Cambium

The cambium is a microscopically thin but critically important tissue layer located between the inner bark (phloem) and the wood (xylem) of a tree. This cylindrical sheath of meristematic cells is responsible for all diameter growth in the trunk and branches. Each growing season, the cambium divides to produce new phloem cells toward the outside and new xylem (wood) cells toward the inside.

The cambium is one of the most vulnerable tissues in a tree. It can be damaged by physical impacts such as mower strikes or animal rubbing, by extreme heat from fires or reflected sun, by herbicide drift, and by boring insects. Because the cambium is just beneath the bark, even superficial bark damage can disrupt this vital growth layer, creating entry points for decay and interrupting the flow of nutrients.

Understanding the cambium's role is essential for proper pruning technique. When a branch is removed, the cut should be made just outside the branch collar, where the cambium of the trunk meets the cambium of the branch. This allows the tree to grow wound wood efficiently over the cut surface, a process called compartmentalization. Flush cuts that remove the branch collar damage the trunk cambium and impede this healing process.