Cedarman, I have found that you can push over one tree and then try another one 5' away and you can't budge it. Postoaks and blackjack oaks are notorious for that. Also there are little trees that have more roots below the ground than above. I push brush all the time with my TC45D and it seems I never have all the power I need (or want).
I don't think a TC24 is going to be a very good tree pusher. Of course, there will be some trees that you can push, but most of the time you will need to dig around the trees first and cut the roots as Youare suggested. for this, a toothbar is a necessary tool. You can do it without the toothbar, but you will spend a lot of time being frustrated.
On a TC33, you'll have more success at pushing trees, but also you will want to have a toothbar. After just one weekend of using a toothbar, I will never go back to not having one.
I think we ask a lot from these little tractors and they perform very well, but tree pushing of any substantial size is best left to dozers. Even digging around a tree with a backhoe is slow compared to a dozer. Unfortunately dozers are also big and they aren't suited too well to thinning. I use my tractor because I can sort and thin trees an not make a complete mess in my woods like a dozer will. Sometimes nothing works quite as good as a chainsaw. /forums/images/graemlins/smile.gif