Tree ring

A tree ring is a layer of secondary xylem formed during one growth period. Its width and structure can record growing conditions and help date wood.

Vascular cambium: A cylinder of plant tissue that produces secondary xylem inward and secondary phloem outward. Its seasonal activity produces the secondary xylem layers that become tree rings.
Dendrochronology: The science of dating and studying trees through patterns of annual growth rings. It uses ring sequences to assign calendar dates to wood.
Xylem: Plant vascular tissue that transports water and dissolved minerals and often provides structural support. Tree rings are made from the secondary xylem produced by woody trees.
False ring: A within-season band of wood that resembles an annual boundary but does not represent a separate year. It can make ring counts too high if mistaken for a true annual ring.
Secondary xylem: The woody tissue produced inward by the vascular cambium in stems and roots. A tree ring is one growth-period layer of this tissue.
Dendroclimatology: The study of past climate using climate-sensitive patterns in tree rings. Ring width and density can preserve signals of temperature and moisture.
Wood: The lignified secondary xylem that forms much of the stems and roots of woody plants. A ring is a visible growth layer within wood.
Missing ring: An annual growth ring that is absent or too faint to detect in part of a tree's circumference. It can make ring counts too low unless sequences are crossdated.
Earlywood: The less dense xylem formed early in a tree's growing season, often with larger conducting cells. Its contrast with latewood often makes annual ring boundaries visible.
Crossdating: A method that matches overlapping patterns in tree-ring series to assign exact calendar years. Overlapping ring patterns extend chronologies beyond the lifespan of a single tree.

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