Overstory tree mortality and wounding after thinning and prescribed fire in mixed pine-hardwood stands
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The William B. Bankhead National Forest in northcentral Alabama is using active management to shift mixed Quercus-Pinus forests toward forests more dominated by upland hardwoods. We studied the impact of three levels of thinning (none, light thin, and heavy thin) and three levels of prescribed fire (none, infrequent fire, and frequent fire) and all combinations in a factorial experimental design to assess overstory (trees >5.5 inches d.b.h.) mortality. All burns were conducted during the dormant season. In all 36 treatment stands, we surveyed five permanent vegetation plots before treatments were initiated and in each subsequent growing season postburn. Overstory stem density was reduced primarily through the thinning operations, and little mortality was detected. Mortality was significantly greater for unthinned stands, regardless of burning regime, compared to the thinned treatments. Although basal wounding from logging may increase susceptibility to fire damage and mortality, the trees that initially died (after thinning and one fire) did not have bole wounds. Thinning with frequent fire resulted in the greatest number of trees with bole wounds, however, trees that died in these treatments did not have any discernable bole wounds.