Effects of hydromulch on post-fire erosion and plant recovery in chaparral shrublands of southern California

Following the Cedar Fire (one of seven large wildfires that burned in southern California during the autumn of 2003), aerial hydromulch was applied at 50 and 100% cover to reduce hillslope erosion in chaparral shrublands. Our objectives were to determine the effectiveness of hydromulch in preventing erosion, and to see if plant recovery was hindered by treatment. We installed 54 silt fences to measure sediment production. Five 1-m(2) grids were placed behind each fence to measure plant recovery. Hydromulch was effective in reducing erosion immediately after the fire; however, its benefits appeared to be limited to the first 2-4 months following fire, raising doubts as to its overall cost-effectiveness. The rapid breakdown of the hydromulch during the first 6 months after the wildfire provided little hillslope protection during the above-average October 2004 storm events. During the October events, both rainfall amount and storm intensity played a role in the magnitude of sediment production. Hydromulch did not affect post-fire plant recovery, with plant cover measuring>60% at all sites less than 2 years following the wildfire. Accelerated growth of chamise and forbs was likely due to hydromulch prolonging soil moisture retention. Large accumulations of dead litter following die-off of the herbaceous species could increase dry fuels, thus promoting wildfire and therefore shortening the fire return interval.