Post-fire Treatment Effectiveness for Hillslope Stabilization
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Introduction
Wildfires continue to be a major land management concern in the United States and throughout the world. The number and severity of wildfires in the United States has increased during the past decade (National Interagency Fire Center webpage) and the rise is likely to continue, especially in the western U.S., where drought and other effects of climate change are exacerbating wildfire conditions (Brown and others 2004, Flannigan and others 2000, Miller and others 2009, Westerling and others 2006). At the same time, the number of people living in the wildland-urban interface continues to grow, putting human life and safety, infrastructure, homes, buildings, and natural areas that support livelihoods (grazing, timber, etc.) at risk from wildfire and secondary fire effects such as increased runoff, flooding, erosion, and debris flows (Stewart and others 2003). Mitigating these fire effects has resulted in increasing use of post-fire treatments (Robichaud and others 2000; Robichaud 2005; Robichaud and Rhee, in preparation).Realistic and verifiable assessments of post-fire treatment effectiveness are essential if post-fire assessment teams are to choose treatments that balance protection of public safety and values-at-risk with justifiable, cost-effective expenditures of public funds (Government Accountability Office 2003, 2006). Managers also need to know how and why treatments work so they can determine the best treatment(s) for a specific location and decide how to adapt treatments to improve their effectiveness. For example, the formulation and application rate of mulches can be modified to enhance specific qualities, such as longevity, adherence to soil, interlocking of mulch strands, etc. Burned Area Emergency Response (BAER) teams and Emergency Stabilization and Rehabilitation (ESR) teams may vary treatment components and implementation processes (for example, mulch type and formulation, seed content, application rate) in response to the specific climate, soil, vegetation, and topography of the treatment area. Consequently, this synthesis of post-fire hillslope treatment effectiveness will examine treatment characteristics as they relate to the treatment performance, as well as the effectiveness of various treatments for emergency hillslope stabilization.
Post-fire Treatment Effectiveness and Treatment Performance
For the purposes of this synthesis, we have differentiated "treatment effectiveness" from "treatment performance." Treatment effectiveness will be used to describe how well a treatment meets emergency stabilization objectives. For example, if straw mulch were applied to burned hillslopes to reduce the peak flow rates and sediment yields, the treatment effectiveness would be the reduction in those two variables that could be ascribed to the treatment. To make that determination, measured peak flow rates and sediment yields from equivalent treated and untreated areas would be compared (Robichaud 2005). Differences between the treated and untreated areas are generally expressed in percent difference (%) and often described as the "percent reduction due to treatment." In contrast, treatment performance characteristics are related to the materials used in the treatment (rice straw, wheat straw, average length of wood strands), installation features (percent cover, depth of straw), and changes over time (movement by wind, decay rate). The treatment performance characteristics can affect treatment effectiveness, which is why they are assessed and monitored in addition to treatment effectiveness. However, emergency hillslope treatment effectiveness information (generally, reduction in runoff, peak flows, and/or sediment yields) can be difficult to interpret when combined with measurements of treatment performance.Although the need to measure treatment effectiveness has gained acceptance, there are limited data to determine if post-fire treatments are practical and effective. Field measurements of runoff and/or sediment yields in burned areas require a rapid response research protocol (Lentile and others 2007) and are generally expensive and labor-intensive. Such studies are challenging to fund and sustain over time. Nonetheless, quantitative treatment effectiveness data does influence treatment decisions. In the 1990s, contour-felled log erosion barriers (LEBs) were applied on 69 percent of the wildfires that included post-fire hillslope stabilization treatments (Robichaud and Rhee). Land managers generally regarded these LEB treatments as effective and useful (Robichaud and others 2000). Throughout the 2000s, BAER treatment area and expenditures increased; yet the use of LEBs decreased rapidly in the first two to three years of the decade. LEBs rarely have been installed since 2002 (Robichaud and Rhee). The transition away from LEBs for post-fire hillslope treatment is directly related to the dissemination of quantitative research results that verified their limited effectiveness (Robichaud 2005; Robichaud and others 2000, 2006, 2008a,b; Wagenbrenner and others 2006).
[title page] [factors that affect post-fire watershed response and treatment effectiveness]
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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