Fire Weather and Smoke Management

Wildland fires consume large areas of forest and grasslands every year. Fires are described in terms of fire behavior, which includes rate of spread and fire intensity. A fire that spreads rapidly burns less of the available fuel per square unit of area than a fire that moves slowly and allows the flaming front a longer residence time. A fire with flames that reach only two feet above the ground produces less heat and is less destructive than an intense fire that crowns, that is, has long flames and burns at the top (i.e., crown) of the forest canopy (figure 13.1). Fire suppression activities are initiated when a wildfire threatens people, property, or natural areas that need protection. These activities include dropping water or chemicals on a fire and establishing a fire line around the fire. A fire line is a zone along a fire’s edge where there is little or no fuel available to the fire. Roads, cliffs, rivers, and lakes can be part of a fire line, or land can be cleared by firefighters. Backfires may be set within the fire line to burn toward the fire, widening the fire line and reducing the likelihood of the fire spreading beyond it (figures 13.2 and 13.3). Fires can cross a fire line if the intensity is high or if spotting occurs, that is, if the wind carries burning material (firebrands) beyond the fire and across the fire line (figure 13.4). A wildland fire can be very destructive, but it can also be beneficial and may be used by land resource managers to accomplish specific ecological objectives. For example, smaller fires can reduce the danger of a large catastrophic fire by burning off underbrush. Fire can also be used to prepare land for planting, to control the spread of disease or insect infestations, to benefit plant species that are dependent on fire, to influence plant succession, or to alter the nutrients in the soil. When a fire is used to manage land resources, it is called a prescribed fire.