Most interesting, John!

I had no idea that fire was the reason to start CWD inventories. Is that
the reason why CWD includes generally only downed (& more or less dead)
wood. Do snags not play a role in fire behaviour at all?

For ecological purposes I would be interested in snags as well. Are they
just not part of CWD, but get usually inventoried as well, but under a
different category?

Another point nobody mentioned yet is minimal length. I assume you wouldn't
count every little stick out there, would you? Or is the minimal length the
same as the minimal diameter?

And finally: could anyone point me towards literature on the ecological
role of CWD (and snags). With regards to maintaining or enhancing
biodiversity? There MUST be some research giving some indication as of how
much is "enough".

Cheers
Daniel Kochli


At 17:25 28.05.2002 -0700, Parminter, John V FOR:EX wrote:
>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/
>
>
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*******************************************************************
Daniel Koechli
Eidg. Forschungsanstalt WSL - Swiss Federal Research Institute WSL
Abteilung Strategien Waldentwicklung
Zuercherstr. 111
CH-8903 Birmensdorf
Switzerland

Phone +41 1 739 25 29
daniel.koechli@...
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