Modeling Trunk Limb Structure
Dec 10, 2005
   Robert Leverett
   Dec 12, 2005 05:13 PST 

Will, Jess, Lee, Dale, Ed, et al:

On Saturday morning as I sat at Monica's kitchen table and looking out
her east window an idea occurred to me. Why not begin modeling the parts
of tree trunks where a split into two or more separate trunks occurs. I
began piddling with the idea by modeled two black oak trees growing in
a neighbor's yard on the other side of the street. There is nothing
conspicuous about either tree. I chose two trees principally because
they are easy to see. Their simple branching patterns are replicated
throughout the surrounding oak woodlands. Their forms speak of
forest-grown influences. The yard that contains these handsome black
oaks was fully forested before most of the trees were cleared for the
current home. Fortunately, individual trees were tastefully left in the
yards by the landscaper-developer to continue the aesthetics of the
surrounding woodlands. There is a nice mix of species. A slender white
oak growing next to the second black oak that I modeled reaches 98.4
feet in height on a slender trunk with a CBH of 5.9 feet. The black oaks
are in the low 90s. Farther down the hill on the next property is where
the MA champion 107-foot scarlet oak grows that Will confirmed this past
October. The area supports several species to heights of over 100 feet.
The Rucker index of the surrounding area that includes maybe 10 acres at
most now stands at 109.6. With more searching, we can eventually get the
index up to 110.5 possibly even 111. But I doubt that growing conditions
in the Broad Brook area can support more than that. By expanding the
geographical area considerably, the index will undoubtedly climb, but by
how much, Iím unsure. But that is another story.

My first objective was to examine the behavior of the trunk-limb
structure on both trees at just below to a few feet above the point of
major branching. The question to be investigated was how does the
cross-sectional area of the trunk just below branching compare with the
combined areas of the limbs just above separation. Visual inspection
suggested them to be about the same.

The first treeís single trunk had a cross-sectional area of 2.2 sq ft
just below the start of the branching. At the point of distinctive
separation, the sum of the two trunks was 2.1 sq ft. So for the first
oak, the continuation of trunks represented the same amount of wood. The
area in which the trunks touch is 7 feet in length. So for the first
tree, the diverging trunks roughly match the upper end of the single
trunk at 7 feet below.

At 37 feet up, the single trunk of the second tree narrows to a diameter of
16.4 inches, representing a 1.5-foot cross-sectional area. For the next
4 feet, the split into two trunks has bark touching bark before a clear
separation occurs. At that point their combined cross-sectional area is
2.0 feet. At another 3 feet higher, the two trunks yield a combined
1.5-foot cross-sectional area.

      This was just piddling, but these complicated trunk areas need to
be examined for common patterns to help us in our onward modeling march.


Bob


Robert T. Leverett
Cofounder, Eastern Native Tree Society
Re: Modeling Trunk Limb Structure
Dec 10, 2005
  Jess Riddle
  Dec 12, 2005 08:53 PST 

Bob,

Thanks for tackling the issue of modeling forking trunks. I think
that structure is one of the two largest challenges we are facing in
modeling trees right now; the other being the wedge of wood below the
level of upslope ground, which BVP probably figured out long ago. I
started playing around with the data from Will's climb of the
Yonaguska hemlock, and I looked at the situation in much the same way
you have. Due to the nature of the forking, about 20 feet separate
the two distinct stems from the last section of single stem with
normal form, and the total cross sectional areas at the two heights
are the same to within a few tenths of feet. I also graphed the
composite area of the two stems against data from other large,
single-stemmed hemlocks to see if the trees tapered differently. The
resulting graphs show very similar rates of taper among the different
trees' tops. Hence, Yonaguska resembles the other big hemlocks, but
with a 25' section of untapered trunk inserted in the middle. Let me
know if you want a copy of the spreadsheet.