Tree Anatomy: Bark

Bark is the sophisticated, multi-layered outer protective covering that envelopes the trunk, branches, and roots of woody plants, acting as the primary barrier between the inner living tissues of the tree and the external environment.

Anatomically, bark is divided into two main zones: the inner bark and the outer bark.

The inner bark consists of living phloem tissues, which form a critical vascular highway responsible for transporting energy-rich sugars produced during leaf photosynthesis downward to nourish the cambium, trunk, and roots.

The outer bark is composed of dead cork cells tightly packed with suberin, a waterproof, waxy substance that prevents moisture loss from the tree's interior. This outer layer serves as a tough shield, protecting the tree from mechanical damage, boring insects, fungal pathogens, extreme temperatures, and woodland fires. As a tree grows radially, the outer bark must expand; in some species, it stretches smoothly, while in others, it splits, cracks, or flakes off in distinctive sheets, ridges, or camouflaged patches, creating a highly textured microhabitat that shelters specialised lichens, mosses, and overwintering insects.