# What does "DBH" mean?



## corndogg (Feb 7, 2008)

Alright, stupid question. What does DBH mean exactly when referring to tree sizes? Diameter breast height? Diameter butt height. Just wanted to know for sure.... Stop laughing.


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## ATH (Feb 7, 2008)

Better to ask then go around ignorant.

Diameter at Breast height. That is defined as 4.5' off of the ground on the uphill side of the tree.


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## corndogg (Feb 7, 2008)

Roger that, Thanks for the quick reply


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## ropensaddle (Feb 7, 2008)

Uhh huh huh a huh huh he said breast shut up bevis


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## Sprig (Feb 7, 2008)

You mean its not 'Dis Butt Here'?

I am, like, so disillusioned 






Serge


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## clearance (Feb 7, 2008)

ropensaddle said:


> Uhh huh huh a huh huh he said breast shut up bevis



Uhh huh huh he said diameter, uhh uhh come to Butthead baby, uhhh uhh see my diameter. huh huh uhhh


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## BC WetCoast (Feb 8, 2008)

ATH said:


> Better to ask then go around ignorant.
> 
> Diameter at Breast height. That is defined as 4.5' off of the ground on the uphill side of the tree.



It may vary from jurisdiction to jurisdiction but in BC it is defined as 4.5' or 1.3 m above the point of germination. This is a delicate point because in BC, timber cruising defines the stumpage rate of timber paid to the Crown (government) for timber cut on provincial land (95% of the provincial cut), and DBH is an important cruising measurement.


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## M.D. Vaden (Feb 8, 2008)

BC WetCoast said:


> It may vary from jurisdiction to jurisdiction but in BC it is defined as 4.5' or 1.3 m above the point of germination. This is a delicate point because in BC, timber cruising defines the stumpage rate of timber paid to the Crown (government) for timber cut on provincial land (95% of the provincial cut), and DBH is an important cruising measurement.




I thought I had this DBH stuff all figured out, until I found the Del Norte Titan in January.

http://www.mdvaden.com/grove_of_titans.shtml

When we tried to measure it, I found an interesting challenge. The ground is higher on one side of the tree, by almost 3' than the other side of the tree.

If the "point of germination" matters, I'm not sure if the point of germination could be determined. It could be in a hidden depression at this point in time.

If I was going to set a standard, I'd take a DBH all around the tree at each elevation, and average it - like 10 measurements, every 2 to 3 feet around the tree.

How many standards are there to approach this kind of measurement?

Here's 3 trees that would be fun to hear replies for:

1. The Del Norte Titan mentioned above.

2. Tree below, fallen, rooted at both ends with no apparent evidence of which end germinated. It looks like a log, but is actually a living tree. Probably fell while young, rooted a tip, and had limbs develop into trunks. If you have to give this tree a DBH, where would you measure it?

3. Tree on a nurse log. Once the nurse log decomposes entirely, does the point for DBH change? What about other similar trees where the nurse log is already gone during first discovery? Does the "point of germination" matter? Is the existing ground level the important factor?


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## M.D. Vaden (Feb 8, 2008)

Here is a fourth.

Was there a nusery log, and is it one tree. Was it two trees grafted into a natural version of arborsculpture?

Where would the DBH be measured on this one? It's not where a single trunk emerges from the ground and then branches. Here is the reverse, where 2 trunks merge. But if it started on a nurse log, we're looking at one organism.


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## Mark Currie (Feb 8, 2008)

http://www.phytosphere.com/treeord/measuringdbh.htm

Shows leaners, trees on hills, etc. I know that we were taught in school along the USDA lines (as opposed to the ISA guidlines which are also shown there). Easily repeatable and for most trees, gives a more accurate DBH.

We did some cruising in upstate NY and VT a couple of years ago and the rules slightly different, when it came to multi-stemmed trees. Then again, we had to paint a red line where we took our DBH from, so that took out any question, when they went in and checked our work.

For your pics, I would say 4.5 feet from where the stem actually starts (ie. roots), for the ones growing from nurse trees, because you're measuring merchantable timber. That last one would be tricky. Me personally, I'd guess what the DBH would be 4.5 feet from where the two trunks merge and note it.

Dunno if that helped or not.

Mark


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## BC WetCoast (Feb 8, 2008)

DBH being measured as 4.5' above point of germination was standardized. In BC, stumpage is based on the total harvestable volume of the trees, not a board foot calculation as used in the US. Therefore, the computer models that calculate tree volumes of the cruise samples have a standardized butt flare for each species. Decisions on how to determine point of germination for non-standard situation have already been made and are included in the cruising instruction manuals. 

For example, for large trees on steep slopes, where the uphill side is greater than 4.5' from the POG, then the diameter is taken at grade on the uphill side.

For trees growing on nurse logs, you would use the top of the nurselog. For wierd situations, a decision has to be made in the field using a reasonable interpretation of the guidelines. The point where DBH is measured has to painted on the sample trees anyway, so if the cruise is checked, the checker can decide if a valid point was chosen.


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## M.D. Vaden (Feb 9, 2008)

It's interesting to see that with some methods, a tree's DBH could actually decrease based on changes in it's habitat. Say if there was a small landslide, or a river's flood deposited eroded material several inches deep.

If the grade was raised, so would the measurement point for the diameter at DBH, making the tree get smaller in point value.

Odds are that those situations are very uncommon though.


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## sawinredneck (Feb 9, 2008)

"Done been had!!"

No idea on the proper measurment for those trees.


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## Sprig (Feb 9, 2008)

I am unclear what the 'point of germination' is, never heared the term before, is it where the roots enter the ground? Just curious as to how that is determined in different species, like a big cedar with flair, or a big ol' maple with exposed high roots? I'm sure there are more than a few variables, is there a rule of thumb for this?



Serge


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## M.D. Vaden (Apr 30, 2008)

Sprig said:


> I am unclear what the 'point of germination' is, never heared the term before, is it where the roots enter the ground? Just curious as to how that is determined in different species, like a big cedar with flair, or a big ol' maple with exposed high roots? I'm sure there are more than a few variables, is there a rule of thumb for this?
> 
> 
> 
> Serge



I've been reviewing the DBH thing for forests lately, after emailing back and forth about redwood giants.

One aspect that seems to be a point of contention, is whether the tree's main stem is single, and where it branches-off or becomes unified with another of it's own stems.

One site that relates, is the Gymosperm Database ...

http://www.conifers.org

As far as "point of germination", here's one more redwood below that would challenge almost anybody to figure out where the point of germination was. And there is about a 3' grade difference between one side of the tree and the other side.


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## pbtree (May 4, 2008)

ropensaddle said:


> Uhh huh huh a huh huh he said breast shut up bevis


I tried to rep ya for that one but I can't yet!


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## Nate Surveyor (May 7, 2008)

I'm a Land Surveyor. And I learned something from this thread. 

Thanks for starting it. 

Nate


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