Post-fire Treatment Effectiveness for Hillslope Stabilization
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MULCH TREATMENTS
Mulch is material spread over the soil surface to protect it. Because mulching can be effective ground cover immediately after being applied, it is an attractive choice for post-fire hillslope stabilization. It is often used in conjunction with seeding to provide ground cover in critical areas and to increase the success of seeding by improving moisture retention.The mulches used in post-fire treatments are generally divided into two groups based on how they are applied. Wet mulches, usually referred to as hydromulch, are prepared by mixing the components with water to form a slurry that is applied to the soil surface. Dry mulches, such as agricultural straws and wood materials, are applied without water.
The amount of bare soil exposed, or stated conversely, the amount of ground cover, is related to watershed response and to the treatment effectiveness of post-fire hillslope mulching treatments whose basic functional feature is coverage of bare soil. Generally, post-fire mulch treatments need to provide 60 to 80 percent ground cover to reduce hillslope erosion (Napper 2006; Pannkuk and Robichaud 2003). However, Foltz and Wagenbrenner (2010) reported that a 50 percent cover of wood shreds significantly reduced sediment yields nearly as well as did 70 percent cover.
Optimizing the thickness of post-fire mulch is a balance between soil protection and suppression of vegetative recovery and establishment of seeded species (Bautista and others 2009). Thick layers of mulch can prevent sunlight from reaching the soil surface and/or physically obstruct seedling emergence. Beyers and others (2006) reported that none of the studied post-fire treatment mulches (wood chips, hydromulch, and rice straw mulch) increased vegetation cover, and wood chip mulching inhibited vegetation recovery more than other treatments while providing the most total ground cover and greatest reduction in erosion for several years. Debats and others found that 100 percent hydromulch coverage reduced initial plant density on post-fire hillslopes in southern California chaparral. They compared their findings with Hubbert and others who reported no apparent vegetation suppression due to the 51 percent coverage of hydromulch on similarly burned landscapes following the 2003 Cedar Fire in southern California.
Longevity or Durability
The amount of time mulch remains in place on a hillslope will impact treatment effectiveness. Residence time of mulches varies depending on the type, size, and amount of the mulch material applied. Woody mulches are decay resistant wood strands were visible 7 years after application. In contrast, hydromulch generally decays within a few months to a year (Bautista and others 2009). The rapid decay of hydromulch may result in much less ground cover than deemed necessary for hillslope stabilization in the first and second post-fire years.[erosion barrier treatment effectiveness] [dry mulches]
Post-fire Treatment Effectiveness for Hillslope Stabilization
Peter R. Robichaud, Louise E. Ashmun, Bruce D. Sims
USDA Forest Service - RMRS - Moscow Forestry Sciences
Laboratory
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