In reply to Offwidth:
I have spoken to them and they would be 'extremely grateful' for help from the climbing community. They are part of the Wharncliffe Heath Trust which manages the enclosed nature reserve. However they have said that they really really DO NOT want people to attack rhododendron randomly. This is because there are a herd of Shetland Sheep who will be poisoned by any branches not removed from the site, and they also have a management plan aimed at the wider ecosystem such as encouraging night jar. Outside the nature reserve it is a different management plan, but the two are joined up. Ad hoc efforts are not encouraged but volunteers for scheduled clearance are welcome. If climbing access is not part of the management plan, then efforts by climbers on the boulders would probably be welcomed but should be made in conjunction and consultation with the trust and landowners.
http://www.wharncliffeheathlandstrust.org.uk/
I will PM contact details for management of the reserve and the outside area to Offwidth.