I think this tree is dead — what should I do?

Bare when everything around it has leafed out. Bark sloughing off in sheets leaving smooth grey wood underneath, shelf fungi or conks on the trunk or root flare, woodpecker excavation, mushrooms in the root zone after rain, and fine branches that snap off cleanly and dry instead of bending. Structural decline on a clock rather than a present emergency. A tree is not dangerous the day it dies — it becomes dangerous as decay fungi consume the wood holding it up, and that consumption runs a predictable route: fine twigs first, then branches, then the trunk, while root decay works upward independently and invisibly.