A sign that the air is very clean is the prevalence of lichen on the trees- and there is a fair amount in Mine Woods, across the road from where I live.
It is also a sign of very old woodland though this wood, bought by Bridge of Allan Burgh council from the local Westerton estate to commemorate the coronation of Queen Elizabeth 11, probably does not qualify as ancient woodland.
Apparently there are 18,000 different types of lichen worldwide and around 1,800 in Britain.
But I have no idea what this one is. Does anyone recognize it?