Question
Mark,
I have an old Red Bud tree.
It's about 18-20 ft tall. The trunk is 18" in diameter and is splitting in two starting at about 16" up from the ground.
This is a seemingly healthy tree, however, I think it is eventually going to totally break apart.
Is there a standard way of helping this tree?
Or, should I just take my chain saw and trim it as I see fit and hope for the best?

Answer
Doug,

If this were on my grounds, I think I'd call this one a goner.  Anything you do to it by way of pruning or bracing the splitting trunk may buy you some time, but won't save it in the long term.

A split in the trunk is that far down means the wood that is or will be rotting inside is  structurally important to holding the whole thing up, even though  it is currently maintaining proper circulation and looks healthy.  My experience has been that Red Buds don't have very strong wood to begin with, so that's a significant problem.

If you decide to prune major limbs off in order to lighten the load on the weakening trunk, the large wounds created will likely never properly heal before more rot sets in from that point of entry.  The clock keeps ticking on the downfall of this tree.

So, 1, you can do nothing and let nature take its course, cleaning up the mess whenever it falls on its own.  

Or, 2,  you can take it down at your convenience ( good weather, a day off, and a chainsaw that's running).

Or, 3, you can do some research into tree bracing.  I would only consider this if it were a significant (historically important/impossible to replace) tree.  You would need to contact an arborist for this.

For what it's worth,
Mark in Portland

If