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Evaluating the effectiveness of wood shred and agricultural straw mulches as a treatment to reduce post-wildfire hillslope erosion in southern British Columbia, Canada
Robichaud, P.R.; Jordan, P.; Lewis, S.A.; Ashmun, L.E.; Covert, S.A.; Brown, R.E. 2013.
Evaluating the effectiveness of wood shred and agricultural straw mulches as a treatment to reduce post-wildfire hillslope erosion in southern British Columbia, Canada.
Geomorphology 197:21–33.
Keywords: Erosion control, Runoff, Burned Area Emergency Response (BAER), Post-fire, Mitigation
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Abstract:
After the 2009 Terrace Mountain fire near Kelowna, BC, Canada, wood shred and agricultural straw mulch effects
on post-fire runoff and sediment yields were compared using three experimental techniques: rainfall
simulations on 1-m2 plots, concentrated flow (rill) simulations on 9-m long plots, and sediment yields from
natural rainfall on 30-m2 plots. All experimental plots were located on and along a planar hillslope burned
at high severity. Experiments were conducted once a year for three consecutive years beginning in Sep
2009, except for the rainfall simulations which only were conducted the first two years. Although results varied
by experiment and time since fire, both agricultural straw and wood shred mulch treatments performed
similarly for reducing runoff and sediment; thus were combined into a single "treated" class for analyses.
The mulch treatments were effective in reducing sediment yields as compared to the controls in all three experiments
in 2009. In the rill simulation experiment, the mulch treatments significantly reduced overland
flow velocity and increased the proportion of overland flow that infiltrated the soil before reaching the plot
outlet. The elapsed time since the fire, which was strongly related to the increase in vegetative ground
cover, was a significant factor for predicting sediment yields in the statistical models. Favorable spring rainfall
in 2010 and 2011 supported rapid regrowth of vegetation, which recovered similarly on all plots regardless of
treatment. The runoff and sediment yields on the treated plots were similar to those measured on the control
plots a year later; we concluded that the mulch was, in effect, a surrogate for a year of recovery. Given that agricultural
straw mulch is an established and effective post-fire hillslope treatment, it was important to find
that wood shred mulch was similarly effective in reducing post-fire runoff and sediment yields. Thus, the
choice of agricultural straw or wood shreds for a post-fire mulch treatment may be based on the performance
characteristics (longevity, potential to carry invasive species seeds, cost, etc.) that best fit the needs of the site.
Moscow FSL publication no. 2013c
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