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Background: Eicosanoid and related docosanoid polyunsaturated fatty acids (PUFAs) and their oxygenated derivatives have been proposed as noninvasive lipidomic biomarkers of nonalcoholic steatohepatitis (NASH). Therefore, we investigated associations between plasma eicosanoids and liver fibrosis to evaluate their utility in diagnosing and monitoring NASH-related fibrosis. Methods: Our analysis used baseline eicosanoid data from 427 patients with biopsy-confirmed nonalcoholic fatty liver disease (NAFLD), and longitudinal measurements along with liver fibrosis staging from 63 patients with NASH and stage 2/3 fibrosis followed for 24 weeks in a phase II trial. Results: At baseline, four eicosanoids were significantly associated with liver fibrosis stage: 11,12-DIHETE, tetranor 12-HETE, adrenic acid, and 14, 15-DIHETE. Over 24 weeks of follow up, a combination of changes in seven eicosanoids [5-HETE, 7,17-DHDPA, adrenic acid, arachidonic acid (AA), eicosapentaenoic acid (EPA), 16-HDOHE, and 9-HODE) had good diagnostic accuracy for the prediction of ⩾1 stage improvement in fibrosis (AUROC: 0.74; 95% CI: 0.62–0.87), and a combination of four eicosanoids (7,17-DHDPA, 14,15-DIHETRE, 9-HOTRE, and free adrenic acid) accurately predicted improvement in hepatic collagen content (AUROC: 0.72; 95% CI: 0.50–0.77). Conclusion: This study provides preliminary evidence that plasma eicosanoids may serve as noninvasive biomarkers of liver fibrosis and may predict liver fibrosis improvement in NASH.

Climate change is modifying the distribution ranges of species worldwide. To better understand and more realistically predict future species ranges, it is critical to account for local adaptation and phenotypic plasticity in populations’ responses to climate. This is challenging, however, because local adaptation and phenotypic plasticity are trait dependent and because traits co-vary along climatic gradients across the range, with differential consequences for fitness. One way to address this challenge is to build models with empirical data from large-scale common-garden experiments such as those that have been established in past decades for some forest tree species. This thesis used individual measurements of several fitness-related phenotypic traits (vertical and radial tree growth, spring and autumn leaf phenology and recruit mortality) of European beech (Fagus sylvatica L.) recorded in the frame of BeechCOSTe52, the largest network of tree phenotypic traits measured in common gardens throughout Europe (>150,000 trees) for modeling the species’ likely response to recent climate change. Specifically, I pursued the following objectives: (i) to quantify range-wide variation and co-variation of local adaptation and phenotypic plasticity for four major phenotypic traits related to fitness (vertical growth, radial growth, survival, and leaf flushing phenology), and to project its species range under current and future climate based on this information (chapter 1); (ii) to quantify variation among populations in spring and autumn leaf phenology and the resulting growing season length, and to predict their patterns at the range-wide scale under current and future climate (chapter 2); and (iii) to quantify phenotypic plasticity at different development stages for vertical growth, radial growth, survival, and spring and autumn leaf flushing phenology, and to determine the extent to which inter-annual climate variation during the 20th century is related to variation in phenotypic plasticity across the species range (chapter 3). After setting up the required databases, I performed different types of linear mixed-effect models that related trait variation and co-variation to local adaptation (i.e., trait variation related to the climate of the planted populations’ origin) and phenotypic plasticity (i.e., trait variation related to the climate of plantation site). Finally, I calculated a phenotypic plasticity index for populations based on their reaction norms (i.e., the shape or specific form of the phenotypic response to the environment of an individual or genotype). My results revealed that: (i) the contribution of plasticity to intra-specific trait variation is always higher than that of local adaptation, suggesting that beech is less sensitive to (moderate) climate change than previously reported; (ii) different traits and underlying climatic drivers constrain beech populations in different parts of the species range; (iii) considering trait co-variation improves predictions based on single traits; (iv) growing season length will increase under climate change in northern beech provenances but shrink in populations from the core and the southern range; (v) northern beech populations show high phenotypic plasticity for the investigated traits; and (vi) phenotypic plasticity tends to increase with age in growth-related traits. My results underline that population responses to climate across large geographical gradients are trait-dependent, suggesting that a complete set of fitness-related traits is required to fully understand species sensitivity to climate change.; Le changement climatique modifie l'aire de répartition des espèces dans le monde. Pour mieux comprendre et prévoir de façon plus réaliste les aires de répartition futures des espèces, il est essentiel de tenir compte de l'adaptation locale et de la plasticité phénotypique dans les réponses des populations au changement climatique. C'est un défi, cependant, parce que l'adaptation locale et la plasticité phénotypique dépendent des caractères et parce que les caractères varient le long des gradients climatiques dans toute la gamme, avec des conséquences différentes pour la condition physique. C'est un défi, cependant, parce que l'adaptation locale et la plasticité phénotypique dépendent des caractères et parce que les caractères varient le long des gradients climatiques dans toute la gamme, avec des conséquences différentes pour la valeur adaptative. Une façon de relever ce défi consiste à construire des modèles à partir de données empiriques issues d'expériences à grande échelle sur les jardins communs, comme celles qui ont été réalisées au cours des dernières décennies pour certaines essences forestières. Cette thèse a utilisé des mesures individuelles de plusieurs caractères phénotypiques liés à la valeur adaptative (croissance verticale et radiale des arbres, phénologie foliaire printanière et automnale et mortalité) du hêtre européen (Fagus sylvatica L.) enregistrés dans le cadre du projet BeechCOSTe52, le plus grand réseau de caractères phénotypiques d'arbres mesurés dans des jardins communs à travers l'Europe (>150 000 arbres) pour modéliser la réponse probable de l'espèce au changement climatique récent. Plus précisément, j'ai poursuivi les objectifs suivants (i) quantifier la variation et la covariation à l'échelle de l'aire de répartition de l'adaptation locale et de la plasticité phénotypique pour quatre caractères phénotypiques majeurs liés à la valeur adaptative (croissance verticale, croissance radiale, survie et phénologie des feuilles au printemps), et de projeter son aire de répartition dans le climat actuel et futur en fonction de cette information (chapitre 1) ; (ii) quantifier les variations entre les populations en ce qui concerne la phénologie foliaire printanière et automnale et la durée de la période de végétation qui en résulte, et prévoir leurs tendances à l'échelle de l'aire de répartition sous le climat actuel et futur (chapitre 2) ; et (iii) quantifier la plasticité phénotypique à différents stades de développement pour la croissance verticale, la croissance radiale, la survie et la phénologie des feuilles au printemps et à l'automne, et déterminer dans quelle mesure la variation climatique interannuelle au cours du 20e siècle est liée à la variation de la plasticité phénotypique dans l'aire de répartition des espèces (chapitre 3). Après avoir mis en place les bases de données requises, j'ai réalisé différents types de modèles linéaires à effets mixtes qui relient la variation et la covariation des caractères à l'adaptation locale (c'est-à-dire la variation des caractères liée au climat d'origine des populations plantées) et la plasticité phénotypique (c'est-à-dire la variation des caractères liée au climat du site de plantation). Finalement, j'ai calculé un indice de plasticité phénotypique pour les populations en fonction de leurs normes de réaction (la forme spécifique de la réponse phénotypique à l'environnement d'un individu ou du génotype). Mes résultats l'ont révélé : [... )

