Bark Char Height

Bark char height is the height from ground level to the highest point on the bole where bark char is evident (outer bark blackened by fire). Char height on individual trees is measured halfway between the upper and lower char heights on opposite sides of the tree. Bark char height is used to approximate flame height or flame length, particularly when measuring these variables during the course of a fire is impractical or impossible. Flame length estimated from bark char height can then be used to reconstruct fireline intensity using Byrams equation (e.g., Waldrop and Van Lear 1984). However, evidence suggests bark char height is not a reliable estimate of flame height, flame length, or indirectly, fireline intensity. For example, Cain (1984) found that for both back fires and head fires in a 9-year-old loblolly-shortleaf pine stand, bark char height underestimated flame length by 50 percent and fireline intensity by 75 percent during prescribed burns. Cain noted, however, that bark char height may provide adequate post-burn measures of relative, but not absolute, fire intensity where better measurements are not possible. In fact, Cain found that crown scorch height estimated fire intensity no better than bark char height.

Bark char height has also been use to predict fire damage. For example, Waldrop and Van Lear (1984) found a direct relationship between bark char height and crown scorch above a threshold value of 3 feet in a loblolly pine plantation. However, since bark char is not a very reliable indicator, it should only be used in cases where attempts are made to reconstruct fire behavior months after the scorched foliage has fallen (Wade and Johansen 1986). The accuracy of bark char height is particularly questionable in previously burned stands because sloughing of charred bark sometimes requires several years (Cain 1984).