Coarse and volatile fuels cause problems when located too close to firebreaks, also called fireguards, during prescribed or controlled burns. Coarse fuels are woody materials that burn for a relatively long time, such as brush piles, snags (dead standing trees), logs or stumps. In the context of prescribed burning, volatile fuels are vegetative materials containing oils, resins, waxes or terpenes that cause them to burn more intensely and typically throw up more embers than similar-sized nonvolatile fuels. Examples of volatile fuels include junipers (also called cedars), pines, briers and weeping lovegrass.
Leaving coarse fuels or relatively tall volatile fuels close to firebreaks is one of the most common mistakes made during site preparations for prescribed fires. During a prescribed fire, a burn crew wants the fire to burn away from a firebreak relatively quickly and all burning materials near the firebreak to completely extinguish so the crew can move on to complete the burn. Coarse fuels can burn for hours or days, requiring extra labor to monitor or extinguish them when located close to firebreaks. If not monitored or extinguished, burning coarse fuels and tall volatile fuels, such as juniper trees or brier thickets, located close to firebreaks can start spot fires that become wildfires via embers blown across a firebreak.
Part of prescribed burn preparation involves examining the perimeter of a burn unit for coarse and relatively tall volatile fuels near firebreaks and moving them well into the burn unit or out of the burn unit. A common mistake when using a bulldozer to prepare firebreaks through wooded vegetation is leaving brush piles along firebreaks. Cleared brush should be pushed well into or out of a burn unit, preferably at least 50 yards into a burn unit so it can safely burn up during a prescribed fire.
When using a plow, mower, rake, blower or grader to prepare firebreaks, another common mistake is leaving piles of grass, leaves or mixtures of soil and vegetation along the inside edge of a burn unit. Piled or packed fine fuels, such as hay or piles of grass or leaves, cause problems similar to coarse fuels. During the preparation process, fine fuel should be moved off a firebreak away from a burn unit or moved a considerable distance inside the burn unit away from the firebreak.
Trees such as junipers or pines can be cut down and moved away from firebreaks. When planning a relatively low intensity fire, lower limbs and ladder fuels (e.g., greenbrier or tall grass) can be removed from the bottoms of such trees within 8 to 10 feet of the ground to prevent the fire from igniting the canopies. Most people choose to cut down Eastern red-cedar near firebreaks because its overabundance is a problem. Greenbrier thickets near fireguards can be cut down with a mower. The resulting brier thatch lying on the ground usually does not cause problems near firebreaks.
For help planning a prescribed burn, contact someone with extensive prescribed burning experience and training. Such individuals usually have expertise in range, wildlife or forestry, and work at places such as Noble Research Institute, state extension offices, Natural Resources Conservation Service, state or federal forestry services, state wildlife agencies, U.S. Fish and Wildlife Service, The Nature Conservancy, or private consulting firms.