Thickening trunk- Prune or No?

[Kahless]

I have a few crabapples and a hackberry growing in the ground to thicken the trunk. Do I just let all branches get wild and long as possible? Do I prune top branches and leave the lower ones? What if all the branches are at the top? Will these high branches still thicken the trunk or do only lower branches do this? I don't want inverse taper. Pics included of some that I have in the garden.

 

[HorseloverFat]

Greetings!

ALL foliar growth equates to “thickening” of the trunk BELOW those leaves... and the next ones up do the same below themselves.. and so on and so on..

I believe i watched a video last year that equated most deciduous to 1:1 / m/cm... so for every meter of growth.. the “wood” behind/beneath said growth will enlarge 1cm comparatively...

This video MAY have been incorrect.. but this is the “formula” I have been using... and SOMETIMES ignoring...

 

[Carol 83]

Pretty garden.

 

[sorce]

I'd wire that low low branch up and get to nurturing it for the future.

You don't NEED to chop until the wound left is too big to heal.

My hack Knowledge comes from @JudyB.

Sorce

 

[Shibui]

All branches will contribute to thickening below.
Maximum thickening is from leaving all the branches to grow wild but that may not be best for bonsai. A thick trunk will need to be cut back at some point to achieve bonsai. If the trunk is tall and thick that will leave a stump with a large cut. It will then take years to grow a new apex to achieve some taper and to heal the cut.
Alternative is to prune occasionally. Cut the trunk low and several new leaders will usually emerge. Leave them to grow and they will also thicken the trunk below but now there will be several options for the next chop, you will already have some taper in the remaining trunk and you will have several smaller cuts that will heal up far quicker. Reaching desired trunk diameter might take an extra year but you will save several years of development after that.

 

[leatherback]

One big cut? Many small cuts?
Let it grow big to nearly the size you want the final trunk to be. Then cut back to a stump. Once you have a new trunk growing from the stum, clean the cut to be a smooth transition between the old and the new. Add cut paste. The wound will callus over and after a few years will be a circle with a line through it as scar.

I am coming to the point where I think is done well, a single big cut looks better than very many small sacrifice branches. So I think I would let it grow.