To answer Daniel Koechli - in British Columbia CWD is defined as being > 7.5
cm in diameter and as we measure to the nearest 0.1 cm, a piece has to be
7.6 cm or greater (with allowances for rounding up) to be counted in a
standard line transect survey. However, that is the standard for surveys
carried out by government resource management agencies - or contractors
working for them. There is nothing to stop a forestry company or a
university researcher, for example, from using a different diameter cutoff.

As Simon Grove noted, you have to state your lower diameter limit to ensure
that others will realize whether or not your CWD volumes, or other
calculations, are directly comparable with other datasets. Although one
medium- or large-sized piece of CWD could easily equal the volume
represented by a size class of CWD created by using a cutoff of > 5.0 cm
instead of > 7.5 cm, or absent by virtue of using > 10.0 instead of > 7.5
cm, it would be advantageous if a standard minimum diameter were used. The
presence (or absence) of a larger piece of CWD is a matter of chance, the
choice of a lower limit is not.

But for some people, the choice of a lower limit for sampling CWD was based
on a pre-existing process. For example, Brown's original sampling design
(1974: Handbook for inventorying downed woody material. USDA Forest Service
General Technical Report INT-16. Ogden, Utah) uses diameter classes
corresponding to those employed to model fuel condition and fire behaviour:

0.0 to 0.6
0.6 to 2.5
2.5 to 7.6 cm

and, naturally, 7.6 cm is equivalent to 3 inches. So many North Americans
can point to forest fire behaviour models and the Imperial system of
measurement as the source of their lower CWD diameter limit of 7.5 or 7.6
cm. Although others, such as

McRae, D.J., M.E. Alexander and B.J. Stocks. 1979. Measurement and
description of fuels and fire behaviour on prescribed burns, a handbook.
Canadian Forestry Service Report O-X-287. Sault Ste. Marie, Ontario.

and

Trowbridge, R., B. Hawkes, A. Macadam and J. Parminter. 1986: Field
handbook for prescribed fire assessments in British Columbia, logging slash
fuels. FRDA Handbook 001. Canadian Forest Service and B.C. Ministry of
Forests, Victoria, B.C.

used 7.0 cm as the lower diameter limit when sampling to quantify larger
woody material. All pieces less than 7.0 were also sampled and tallied in
both of these procedures. Simon Grove raises a good point that with more
smaller material, the greater the sampling effort. I can vouch for that in
logging slash but the effect would not be as great under an intact forest
canopy.

For sampling purposes we consider CWD to be either fallen and on the ground
or suspended but not self-supporting. Standing dead trees and stumps are
not considered to be CWD for sampling purposes, but as (self-supporting)
dead trees. Uprooted stumps and exposed dead roots > 7.5 cm are classed as
CWD. From the survey data we can calculate the total deadwood volume and
break it down into various components.

Our CWD management directives have defined CWD as being > 10.0 cm in
diameter for operational purposes, that being the usual top diameter
utilization limit. As our field sampling goes below 10.0 cm, we can produce
data summaries based on a > 10.0 cm CWD diameter criterion.

Resource management agencies in B.C. seem to be on par with Simon Grove - we
use 7.5 cm as the cutoff for sampling and consider CWD to be a component of
the total deadwood but can calculate total deadwood volumes. We also have
sampling procedures in place to deal with fine woody debris, at least as
logging slash.

At this point, after 7 years of collecting CWD data in resource inventories,
I can't see us changing the diameter limit - certainly not upwards. It
could go down to > 5.0 cm if we anticipate an operational need. The
research community generally uses the standard inventory as the minimum for
sampling and may be interested in all fine material (foliage and twigs,
branchwood) as well as CWD.

Practically, our current CWD inventory standards meet our operational needs
and individual research projects may go to a finer level of detail. As to
adopting a universal standard, that would prove easier for the research
community than resource management agencies with a history of CWD data
collection and a desire for long-term standards.

Regards,


John Parminter, RPF
Research Ecologist
Research Branch, Ministry of Forests

Phone: (250) 356-6810
Fax: (250) 387-0046

mailto:John.Parminter@...

P.O. Box 9519 Stn Prov Govt
Victoria BC
Canada V8W 9C2

Website: http://www.for.gov.bc.ca/research/