Éditeur(s) : HAL CCSD
Résumé : International audience
Over the past decade, much attention has been devoted to the development of forest biomass estimation methods at a stand scale, leading to the establishment of allometric models (Chave et al., 2014). These allometric equations use a unique wood specific gravity value (WSG) per species, but neglect the within tree variations of WSG found by others (Wiemann & Williamson, 1989).The main objectives of this study are (1) to illustrate the diversity of radial (from pith to bark) and longitudinal (from bottom to top) patterns of WSG variation within and between species, (2) to highlight different trends of WSG radial variations and the possible misinterpretations of these trends due to the effect of heartwood and (3) to link these variations and patterns to the successional status of the species (from pioneer to sciaphilic species).We sampled 33 small trees (10 Wood sciences underpinning tropical ecology and management. International closing symposium of the XYLAREDD project.
Tervuren, Belgium

hal-01188894
https://hal-sde.archives-ouvertes.fr/hal-01188894

Éditeur(s) : HAL CCSD
Résumé : International audience
BackgroundTree above ground biomass (AGB) is currently estimated by tree-level allometrical models that take into account, tree volume estimated from proxy variables of tree size (DBH) and species average wood specific gravity (WSG). These methods are common and realistic from a practical point of view. However, they do not take into account deviance from fixed allometrical trajectories and species or tree level WSG variations. Here, we present Xtrawood software that allows computation of tree AGB according to structure and WSG variations.MethodXtrawood reconstructs tree structure and integrates WSG variations by merging tree structure and WSG data measured at different position in trees, leading to the computation of global AGB and visualization of WSG variation along tree structure. Tree structure is measured according to stem dimensions (length, diameter) and positions within tree, and encoded in Multiscale Tree Graph format (MTG). WSG data is made of radial WSG profiles (1 measure each 0,5 cm from pith to bark) sampled at different heights within whole tree. Xtrawood output are illustrated using a dataset collected on an Amazonian forest ‘biomass dominant species’, Dicorynia guianensis Amsh., also known to exhibit substantial WSG gradients along both radial and vertical axis. 9 trees ranging from 15 to 60 cm DBH were measured by climbers. Each tree was felled and samples were collected at different positions (3 in trunk, 1 to 5 in crown) to record WSG radial profiles.ResultsXtrawood allows computation of tree volume, but also visualization of WSG variations in tree as well as inference of WSG radial profiles at different heights. Output variables are decomposed according to different tree scale and locations (axis, trunk/crown) and easy to extract. Xtrawood results will be compared to those of standard estimation method and can be used to identify positions in trees where WSG value leads to the better estimate of tree AGB.Conclusion/perspectiveXtrawood produces AGB estimate with data from intensive measurements practices. The sampling protocol, used here, remains destructive and time-consuming because Xtrawood is not directly dedicated to forest managers, but to help calibration of realistic sampling strategies. Moreover, Xtrawood offers a way to understand relationships between tree development, WSG variations within tree structure and biomass accumulation in the context of natural forests or plantations. A software demo is available at coffee break.
53rd Annual Meeting of the Association for Tropical Biology and Conservation (ATBC 2016)
Montpellier, France

Droits : http://creativecommons.org/licenses/by/
hal-01349613
https://hal.archives-ouvertes.fr/hal-01349613

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Heartwood/sapwood profile and the tradeoff between trunk and crown increment in a natural forest: the case study of a tropical tree (Dicorynia guianensis Amsh., Fabaceae) Key message Sapwood area and the radial growth rate of the trunk follow the same pattern at breast height, with an initial increase and subsequent constant value, resulting from the increasing growth allocation toward the crown rather than tree decline. Heartwood area and heartwood volume in the trunk increase more rapidly after this shift occurs. Abstract Sapwood (SW) and heartwood (HW) are two functionally distinct classifications of wood in perennial stems for which quantities can vary greatly in tropical trees. Numerous positive correlations have been found between the radial growth rate (RGR) and SW quantity; however, variations in the SW/HW quantities have not been studied in light of the ontogenetic variation of RGR. Wood core sampling, intensive measurements of tree structure (number of branches, stem volumes), and radial growth monitoring were performed on an abundant and highly exploited tree species in French Guiana (Dicorynia guianensis) to investigate the relationship between RGR, SW/HW quantity, tree structure, and their variations on the course of a tree's ontogeny. SW area and RGR followed the same pattern of variation throughout tree development, both increasing first and reaching a steady state after 50 cm DBH (diameter at breast height). After this value, we observed a strong increase in both the HW area and HW volume increment, concomitant with a more rapid increase in crown volume. The stabilization of RGR for trees with DBH >50 cm was related not to a tree's decline but rather to an increasing wood allocation to the crown, confirming that RGR at breast height is a poor indicator of whole-tree growth for bigger individuals. We also confirmed that HW formation is an ontogenetic process managing SW quantity that is continuously and increasingly produced within the crown as the tree grows. This study highlights the effect of growth-mediated ontogenetic changes on the localization of water and carbohydrate storage within a tree, resulting from SW and HW dynamics throughout tree ontogeny.
ISSN: 0931-1890

hal-01654003
https://hal.archives-ouvertes.fr/hal-01654003
https://hal.archives-ouvertes.fr/hal-01654003/document
https://hal.archives-ouvertes.fr/hal-01654003/file/Lehnebach%20et%20al.%E2%80%94Trees%202016-%20Own%20version.pdf
DOI : 10.1007/s00468-016-1473-7

Éditeur(s) : HAL CCSD
Résumé : International audience
L'Angélique (Dicorynia guianensis Amsh.) représente environ 35% de laproduction de bois d'oeuvre en Guyane. Cependant, la stratégie de duraminisationdite ‘tardive’ chez cette essence entraîne une grande variabilité de l'épaisseurd'aubier (Fig. 1A) et par conséquent, influence la proportion exploitable de lagrume. La relation entre quantité de bois de coeur et diamètre à 1m30 (DBH) (e.g.Carrodus (1972), Wilkes (1991), Pinto et al. (2004), Wang et al. (2010)), ne permetpas une estimation suffisamment précise de la quantité de duramen et/ou d’aubier.A ce jour, très peu d’études mettent en lien la structure de la couronne et/ou lestatut social de l’individu avec la quantité de duramen (e.g. Pazdrowski et al.(2009), Nawrot et al. (2008)). Or, une grande diversité de structures des couronnesest observable au sein d’une même classe de diamètre (Fig. 1B).Ici, nous proposons une méthode visuelle et rapide de diagnostic architectural desarbres permettant d’améliorer l’estimation de la quantité de duramen dans letronc.
Les 2èmes Journées scientifiques du GDR 3544 « Sciences du bois »
Champs sur Marne, France

Droits : info:eu-repo/semantics/OpenAccess
hal-01215800
https://hal-sde.archives-ouvertes.fr/hal-01215800
https://hal-sde.archives-ouvertes.fr/hal-01215800/document
https://hal-sde.archives-ouvertes.fr/hal-01215800/file/Poster%20R.%20Lehnebach%20-%20GDR%20Bois%202013%20Structure%20couronne%20et%20variation%20de%20l%E2%80%99%C3%A9paisseur%20et%20surface%20aubier%20Ang%C3%A9lique.pdf