Prescribed fire is an excellent and cost-effective technique for setting back existing vegetation and stimulating fresh growth from the seedbank and from sprouting, which increases the quality and quantity of deer forage and cover. To help ensure a safe and effective burn, read my article on preparing to use prescribed fire, then you’ll be ready to apply the four firing techniques listed here.
There are four main firing techniques commonly used when the goal is a low-intensity prescribed fire for habitat improvement. The recommended firing technique varies with landowner objectives, condition of fuels, topography, and weather. Different firing techniques allow you to adjust fire intensity to the desired level. I will provide a general description here to introduce you to firing techniques that may be used. For additional information, contact your state forestry agency and review more detailed publications on using prescribed fire. One such publication, the USDA’s A Guide For Prescribed Fire in Southern Forests, is available free online.
1. Backing Fire – A backing fire moves against the wind. Thus, it is relatively slow moving and generally consumes fuel more completely than fire moving with or parallel to the wind. Backing fires are set along a firebreak (or other barrier, such as a creek or road) on the downwind side of the area to be burned and allowed to back into the wind. A steady wind speed and direction is important for consistent and predictable burning. Backing fire is less intensive with lower flame heights than other firing techniques. This produces less scorch (if any) when burning oak woods. However, the slower moving fire can have a longer residence time and can possibly damage fine feeder roots of trees if the duff layer below the leaf litter is dry. This is another reason to burn when adequate duff moisture is present. Backing fire should be used when considerable fuels are present, especially vertical fuels (dense shrub layer), as they can elevate fire intensity if a heading fire is used (a fire that burns with the wind), which may damage/kill desirable overstory trees. Backing fire is typically the easiest to implement. Although it takes longer to implement a backing fire, it is the recommended firing technique when burning woods where damage to overstory trees is not desirable.
2. Strip-Heading Fire – A strip-heading fire involves both backing fire and heading fire. A backing fire is first set along a firebreak, then lines of fire are set sequentially upwind of the backing fire and allowed to move into the backing line of fire. The distance of the strip-heading firelines from the backing fireline is set according to the desired level of fire intensity. Normally, the strip-heading fireline is set 50 to 200 feet upwind of the backing fire. Fuel conditions, windspeed, relative humidity, and landowner objectives determine the distance that should be used. A major advantage of strip-heading fires over backing fires is strip-heading fires require much less time, allowing quick ignition and burnout. A major consideration when using strip-heading fires is to create an adequate blackline (at least twice the distance that will be used between the backing fire and the strip-heading fireline) with the initial backing fire prior to setting the first strip-heading fireline. When burning hardwoods, strip-heading fires are applicable when relatively flat fuels are present. Presence of vertical fuels may demand increased use of backing fires.
3. Flanking Fire – Flanking fires are set directly into the wind, allowing the fire to burn at right angles to the wind. Obviously, this can be dangerous if wind direction is inconsistent. Typically, several people are necessary to implement a flanking fire. Coordination is critical so that all the lines of fire are set at the same time and all the burners know where each other are and move at the same speed. Flanking fire is also used to secure the flanks of backing and strip-heading fires along firebreaks. Flanking fire is usually intermediate in intensity between backing and strip-heading fires. Implementation is more difficult, however, as coordination is critical among burners.
4. Point-Source Fires – Point-source fires can be viewed as modified strip-heading fires, where spot ignition is used instead of strip ignition. Spot ignition produces more intensity than the backing fire, but less intensity than strip ignition. This can help speed-up the line-backing fire with less intensity than would be produced with a strip-heading fire. Point-source ignition spots are ignited upwind of the backing fireline. The distance of the point-source ignition spots from the backing fireline are determined just as those in a strip-heading fire. It is important to realize point-source ignition spots are not placed randomly. To safeguard against hot spots, point-source ignition spots should be equidistant along each fireline. If not equidistant, a point-source ignition spot on one fireline may burn between two point-source ignitions spots on the adjacent downwind fireline and produce a heading fire that exceeds desired intensity levels. Firelines may be set by a single burner, or firelines may be set simultaneously by multiple burners. If multiple burners set firelines, it is critical that they are able to communicate (they should be able to see each other and communicate via radio) and are coordinated in setting the firelines.
Remember, until you have experience with prescribed fire, contact your state forestry agency for guidance and direct assistance with conducting the burn. This will ensure a safe, effective burn that accomplishes your habitat goals.