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ForestERA Data Layer Detail - Fuel Models

Note to data users: Please carefully review the metadata provided with each layer. We request that users consult with the ForestERA project in advance of using these data in publications and/or presentations to ensure that the strengths and limitations of the data are considered.

Description

Fuel models are developed for the purpose of fire behavior modeling. They represent the ground fuels available to a burning fire and allow prediction of fire behavior through mathematical models that link the fuels to the attributes of a fire burning those fuels (Rothermal, 1972; Albini, 1976). Two different groups of fuel models are typically used in fire behavior modeling: a set of 20 created under the National Fire Danger Rating System, and the 13 “Anderson” fuel models (Anderson, 1982) originally created for use in the BEHAVE fire modeling program (Burgan & Rothermal, 1984), and also used in the FARSITE and FlamMap fire behavior modeling programs (Finney, 1998, in press).

Purpose

This data layer was created as part of the ForestERA project to support landscape-scale forest restoration planning efforts by a broad group of stakeholders including federal and state agencies, academic institutions, and non-governmental entities. These data are intended for regional analyses over spatial extents on the order of tens to hundreds of thousands of acres, and were not developed for use at finer spatial scales, although they may be useful for some applications at finer scales.

Development

This layer was created using the dominant overstory vegetation layers developed by the ForestERA team using Enhanced Thematic Mapper (ETM) imagery. Ground fuel models cannot be directly measured using readily available types of remote-sensing imagery and sufficient field data do not exist. Because of this, it was necessary to predict the fuel models across the landscape based on vegetation characteristics (e.g. Keane et al., 2000). We categorized the fuel models across our region based on our dominant overstory vegetation model, using Anderson (1982) as a reference guide;

Dominant Overstory Vegetation Type Fuel Model
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Grassland and other Open Areas 1
Pinyon - Juniper or Juniper Dominated Mix 6
Aspen 8
Ponderosa Pine, Pine - Oak, or Pine - Aspen 9
Mixed Conifer or Mixed Conifer - Aspen 10
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The major problem with using these fuel models, is that some of them were not specificially created for southwestern vegetation types, and may not adequately mimic fire behavior in ground fuels of the southwest. In particular, fuel model 9 was developed for eastern long-needle pine types (Anderson, 1982) and does not adequately predict the intensity with which a fire burns in ponderosa pine needle beds (Chuck McHugh & others, pers. comm.). Therefore, we typically create custom fuel models for ponderosa pine by “boosting” fuel model 9 using a tool provided in the FARSITE fire modeling program (Finney, 1998). We have created a custom fuel model 17 by boosting fuel model 9 by 40%. The use of this custom fuel model simply involves changing all areas of fuel model 9 in the fuel models layer to fuel model 17 and the addition of a custom fuel models file (see below) in FARSITE or FlamMap. The primary difference between fuel model 9 and fuel model 17 is that fuel model 17 has longer flame lengths. These flame lengths are more typical of the maximum flame lengths that would be expected from a fire burning in ground fuels under ponderosa pines. In addition, some users may wish to adjust fuel models in ponderosa pine based on forest conditions. Ffolliott, et al. (1968) found increasing fuel loadings as basal area increased in stands of ponderosa pine in Arizona. However, Sackett (1979) did not find significant relationships between basal area and fuel loadings in ponderosa pine after sampling stands over a much wider spatial extent and under a wider range of management conditions. If the user is comfortable with evidence that increasing basal are results in increasing fuel loadings on the ground, we provide some variations of fuel model 9 that have been “boosted” based on basal area of pine (fuel models 14 - 17) as follows:

Ponderosa Pine Basal Area Boosted Fuel Model 9 New Fuel Model
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< 10 m2 / ha 10% 14
10 - 25 m2 / ha 20% 15
25 - 40 m2 / ha 30% 16
> 40 m2 / ha 40% 17
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Finally, some users may wish to modify fuel models based on treatments or management history. In this case we suggest that post-treatment fuel models be set to the basic fuel model 9 if prescribed fire was used in the treatment. If prescribed fire was not used in the treatment, or if more than 3 years has passed after treatment, we recommend using the post-treatment basal area to classify the appropriate fuel model. A custom fuel models (.fmd) file describing fuel models 14-17 is provided with the fuel models layer for use in the FARSITE and FlamMap fire modeling programs.

