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TOPIC: Pin oak tells the story
http://groups.google.com/group/entstrees/browse_thread/thread/04848db8a70f2034?hl=en
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== 1 of 7 ==
Date: Mon, Jun 9 2008 4:18 pm
From: dbhguru@comcast.net
ENTS,
Today, I went back to Childs Memorial Park and did a mini-study of
another splendid pin oak. The attached spreadsheet tells the story.
Not much more to be said. I'm happy to discuss the numbers with
anyone who wishes to. Otherwise, as stated, the numbers speak for
themselves.
These individual tree studies are pretty revealing. From a small
sample of trees, it is easy to see why tree height data as reflected
anecdotally and in the champion tree programs is so screwed up. In
the hands of an expert a clinometer and tape measure can be made to
suffice on a high percentage of trees - but not without a lot of
extra work. The solution is a laser rangefinder, clinometer,
scientific calculator, and the sine method. Not much else needs to
be said.
Bob
== 2 of 7 ==
Date: Mon, Jun 9 2008 7:44 pm
From: "symplastless"
I thought London Plane had a white look when outer phellem is shed.
The sycamore was kind of yellow and not white. I thought there was
either sycamore or London plane in my area of SE PA. Any thoughts?
John
== 3 of 7 ==
Date: Mon, Jun 9 2008 9:02 pm
From: DON BERTOLETTE
Bob-
The only thing that jumped out at me was the 66 foot reading...if
the spread sheet were graphed, it would be way off the curve...
-Don
== 4 of 7 ==
Date: Mon, Jun 9 2008 9:23 pm
From: "Edward Frank"
Bob,
Interesting data set. I am not sure that the average of the height
errors for the tangent method at the various distances (16.84 feet)
is a meaningful number. it can be calculated, but does it mean
anything? Why the big error at 68 feet? Were you hitting a forward
branch?
Ed
== 5 of 7 ==
Date: Mon, Jun 9 2008 10:44 pm
From: dbhguru@comcast.net
Don,
Do you mean the 68-foot distant reading? The reading taken at that
distance was a case where outstretched branches completely obscured
the upper parts of the tree. An experienced measurer would have
recognized the problem and not have measured from that spot.
However, I included it to further illustrate the danger of blindly
following a convention and because the scales of some clinometers
are based on chains you know, althoughly usually not the only
option.
Bob
== 6 of 7 ==
Date: Mon, Jun 9 2008 10:50 pm
From: dbhguru@comcast.net
Ed,
Yes, the huge error made at the 68-foot distance resulted from
catching a forward thrusting limb. As I mentioned to Don Bertolette,
from the location, all upper parts of the crown were obscured. No
competent measurer would use a chain length as a baseline to measure
a broad-crowned tree. But I wanted to include a measurement from a
large, spreading tree to illustrate the range of results one gets by
blindly following a convention.
Bob
== 7 of 7 ==
Date: Mon, Jun 9 2008 11:27 pm
From: dbhguru@comcast.net
Ed,
One interpretation is that for this particular tree, the 16.84-foot
average error shows us how different people measuring the tree from
different spots, using the tangent method would do. On that
particular pin oak, from some directions, you don't see the top at
all. Where the true top can be seen from a narrow window from one
side, you must be back 160 feet or more and the true top looks no
higher than 4 or 5 other spots. On the down sloping side of the
tree, I had to go all the way back to 320 feet to eventually locate
the high spot, and from there, the true top does not look like the
highest spot. I'll expand the experiment in the future to reflect
the percentage of spots where the highest spot is visible and how
far from the trunk you have to be.
My overall conclusion is that if you were using just a clinometer
and tape on this tree, it would be a bloody miracle if you measured
the height of the tree accurately. If you did get the right height,
it would, with a high probability, be just an accident, i.e. you'd
be measuring a different spot in the crown and be making an error,
but unknowingly arrive at the true height of the tree.
