Why do tree trunks have two colors?

Why do tree trunks have two colors?

If you have the chance to observe a sawn tree trunk, you might notice that some trunks have a darker color in the middle and a lighter color on the outer edge. This is not a disease, but rather a normal part of the tree's structure. These two parts are the "sapwood" and the "heartwood," respectively.

A tree trunk is not a single, homogeneous piece of wood. The lighter-colored outer part is called sapwood; its cells remain active and are responsible for transporting water and minerals upwards.

The darker-colored middle part is the heartwood. It was originally sapwood as well, but as the tree grows, it gradually loses its transport function, and resins, tannins, and other substances accumulate within its cells, making the wood denser, stronger, and more resistant to decay and insects.

Depending on the deposited substances, the color of the heartwood varies from tree to tree, and some trees do not have a distinct heartwood.