"If you girdle a black locust you will create a firestorm of new sprouts...not a few dozen...hundreds!! Honey locust you can get away with but not black locust "

Yes, I forgot to add that right after girdling apply herbicide to the cut area. I used Garlon 3a on a fence row(garlon 4 may also work), you must use one that works on cut surfaces and not just foliar. The girdle kills the tree and the herbicide should stop most of the sprouts from the roots out. Since the tree is girdled it is still alive enough to distribute the herbicide. If you just cut it down you will need to mow the sprouts constantly for a couple of years or apply foliar herbicide over a wide area. If it has lots of thorns and they each have 3 points, then it is probably honey locust. Easier to kill, but the wood is not as rot resistant. It may not make good posts.

http://texaswoodlot.blogspot.com