an identifiable association of wildland fuel elements of distinctive species, form, size, arrangement, or other characteristics that will cause a predictable rate of spread or resistance to control under specified weather conditions; kinds of fuel include the following:

—activity fuel the combustible material resulting from or altered by forestry practices such as timber harvest or thinning, as opposed to naturally created fuels

—aerial fuel the standing and supported live and dead combustibles not in direct contact with the ground and consisting mainly of shrub and tree crowns, stems, foliage, branches, and vines

—fine fuel fast-drying dead combustible material, generally characterized by a comparatively high surface area-to-volume ratio and diameters of less than 0.25 in (0.64 cm), that is consumed rapidly by fire when dry, e.g., grass, leaves, and needles —note fine fuels have a timelag of one hour or less —synonym flash fuels, light fuels

—ground fuel combustible material below the surface fuel layer such as peat, duff, and roots

—heavy fuel combustible material of large diameter, usually > 3 in (7.6 cm), that ignites and burns more slowly than fine fuels, e.g., snags, logs, large branchwood, and peat —synonym coarse fuel —see black line

—ladder fuel combustible material that provides vertical continuity between vegetation strata and allows fire to climb into the crowns of trees or shrubs with relative ease —note ladder fuels help initiate and ensure the continuation of a crown fire —synonym fuel ladder

—natural fuel combustible material resulting from natural processes and not directly generated or altered by land management practices

—surface fuel the loose surface litter on the soil surface, e.g., fallen leaves or needles, twigs, bark, cones, branches, grasses, shrub and tree reproduction, downed logs, stumps, seedlings, and forbs interspersed with or partially replacing the litter This definition last updated 10/24/2008