From John Knapp
Many of our local fields have horses in them. These same fields also often contain trees. Horses and trees do not get on together because horses are inveterate chewers and will strip all the bark off a tree, thus killing it. It makes no difference whether there is ample food for the horses or not.
I have noticed many local mature trees, some at least 150 year old that have been killed by horses removing the bark. This is heartbreaking to see, particularly when the problem is so easily solved.
Can I make a plea for our horsey people to put a simple fence round any trees within range of horses teeth; even some chicken wire round the trunk would prevent this. If someone with a chain saw felled these self same trees, there would be concern shown but their slow insidious death seems to pass people by. These are the trees we do not wish to have destroyed. These are our landscape features which have been around and shaped our fields for a long time. Being open grown they have expanded crowns and are full of character. When gone, no one is replacing them and our landscape will be the poorer for it.
From Andy M
And may, apparently, be linked to diet deficiencies - see this web page.