(* 1988 Version Fuel Model Revisions)
2016 Fuel Model V
Fuel Model A – This fuel model represents western grasslands vegetated by annual grasses and forbs. Brush or trees may be present but are very sparse, occupying less than one-third of the area. Examples of types where Fuel Model A should be used are cheatgrass and medusa head. Open pinyon-juniper, sagebrush-grass, and desert shrub associations may appropriately be assigned this fuel model if the woody plants meet the density criteria. The quantity and continuity of the ground fuels vary greatly with rainfall from year to year.
Fuel Model L – This fuel model is meant to represent western grasslands vegetated by perennial grasses. The principal species are coarser and the loadings heavier than those in Model A fuels. Otherwise the situations are very similar; shrubs and trees occupy less than one-third of the area. The quantity of fuels in these areas is more stable from year to year. In sagebrush areas Fuel Model T may be more appropriate.
2016 Fuel Model W
Fuel Model C – Open pine stands typify Model C fuels. Perennial grasses & forbs are the primary ground fuel but there is enough needle litter & branchwood present to contribute significantly to the fuel loading. Some brush & shrubs may be present but are of little consequence. Types covered by Fuel Model C are open, longleaf, slash, ponderosa, Jeffery, & sugar pine stands. Some pinyon-juniper stands may qualify.
Fuel Model D – This fuel model is specifically for the palmetto-gallberry understory-pine association of the southeast coastal plains. It can also be used for the so-called “low pocosins” where Fuel Model O might be too severe. This model should only be used in the Southeast because of the high moisture of extinction associated with it.
Fuel Model N – This fuel model was constructed specifically for the sawgrass prairies of south Florida. It may be useful in other marsh situations where the fuel is coarse and reed like. This model assumes that one-third of the aerial portion of the plants is dead. Fast-spreading, intense fires can occur over standing water.
Fuel Model S – Alaskan and alpine tundra on relatively well-drained sites fit this fuel model. Grass and low shrubs are often present, but the principal fuel is a deep layer of lichens and moss. Fires in these fuels are not fast spreading or intense, but are difficult to extinguish.
Fuel Model T – The sagebrush-grass types of the Great Basin and the Intermountain West are characteristic of Fuel Model T. The shrubs burn easily and are not dense enough to shade out grass and other herbaceous plants. The shrubs must occupy at least one-third of the site or the A or L fuel models should be used. Fuel Model T might be used for immature scrub oak and desert shrub associations in the West and the scrub oak-wire grass type of the Southeast.
2016 Fuel Model Y
Fuel Model H – Used for short-needled conifers (white pines, spruces, larches, & firs). In contrast to FM G fuels, FM H describes a healthy stand with sparse undergrowth and a thin layer of ground fuels. Fires in FM H are typically slow spreading and are dangerous only in scattered areas where the downed woody material is concentrated.
Fuel Model G – Used for dense conifer stands where there is a heavy accumulation of litter & down woody material. They are typically over mature & may be suffering insect, disease, & wind or ice damage—natural events that create a very heavy buildup of dead material on the forest floor. The duff & litter are deep and much of the woody material is >3” in diameter. The undergrowth is variable, but shrubs are usually restricted to openings. Types represented here are hemlock-Sitka spruce, coastal Douglas fir, and wind thrown or bug-killed stands of lodgepole pine & spruce.
Fuel Model E – Used after fall leaf fall for hardwood and mixed hardwood-conifer types where the hardwoods dominate. Fuel is primarily hardwood leaf litter. It best represents the oak- hickory types & is a good choice for northern hardwoods and mixed forests of the Southeast. In high winds, the fire danger may be underrated because rolling and blowing leaves are not accounted for.
Fuel Model R – This fuel model represents hardwood areas after the canopies leaf out in the spring. It is the growing season version of FM E. It should be used during the summer in all hardwood and mixed conifer-hardwood stands where more than half of the overstory is deciduous.
Fuel Model U – This fuel model represents the closed stands of western long-needled pines. The ground fuels are primarily litter and small branchwood. Grass and shrubs are precluded by the dense canopy but may occur in the occasional natural opening. Fuel Model U should be used for ponderosa, Jeffery, sugar pine stands of the West and red pine stands of the Lake States. Use FM P for southern pine plantations.
Fuel Model P – Closed, thrifty stands of long- needled southern pines are characteristic. A 2-4 inch layer of lightly compacted needle litter is the primary fuel. Some small diameter branchwood is present but the density of the canopy precludes more than a scattering of shrubs/grass. FM P has the high moisture of extinction characteristic of the Southeast. The corresponding model for other long-needled pines is FM U.
2016 Fuel Model X
Fuel Model B – Mature, dense fields of brush six feet or more in height is represented by this fuel model. One-fourth or more of the aerial fuel in such stands is dead. Foliage burns readily. Model B fuels are potentially very dangerous, fostering intense, fast-spreading fires. This model is for California mixed chaparral, generally 30 years or older. The F model is more appropriate for pure chamise stands. The B model may also be used for the New Jersey pine barrens.
Fuel Model O – The O fuel model applies to dense, brush like fuels of the Southeast. In contrast to B fuels, O fuels are almost entirely living except for a deep litter layer. The foliage burns readily except during the active growing season. The plants are typically over six feet tall and are often found under open stands of pine. The high pocosins of the Virginia, North and South Carolina coasts are the ideal of Fuel Model O. If the plants do not meet the 6- foot criteria in those areas, Fuel Model D should be used.
Fuel Model F – Fuel Model F represents mature closed chamise stands and oak brush fields of Arizona, Utah, and Colorado. It also applies to young, closed stands and mature, open stands of California mixed chaparral. Open stands of pinyon-juniper are represented; however, fire activity will be overrated at low wind speeds and where ground fuels are sparse.
Fuel Model Q – Upland Alaska black spruce is represented by Fuel Model Q. The stands are dense but have frequent openings filled with usually flammable shrub species. The forest floor is a deep layer of moss and lichens, but there is some needle litter and small diameter branchwood. The branches are persistent on the trees, and ground fires easily reach into the crowns. This fuel model may be useful for jack pine stands in the Lake States. Ground fires are typically slow spreading, but a dangerous crowning potential exists. Users should be alert to such events and note those levels of SC and BI when crowning occurs.
2016 Fuel Model Z
Fuel Model I – Fuel Model I was designed for clear-cut conifer slash where the total loading of materials less than six inches in diameter exceeds 25 tons/acre. After settling and the fines (needles and twigs) fall from the branches, Fuel Model I will overrate the fire potential. For lighter loadings of clear-cut conifer slash use Fuel Model J, and for light thinnings and partial cuts where the slash is scattered under a residual overstory, use Fuel Model K.
Fuel Model J – This model complements Fuel Model I. It is for clear-cuts and heavily thinned conifer stands where the total loading of material less than six inches in diameter is less than 25 tons per acre. Again as the slash ages, the fire potential will be overrated.
Model K – Slash fuels from light thinnings and partial cuts in conifer stands are represented by Fuel Model K. Typically the slash is scattered about under an open overstory. This model applies to hardwood slash and to southern pine clear-cuts where loading of all fuels is less than 15 tons/acre.
The loading of fine fuels associated with annual grasses shift from live to dead and stays there for the duration of the season. For perennial grasses, the shift from live to dead is much and may even stop or reverse if the right combinations of temperature and precipitation occur during the season.
In the 1988 revision to the NFDRS, separate equations were developed for deciduous and evergreen shrub vegetation, requiring users to enter a code indicating whether their local shrub vegetation is deciduous (D) or evergreen (E)
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