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International audience; Wood density (WD) relates to important tree functions such as stem mechanics and resistance against pathogens. this functional trait can exhibit high intraindividual variability both radially and vertically. With the rise of LiDAR-based methodologies allowing nondestructive tree volume estimations, failing to account for WD variations related to tree function and biomass investment strategies may lead to large systematic bias in AGB estimations. Here, we use a unique destructive dataset from 822 trees belonging to 51 phylogenetically dispersed tree species harvested across forest types in Central Africa to determine vertical gradients in WD from the stump to the branch tips, how these gradients relate to regeneration guilds and their implications for AGB estimations. We find that decreasing WD from the tree base to the branch tips is characteristic of shade-tolerant species, while light-demanding and pioneer species exhibit stationary or increasing vertical trends. Across all species, the WD range is narrower in tree crowns than at the tree base, reflecting more similar physiological and mechanical constraints in the canopy. Vertical gradients in WD induce significant bias (10%) in AGB estimates when using database-derived species-average WD data. However, the correlation between the vertical gradients and basal WD allows the derivation of general correction models. With the ongoing development of remote sensing products providing 3D information for entire trees and forest stands, our findings indicate promising ways to improve greenhouse gas accounting in tropical countries and advance our understanding of adaptive strategies allowing trees to grow and survive in dense rainforests. Terrestrial plants account for 83% of the living carbon on Earth 1 , of which tropical forests are estimated to account for close to half 2 , principally contained within woody plant parts. Tropical forests are therefore becoming a key element in international carbon trading schemes despite obvious difficulties in accurately estimating stocks

International audience

International audience; To grow straight, plants need a motor system that controls posture by generating forces to offset gravity. This motor function in trees was long thought to be only controlled by internal forces induced in wood. We grew artificially tilted seedlings and measured the change in curvature when removing the bark and evidenced a differential mechanical state of the bark on both side of the stem. In several species, bark contributes to the up righting of trees. Combined mechanical measurements and microstructural observations on adults trees enabled us to identify the mechanism responsible for the development of mechanical stress in the bark of plant stems.This mechanism does not result from cell wall maturation like in wood, or from the direct action of turgor pressure like in unlignified organs, but is the consequence of the interaction between wood radial pressure and a smartly organized trellis structure in the inner bark.

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.

Wood is a multifunctional tissue involved in sap conduction, storage of water and reserves as well as mechanical support. Tree during its development experiments various constraints due to its environment and its growing size. In response to these constraints, wood functional performances are adjusted by variations of property values, which are dependent on the xylogenesis product. However, wood properties may be modified by the deposition of chemical extractives during heartwood formation. Thus heartwood properties are the result of xylogenesis, heartwood formation and their interactions. This work gave rise to the term 'wood profile', designating all variations of wood properties at different scales and in an ontogenetic dimension, resulting from both processes described above. The diversity of shade tolerance (heliophilic to sciaphilic) strategies species suggests a diversity of wood profile expressions. The description of these different expressions could be a way to better understand plant strategies. Understanding and characterizing wood profile and variations in heartwood quantity in tree, is an economical issue since the Guyanese timber industry has been identified as a promising sector. The analysis of the diversity of wood profile—using a bottom-up approach, from the individual level to the interspecific level—proves to discriminate shade tolerance strategies efficiently. Wood specific gravity variation is especially relevant. However, its relevance is based on (1) combinations of both radial and vertical variations and (2) integration of heartwood that may impact range and direction of the gradient and shape of the profile as well. Effect of heartwood formation on wood specific gravity variations is suggestive of shade tolerance strategy as well as quality and/or quantity of chemical extractives. Relevant characterization of shade tolerance strategies by wood profile is the result of the integration of diverse processes and properties. To the view of growth allocation shift (from trunk to crown) observed in Dicorynia guianensis and of previous studies on tree growth, a potential link between wood profile diversity and growth allocation strategies may exist.; Le bois est un tissu plurifonctionnel permettant la conduction de la sève brute, le stockage de l’eau et des sucres ainsi que le soutien mécanique de la plante. L’arbre au cours de son développement expérimente différentes contraintes liées à son environnement et à sa taille croissante. En réponse à ces contraintes, les performances fonctionnelles du bois sont ajustées par des variations de valeurs de propriétés, elles-mêmes dépendantes du produit de la xylogénèse. Cependant les extrais chimiques déposés lors du processus de duraminisation, entraine la modification des propriétés du bois. Les propriétés du duramen sont le fruit de la xylognénése et de la duraminisation ainsi que de leurs interactions. Ce travail de thèse a donné naissance au terme ‘profil ligneux’, désignant l’ensemble des variations des propriétés du bois à différentes échelles et dans une dimension ontogénique résultant des deux processus cités précédemment. La diversité de tempéraments vis-à-vis de la lumière (héliophilie à sciaphilie) des essences tropicales suggère une diversité d’expressions du profil ligneux.La description de ces différentes expressions serait gage d’une meilleure compréhension du tempérament.Comprendre et caractériser le profil ligneux et la variation de la quantité de bois de coeur dans l’arbre, représentent également un enjeu économique puisque l’industrie du bois Guyanaise a été identifiée comme une filière d’avenir. L’analyse de la diversité du profil ligneux—par une approche ascendante, de l’échelle individuelle à l’échelle interspécifique—a prouvé son efficacité dans la discrimination du degré d’affinité à la lumière. La variation de densité est particuliérment pertinente. Néanmoins, sa pertinence réside dans (1) la combinaison du gradient radial et vertical et (2) la prise en compte du duramen qui modifie parfois, l’amplitude et la direction du gradient ainsi que la forme du profil. L’effet de la duraminisation sur la variation de densité devient alors évocateur du tempérament de l’espèce au même titre que la qualité et/ou la quantité d’extraits chimiques mis en jeu. La pertinence du profil ligneux dans la caractérisation du tempérament écologique est due à son aspect intégrateur de divers processus et propriétés. En regard du changement de l’allocation de croissance (i.e. du tronc vers la couronne) observé chez Dicorynia guianensis et de travaux précédents sur la croissance des arbres, un lien potentiel entre la diversité du profil ligneux et la stratégie d’allocation de la croissance pourrait exister.

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

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.

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 to (1) illustrate the diversity of radial and vertical patterns of WSG variation within tree trunks belonging to different ecological groups (from pioneer to sciaphilic species) and to (2) develop an estimation method of trunk biomass taking into account WSG variations. We sampled 33 young trees (10

Background: Tree 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 spe-cies or tree level WSG variations. Here, we present Xtrawood software that allows computation of tree AGB according to structure and WSG variations. Method: Xtrawood 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. Results: Xtrawood 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: Xtrawood 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 coffe break. (Texte intégral)