permaculture

[Steve Diver <steved@ncat.org>]

The equipment that cuts thru small trees and brushy
undergrowth to create mulch is used in forestry, landscape
clearing, and ecological restoration projects.  This equipment
converts overgrown brush and woody lands into open lands,
park lands, fire breaks, power line clearnings, etc.

See:

Forest Products Equipment magazine
http://www.fpemagazine.com

For example, see:

Fecon Bull Hog Brush Cutter/Mulcher
http://www.fecon.com/bullhog/

These can be mounted on a big tractor or
a skid steer and powered by PTO or hydraulics.

There's several equipment manufacturers that
make these kind of brush chippers and mulchers.

The low-cost alternative is to get a few dozen goats and turn
them loose on an overgrown patch of woodland, then collect
their manure and bedding for building a compost pile.  

Steve Diver
NW Arkansas