Effects of Understory Burning in a Mesic Mixed-Oak Forest of the Southern Appalachians
Information is lacking on ecosystem effects of understory burning in mesic mixed-oak (Quercus spp.) forests of the southern Appalachians. Native Americans used periodic fires in these forests for driving game and opening the forest. In April 1998, we conducted a low- to moderate-intensity fire in a covehardwood forest in the Nantahala National Forest, western North Carolina. In March 1998, before burning, permanent plots were established along three parallel transects to measure forest floor mass, carbon (C), and nitrogen (N); soil nutrient (NO-3, NH+4, PO-4, Ca, Mg, and K) availability; and vegetation mortality and regeneration. Forest floor material was sampled by components: small wood, litter (Oi), and a combined fermentation and humus component (Oe + Oa). Soil nutrient availability was estimated using cation and anion exchange membrane sheets. Vegetation measurements included the overstory and understory layers. All parameters were resampled during summer 1998 and 1999 in the same manner as the pre-burn inventories. Burning reduced the total mass, carbon, and nitrogen of the Oi layer by 92%, 93%, and 91%, respectively. Reductions in mass, carbon, and nitrogen of the Oe + Oa layer were 48%, 46%, and 56%, respectively. Burning resulted in increased exchangeable K, Ca, Mg, NH4, PO4, and NO3 availability in soil on the burned area compared with the control. One year after burning, there were no significant differences in exchangeable nutrients between the burned and the control area. Overstory mortality was substantial, with 55% of the trees killed by the fire. However, most of the mortality occurred in trees <10 cm diameter at breast height (DBH) and no trees >20 cm DBH were killed. In the understory, all the aboveground stems were killed; although 50% of these individuals sprouted during the growing season (July 1998), some of these sprouts did not survive through the following year (July 1999). Moderate-intensity understory burning may be a useful tool to restore mesic mixed-oak communities in the southern Appalachians. Reintroduction of fire into these ecosystems may be beneficial by increasing soil nutrient availability, promoting regeneration and survival of Quercus spp., increasing diversity of understory species, and reducing abundance of shade-tolerant and fire-intolerant species such as Acer rubrum.