Heartwood

Heartwood is the central, woody core of a tree, composed of older xylem that has ceased to transport water. It lies at the center of the trunk and branches, surrounded by sapwood, and is typically darker in color.

Heartwood forms as trees age. Through gradual deposition of extractives—substances such as tannins, resins, and essential oils—the inner xylem becomes chemically distinct from active sapwood. These compounds lend color and often increase resistance to decay and insect attack. In many species the vessels and tracheids in the heartwood are partially occluded by tyloses, further reducing permeability.

Compared with sapwood, heartwood is usually less able to conduct water and nutrients, and it is commonly more durable. The presence of extractives can influence how the wood finishes and how metal fasteners interact with it, and it can affect workability in some species. Not all trees show a strong color contrast; in some species heartwood is only modestly darker than sapwood.

Heartwood is valued in timber production for its strength and durability, and is often prized for furniture, flooring, and cabinetry. Its properties can vary widely among species and even within a tree, reflecting different extractive contents and age.