A tree wears its life on its skin.
Its roots may be hidden as it digs the ground; the rings in its trunk counted only when it falls. The leaves and twigs may be broken by the wind, but they will grow anew.
The bark shows all the scars of the seasons, the callouses from insects that burrow into it, the small garden of lichen and moss that it carries, the sap that oozes when it is wounded.
If a tree had a heart, it would be in its bark.