By Markcheckley
United Kingdom 
I want to know what this mossy stuff that grows on the branches is ?
It makes the branches die off one by one and any new branches that grow are all stubby and short
8 May, 2011
That's lichen. It doesn't harm the tree - it's a sign that the air is clean where you live. Whatever your tree's problem is, the lichen isn't causing it.
What sort of tree is it? Where do you live? How long has your tree had this problem? Have you had the very dry weather following an exceptionally cold and dry winter most areas have had? Could you post a pic or two of the dying back branches please?
8 May, 2011