We have an ornamental cherry tree that was here when we bought our house 12 years ago. Then it was an apparently mature tree. Now it shows many dead limbs and we wondered if we could prune severely in order to eke a few more years from the tree. It has white blossoms and is an upright rather than a weeping variety. But we don't know anything else about it. The main trunk has a bit of green at the top and several lateral branches are dead.