My shad (which I thought was a tree, but turned out to prefer being a shrub) lost its center trunk about 10 years ago (it is about 25 years old). So I stopped trying to make it into a tree and stopped cutting back the extra shoots from the roots. It was happy for a while but last year about a 10th of it lost all its leaves but that tenth came back this year. But now, July, many of the leaves are turning yellow and dropping. What should I do? Prune? and how to do that?