There is a very large locust tree in the backyard of my family's house on Long Island, New York. I do not know how old it is, but it has been there, as a mature tree, ever since we moved in, about 15 years ago. We have noticed that over the past 5 years or so, limbs have been slowly dying (a couple each season) from the bottom-up. There is also a part of the trunk where the bark and a layer of the trunk underneath has opened up, apparently from a spot where a limb fell off. Although the tree still blooms profusely, we are concerned that the tree itself is dying and think that we should have it removed before it falls onto the house or garage. Is there any sure way to know if the tree is indeed dying? What is the normal life-span of a locust tree?