Water use of forest trees : a possibility of combining structures and functional models

This paper aims to give an overview on the possibilities opened by the combination of process-oriented models and tree structure simulated by a plant growth generator. It shows the concept of one of their combinations, which is currently under construction. This combination will open the door to investigate some recent questions in the research field of tree hydraulics on real or realistic tree structures. The general concept of sub-model connection is presented by dividing the participating models into three categories. First, a growth-engine for the topological description of the tree is shown. The software AMAP-SIM, developed by the Plant Modeling Unit of the CIRAD, simulates the dynamics of plant development and provides detailed structural information. Second, the numerical water transport simulator HYDRA is characterized briefly. It calculates the dynamic hydraulic behaviour of the given structures depending on soil-water conditions, transpiration and hydraulic properties. It was developed at the Forest Ecosystem Research Center at Goettingen. The third category of models calculates the tree transpiration term. A choice out of a great multitude of possible functions is necessary. The here-presented way consists of several interconnected calculation modules which were developed and tested on Coffee tree at the CIRAD. They calculate the transpiration, the energy-balance, and the stomatal conductance on leaf level. Furthermore, some technical aspects of connecting the participating models are discussed. Last, the expected benefits of this project are discussed. (Resume d'auteur)