To improve the value of secondary quality hardwood, it is important to understand its wood properties and optimize its mechanical properties. The variability of some structural, physical and mechanical properties of wood from beech and oak trees issued from thinning was studied. Logs from these trees were rotary peeled in three different veneer thicknesses (2.1, 3, and 4.2 mm). Veneer quality was assessed by measuring the veneer knot proportion and checking properties. The mechanical properties of LVL (laminated veneer lumber) made from these veneers were measured using the static and dynamic method. Juvenile wood in both species is concentrated in a very small area near the pith thus there will be no or low part juvenile wood peeled. The wood mechanical and physical properties of both species were strongly influenced by the wood density. The 3 mm thick veneer provided the optimal mechanical properties for LVL for both species. Such mechanical properties are comparable to LVL made with other hardwood species. The internal veneer provided LVL with higher density, but lower mechanical properties as a result of its higher proportion of knots.; Afin de valoriser au mieux le bois de feuillu de qualité secondaire, il est important de comprendre ses propriétés et d'optimiser ses propriétés mécaniques. La variabilité de certaines propriétés structurelles, physiques et mécaniques du bois de hêtres et de chênes issus d’éclaircis a été étudiée. Des billons tirés de ces arbres ont été déroulés en trois épaisseurs (2.1, 3, and 4.2 mm). La qualité du placage a été évaluée en mesurant la proportion du nœud et les fissurations. Les propriétés mécaniques du LVL (lamibois) réalisé à partir de ces placages ont été mesurées par méthode destructive et non destructive. Chez les deux espèces, le bois juvénile est concentré dans une petite zone près de la moelle, de sorte qu'il y aura peu ou pas de bois juvénile déroulé. Les propriétés mécaniques et physiques du bois des deux espèces sont fortement influencées par sa densité. Le placage de 3 mm d'épaisseur a fourni les propriétés mécaniques optimales pour le LVL pour les deux espèces. Ces propriétés mécaniques sont comparables à celles de LVL réalisés à partir d'autres essences de feuillus. Le placage interne a fourni du LVL avec une densité plus élevée, mais des propriétés mécaniques plus faibles en raison de sa proportion de nœuds plus élevée.

