Closing the wildland fire heat budget involves characterising the heat source and energy dissipation across the range of variability in fuels and fire behaviour. Meeting this challenge will lay the foundation for predicting direct ecological effects of fires and fire–atmosphere coupling. In this paper, we focus on the relationships between the fire radiation field, as measured from the zenith, fuel consumption and the behaviour of spreading flame fronts. Experiments were conducted in 8 × 8-m outdoor plots using preconditioned wildland fuels characteristic of mixed-oak forests of the eastern United States. Using dual-band radiometers with a field of view of ~18.5 m2 at a height of 4.2 m, we found a near-linear increase in fire radiative energy density over a range of fuel consumption between 0.15 and 3.25 kg m–2. Using an integrated heat budget, we estimate that the fraction of total theoretical combustion energy density radiated from the plot averaged 0.17, the fraction of latent energy transported in the plume averaged 0.08, and the fraction accounted for by the combination of fire convective energy transport and soil heating averaged 0.72. Future work will require, at minimum, instantaneous and time-integrated estimates of energy transported by radiation, convection and soil heating across a range of fuels.
Data from 69 experimental, small-plot fires are used to describe relationships among fire intensity, barksurface 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.Résumé : Les données provenant de 69 petites parcelles brûlées à des fins expérimentales sont utilisées pour décrire les relations entre l'intensité du feu, le flux de chaleur à la surface de l'écorce et la profondeur de la nécrose dans les tissus du tronc de l'érable rouge (Acer rubrum L.) et du chêne des montagnes (Quercus prinus L.). Une technique de coloration au tétrazolium a été utilisée pour déterminer la profondeur de la nécrose dans le tronc des arbres exposés à des feux dont l'intensité variait de 20 à 2000 kW/m. Pour une gamme de teneurs en humidité (28 % -83 %) et de diamètres du tronc (3-20 cm), la profondeur de la nécrose semble principalement fonction de l'intensité du feu, du temps de résidence des flammes sur le tronc et du flux de chaleur pour la durée correspondante à la surface de l'écorce. Les résultats combinés aux relations connues entre le diamètre du tronc et l'épaisseur de l'écorce, ainsi que de meilleurs modèles du comportement du feu et des transferts de chaleur, peuvent être utiles pour estimer la mortalité des arbres à la suite de brûlages dirigés.[Traduit par la Rédaction] Bova and Dickinson 822
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