Though the grassland associated with the sugar limestone outcrops in Upper Teesdale supports the richest terricolous lichen assemblage of any calcareous site so far discovered in England or Wales it may not have acted as a significant refugium for late-glacial lichens. A possible reason for this is suppression by open canopy forest during the boreal and atlantic periods. The current high density of terricolous lichens may, to some extent, be a result of intensive grazing over the last few centuries which has favoured the development of an extremely short, open sward offering a wide range of microhabitats.