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Why do conifers and many flowering trees develop wood through secondary growth?

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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.

Conifers and many flowering trees develop wood through secondary growth to facilitate the structural and physiological demands of becoming a tree. This process is driven by the vascular cambium, a lateral meristem that organizes between the primary xylem and primary phloem.1

The development of wood serves several critical functions:

Structural Support: As trees grow taller, they require increased mechanical strength to remain upright. The vascular cambium produces secondary xylem—commonly known as wood—to the inside, which provides the necessary support to sustain the tree's height and mass.12
Conduction and Storage: The secondary vascular system creates a continuous network for the transport of water and nutrients. While the apical meristems are responsible for primary growth (elongation), the vascular cambium is responsible for thickening the plant, allowing for the increased capacity needed to transport water and carbohydrates as the tree expands.1
Growth and Longevity: By continuously adding new layers of xylem, the tree can increase its circumference to keep pace with its overall growth. This secondary growth allows trees to achieve significant size and longevity, with some species surviving for thousands of years.314