As climate change should lead to an increase in the vulnerability and the sensitivity of forests to extreme climatic events, quantifying and predicting their response to more severe droughts remains a key task for foresters. Furthermore, recent works have suggested that tree diversity may affect forest ecosystem functioning, including their response to extreme events. In this study we aimed at testing whether the growth response of forest stands to stressful climatic events varied between mixed and monospecific stands, under various environmental conditions. We focused on beech-fir forests (Fagus sylvatica [L.] and Abies alba [L.]) and beech-oak forests (F. sylvatica [L.] and Quercus pubescent [L.]) in the French Alps. We used a dendrochronological dataset sampled in forest plots organized by triplets (one mixture and two monospecific stands) distributed in six sites along a latitudinal gradient. We tested (1) whether stand diversity (two-species stands vs monospecific stands) modulates the stands’ response to drought events in terms of productivity, (2) whether species identity may drive the diversity effect on resistance and recovery, and (3) whether this can be explained by interspecific interactions. We found that (1) interspecific differences in response to extreme drought events (possibly due to interspecific differences in hydraulic characteristics) can induce a mixture effect on stand growth, although it appeared (2) to be strongly depending on species identity (positive effect only found for beech-fir mixed stands), while (3) there were no significant non-additive effects of diversity on stand resistance and recovery, except for some specific cases. Overall, our study shows that promoting selected mixed stands management may buffer extreme drought effect on stand productivity.

Phloem failure has recently been recognized as one of the mechanisms causing tree mortality under drought, though direct evidence is still lacking. We combined 13C pulse-labelling of 8-year-old beech trees (Fagus sylvatica L.) growing outdoors in a nursery with an anatomical study of the phloem tissue in their stems to examine how drought alters carbon transport and phloem transport capacity. For the six trees under drought, predawn leaf water potential ranged from -0.7 to -2.4 MPa, compared with an average of -0.2 MPa in five control trees with no water stress. We also observed a longer residence time of excess 13C in the foliage and the phloem sap in trees under drought compared with controls. Compared with controls, excess 13C in trunk respiration peaked later in trees under moderate drought conditions and showed no decline even after 4 days under more severe drought conditions. We estimated higher phloem sap viscosity in trees under drought. We also observed much smaller sieve-tube radii in all drought-stressed trees, which led to lower sieve-tube conductivity and lower phloem conductance in the tree stem. We concluded that prolonged drought affected phloem transport capacity through a change in anatomy and that the slowdown of phloem transport under drought likely resulted from a reduced driving force due to lower hydrostatic pressure between the source and sink organs.

