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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.

Rich
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    "...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.) – anongoodnurse Feb 10 '24 at 02:09
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    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. – John Feb 10 '24 at 03:15
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    @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. – Rich Feb 10 '24 at 14:46
  • In PA the sun spends a lot of time in the morning and evening in the north half of the sky during summer thanks to the Earth's tilt. – Bryan Krause Feb 10 '24 at 16:52
  • @BryanKrause You're right. Never realized that. – Rich Feb 10 '24 at 17:36
  • Perhaps set a condition of trees growing without light obstruction and high wind. Conifers are very simmetric and so are other trees. You should read about the chemical signalling which tells each cell it's distance from the trunk and how targeted growth is promoted. – bandybabboon Feb 10 '24 at 19:30
  • @Rich - I built a house in the middle of acres of woods, clearing the site myself. Ten years later, the trees left standing on the entire periphery of the clearing grew into the clearing so much that I had to cut them down to regain the sunlight I originally had. I don't think I'd have known it was so dramatic if I hadn't seen it myself. – anongoodnurse Feb 10 '24 at 22:09
  • @bandybabboon That is the sort of information I was looking for. Can you give me a reference for this type of chemical signaling? – Rich Feb 11 '24 at 16:58
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    Does this answer your question? How do trees manage to grow equally in all directions? – Nilay Ghosh Feb 13 '24 at 04:33
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    @NilayGhosh Yes, that's a very complete answer. Thanks. Knew there had to be some kind of regulatory feedback going on. – Rich Feb 13 '24 at 14:11
  • Not an answer, but the history of people investigating spiral patterns of plant growth may be interesting to you. – Maximilian Press Feb 13 '24 at 17:59

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