How do trees decide when and where their branches grow?
In: Biology
How do you decide how long to make your arms and legs?
Have you ever thought about how boring it must be to be a tree? You literally just stand there, and your leaves always make it cold for you cuz you’re permanently in the shade. Therefore, trees go where the sun is, and sometimes they do some funky stuff with their limbs to show off to the other trees.
Also related, the Fibonacci Sequence.
1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377…
If you divide each term by the previous, you get
1, 2., 1.5, 1.66, 1.6…, all converging on 1.618…, the golden ratio.
If you start at one point, shoot a branch, then turn 1.618…times around the trunk and shoot another, and go along that way, you get the most efficient structure for a plant to produce a canopy for maximum top down area.
Which is really weird.
By default, trees want to make branches everywhere, but the top of the tree sends a signal down saying, “no!” As the trunk grows higher, the lower parts of the tree start to have trouble hearing the top and start to grow a branch. That branch turns into a mini-trunk, also saying, “no!” to all the other parts of the tree thinking of making a branch. This keeps happening over and over again. Different trees have louder tips, parts that have better or worse hearing, and parts that eventually decide to stop growing, which is how we get so many different shapes of trees.
Tree top shouting = auxin and other hormones released from meristems.
Rest of the tree = active layers of cells just under the bark / dermis.
Listening = genetic regulatory responses to the auxin / hormones.
As mentioned by others, hormones. The lead of a certain growth, like the top of the tree or the tip of the branch, it produces a hormone that hinders growth of new branches. When it has grown far enough from where a new branch would sprout, the concentration of that hormone is low and as such less effective, eventually low enough fow a branch to grow.
Want a real ELI5? They’re living beings too, and they just know. Just like how your body grows without you needing to tell it to
The answer to this is hugely complex and dependent on the species of tree among other things. The hobby/art of Bonsai is pretty much all about controlling where and how the branches on trees grow to produce an old looking tree in miniature. The vast majority of how this is done is around your question. Masters of the art have degrees in biology and spend 6+ years in apprenticeships as well as dedicating their life to learning how to do it efficiently. You can probably get an ELI5 for one specific species of tree but it will take 30+ minutes to explain it so not sure even that would be simple enough to qualify.
The trunk as it grows up taller and wider will grow some new places where branches might go. The trunk decides how often to make new branches by following a bit of math that tells it to make branches only as often as necessary to create armfuls of leaves that will cover the sky without covering each other. The trunk knows that branches it has grown are still alive because the leaves at the ends make a…well let’s call it a smell. As the Sun shines on the leaves and they grow they make a smell that the trunk can smell and that way it knows the branch is alive and won’t try to grow another branch at that spot. If the trunk doesn’t smell any leaves coming from a branch, it may start to try growing new branches in that spot. When a tree is cut down and only the trunk is left it won’t smell any leaves at all coming from above and it will try to grow branches all over the place to start anew. We call these “suckers” coming from the old stump and if they are left long enough then one of them will grow bigger and make many leaves and the smell of those leaves will come down to the stump and it will stop growing the other suckers and focus only on growing that one successful sucker and that’s how a tree may recover from being cut down.
So, in very short, leaves make a sort of smell that tells the trunk that it doesn’t need to grow another branch in that spot. The trunk will create new branches above old branches as it grows taller according to some basic math that helps it to spread branches out so they don’t overlap and cover each other from the Sun.
Think of it like survival of the fittest. Trees send out multiple branches each year. The branches that get the most sunlight, survive.
Trees don’t “Decide” anything just like you don’t “decide” to let your heart keep beating, and at what bpm.
All flora operate under hormone induced involuntary actions exacerbated by ecological surroundings.
Latest Answers