Surface and Ground Fuels - Wildland Fuel Fundamentals and Applications - page 48

fuel properties than wood, shrub, or herbaceous fuels (Sylvester and Wein 1981 ;
Chap. 5). In general, mosses and lichens have high SAVR, low heat content, and
low particle density that allow for their ability to dry quickly and facilitate fire
spread. Many fires in the boreal forests of North America and Europe are spread
through surface fuels that are primarily live and dead feather and sphagnum mosses
(Shetler et al. 2008 ).
One fuel type or component that often gets ignored in many fuel and fire applica-
tions is tree regeneration (tree seedlings below 2 m from the ground; Fig. 3.3c ). Tree
seedlings are sometimes inappropriately included in the shrub and herbaceous fuel
components for simplicity, but tree regeneration differs from shrubs in leaf mor-
phology, particle types and sizes, and moisture dynamics. Sometimes, tree seedlings
are included in the canopy fuels (Chap. 4), but most of this biomass occurs within
the surface fuel layer and will contribute to surface fire spread under the right con-
ditions. That said, tree seedling loadings are not inputs into most fire behavior and
effects models. Future fire models should endeavor to include tree regeneration as a
unique fuel component and future sampling efforts should include a quantification
of tree seedling loadings in their design.
Dead plant parts that fall and get hung up on living and dead plants are also diffi-
cult to categorize. When foliage and branches fall, they sometimes catch on upright
plants and remain there throughout the fire season or maybe longer. “Needle drape”
is well known in the southwestern USA where fallen dead needles from productive
pine stands get caught in understory shrub and understory tree layers to create a
surface fuel layer that is highly flammable (Andreu et al. 2012 ).
Litter accumulation around the base of trees is another specialized case of litter
fuels. Needles and bark often accumulate around large fire-adapted trees in stands
that haven't experienced fire in a long time (Fig. 3.1b ). These litter mounds can
cause substantial damage to the central tree when they eventually burn either by
prescribed burns or by wildfire. Few litter sampling protocols include modifications
in sampling methods or intensities to sufficiently estimate the loadings and proper-
ties of these litter mounds.

3.2.5.2 Animal Origin

An important fuel type that is present in many sylvan communities is squirrel mid-
dens (Fig. 3.3d ). Middens are places where squirrels have cached cones over gen-
erations. These middens consist of intact cones, cone scales, and cone cores. Some
middens can be quite large (2-5 m in diameter) but they are widely scattered across
the landscape. These piles burn more like duff than litter in that they mostly smolder
during a surface fire. Middens may contain up to 5-10 kg m −2 of organic material
that could be an important carbon pool (Riccardi et al. 2007b ).
Animal scat or droppings is another interesting fuel type that can be quite diverse.
Scat, when burned, also smolder, pulsing heat deeper into the soil profile and some-
times causing high mortality in soil biota. Again, most fuel applications lump wild-
life droppings in with the litter, but areas with high scat densities may need to have
a more comprehensive description and quantification of these unique fuel types.