Etude de la variabilité ontogénique du profil ligneux chez quelques espèces forestières tropicales de Guyane Française

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 cœur 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 chimique 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 l’allocation de croissance (i.e. du tronc vers la couronne) observée 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

Structure des couronnes et variation de l’épaisseur et de la surface d’aubier chez l’Angélique deGuyane (Dicorynia guianensis Amsh., Caesalpinioideae, Fabaceae)

International audienceL'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

Within-site variability of liana wood anatomical traits : a case study in Laussat, French Guiana

Research Highlights: We investigated the variability of vessel diameter distributions within the liana growth form among liana individuals originating from a single site in Laussat, French Guiana. Background and Objectives: Lianas (woody vines) are key components of tropical forests. Lianas are believed to be strong competitors for water, thanks to their presumed efficient vascular systems. However, unlike tropical trees, lianas are overlooked in field data collection. As a result, lianas are often referred to as a homogeneous growth form while little is known about the hydraulic architecture variation among liana individuals. Materials and Methods: We measured several wood hydraulic and structural traits (e.g., basic specific gravity, vessel area, and vessel diameter distribution) of 22 liana individuals in a single sandy site in Laussat, French Guiana. We compared the liana variability of these wood traits and the correlations among them with an existing liana pantropical dataset and two published datasets of trees originating from different, but species-rich, tropical sites. Results: Liana vessel diameter distribution and density were heterogeneous among individuals: there were two orders of magnitude difference between the smallest (4 µm) and the largest (494 µm) vessel diameters, a 50-fold difference existed between extreme vessel densities ranging from 1.8 to 89.3 vessels mm−2, the mean vessel diameter varied between 26 µm and 271 µm, and the individual theoretical stem hydraulic conductivity estimates ranged between 28 and 1041 kg m−1 s−1 MPa−1. Basic specific gravity varied between 0.26 and 0.61. Consequently, liana wood trait variability, even within a small sample, was comparable in magnitude with tree surveys from other tropical sites and the pantropical liana dataset. Conclusions: This study illustrates that even controlling for site and soil type, liana traits are heterogeneous and cannot be considered as a homogeneous growth form. Our results show that the liana hydraulic architecture heterogeneity across and within sites warrants further investigation in order to categorize lianas into functional groups in the same way as trees

Xtrawood: refining estimation of tree above ground biomass using wood density variations and tree structure

International audienceBackgroundTree 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 specific gravity variations within tree trunk: the case study of Legumes representatives in French Guiana

International audienceOver 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<DBH<15cm) at the Paracou field station in French Guiana, belonging to 14 Legumes species, and to different ecological groups according to light. WSG radial profiles were measured at 3 heights along the trunk, and 2 heights along the crown, of each tree.We observed different radial and longitudinal patterns of WSG variation. Pioneer and heliophilic species show both radial and longitudinal increases in WSG, while shade-tolerant and sciaphilic species show the reverse pattern. Hemi-tolerant species show an intermediate pattern, with WSG increasing radially, but decreasing or increasing longitudinally. Decreasing radial pattern in sciaphilic species is due to the presence of heartwood relatively denser than sapwood. When a corrected WSG is used, sciaphilic species show the same radial pattern as hemi-tolerant species (i.e. increasing) or no radial pattern (i.e. ‘flat’ from pith to bark).Decreasing WSG from bottom to top is a general case, excepted for species with low WSG (i.e pioneers). All studied species tend to the same range of WSG values with height (~ 0.6-0.9), supported by a higher WSG under bark within trunk.We also developed a biomass model, implemented under Xplo software (Griffon et al., 2011) to infer trunk biomass from WSG profiles, allowing comparisons of both single- and varying-WSG models.Wood specific gravity variations within tree trunk: the case study of Legumes representatives in French Guiana

Study of the ontogenic variability of wood profile in some forest tree species in French Guiana.

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 cœur 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 chimique 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 l’allocation de croissance (i.e. du tronc vers la couronne) observée 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.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

How does bark contribution to postural control change during tree ontogeny? A study of six Amazonian tree species

International audienceRecent works revealed that bark is able to produce mechanical stress to control the orientation of young tilted stems. Here we report how the potential performance of this function changes with stem size in six Amazonian species with contrasted bark anatomy. The potential performance of the mechanism depends both on the magnitude of bark stress and the relative thickness of the bark. We measured bark longitudinal residual strain and density, and the allometric relationship between bark thickness and stem radius over a gradient of tree sizes. Constant tensile stress was found in species that rely on bark for the control of stem orientation in young stages. Other species had increasing compres-sive stress, associated with increasing density attributed to the development of sclereids. Compressive stress was also associated with low relative bark thickness. The relative thickness of bark decreased with size in all species, suggesting that a reorientation mechanism based on bark progressively performs less well as the tree grows. However, greater relative thickness was observed in species with more tensile stress, thereby evidencing that this reduction in performance is mitigated in species that rely on bark for reorientation

Lehnebach et al 2018

<p><i>This set contains datasets collected and used in the original research article Lehnebach et al 2018 - Wood density variations of Legume trees in French Guiana along the shade tolerance continuum: heartwood effects on radial patterns and gradients</i></p><div><br></div

High-Resolution X-Ray Computed Tomography: A New Workflow for the Analysis of Xylogenesis and Intra-Seasonal Wood Biomass Production

International audienceUnderstanding tree growth and carbon sequestration are of crucial interest to forecast the feedback of forests to climate change. To have a global understanding of the wood formation, it is necessary to develop new methodologies for xylogenesis measurements, valid across diverse wood structures and applicable to both angiosperms and gymnosperms. In this study, the authors present a new workflow to study xylogenesis using high-resolution X-ray computed tomography (HRXCT), which is generic and offers high potential for automatization. The HXRCT-based approach was benchmarked with the current classical approach (microtomy) on three tree species with contrasted wood anatomy ( Pinus nigra, Fagus sylvatica , and Quercus robur ). HRXCT proved to estimate the relevant xylogenesis parameters (timing, duration, and growth rates) across species with high accuracy. HRXCT showed to be an efficient avenue to investigate tree xylogenesis for a wide range of wood anatomies, structures, and species. HRXCT also showed its potential to provide quantification of intra-annual dynamics of biomass production through high-resolution 3D mapping of wood biomass within the forming growth ring