The bark on the sunny side of my young tree is cracked, sunken, and peeling off — what should I do?

A patch of dead bark on the south or southwest face of a young, thin-barked tree, usually between the ground and the lowest branches. Early on it looks faintly sunken and off-color and sounds hollow when tapped; later the bark cracks at the edges and sheets off, leaving dry bare wood with a sharp raised callus rolling in from both sides. If a row of trees was planted together, the damage lands on the same face of every affected one — that repeating pattern is what separates it from a mower or animal wound. Newly planted maple, cherry, crabapple, linden, honeylocust, and young thin-barked oak are the usual patients. The cambium — the living layer just under the bark that builds new wood and moves food down to the roots — was killed in that patch, and the tree is now conducting around a dead strip. A narrow strip gets grown over in a few seasons and leaves a scar. A strip that wraps far enough around leaves the tree partly girdled, and the crown above it thins as the remaining live tissue gets overloaded. Either way the exposed wood becomes an open invitation to borers and canker fungi that would not touch intact bark.