Half the tree is dead and the other half looks fine — what should I do?

One side or the top bare while the rest leafs out normally, often with a surprisingly distinct vertical dividing line. Thinning and smaller, paler leaves on the affected side, sprouts erupting along the trunk below the dead section, and frequently a strip of dead, cracked or sunken bark running down the trunk on that same side. A directional signal, not a diagnosis. Because a tree's vascular system is sectored — water and sugars move in vertical strips rather than mixing freely around the trunk — a dead sector usually points straight down at its own cause. The dead half is telling you which side of the root system, root flare or trunk to go inspect.