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OUTSIDE: The intelligent design of trees

By Steve Roark

Tri-State Outside

As the largest plants around trees dominate our view when taking a woodland walk, and we enjoy the beauty of their trunk and branches as well as the leaf shade they provide on a warm day. There’s another cool aspect about trees that’s overlooked, and that’s the beauty of their design.

Here’s a quick review of tree function: trees have a fractal structure, meaning their various parts are created in a repetitive pattern: trucks branch off into limbs, limbs into branches, branches to twigs. There are two primary purposes of this sort of structuring: to hang the many thousands of tree leaves (up to a half million on a mature white oak) out in the sun so they can do the photosynthesis thing and produce food and building material for the tree to use, and to provide the plumbing to move water and nutrients up from the roots and sugars suspended in sap down from the leaves. A third purpose of the repeated branching structure that is underappreciated is the ability to resist wind damage.

When you think about it though this is certainly a necessity. A tree with leaves has a lot of surface area that is suspended high in the air and so catches a lot of wind force. Amazingly many trees remain standing after strong wind events such as tornadoes. How a tree is designed to resist breaking was discovered long ago, but it’s only recently been understood why it works.

Leonardo da Vinci made an observation 500 years ago, noticing that when trees branch, smaller branches have a mathematical relationship to the branch from which they sprang. When two branches sprout off a bigger branch, the diameter surface area of the two small branches is equal to the surface area of the bigger branch. And this ratio holds up for any part of the tree you care to look at high or low, from the largest limbs to the smallest twigs. This ratio has been named Leonardo’s Rule.

Da Vinci of course did not realize the ratio created a wind resistant tree structure, and the fact that it does has only been researched over the last ten years. Earlier theories proposed that the branch diameter ratio provided a higher efficiency in transporting sap throughout the tree. But French physicist Christophe Eloy conducted research through computer simulations to determine the diameter of each tree component (limbs, branches, etc.) that was most resistant to snapping in high winds. When all the data was observed as a whole, the most damage resistant branching structure followed Leonardo’s Rule.

I think it is awesome that our Creator is so good at designing natural systems that are not only beautiful to but highly functional. It makes sense to mimic nature’s good design features into man-made structures. The Eiffel Tower is a prime example of a structure that provides both beauty and strength in high winds.