Post fire seeding

Wildfires consume live and dead fuels, destabilize physical and ecological landscapes, and impact human social and economic systems.Post-fire seeding was initially used to stabilize soils. More recently it is being used to recover post wildfire plant species, manage invasive non-native plant populations and establish valued vegetation compositions.

Post fire seeding evolved from a desire to stabilize hillslope soils in hilly terrain after a wildfire and prevent downstream flooding and debris/mud flows. The assumption being supplemental seeding immediately after a wildfire would provide vegetation cover lost in the wildfire. Some of the earliest seedings were in Southern California after wildfires burned through fire prone foothills and alluvial fans developed with homes. Although recent studies confirm that the probability of flooding and debris/mud flows significantly increase following a wildfire and that rainfall intensity, burn severity and ground cover reduction accounts for most hillside erosion, post fire seeding is not the most effective treatment.

A review of 37 publications and 25 monitoring reports on soil stabilization seeding discovered that less than half showed any reduced sediment movement with seeding. Seeding was not found to be effective in increasing cover or reducing sediment yields on burned areas in the Colorado Front Range compared to controls, even for storms with return periods of less than one year. A comparison of commonly used soil stabilization treatments found that wood and straw mulch reduced water erosion rates by 60 to 80%, contour-felled log erosion barriers 50 to 70%, hydromulch 19% and grass seeding had little effect the first year during low intensity rainfall events and all were relatively ineffective in high intensity rainfall events. Vegetation cover from supplemental seeding was not significantly different from natural vegetation recovery.

In arid communities post fire seeding is attempted to reduce wind erosion and deposition. There is little objective evidence that supplemental seeding is any better than natural vegetation recovery from the post fire seedbank. After the Railroad Fire in Utah, neither seeded (drilled or aerial) or unseeded areas showed significant signs of wind erosion or deposition as evidenced by little difference (<2mm) in the height of washers on erosion measurement stakes. Soil wind erosion was observed to have been moderated to some degree after the Command 24 Fire in Washington by natural site recovery alone.

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