Linking surface-fire behavior, stem heating, and tissue necrosis

Data from 69 experimental, small-plot fires are used to describe relationships among fire intensity, bark-surface heat flux, and depth of necrosis in stem tissue for red maple (Acer rubrum L.) and chestnut oak (Quercus prinus L.). A tetrazolium staining technique was used to determine the depth of necrosis in tree boles subjected to fires with intensities of 20 to 2000 kW/m. Over a range of bark moistures (28%-83%) and bole diameters (3-20 cm), depth of necrosis appears to be primarily a function of fire intensity, flame residence time at the stem, and the corresponding time-integrated heat flux at the bark surface. Our results, along with known relations between bole diameter and bark thickness, and improved models of fire behavior and heat transfer, may be useful for estimating tree mortality resulting from prescribed fires.