Techniques for Fuel Rank Maps & Data

Techniques for Fuel Rank Maps & Data (part 2)

The procedure makes an initial assessment of fuel rank based on an assigned fuel model and slope (see Techniques, Part 1). Then raises ranks based on the amount of ladder and/or crown fuel present to arrive at a final fuel rank.

Surface Rank: explained in Techniques, Part 1

Ladder and Crown Fuel Indices:

Estimates of ladder and crown fuels support assessment of crown fire potential. The ladder and crown fuel indices estimate the relative abundance of these fuels. These indices measure in a rough manner the probability that individual tree torching and/or crown fire would occur if the stand experienced a wildfire during extreme weather conditions. The indices take values ranging from 0 to 2, with 0 indicating "absent", 1 representing "present but spatially limited", and 2 indicating "widespread".

Table 3
Ladder and crown fuel indices
0	not present
1	present but spatially limited
2	widespread

The surface rank is raised a maximum of one rank level to yield the final rank if the sum of the ladder index and crown index is greater than or equal to 2. Otherwise the final fuel rank is identical to the initial surface rank. Table 2 shows all possible relationships between surface rank, ladder and crown fuel indices and final fuel rank. For instance, lodgepole pine types modeled as fuel model 8 have a moderate surface rank on all slopes. However, the presence of ladder fuels in areas of dense canopy cover would result in a final fuel rank one class higher than the surface rank (high instead of moderate) in such areas.

Ladder and crown fuel indices are assigned to areas in two ways:

If the vegetation data provide sufficient structural detail, the method assigns these additional indices from those data.
If the vegetation data lack structural detail, the method assigns indices based on the fuel model. Table 3 provides an example of the ladder and crown fuel indices assigned to fuel models found in Riverside Ranger Unit. The relationship between a given fuel model and the ladder and crown fuel indices is not constant across the state, but may vary for each Ranger Unit as a result of field validation.

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