Effects of fire and emergency seeding on hillslope erosion in southern California chaparral

Abstract

Catastrophic wildfires can set the stage for massive postfire erosion and sedimentation in southern California chaparral ecosystems with the onset of heavy winter rainstorms. As a mitigation measure, land managers have typically used grass seeding as a standard emergency rehabilitation technique. However, the effectiveness of grass seeding as a watershed protection practice remains uncertain. To address this problem, we conducted field experiments on southern California chaparral-covered hillsides involving burning and seeding to quantify the magnitude of postfire hillslope erosion and the effect of annual ryegrass (Lolium multiflorum) for erosion control. After fires in chaparral, there is a dramatic increase in both dry season and wet season sediment production, resulting in hillslope erosion up to 100 times greater than prefire amounts. Hillslope erosion generally takes 2 to 4 years to return to prefire levels, after which it may actually dip below the baseline. After a wildfire, the erosion response of a recently burned site was similar to that after the original prescribed fire, but lower in amplitude than a previously unburned companion site. Seeding with annual ryegrass may reduce postfire hillslope erosion on some sites in southern California chaparral ecosystems, but only after erosion has dropped to baseline levels.

Citation

Wohlgemuth, P.M.; Beyers, J.L.; Wakeman, C.D.; Conard, S.G. 2002. Effects of fire and emergency seeding on hillslope erosion in southern California chaparral. Association for Fire Ecology Miscellaneous Publication No. 1: 279-285.