HR: 08:30h
AN: H51M-03    [Abstracts]
TI: Post-fire Erosion and Recovery in Chaparral Steeplands, Southern California
AU: * Wohlgemuth, P M
EM: pwohlgemuth@fs.fed.us
AF: USDA Forest Service, 4955 Canyon Crest Drive, Riverside, CA 92507, United States
AB: In fire-prone southern California chaparral environments, wildfire is a significant disturbance event. It incinerates vegetation, alters soil properties, and renders the landscape susceptible to the agents of erosion. Accelerated erosion can cause site degradation, can extirpate refugia populations of endangered species, and can harm human communities at the wildland/urban interface. The San Dimas Experimental Forest (SDEF) is a nearly 7000 ha research preserve located in the San Gabriel Mountains. Native vegetation in the SDEF consists primarily of mixed chaparral. Management treatments following a wildfire in 1960 involved the vegetation type-conversion of some native chaparral watersheds to a mixture of perennial grasses. In 1994, a study was initiated to quantify sediment fluxes through several small (1-3 ha) headwater catchments in the SDEF under both brush and grass vegetation. Several of these watersheds burned in a prescribed fire in May 2001. The remainder burned in a wildfire in September 2002. These burns provided a unique opportunity to quantify post-fire erosion on the same sites for which there were extensive pre- fire measurements. Hillslope erosion was sampled using sheet metal collector traps with a 30 cm aperture. Seventy-five traps were placed on unbounded plots scattered throughout each of four watersheds. Sediment yield was measured behind earthen dams in 17 small watersheds. A centrally located raingage recorded precipitation amounts and intensities. During this study period, the SDEF experienced both the wettest (2005) and driest (2007) years in its 74-year history. The values for the 15-minute maximum rainfall intensity show no relation to annual erosion (hillslope or small watershed) for either vegetation type before or after fire. Both hillslope erosion and small watershed sediment yield display remarkably similar patterns of post-fire erosion response: a one to two order of magnitude increase in first-year erosion followed by a relatively rapid recovery (2-3 years) to baseline levels. Post-fire erosion was very similar whether the watersheds burned in a prescribed fire or a wildfire. Although rainfall is a necessary driver, post-burn erosion is governed more by the fire-induced increased landscape sensitivity to the agents of erosion.
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting