Fire Ecology, 2008
Volume 4, Issue 1
Measuring the Rate of Spread of Chaparral Prescribed Fires in Northern California
Authors: Scott L. Stephens, David R. Weise, Danny L. Fry, Robert J. Keiffer, James Dawson, Eunmo Koo, Jennifer Potts, and Patrick J. Pagni
Prescribed fire is a common method used to produce desired ecological effects in chaparral by mimicking the natural role of fire. Since prescribed fires are usually conducted in moderate fuel and weather conditions, models that accurately predict fire behavior and effects under these scenarios are important for management. In this study, explosive audio devices and steel stakes were used to record the location of the flaming front during seven prescribed fires in mature, chamise (Adenostoma fasciculatum) dominated chaparral in northern California. Intervals between detonations measured the time required for five fires to transverse a fixed distance and were used to estimate the rate of spread (ROS) during headfire burning conditions. In two other fires, a stopwatch was used to measure the time required to travel successive 5 m distances and ROS was calculated. Burns were completed during moderate weather conditions: average temperature 17 ˚C, average relative humidity 42 %, and wind light and variable, generally from the west ranging from 0 km h-1 to 8 km h-1. Average percent moisture was 92.1 % for chamise live one-hour fuels, and 8.8 % for chamise dead one-hour fuels. Live fuel height averaged 1.2 m. Overall average ROS was 0.36 m s-1 (range 0.22 m s-1 to 0.56 m s-1) for areas where the flaming front advanced upslope. Measurements of ROS were indeterminable for many of the points along the line transects due to lack of visibility from smoke and from fire not traversing the terrain as predicted. For comparison, BehavePlus fire modeling was performed using five different shrub fuel models (NFFL 4, SH5, SH7, SCAL15, SCAL17); all models underestimated ROS and flame length with NFFL model 4 producing values most similar to that recorded during the prescribed fires. Users of the recently developed fuel models may benefit from field studies to verify model adequacy and fire behavior predictions.