What is bark

Bark is the many layered, outer covering or skin of a tree. Bark adapts to protect the living tree from its environment. The outer bark, the periderm, has several layers - as in the nearby drawing.

Drawing of tree section showing bark layers Drawing of tree section showing bark layers

Beneath the periderm a woody stem is encircled by a layer of living cells called the vascular cambium. As these cells divide and multiply the stem expands and, like skin, bark stretches, cracks and is shed to fit the new girth.

The vascular cambium cells divide to form an inner layer of wood and an outer layer of phloem, or soft bast. Soft bast is a system of fibrous tubes, which draw food from the leaves down to the roots to nourish the tree. It is this bast layer, the inner skin, which is used to make cloth in tropical climates.