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Abstract
Fire is a major disturbance event in southwestern ecosystems. A prescribed burn in the San Dimas Experimental Forest provided an opportunity to quantify the effects of fire on soil hydrologic properties and sediment fluxes in chaparral-covered steeplands. Located in the San Gabriel Mountains about 50 km northeast of Los Angeles, a 1.28 ha watershed was instrumented with hillslope sediment collectors and a debris basin. Sediment fluxes were measured for seven years prior to the fire and through the first post-fire winter. Soil samples taken just before and after the fire were analyzed for bulk density, texture, and moisture content. Soil non-wettability was determined pre- and post-fire at the same 105 locations using the water drop penetration test. Post-fire soils were denser, coarser, and much drier than prior to the burn. Although extremely variable, non-wettability generally increased after the fire. Post-fire hillslope erosion was twice as great as pre-burn levels during the dry season and increased by 10-fold in the wet season, despite a record drought year. Post-fire sediment yield was 20 times greater than the unburned annual average. We believe the fire-induced changes in soil properties coupled with reduced ground cover caused an increase in surface runoff that accounts for the large increases in post-fire sediment fluxes.
Parent Publication
Citation
Wohlgemuth, P. M.; Hubbert, K. R. 2008. The effects of fire on soil hydrologic properties and sediment fluxes in chaparral steeplands, southern California. In: Narog, Marcia G., tech. coord. 2008. Proceedings of the 2002 Fire Conference: Managing fire and fuels in the remaining wildlands and open spaces of the Southwestern United States. Gen. Tech. Rep. PSW-GTR-189. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. p. 115-121.
