Fuel Sampling - Wildland Fuel Fundamentals and Applications - page 135

line for operational sampling of FWD and CWD in forests (Brown 1974 ; Brown
et al. 1982 ). Many still locate the bottom of the plane using a line transect that is
often represented by a cloth tape.
The advantages of the PI method are that it is easy to use and easy to teach
(Lutes et al. 2006 , 2009a ). Novice field technicians can be taught this method in
a short time (1 h) to achieve moderately repeatable measurements. The method
can also be easily modified to adjust for local conditions, available expertise, and
sampling conflicts, such as long plot times, scattered woody fuels, and slash. The
sampling plane can be any size, shape, or orientation in space and samples can be
taken anywhere within the limits set for the plane (Brown 1971 ). It also requires few
specialized equipment; often a plastic ruler and cloth tape are the only gear needed.
However, there are some problems to the PI method. First, it only can be used for
estimating downed dead woody loading; loadings for other fuel components, such
as canopy fuels, litter, and duff, must be estimated with entirely different methods.
This is somewhat problematic because the sampling unit for PI (transect) does not
always scale to the FAP methods used for sampling other components or used in
other forest and range inventories (Keane and Gray 2013 ). The CWD transects, for
example, are usually too long to fit within the area of standard fixed area plots. PI
sampling designs are also difficult to merge with other sampling designs because
the PI was designed to sample entire stands, not FAPs. PI methods also require a
large number of transects under highly variable fuel conditions, which may be time-
and cost-prohibitive for operational sampling efforts. Keane and Gray ( 2013 ) found
that over 200 m of transect were needed on a 0.05 ha plot to sample FWD within
20 % of the mean. Moreover, some feel that it is difficult to repeat particle intercept
counts with any degree of reliability (Sikkink and Keane 2008 ). Particles are often
hidden by other fuels often partially buried in the litter and duff making repeatabil-
ity across and within observers difficult.

8.3.2.2 Fixed-Area Plots (FAP)

In contrast to unequal probability strategies (e.g., PI), FAP are based on equal prob-
ability sampling methods and have been adapted from vegetation composition and
structure studies to sample fuels (Mueller-Dombois and Ellenberg 1974 ). In FAP
sampling, a plot of any geometric shape, often round or square, is used as a sam-
pling unit and all fuels within the plot boundary are measured using any number of
fuel measurement methods including destructive collection (cut, dry, and weigh fu-
els; see Sect. 8.3.3.5), volumetric measurements (measure diameter, length to com-
pute volume, then use density to estimate weight), vertical depths of duff and litter
layers (measure thickness of duff and litter layer), and particle counts by size class
(count particles, assume standard length, diameter, then compute weight) (Keane
et al. 2012b ). FAPs can be any size, and the most effective sampling efforts scale
the size of the FAP to the fuel being measured. Because FAP approaches require
significant investments of time and money, they are more commonly used to an-
swer research questions rather than to monitor or inventory fuels for management