Cambium Layer
AnatomyThe thin cylinder of actively dividing meristematic cells between bark and wood that is responsible for producing all new wood and inner bark growth.
The cambium layer (also called the vascular cambium) is a continuous cylinder of meristematic tissue, just one to several cells thick, that encircles the trunk, branches, and roots of a tree beneath the bark. Despite its microscopic thickness, it is the single most important growth tissue in a tree, responsible for producing all increases in girth throughout the tree's life.
During each growing season, cambial cells divide to produce new xylem (wood) cells on their interior face and new phloem (inner bark) cells on their exterior face. This process creates the familiar annual growth rings. The cambium is most active in spring and early summer, and may go dormant during drought or winter. Growth rate varies around the trunk and is influenced by hormone distribution from the canopy above.
The cambium layer's critical role makes its protection paramount in tree care. When grafting, the cambium of the scion must align with the cambium of the rootstock for a successful union. Proper pruning cuts preserve the cambium at the branch collar to enable wound closure. Construction damage that strips bark exposes and kills the underlying cambium. Even paint or adhesive applied to bark can damage this sensitive tissue. Any activity within a tree's space should consider the potential impact on this vital growth layer.