Your Assignment: Fuel Load Calculations Cheatsheet
To Do: Use this cheatsheet to calculate the fuel loading for the downed woody debris, litter
and duff, and shrub and herbaceous fuels in the two sites. Input the data into the Excel
worksheet you were given, and email to lkobziar@ufl.edu before Tuesday of next week.
I. Downed woody Debris (from Brown 1974):
Computing Tons per Acre:
1, 10 hr size class: 0-3 in:
(tons/acre) = (11.64 * n * d2 * s * a * c )/ Nl
100, 1000 hr size classes: 3+ inches: (tons/acre) = (11.64 * ∑d2 * s * a * c )/ Nl
Where:
c = slope correction factor
(From Brown 1974)
n = total number of intersections over all sample points (for each of the 1-hr, 10-hr and 100-hr
samples)
d2 = squared average diameters
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
For 1, 10 and 100-hr fuels these have been measured in the field and constants for
different species and systems have been derived. For our purposes, use the following
(nonslash composite values from Brown 1974):
Diameter class (inches) : 0-0.25
d2 (inches2):
0.0151

0.25-1
0.289
1-3
2.76
For 1000-hr fuels (3+ in), the actual diameters of each piece are squared and added
together to get ∑d2
s = specific gravity of the materials
Approximate Specific gravities for conifers given by Brown (1974) were:
Diameter class (inches) :
Specific gravity :
0-0.25 0.25-1 1-3
0.48 0.48 0.40
3+Sound
0.40
3+Rotten
0.30
a = the nonhorizontal angle correction factors


The correction factor adjusts weight estimates for the fact that all particles do not lie
horizontally as assumed in the planar intersect theory.
Brown provides the following:
0 to 3 inches: 1.13
3+ inches: 1.00
Nl = the total length of the sampling line
These lengths are different for different protocols: FIREMON Sampling Scheme:
Fuel Size Class
Length of Transect Sampled
1-hr
6ft
10-hr
6ft
100-hr
15ft
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1000-hr
60ft
II. Litter and Duff:
Litter and Duff loadings are calculated by multiplying the average depth by the bulk
density of litter (or duff). Use bulk density values of 2.75 lbs/ft3 for litter and and 5.5
lbs/ft3 for duff. Note that you will need to convert to tons/acre.
III. Live and dead herbaceous and woody loads:
For each transect, average the two fixed-area plot estimates for live shrub cover, dead
shrub cover, live herbaceous cover, and dead herbaceous cover. Find the average
shrub height and average herbaceous height. Biomass of live and dead shrubs and
biomass of live and dead herbaceous plants are calculated using the equation,
B=H*C*BD
Where:
B = biomass (kg/sq. m)
H = height (m)
C = percent cover/100
BD = bulk density (kg/cu. m)
Bulk density used for the herbaceous and shrub components are 0.8 kg/m3 and 1.8
kg/m3, respectively.
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