Genetic pre-programmed apex?

[TheDarkHorseOne]

I was watching a thing the other day here on the 'net and it had a pretty fine explanation for how trees grow naturally. From what I could gather, it seems species of tree have a sort of 'You can only ride this ride if you're __ tall' gene within them. In other words, once they achieve what the approximate height of their species is, they sort of top off the apex, and then begin to develop outward, or sort of fill out their genetic outline, which, in turn, makes the tree look older as a result. I think you can find examples in nature of that happening, Bald Cypress being an example, but many deciduous trees might have this built in mechanism of growth.

I'm just a rookie and when I heard this, it made a lot of sense to me as to how the trees I see daily act. I was wondering your thoughts on it, and if you find that such knowledge might be used to further define the aesthetics of a large part of bonsai species, as in, if we know this in nature, we should be trying for this in the pot...

I'm not advocating this at all, but I DO see a logic in it, and while the rule of thirds is very pleasing to the eye, nature sometimes comes up with better.

So this is just tentacles of a thought process out to you all to get a feel of what you might think.

 

[bonsai barry]

Another factor in determining apex growth is a type of chemical compound known as Auxin. Here is a definition from the American Heritage Scientific dictionary:

auxin (ôksn)
Any of various hormones or similar substances that promote and regulate the growth and development of plants. Auxins are produced in the meristem of shoot tips and move down the plant, causing various effects. Auxins cause the cells below the shoot apex to expand or elongate, and this (rather than cell division) is what causes the plant to increase in height. In woody plants, auxins also stimulate cell division in the cambium, which produces vascular tissue. Auxins inhibit the growth of lateral buds so that the plant grows upwards more than outwards. They can be produced artificially in laboratories for such purposes as speeding plant growth and regulating how fast fruit will ripen.
The American Heritage® Science Dictionary Copyright © 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved

As I understand it, the auxins in the apex inhibits the growth of surrounding branches. Often in nature you can see a tree that has lost its apex and the other branches now shoot up in in response, growing taller, wider and thicker.

This photo of the Grizzly Giant (Sequoia tree) shows lateral branches that exhibit this phenomenon when the apex is lost.

 

[0soyoung]

... it seems species of tree have a sort of 'You can only ride this ride if you're __ tall' gene within them. In other words, once they achieve what the approximate height of their species is, they sort of top off the apex, and then begin to develop outward, ...

In simplistic terms, the foliage of the tree sucks (by transpiration) water and nutrients from the roots though the 'soda straw' of the xylem. Depending on the diameter of the soda straw, the water column will cavitate (make a vapor bubble) preventing water and nutrients from flowing - this is the height limit of the tree. In general, gymnosperms (conifers) have the narrowest 'soda straws' (tracheids) and are the tallest trees. Once the tree has reached its height limit, growth can only be lateral; that is, lateral branches can continue to grow upward until they too reach the height limit dictated by the xylem cell diameter or until the branch can no longer be mechanically supported. This much is all physics and DNA.

 

[rockm]

Osoyoung's explanation is a good one. There is a theory that trees can live a lot longer than they do, but simple physics prevents them from doing so.
They simply reach the limits of their physical ability to expand (laterally too).

In bonsai, we short circuit those limitations to some extent through pruning top and bottom growth. The tree replaces the growth removed with more efficient new roots and top growth...theoretically allowing the tree to remain "young"

 

[TheDarkHorseOne]

Very interesting, folks. thanks for the replies.

 

[Ang3lfir3]

funny that you should happen upon this video ... this knowledge is basically the essence of how we think about bonsai.... think of the lifelines of trees as being "pumps" .... as the trees roots grow and the tree ages you can see the pump beginning to fail this is the idea of the "genetic apical height" .... or at least a decent analogy that can be used to understand the idea if you consider different species as having different strength pumps ....