Which part of a tree is often darker and denser?

The heartwood is the central part of a tree, and it is often darker and denser compared to the outer layers. This is due to the accumulation of various substances such as resins, tannins, and oils, which provide structural support and make it resistant to decay. As the tree matures, the inner sapwood turns into heartwood, which no longer participates in water transport; instead, it serves primarily a supportive role. The density of heartwood contributes to its strength, making it a desirable material for construction and woodworking, as it possesses greater durability and weight compared to younger sapwood, which is lighter and more permeable. Understanding the properties of heartwood is crucial for applications in surveying and timber management, as it directly relates to the quality and usability of the wood.