Measuring DBH of cavity trees using circumference

Eric Frei

Now attached is a diagram.

There's 2 methods ... A or B

We all know to get DBH you get circumference and Divide by 3.1416

But which of the two methods is correct?

Attached Thumbnails

 

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Sean Freeman

I voted A, when I have trees with significant hollows, or cavities I'll calculate the % of wood tissue lost apply Mattheck's formula of t/R where t is the thickness of sound wood (bark not included) and R is the radius of the part. If the loss of supportive wood tissues exceeds 30% then action should be considered. You can only determine this ratio (%) by calculating the DBH as in A.
Yes there are lots of other considerations to be taken into account before recommendations are made, and I'll gladly talk about them if you guys like but basically thats my rational.

Sean Freeman

For some reason this thread came up as new on my visit here, but good hint for me to correct something....I no longer apply Matthecks t/R ratio as a means to determine the fate of trees with hollows. I don't any simple formula will ever manage to cover the enormous range of different tree species and wood properties we encounter, nor the history of their care (or lack thereof) and more importantly it does not relate to target which is the most import aspect of determining the best course of action.

OutofMytree

A thought provoking question which requires much debate, possibly running into the night, which as we all know is quite cold at this time of the year. Got any firewood? What about the hollow tree over there........

newguy18

I say method a.Unless the cavity is big enough for you to stick your head in and look.Method b is good after the tree is down imo.

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old schooler

treeseer

Mattheck: "If the loss of supportive wood tissues exceeds 30% then action should be considered. "

I think as stated above it is good to have a guideline for further attention, as long as it's not interpreted as a SHALL.

re the pic I don't understand what the gray part is--the whole tree or the cavity? If it's the whole tree, is the cavity open?

Bernard Keays

How do you measure bifurcated or multi trunked trees?

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Bernie

Sean Freeman

There are a few very similar methods that give uniformity to the taking of those measurements Bernard, here's the one I use.

If a tree forks at or below 1.doc

Bernard Keays

Thanks Sean...This is what I was after. Just another question... Where do you measure trees on steep slopes?

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Bernie

Eric Frei

At the same contour level, the side ways level, not down hill or up hill.

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Bernard Keays

Ok I would agree with that too...What about fallen or harp trees?

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Bernie

Eric Frei

Fallen .... 1.2m along from base.

Now harp trees would be interesting, I'd say average of stems with a multiplier like this.... DBH 30cm x 5 (Multi-stem harp tree)

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treesandsurf

Are you using a different formula now Sean?

The 30% has been a suggested guideline by many arborists, but when you say 30% of supporting tissue, does this percentage apply only to those fibres that exist around the circumference of the tree that Brudi et al. suggest are the only load bearing fibres in the tree; or... are people using this guideline as 30% loss regardless of where it is spread at the site inwards or when confined to the perimeter?

jp

Therrin

Ooooh, I wanna know who answered with B!!!!

Eric Frei

USFD use 30% on hollow trees and step up to 60% on trees where over 40% of the circumference is open cavity. To clarify, 100% of circumference is all the way around, 50% is half way around so 40% is almost a half open cavity tree, they expect 60% solid wall.

Hope that helps you.

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