"Bob Weinberger" wrote in message
...

"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.




Such debates are the like the Medieval debates about how many angels can
dance on the head of a pin.

What really counts is having a brain and experience so that you can tell
what the situation really is and what needs to be done in each stand.

Let's compare- forester "A" who gets more accuarate numbers than forester
"B". But, "A" doesn't know what to do with the numbers, but "B" does. I'd
rather have "B" working for me. If "B" can get numbers 80% as good as "A" in
one third the time- then "B" is the superior employee, especially if he
really knows how to interpret the stand based on LOOKING at it.

In my ideal world, for modest sized properties of not more than a few
hundred acres- I'd have all this cruising kept to a minimum. With good
aerial photos and a quick reconnaisance of each stand- maybe a few plots in
each- with some good thought about what is needed in the stand, less
thought about the numbers- and good thought about access, markets, wetlands-
etc..... all this could and should be done quickly. Producing fancy mgt.
plans with fancy numbers is hardly worth the cost of the paper- and
producing those fancy plans has to be paid by somebody- either the owner or
the taxpayers. I'd rather have that expense go into carefull silviculture-
each tree for harvesting should be marked by a forester.






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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