Living Trees are Mostly Dead

Most mature trees are made up of 99% dead cells. The only living parts are the leaves, the buds, the apex of the branches, the root tip and a thin layer under the bark (the cambium) which serves a food and moisture delivery system.

That’s why a hollow tree can live for decades even if its wood has almost entirely disappeared: the heart of any tree is dead anyway and its absence makes little difference to the tree’s survival.