Fire behavior modeling also requires the input of moisture content for ground fuels. A fuel moisture (.fms) file with moistures representative of very dry (approximately 90th percentile drought) conditions for this region has been provided with the fuel models layer. This fuel moisture file can be used in the FARSITE and FlamMap fire modeling programs.

Accuracy Assessment

No accuracy assessment is possible for this layer as we do not have comprehensive measurements of ground fuels across this region. Use of vegetation characteristics is a standard methodology for creating maps of ground fuels, and we use our dominant overstory vegetation layer as the predictive layer for ground fuels layer. The accuracy of the dominant overstory vegetation layer is described in the metadata distributed with that layer.

Sources of errors

The fuel models layer is one of the most uncertain layers in fire behavior modeling. There is no way to accurately predict ground fuels without extensive measurements on the ground. Fuel models may change depending on weather, management history, fire history, and a number of other factors (e.g., Sackett, 1979). In addition, fuel models are highly generalized and do not always adequately represent fire behavior. However, we are using standard techniques for fire modeling and making the same assumptions used in other fire modeling exercises. Therefore, we believe that these fuel models can be used to make comparisons of relative fire behavior across the landscape even though the fire models do not represent absolute predictions of fire behavior.

Recommendations

We recommend that this layer be used at a minimum resolution of 90m (0.8 ha or 2 acres) for purposes of analysis and display. However, ForestERA data layers were not designed for analyses at the level of individual pixels, and uncertainty in the data will generally decline over greater spatial extents. Therefore, we recommend using larger analysis units, with groupings of at least 50 cells (40 ha or 100 acres). Finally, we reiterate that ForestERA data layers were developed for the purpose of regional landscape-level planning, and we suggest that the analyses be applied over spatial extents of tens to hundreds of thousands of acres. We recognize, however, that this layer may be useful for analyses over smaller spatial extents depending on the type and purpose of those analyses.

References

Albini, F. A. 1976. Estimating wildfire behavior and effects. USDA Forest Service General Technical Report INT-GTR-30.

Anderson, H. E. 1982. Aids to determining fuel models for estimating fire behavior. USDA Forest Service General Technical Report INT-GTR-122.

Bergan, R. E. and R. C. Rothermal. 1984. Behave: fire behavior prediction and fuel modeling system - fuels subsystem. USDA Forest Service General Technical Report INT-GTR-122.

Bradshaw, L. S., J. E. Deeming, R. E. Burgan, and J. D. Cohen. 1983. The 1978 national fire-danger rating system: technical documentation. USDA Forest Service General Technical Report INT-GTR-169.

Ffolliott, P. F. W. B. clary, and J. Davis. 1968. Some characteristics of the forest floor under ponderosa pine in Arizona. USDA Forest Service Research Note RM-RN-127.

Finney, M. A. 1998. FARSITE: Fire area simulator - model development and evaluation. USDA Forest Service Research Paper RMRS-RP-4.

Finney, M. A. In press. FlamMap: fire behavior mapping and analysis system. USDA Forest Service General Technical Report.

Keane, R. E., S. A. Mincemoyer, K. M. Schmidt, D. G. Long, and J. L. Garner. 2000. Mapping vegetation and fuels for fire management on the Gila National Forest complex, New Mexico. USDA Forest Service General Technical Report RMRS-GTR-46-CD.

Rothermal, R. C. 1972. A mathematical model for fire spread predictions in wildland fuels. USDA Forest Service Research Paper INT-RP-115.

Sackett, S. S. 1979. Natural fuel loadings in ponderosa pine and mixed-conifer forests of the southwest. USDA Forest Service Research Paper RM-RP-213.

Page last updated February 11, 2005