Bark is the outer protective layer of a tree, serving as a shield against environmental factors such as pests, diseases, and physical damage. It consists of two main parts: the outer bark, which is rough and protective, and the inner bark, or phloem, which transports nutrients throughout the tree. Bark varies in texture, color, and thickness depending on the species of tree. For example, the cork oak has thick, spongy bark, while the birch tree is known for its distinctive peeling bark. Understanding bark is essential for studying tree health and ecology.