Cross section of a Douglas Fir (Pseudotsuga menziesii) showing annual rings. Faster growth occurs when the stem is young, and hence the inner rings are broader than the outer ones. The ring system is eccentric in this example because the stem was bent.
An annual ring is any of the concentric rings of wood seen when the stem of a tree or shrub is cut across. Each ring shows one year's growth and is usually composed of two growth layers – a broad, large-celled layer representing spring growth and a narrow, denser layer showing summer growth. The relative amounts of these layers are affected by the environment, a fact that forms the basis of the science of dendrochronology.