Jahresring

A Jahresring (German for "annual ring") is a concentric layer of wood produced by a tree during a single year of growth. Visible in cross-sections of trunks and branches, each ring typically consists of an earlywood portion formed in the spring and a denser latewood portion formed later in the growing season. The width, density and anatomical features of Jahresringe vary with species, age and environmental conditions.

Jahresringe are central to dendrochronology, the science of dating and studying annual growth rings. Counting rings gives a minimum age for a tree or wooden object; comparing patterns of ring-width variation among samples (crossdating) allows precise calendar dating of timber and reconstruction of regional growth histories. Because ring characteristics respond to climatic and ecological factors such as temperature, precipitation and soil moisture, series of Jahresringe are widely used to infer past climate variability, date past disturbances (fires, insect outbreaks) and calibrate radiocarbon chronologies.

Interpretation of Jahresringe requires care: some species form indistinct or missing rings in certain years, while false rings can arise from unusual weather within a season. Tropical trees often lack clear annual rings. Human uses of Jahresringe include archaeological dating of wooden artifacts and buildings, forensic analysis of timber, and informing sustainable forest management.