There are machines called "Mulchers" that go on medium to large track equipment (ASV is popular). They can turn a 4-6" hardwood tree into mulch in no time at all. It sounds like a match to your needs. You would probably have to hire in a service as they don't rent the equipment (usually).
You can find out about the equipment in the "construction" section of the forum - search for mulching.
I used to live in Rio Rancho - back when it was a small town '85-'88. Talk about growth!
We had our property logged out in 99, As part of the deal the logger ran on all flat areas a "I think it was called a hydro ax". Could grind down stumps or anything. Just left bare earth. Was quick and dramatic.