Crown-Fire Potential in a Sequoia Forest After Prescribed Burning
Prescribed burning in a giant sequoia-mixed conifer forest reduced the potential for high intensity surface fires and crown fires. Based on three burned plots and three control plots, fuels on the ground were reduced from 203.5 to 30.1 tonnes/ha, while live crown fuels were reduced from 18.0 to 7.8 tonnes/ha. The lowest segment of the forest crown having more than 45.4 kg of fuel per 30.5 cm per 0.4 ha increased from about 0.9 to 4.9 m. Fuel complex porosity for the unburned plots indicates little chance of a sweeping crown fire independent of a surface fire, but heavy ground fuels can support a fire of intensity sufficient to burn individual tree crowns. Under preburn fuel and severe weather conditions, a wildland fire spread model predicted a forward rate of spread of 3.8 cm/sec for a ground fire and a reaction intensity of 28.8 cal/cm²/sec. After prescribed burning, the same model predicted a spread rate of 0.05 cm/sec and a reaction intensity of 0.25 cal/cm²/sec. Surface fuels accumulate again rapidly. The longer term impact of prescribed burning was killing smaller trees and the lower levels of live crowns in larger trees, thus removing fuel from the intermediate layer between surface and crown fuels. Forest Sci. 21:83-87.
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