Bob
==============================================================================
TOPIC: Pin oak tells the story
http://groups.google.com/group/entstrees/browse_thread/thread/04848db8a70f2034?hl=en
==============================================================================
== 2 of 4 ==
Date: Tues, Jun 10 2008 12:00 am
From: DON BERTOLETTE
Bob-
Much of my time measuring trees in the woods was a function of my
various employers, and until the late 1980s, in the western US where
coniferous species are commercially dominant. In the year in year
out life of a forester, much of the measuring of trees that is done,
is done to predict volume for timber sales, so as to advertise it
with an idea of the value of what was to be offered up for contract
bidding. We got good at estimating volume and grade for fairly large
stands. Commercial valuation didn't include tree height, but height
to a predetermined commercial diameter limit (usually 4 to 6
inches). In our prime, I'd put us against your digital devices and
win a bunch of beers estimating height at which 4 or 6 inches
diameter was reached. Our work was randomly checked, and a lot of
integrity was tied up in how accurate we were.
In my third year as a forest tech, still in school at Humboldt, I
was crew chief on a Continuous Forest Inventory crew, on the
Shasta-Trinity National Forest in Northwestern California. Our
stands were overwhelmingly evergreen/coniferous, and simple to
measure. We visited probably 75 plots over the summer we had in
between classes, and carefully measured height, diameter at breast
height, species, grade, community/habitat type, etc. We measured
tree heights, from a two foot stump height which many times would be
outside the 'butt swell'. Height was measured according to the
tangent rule, although we didn't refer to it that way. Most of us
operated by rules of the thumb. Rule 1, horizontal distance needed
to exceed vertical distance. Rule 2, determine direction of lean
(sweep) and measure at right angles to it. Rule 3, once Rule 1 was
achieved, walk to a distance easy to convert in your head (200, 150
feet, 125 feet, 133 feet (or 132, if using topo clinometer)., Rule
4, measure top and bottom from same location. Acute angles were
better than obtuse (topographically, measure from as much above as
possible, as some coniferous species had rounded top that could
cause error from not seeing actual top).
When possible, for efficiency, we'd often walk out equidistant from
two or more trees if conditions permitted, which would allow us to
measure two or more trees from same location. Not often, but not
infrequently either, a series of trees would describe a rough line,
or better, an arc that permitted 'two birds with one stone'
opportunities.
When I went back East as a forest tech to Kentucky's Daniel Boone
National Forest, it was more of the same, but deciduous trees posed
special problems, as you well know. Even so, we had no real occasion
on year in year out basis for measuring total tree height to the
level of accuracy that ENTS achieves. We still measured to height of
commercial top (when the final info you need is number of 4/8/16
foot logs, there are very distinct points of diminishing returns in
careful measurement of top twigs). One tree in a hundred (not
actually, but indeed a small fraction) where measured accurately to
"top twig", as sample trees, but these weren't selected as
champion trees, but random stand height trees, where being accurate
to feet was adequate for the task. One further level of checks was
having a limited sample of the "sample trees" taken to the
mill for accuracy of volume measurements and tree grade (quality
issues, clear, knot free, extent of rot, etc.).
I have tried to relate all this in a non-defensive tone, as I feel
no need to rationalize my career as a forester. we did what was
needed to be done for the time, and did it with all our hearts.
Would I in retrospect, with omnicience, change anything? Oh, yeah,
you bet...but that's another story.
-DonRB
== 3 of 4 ==
Date: Tues, Jun 10 2008 12:07 am
From: DON BERTOLETTE
Bob/Ed-
Just a quick comment, even by crude western standards, a 100 foot
tall tree (conifer or deciduous) wouldn't have been measured from
less than a 100 foot horizontal distance...99 foot maybe, if topo-scaled
clinometer was used (1.5 chains), but more likely from 132 feet, and
from as high a vertical position in the topography as possible.
