in frequent fire ecosystems (fire regimes I and II) — most grass and brush ecosystems and many forest ecosystems (e.g., southern yellow pines and Ponderosa pine) that evolved with frequent surface fires that burned grasses, pine needles, and other small fuels at least every 35 years, depending on the site and plant species. Surface fires reduce fuel loads by mineralizing biomass that may take decades to rot, and thus provide a flush of nutrients to stimulate new plant growth. Historically, many surface fires were started by lightning, although Native Americans used fires to clear grasslands of encroaching trees, to stimulate seed production, and to reduce undergrowth and small trees that often provide habitat for undesirable insects (e.g., ticks and chiggers) and inhibit mobility and visibility when hunting. [24]

Eliminating frequent surface fires through fire suppression and other activities has led to unnaturally high fuel loads, by historic standards, in frequent fire ecosystems. These historically unnatural fuel loads can lead to stand replacement fires in ecosystems adapted to frequent surface fires. In particular, small trees and dense undergrowth can create fuel ladders that sometimes cause surface fires to spread upward into the forest canopy. In these ecosystems, the frequent surface fires had historically eliminated much of the understory before it got large enough to create fuel ladders. Stand replacement fires in frequent-fire ecosystems might regenerate new versions of the original surface-fire adapted ecosystems, but some observers are concerned that these ecosystems might be replaced with a different forest that doesn’t contain the big old Ponderosa pines and other traditional species of these areas.

Stand replacement fires are not, however, an ecological catastrophe in other ecosystems. Perennial grasses and some tree and brush species have evolved to regenerate following intense fires that kill much of the surface vegetation (fire regimes II, IV, and V). Aspen and some other hardwood tree and brush species, as well as most grasses, regrow from rootstocks that can survive intense wildfires. Some trees, such as jack pine in the Lake States and Canada and lodgepole pine in much of the west, have developed serotinous cones, that open and disperse seeds only after exposure to intense heat. In such ecosystems, stand replacement fires are normal and natural, although avoiding the incineration of structures located in those ecosystems is obviously desirable.

Some uncertainty exists over the extent of forest and rangeland health problems and how various management practices can exacerbate or alleviate the problems. In 1995, the FS estimated that 39 million acres in the National Forest System (NFS) were at high risk of catastrophic wildfire, and needed some form of fuel treatment.25 More recently, the Coarse-Scale Analysis reported that 51 million NFS acres were at high risk of significant ecological damage from wildfire, and another 80 million acres were at moderate risk. (See Table 2.) The Coarse-Scale Analysis also reported 23 million acres of Department of the Interior lands at high risk and 76 million acres at moderate risk. All other lands (calculated as the total shown in the Coarse-Scale Analysis less the NFS and DOI lands) included 107 million acres at high risk and 314 million acres at moderate risk of ecological damage.

Table 2. Lands At Risk of Ecological Change, by Historic Fire Regime
(in millions of acres)


0-35 years; surface fire

0-35 years; crown fire
Regime II
I 35-100+; mixed fire

35-100+; crown fire

200+ yrs; crown fire
National Forest System lands
Class 1: low risk
Class 2: moderate risk
Class 3: high risk
Department of the Interior lands
Class 1: low risk
Class 2: moderate risk
Class 3: high risk
Private, state, and other federal lands
Class 1: low risk


Class 2: moderate risk
Class 3: high risk

Source: Kirsten M. Schmidt, James P. Menakis, Colin C. Hardy, Wendel J. Hann, and David L. Bunnell, Development of Coarse-Scale Spatial Data for Wildland Fire and Fuel Management, Gen. Tech. Rept. RMRS-87 (Ft. Collins, CO: USDA Forest Service, April 2002), pp. 13-15.

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15 For example, see R. Neil Sampson, David L. Adams, Stanley S. Hamilton, Stephen P. Mealey, Robert Steele, and Dave Van De Graaff, “Assessing Forest Ecosystem Health in the Inland West: Overview,” Assessing Forest Ecosystem Health in the Inland West, pp. 3

16 Wildfire Strikes Home! The Report of the National Wildland/Urban Fire Protection Conference, sponsored by the USDA, Forest Service; the National Fire Protection Association; and the FEMA, U.S. Fire Administration (Jan. 1987), p. 2.

17 U.S. Dept. of Agriculture, Forest Service and Dept. of the Interior, Bureau of Indian Affairs, Bureau of Land Management, Fish and Wildlife Service, and National Park Service, “Urban Wildland Interface Communities Within the Vicinity of Federal Lands That Are at High Risk From Wildfire,” Federal Register, v. 66, no. 3 (Jan. 4, 2001): pp. 751-754.

18 Jack D. Cohen, “Preventing Disaster: Home Ignitability in the Wildland-Urban Interface,” Journal of Forestry, v. 102, no. 3 (March 2000): 15-21.

19 U.S. Dept. of Agriculture and Dept. of the Interior, “Urban Wildland Interface Communities Within the vicinity of Federal Lands That Are at High Risk From Wildfire,” 66 Federal Register 751-754 (Jan. 4, 2001).

20 W. W. Covington and M. M. Moore, “Postsettlement Changes in Natural Fire Regimes and Forest Structure: Ecological Restoration of Old-Growth Ponderosa Pine Forests,” Assessing Forest Ecosystem Health in the Inland West, pp. 153-181.

21 Jay O’Laughlin, “Assessing Forest Health Conditions in Idaho with Forest Inventory Data,” Assessing Forest Ecosystem Health in the Inland West, pp. 221-247.

22 Federal Interagency Committee for the Management of Noxious and Exotic Weeds,
Invasive Plants: Changing the Landscape of America (Washington, DC: 1998), pp. 23-24.

23 Kirsten M. Schmidt, James P. Menakis, Colin C. Hardy, Wendel J. Hann, and David L. Bunnell, Development of Coarse-Scale Spatial Data for Wildland Fire and Fuel Management, Gen. Tech. Rept. RMRS-87 (Ft. Collins, CO: USDA Forest Service, Apr. 2002). Hereafter referred to as the Coarse-Scale Analysis.

24 James K. Agee, Fire Ecology of Pacific Northwest Forests (Washington, DC: Island Press, 1993), pp. 54-57. Hereafter referred to as Agee, Fire Ecology of PNW Forests.

25 Enoch Bell, David Cleaves, Harry Croft, Susan Husari, Ervin Schuster, and Dennis Truesdale, Fire Economics Assessment Report, unpublished report submitted to Fire and Aviation Management, USDA Forest Service, on Sept. 1, 1995.

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