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Post-fire mulching for runoff and erosion mitigation; Part I: effectiveness at reducing hillslope erosion rates

Author(s): Peter R. Robichaud, Sarah A. Lewis, Joseph W. Wagenbrenner, Louise E. Ashmun, Robert E. Brown
Year Published: 2013

Mulch treatments often are used to mitigate post-fire increases in runoff and erosion rates but the comparative effectiveness of various mulches is not well established. The ability of mulch treatments to reduce sediment yields from natural rainfall and resulting overland flow was measured using hillslope plots on areas burned at high severity following four wildfires in the western United States. Wheat straw mulch, wood strand mulch, and hydromulch were evaluated along with untreated control plots on multiple fires for 4 to 7 years after burning. Needle cast from fire-killed conifer trees was evaluated in an area of moderate burn severity at one fire, and seeding with genetically native seed was tested, with and without hydromulch, at another fire. Rainfall, ground cover, and soil water repellency were measured in each treatment site at all 4 fires.Mean sediment yields on the control plots ranged from 0.3 to 7.5 Mg ha-1 in the first post-fire year, from 0.03 to 0.6 Mg ha-1 in the second, and from 0 to 0.4 Mg ha-1 in the third and fourth post-fire years. Assuming a linear fit between sediment yield and rainfall intensity, storms with equivalent rainfall intensities produced nearly an order ofmagnitude less sediment on the control plots in the second post-fire year as compared to the first post-fire year. Large storms (at least a 2-year return period, 10-min maximum rainfall intensity) produced sediment on all fires in all years where they occurred; however, sediment yields produced by large storms that occurred in the first post-fire year were larger than the sediment yields from equivalent storms that occurred in later years at the same fire. Sediment yields decreased as ground cover increased and all the mulch treatments increased total ground cover to more than 60% immediately after application. However, the longevity of the mulches varied, so that the contribution of the treatment mulch to total ground cover varied by mulch type over time. The wood strand mulch was the most long-lived of the mulch treatments and was observed in ground cover assessments throughout the study period (4 and 7 years) at two fires. The wheat straw mulch decreased nearly twice as fast as the wood strand mulch, and no hydromulch was detected after the first post-fire year on either fire where it was tested.

Citation: Robichaud, Peter R.; Lewis, Sarah A.; Wagenbrenner, Joseph W.; Ashmun, Louise E.; Brown, Robert E. 2013. Post-fire mulching for runoff and erosion mitigation; Part I: effectiveness at reducing hillslope erosion rates. Catena. 105: 75-92.
Topic(s): Management Approaches, Post-fire Management, Burned Area Emergency Rehabilitation
Ecosystem(s): Montane wet mixed-conifer forest, Montane dry mixed-conifer forest
Document Type: Book or Chapter or Journal Article
NRFSN number: 11994
FRAMES RCS number: 15199
Record updated: Apr 6, 2015