Årsring

Årsring, or annual ring, is the layer of wood produced by a tree during one growing season. In a cross-section of a trunk the ring appears as a complete circle, typically separated into two parts: earlywood formed at the start of the season, usually lighter and less dense, and latewood formed later, which is darker and more densely packed. The cambium generates xylem tissue each year, and the size and density of the ring reflect environmental conditions such as temperature, moisture, soil nutrients, and competition for resources.

The anatomy of årsringar varies with species. In conifers and many hardwoods, earlywood consists of large, thin-walled cells or tracheids, while latewood contains smaller, thicker-walled cells. The contrast between earlywood and latewood is what makes the ring visible in a radial cross-section and helps distinguish one year from the next.

Formation and interpretation of årsringar depend on climate and geography. In temperate regions rings are typically annual, providing a reliable record of yearly growth. In tropical and subtropical areas rings may be absent, indistinct, or irregular, and drought or other growth disturbances can produce false rings or missing rings. These variations must be considered when using rings for age estimation or climate reconstruction.

Applications of årsringar include dendrochronology, where cross-dating of wood samples extends calendar histories and calibrates radiometric data. They are used to infer past environmental conditions, growth responses to climate variability, and the age of wooden artifacts and structures.