07, 2003 16:03 PST
Our discussions on tree measuring methods
periodically make the rounds. I think we've circled back and are
ready for a new round.
In some ways the errors that other, otherwise
qualified, people make is frustrating and in other ways, pretty
funny. Understanding why so many forest-savvy people screw up so
badly on tree measuring amounts to a study in human psychology.
Lots of emotional ingredients: turf issues, personal pride,
arrogance, foolishness, lack of mathematical maturity.
In May 2000, a number of us met at Sweetbriar
College in VA for an old-growth conference. As part of the
post-lecture entertainment, Will climbed a southern red oak near
a campus building. There was quite a group watching the event.
While he was climbing, I scampered up a hill and shot the broad
crown several times. It looked like the top was going to be
about 93 feet. However, when Will got near the top he called out
to me. I told him I couldn't see the branch he was measuring, so
he wiggled it. I hadn't measured that branch. It was farther
back in the crown and looked lower. So, I took three separate
measurements of the branch and averaged the measurements. The
height came out to exactly to 95 feet. I thought about it and
started to add a decimal position (like Mt Everest's original
29,002-foot measurement, which had actually been an average of 5
that came out exactly to 29,000), thinking that 95 wouldn't
sound accurate. Then I thought better of it - had to be honest
and faithful to the cause. When I went down hill and told Will
that I'd done my best and got 95 feet, he called out to Rick Van
de Poll who was holding the tape to the ground to read the tape
aloud. Rick called out 95 feet! I let out an ape call.
There's more to the story - the humbling part.
An old horse logger who was attending the conference had
eye-balled the tree and told those standing close by that he
estimated the tree at 95 feet. So Will's actual taped height, my
laser-clinometer measurement, and the logger's eye-ball all
agreed. So the logger's field experience proved its value. Will
and I had plenty of measuring experience and the old logger had
felled many trees and had developed a keen eye for height.
I had hoped the lesson to all would be that
when it comes to tree measuring, ENTS measurers are THE experts.
End of story. Actually, we were happy to share the accolades
with the horse logger. He reminded us of what a well trained eye
can do without equipment.
Coast Redwoods in the South & more Champion Tree Bull_ _ _
09, 2003 05:36 PST
I hear your story, and I see a 2' height error (without the
Will's climbing effort) on an open grown hardwood with good site
lines. That does not sound substantially better a clinometer and
Coast Redwoods in the South & more Champion Tree Bull_ _ _ _
09, 2003 09:50 PST
Someday I hope to venture down from Maryland to the Congaree,
meet you, and
see some of your super trees. In the meantime, let's look at
measuring adventure at Sweetbriar.
To simplify, let's suppose Bob was standing downhill so that the
base of the
tree was exactly at eye level. That makes for a simple diagram
triangle. Let's suppose the 93' elevation was shot at 45
degrees, and was
on a "shoulder" of the broad crown, 20' out from the
centerline of the
Now, Bob's elevation of the shoulder twig (93') was accurate.
You or I
might sight by clinometer or stick to the same prominent point.
If we took
care to find the spot directly under the twig (20' from the
trunk), we could
pace the distance from the sighting point to the said spot and
it would be
93'. Indeed, as you suggest, the laser, stick and 45 degree
methods could all be accurate in determining the height of the
twig on the
shoulder of the tree.
Unfortunately, many practitioners of the stick method assume the
see (a spot on the shoulder of the crown) is synonymous with the
top of the
crown, and they pace a baseline right up to the trunk. With
that would be an extra 20', for a total of 113', or 18' above
top. I call this "false-top triangulation;" it's the
triangle formed above
the crown by an extension of the vertical line above the base,
oblique line of sight; it's just air. If the measurer is using a
clinometer, the angle can be steeper than 45 degrees, and the
false top increases rapidly. That's how that swamp chestnut oak
got to 200 feet on the national list. A white oak near here was
our state list as 143', but proved to be 104'; it had a broad
With a clinometer, most people use a fixed baseline. They
measure out 100'
from the trunk, find a target, shoot up with the clinometer and
dial. It's sort of automatic, and they don't consider the true
of the target twig where crown meets sky. Of course, if the tree
things can get worse. Before I had a laser, I spent a day with a
measuring trees. We put a lot of faith in the clinometer;
make no mistakes; just go 100 feet and read the dial. We both
thought a big
tuliptree was 170 feet; it's actually 143'.
