MrsB
"Can you set up physical boundaries?"
Technically yes - but think how awful it would be if every wood that was bought and cut up into little pieces was suddenly riven with fences? Owning woodland is very different from owning a property on Acacia Avenue. "You can fence yourself in, but you can't fence the world out."
"...Public rights of way.."
You are responsible for overhanging vegetation - branches etc. - but the council is responsible for maintaing the surface - unless you damage it (extracting timber etc.) in which case they will ensure you rectify the problem. No you can't reroute them!!
"...someone is injured..."
You are responsible for injuries due to man made structures and if you can be shown to have been negligent in the case of natural hazards. The risk of someone successfully suing you over a natural hazard is much less than the insurance companies would have you believe - negligence has to be proved.
"...park a car..."
Yes.
"...permanent structures.."
Certain structures are allowed- google "permitted development forestry". You can expect a shed to be allowed - you would need a fairly large woodland to justify that a static caravan was "reasonably necessary". Technically tree houses are not allowed - they represent a "change of use" to leisure - I have never heard of anyone having problems from planning departments over tree houses though.
"..access routes.."
Again this comes under permitted development, and so if you can demonstrate that the track is reasonably necessary then you will be allowed to make it. If there is already access to your woodland and you just want a private access then you would be refussed on the grounds that is isn't "reasonably necessary" -even if you have a contractual right from the vendor to make an access track over adjacent land this would still have to be agreed to by the planning department.