Why DBH usually, and not Circumference?

[M.D. Vaden]

In our area, and up near Portland, Beaverton, Lake Oswego, Oregon, etc., trees are typically measure in DBH - say, regarding permits for removal, and other.

Recently, I was looking at our own Arbutus / Madrone, and its about 34" in diameter facing one way, and about 42" in diameter facing the other way.

That got me thinking about DBH vs. Circumference.

Wouldn't Circumference at diameter breast high, be more realistic?

It would still work for a tree with an even diameter all the way around.

 

[PA Plumber]

I understood DBH was the circumference divided by pi. That would be more a more consistent measurement as you have pointed out.

I.E. 50.24" circumference breast heighth tree would be 16" diameter.

 

[ATH]

I think dbh is the standard because we are dealing with systems that were set up for traditional forestry uses. In traditional forestry, the diameter was important because it helped estimate board footage. If you need volume, you need diamter at some point, so rather than reporting circumference (which is a means to an end), we have always reported straight to diameter.

Whether you report diameter or circumference, you still loose information about trees that are assymetrical. If you wanted to keep this information, the best way to report would be caliper of smallest diameter, and caliper of largest diameter. Ideally, you would also write the axis of those measurements--for example:
"The tree measures 22 inches caliper on the North-South axis and 20.5 inches on the East-West axis."

Biltmore sticks are a rough way to get this. A caliper is best. Have you ever seen a set of calipers for measuring 30" trees - how about for measuring 8' diameter trees.

So we are back to diameter being an easy number to report that provides adequate (but not perfect) information. In reality, if you are using a D-tape to measure,you are measuring and reporting circumference. You are just reporting it in "pi inches" instead of "inches"...

 

[elmnut]

Diameter tapes take the math out it, they tell dbh, and circum. ATH is right on!

 

[TheTreeSpyder]

The diameter × Pi formulæ for circumference will only work on true round, logically. The DBH thing does give some ambiguity and seem unreal; but perhaps that is a lysdexic view.

i think DBH should be given on a minor and major axis caliper for true sizing up. This could give better picture of how much wood to be retrieved in harvest and also (with lean stated) tell how much leveraged diameter is on loaded / lean axis; and the leveraged/ perpendicular axis to lean in life. The measurements when not being harvested will partially show stability in reference to the loaded/ lean axis.

 

[treeseer]

I agree with ATH; it is a forestry relic and best cast aside. For appraisals the form allows both so I always give circumference first then dbh. Some inventories use dbh automatically--harder to change them because the protocols are set by the USFS and Davey, which are relic-based.

Circumference is more accurate so it is best. Oh, and if you ever hear of "dsh", the "s" is for standard. This was developed in California, where certain feminazi groups thought it was wrong to refer to "breast".

 

[ATH]

Treeseer, how are you measuring circumference? Are you reporting more than one axis?

As for dsh...I have never heard or seen that term, but do they ever use higher heights as a standard on some of the western species? On a huge sequioa, redwood or sitka spruce 4.5' is still at the buttress.

 

[BonsaiJedi]

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[BonsaiJedi]

I posed the same dbh vs cbh to my forest mensuration professor at UMN. He said two things:

1. dbh is a really 2-Dimensional measurement thus one only has to see a tree from a distance to estimate its diameter using tools like prisms or Biltmore sticks. Heck of a lot easier than estimating cbh from a distance.

and 2. dbh inherently overestimates tree size thus helps bloster qmd and other stand size indicators thus increasing a stands value.