It's easy to go 100' and read the dial; probably no one is going
and doubling the reading on the dial. Few use the half-stick
halve the baseline measurement. It's even less likely that
locating a window to the true top, shooting the angle, then
actual baseline and doing the trigonometry.
Anyway, there's a lot of very decent people out there who have
faith in their clinometers. Sometimes they get good readings,
not, but it's very hard for them to broaden their understanding.
we get frustrated. All of us can spot the truly bad readings.
height is far beyond known maximums for the species, or
impractical. Trees with broad crowns just aren't as tall as
Now, if Bob thought the tree was 93', and another twig went to
95', is that
a 2' measurement error? It's not always possible to locate the
point. That's different than getting a bad measurement of a
What's most significant is that he didn't exceed the actual
height of the
tree. With laser-based hypotenuse measurements, you don't go
don't get false-top triangulation, and you don't get 200' basket
Your input is most valuable, because you are in a position to
sides of the situation. I'd enjoy hearing from you and
discussing how we
can encourage others to understand the care needed in using the
methods, and why a $199 laser is a good investment.
rap on the old knuckles
09, 2003 15:17 PST
Colby's accompanying explanation is
appropriately civil. It adds significantly to the credibility of
these discussions on measurement methodology. I'm sure we both
thank him for taking the time and taking a measured tone.
Over the life of this list, we've drawn many
diagrams identifying where and why clinometer only measurements
lead to significant measurement errors - unless adequate
precautions are taken. I just don't know what else we can do.
Colby has identified huge measurement errors as have Will
Blozan, Bob Van Pelt, Mike Davie, Howard Stoner, Jess Riddle,
Jack Sobon, Dale Luthringer, and myself. Others including Lee
Frelich, Paul Jost, and Tom Diggins may have also identified
them. Incidentally, super scientist Dr. Lee Frelich uses the sin
top-sin bottom method for measuring trees. He changed from the
clinometer only method of measuring tree height for the same
reasons that the rest of us did. It wasn't a case of rolling
dice on which method to use. He chose the more advanced one.
Bruce, it isn't that we are purposely trying
to be elitists in ENTS by pushing hard for broader acceptance of
more accurate measurement techniques. It is that we have put
tons of time into perfecting our methods, which are demonstrably
more accurate than the clinometer only methods for the reasons
we state. Bob Jones's methods are NOT equal to ours unless he
takes into full consideration where the top of the tree is
relative to the base and succeeds in doing it accurately, so
that he doesn't create a triangle with a false top. It's just
the trigonometry that has to be applied to the tree form.
Nothing personal. It's just business. We're not measuring
vertical telephone poles in level parking lots where a
clinometer only and a 100-foot baseline would be completely
With respect to my measurement in Sweetbriar
College, I got exactly the same result (95 feet) as Will's
measurement in the southern red oak once I knew which twig he
was measuring. Could I have done better than achieving 100% in
the accuracy of the measurement? The southern red had a broad
crown with many potential highest points. The one at 95 feet was
not highest apparent point via the angle it subtended because it
was well back into the crown and didn't stick up as high as
closer points. The point I first measured was a more obvious
choice since it stuck up higher and it did measured to 93 feet.
That isn't far off the point Will chose, so my first choice
wasn't a bad one. The high point was definitely not over the
base of the tree and not visible standing beneath the tree
looking up through the foliage. Identifying where a plumb line
from that point would intersect the ground would require cross-
triangulation of the point. Will and I used that technique many
times before the days of lasers and hypotenuse-based
measurements. I'd be interested in watching clinometer only
measurers tackle that broad-crowned tree. The odds are high that
they would over-measure it by 10 feet or more.
