Modeling
Trunk Limb Structure
Dec 10, 2005 |
Robert
Leverett |
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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, I’m 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 tree’s 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
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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.
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