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A 102 , December 2008 THE LIGNUM FUNCTIONAL-STRUCTURAL TREE MODEL

The aim of this thesis was to construct a single tree model that builds a bridge between traditional process based tree models and detailed, three-dimensional architectural tree models. The result of the thesis, the functional-structural tree model LIGNUM, integrates both the functional and the structural aspects of woody arborescent plants in a single generic modelling framework. The thesis consists of five articles and the summary part. The first article presents the model structure of LIGNUM based on simple recurring botanical units, their metabolic processes and the allocation of photosynthates on the basis of the carbon balance resolved according to the specific growth potential in different parts of the tree crown. The model is applied to young Scots pine (Pinus sylvestris L.). The second article studies alternative formulations of sapwood senescence in Scots pine. The third article presents an improvement in assessing solar radiation absorption on the basis of the mutual shading of tree segments. The fourth article adapts the LIGNUM model to deciduous species with sugar maple (Acer saccharum Marsh) as an example. The fifth article introduces Lindenmayer systems for defining the architectural development of the tree crown. The central problem in process-based tree models has been resource capture and allocation in a dynamically growing tree. The main contribution of this thesis is to present a solution to how photosynthates can be allocated among possibly thousands of botanical units in a tree. The LIGNUM model can simulate the three-dimensional architectural development of a tree crown, keep track of each elementary functional unit, define their local capacity to produce and use resources, and determine the interactions with each other and the external environment.