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How do conifer growth rings form in wood?

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The massive Grizzly Giant sequoia tree stands with a wide, reddish-brown trunk and a hollowed base, surrounded by other tall trees in Mariposa Grove, Yosemite National Park. — Conifer A giant sequoia (*Sequoiadendron giganteum*) estimated to be between 1,900 and 2,400 years old, Grizzly Giant is the oldest tree in the Mariposa Grove, Yosemite National Park, California.

Conifer growth rings form through the seasonal activity of the vascular cambium, a layer of meristematic cells responsible for secondary growth in the tree's stem.1

At the beginning of the growing season, the cambium produces cells known as earlywood. These cells, primarily tracheids, are characterized by larger radial diameters and thinner walls, which facilitate rapid water conduction. As the season progresses, the cambium produces latewood, which consists of cells with smaller diameters and thicker walls.23

This transition from the larger, thinner-walled cells of earlywood to the denser, darker, and thicker-walled cells of latewood creates the visible contrast that defines a growth ring. In temperate regions, this process typically results in the development of a single ring per year. However, environmental stressors such as drought can interrupt this cycle, potentially causing the formation of "false rings," where the tree produces latewood-like cells mid-season before resuming normal growth.432