I have 70 wooded acres, and had controlled burns several times over the years to clear parts. It isn't particularly hard or dangerous if done right.
1st I hire a guy that has a large excavator with a thumb. He pushes down the trees, I cut off anything I want for saw logs (I have a small bandmill) or firewood, the rest gets shoved in a pile with his 650 JD dozer w/root rake. If you don't want the logs or firewood, they should be an easy sell, or worst case, give away free.
2nd, he digs a 6-10' deep pit near the brush/tops pile, and starts a fire with some of it in the pit. He puts the machine between the pile and pit, reaches around and grabs a bunch, shakes it to get as much dirt off it as will come off, then rotates over the pit and drops it on the fire. Repeat until gone, mixing in stumps as the fire gets really hot.
Of course, you want to wait to do this until you have fairly wet weather so any flying embers don't have any chance to catch, but the kind of weather we've had in the last few weeks is great...couple inches of rain per week, you'd be hard pressed to set the woods on fire with a drum of diesel fuel.
Final is grade the dirt back over the hole to bury the pit, and any stumps that didn't burn up 100%.
Most recently, we did a 3acre patch last year about this time, cost me $5,000 for him, another couple hundred for some day laborers to put up rocks/roots that slip thru the dozer rake, then I sowed it in fescue and red clover....well on it's way to making pasture now.
