For ground that has gone past what a flail or topper can handle: dense scrub, bramble and blackthorn, self-set birch and willow, or brash left after felling. A fixed tooth mulcher shreds it where it stands and leaves a layer of mulch, with no burning and nothing to cart away.
A fixed tooth mulcher is a heavy rotor fitted with hardened teeth, mounted on a high-powered tractor or a tracked carrier. It is lowered onto the vegetation and chews through stems, small trees and brash, leaving the material as a mat of chip on the surface.
It handles far thicker material than a flail mower. Saplings and small trees go straight through it, and larger trees are usually felled first and the brash mulched after. Many machines can take stumps down to ground level or a little below, which leaves the ground ready for mowing or cultivation.
The result is rough at first: a layer of mulch over bare soil. On grassland it breaks down over a season or two, and grass will come back through it, though reseeding speeds things up.
Autumn and winter are the main season, outside the bird nesting period that runs roughly from March to August. Dense scrub is prime nesting habitat, so summer work needs a careful check for active nests first, and is often best avoided altogether.
Firm ground matters. These are heavy machines, and on wet clay they will rut badly. Tracked carriers spread the weight better than tractors, but a dry or frozen spell gives the cleanest finish.