trunk, the main stem of a tree, from the ground to the first branches or, in the case of a grapevine, to the cordons or head. Newly formed vine trunks are pliable and need support (see vine training). The height of the trunk of a grapevine is variable, from 10 cm/4 in (in bush vines) to more than 10 m/30 ft (in vines growing up trees), and is determined by the specifications set for each training system and trellis. The trunk height determines the position of the canopy relative to the ground. Vine trunks are woody and form part of the bulk needed for storage reserves, especially of carbohydrates and nitrogen compounds. In climates with freezing winters, multiple trunks are used to facilitate replacement after winter killing, and in extremely cold climates trunks are buried during the winter (see winter protection).
