I was just thinking, it wouldn't take much of an imbalance in off shoots from a branch, or shape of that branch, to but a high torque on the main branch, leading to deformity and/or breakage.

I wonder how trees keep that balance.

The wood is strong enough to resist the stress created by these gravitational forces. If we pile on enough extra weight, such as a buildup of ice from freezing rain, the limbs can and do break.

What I remember from looonnng ago is that, at stress points/stress lines, the trees (and other plants) produce more substance (cellulose? lignin?) to overcome the stress. And I also remember that finite element methods have been used to prove this, and have been used to construct "tree-like" buildings, aiming at "highest-strength-lowest-material-consumption" structures.
How nature does it? Some four billion years of trial and error (read Charles Darwin)

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If everyone had even a basic grasp of scientific principles, this planet would be a better place (Phil Plait)

Die Lücke, die wir hinterlassen, ersetzt uns vollkommen (Carl Heinz Schroth)

never 'erd of 'im.

Wood that's oriented horizontally (like branches usually are) don't have quite the same composition/structure as wood that's oriented vertically (like trunks usually are). Depending on which taxonomic group a tree belongs to, it will produce either "tension wood" along the top of the branch or "compression wood" along the bottom, modified to hold up more weight. (Either way, the other side of the branch has "normal" wood.) I can't describe the exact nature of the difference at the molecular level, but the farther from vertical it is, the more drastic the change is, regardless of whether you'd call it a "trunk" or a "branch". So a tree that's leaning over far enough (which tends to happen if they're pinned down by another object or if they're reaching for sunlight that's more available from the side than from above) will have tension/compression wood in its angled "trunk" and only normal wood in its upright "branches".

The different physical and chemical traits of the wood are the reason why mills don't take branches no matter how big they are, and why they don't take trunks that had been leaning over too far.

I googled for this:

tree growth and finite element method

and found this (from 2006):

http://publications.lib.chalmers.se/...ql?pubid=23505

There should be much more information available because my vague recollection is from approx. 1980

__________________
If everyone had even a basic grasp of scientific principles, this planet would be a better place (Phil Plait)

Die Lücke, die wir hinterlassen, ersetzt uns vollkommen (Carl Heinz Schroth)

As a point of interest to this thread, most trees will grow in a semblance of uniformity if allowed to. Meaning that as one branch grows on one side so another will grow on the other side to balance the tree and relieve the stress through the trunk. When trees are being worked on and, say, a large branch has to be removed (bear in mind wood full of sap is surprisingly heavy), a tree surgeon will also remove a corrosponding branch from the other side to stop stress building up within the tree and to balance the load (it also looks more pleasing to the eye). If too many branches are removed only from one side, a tree can snap under the stress caused by the uneven load.

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Biologically speaking, if something bites you it's more likely to be female. Desmond Morris.

Quantum analysis is scientific dithering

Professor Frink: My observations n'hey, n'hey, show the universe could be a torus Weh, uh, or toriod it may like the typewriters and bananas and the monkeys with big teeth the biting the screaming Mm-hai!

Homer: mmmmm... doughnuts!

It should be not surprising that trees grow in such a way as to support their own weight, and to resist the force of the wind. It would be surprising if they did not!

What you may not realise is that our bones do exactly the same. Here's an xray of a (very arthritic) hip joint. The lines of bone formation alng the lower side of the neck of the femur - the narrow bit below the round ball of the femoral head - are very clear, as they cluster along lines of strain from the patient's weight. They can also be seen, but less prominently, along the upper side of the neck.
All bones will 'remodel' - change their shape - in response to differing needs. Indeed, they are the shape they normally are because they so respond! A child's broken bone will, in a few months and in the absence of gross displacement or infection, have reshaped itself back to what is was before the break. Adults are not as good at it as that but still will obliterate the 'scar' of the knitted bone eventually.

John

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