THE DEVELOPMENT OF THE TREE TRUNK IN RELATION TO APICAL DOMINANCE AND OTHER SHOOT ORGANISATION CONCEPTS

Abstract

Trunk development is an expression of tree architecture. All trees begin as seedlings with a simple unbranched shoot. Trees that remain unbranched throughout their whole lives are referred to as unbranched trees. Trees which eventually branch to produce multiple shoots, all of one type, are
referred to as 'monomorphic' trees. In the next class, branch shoots are differentiated from the leader (trunk) shoot, the most important difference being that branches are designed to be shed, while the trunk is permanent; such trees are 'dimorphic' because they consist of two types of shoots. In the fourth class (containing most of the big timber trees of the world), trees grow through the seedling unbranched phase, followed by an intermediate dimorphic phase (with sheddable branches), followed by a 'metamorphosed' phase in which the crown is made up of limbs that do not get shed; such trees are 'metamorphosed'. The fifth class of trees are 'plagiotropic'
because their apical buds grow sideways, but an erect trunk is formed because the leader shoot straightens up by secondary erection. The trunk height of unbranched and dimorphic trees is indeterminate because the upper limit of the trunk moves up as leaves or branches are shed. The trunk height of monomorphic trees is determined by the onset of branching, that of metamorphosed trees by the onset of metamorphosis, and that of plagiotropic trees by the cessation of secondary erection.