Contradictory Evidence

Studies of effects of single fires on composition of mixed stands have produced varied results. McGee (1979) found that single spring and fall burns in small sapling-sized mixed hardwood stands in northern Alabama had little effect on species composition other than to increase relative dominance of red maple and the number of multiple stem oak clumps. However, a single intense wildfire in a young mixed hardwood stand in West Virginia shifted species composition to a predominately oak stand (Carvell and Maxey 1969, Van Lear and Watt 1993)

Several studies of prescribed burns have shown little or no increase in oak seedling establishment after the burn. In several cases, the fire resulted in a great influx of other species or resprouting of competitors as multiple-stemmed clumps (Sims 1932, Johnson 1974, McGee 1979, Nyland and others 1982, Wendel and Smith 1986, Merritt and Pope 1991). Others have produced evidence that burning can substantially increase oak numbers (Keetch 1944, Carvell and Tryon 1961, Carvell and Maxey 1969, Niering and others 1970, Thor and Nichols 1973, Little 1973, Lorimer 1993).

There may be several reasons for these discrepancies. Many of the studies reporting discouraging results are based on short-term observations (2 years or less) after single, low-intensity prescribed burns on good sites. If a good acorn crop doesnt occur during this period, a substantial improvement in oak seedling establishment is not likely. A single burn often will not accomplish much, and may even be counterproductive on mesic sites, where it may simply aid the establishment of competing vegetation. A number of researchers have suggested that repeated burning over a period of time may be necessary (Van Lear and Waldrop 1988, Loftis 1990, Johnson 1992).  As Komarek (1974) once commented in relation to southern pine: "All too often investigators in the past have expected miraculous results with one light burn after years of fire exclusion." Nearly all of the studies reporting increases in oak seedling establishment involved several burns. Unfortunately, however, most of the reported successes with fire have occurred on dry sites. Clearly, we need more evidence on the long-term effects of repeated burns on mesic sites (Lorimer 1993).