Thanks for all the responses. So far no one seems to have attempted my idea of using a debarker.
I'm nor certain what sort of plants these "trees" were/are. The tallest ones are maybe 15 feet high, most are 10 feet or less. They propagate by sending out shallow root runners, they grow very close to each other. Quite often there are 2 or three sharing the same roots. The area they are in was farm field about 35 years ago.
I had use of a mini excavator for a week last year. I did pull out hundreds using the backhoe and thumb.
My riding tractor is a Steiner 420 with 20 hp gas engine. I pulled maybe a dozen trees using it, but that was a slow go and I think it was pretty hard on the tractor.
I have a 2 wheeled tractor that I have cut a lot of them, using the brush hog attachment. Those stumps are shattered and I can usually just step on them and snap them well enough that I believe they won't be a problem anymore.
It's the ones that I cut using a chain saw that I need to remove.
I will try the sledge hammer method suggested by pmsmechanic.
Failing that I'll see about putting a ripper on the back of the Steiner (no FEL on it).
Unless someone comes along and tells me they used a debarker and it wasn't a pita.