Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
ISSN: 0028-646X

hal-01080855
https://hal-agroparistech.archives-ouvertes.fr/hal-01080855
DOI : 10.1111/j.1469-8137.2007.02227.x

Éditeur(s) : HAL CCSD
Résumé : Wood samples were taken from the upper and lower sides of 21 naturally tilted trees from 18 families of angiosperms in the tropical rainforest in French Guyana. The measurement of growth stresses ensured that the two samples were taken from wood tissues in a different mechanical state: highly tensile stressed wood on the upper side, called tension wood and lower tensile stressed wood on the lower side, called opposite wood. Eight species had tension wood fibres with a distinct gelatinous layer (G-layer). The distribution of gelatinous fibres varied from species to species. One of the species, Casearia javitensis (Flacourtiaceae), showed a peculiar multilayered secondary wall in its reaction wood. Comparison between the stress level and the occurrence of the G-layer indicates that the G-layer is not a key factor in the production of high tensile stressed wood.
IAWA Journal

hal-00112579
https://hal.archives-ouvertes.fr/hal-00112579
https://hal.archives-ouvertes.fr/hal-00112579/document
https://hal.archives-ouvertes.fr/hal-00112579/file/IAWA2006_ClairRuelleBeauchenePrevostFournier_ccsd.pdf
IRD : PAR00001136

Éditeur(s) : HAL CCSD
Résumé : International audience
The main biological function of reaction wood is to act as “muscle” for trees, enabling them to control their posture and right stems when they are permanently disturbed from their set-point inclination by gravity or winds. The key property to achieve this function is the development of high mechanical stress during the formation of reaction wood cells, called “maturation strains”. Moreover, this function is basically performed through the asymmetric formation of wood (in quantity or quality) around the tree circumference. This asymmetry enables stems to bend upward or to compensate for the downward bending induced by gravity, as an asymmetric force associated to maturation strains creates a bending moment (i.e. one side of the stem “pulls” the other one). We will discuss the traits (cross sectional size and shape, wood features as G fibers or microfibril angle, eccentric growth even in usual or extreme cases as buttresses, total biomass growth and height of center of mass, stem lean and set-point angle) involved to understand how the posture control works. We will give simple formulas to estimate a “muscle efficiency” from biomechanical modeling. We will give practical methods to estimate all the involved traits, especially maturation strains from direct and indirect measurements, in peripheral functional wood or by retrospective dendrochronological analysis. Then, we will illustrate how tree stem tropisms and especially gravitropism, widely studied by physiologists, are key processes in natural ecosystems, through practical examples from tropical rainforest tree communities and regeneration of European mixed beech forests. Using the previous definition of postural control efficiency, we will show that the cross section size is rapidly a limiting factor, opposing the extreme strategies of flexible small stems, which bend easily but also right themselves quickly, to stiff big stems. Lastly, as wood in living trees ensures general storage, defence, vascular and skeletal functions, we will ask general questions about synergies and trade-offs between posture control and other functions.
Botany 2014 : new frontiers in botany
Boise, United States

hal-01627031
https://hal.archives-ouvertes.fr/hal-01627031

Éditeur(s) : HAL CCSD
Résumé : Gravitropism is a major process in vertical growth as it allows the positioning of plant in the gravity field and thus, for trees, it takes part in the light foraging strategies. Without any gravitropism, trees would adopt a weeping habit or fall on the ground due to the increasing with growth supported weight, especially at the advance regeneration stage (sapling stage) in the understorey, where tree are very slender and poorly stiff. Most of the gravitropic studies are made by physiologists in order to understand the process and thus are associated to complex laboratory methods (genetic engineering, anatomical studies, accurate 2D ou 3D measurements of form changes with time). In order to study the ecological relevance and the specific diversity of gravitropic performances in natural forests, we developed a framework that uses different kinds of datas. Synchronical analysis has been done i) at the population level in large sample of trees and ii) at the tree level from destructive measurement of the dissymmetry maturation strains known to be the main motor of the posture control reaction of trees. In both cases, biomechanical models allows to estimate some aspects of the dynamic gravitropic process. Diachronical analysis has been done in natural conditions on permanent plots, or in a more traditional way, by observing in greenhouse experiments the righting movements of plants artificially tilted. In the first case, the problem is the high variability of natural disturbances and the slowness of growth and movements in the dark understorey. The second choice allows a measurement of a capacity (i.e. the ability of the species to react in quite extreme conditions of verticality disturbance but good for growth light and nutrient conditions) that is more easy to analyse, but is maybe not so relevant for estimating the ecological strategy (some species could have developed a high efficience of gravitropic reaction in natural conditions by avoiding the mechanical disturbance or adapting the reaction to slow growth and changing environments in natural conditions). All approaches use the same basic biomechanical modelling, i) to analyse simultaneously the reaction and the disturbance (due to the weight increase) during growth, or ii) to combine different parameters (geometry, growth, weight, maturation strains) involved in shape changes and posture control. They give a classification of the species according to their gravitropic performances. Results on 15 species are discussed, with relation to shade-tolerance or avoidance.
6th Plant Biomechanics Conference
Cayenne, France

