Application of the Functional-Structural Tree Model LIGNUM to Sugar Maple Saplings (Acer saccharum Marsh) Growing in Forest Gaps

LIGNUM is a functional-structural model that represents a treeusing four modelling units which closely resemble the real structureof trees: tree segments, tree axes, branching points and buds.Metabolic processes are explicitly related to the structuralunits in which they take place. Here we adapt earlier versionsof LIGNUM designed to model growth of conifers for use withbroad-leaved trees. Two primary changes are involved. First,the tree segment for broad-leaved trees consists of enclosedcylinders of heartwood, sapwood and bark. Leaves consistingof petioles and blades are attached to the segments. Secondly,axillary buds and rules governing their dormancy are includedin the model. This modified version of LIGNUM is used to simulatethe growth and form of sugar maple saplings in forest gaps.The annual growth of the model tree is driven by net productionafter respiration losses are taken into account. The productionrate of each leaf depends on the amount of photosyntheticallyactive radiation it receives. The radiation regime is trackedexplicitly in different parts of the tree crown using a modelof mutual shading of the leaves. Forest gaps are representedby changing the radiation intensity in different parts of themodel sky. This version of LIGNUM modified for use with broad-leaf,deciduous trees and parameterized for sugar maple, yields goodsimulations of growth and form in saplings from different forestgap environments. Copyright 2001 Annals of Botany Company LIGNUM, functional-structural tree model, tree architecture, sugar maple, modelling growth and form