I recommend this article:
http://www.suite101.com/article.cfm/18505/105386

Apical dominance happens when the auxins (which were very plentiful in the growing point) no longer apply heavy dominance on the growing points below. The ratio of cytokinins : auxins has now increased and that will prompt elongation of the secondary growing points which were previously dormant/surpressed.

Here is a link that might be useful: article

the plants need meristematic tissue in order to continue growing. when you remove the shoot apical meristem from the top of the plant (we're talking about the top of the shoot that you removed from your silk tree), then the plant must compensate for this loss by growing from one or several of the dormant axillary meristems found in the axillary buds. as for why it is growing out sideways now: well, that's because the plant started growing from the lower axillary buds that were present...this is why it is important to check where the axillary buds are before lopping off the top of a tree...on the other hand, if you did pay attention to this and it is still growing like a bush (what do you mean by "like a bush"?) then it could be due to some other factors...i hope that i answered the question that you asked. good luck.

alex

Great article, Kenneth. Thanks for sharing!

Shelley

The principles in apical dominance are easily observed in the growth of climber roses. Roses have especially long lives and so are easier to observe. Rose blooms will occur at the apex of a cane. Therefore, to achieve lots of blooms, lower the end of the cane and the apex is now a long length of cane and will result in a bounty of blooms along the whole cane instead of the tip.
Dave

Speaking of apical dominance, We are doing some rather interesting research. We are top mowing conifers, at the 'right time' and getting shorter trees with more caliper and bigger root system. The point of wanting shorter trees is for outplanting into the forest. From being knee high to yada yada yada, we have always heard NEVER top a conifer. We are doing it and getting good results. Obviously I have left a bit of info out, just to tap your curiosity and try to start a discussion...

Any comments?

Weebus

This seems a particularly worthy technique to achieve a very specific goal. " ... NEVER ... " causes more problems than it prevents. Have you been doing this long enough to know if you have altered the sexual reproduction cycle of the trees?
Dave

No, we just started really doing extensive trials. These are definatley seedlings. First year of life. We grow from seed, get some height to them and then we top mow them. The timing is the key. Many of the conifers people see in the forest, were once 'top mowed' by deer. Can you tell which ones? Nope, same idea we are doing.