bark

Bark is the outer covering of many trees and shrubs. It comprises all tissues outside the vascular cambium, including the inner bark (phloem) and the outer bark (periderm). In common usage, the term can refer to the protective outer layer or the living inner bark in some contexts. Bark protects the underlying tissues from mechanical damage, temperature fluctuations, desiccation, and attack by pests and pathogens, and it often contains chemical compounds that deter herbivores. Lenticels on bark allow limited gas exchange.

Anatomically, bark consists of several layers. The inner bark, or phloem, transports sugars from leaves to other parts of the plant. The outer bark includes the cork cambium (phellogen) and cork (phellem), with phelloderm on the inside. The periderm replaces the epidermis in older stems. Cork tissue is rich in suberin, forming a barrier to water loss and microbial intrusion. Lenticels provide pathways for gas exchange between the internal tissues and the atmosphere.

Bark has ecological and economic importance. Thick bark can protect trees from fire, cold, and pests. Some species produce notable bark characteristics, such as cork oak, whose bark is harvested to yield cork without killing the tree. Bark also factors into plant pathology, as bark beetles and fungal pathogens exploit bark to reach the vascular system or to spread infections.

Related meaning: bark is also the vocalization of dogs and some other animals, a short, sharp sound used in communication and warning. Bark patterns vary in pitch, duration, and context and can convey different messages in social interactions.