BOX 10.1 Prescribed Burning for Understory Restoration

Role of Prescribed Burning. Because the longleaf ecosystem evolved with and is adapted to frequent fire, every 2 to 8 years, prescribed burning is often useful for restoring understory communities to a diverse ground layer of grasses, herbs, and small shrubs. This restoration provides habitat for a number of plant and animal species that are restricted to or found mostly in longleaf pine communities. Burning can also be used to reduce the midstory layer, which catches shed needles and serves as a ladder to carry understory fires into the crowns of the trees resulting in catastrophic wildfires that can kill vast areas of pines. Prescribed burning also recycles nutrients by releasing those tied up in litter and duff and significantly reduces brown spot needle blight, which attacks longleaf seedlings. Terms and Techniques. Prescribed burning is the application of fire by trained professionals following a well-developed plan to obtain desired management objectives. Restoration is often done with understory burning or underburning, which is prescribed burning under a forest canopy (McPherson et al. 1990). The fuel for these fires is the understory rough that consists of the accumulated living and dead grasses, forbs and shrubs plus draped needles and the litter layer. The litter layer, the top layer of the forest floor, is composed of recently fallen and largely intact dead needles, leaves, twigs, and branches. A duff layer, composed of partially decomposed litter or fermentation layer and decomposed humus, lies between the litter and mineral soil. Underburning can be done using heading, backing, flanking, or spot fires, or a combination of these techniques. Heading fires are fire fronts ignited to spread with the wind while backing fires are ignited so the fire front spreads against the wind. Flanking fires are ignited in a line into the wind and thus spread at approximately right angles to wind direction. Spot fires are a series of separate ignition points that are allowed to spread in all directions and thus contain heading, backing, and flanking fires at each spot. Both heading and backing fires can be set as a series of strip fires. Strip heading fires are used to control how fast the fire spreads and thereby the fireline intensity, i.e., the rate of heat energy release (Box A Fig. 1). Placing strips closer together reduces the rate of spread and intensity. Backing fires have low intensities but move slowly and therefore require a lot of time to burn each unit. In addition, backing fires under certain conditions may be quite severe, i.e., cause much of damage to the site, because of excess duff consumption. Internal firebreaks can be constructed for strip backing fires to significantly reduce time to complete the burn. An alternative is to use flanking or spot fires to reduce intensity but speed up the burn without internal fire breaks. These techniques require considerable experience, especially spot firing as you must continually adjust both the spacing and the timing between spots to obtain the desired intensity with changing fuel and weather conditions (Wade and Lunsford 1989).