Hey Ekka... time for another page !!!
Atula...
It happens in nature. I see trees constrained in small amounts of soil when I hike up this rock - Beacon Rock: not much soil up there at all. The trees don't live too long up there...
http://www.mdvaden.com/beacon_rock.shtml
There are medium trees and stunted trees and windswept trees. Not quite as tiny as man-made bonsai, but still a natural version of restricted roots and growth.
It's not just an accident that I put a statement about "blending lessons from nature with landscape technology" on my home page.
1. Now, on that BEACON ROCK page, go to the bottom of the page and click the right photo album link for Oregon and the Columbia river Gorge.
2. Go to about #49 and click the image to enlarge.
3. Next - careful - look a ways under the image - even below the table of EXIF data. There will be tiny text that says "original" - click that text link "original" for a full-screen image and check out how big the rock is. You can see the tiny metal rails for the trail. Anyway, it give a better idea of how much rock is up there, and how little soil there must be for the trees to grow in. Most vegetation is growing in small cracks and crevices.
Have you heard of arborsculpture?
First, go to this other page of mine. It has an image of a natural occurance of merged or grafted trunks...
Arborsculpture, Pruning. Tree. Trees. M. D. Vaden. Portland.
Next, be sure to visit the links on that page to head over to the Wikipedia article on Arborsculpture.
So, with that all said and written, I think that nature already does this stuff, and man just tinkers with it in various ways.
As long as a tree will grow in a pot, it can't be unnatural, because it's genetics are natural, its growth cell division is natural, it's foliage is natural, and they smell natural.
It wouldn't be the "norm" or average thing to witness in natural settings, but it is not totally contrary to what can be found in natural settings.