sapwood

Sapwood is the younger, outer portion of a tree’s xylem. It conducts water and dissolved minerals from roots toward the crown and consists of living cells. It lies between the cambium and the heartwood and is typically lighter in color than the inner wood.

Anatomy and function: In hardwoods, sapwood includes vessels or tracheids for water transport and ray cells for radial transport and storage of carbohydrates. In conifers, it is primarily composed of tracheids with living parenchyma. The primary role is active transport of water and nutrients, along with storage of reserves.

Transition to heartwood: With time, sapwood gradually converts to heartwood, a nonconductive inner wood formed as extractives accumulate and vessels become blocked by tyloses. Heartwood is usually darker, less permeable, and more resistant to decay compared with sapwood.

Variation and practical notes: Sapwood thickness varies by species, age, and environmental conditions. In lumber and wood treatment, sapwood is generally lighter in color, more permeable to water and preservatives, and more susceptible to fungal attack than heartwood.