Search

Process-based tree growth models are recognized to be flexible tools which are valuable for investigating tree growth in relation to changing environment or silvicultural treatments. In the context of forestry, we address two key modelling problems: allocation of growth which determines total wood production, and distribution of wood along the stem which determines stem form and wood quality. Growth allocation and distribution are the outcome of carbon translocation, which may be described by the Münch theory. We propose a simpler gradient process to describe the carbon distribution in the phloem of conifers. This model is a re-formulation of a carbon diffusion-like process proposed by Thornley in 1972. By taking into account the continuity of the cambium along the stem, we obtain a one dimensional reaction-diffusion model which describes both growth allocation between foliage, stem and roots, and growth distribution along the stem. Distribution of wood along the stem is then regarded as an allocation process at a smaller scale. A preliminary sensitivity analysis is presented. The model predicts a strong relationship between morphology and foliage:root allocation. It also suggests how empirical data, such as stem analysis, could be used to calibrate and validate allocation rules in process-based growth models.

Die Stichhaltigkeit der Schaftformtheorie nach C. Metzger kann nur dadurch bewiesen werden, das die verschiedenen Einflusfaktoren studiert werden. Die theoretischen Werte lassen sich dann durch physikalische Messungen nachprufen. Messungen der Stromungsverhaltnisse an verschiedenen Baumkronen ergeben unterschiedliche Widerstandsbeiwertec w. Zur Uberprufung der Brucherscheinungen an Stammen untersucht man statt der Biegefestigkeit lieber die „Bruchzusammendruckung”, die eine Invariante des Gesetzes darstellt. Man erhalt so die Grundgleichungen der mechanischen Schaftformtheorie, die sich durch Iteration auflosen lassen. Fur die Festigkeit des Stammes hat auserdem der Wurzelansatz eine hervorragende Bedeutung.