Surface and Ground Fuels - Wildland Fuel Fundamentals and Applications - page 38

Table 3.1 Descriptions of the seven most common surface fuel components and the one most
common ground fuel component found in ecosystems worldwide. FWD is fine woody debris, a
term often given to wood fuel particles less than 8 cm in diameter. CWD is coarse woody debris,
a term used to woody fuel particles greater than 8 cm in diameter
Fuel type Fuel

component

Common name Size Description

Surface fuels
Downed
dead woody

1-h woody Twigs, FWD < 0.6 cm (0.25 in)

diameter

Detached small woody
fuel particles on the
ground

10-h woody Branches, FWD 0.6-2.5 cm

(0.25-1.0 in)
diameter

Detached small woody
fuel particles on the
ground

100-h woody Large branches,

FWD

2.5-8 cm (1-3 in)
diameter

Detached small woody
fuel particles on the
ground

1000-h woody Logs, CWD 8+ cm (3+ inch)

diameter

Detached small woody
fuel particles on the
ground

Shrubs Shrub Shrubby All shrubby

material less than
5 cm diameter

All burnable shrubby
biomass with branch
diameters less than 5 cm

Herbaceous Herb Herbaceous All sizes All live and dead grass,

forb, and fern biomass

Litter Litter Litter All sizes, exclud-

ing woody

Freshly fallen nonwoody
material which includes
leaves, cones, pollen
cones

Ground fuels
Duff Duff Duff All sizes Partially decomposed

biomass whose origins
cannot be determined

FWD fine woody debris , CWD coarse woody debris

3.2.1 Litter

Litter is considered freshly fallen, readily identifiable dead plant biomass (Fig. 3.1a ).
It is often called the L layer in vegetation and soils studies (Soil Classification Work-
ing Group 1998 ). Of all the surface fuel components, litter is often the most diverse
because it may consist of a wide variety of fallen plant parts, such as bud scales,
pollen cones, and dead grass blades. However, the most common constituent of lit-
ter is plant foliage, often needles and leaves, and these discarded plant parts readily
facilitate the spread of fire. In ecology, litterfall is a term often used to describe
the biomass dropped by plants and so it follows that the litter layer may contain
all types of plant material, including woody particles. But, in fuel science, litter
excludes woody material as woody fuels are a separate component with completely