Limb Volumes   Edward Frank
  Sep 28, 2005 19:22 PDT 

Bob and I have had some discussions off list about measuring tree volume.
I sent this comment to him concerning limb volume. Perhaps some of you
could address this question or point to the right data set.

I am wondering about limb volumes. Are these estimates in the right
ballpark? Are these published estimates or how are they derived? If you
would have a tree cut down in a timbering operation, then a comparison could
be made between the weight of the trunk (I am not sure how to weigh it -
maybe weight the log truck before and after loading) and the weight of the
limbs (without foliage). The ration of trunk weight to limb rate should be
approximately the same as the ration between limb volume and trunk volume.
The bark on the limbs would be thinner, but still represent a slightly
higher percentage of the total weight than would the bark on the trunk. The
limb wood might be less dense (I am guessing), but still the ratios between
limb weight and trunk weight should approximate the ratio of their volumes.
This would vary from tree to tree and likely from species to species. This
type of information has probably been collected somewhere from years of
timber research, and it would be good to have some hard numbers to compare
to the limb volume percentage estimates.

Limb Volumes   Edward Frank
  Sep 28, 2005 19:22 PDT 

I have been trying to figure out about Limb volume. In your post dated Aug 29 you wrote:

"After computing trunk volume, I added 4% volume for the limbs, a 
moderately conservative figure. Incidentally, the 3rd trunk is 
considerably smaller than the first two. I modeled it as 1/7th the 
volume of either of the larger two. This actually may be liberal. "

I made the suggestion that there would be a relationship between weight of the limbs compared to the weight of the trunk that would correspond reasonably well to the ration of the volumes of the two. Nobody responded to the idea, but I think some such measurements must have been done sometime. 

From materials on the website:

Sag branch tulip - limbs 40%, main trunk 60%
Middleton Oak - limbs 80%, main trunk 20%
Douglas Fir and Eucalypts - limbs 8-10% BVP dec 7, 2003
Tane Mahuta - limbs 38% BVP dec 7, 2003 

The Sag Branch and Middleton Oak are extreme examples, but even the relatively narrow crowned Douglas fir BVP measured (data is in his book) have a limb volume of 8 - 10%. 

At this point perhaps it would be better to characterize the volume calculations as "This is the volume of the trunk at XX cubic feet. If we make a conservative estimate of 8% of the volume for limbs, they would add YY cubic feet to this total. Until a good handle can be made on the limb volume it would be more reasonable in my mind to be comparing just the trunk volumes between trees rather than total volumes including limbs. It just bothers me that with all the effort being made to calculate trunk volumes within as close of percentage as possible that an arbitrary estimate of limb volumes is added that may vary from 8 to 40% in reasonably sized crowns and may be up to 80% in extremes like the Middleton Oak. I don't think a conservative estimate of limb volume or a consistent percentage used for limb volume offsets the amount of inherent error in the estimate.

Go back and reread some of the discussions leading up to the measurement of the Middleton Oak. It is an interesting read considering the results of measuring it and the the Sag Branch Tulip. Bob Van Pelt, an expert in tree volume calculations underestimated the volume of branches in a similar tulip tree by a factor of three:

"A giant tulip such as the Mill Creek Monster might have 12-15 percent branch volume. Some of the live oaks are nearing 100 percent." 

RE: Passing of the guard LIMBS    Will Blozan
   Nov 13, 2005 04:27 PST 
I agree Bob, good work. I also have questions about limb volume. I suggest
we leave it out altogether since it has NEVER been measured and is simply
making any attempt at accuracy decidedly inaccurate. We still will have a
decent model for 95% of the tree. I suspect there are limb mass differences
in white pine between northern and southern populations; a trend that may be
reversed in hemlock. Cool stuff, but not something that can be measured from
the ground!