There's a big mushroom growing out of my tree — what should I do?

A hard, woody, hoof-shaped or plate-shaped growth pushing straight out of the bark — often white or cream underneath, brown, gray, or banded on top. Sometimes a single shelf, sometimes a stack. Common spots are the base, an old wound, a branch stub, or the flat face where a limb was cut years ago. Some kinds are soft, orange or yellow, and grow in overlapping clusters. Some return to the same spot every year; others rot away over winter and come back. The shelf is a fruiting body — the reproductive structure. The organism has been living inside the wood digesting it long before anything appeared on the outside. So the shelf is not the problem, it is the announcement. The practical translation is that there is a volume of decayed wood inside the trunk or the root collar, and the real job is establishing how much sound wood remains around it and whether that remaining shell is enough to hold the tree up.