Agriculture Reference
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the large diameter class ranges causes high amounts of uncertainty in sampling es-
timates (Keane and Gray 2013 ). Moreover, biophysical processes that control fuels,
such as decomposition and deposition (Chap. 6), vary greatly across the particle siz-
es within the conventional 10-, 100-, and 1000-h woody fuel size classes. Therefore,
to improve future fuel assessments, a new size classification is needed that stratifies
woody fuels according to ecological characteristics rather than their drying rate.
Woody fuels are also often divided into two general fuel types. Fine woody de-
bris (FWD) are generally those woody fuel particles less than 8 cm (3 in) in diam-
eter, while coarse woody debris (CWD) are fuel particles greater than or equal to
8 cm diameter (Fig. 3.1c , d , e ). FWD includes the 1-, 10-, and 100-h woody fuel
components which are the input fuel components in the US fire behavior models.
FWD is important in fire dynamics because they both facilitate fire spread and con-
tribute to fire intensity.
Coarse woody debris (CWD) consists of fallen logs on the forest floor that fire
managers and scientists refer to as 1000-h woody fuels (8 + cm diameter; Table 3.1 ,
Fig. 3.1f ). CWD also has size classes but they are not standardized across all fire
management applications; diameter ranges for CWD fuel components are designed
for specific purposes (Riccardi et al. 2007a ). Some fuel classifications divide the
CWD into three fuel components: particle size diameter classes of 8-23 cm (3-9 in),
23-51 cm (9-20 in), and 51 + cm (20 in) that define 1000, 10,000, and 10,000+ h
time lag fuels respectively (Riccardi et al. 2007a ). As far as fire behavior is con-
cerned, 1000-h fuels contribute little to fire spread (Anderson 1969 ), so finer divi-
sions of CWD size classes were unnecessary for the simulation of fire propagation
so all CWD biomass was grouped into one class regardless of size, length, or con-
dition of the fuel particle. However, the CWD fuel component may often have the
highest loadings in forested settings (Brown and Bevins 1986 ; Table 3.1 , Fig. 3.2b ),
so CWD can contribute to high fire intensities. Moreover, larger logs burn or smol-
der longer than smaller logs that usually results in more heat pulsed into the ground
(Albini and Reinhardt 1995 ). If fuel inventories and data are to be useful to other
resource applications, such as wildlife habitat determination, fuel consumption, and
smoke emissions modeling, there must be finer divisions of CWD size classes (Al-
bini and Reinhardt 1995 ).
An important quality of woody fuel is the degree of rot (decomposition) in the
woody fuel particle. The level of rot in woody fuels affects many other fuel proper-
ties. As woody fuels rot, for example, there are increases in SAVR and decreases
in particle density and heat content. These changes also affect drying and wetting
rates, ignitability, and fire intensity (Pyne et al. 1996 ). Rotten wood, for example,
often burns in smoldering combustion and can ignite at higher moistures than sound
wood. As a result, woody fuel types and components are also described by their
degree of rot (Chap. 8).
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