Using Prescribed Fire for Hazardous Fuel Reduction
Hazard reduction burns in the Coastal Plain
Prescribed fire is the most practical way to reduce dangerous accumulations of combustible fuels under southern pine stands. Forest fuels accumulate rapidly in pine stands on the Coastal Plain. In pine stands, understories become highly flammable when hardwoods, shrubs, and vines are draped with pine needles. This understory fuel complex, called a rough, can build up within 5 to 6 years, placing the forest at risk to destruction by wildfire. Wildfires that burn into areas where fuels have been reduced by prescribed burning cause less damage and are much easier to control. The need to reduce hazardous fuel accumulations in the pine stands of the South is increasing. Without fuel reduction, fire hazard is extremely high in these vast contiguous stands.
The appropriate interval between prescribed burns for fuel reduction varies with several factors, including:
- the rate of fuel accumulation,
- past wildfire occurrence,
- values at risk, and
- the risk of a fire.
The time interval between fires can be as often as every year although a 3- or 4-year cycle is usually adequate after the initial fuel-reduction burn.
The initial hazard-reduction burn in a young pine stand requires exacting conditions of wind, humidity, and temperature. Higher wind velocities and cooler temperatures minimize scorch damage. Because cooler temperatures are desired, winter is generally a good time for hazard reduction burns. One reason excessive crown scorch should be avoided is because, under some circumstances, it can add more fuel to the forest floor than the fire consumed. Southern pine plantations averaging 10 to 12 feet in height can be burned by experienced people under the right conditions without damage. Young plantations on industrial lands are often burned for the first time when they are 15 to 20 feet tall using aerial ignition; close spacing of ignition spots (e.g., 2 chains by 2 chains), and cool, damp conditions with some wind are a must to avoid crown damage.
Subsequent fuel reduction burns need not cover the entire area. The objective is to break up fuel continuity. Fuel reduction on 75 to 80 percent of the area is sufficient. An added advantage of "patchy" burns is that the unburned islands provide cover for wildlife. These unburned patches will not have a dangerous accumulation of fuels at the time of the next burn if they resulted from a lack of fuel during the previous fire. If, however, they were too wet to burn, these islands could result in a hot spot the next time if a heading fire was allowed to sweep through them under appreciably drier conditions.
Hazard reduction burns in the Southern Applachians
Though a less serious problem than in Coastal Plain forests, wildfires are still a problem in the Southern Appalachians and are usually difficult to control because they occur during times of extreme fire danger and on steep and varied terrain in remote areas. Moreover, recently harvested stands can carry heavy fuel loadings, ranging up to 50 tons per acre (Sanders and Van Lear 1987 in Van Lear and Waldrop 1988). In unharvested hardwood stands, rhododendron and mountain laurel often form thickets of highly flammable ladder fuels that allow fire to climb into the canopy.
Hazard-reduction burns conducted in mature stands in the southern Appalachians are usually low-intensity winter burns, often set along roads where arson is most common (Van Lear and Waldrop 1988). Studies in the Appalachians of South Carolina have shown that broadcast burning of logging slash under proper weather and fuel-moisture conditions can reduce highly flammable fine woody fuels following clearcutting by over 90 percent (Sanders and Van Lear 1987 in Van Lear and Waldrop 1988). Hardwood stands are generally safe from wildfire until the next leaf fall, and the wildfire threat is small for 3 to 7 years after a hazard reduction burn.
Encyclopedia ID: p575
