We have 2 articles written by planning consultants that discuss the various issues concerned. They cover similar ground, but are both well worth a read.

Remember to be sure of your rights before you embark on any construction, it could save you a lot of time and expense later.

Woodlands and planning legislation By Lucy Nichol, Lecturer in Planning Policy at Oxford University.
Woodlands and the planning system By Mr Rhys Roberts, Cynefin Consultants, Bangor, Gwynedd.