As arthur says, most of the area was already void of vegetation by the time of the neolithics. If there ever was to be a silbury game, then the landscape must have been cleared by - let's not forget - the first farmers, which means, the first forest clearers. The neolithic was a time of change, from an awe-ful time of utter respect to the environment to a time of plenty and settling down.

Another proof is in the RSC's in scotland. Most plantations in many parts there have destroyed vision. I have also observed this in other parts of Britain, France, Portugal, Malta and Spain. Housing developments or indiscriminate plantations with conifers, apart from destroying loads of graves, also do not discriminate and block vision and landscape.