hal-00565956
https://hal.archives-ouvertes.fr/hal-00565956

Éditeur(s) : HAL CCSD De Gruyter
Résumé : A method for measuring shrinkage resulting from drying in the three anisotropic directions is developed and tested. Measurements are performed on sawn discs, a technique which simplifies preparation and enables large numbers of measurements. Shrinkage values can be represented as a map of the disc surface; the results indicate that comparisons between shrinkage distribution and tension wood distribution on the discs show a clear relationship and can be measured with relatively high accuracy in reference to the "shrinkage map". In the long term, this method could be useful in the timber industry as a means for choosing the direction in which logs are cut depending on their type of wood composition.
ISSN: 0018-3830

hal-00004531
https://hal.archives-ouvertes.fr/hal-00004531
https://hal.archives-ouvertes.fr/hal-00004531/document
https://hal.archives-ouvertes.fr/hal-00004531/file/Holzforschung2003_Clair-Jaouen-Beauchene-Fournier_ccsd.pdf

Éditeur(s) : HAL CCSD
Résumé :   Diffusion du document : INRA Antilles-Guyane, UMR ECOFOG, 97387 Kourou, Guyane (France) Diplôme : Master Recherche
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
The gravitropic reaction is a fundamental phenomenon in the life of the young trees in under-storey of a tropical rain forest. It enables them to preserve a growth in height even after a fall of remains or a wind fallen wood had leaning them. This reaction passes mainly by the differentiation of reaction wood and the offsetting of the radial growth. The gravitropic reaction is also under the control of various parameters such as the diameter of the stems, the hardness of wood, or masses they carried. The tropical rain forest contains a great specific diversity and ecological strategies. In this work we seek to know if this diversity is reflected in the strategies of recovery of the species in particular on a level of efficiency of reaction. We compared eight species of tropical rain forest with various ecological behaviours. We studied their changes in form in the course of time, as to their growth. We showed that there are indeed interspecific differences in the gravitropic reaction. Some behaviours are specific to some species. We also showed that for the majority of the species, the deformation energy is strongly correlated with the relative growth of the species.
Le redressement gravitropique est un phénomène fondamental dans la vie des jeunes arbres en sous-bois de forêt tropicale. Il leur permet de conserver une croissance en hauteur même après avoir subi la chute de débris ou même un chablis ayant conduit à leur inclinaison. Ce redressement passe principalement par la différentiation de bois de réaction et l’excentrement de la croissance radiale. Le redressement gravitropique est également sous le contrôle de différents paramètres tels que le diamètre des tiges, la dureté du bois, ou les masse portées. La forêt tropicale humide contient une grande diversité spécifique et de stratégies écologiques. Dans ce travail nous cherchons à savoir si cette diversité se reflète dans les stratégies de redressement des espèces notamment au niveau de l’efficience de la réaction. Nous avons comparé huit espèces de forêt tropicale humide avec différents comportements écologiques. Nous avons étudié leurs changements de forme au cours du temps, ainsi que leur croissance. Nous avons réussi à montrer qu’il existe effectivement des différences interspécifiques de redressement. Des comportements particuliers à certaines espèces ont pu être dégagés. Nous avons également montré que pour la majorité des espèces, l’énergie de déformation est fortement corrélée à la croissance relative de l’espèce.
https://hal.archives-ouvertes.fr/hal-01189172

hal-01189172
https://hal.archives-ouvertes.fr/hal-01189172
PRODINRA : 11396

Éditeur(s) : HAL CCSD
Résumé :  
The anatomy of tension wood and opposite wood was compared in 21 tropical rain forest trees from 21 species belonging to 18 families from French Guyana. Wood secimens were taken from the upper and lower sides of naturally titled trees. Measurement of the growth stress level ensured that the two samples were taken from wood tissues in a different mechanical state: highly tensile-stressed wood on the upper side, called tension wood and normally tensile-stressed wood on the lower side, called opposite wood. Quantitative parameters relating to fibres and vessels were measured on transverse sections of both tension and opposite wood to check if certain criteria can easily discriminate the two kinds of wood. We observed a decrease in the frequency of vessels in the tension wood in all the trees studied. Other criteria concerning shape and surface area of the vessels, fibre diameter or cell wall thickness did not reveal any general trend.At the ultrastructural level, we observed that the microfibril angle in the tension wood sample was lower than in opposite wood in all the trees except one (Licania membranacea).
IAWA Journal

hal-01032149
https://hal.archives-ouvertes.fr/hal-01032149