An increase in forest dieback has been observed in recent decades and the question of how trees will react to these brutal changes is raised by the scientific community but not yet resolved. The multiplicity of studies made it possible to draw several hypotheses on the functional mechanisms put into action during a death event leading to mortality, two of which emerge: a dysfunction of the hydraulic system or a depletion of carbon reserves. Nevertheless, these assumptions turned out to be neither exclusive nor exhaustive. Other hypotheses were then proposed in addition to existing ones, in particular the contribution of nitrogen metabolism during a mortality event. Numerous observations point to a potential risk to the ecological status of beech in the face of these global climate changes, in particular a decrease in the availability of soil nitrogen and an increase in drought events. The work in this thesis has therefore sought to evaluate the contribution of nitrogen and carbon metabolisms to dysfunctions observed during an episode of dieback leading to mortality. During the 3 years of the project, we studied how the nitrogen and carbon metabolism could be impacted by successive annual defoliation or a long and intense drought. Our study has shown the internal tree nitrogen cycle is conserved with a strong allocation of nitrogen to the leaf compartment in the spring, its conservation in the foliage during the growing season and an efficient recycling of the leaf nitrogen to the perennial organs during nitrogen winter remobilization. We have been able to estimate that this recycled nitrogen in the fall contributes significantly to the setting up of the new leaf compartment the following spring, even in the face of significant constraints. We have also been able to show that the quantity of carbon reserves is maintained in the face of defoliation and, at least initially, in the face of drought. Nevertheless, the proportional demand for osmotic requirements in the face of a long and intense drought has led to a decrease in the amount of carbon reserves. When the tree dies, the carbon reserves are greatly reduced, but not until exhaustion, contrary to the theory. Finally, the mortality rate in our experiment was quite low indicating the resistance of the Lorraine beech to extreme constraints such as successive defoliation or a long and intense drought. Our results emphasize the resistance character of the beech against a constraint via internal metabolism adjustments but this resistance could be lost if the stress is longer and more recurrent. These elements can question the possible maintenance of beech in the face of climate change, Une augmentation des dépérissements forestiers a été observée ces dernières décennies et les mécanismes écophysiologiques sous-jacents à un phénomène de mortalité sont aujourd’hui mal connus. La multiplicité des études a permis de dégager plusieurs hypothèses sur les mécanismes fonctionnels mis à l’œuvre lors d’un événement de dépérissement menant à la mortalité dont deux se dégagent : un dysfonctionnement du système hydraulique ou un épuisement des réserves carbonées. Néanmoins, ces hypothèses se sont révélées être non exclusives, ni exhaustives. D’autres hypothèses ont alors été proposées, notamment la contribution d’un dysfonctionnement azoté. De nombreuses observations font état d’un risque potentiel sur l’état écologique du hêtre face à ces changements climatiques globaux par notamment une baisse de la disponibilité en azote du sol et une augmentation des événements de sécheresse. Le travail au sein de cette thèse a donc cherché à évaluer la contribution des métabolismes azoté et carboné aux dysfonctionnements observés lors d’un épisode de dépérissement menant à une mortalité. Durant les 3 ans du projet, nous avons étudié comment le métabolisme azoté et carboné pouvaient être impactés par des défoliations annuelles successives ou une sécheresse longue et intense. Notre étude a permis de montrer que face à une contrainte hydrique sévère ou une défoliation, le cycle azoté interne à l’arbre est conservé avec une forte allocation de l’azote vers le compartiment foliaire au printemps et un recyclage efficace vers les organes pérennes à l’automne. Nous avons pu estimer que cet azote recyclé à l’automne contribue fortement à la mise en place du nouveau compartiment foliaire au printemps suivant et ce, même face à des contraintes importantes. Nous avons pu également mettre en évidence que la quantité de réserves carbonées est maintenue face à une défoliation et, au moins dans un premier temps, face à une sécheresse. Néanmoins, la demande proportionnelle pour des besoins osmotiques a mené à des changements de la composition des sucres de jeunes branches et, face à une sécheresse longue et intense, à une baisse de la quantité de réserves carbonées jusqu’à la mort de l’arbre où les réserves carbonées sont fortement diminuées mais pas totalement épuisées. Finalement, le taux de mortalité dans notre expérimentation fut très faible indiquant la résistance du hêtre lorrain à des contraintes extrêmes. Nos résultats soulignent le caractère de résistance du hêtre face à une contrainte via des ajustements des métabolismes internes mais cette résistance pourrait être perdue si la contrainte est plus longue et plus récurrente. Ces éléments peuvent questionner sur le possible maintien du hêtre face aux changements climatiques

Eddy covariance (EC) measurements are widely used to estimate the amount of carbon sequestrated by terrestrial biomes. The decision to exclude an EC flux from a database (bad quality records, turbulence regime not adequate, footprint problem,...) becomes an important step in the CO2 flux determination procedure. In this paper an innovative combination of existing assessment tests is used to give a relatively complete evaluation of the net ecosystem exchange measurements. For the 2005 full-leaf season at the Hesse site, the percentage of rejected half-hours is relatively high (59.7%) especially during night-time (68.9%). This result strengthens the importance of the data gap filling method. The data rejection does not lead to a real improvement of the accuracy of the relationship between the CO2 fluxes and the climatic factors especially during the nights. The spatial heterogeneity of the soil respiration (on a site with relatively homogenous vegetation pattern) seems large enough to mask an increase of the goodness of the fit of the ecosystem respiration measurements with a dependence on soil temperature and water content when the tests are used to reject EC data. However, the data rejected present some common characteristics. Their removal lead to an increase in the total amount of CO2 respired (24%) and photosynthesised (16%) during the 2005 full-leaf season. Consequently the application of our combination of multiple quality tests is able improve the inter-annual analysis. The systematic application on the large database like the CarboEurope and FLUXNET appears to be necessary.

