What is the first layer in a trunk cross-section from center to outside?

The pith is the central core of a trunk cross-section that serves as the innermost layer of the tree. It is composed of soft, spongy tissue and is crucial for the initial growth of the tree, as it stores nutrients and water during the tree's early development.

As the tree matures, the pith is encircled by the heartwood, which comprises older, non-living wood that supports the tree structure. Beyond the heartwood is the sapwood, which consists of living cells responsible for conducting water and nutrients. The cambium layer is located just outside the sapwood and is essential for producing new cells that contribute to the tree's growth in circumference. Finally, the outer bark protects the inner layers of the tree from environmental damage and disease.

Understanding the arrangement of these layers is important for grasping tree biology, growth processes, and the overall health of forest ecosystems.