Surface and Ground Fuels - Wildland Fuel Fundamentals and Applications - page 46

rant attention because they represent a significant fuel source in some areas and
they can't be grouped into the seven common surface fuel types mentioned above.
Historically, fuel inventories have ignored them, lumped them into the common fuel
types, or measured them separately using specialized sampling techniques. Again,
the recognition of special fuel types for local evaluations would ultimately depend
on the sampling objective. If smoke emissions were a concern, for example, then it
would be important to get loading estimates of everything that can burn, including
the special fuel types, but if fire spread predictions were desired, then the quanti-
fication of special fuel types that don't contribute to fire spread becomes less im-
portant. The following are some examples of special fuel types, stratified by their
origins, that may be important in some areas. This list is by no way exhaustive since
there are many more special fuel types in the ecosystems of the world.

3.2.5.1 Plant Origin

Most fuel bed descriptions do not include snags in CWD fuel components, although
there are some studies that consider snags as CWD (Harmon et al. 1986 ). A snag
is a standing dead tree, but sometimes it is difficult to determine if a snag is a log,
especially when it is leaning (Fig. 3.3a ). When trees or snags fall, they often get
caught or hung up against other trees such that the fallen log looks very much like
an upright snag. This poses a dilemma because snags contribute little to fire spread
or intensity, but logs are important in the calculation of fire intensity. From the fuel
perspective, snags are tomorrow's 1000-h fuel, but they contribute little to fire in-
tensity and spread when they are erect. In a biological sense, snags are completely
different from logs and have their own inherent ecological value, such as provid-
ing nesting and foraging habitat for a number of common to rare avian wildlife,
including the spotted owl and pileated woodpecker (Hutto 2006 ). Snags also con-
tain unique assemblages of other organisms (Nappi et al. 2004 ). Therefore, to lump
snags in with CWD seems inappropriate for both ecological and physical reasons.
So, when does a snag behave like a log when it is burned? In this topic, CWD are
considered downed if the long axis of the log is at an angle greater than 45° from
the vertical (< 45° from ground line). This distinction is more related to combustion
physics than ecology or any other field of study because the ecosystem processes
acting on a snag regardless of its angle are completely different from those acting on
a log that is in contact with the ground. Moreover, snags are often more dangerous
to firefighters than logs because snags may fall, especially when fire burns around
the trunk, and the falling material can hurt people. A quantification of the snag
component might be important, not so much for fire modeling, but as an additional
assessment of fire risk and hazard, and for ecological concerns.
Mosses and lichens are present in many ecosystems but at such low amounts that
they often contribute little to fire spread and intensity. However, there are extensive
land areas of the world where live and dead lichen and moss can accumulate to
create thick litter layers that foster intense fires (Fig. 3.3b ). Mosses and lichens,
whether they are dead or alive, have dramatically different moisture dynamics and