This thesis deals with the impact of soil type on the biogeochemical functioning of a typical forest ecosystem of Central and Western Europe. For this study, a strongly instrumented experimental site was implemented in a beech stand (Fagus sylvatica) within the state forest of Montiers-sur-Saulx (Meuse, France), in order to monitor the biogeochemical cycling between the different compartments of the ecosystem (the atmosphere, the canopy, the forest floor and the soil). The particular value of the Montiers experimental site resides in the strong contrast between soil types under the same beech stand: Rendzic Leptosol, Eutric Cambisol and Dystric Cambisol. For the first time, stocks and fluxes of water and elements were measured and compared in situ and over the long term (from January 2012 to December 2015) on different forest soil types, all other site conditions being equal (climate, atmospheric inputs, stand age and structure). Total and exchangeable pools in the soil and stocks in the different compartments of the vegetation (branches, trunk, fine and coarse roots) were determined via chemical analysis and modelisation. Fluxes of elements were calculated from monthly sampling of the ecosystem’s solutions (atmospheric deposition, throughfall, stemflow, gravitational and bound soil solutions) and of litter fall. The water balance model BILJOU© was used to estimate the different components of the water budget. The results show that the soil water holding capacity, the stocks of elements in the soil, the chemical composition of soil solutions, the rooting strategy and the perennial biomass production differ strongly between soil types. Contrary to what might have been expected in regard to the marked differences between the chemical signatures of the soils solutions in the three soils, the foliar elemental composition of the beech stand and the aboveground fluxes of elements in solution (canopy exchange, stand deposition) and in solid state (litter fall) do not differ significantly between the three experimental stations for the majority of the studied elements. The biological part of the mineral cycles is overall predominant and the recycling through fine roots turnover is generally higher than litter fall. We also show that the quantity of water transpired by the forest canopy, directly linked to the soil water holding capacity, is the primary control factor of the annual stand productivity. Stand adaptation mechanisms to physico-chemical soil properties seemed to reduce, or even entirely compensate for, secondary factors controlling the stand productivity (in particular nutrient availability in the soil). Thus a significant issue for forest managers might be to further adapt forestry practices to management units based on soil physical properties, especially depth to the bedrock and rooting depth, Cette thèse porte sur l’impact du type de sol sur le fonctionnement biogéochimique d’un écosystème forestier typique d’Europe centrale et occidentale. Pour cette étude, un dispositif expérimental a été mis en place par l’INRA et l’ANDRA au sein d’une hêtraie (Fagus sylvatica) dans la forêt de Montiers-sur-Saulx (Meuse, France) afin de suivre les cycles biogéochimiques entre les différents compartiments de l’écosystème (l’atmosphère, la canopée, la litière et le sol). L’intérêt particulier du site expérimental de Montiers vient du contraste important entre les types de sols pour un même peuplement : rendisol, calci-brunisol et alocrisol/brunisol. Pour la première fois, les stocks et les flux de l’eau et des éléments ont été mesurés et comparés in situ et sur le long terme (entre janvier 2012 et décembre 2015) sur des sols forestiers différents, toutes les autres conditions du site égales par ailleurs (climat, apports atmosphériques, âge et structure du peuplement). Les stocks totaux et échangeables dans le sol et les stocks dans les différents compartiments de la biomasse végétale (branches, tronc, racines grosses et fines) ont été déterminés par le biais d’analyses chimiques et de modélisations. Les flux élémentaires ont été calculés à partir des prélèvements mensuels des solutions de l’écosystème (dépôt atmosphérique, pluviolessivat, écoulement de tronc, solutions libres et liées du sol) et des chutes de litière. Le modèle hydrique BILJOU© a été utilisé pour estimer les composantes du bilan hydrique de l’écosystème. Les résultats montrent que la réserve utile du sol, les stocks des éléments dans le sol, les compositions chimiques des solutions du sol, la stratégie de colonisation racinaire et la production de biomasse pérenne diffèrent fortement en fonction du type de sol. Contrairement à ce que l’on pouvait supposer compte tenu des différences marquées entre les signatures chimiques des solutions des trois sols, les compositions foliaires du peuplement et les flux des éléments hors sol en solution (échange de la canopée, apport au sol) et sous forme solide (chute de litière) ne diffèrent pas ou peu entre les trois stations expérimentales pour la majorité des éléments. La part biologique des cycles minéraux est globalement prédominante et le renouvellement des racines fines représente un flux de recyclage généralement supérieur à la chute de litière aérienne. Nous montrons également que la quantité d’eau transpirée par la canopée, directement liée à la taille de la réserve utile du sol, est le facteur de contrôle principal de la productivité du peuplement à l’échelle annuelle. Des processus d’adaptation du peuplement aux conditions physico-chimiques du sol semblent réduire, voire compenser entièrement, les facteurs secondaires de contrôle de la productivité du peuplement (notamment la disponibilité des nutriments dans le sol). Ainsi un enjeu significatif pour les gestionnaires forestiers pourrait être l’adaptation des pratiques sylvicoles à des parcelles de gestion davantage basées sur les propriétés physiques des sols, et en particulier les profondeurs d’apparition de la roche-mère et de colonisation racinaire

