Well having gone back to the primary legislation of the CRoW act I can now answer these queries without relying on faded half memories...
With regard to the OL acts, CRoW takes primacy because it amends the earlier legislation and contrary to my previous recollection it is explicit on the relevance to trees(my empasis in bold);
"13 Occupiers’ liability.
(1)In section 1 of the Occupiers’ Liability Act 1957 (liability in tort: preliminary), for subsection (4) there is substituted—.
“(4)A person entering any premises in exercise of rights conferred by virtue of—.
(a)section 2(1) of the Countryside and Rights of Way Act 2000, or.
(b)an access agreement or order under the National Parks and Access to the Countryside Act 1949,.
is not, for the purposes of this Act, a visitor of the occupier of the premises.”
(2) In section 1 of the Occupiers’ Liability Act 1984 (duty of occupier to persons other than his visitors), after subsection (6) there is inserted—.
“(6A)At any time when the right conferred by section 2(1) of the Countryside and Rights of Way Act 2000 is exercisable in relation to land which is access land for the purposes of Part I of that Act, an occupier of the land owes (subject to subsection (6C) below) no duty by virtue of this section to any person in respect of—.
(a) a risk resulting from the existence of any natural feature of the landscape, or any river, stream, ditch or pond whether or not a natural feature, or.
(b) a risk of that person suffering injury when passing over, under or through any wall, fence or gate, except by proper use of the gate or of a stile.
(6B) For the purposes of subsection (6A) above, any plant, shrub or tree, of whatever origin, is to be regarded as a natural feature of the landscape.
(6C) Subsection (6A) does not prevent an occupier from owing a duty by virtue of this section in respect of any risk where the danger concerned is due to anything done by the occupier—.
(a)with the intention of creating that risk, or.
(b)being reckless as to whether that risk is created.”
So, landowners still have a duty of care on access land but the liability is relaxed. Not all visitors are visitors and trees are natural regardless of the inequitious intervention of 'man'. Doesn't that seem sensible?
Even better, in deciding liability, the act specifically mentions that there may be special consideration given to the finacial burden of allowing access and the responsibilities of maintaing the character of the countryside. To that end I've attached a English Nature Guidance note which essentially covers the issue.
English Nature CRoW Liability.pdf