Whilst very appreciative of your effort, I must say that I totally disagree with most of the views you expressed. The idea that experts should decide that certain trees and shrubs are exotic and need to be exterminated like goats of impure breed is anathema to me. I am not alone in this view. I grant that certain plants should not be encouraged like rhododendron and knotweed because their presence is destructive. However, other exotics such as buddleia which are not are much appreciated by us non experts. What I am saying is that diversity is a good thing, whether exotic or native or not, it is only when a new species presents a threat that we should intervene.
The problem with Hollerday Hill is that there has been too much management. The hill looked best after if was re-opened after the foot and mouth epidemic. The experts always want to maintain the status quo oddly by their own interference whereas nature is cyclic. Change is natural stasis is death.
Notwithstanding all this, the site is about goats. People count the goats and say there are too many. What there is too many of is experts. People in the country should protect their land from wild animals. If they become a hazard or nuisance to people who cannot protect themselves then these people should have the right to shoot them (and eat them if they want to). This way the wayward goats would be eradicated and the shy ones under the cliffs would be left in peace. Everyone wants to be important and interfere with people and the natural course of things. If there was a population explosion of goats then the surplus would (a) wander away (b) die and be eaten or (c) not survive to adulthood. There would not be dead bodies strewn over the hill for the crows and ravens would flourish and grow fat. How many times do people see carcasses - I have never seen a dead goat.
A final thought. It would be natural for trees to return to Exmoor but no yesterday is more important than the day before yesterday.