Compaction and cover effects on runoff and erosion in post-fire salvage
logged areas in the Valley wildfire, California
Abstract
Runoff and erosion can increase after wildfires, but little is known
about the effects of wildfire plus post-fire salvage logging, or
mitigating these effects. Past research has identified soil compaction
and reduced surface cover as controls on runoff and erosion, but the
relative contributions of these changes are not clear. Two years after
high severity burning by the 2015 Valley Fire in California, replicated
rainfall simulations were carried out in four soil conditions across
compaction and cover factors: uncompacted/compacted by logging machinery
and bare soil/60% wood slash-cover. Runoff after 71 mm of rainfall
totaled 27 mm in the uncompacted bare plots and 39 mm in the compacted
bare plots. Runoff in the slash-covered plots decreased by 50% and 33%
as compared to the uncompacted and compacted bare plots, respectively,
although none of the differences in runoff were significant. Rainsplash
averaged 30 g for the bare plots, regardless of compaction, and
decreased significantly by 70% on slash-covered plots. Sediment yield
totaled 460 and 818 g m-2 for the uncompacted and compacted bare plots,
respectively, and slash significantly reduced these amounts by 72% and
69%, respectively. Our results showed that post-fire soil erosion in
high severity burned unlogged areas was still very high two years after
the wildfire. The combination of wildfire and salvage logging doubled
soil erosion by increases in both runoff amount and sediment
concentration. Antecedent soil moisture (dry or wet) was the dominant
factor for runoff, while surface cover was the dominant factor for
erosion and sediment delivery. Covering the soil with slash reduced both
runoff and erosion, suggesting this treatment would reduce long‐term
sediment delivery from burned areas and skid trails. Saturated hydraulic
conductivity (Ks) and interrill erodibility (Ki) calculated from these
simulations confirmed previous research and will support modeling
efforts related to wildfire and post-fire salvage logging.