Hello

I am doing a point-in-polygon GIS analysis and need to know what would be
the acceptable sample size (ground area) represented by a 10 BAF prism (10
ft2 per acre) at each point.

Regards

LugNut

LugNut wrote:

I'm not quite sure what you're asking. Acceptable sample size (ie number of
plots required to achieve a required Standard Error) is not directly
related to the prism size. Ideally, you wouldn't choose a prism until you
saw the size and number of stems in a stand.

And as for ground area represented by a prism, I really don't understand
the question. The plot radius of each tree is a function of the BAF and
the tree's diameter.

So, I guess I'm no help, I just felt like babbling

Joe


Hello

I am doing a point-in-polygon GIS analysis and need to know what would be
the acceptable sample size (ground area) represented by a 10 BAF prism (10
ft2 per acre) at each point.

Regards

LugNut

Where I was froming come is that I was always told to use 0.004 hectare
to represent the amount of ground area in a prism sweep as a rough and dirty
number for a 2 BAF (metric) prism. I know that it will vary based on stem
diameters but I was wondering what the same rough and dirty number was for a
10 BAF Imperial.

Cheers

LugNut

"Joe Shmoe" wrote in message
...
LugNut wrote:

I'm not quite sure what you're asking. Acceptable sample size (ie number
of
plots required to achieve a required Standard Error) is not directly
related to the prism size. Ideally, you wouldn't choose a prism until you
saw the size and number of stems in a stand.

And as for ground area represented by a prism, I really don't understand
the question. The plot radius of each tree is a function of the BAF and
the tree's diameter.

So, I guess I'm no help, I just felt like babbling

Joe


Hello

I am doing a point-in-polygon GIS analysis and need to know what would
be
the acceptable sample size (ground area) represented by a 10 BAF prism
(10
ft2 per acre) at each point.

Regards

LugNut

Hey Joe Shmoe and LugNut- how about giving us your real names?
--
Joe Zorzin
http://www.forestmeister.com




"LugNut" wrote in message
...
Where I was froming come is that I was always told to use 0.004 hectare
to represent the amount of ground area in a prism sweep as a rough and
dirty
number for a 2 BAF (metric) prism. I know that it will vary based on stem
diameters but I was wondering what the same rough and dirty number was for
a
10 BAF Imperial.

Cheers

LugNut

"Joe Shmoe" wrote in message
...
LugNut wrote:

I'm not quite sure what you're asking. Acceptable sample size (ie number
of
plots required to achieve a required Standard Error) is not directly
related to the prism size. Ideally, you wouldn't choose a prism until
you
saw the size and number of stems in a stand.

And as for ground area represented by a prism, I really don't understand
the question. The plot radius of each tree is a function of the BAF and
the tree's diameter.

So, I guess I'm no help, I just felt like babbling

Joe


Hello

I am doing a point-in-polygon GIS analysis and need to know what would
be
the acceptable sample size (ground area) represented by a 10 BAF prism
(10
ft2 per acre) at each point.

Regards

LugNut

Lugnut,

I see the same problems in your attempt at analysis that Joe Shmoe sees.
There is no "representative ground area" when you're doing prism plots. Like
Joe says, it depends on the level of error you want to achieve, what type of
sample your after, etc. You need to decide what "n" you need to represent
"N" based on a number of specifics.

If you're looking for a representative plot, why not do fixed plots? If you use

a 1/10 acre plot, it will be 1 chain x 1 chain square, which is very simple
to set up, and the statistics are much more easier to calculate.

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

LugNut wrote:

Where I was froming come is that I was always told to use 0.004 hectare
to represent the amount of ground area in a prism sweep as a rough and dirty
number for a 2 BAF (metric) prism. I know that it will vary based on stem
diameters but I was wondering what the same rough and dirty number was for a
10 BAF Imperial.

Cheers

LugNut

"Joe Shmoe" wrote in message
...
LugNut wrote:

I'm not quite sure what you're asking. Acceptable sample size (ie number
of
plots required to achieve a required Standard Error) is not directly
related to the prism size. Ideally, you wouldn't choose a prism until you
saw the size and number of stems in a stand.

And as for ground area represented by a prism, I really don't understand
the question. The plot radius of each tree is a function of the BAF and
the tree's diameter.

So, I guess I'm no help, I just felt like babbling

Joe


Hello

I am doing a point-in-polygon GIS analysis and need to know what would
be
the acceptable sample size (ground area) represented by a 10 BAF prism
(10
ft2 per acre) at each point.

Regards

LugNut

"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

Remove "invalid" and place a dot between bobs and stuff to reply email

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.

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.

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.

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.

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.

