Introduction - Wildland Fuel Fundamentals and Applications - page 9

is extremely difficult, although they may be extrapolated to a wide variety of fire
situations. These models may also be called mechanistic or process models because
they take a reductionist approach by explicitly representing the mechanisms that
lead from cause to effect. For example, tree growth may be simulated using the
ecophysiological processes of photosynthesis and respiration in a mechanistic ap-
proach. Semiempirical or quasi-empirical models are terms used for models that
were developed using theoretical equations, but these equations were parameterized
using empirical techniques (Sullivan 2009b ).
Four key modeling terms are important tasks in fire simulations. Initialization is
the process of inputting initial parameters into the model. These starting conditions
are usually the quantification of fuel properties, such as loading and moisture. Pa-
rameterization is a term used to describe how the parameters in various equations
and algorithms in the model are quantified. Some fuel attributes, such as mineral
content, are not dynamic variables that users can input into fire models, but instead
they are static parameters that the user cannot modify so it is important to know how
these parameters were estimated. Statistical techniques are used for most parameter
quantification, but some parameters in theoretical or physical equations can be es-
timated from the literature. Calibration is a term used to describe the adjustment
of model inputs and parameters to achieve realistic results. There is always error in
the quantification of both parameters and initial conditions in most models, and this
error is often reduced by adjusting parameters or inputs so that subsequent simula-
tions produce believable results. And last, validation is the process of describing the
accuracy and precision of model results. Validation relies on comprehensive data-
bases to use as reference for comparison against simulation results. Every modeling
project should involve each of these four phases.

1.3 An Abridged History of Wildland Fuel Science

To fully understand why wildland fuels are described and defined the way there are
today, it is important to trace the history of the application of fuels in fire manage-
ment. Historically, most fuelbeds were described using terms that related more to
fire behavior than ecology. Starting in 1919, Show and Kotok ( 1930 ) correlated fire
behavior and firefighting descriptors to vegetation cover types to represent fuels,
and called categories in this classification “hour control zones,” which represented
the time it took for a suppression force to arrive after an ignition. Hornby ( 1935 )
described fuels of the northern Rockies as categories in an ordinal fire behavior
classification that integrated resistance to spread and suppression effectiveness lev-
els. This approach was then employed to describe and map fuels for many other
areas of the USA including the mid-west (Jemison and Keetch 1942 ), the mountains
and seaboard of the Atlantic region (Banks and Frayer 1966 ), the Pacific North-
west (Abell 1937 ), and parts of New Jersey (New Jersey Department of Conser-
vation and Development and US Department of Agriculture 1942 ). Both Barrows
( 1951 ) and Banks and Frayer ( 1966 ) revised the Hornby ( 1936 ) methods to include