I have 80 acres and have made trails/fire breaks. Was going to rent a small dozer until I saw the mess it could create. Actually, JMHO, but I think a dozer will create more work than it will resolve. All my trails have been cut by hand with my trusty chain saw. Just flag out the path and whack everything down with a good 'ol chain saw. Then I cleaned up by sawing everything to length - piling in my farm wagon - on to the burn pile. My big, brand new farm wagon was a real help in this situation. This was all completed prior to my tractor grapple. Truth be known - the grapple on the tractor probably would have been zero help. Too much twitching, fidgeting around to make a grapple effective. Besides - picture this. A twelve foot wide trail cut thru the trees - all the trees you have cut to make this trail are 2" to 6" in diameter and 30 to 50 feet tall. There is no way a grapple will help in this situation. As you cut these trees to length - you might as well be chucking them into the farm wagon.
I'll second this suggestion. That's the way I have been doing mine. On the steep hills, that's the only option anyway.