Bruce, if clinometer only methods worked as
well as those we use, we wouldn't be spending all the money that
we spend on lasers. What would be the point? Our purpose in
going the extra yard is to bring accuracy into the picture for
science-based reasons and also for historical documentation
purposes. I can't say enough about the importance of the latter
especially where important, but threatened, properties like Zoar
Valley are concerned. Tom Diggins once wrote an eloquent defense
of accuracy for reasons of establishing site significance.
Perhaps Will and I shouldn't get frustrated
when others make extraordinary claims on tree dimensions that we
know are wrong and/or don't make sense of the species being
measured (179 feet for a red maple in Michigan). We could
discuss this point for a long time, but you are correct to call
us to task when we get too testy. I'll gladly take a knuckle rap
in the proper spirit when I allow lapses to occur in my
You are a valued member of this list and we
certainly don't want to lose you. Hopefully, we can agree to
disagree at times without either of us taking offense, If my
posts on measuring methodology have given you cause for feeling
offended, I apologize. That has certainly never been my purpose.
A rap on the old knuckles
10, 2003 07:43 PST
Bob et al.:
The tangent method and all baseline to the trunk methods for
measurement assume that the high point of the tree is directly
base of the trunk. If it is, it yields the correct height. If
the formula and resulting triangulation are mathematically
The problem is that for old growth forests and record sized
assumption is rarely true. The sine method does not assume that
point is above the base of the trunk, so the triangulation there
regardless of the shape of the tree's crown.
The tangent methods usually yields errors of 5-10 feet in old
forests, and to correct those errors by shooting the baseline
the point on the ground directly beneath the high point of the
tree is a
lot of work. I know since I measured a thousand trees that way
lasers were available.
It is much easier to use the sine method with a laser and
within 2 feet of the actual height. Then all you have to worry
about is to
find the highest twig and a spot where you can see it.
14, 2003 08:28 PST
The flurry of e-mails discussing how we
fine-tune our tree
measurements to take into consideration the limits of our
might seem like overkill to those with only a casual interest in
dimensions, but our obsession is no more nor less than that of
members of any group who seek to push the envelope for their
or sport. Consider how far technical climbing has evolved to
faces to be routinely scaled that once appeared unclimable.
pushing the envelope and we know it, but we don't expect those
less intense interest in tree measuring to adopt our methods or
pressured into seeking ultra precision. There's ample room for
intensity in keeping with the objectives of the champion tree
which we believe are important.
We will continue to make our expertise
available to American
Forests, the state champion tree coordinators, and are quite
help one of our own - Will Fell develop a measuring guide. More
measuring workshops will be scheduled. However, through it all,
promise to remain sensitive to those gentle spirits who just
admire trees for their beauty.
As we gain in reputation and
accomplishment, our pugnacity will
diminish. We needed to stand our ground early on came to offset
of understanding on the part of others as to what ENTS was all
to draw attention to entrenched tree-measuring methods in need
change. As Russ Richardson stated, we're taking tree measuring
higher level, albeit to nowhere near the level that Bob Van Pelt
it to in his research. I do sense real progress on both fronts,
need to be openly combative/iconoclastic is subsiding. However,
still encounter reactionaries on occasion and have to administer
verbal spanking. We'll do it with increased sensitivity, though.
be a nice spanking.
Our site documentation methodology is
taking on a life of its own
thanks to the inner group. However, we now need to expand the
Index concept to encompass both height and circumference
could even add a third index devoted to circumference x height.
three indices, taken together, would reveal much more about a
Given the large girth cottonwoods out Lee Frelich's way, it
to add both the Rucker Circumference Index and the Rucker Point
paint a more complete picture of the distinctions between eastern
mid-western forests of the same species. Differences in forest
that can be reflected in the indices that are attributable to
frequency and intensity of storms and other climate features
Well, enough rambling. Someone else's turn.