Your Neighbors. Your Arborists.
From North Carolina Forestry Association Site: (https://www.ncforestry.org/teachers/parts-of-a-tree/)
“The cambium is a very thin layer of growing tissue that produces new cells that become either xylem, phloem or more cambium. Every growing season, a tree’s cambium adds a new layer of xylem to its trunk, producing a visible growth ring in most trees. The cambium is what makes the trunk, branches and roots grow larger in diameter.”