METHODS FOR QUANTIFYING FIRE SEVERITY IN SHRUBLAND-FIRES

Methods are presented to relate temperature-residence-time at the soil surface, i.e., time above 150 degrees C as an estimation of the sever ity of a fire,, with measurements made during an experimental fire or on two past hoc measurements. The experiment was carried out in a shru bland dominated by the woody-legume Cytisus striatus subsp. eriocarpus , in Central Spain. Temperature-sensitive paints, and steam-releasing open-calorimeters were used as fire-meters during the burn. Post hoc m easurements used were estimations of heat output per unit area, and me asurements of the minimum diameter of branches of Cytisus remaining af ter the fire. Time above 150 degrees C was obtained from measurements made with thermocouples placed at the soil surface in 20 contiguous 1 x 1 m squares of the burn plot. All other measurements were made at ea ch 1 x 1 m in the 22 x 3 m rectangle surrounding, and including, the t hermocouple squares. Various simple and multiple regression models wer e constructed to predict time above 150 degrees C from each of the fou r measurements made during or after the fire. Maximum coefficients of determination obtained for regressions were 0.61 and 0.62 for water ma ss loss from open-calorimeters and branch diameter, respectively. Usin g all the variables in a multiple regression model, time above 150 deg rees C was related to water mass loss from open-calorimeters and heat output per unit area with a coefficient of determination of 0.77. It i s concluded that estimations of time above 150 degrees C at the soil s urface during the passage of fire may be possible based on simple devi ces, such as open-calorimeters, or on biological indicators, such as m inimum branch diameters. Additionally, combining two methods (open-cal orimeters, estimations of heat output per unit area) may allow the rec onstruction of the time above 150 degrees C during the fire at a scale of 1 m(2), an important characteristic of a burn to understand ecosys tem response to fire.