Hillslope erosion two and three years after wildfire, skyline salvage logging, and site preparation in southern Oregon, USA

Abstract

Harvest of dead timber following wildfire is contentious because of a perception that the benefits are outweighed by environmental costs. One primary concern is the potential for increased erosion susceptibility associated with timber extraction (i.e. salvage logging) and site preparation. We measured erosion at the Timbered Rock Fire in southwestern Oregon on replicated sites that were either salvage logged on private land or non-salvage logged on adjacent public lands. Sediment was collected from silt fences placed in locations with relatively uniform hillslope surface conditions beginning in 2004 (2years post fire) for a period of two years. Mean erosion was 0.02 and 0.05Mgha−1yr−1 for 2004–05, and 0.04 and 0.14Mgha−1yr−1 for 2005–06, for non-salvage and salvage-logged areas, respectively. Vegetation cover was much lower in the salvage-logged areas (5–20%) than the non-salvage areas (70–80%), and was negatively correlated with erosion in the first year of measurement (r=−0.58, p=0.02). Increased erosion at salvage-logged plots is most likely associated with competing vegetation control and slash removal, but may have also been caused by some other management factor or preexisting condition that differed between measurement locations on private and public land. Increased erosion in the second year of measurement at all sites was associated with increased rainfall and storm frequency. Although control of competing vegetation may be critical for successful tree establishment following wildfire, our results suggest that site preparation techniques which inhibit growth of vegetation may contribute to increased hillslope erosion in high-risk areas, especially when increased rainfall and storms occur.