Christine Deleuze

Within-stem maps of wood density and water content for characterization of species: a case study on three hardwood and two softwood species

Key message Variability and interrelations between wood density, water content, and related properties were analyzed by CT scanning of five species. Relative water content of lumens is proposed as the best complement to basic specific gravity for discrimination of species with respect to their functioning.Context X-ray computed tomography (CT) is an efficient tool for analysis of wood properties related to density and water content all along a tree stem. Basic specific gravity, an inherent property of the wood material, is well known and widely used in wood sciences.Aims The first aim of this study was to describe a method for mapping a set of wood properties within a tree stem. The second objective was to analyze the relations among these properties and to identify the one that offers the best information in addition to basic specific gravity for discrimination of species.Methods Wood discs were collected at various heights along a tree stem. We used a method consisting of comparing the CT images of the discs in the green state and after oven drying. Finally, 10 variables were computed for 115 trees of five temperate species: green, oven-dry, and basic specific gravities; moisture content; relative water content; relative water content of lumens; and fractions of air, water, free water, and cell walls.Results Maps of wood properties summarizing the radial and vertical variations were obtained, allowing us to highlight species-specific patterns. The five species were discriminated best when plotted in the plane defined by basic specific gravity and relative water content of lumens.Conclusion The proposed method is original and simple enough to process large samples. Because it correlated less with basic specific gravity than with moisture content, relative water content of lumens was selected for species characterization. This is the first study of such wood properties at this fine scale within a tree stem, simultaneously and for a substantial number of trees of five species including both hardwoods and softwoods.

Patterns of within-stem variations in wood specific gravity and water content for five temperate tree species

Abstract• Key messageIntensive measurements of basic specific gravity and relative water content of lumens show that within-stem variations strongly depend on species and cannot be summarised through the typical patterns reported in the literature; breast height measurements are not always representative of the whole stem.• ContextKnowledge of the distribution of wood properties within the tree is essential for understanding tree physiology as well as for biomass estimations and for assessing the quality of wood products.• AimsThe radial and vertical variations of basic specific gravity (BSG) and relative water content of lumens (RWCL) were studied for five species: Quercus petraea/robur, Fagus sylvatica, Acer pseudoplatanus, Abies alba and Pseudotsuga menziesii. The observations were compared with typical patterns of variations reported in the literature.• MethodsWood discs were sampled regularly along tree stems and X-rayed in their fresh and oven-dry states.• ResultsAt breast height, BSG was found to clearly increase radially (pith to bark) for two species and to decrease for one species. For F. sylvatica and A. alba, the radial variations of BSG were rather U-shaped, with in particular inner wood areas showing respectively lower and higher BSG than the corresponding mature wood. RWCL increased generally from inner to outer area but wet sapwood was clearly distinguishable only for the coniferous species. Vertical variations of BSG and RWCL were strongly dependant on the species with usually non-linear patterns.• ConclusionThe observed variations of BSG were only partially in agreement with the reported typical radial patterns. Despite the vertical variations, the mean BSG of a cross-section at breast height appeared to be a good estimator of the mean BSG of the whole stem (although the difference was statistically significant for coniferous species), whereas breast height measurement of RWCL was not representative of the whole stem.

Gestion des peuplements en forêt publique : nouvelles pistes de recherche, développement et innovation

NDLR : La première version de cet article est parue dans Innovations agronomiques, 56, 2016. Nous remercions la rédaction de Innovations Agronomiques de nous avoir autorisés à en publier une deuxième version dans la Revue forestière française. L’objet de cet article était de rendre compte de la démarche d’appropriation des travaux de recherche par les gestionnaires et notamment par le département Recherche, Développement et Innovation de l’ONF. Les auteurs de ce département tiennent à remercier les laboratoires associés à ces travaux et qui sont cités tout le long du texte : INRA, Irstea, FCBA, IRD, CIRAD...