-Don
== 2 of 3 ==
Date: Wed, Jun 11 2008 6:35 am
From: doncbragg@netscape.net
Bob--
I've sent Lee the analysis I've done comparing the sine and tangent
methods for height determination.? Your testing further affirms the
value and consistency of the sine method.
One note, though--when determining the sine height to use for the
basis of comparison, averaging the numbers is not the best answer.?
Since it is not possible to overestimate height using the sine
method (this assumes you're measuring the correct tree, and
instrument error is negligible), the best estimate of total tree
height is the maximum value of your sine height measurements, not
the average.? Thus, for the ten sine heights you took, total tree
height = max(99,99.5,99.5,100,100,100.5,100.5,100.5,100.5,100.5) =
100.5 ft.? The average of this data set (100.05) is not far from
this, but why lose the information you have?? After all, you have
five measurements of 100.5 ft--pretty clear evidence this is the
maximum tree height.? Suppose you had one measurement that was way
off (say, 50 ft) due to taking a height on a subordinate branch that
projects towards the observer.? Taking this average
(avg(50,99.5,99.5,100,100,100.5,100.5,100.5,100.5,100.5)), you get
95.15 ft--a noticeable error, while you still get the correct
maximum height using max().? You shouldn't use the maximum with
tangent because you don't know how the height errors are
distributed, or how they're biased.? Averaging is somewhat better
with the tangent method, especially if the bias in height estimates
offset--but then again, this can't be assumed, and with wide,
spreading crowns, tangent height estimates may always be
overestimates.
Don
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Don C. Bragg, Ph.D.
Research Forester
USDA Forest Service
Southern Research Station
DonCBragg@netscape.net
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The opinions expressed in this message are my own, and not
necessarily those of the Southern Research Station, the Forest
Service, or the USDA.
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TOPIC: Pin oak tells the story- back to Don Bragg
http://groups.google.com/group/entstrees/browse_thread/thread/4af55566158073f8?hl=en
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== 1 of 1 ==
Date: Fri, Jun 13 2008 8:43 am
From: dbhguru@comcast.net
Don,
I hear what you say. I guess I'm just not quite confident enough of
the lasers and tilt sensors on my two TruPulses or the laser
clinometer combination for my other instruments to trust the highest
readings. With the TruPulse the accuracy of the laser is in the
range of +/- 0.5 feet, but I don't yet know what kind of rounding
aglorithm they use. The clinometer is rated to +/- 0.25 degrees.
My experience with both features of the TruPulse instruments is that
on distances of under 150 feet, the laser is accurate to +/-0.2
feet. I'm less sure about the tilt sensor. However, if the
background to a target is blue sky, the Laser tech lasers have
trouble, especially at greater distances. Laser Technologies Inc
warns users about this situation. What they don't say much about is
the directions (+/-) of errors when they occurs. What has been your
experience here?
In terms of what I actually average when shooting to a target, I
toss out any apparently anamolous readings. I acknowledge that judgment
enters the picture on what to retain or toss, but a value
that differs significantly from the pattern shouldn't be averaged in
by my rules. However, in the case of the highest point of the pin
oak, I do believe it is 100.5. The illustrated averaging process in
my e-mail was more for the benefit of those whose distance and angle
measurers are different instruments instead of taken from the same
measured point as with the TruPulse. But to reinforce your point,
I've since remeasured the oak several times and a 100.5-foot height
determination is holding up well.
Bob
==============================================================================
TOPIC: Pin oak tells the story- back to Don Bragg
http://groups.google.com/group/entstrees/browse_thread/thread/4af55566158073f8?hl=en
==============================================================================
== 1 of 2 ==
Date: Sat, Jun 14 2008 7:07 am
From: doncbragg@netscape.net
Bob--
I haven't noticed the problem with the TruPulse as you mention it,
but then again I haven't been looking.
I would think that as long as you have a clear shot at the top and
bottom of the tree, there is no reason to think that the lower
readings are any more or less accurate than the higher ones,
especially when you get multiple identical values.
