Trees need friends and we can all do our little bit for them. If you have a love of nature and trees in particular then you have to get out there and kill some ivy.
You will need sharp tools and some protection in the shape of gloves and some eye protection.
A Tool List:
Pruning Saw
Timber Saw or small Chain Saw
Pruning Shears
Another requirement is a killer instinct coupled with a hatred of parasites, ivy is definitely not a friend of trees and in many places ivy is damaging and inhibiting their growth.
If one wishes to keep some ivy on a tree, perhaps because some wildlife has used it for nesting then one can disconnect roots that are heading towards adjacent trees.