Le pays de Caux (Normandie) offre un paysage de plateaux cultivés ponctués de bosquets. Les anciens corps de fermes y sont entourés d’arbres, les fameux clos-masures. Leur vocation agricole disparaît, mais les rideaux de hêtres sont encore bien présents dans le paysage. Aux abattages des années 1950-1970 a succédé une période de replantation de « brise-vent » soutenue par les pouvoirs publics au titre du paysage. L’article analyse les valeurs aujourd’hui attribuées à ces rideaux d’arbres en termes d’agronomie, de paysage et d’environnement. Cette recherche s’est développée dans le cadre d’un projet d’inscription des clos-masures au patrimoine mondial de l’Unesco. Les résultats sont issus d’une enquête ethnographique menée dans les environs d’Yvetot. L’arbre a perdu ses fonctions agricoles de protection du bétail et de production de bois ; c’est désormais par le paysage et l’environnement qu’il retrouve du sens auprès des agriculteurs. Ce sens de l’intérêt général est un élément clé du renouveau agricole et urbain des clos-masures du pays de Caux. The Pays de Caux (Normandy) offers a landscape of cultivated plateaux dotted with thickets. Ancient farmhouses are often surrounded and protected by trees, these are the famous clos-masures. Their agricultural function is disappearing, but the rows of beech trees are still very much present in the landscape. After a period during which most of the trees were felled (from 1950 to 1970) followed a period of replanting of “windbreaks” with the support of the public authorities and in defence of the landscape. This article analyses the values attributed today to these curtains of trees in agronomic, landscaping and environmental terms. The study was conducted within the framework of a project for the listing of the clos-masures as part of the UNESCO world heritage. The findings come from an ethnographic survey conducted in the area of Yvetot. The tree has lost its agricultural function of protecting cattle and producing wood ; it is now through the landscape and the environment that it has meaning for the farmers. This notion of common interest is a key element in the agricultural and urban revival of the clos-masures of the Pays de Caux region.

International audience; Plant competition and deer browsing are two main factors which limit tree recruitment. We examined natural tree-recruitment processes under continuous-tree-cover management. Changes in plant communities and tree regeneration were monitored over an eight-year period at two different sites in a temperate hardwood forest in the North-East of France. We used paired control plot (unfenced areas, free access to deer) and exclosures (fenced areas, excluding deer) at both sites. Shade-tolerant browsing-tolerant opportunistic species (beech, Fagus sylvatica at site 1 and bramble, Rubus spp. at site 2) were present in low numbers at the beginning of the study. We found that these species used a sit-and-wait strategy, waiting for opportunities to proliferate (thinning and deer exclusion). In the exclosure at site 1, beech proliferate slowly. In the exclosure at site 2, bramble proliferated enough during the first two growing seasons to prevent tree recruitment. Thus, fencing encouraged beech sapling or bramble growth, and this growth in turn was detrimental to the richness and diversity of the plant community. The two study cases presented show that both plant competition and deer browsing can be problematic for tree recruitment. Our results further suggest that excluding deer is not sufficient to enhance the growth of browse-sensitive and moderately shade-tolerant tree species such as oaks (Quercus petraea and Q. robur).

Climate change is expected to increase the frequency and intensity of droughts and heatwaves in Europe, leading to effects on forest growth and major forest dieback events due to hydraulic failure caused by xylem embolism. Inter-specific variability in embolism resistance has been studied in detail, but little is known about intra-specific variability, particularly in marginal populations. We evaluated 15 European beech populations, mostly from geographically marginal sites of the species distribution range, focusing particularly on populations from the dry southern margin. We found small, but significant differences in resistance to embolism between populations, with xylem pressures causing 50% loss of hydraulic conductivity ranging from −2.84 to −3.55 MPa. Significant phenotypic clines of increasing embolism resistance with increasing temperature and aridity were observed: the southernmost beech populations growing in a warmer drier climate and with lower habitat suitability have higher resistance to embolism than those from Northern Europe growing more favourable conditions. Previous studies have shown that there is little or no difference in embolism resistance between core populations, but our findings show that marginal populations have developed ways of protecting their xylem based on either evolution or plasticity.

