STRUCTURE AND BASIC EQUATIONS OF A SIMULATOR FOR BRANCH GROWTH IN THE PINACEAE

The structure of a simulator for branch growth and morphological development in the Pinaceae is described. Growth is defined as the net production of foliage, the increment of branch thickening and the export of photosynthate to the trunk. Branch morphology is described by the spatial distribution of the branch segments, or branchlets, and a curvilinear profile of the whole branch as it bends under its own weight. Growth is the result of five interacting processes. Foliage development is the result of foliage production on the annual production of new branchlets and foliage death from older branchlets. Biomass production, (g biomass produced). (g foliage)-1, depends upon both the rate of production, which can vary with age of foliage, and the total amount of foliage of different ages. The distribution of biomass between the growth of the branch and export to the trunk of the tree is controlled by the phenology of shoot (branchlet) growth. During the period of branchlet growth biomass increment is distributed between branchlet elongation and the associated foliage growth and branchwood thickening. This is done so that branch posture in the vertical plane follows a particular deflection profile. The production of new branchlets is from the terminals of previous year's branchlets and is made according to morphological rules. Two types of rules are described; simple numerical sequences where branchlet number depends upon the order and length of the parent branch and a process of lateral inhibition between branchlets combined with dependence upon branchlet order. © 1990 Academic Press Limited.