What is heartwood in a tree?

Heartwood is indeed the term used to describe the central, older, nonliving wood of a tree. As trees age, the innermost wood becomes hardened and darkens, typically losing its function in water transport and instead serving as a structural support for the tree. This heartwood is often denser and more durable than the outer layers, which are actively involved in transporting water and nutrients. Heartwood can also contain extracts that give it resistance to decay and pests, making it a valuable material in woodworking and construction.

In contrast to heartwood, the other choices refer to different parts or functions of the tree. The area active in fluid transport refers to the sapwood, which is the outer living layer that conducts water and nutrients. The outer layer of a tree consists of the bark, which protects the inner wood. The region of new growth, known as the cambium, is where growth occurs in the tree's diameter. Thus, heartwood stands out as a specific, mature component of the tree, playing a critical role in its longevity and structural integrity.