Most temperate forest tree species will suffer important environmental changes as result of the climate change. Adaptiveness to local conditions could change at different sites in the future. In this context, the study of intra-specific variability is important to clarify the singularity of different local populations. Phenotypic differentiation between three beech provenances covering a wide latitudinal range (Spain/ES, Germany/DE and Sweden/SE), was studied in a greenhouse experiment. Non-target leaf metabolite profiles and ecophysiological response was analyzed in well-watered and water stressed seedlings. There was a provenance-specific pattern in the relative concentrations of some leaf metabolites regardless watering treatment. The DE and SE from the center and north of the distribution area of the species showed a clear differentiation from the ES provenance in the relative concentration of some metabolites. Thus the ES provenance from the south maintained larger relative concentration of some organic and amino acids (e.g. fumaric and succinic acids or valine and isoleucine), and in some secondary metabolites (e.g. kaempferol, caffeic and ferulic acids). The ecophysiological response to mild water stress was similar among the three provenances as a consequence of the moderate water stress applied to seedlings, although leaf N isotope composition (δ15N) and leaf CN ratio were higher and lower respectively in DE than in the other two provenances. This would suggest potential differences in the capacity to uptake and post-process nitrogen according to provenance. An important focus of the study was to address for the first time inter-provenance leaf metabolic diversity in beech from a non-targeted metabolic profiling approach that allowed differentiation of the three studied provenances. © 2017 Elsevier Masson SAS

Beech is a wood species present in the French territory, particularly in the Grand-Est region. However, beech is a under used wood, especially for outdoor uses, because it is non durability and it is dimensional unstability. To promote and develop its use, it is necessary to limit its recovery in moisture and treat to protect it against fungi decay. Futhermore, current regulation on wood treatment products imposes the development of alternative wood treatments more respectful of the environment and health. In this context, the work developed during this thesis is focused on valorisation of beech as a material through its protection by a “non-biocide” treatment, furfurylation. This method consists in an polymerisation in situ by heating a furfuryl alcohol solution into beech solid wood. The development of process led to a bio-based beech composite with significantly improved durability and dimensional stability.On the other hand, beech is a hardwood species in which the hemicellulosic fraction is rich in pentoses, and more precisely in xylose, precursor of furfural. Work has been done to produce furfural by acidic steam distillation, from beech primary wood processing by products. This molecule is then chemically reduced to furfuryl alcohol by hydrogen transfer.These promising results to show that it is possible to set up a local production combining beech as a local source of furanic molecules and beech wood as a solid material, Le hêtre est une essence très répandue sur le territoire français et plus particulièrement dans la région Grand-Est. Toutefois, son bois est peu exploité, notamment pour des utilisations en conditions extérieures en raison de sa faible durabilité et son instabilité dimensionnelle. Pour favoriser et développer son utilisation, il est nécessaire de le traiter afin de limiter sa reprise en humidité et de le protéger contre les champignons de pourriture. Par ailleurs, la réglementation actuelle sur les produits de traitement du bois impose la mise au point de solutions alternatives respectueuses de l’environnement et de la santé. Dans ce cadre, les travaux développés durant cette thèse visent la valorisation du hêtre en tant que matériau via sa protection par un traitement « non-biocide », la furfurylation. Cette méthode consiste à polymériser in situ de l’alcool furfurylique dans le bois de hêtre. La mise au point du procédé a permis d’aboutir à du hêtre composite dont la durabilité et la stabilité dimensionnelle sont nettement améliorées. D’autre part, le hêtre est une essence feuillue pour laquelle la fraction hémicellulosique est riche en pentoses et plus précisément en xylose, précurseur de furfural. Des travaux ont donc été menés pour produire du furfural par hydrodistillation acide à partir de connexes issus de l’industrie de la première transformation du hêtre. Le furfural a ensuite été réduit en alcool furfurylique par transfert d’hydrogène. Les résultats prometteurs obtenus montrent qu’il est possible de mettre en place une filière locale alliant le hêtre comme source de molécules furaniques et le bois de hêtre comme matériau