Don
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Don C. Bragg, Ph.D.
Research Forester
USDA Forest Service
Southern Research Station
DonCBragg@netscape.net
~~~~~~~~~~~~~~~~~~~~~~~~~~~
== 2 of 2 ==
Date: Sat, Jun 14 2008 11:01 am
From: dbhguru@comcast.net
Don,
You have a point. Where the highest number is repeatable, I would
agree to go with it unless calibration testing suggests otherwise.
Early this morning, I decided to test the calibration of three of my
lasers: the Bushnell Yardage Pro 800, the Nikon Prostaff 440, and
the TruPulse 360. I also did a tape to TruPulse test including
distances to close to the target use the other lasers. The results
are shown in the table below.
Tape |
TruPulse |
Diff |
Abs
Diff |
50.00 |
49.50 |
0.50 |
0.5 |
60.00 |
59.50 |
0.50 |
0.5 |
40.00 |
40.00 |
0.00 |
0 |
30.00 |
30.50 |
-0.50 |
0.5 |
20.00 |
20.50 |
-0.50 |
0.5 |
10.00 |
10.50 |
-0.50 |
0.5 |
25.00 |
25.50 |
-0.50 |
0.5 |
70.00 |
69.50 |
0.50 |
0.5 |
80.00 |
79.50 |
0.50 |
0.5 |
90.00 |
90.00 |
0.00 |
0 |
100.00 |
99.50 |
0.50 |
0.5 |
35.00 |
35.00 |
0.00 |
0 |
15.00 |
15.50 |
-0.50 |
0.5 |
20.00 |
20.00 |
0.00 |
0 |
20.00 |
20.50 |
-0.50 |
0.5 |
5.00 |
5.50 |
-0.50 |
0.5 |
45.00 |
45.00 |
0.00 |
0 |
65.00 |
64.50 |
0.50 |
0.5 |
43.00 |
43.00 |
0.00 |
0 |
44.00 |
44.00 |
0.00 |
0 |
25.00 |
25.00 |
0.00 |
0 |
49.50 |
49.50 |
0.00 |
0 |
|
|
|
|
Avg |
|
-0.02 |
0.30 |
Target |
Bushnell |
Nikon |
TruPulse |
Tape |
Wall |
99.00 |
99.00 |
97.70 |
98.00 |
Flower
Pot |
69.00 |
69.00 |
67.50 |
68.00 |
Mail
Box |
54.00 |
55.50 |
54.50 |
55.00 |
Road
Sign |
111.00 |
111.00 |
111.50 |
112.00 |
Rock
Wall |
69.00 |
70.50 |
68.50 |
69.00 |
Rocks |
108.00 |
109.50 |
108.00 |
108.00 |
Orange
Tape |
108.00 |
109.50 |
108.00 |
108.00 |
Rocks |
147.00 |
147.00 |
146.50 |
146.00 |
Door |
99.00 |
102.00 |
99.50 |
100.00 |
Rock |
63.00 |
64.50 |
62.50 |
63.00 |
Wall |
66.00 |
66.00 |
64.50 |
65.00 |
|
|
|
|
|
Avg |
90.27 |
91.23 |
89.88 |
90.18 |
Avg
Diff Tape-Laser |
-0.09 |
-1.05 |
0.30 |
|
Direction
of Error |
Over |
Over |
Under |
|
My Bushnell has always been an extremely accurate instrument. Two
other Bushnells I own aren't as accurate. One tends to shoot high by
a yard and the other low by a yard. The Nikon shoots high by between
1 and 1.5 feet on about a third of the shots and about 80% of the
time on a high reflectivity target (go figure).
Based on the accuracy of my Bushnell, I feel I can trust the
measurements for the Jake Swamp pine. I think New England has one
legitimate 170-footer. Maybe it is worth an article in a paper or
magazine.
Bob
|