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

The first layer in a trunk cross-section, moving from the center towards the outside, is the pith. The pith is the central core of the tree trunk, consisting of soft, spongy tissue that is the first part to form when the tree is growing. It serves as the tree's initial growth center and can store nutrients.

As a tree matures, the pith is surrounded by heartwood, which is composed of denser, older wood that provides structural support. Moving outward from the heartwood, the next layer is the cambium, which is responsible for producing new cells for the tree’s growth. The outer bark then provides protection against environmental factors and pests.

Understanding the structure of a tree is crucial for forestry studies, as each layer plays a specific role in the overall health and functionality of the tree.