Effects of Fire on Hardwoods Other Than Oak

Hardwood species other than oak possess several fire-adapted characteristics. For example, some hardwoods develop exceptionally thick bark upon maturity. Mature yellow-poplar becomes very fire-resistant when its bark thickness exceeds 0.5 inch (Nelson and others 1933). On the coastal plain, many hardwood stems over 6 inches d.b.h. survived after 30 years of low-intensity annual and biennial burning (Waldrop and others 1987) with little or no damage to boles. In the southern Appalachians, bark thickness is not as critical to hardwood survival because fires normally burn in light fuels and are of low intensity (Komarek 1974). Among exceptions, however, are understories of mountain laurel which "explode" and produce high-intensity fires in hardwood stands. In general, most hardwood species have thinner bark than either pines or oaks and therefore are less resistant to fire damage (Van Lear and Waldrop 1988).

Hardwood species sprout from the base of the stem or from root suckers when their tops are killed by fire. Suppressed buds at or below ground level often survive the heat of a surface fire and sprout in response to the loss of apical dominance. Fire thus promotes good-quality sprouts by forcing them to develop from the ground line or below, resulting in stems that tend to be free of rot and well anchored (Roth and Hepting 1943, Roth and Sleeth 1939). Although some studies show that fire does little to change species composition of young coppice stands (Augspurger and others 1987, Waldrop and others 1985), sprouts of different hardwood species show differential growth and mortality after fire. For example, oak sprouts often have greater growth rates after fire than red maple sprouts (Curbs 1959, Grimm 1984, Hengst and Dawson 1994, Huddle and Pallardy 1996, Huddle and Pallardy 1999). For this reason, fires have been used to give oaks competitive advantage over red maple and other hardwood species.

Many hardwood species have light, wind-dispersed seeds, which can be disseminated over large areas. These light-seeded species often pioneer on burned seedbeds. Some species, such as yellow-poplar, produce seeds that remain viable for years in the duff. Yellow-poplar seeds stored in the lower duff germinate rapidly after low-intensity prescribed fires (Shearin and others 1972, Van Lear and Waldrop 1988).