Volume 1/Chapter 4/Fire And Fuels

* Critical Findings

ASSESSMENT

* Fire-Alternative Views

* Careless and Indiscriminate Fire Use

Strategies

CURRENT PAGE:
4 of 9

Trends in Fire Size

Total area burned in the Sierra shows no overall trend during the twentieth century, in contrast to the marked reduction in burned area from the presettlement era to the twentieth century. This stability contrasts with striking declines in area burned during the first half of the century and increases in area burned after about 1970 that have been documented for other areas in the western United States. Other patterns also have remained stable, including (1) the relationship between fire occurrence and elevation (i.e., more area burns at lower elevations); (2) the relationship between climate and annual area burned (i.e., more area burns in warmer, drier years); and (3) average fire sizes for most national forests in the Sierra Nevada.
In other significant respects, however, fire characteristics have changed. Although human-caused fires have exceeded lightning fires in number and total area throughout this century (figure 4.2), the proportion of total area burned by lightning-caused fires and the average size of lightning fires have increased in recent decades, particularly in the late 1980s and early 1990s.

Figure 4.2

Acres burned by fires in the Sierra Nevada, 1908-92. Top.
(a): Human-caused fires. Bottom (b): Lightning-caused fires.
(From volume II, chapter 41.)

A likely explanation stems from the fact that, unlike human ignitions, many lightning ignitions occur simultaneously during thunderstorms, stretching available fire-fighting resources so thin that not all fires receive adequate initial attack. The increase in total area and average size of lightning fires in recent decades may reflect, in part, a reduction in overall suppression resources. At least as important may be general increases in wildfire hazard (fuel quantities), which tend to increase difficulty of control and exacerbate limitations in fire-fighting resources. Expanded human settlement in the urban-wildland intermix has also complicated fire suppression by focusing resources on protection of structures.
An evaluation of fire-occurrence risk based on U.S. Forest Service records of twentieth-century fires identified an elevation pattern, with the highest risk in the foothill and lower mixed conifer zone (figure 4.3 and plates 4.1 and 4.2). Maps documenting fuel loads on national forest lands in the Sierra reflect another estimate of risk (plate 4.3).


Figure 4.3 Fires on and around USFS national forest lands within the SNEP core area. Left: Fires from 1900 to 1939 (Actual View 42K). Right: Fires from 1940 to 1993 (Actual View 48K). (From volume II, chapter 41.)

Prescribed Fire

Prescribed fire has proven an effective tool to reduce fuel loads and fire hazards while restoring a process important for maintaining ecosystem functions. However, practical and political considerations may limit future expansion of this approach. Although prescribed fire is useful in restoring and maintaining natural fire regimes in parks and wilderness areas, it remains to be seen whether the logistical, economic, and social constraints on widespread deployment of prescribed fire for fuel hazard reduction can be overcome. In some places, mechanical fuel reduction, often in conjunction with prescribed fire, can also be of use in reducing fuels and fire hazards.

Challenges for Fire Management

Human activities during the past 150 years have caused a number of fire-related changes in the Sierra Nevada. Fires occur less frequently and collectively cover much less area than they did in the presettlement era. Widespread low- to moderate-severity wildfires have been virtually eliminated because these are the fires that are suppressed most easily. As a result, the ecological functions performed by such fires (e.g., nutrient mineralization, soil sterilization, and understory thinning) have been largely lost, with some known and many unknown consequences. Furthermore, largely because of fire suppression, fuelsboth live and deadhave increased in quantity and continuity, thereby increasing the probability of large, high-severity wildfires. In fact, the fires that do occur are likely to be large and more uniformly severe; these are the fires not readily suppressed. It is these high-severity fires that most conflict with human values and thus pose the greatest concerns about life, property, and natural resource values. The propensity for the rapidly increasing population of the Sierra Nevada to build in flammable areas without mitigating fire hazards and risks has increasingly placed homes and other valuable property at risk of loss to severe wildfires, making potential solutions to the problem increasingly difficult. Many hundreds of homes have been destroyed by wildfires in the Sierra Nevada over the past few decades (e.g., 148 homes and 164 other structures were destroyed in the 1988 49er fire near Nevada City).
In short, we have three major fire-related problems in the Sierra Nevada: (1) too much high-severity fire and the potential for much more of the same; (2) too little low- to moderate-severity fire, with a variety of ecological changes attributable at least in part to this deficiency; and (3) a large number of homes and other structures at risk due to both existing and continued rural development in areas with extreme fire hazards that are not reduced to acceptable levels. Clearly, these are not just fire problems. They influence virtually all resources and values in the Sierra Nevada and cut across all of SNEPs subject areas. These three problems can be translated into three closely related and complementary broad goals for fire management in the Sierra Nevada: (1) reduce substantially the area and average size of acres burned by large, high-severity wildfires; (2) restore more of the ecosystem functions of frequent low- to moderate-severity fire; and (3) encourage a more rational approach for the intermix of homes and wildland vegetation with high fire-risk hazard. Making significant progress toward these goals will require long-term vision, commitment, and cooperation across a broad spectrum of land-management agencies and other entities. The problems were created over a long time, and they certainly cannot be solved rapidly.