"Geoff Kegerreis" wrote in message
...
Bob,
If you look carefully again at my last message, you will see that I mentioned
volume in the text. Also, I have a tendency to think that 3-5 trees per point is low.
This is supported by expert biometrists US wide, including both Dillworth and Bell
from out in your neck of the woods. Avery (1967) suggests 5-12 trees per point.
I suggest that At least 7 trees should be tallied on average per point for a reasonable
measure.

John Bell is a personal friend, and we have had numerous discussions on the proper number of trees
/plot. Though he cites higher figures in his texts , he concedes that he had a specific set of
conditions in mind when giving those numbers, and that you are more likely to get good representative
results with more plots of fewer trees /plot than the reverse.

BAF=10 is pretty common here East of the major divide. In North Carolina I used to use 20
on the big hardwood stands down there, and I don't see that being a problem in
a Eastern pine plantation, or a sawlog-sized dense aspen stand, but 40BAF
is probably what guys like you use in Oregon big conifer stands. In fact, I'd bet a dollar
you have a relaskop instead of a prism, or both. When I worked in Montana, the
forest circus required a relaskop for certain contracted jobs, and I'll bet it's the same in Oregon
too. Not sure if you contract for the circus, but even if you didn't, a relaskop would be
too practical for use out there not to have one. It's not practical here in Michigan, and I've
only seen one state forester use one. If he had to pay the $1300 for it out of his own pocket,
I doubt he'd have it.

These days I leave the actual field cruising to younger legs, but yes I used both a relaskop and
prisms.
I'm in Northeast Oregon, with conditions more like Idaho or Montana - rarely is 40 BAF used here, 10-
30 BAF is most common.

While responding to E-mails, I think it is important to:
-Listen to what the person is asking for as advice -he's trying to obtain a sample which is
representative of ground area, and did not mention the specifics! Chances are, if he's
doing point in polygon cruising for gathering GIS data, he will need more data than just
standing volume and relative density. Not all timber is even-aged second or third growth conifers
that are
all the same size (thank God). If it was, we could come up with a representative area based on
a low variation average diameter using the figures you mentioned.
-Definitely oversimplify, because the guy is obviously not from this country, and it's
just as obvious that he may not understand the concept of point cruising with a prism.
There is no such thing as a representative ground area for a prism (with the exception mentioned
above), and suggesting that there is any general one number for such explemplifies ignorance
of the concept.
-Instead of criticising someone for sleeping through forest measurements, maybe you should
re-examine your method of obtaining a solution to a problem.

Good points,though I suspect that we may both be guilty of assuming too much about the knowledge and
meaning of the person whose posts we responded to.
Please also note that I was responding to only one paragraph of your post, in which you made some
statements about prism cruises that were, at best, over simplifications, and in which you also stated
unequivicably, without knowing what his cruise conditions and needs were, that he would be better off
sticking to square fixed area plots.

Additionally, I would like to see your dumb ass go out and try to get a reasonably accurate
estimate of trees per acre figure with a 10BAF (or any) prism in a stand of 2-year old aspen.
While it may look good on paper, it's not going to give you enough information on trees/acre
data. If you were to try this once, you would definitely come to the conclusion that
no matter how fast a point cruise is, or what kind of mathematics you use, it will not give you
an acceptable trees/acre figure, unless you are only considering merchantable timber, and
then the figure will likely still be unacceptable, due to the fact that larger trees are
overrepresented
and smaller trees (specifically unmerchantable trees) are underrepresented in a point cruise
regarding trees/acre figures.

I obviously wouldn't use prism plots for 2 yr old Aspen - I would class those conditions as being part
of the exception I stated for heavy underbrush.
However, a 1/10 acre sized plot would be almost as bad and inefficient for that purpose as well. Often
the best solution for gathering a good sample, where there is a broad range of diameters in the
population to be sampled, is to use nested plots, e.g. a small (e.g. milacre) fixed plot for trees
below a certain size, within a prism plot for trees above that size. Not all forest information is
best gathered by the same method, for some data types neither fixed area plot nor a prism plots are
suitable, and a transect or some other method, such as distance from plot center to nearest occurance
are best.

Great for merchantable volume, or as the best guess of what kind of relative density stock is
presently at, but not worth a shit for compiling stock & stand tables (which of course, includes
unmerchantable trees among the forest) or gathering similarly necessary sound forest
management data.

I totally disagree with your assessment that variable plot cruises are not good for creating stand and
stock tables. As I stated previously,
when the known "multiplier" effect for the diameter of each tree that is "in" a prism cruise is
applied, there is no difficulty coming up with accurate numbers of trees/ac. for all trees that are
big enough to have a DBH. Trees that are not big enough to have a DBH can easily be counted on a
small nested fixed plot.

Bitterlich made a good discovery, perhaps the most significant discovery in Biometrics, but
it is not the magical cure for everything surrounding forest inventories.

Agreed.

Hopefully this is simplified enough for you.
Later,
Geoff Kegerreis
www.timberlineforestry.com
P.S. Not that I'm proud to still be a member of SAF (my membership will expire this year), but you
might want to check my working groups in the members only section.



Bob Weinberger wrote:
"Geoff Kegerreis" wrote in message
.. .
snip
Typically, the only reason you would use a prism is to estimate square foot
basal area, while sampling trees for volume. It can give you an estimate of
trees/acre, but it will always steer you wrong because larger trees are certain
to overrepresent themselves vs. saplings. Stick with the square, you'd be much
better off!
-Geoff Kegerreis
www.timberlineforestry.com
Geoff,
Either you are oversimplifying for Lugnut, or you slept through your forest mensuration class.
Prism cruises are commonly used for volume cruises, and if done properly, are every bit as accurate
and much faster than fixed area plots (the exception being areas w/heavy underbrush). Depending on
the distance between plots, a person can take 3-10 variable plots in the time it takes to set up and
measure one 1/10 ac. fixed plot - especially if they are square rather than circular fixed plots.
The key is to chose a BAF that "hits" an average of 3-5 trees/plot in the area to be sampled. BTW
the
"multiplier factor" for each tree diameter for each BAF is readily calculated and is also published
in
most mensuration texts. For instance the plot radius for a 10"DBH tree with a 10 BAF is 27.5', while
the radius for a 20"DBH tree is exactly double (55.0'). Thus each "in" 10" tree with a 10 BAF
represents 18.335 trees/ac., while each "in" 20" tree represents 4.584 trees/ac.
[43560/(3.14159*plot radius^2 )].
--
Bob Weinberger
Forest Management Consulting
Land and Natural Resource
Management Analysis
401 Cedar St.
La Grande, OR 97850
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