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Here in the southern coastal plain there’s often an added complexity to our prescribed burn areas, the green stuff. We’re referring to the dense layer of evergreen shrubs that blanket many of our tracts. Commonly referred to as pocosin fuels, these evergreen shrubs can become highly volatile during late spring or any period of hot weather and extended drought. The most common species are Gallberry, Fetterbush, and Titi (pronounced ty-ty) and have unique chemical compositions that make them flammable. The mature foliage usually has a waxy coating that helps preserve moisture and helps insulate the leaf from radiant heat. The new foliage shoots in the spring however don’t yet have that protection. In addition, these shrubs try so hard to leaf out that they will deplete their own moisture supply, causing a dip in the annual moisture buildup of the plant. These shrubs are also documented to have a significant diurnal fuel moisture change, meaning that the foliage also dips in moisture content during peak burning hours. Given the unique qualities of these pocosin fuels, they really don’t fit in any of our local area fuel models. The closest thing it can be compared to is chaparral, the brushy hillsides seen in California or the Southwest. Spring green up, which is usually a good thing that reduces fire danger, is not the same as pocosin shrub green up, which increases fire danger. These more dangerous periods usually exist through April and May. Soon after the new foliage matures, builds its waxy coating (often referred to as “hardening off”), plant moisture returns, and humid summer weather sets in. Extended drought though can extend these volatile times, exasperating the scenarios where pocosin fuels are combined with organic soils. At times it’s hard to predict if these shrub fuels are going ignite or not. In most cases it’s either all or nothing. On borderline days it often seems like only the ground fuels will carry fire, but when the scale tips it’s like flipping a light switch and the entire shrub layer carries it’s own flaming front. So how do you know? How do you factor this characteristic into your burn planning. Shrub height means a lot, which ties directly to flame length. Timing of the year is critical. Pay attention to the state of the shrub from winter to spring. Is the stem color changing or are new buds present? Ground moisture is a great indicator and saturated soils are even better. Otherwise you just have to take a conservative approach and observe the times and conditions when these fuels begin to influence fire behavior. There are many days where plants like Gallberry and Fetterbush can be burned, and this is likely built into your burn objectives. You just have to know when to stop.
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