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Many trees have a quite symmetrical overall shape. Some are extremely symmetric. Yet when you look at the branches and limbs of any tree their distribution seems completely random. Often even the trunk will bend or divide. So how does the overall shape attain symmetry? I understand that there is gravitotropism and phototropism acting, but it seems to me that then if one branch extended outside of the general canopy it should grow even faster as it is more exposed to sunlight, thus producing a more irregular shape. What mechanisms are working here? There must be some kind of negative feedback (I'm a retired engineer) or inhibitory mechanism that slows growth on the more exposed branches. I can understand that a spruce or similar would be so. If all the branches grow at the same rate, those lower on the tree will be longer, having had more time to grow and you'll naturally get a triangular shape, but this is not what captured my attention.

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    $\begingroup$ "...if one branch extended outside of the general canopy it should grow even faster as it is more exposed to sunlight, thus producing a more irregular shape." Are you sure this doesn't happen? (It won't happen with one branch, but it will generally on that side of the tree.) $\endgroup$ Commented Feb 10 at 2:09
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    $\begingroup$ if you think trees are mostly symmetric you need to go look at more trees, and then look up phototropism. a unobstructed tree with light levels the same in all directions will be symmetric sometimes, otherwise no so much. $\endgroup$
    – John
    Commented Feb 10 at 3:15
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    $\begingroup$ @anongoodnurse That's true. I have two maples in my front yard growing close together. There are no branches that grow on the sides of the trees facing each other - and yet the two trees together make one symmetric whole. $\endgroup$
    – Rich
    Commented Feb 10 at 14:46
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    $\begingroup$ Does this answer your question? How do trees manage to grow equally in all directions? $\endgroup$ Commented Feb 13 at 4:33
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    $\begingroup$ @NilayGhosh Yes, that's a very complete answer. Thanks. Knew there had to be some kind of regulatory feedback going on. $\endgroup$
    – Rich
    Commented Feb 13 at 14:11

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