Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: CliffordK on 30/03/2014 22:03:40
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Some trees such as fir trees may exclusively, or mostly grow branches as new growth, and one often sees the branches organized in annual rings.
However, leaf-type trees seem to be less restrictive, and seem to be able to put on new branches along any of the limbs, and even frequently on the main trunk. Pruning can apparently cause them to make several new branches.
What causes buds and branches to occur? Sunlight? How is the new branch formation maintained symmetrical so the trees don't fall over?
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... How is the new branch formation maintained symmetrical so the trees don't fall over?
Plants do respond to gravity ... http://en.wikipedia.org/wiki/Gravitropism#Gravitropism_in_shoots
http://upload.wikimedia.org/wikipedia/commons/5/55/Apex_reorientation_in_Pinus_pinaster_during_the_first_24h_after_plant_inclination_-_1471-2229-10-217-S1.ogv
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There have been various attempts to model trees and forests using fractals, and some of the attempts (http://davis.wpi.edu/~matt/courses/fractals/trees.html) don't look too bad.
The model applies a formula that lets a limb grow for a certain time, and then it grows a new limb. Different formulas produce something that looks more like certain species of tree.
Conceivably, something like this formula is built into the DNA of a tree - a sequence of DNA that allows the tree to grow for a certain time before sprouting another branch, or a twig, or a leaf.
Of course, real trees are affected by more factors than are included in a simple formula.
- Some mathematicians see patterns in the way that leaves are arranged on a stem, so that a higher leaf provides minimal shade on lower leaves - this tends to produce a spiral pattern of leaves along a stem.
- Real trees seek the Sunlight
- Real trees try to outgrow their neighbours
- Real trees are affected by winds, borers and fires.
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Of course one might make a computer simulation of a tree... However, that doesn't really explain how a tree chooses to make a new branch.
Attrition can be due to a lack of sunlight, although a tree still must maintain a certain amount of symmetry to remain upright (so all the north branches couldn't die (or south for Evan)).
What about fluid flow and pressure? Either too little flow of fluid towards the leaves, or too high of pressure, and it would be a trigger to create a new branch. Likewise a lack of nutrient return from the leaves indicates a need for more branches and leaves.
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Of course one might make a computer simulation of a tree... However, that doesn't really explain how a tree chooses to make a new branch.
Attrition can be due to a lack of sunlight, although a tree still must maintain a certain amount of symmetry to remain upright (so all the north branches couldn't die (or south for Evan)).
What about fluid flow and pressure? Either too little flow of fluid towards the leaves, or too high of pressure, and it would be a trigger to create a new branch. Likewise a lack of nutrient return from the leaves indicates a need for more branches and leaves.
Mmm, shape is pretty much genetic, and it depends on every specie. Turger pressure and nutrition has nothing to do with branching.
Google about apical dominance, basically, a substance called indol-3-acetic acid is produced in the tip of the plant (the shoot apical meristem) and inhibits the growth of axillary buds (potential branches). If a plant is really tall, the concentrations of this hormone may be to low to inhibit the growth of lower buds, so you have branching on those sites. But it depends on the specie. Some plants have a strong apical dominance, some do not.