Fundamentals - Wildland Fuel Fundamentals and Applications - page 16

Fig. 2.1 A new variation on
the traditional fire triangle
often used to teach fire sci-
ence to managers. The inner
triangle refers to combustion
at the flame level, the middle
triangle refers to fire spread
at a stand level, and the
outside triangle refers to fire
growth at the landscape level
more oxygen than can be supplied by the atmosphere, thereby governing burning
rates. And last, there is fuel. As Van Wagner ( 1983 ) mentions, the fuel must be the
appropriate size and arrangement to facilitate fire spread and it must be dry enough
for combustion (i.e., low moisture content). Unfortunately, the inner fire triangle in
Fig. 2.1 really only works at very small scales; perhaps the scale of the flame, which
may be useful for firefighters but somewhat ineffectual for the diverse and complex
issues facing a wildland fuel manager. Therefore, many have added additional fire
triangles to represent the scaling of combustion to a fire event (Fig. 2.1 ; Alexander
2014 ).
However, to fully understand fuels, it is important to recognize that the process
of combustion scales from the flame to burning period to fire event over various
time and space scales (Fig. 2.1 ). A more comprehensive representation of the fire
triangle is detailed by Moritz et al. ( 2005 ; Fig. 2.2 ) where fire moves across an area
and interacts with topography (slope, aspect), weather (temperature, humidity), and
the fuel complex. At coarser scales, the fuel properties important to fire spread are
governed more by the distribution of fuels across the landscape or contagion (con-
tinuity of a fuelbed). The landscape-level spatial scale of fire spread best describes
the operational management of fuels and is probably the most appropriate for de-
signing fuel treatments (Agee and Skinner 2005 ). However, some large fires can
burn entire landscapes over the course of weeks, and as more fires burn the same
landscape over hundreds of years, these fires interact with previous fires, climate
(drought, warming), ignition patterns (lightning, humans), and vegetation to create
a fire regime (Chap. 6). In Fig. 2.2 , fuels are represented by vegetation to signify
that fuel conditions change over time and this change is mediated by vegetation
development processes (regeneration, growth, mortality) and succession (species