Variability in surface fuel loads following various fuel reduction treatments
Brandon Collins
Gary Roller
Inventory methods to sample surface fuel loads are necessary to evaluate the effects of
various fuel reduction treatments. There are multiple methods utilized to sample surface fuel
loads, with varying levels of accuracy and sampling/processing time required. One of the most
robust methods is the planar-intercept method developed by Brown (1974). This method is
widely considered to be accurate, repeatable, and can be adjusted to fit various sampling designs
in many different environments. However, there is uncertainty as to what the optimal level of
sampling may be to capture the inherent variability in surface fuel loads, particularly with respect
to sampling following different fuel treatment types (e.g., prescription burning, mastication,
piling and burning). This study seeks to both characterize variability in post-treatment surface
fuel loads for multiple treatment types and determine optimal levels of sampling to capture the
variability in a given treatment type.
We selected four different broad treatment types from various HFQLG treatments
implemented around the Meadow Valley area on the Plumas National Forest: mastication,
commercial thinning combined with biomass harvesting, hand-thinning followed by pile burning,
and prescribed burning. We additionally selected untreated areas adjacent to sampled treated
areas to serve as controls for comparison among treatment categories. The number of sampled
stands within each type is listed in Table 1. The sampling conducted within control areas was
only conducted within a small portion of the overall stand, and as such there is no meaningful
estimate of the total stand area sampled. A sampling grid of 100 meters by 100 meters was laid
out in each treatment stand sampled. At each chosen grid point a 50 meter transect was installed
at a random azimuth. Ground and surface fuel characteristics, tree size, canopy cover, and shrub
cover were sampled on discrete10 meter sub-sections of the larger 50 meter transect. On each 10
meter sub-transect duff and litter depths were sampled at three random points and fine woody
fuels (1, 10, and 100hr timelag classes) were sampled over a random 3 meter portion. Coarse
woody fuels (1000hr) were sampled along the entire 10 meter length. Canopy cover was sampled
using a densitometer (sight tube) at nine points per sub-transect. Shrub cover was sampled by
species, total length, and average height along the entire 10 meter length. Trees with a diameterat-breast height >1 inch to 18 inches were sampled on a 5 meter wide belt transect and trees >18
inches on a 10 meter wide belt transect. Tree characteristics sampled include; diameter, species,
total height, height to live crown base, and crown class.
Summary fuel load calculations are shown in Table 2. Preliminary analysis indicates that
fuel loads varied considerably across all treatment types with a majority of the fuel loads being in
the duff and litter classes. Duff, litter, and fine woody fuel loads were highest in commercially
thinned stands and control areas, while coarse woody fuel loads were highest in hand-thinned
stands. Control areas had the highest total load (33.4 tons/ac.), while masticated stands had the
lowest (9.2 tons/ac.). Prescription burned stands had the lowest litter and fine woody fuel loads.
We intend to analyze the relationship between tree density and fuel loads, as well as the
variability in fuel loads among treatment types. We also intend to analyze potential sampling
saturation to answer the question of how many fuel transects would be needed to adequately
sample fuel loads in a given area. This will be accomplished by determining the point at which
the mean is stabilized and any further sampling is not required.
Table 1. Summary of sampling by treatment type and average forest stand structure for sampled
stands within the Meadow Valley area.
Number
Number of
Total stand area Basal area Canopy
Treatment Type
of stands 50m transects
sampled (ac.)
(ft²/ac)
cover (%)
Prescription burned
10
41
247
149
47
9
25
225
188
58
8
17
408
151
40
Masticated
5
17
216
82
27
Control (untreated)
7
20
-
336
77
Commercial thinned
& biomass harvested
Hand-thinned &
pile/burned
Table 2. Average fuel loads by treatment type
Fuel loads (tons/ac)
Treatment Type
Fine woody Coarse woody
Duff Litter
(1-100 hr)
(1000 hr)
Prescription burned
Total
1.66
4.94
1.36
3.48
11.45
7.96
9.79
3.52
3.61
24.89
3.86
7.73
1.36
11.69
24.64
Masticated
0.13
5.71
1.70
1.68
9.22
Control (untreated)
8.46
13.99
3.66
7.32
33.43
Commercial thinned
& biomass harvested
Hand-thinned &
pile/burned
References
Brown JK (1974) Handbook for inventorying downed woody material. U.S. Department of Agriculture, Forest
Service, Intermountain Forest and Range Experiment Station General Technical Report INT-16,32 p.
(Odgen, UT)