Which layer of a tree is responsible for outward growth and increased trunk girth?

The cambium is a critical layer in a tree that is responsible for outward growth and increased trunk girth. It acts as a layer of actively dividing cells located between the xylem and phloem. As the cambium produces new cells, it generates more xylem (which transports water and nutrients from the roots to the leaves) on the inside and more phloem (which transports sugars and organic compounds produced by photosynthesis from the leaves to the rest of the tree) on the outside. This process of cell division is essential for the tree to grow in width, allowing it to support the increasing weight of the branches and foliage as it matures.

Understanding the role of the cambium is crucial, as it is the main area of growth for the trunk and branches, contributing significantly to the overall structure and health of the tree. Without the cambium's activities, trees would not be able to expand their girth adequately to sustain their height and biomass over time.