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

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

Remove "invalid" and place a dot between bobs and stuff to reply email

"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
Remove "invalid" and place a dot between bobs and stuff to reply email

"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
Remove "invalid" and place a dot between bobs and stuff to reply email

This is good content - not theoretical at all. In the PNW, this is how
we cruise. Yes, a forester had better know what his findings mean in
the "real world" of non-mensurationists, on the other hand, he had
better be able to explain his procedures professionally too. If photo
cruises can do that for you back east, fine. That's not done often here,
except for cursory overviews. Partly that's because of the way we sell
timber - we have a lot of cash sales rather than stumpage sales and
values had better be nailed down to a few percent.

Back to the original question: having to derive a sample area when
using a relaskop is not kosher, but its done all the time to estimate
the number of plots needed before a cruise. Then sampling intensity is
adjusted in the field, depending on the findings. An BAF of 40 in large
timber is approximately equivalent to a 0.2 acre fixed plot for
estimating purposes only. As to whether one would actually DO a fixed
area plot, the advantages of using variable plots are so great in this
region (see that caveat?) that fixed plots are used only for
regeneration or research.

"mhagen" wrote in message
...
This is good content - not theoretical at all. In the PNW, this is how
we cruise. Yes, a forester had better know what his findings mean in
the "real world" of non-mensurationists, on the other hand, he had
better be able to explain his procedures professionally too. If photo
cruises can do that for you back east, fine. That's not done often here,
except for cursory overviews. Partly that's because of the way we sell
timber - we have a lot of cash sales rather than stumpage sales and
values had better be nailed down to a few percent.


Oh, you're talking about a cruise for a timber sale? I thought the
discussion was cruising for mgt. plans. Certainly for a timber sale- you
need very good information. Here, only timber beasts cruise for a timber
sale, before they rip off the owner. Any reputable forester will mark and
tally each and every tree- a 100% tally. However, not even doing a 100%
tally, here, will give anyone accuracy to a few percent- since the trees are
difficult to accurately measure. Most hardwoods have irregular shapes,
forking- defects of all kinds, etc. so it becomes as much art as science.
What really counts is consistancy. The wood buyers keep a good record of the
results they get from each forester- so if I'm consistantly over by 15% on
some species and 5% on another- they know it- and they bid accordingly-
which makes everyone happy. Consistancy is the key. I suppose since you work
with mostly conifers which are more likely to be straight and round and not
forked- if you're carefull you should get much better accuracy- but with any
sort of a cruise that's not 100% I doubt anyone can get within a few
percent.



Back to the original question: having to derive a sample area when
using a relaskop is not kosher, but its done all the time to estimate
the number of plots needed before a cruise. Then sampling intensity is
adjusted in the field, depending on the findings. An BAF of 40 in large
timber is approximately equivalent to a 0.2 acre fixed plot for
estimating purposes only. As to whether one would actually DO a fixed
area plot, the advantages of using variable plots are so great in this
region (see that caveat?) that fixed plots are used only for
regeneration or research.


--
Joe Zorzin
http://www.forestmeister.com

Joe Zorzin wrote:

"mhagen" wrote in message
...

This is good content - not theoretical at all. In the PNW, this is how
we cruise. Yes, a forester had better know what his findings mean in
the "real world" of non-mensurationists, on the other hand, he had
better be able to explain his procedures professionally too. If photo
cruises can do that for you back east, fine. That's not done often here,
except for cursory overviews. Partly that's because of the way we sell
timber - we have a lot of cash sales rather than stumpage sales and
values had better be nailed down to a few percent.



Oh, you're talking about a cruise for a timber sale? I thought the
discussion was cruising for mgt. plans. Certainly for a timber sale- you
need very good information. Here, only timber beasts cruise for a timber
sale, before they rip off the owner. Any reputable forester will mark and
tally each and every tree- a 100% tally. However, not even doing a 100%
tally, here, will give anyone accuracy to a few percent- since the trees are
difficult to accurately measure. Most hardwoods have irregular shapes,
forking- defects of all kinds, etc. so it becomes as much art as science.
What really counts is consistancy. The wood buyers keep a good record of the
results they get from each forester- so if I'm consistantly over by 15% on
some species and 5% on another- they know it- and they bid accordingly-
which makes everyone happy. Consistancy is the key. I suppose since you work
with mostly conifers which are more likely to be straight and round and not
forked- if you're carefull you should get much better accuracy- but with any
sort of a cruise that's not 100% I doubt anyone can get within a few
percent.

Conifers are pretty variable too, though the variability lies more in
defect and breakage than in tree form, though that can be wild too.
There's a world of difference between the difficulty of cruising an old
growth cedar stand and a second growth fir stand. Log buyers act the
same way here too. They definitely keep score sheets on cruisers and
compare notes at auctions. The one's who stay in business are pretty
sharp and do not miss a trick. I've gotten involved in discussions
after auctions where several cruises on the same sale were compared -
ones which arrived at the same volume but lower CV and more sample
points - higher costs, vs ones with less points but high CV and some
complete misses on sort breakdown, but lower costs. And perhaps only a
few sorts are really wanted by that particular buyer, they can turn
around and sell the others to someone else. Throw in cruiser windage and
you've got a challenge for the buyer.

No stress here, eh?