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Experimental analysis of the formation of tension wood induced by gravity for three mature beech trees on a 25 years duration
Adelin Barbacci, thiery Constant, Magnenet Vincent, Nepveu Gérard, Fournier Meriem
Last modified: 2009-11-06
Abstract
Adelin Barbacci1, Thi'ery Constant1, G'erard Nepveu1, Meriem Fournier2
1 INRA, UMR1092, Laboratoire d'Etude des Ressources For^et-Bois(LERFoB), Centre INRA de Nancy, F-54280 Champenoux, France
2 AgroParisTech, UMR1092, Laboratoire d'Etude des Ressources For^et-Bois(LERFoB), ENGREF 14 rue Girardet, F-54000 Nancy, France
Morphology of trees must be very plastic to increase the capacity of the plant to exploit available resources. Thus, the morphology and the architecture of a tree are time and environment dependent, lead by different tropisms. Maturation stresses in the last age-ring act an important role in the tropisms allowing axes reorientation all along the life of the tree. During the first development stages, the existence of a growth maturation differential is without effect on the future wood quality. Nevertheless, for mature trees, the accumulation of important growth stresses could decrease the technological and the financial value of a tree. In beech trees (Fagus Sylvatica L.), high growth stresses level, must of time associated with reaction wood, are known as one of the main factors decreasing the wood quality.
In a context of variation of the traditional beech sylviculture, functional approach concerning the formation of high growth maturation stresses is needed but, for such answers, limits of empirical models are often reached and simple mechanical approaches, at tree scale, could be efficient enough.
Conceptually, the annual growth of a tree could be divided in two parts. In the first one, the elongation of the apical parts and the cambial growth, equivalent to a biomass increment, could participate in the global disequilibrium of the whole tree then, in the second part, a differential of wood maturation in the last age-ring could be created in order to oppose the effect of this differential to the disequilibrium. This conceptual sketch has ever been investigated by several mechanical models and the purpose of this work consists in an experimental validation of this scheme. So, we considered the tree as a trunk and a crown without architecture and reduced to its barycenter and its self-weight. These simplifications have been justified by sensitivity tests establishing, for example, a method to find a good approximation of the position of the barycentre using the projection of the crown on the ground. Thanks to a software based on the mechanical model, a virtual experiment has been performed in retrospect (from the last position of the tree to the virtual position of the tree 25 years ago) using the measured configuration of the tree on the year 2005 and some time-dependent measurement available for three mature beech trees. Thus, from the last configuration of the tree, the position of the barycenter of the crown and its biomass increment between these two years were estimated and an assumed areas of tension wood are virtually reported. Then the biomass of the last age-ring in the trunk is removed to obtain the tree in a configuration corresponding to the year before. This loop was repeated twenty four times. Several hypotheses concerning the position of the assumed position of tension wood could be tested and discussed.
Keyword: gravitropism, tension wood, growth stresses, experimental validation, sensitivity analyse.
1 INRA, UMR1092, Laboratoire d'Etude des Ressources For^et-Bois(LERFoB), Centre INRA de Nancy, F-54280 Champenoux, France
2 AgroParisTech, UMR1092, Laboratoire d'Etude des Ressources For^et-Bois(LERFoB), ENGREF 14 rue Girardet, F-54000 Nancy, France
Morphology of trees must be very plastic to increase the capacity of the plant to exploit available resources. Thus, the morphology and the architecture of a tree are time and environment dependent, lead by different tropisms. Maturation stresses in the last age-ring act an important role in the tropisms allowing axes reorientation all along the life of the tree. During the first development stages, the existence of a growth maturation differential is without effect on the future wood quality. Nevertheless, for mature trees, the accumulation of important growth stresses could decrease the technological and the financial value of a tree. In beech trees (Fagus Sylvatica L.), high growth stresses level, must of time associated with reaction wood, are known as one of the main factors decreasing the wood quality.
In a context of variation of the traditional beech sylviculture, functional approach concerning the formation of high growth maturation stresses is needed but, for such answers, limits of empirical models are often reached and simple mechanical approaches, at tree scale, could be efficient enough.
Conceptually, the annual growth of a tree could be divided in two parts. In the first one, the elongation of the apical parts and the cambial growth, equivalent to a biomass increment, could participate in the global disequilibrium of the whole tree then, in the second part, a differential of wood maturation in the last age-ring could be created in order to oppose the effect of this differential to the disequilibrium. This conceptual sketch has ever been investigated by several mechanical models and the purpose of this work consists in an experimental validation of this scheme. So, we considered the tree as a trunk and a crown without architecture and reduced to its barycenter and its self-weight. These simplifications have been justified by sensitivity tests establishing, for example, a method to find a good approximation of the position of the barycentre using the projection of the crown on the ground. Thanks to a software based on the mechanical model, a virtual experiment has been performed in retrospect (from the last position of the tree to the virtual position of the tree 25 years ago) using the measured configuration of the tree on the year 2005 and some time-dependent measurement available for three mature beech trees. Thus, from the last configuration of the tree, the position of the barycenter of the crown and its biomass increment between these two years were estimated and an assumed areas of tension wood are virtually reported. Then the biomass of the last age-ring in the trunk is removed to obtain the tree in a configuration corresponding to the year before. This loop was repeated twenty four times. Several hypotheses concerning the position of the assumed position of tension wood could be tested and discussed.
Keyword: gravitropism, tension wood, growth stresses, experimental validation, sensitivity analyse.