The base of a Yellow Birch trunk
In botany, trunk refers to the main structural member of a tree that is supported by and directly attached to the roots and which in turn supports the branches. The trunk is also often called the bole. The trunk is covered by the bark, which is an important diagnostic feature in tree identification, and which often differs markedly from the bottom of the trunk to the top, depending on the species. The trunk, or bole, is the most important part of the tree for timber production.