Effects of Roads on Fire

Most of the concerns addressed here apply primarily to the western United States. In much of the East, road networks are well developed and relatively stable because of terrain and vegetation differences. Wildfire interactions are likely to be similar to those described for the West, but the effects are likely to be significantly less. In the Southeast, where use of prescribed fire is widespread, roads are frequently used as firebreaks. Much of this activity is on private land, but a high proportion of the road network is state and county highways rather than Forest Service roads.

The increasing density of road networks in and adjacent to many forest, shrub, and rangeland areas has been an important factor in changing patterns of disturbance by fire on the landscape. Roads provide access that has increased the scale and efficiency of fire suppression, and roads have created linear firebreaks that affect fire spread. These factors can be useful in both fire suppression and prescribed fire operations. In addition, road access has undoubtedly contributed to increased frequency of human-caused ignitions in some areas.

Roads Provide Increased Access for Fire Control and Suppression

That improved road access leads to increased efficiency and effectiveness of fire-suppression activities is a long-held tenet of fire fighting. Much of the effectiveness of past fire-suppression policies probably can be attributed to increased access for ground crews and equipment, particularly under weather and fuel conditions where fire behavior is not severe. Under the severe conditions associated with intense, rapidly spreading fires, the value of forest roads for access or as fuelbreaks is likely to be minimal. Although little has been published in the science literature to quantify these effects, a study in southern California concluded that the road network had been a key factor in determining what suppression strategies were used, both in firefighter access and in use for backfiring and burning-out operations (Salazar and Gonzalez-Caban 1987). Early studies of fuelbreak effectiveness in southern California came to similar conclusions (Green 1977). It is uncertain how much road access increases efficiency, but there is little doubt that there is an increase.

An important issue in the western United States is building new roads to allow harvest and prescribed fire to reduce fuel accumulations in ecosystems where past management (principally fire suppression and harvest) have increased the risk of large, severe wildfires (Lehmkuhl and others 1994). The principal concern here is the tradeoff between reducing the effects of wildfire and increasing the risks of road effects on aquatic habitat. In the Columbia Basin, scientists concluded that "it is not fully known which causes greater risk to aquatic systems, roads to reduce fire risk, or realizing the full potential risk of fire" (Quigley and others 1997). An adaptive management framework has been suggested for addressing this concern (Rieman and Clayton 1997). We currently have few data on how these processes might be affected by road networks, but a study after the 1987 Stanislaus fires in California suggests that cross-slope road networks reduced sediment delivery to debris basins (Chou and others 1994).

Roads Increase Access for Human-Ignited Fires

The benefits that roads provide for fire prevention and fire management carry an associated cost. Roads have increased the frequency of human-caused ignitions, particularly in areas of expanding urban and rural development into wildland interfaces (Hann and others 1997). The high rate of human-caused fires in the Blue Mountains of eastern Oregon is associated with high recreational use in areas with high road densities (Hann and others 1997). In the Southwest, however, numbers of ignitions are less important in fire management than are fuel loadings and climatic conditions are (Swetnam and Baisan 1996). Nevertheless, numbers of ignitions are important determinants of fire risk (Conard and Weise 1998).

Roads Affect Fire Patterns and Fire Regimes

Road networks have changed fuel patterns and fire regimes at the broad scale. If we accept that road networks have been important in effectively suppressing fire and that they alter fire patterns on the landscape, then road systems are, in some sense, linked to changes in fuel patterns and fire regimes. Before fire-suppression activity in the western United States, fuel loads remained relatively low in dry forest types; high fuel loads were restricted to small, isolated patches (Agee 1993). As access increased, areas burned by wildfire declined, at least through the 1960s. As a result of suppression supported in part by access, fuel accumulations increased and areas with moderate to high fuel loadings became larger and more contiguous. This pattern of change has been documented for the entire upper Columbia River Basin. There, scientists assert that fire suppression has generally been more effective in roaded areas, causing those areas in the upper basin to depart further than unloaded areas from unaltered biophysical templates (Hann and others 1997). Roads, along with other human disturbances such as clearcutting, contribute to new disturbance patterns at the landscape scale, both by increasing efficiency of fire fighting and providing barriers to firespread that are different from natural barriers (Swanson and others 1990). Increased emphasis on removing roads in certain environmentally sensitive areas will reduce access for fire suppression and prescribed fires, potentially leading to increased fuel accumulation and increased fire hazard in some areas.