In botany, trunk (or bole) refers to the main wooden axis of a tree, 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 is the most important part of the tree for timber production.

Trunks occur both in "true" woody plants as well as non-woody plants such as palms and other monocots, though the internal physiology is different in each case. In all plants, trunks thicken over time due to formation of secondary growth (or in monocots, pseudo-secondary growth). Trunks can be vulnerable to damage, including sunburn. Trunks which are cut down in logging are generally called logs and if cut to a specific length bolts.

Raft of timber logs

Raft of timber logs

Cross section of a hazel bole

Cross section of a hazel bole

Log being decomposed by bracket fungi

Log being decomposed by bracket fungi

See also