Une approche multiacteur et multidisciplinaire pour innover dans les pratiques de plantation forestière

La plantation forestiere est un outil majeur pour l’adaptation des forets aux changements globaux. Les echecs parfois recurrents dans certains contextes, les couts associes a la plantation, la penibilite du travail pour les ouvriers forestiers ainsi que les impacts environnementaux parfois negatifs sont autant de facteurs qui freinent le recours a la plantation et peuvent ainsi limiter la capacite d’adaptation des forets. Un ensemble de travaux ont ete menes pour repondre aux besoins en innovation technique sur les methodes de plantation exprimes par les praticiens. Ces travaux portent sur le processus d’innovation en sylviculture et sur l’amelioration technique des methodes de plantation. L’analyse du processus d’innovation indique une faiblesse des reseaux sociotechniques associee a un mauvais partage des connaissances entre acteurs et une reticence a l’investissement dans du nouveau materiel, dans un contexte economique percu comme incertain. Ces observations suggerent qu’un des principaux leviers possibles serait une meilleure mise en reseau des acteurs, a travers differents liens fonctionnels : partage d’information, echanges de services, construction de partenariats economiques. Des exemples de methodes innovantes pour realiser chacune des differentes etapes de l’itineraire de plantation (preparation du site, plantation, entretiens), repondant aux besoins d’innovation technique exprimes par les praticiens, sont ensuite presentes.

Plantations résineuses en conditions forestières : analyse économique des itinéraires dédiés et semi-dédiés pour augmenter la production de bois

Les politiques nationales sur l’atténuation du changement climatique telles que le Grenelle de l’environnement, le paquet Énergie Climat et le discours présidentiel d’Urmatt du 19 mai 2009, visent à augmenter la consommation de bois pour les différents usages et particulièrement en bois construction (Chopard et al., 2013) et en biomasse énergie. L’intensification de la production forestière est ainsi un enjeu politique, climatique et économique. Or, à l’heure actuelle, les itinéraires sylvicoles permettant aux forestiers d’augmenter l’offre en bois n’ont pas été suffisamment analysés sous l’angle économique.

Pas de vent, pas de bois. L’apport de la biomécanique des arbres pour comprendre la croissance puis la vulnérabilité aux vents forts des peuplements forestiers

La biomecanique etudie les reactions et adaptations des etres vivants a leur environnement mecanique, par exemple aux oscillations et forces exercees par le vent. Au-dela des theories anciennes de la securite mecanique constante, la mecanobiologie a recemment formalise les signaux mecaniques, la perception des cellules vivantes et les reponses de croissance. Ces mecanismes physiologiques font que l’arbre ne forme vraiment du bois, tissu de soutien, que lorsqu’il est mecaniquement stimule. La croissance est controlee par les deformations mecaniques percues, qui deviennent alors pour l’arbre de bons indicateurs de securite. Pour appliquer ces connaissances aux forets, le projet ANR FOR-WIND a l’ambition de developper une mecanobiologie adaptee aux temps longs et aux conditions naturelles complexes. L’enjeu est de concevoir les pratiques d’amenagement avec de nouveaux indicateurs de vulnerabilite aux vents forts, qui raisonnent l’effet du changement climatique, de la structure du paysage, de la sylviculture ou de l’amelioration genetique au travers des processus cles mais negliges d’endurcissement des arbres aux vents usuels.

Une base de données unique en France de cubages d’arbres individuels (volumes, biomasses) au service d’une modélisation générique de la ressource en bois énergie

A base for volume and biomass data of the aerial woody compartments of individual trees was constituted under the ANR EMERGE (French acronym for ‘designing models for a robust, all-purpose estimation of wood energy’) project by seven bodies involved in forest research and management in France (ONF, INRA, Cemagref, IFN, FCBA, CNPF and CIRAD) so as to come up with a robust model of woody resources in forests. These measurements, taken for various logging diameters, sometimes down to the slenderest branches, have been performed since the beginning of the 20th century forming a unique data base in France. The data cover a broad range of age groups, sizes, species, stand structures and environmental factors (soil, climate). Of particular interest is the distribution of the available data in relation to French resources as estimated in the National Forest Inventory so as to use sampling campaigns to collect missing information under the EMERGE project. Another significant feature is the potential for designing robust, all-purpose models of volumes and biomass for various logging diameters depending on species, stage of development, geographic gradients, variations in silvicultural practises and possible effect of date of measurement.