This morning I came across a group of holly trees all of which had extensive areas of bark removed from near the ground up to a height of about 1.5 metres. The exposed trunks are covered in these strange blister-like swellings. I'm curious as to what has cause this. Perhaps the bark has been removed by deer and the swellings are where the tree has tried to repair the damage. Or perhaps its a disease or insect damage. Other trees in the same copse (birch, oak, alder and hazel) were unaffected.