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than some limiting distance that changes along the log length in a manner that is
based on the sampling design. There are many variants of PDS including the dis-
tance-limited protocol for PDS, which uses a fixed distance from the perpendicular
line to estimate volume then loading (Ducey et al. 2013 ). Transect relascope, point
relascope, and prism sweep sampling use angle gauge theory to expand on the PDS
and line-transect method for sampling CWD (Bebber and Thomas 2003 ; Gove et al.
2005 ; Stahl 1998 ).
This method is most effective for measuring only one fuel component, CWD
(Gove et al. 2012 ), but Ducey et al. ( 2008 ) demonstrated how PDS can be used to
estimate other ecological attributes, perhaps finding a future use in FWD loading
estimation. Several studies have compared traditional sampling techniques and PDS
methods and variants to evaluate their performance, accuracy, and bias in measur-
ing CWD (Bate et al. 2004 ; Delisle et al. 1988 ; Lutes 1999 ; Jordan et al. 2004 ;
Woldendorp et al. 2004 ). Gove et al. ( 2013 ) compared PDS variants using simula-
tion modeling and found unbiased estimators of CWD using all variants and the
differences in variances were small across all variants so selection of the most ap-
propriate variant depends on field conditions. Affleck ( 2008 ) merged PDS with PI
sampling to create line intercept distance sampling to improve fuel sampling and
got similar performances to PDS. Ståhl et al. ( 2010 ) merged critical length methods
with PDS which appears to have improved CWD sampling. However, few studies
have yet examined the performance of various sampling techniques for measuring
across multiple fuelbed components, such as combinations of FWD and CWD, live
and dead shrubs, and herbs on the forest. Because of this, there are few operational
protocols that use PDS methods or variants for fuel inventory and monitoring.
8.3.2.4
Cover and Volume Sampling
An alternative to the above direct methods that measure fuel particle dimensions is
applying the abundant methods that directly measure canopy cover in vegetation
sampling efforts to fuel sampling, as opposed to visually estimating canopy cover as
presented in Sect. 8.3.1.2. Canopy cover is directly measured using a suite of meth-
ods, techniques, and protocols for ecological inventories and research efforts (Krebs
1999 ; Mueller-Dombois and Ellenberg 1974 ), and some of these may potentially be
applied to measuring fuel loading. Point sampling, for example, involves using a
vertically placed rod of a small diameter to determine the particle that it contacts,
and the number of contacts per particle type (i.e., fuel component) is then used to
estimate cover. If applied to fuel sampling, the number of contacts can be correlated
with the destructive sampling estimates of biomass. Measures of the height of each
contact can be augmented with number of contacts to associate both cover and aver-
age height with loading (Catchpole and Wheeler 1992 ). Axelson et al. ( 2009 ), for
example, used point and height methods to estimate shrub biomass for the western
Australian karri forest. Line intercept techniques, where the length of intercept of
plant parts are used to estimate cover, can also be used to estimate fuel loading.
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