Frequency of Lightning-caused fires

Ecological and meteorological evidence suggests that lightning-caused fires were a major environmental force shaping the vegetation of the Southeast for millions of years before Indians arrived (Komarek 1965, 1974). Although forests of the southern Appalachians probably did not burn as frequently as the pine-grasslands of the adjacent Piedmont and coastal plains, there is evidence that they did burn periodically. Several authors assert that the frequency of lightening caused fires was sufficient to maintain oak-pine forests in the southern Appalachians, particularly forests composed of pine species dependent upon fire for most of their reproduction (Whittaker 1956, Zoebel 1969, Komarek 1974, Barden and Woods 1976, White and Lloyd 1997). Other authors point out that the mesic, broad-leaved forests of the southern Appalachians are not conducive to large catastrophic fires, and therefore lightning strikes in these forests result in mostly small, low-intensity, down-slope burns (Barden and Woods 1974; Buckner and Turrill 1999).

Lightning strikes cause forest fires by igniting a mixture of volatile extractives and finely divided bark, wood, and needle particles to an intense, short-lived ball of fire which in turn ignites flash fuels in the tree crown or on the forest floor (Taylor 1973). Lightning strikes and subsequent fires are more common on dry, exposed ridges and south facing slopes at higher elevations. Frost (1995) estimated presettlement fire frequency on ridges and upper slopes in the Appalachians was 7-12 years in the lower mountains and >12 years in higher mountains (>3,000 ft). (Buckner and Turrill 1999)

Today, only 12% of wildland fires in the southern Appalachians are caused by lightning; approximately 88% are caused by man. Annually, an average of six lightning fires per one million acres occurs in the Southern Appalachians. This frequency is greater than that recorded for the Great Plains, Mississippi Basin, or northeastern United States, but less than portions of the western and southeastern United States (Schroeder and Buck 1970; SAMAB 1996e).