“Between the bark and the wood is the delicate undergarment of living tissue called cambium. This is disappointing when one comes to look for it, for all there is of it is a colorless, slimy substance that moistens the youngest layers of wood and bark, and forms the layer of separation between them. This cambium is the life of the tree. A hollow trunk seems scarcely a disability… But girdle its trunk, exposing a ring of the cambium to the air, and the tree dies. The vital connection of leaves and roots is destroyed by the girdling; nothing can save the tree’s life.””
The Nature Library: Trees