DBH vs. CBH ... regional ??

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DBH vs. CBH ... regional ??

Post by mdvaden » Sun Oct 09, 2016 4:14 pm

Ever notice a difference between parts of the United States, or elsewhere, how people post about trunk girth? Some refer to CBH (circumference), and other's use DBH (diameter). Here in the west, it seems that DBH is what is used more commonly, except maybe in forestry. But for arborist reports and various big tree champions, DBH is commonly noted. I noticed that a few signs in west coast parks like diameter and circumference for trees.

In the east USA, it looks like most posts at ENTS use CBH when trees are introduced or talked about.
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Re: DBH vs. CBH ... regional ??

Post by Matt Markworth » Sun Oct 09, 2016 4:57 pm


Good topic! I think there probably is some preference depending on region.

For me, the preference towards CBH was rooted in the AF formula and ENTS. Also, I lean towards CBH because it is a direct measurement. DBH implies that a circle is present, which of course often isn't. But, I think people should use whichever one they're more comfortable with and whichever one gives them the most intuitive perception of size.



Re: DBH vs. CBH ... regional ??

Post by Joe » Sun Oct 09, 2016 7:51 pm

Foresters in the east use DBH- at least all the ones I know in the Northeast. It's easier and quicker to measure- which is why, I think, it's preferred. Serious tree measurers should use CBH. Foresters are in too much a hurry to take the extra time- we may have to measure hundreds of trees per day- if marking or cruising- DBH is "good enough".

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Re: DBH vs. CBH ... regional ??

Post by John Harvey » Mon Oct 10, 2016 12:05 am

I agree with Mark, great topic.

As a big tree guy with 10+ years on the East Coast and now living in the redwoods this comes into my mind all the time. My buddies out here all use DBH and I use CBH. I have changed that in group settings (sometimes) just so everyone is on the same page. I still prefer CBH though.

Cbh for me reveals the true trace of the tree, especially with redwoods and other fused and oblong trees. It is the true outline of the trunk for me. Let me give an example. Pictured is the Flat Iron tree. It blew over decades ago and was situated near the famous Giant Tree redwood. It was 3ft across by 20ft across. It was like a wall, literally. Do the math on this one. It comes out the same either way. Lets say the tree was 46ft all the way around. Can you really say it has a 14.6ft dbh? Mathematically you can but depending on the angle your on, you would think I was crazy. I have also been told that "circumference" should only be used in the case that the tree is a "circle". This entire thread kind of proves why we need volume measurements, especially on western coastal trees or better yet why only seeing them in person can give true perspective.
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Flat Iron
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Re: DBH vs. CBH ... regional ??

Post by Don » Tue Oct 11, 2016 4:34 pm

This thread set me to wondering...with regard to diameter, I measured trees that way since 1967 with three really independent land management agencies. It seemed intuitive, as with all my observations, it was the 2D view as I approached the tree that I was measuring what I was seeing. A tree's circumference was an abstraction, and in the somewhat crude measuring requirements of real world forestry, of little value to us in the field. At some point, research foresters in the office worked through formulas that were effective across a broad spectrum of species, species locations, site classes, etc.

In retrospect, I was really equating the breadth of the the tree with it's volume (which more and more I define a tree's "bigness" with its volume). It takes a really long time to accurately assess a tree's volume by "eye", and it's a very subtle, abstract process that is involved.

The closest analogy I can draw is the technique of "cloud mapping" where the "eye" is the 3D assembly of images captured, and then mathematically related to any and all pixels in that "mapped cloud". Although the most common algorithm would be to assess the tree's volume, I suspect one could put an algorithm together that averaged all possible 'diameters' around the 4.5' high cross-section (or at least for a reasonable computational tasking, say every twenty seconds through a 360 degree circle).

Would not that provide a volume approximation (for that section of similar measure) that would be sufficient for our needs?
A quick aside, Bob Leverett has been working through some ways of modeling a tree that goes from say a parabola that was 3 ft deep and 20 ft. across, and estimating its volume as it progresses up the tree, eventually into a cylindrical column (don't most?) before branching.

At some point, one could argue for not just volume, but involve the specific density of trees being considered for candidacy (how would we rule on two trees of drastically different specific densities, but identical external dimensions,say an elm (35#/cu. ft) versus ebony (70#/cu.ft.) ?).

Enough rambling, whattaya think?
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Re: DBH vs. CBH ... regional ??

Post by edfrank » Wed Oct 12, 2016 7:52 pm

I would like to back track to the original comment. Why CBH rather the DBH? The initial Big Tree Formula incorporated CBH so that to a degree was the pattern followed by big tree measurers thereafter. Another factor that makes me want to use CBH relates tomy sense as a scientist. CBH is something you physically measure. Ypu can wrap a tape around a tree trunk and measure it. DBH is something that you to a degree interpret using various devices. DBH can change for a single tree if you look at it from different angles, while the CBH is a single comprehensive measurement that doesn't change depending on your perspective. The two are virtually interchangeable with CBH/pi = DBH. But not exactly because the cross-sectional area of a slightly irregular out of round object will be different whether you use the larger diameter or the small one. This approximation of a round tree based upon CBH measurements is used in other formula calculations for volume and so forth, but it is a "clean" measurement that does not have any interpolation or averaging. From my perspective, I would rather start with a clean number that was physically measured, than one that was generated that already incorporates some minor (and arguably insignificant) interpretations right off the bat. Get the clean number, then play with it however is appropriate.

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