Pin Oak Tells the Story

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TOPIC: Pin oak tells the story
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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

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TOPIC: Pin oak tells the story
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== 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
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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

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TOPIC: Pin oak tells the story- back to Don Bragg
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== 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