Cambium is a thin layer of growing tissue inside trees and other woody plants that creates new wood and bark. Think of it as a ring of living cells just beneath the bark, constantly dividing to make the tree thicker and stronger year after year.

When you peel bark off a fallen branch, that slippery, slightly greenish layer underneath is the cambium. It's incredibly thin, sometimes just a few cells thick, but it does crucial work. The cambium produces wood cells (called xylem) toward the inside of the tree and bark cells (called phloem) toward the outside. This is how trees grow wider over time while keeping their protective bark coating.

The cambium creates those growth rings you see when a tree is cut down. Each ring represents one year of growth, with the cambium adding a new layer of wood every growing season. Scientists can count these rings to determine a tree's age.

Because the cambium is alive and actively growing, it needs protection. Carving initials into a tree damages this vital layer, which is why foresters and arborists discourage it. The tree will try to heal around the wound, but deep cuts can harm or even kill parts of the cambium, affecting the tree's health for years.