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How do environmental stresses change the amount of wood and phloem a tree produces?

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Tall giant sequoia trees with reddish bark and thick trunks rise closely together in a dense forest at Sequoia National Park, California. — Tree A stand of giant sequoia trees (*Sequoiadendron giganteum*) in Sequoia National Park, California.

Environmental stresses, such as drought, significantly influence the production of secondary vascular tissues by the vascular cambium, which is responsible for generating both secondary xylem (wood) and secondary phloem.1

When a tree experiences adverse conditions like drought, the rate of cell division and the magnitude of cell expansion are altered, directly impacting the width and structure of the growth increment. Specifically:2

Wood Production: Under drought stress, the radial diameters of secondary tissue cells decrease, and cell walls may thicken, causing the wood to take on the appearance of latewood. If conditions worsen significantly, a tree may produce incomplete or missing rings, where no wood is formed at all during that period. Conversely, if drought interrupts the growing season, a tree may produce "false rings"—an appearance of a new ring caused by a temporary shift in cell size and wall thickness.2
Phloem and General Growth: Because the cambium produces more cells internally (xylem) than externally (phloem), environmental stress primarily manifests in the visible patterns of the wood. However, as the cambium continues to produce new tissue, older layers of phloem are crushed and eventually sloughed off as bark. Stress-induced changes in cambial activity affect the overall circumferential growth of the stem, which can lead to eccentric or fluted ring patterns.12