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Terracette: See Contour-Felled Logs. Tilling: Mechanical turning of the Boil with a plow or ripping device. Often used to promote soil infil- tration by breaking up water repellent soil layers. Trash Rack: Barrier placed upstream of a culvert to prevent woody debris From becoming jammed into the inlet. Ungulate: Herbivorous animals with hooves, e.g., cow, elk, deer, horses, etc. Water Bar: Combination of ditch and berm installed perpendicular or skew to mad ortrail centerline to facilitate drainage of surface water; some- times nondriveable and used to close a road. W ater Repellency: Tendency of soil to form a hydro- phobic (water resistant) layer during fire that subsequently prevents infiltration and perco- lation of water into the soil mantle. Watershed: An area or region bounded peripher- ally by ridges or divides such that all precipi- tation falling in the area contributes to its watercourse. Water Yield: Tots] runoff from a drainage basin. Literature Review Our evaluation of BAER treatment effectiveness began with the published scientific literature. The general effects of fire on Western forested landscapes are well documented (Agee 1993, DeBano and others 1998, Kozlowski andAhlgren 1974}, Conversely, many of the pmceesee addressed by BAER treatments have not been extensively studied, and relatively little in- formation has been published about moat emergency rehabilitation treatments with the exception of grass seeding. To put BAER treatment effectiveness into ecosystem context, we summarize the scientific litera- ture on postfire conditions that are relevant to BAER evaluations. Then we examine published studies on specific BAER treatments. Fire's Impact on Ecosystems All disturbances produce impacts on ecosystems. The level and direction of impact (negative or positive) depends on ecosystem resistance and resilience, as well as on the severity of the disturbance. The vari- ability in resource damage and response from site to site and ecosystem to ecosystem is highly dependent on bum or fire severity. Burn severity {fire severity) is a qualitative measure of the effects of fire onsite resources (Hartford and Frandsen 1992, Ryan and Noate 1983). As a physical- chemical process, fire produces a spectrum of effects that depend on interactions of energy release (inten- sity), duration, fuel loading and combustion, vegeta• tion type, climate, topography, soil, and area burned. Fire intensity is an integral part of burn severity, and the terms are often incorrectly used synony- mously. Intensity refers to the rate at which a fire is producing thermal energy inthe fuel-climate environ- ment (DeBano and others 1998). Intensity is mea- sured in terms of temperature and heat yield. Surface temperatures can range from 120 to greater than 2,730 °F (50 to greater than 1,600 °C). Heat yields per unit area can be as little as 69 BTU ft-2 (260 kg-calm 2) in short, dead grass to ae high as 3700 BTU ft-2 (10,000 kg-cal m a) in heavy logging slash (Fyne and others 1996). Rate of spread is an index of fire dura- tion and can vary from 1.6 ft week-1(0.5 mweek-1) in smoldering peat fires to as much as 15 mi hr 1 (25 km hr 1) in catastrophic wildfires. The component of bum severity that results in the most damage to soils and watersheds, and hence ecosystem stability, is duration. Fast moving fires in fine fuels, such ae grass, may be intense in terms of energy release per unit area, but do not transfer the same amounts of heat to the Forest floor, mineral soil, or soil organisms as do slow moving fires in moderate to heavy fuels. The impacts of slow moving, ]ow or high intensity fires on soils are much more severe and complex. The temperature gradients that develop can be described with alinked-heat transfer model (Campbell and others 1995) and are a function of moisture and fuel loadings. Some aspects of bum severity can be quantified, but burn severity cannot be expressed as a single quantitative measure that relates to resource impact. Therefore, relative magnitudes of bum or fire sever- ity, expressed in terms of the poatfire appearance of litterand soil (Ryan and Noate 1983), are better criteria for placing burn or fire severity into broadly defined, discrete classes, ranging from low to high. A general burn severity classification developed by Hungerford (1996) relates bum severity to the soil reaoume re• sponse (table 1). Fire E1Fects on Watersheds--Soils, vegetation, and litter are critical to the functioning of hydrologic processes. Watersheds with good hydrologic condi- tions and adequate rainfall sustain stream baseflow conditions for much or all of the year and produce little sediment. With good hydrologic condition (greater than 75 percent of the ground covered with vegetation and litter), only about 2 percent or leas of rainfall becomes surface runoff, and erosion is low (Bailey and Copeland 1961). When site disturbances, such as se- vere fire, produce hydrologic conditions that are poor (less than 10 percent of the ground surface covered with plants and litter), surface runoff can increase over 70 percent and erosion can increase by three orders ofmagnitude. Within a watershed, sediment and water responses to wildfire are often a function ofburn severity and the USDA Forest Service Gen. Tech. Rep. RMRS-GTR-63. 2000