International audience; Beech (Fagus sylvatica L.) is a shade tolerant species of broadleaved temperate forests from the northern hemisphere. However, how it manages to survive low irradiance conditions is debated. This must involve both carbon balance components (mainly photosynthesis vs. respiration) and efficient utilization / partitioning of the available C resource among the different sinks (mainly growth vs. reserve storage). This survival strategy was investigated through a combined experimental and modelling approach. Four-year-old beech seedlings growing in the understorey of natural Scots pine stands were 3D-digitized in summer for architecture, including woody parts (growth units) and leaves. Then seedlings were harvested in autumn and winter to quantify biomass and carbohydrate reserve contents of each organ, both above and below ground. Roots were separated into 3 classes: taproot, main lateral roots and fine roots, and shoot segments according to their age. These data were used to construct 3D-digital mockups of the young trees and to parameterize and initialize the carbon-based functional-structural model PIAF-1. Additional beech-specific parameters relevant to phenology and gas exchange rates were derived from similar experiments or literature. Meteorological data (daily radiation and temperature) were generated for each tree based on recorded weather data. Transmitted solar irradiance above each seedling was calculated from hemispherical photographs and the global radiation above the stand. The first results suggest that under the most restrictive light conditions, the reserve store was just sufficient for the spring outgrowth. The major factor allowing the seedling to pass the short but critical near-zero-reserve phase appeared to be the leaf growth strategy, with surface area expanding prior to structural hardening. The reserve mobilization strategy showed only as a second factor, with the mobilization rate likely not limiting in contrast to the total reserve store.

International audience; Maintaining the coexistence of multiple tree species is one of the greatest issues of uneven-aged silviculture. In many places, while forest managers have successfully maintained complex stand structure with continuous cover silviculture, they have often faced difficulties to maintain some desired species mixtures. The composition of uneven-aged forests naturally evolves as few species successfully regenerate and suppress the others. Maintaining the coexistence of various tree species is however of great interests, for example, regarding biodiversity issues or resilience to global changes. Since uneven-aged silviculture usually maintains a continuous canopy cover, wherever nutrient and water availability satisfies regeneration requirements, the availability of light in the understory is the driving factor of natural regeneration dynamics. The amount of transmitted radiation determines, at least partly, regeneration composition because of interspecific differences in growth and survival under shade. In theory, shade-tolerant species generally dominate the regeneration under closed canopies whereas less shade-tolerant species dominate the regeneration under partially open canopies. We hypothesized that, along a gradient of light availability, there is a rank reversal of sapling growth of species with contrasting shade-tolerance. In addition, we expected that forest managers can effectively control understory light with appropriate modifications of forest structure and density. We examined mixtures of sessile oak (Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.) in the Belgian Ardennes. We selected 23 sites with favorable water and nutrient supply. Regeneration areas (100-6500m²) were fenced off to protect them from browsing by deer. Saplings were sampled in 241 subplots and their height growth was annually monitored during two years. Understory light transmittance was measured in each subplot using hemispherical photography. The height growth of beech and oak saplings was modeled with mixed non-linear models. In order to simulate various silvicultural treatments, we used a model of light interception by heterogeneous canopies (SAMSARALIGHT). We simulated selective thinnings of 5 different types: harvesting preferentially small trees, large trees, or trees of shade-tolerant species or creating circular gaps. Understory light was found to be a key parameter in the dynamics of heterogeneous stands, as it affects regeneration growth and composition. There were interspecific differences in growth response to light availability. The optimum height growth of beech and oak regenerations were reached at 10% and 20% of transmittance, respectively. Our simulations highlighted that various silvicultural treatments can effectively be used to control understory light as long as harvest intensity is adapted to the chosen strategy. The results of this study also underscore the problem that even under good light conditions (transmittance > 20 %), regeneration of less shade-tolerant species might not overcome the regeneration of shade-tolerant species. Contrary to our hypothesis, we found no rank reversal of the height growth of the two study species along a wide light gradient. Consequently, maintaining less shade-tolerant species in stands with shade-tolerant species might require silvicultural interventions jointly in the overstory and regeneration layers.

Storms are by far the major hazard damaging the trees. However, trees do not just behave passively in the wind. They sense their own strains under the influence of an external force such as wind andrespond by modifying their growth and the mechanical properties of their tissues. But this process, called thigmomorphogenesis, has mainly been studied in very young trees in controlled conditions. This thesis aims to expand for the first time such studies at the scale of a forest stand in order to understand how adult trees acclimate to the wind in natural conditions by adapting their growth. It relies on an experimental set up in a regular stand of beech (Fagus sylvatica) which have never be thinned. The wind speed, the longitudinal strains and the radial growth of fifteen pairs of trees with contrasted sizes and wind exposures (split into two social status, dominant and suppressed trees) were monitored for one year. By controlling the strain intensity experienced by the trees, either by guying or by additional bendings, we show that the trees respond only to mechanical stimulation caused by rather strong winds with a return period higher than a week. This response leads however to a very strong increase in radial growth. And it follows a law of mecano-sensing uniform among the trees, regardless of their sizes. We then studied the effects of the strain regulation on the mechanical design of the trees and the potential risk of stem breakage. Despite the contrasted sizes and wind exposures, the strain regime remained uniform within the beech stand, in agreement with the hypothesis of an optimal mechanical design often inferred but never validated in its mechanism. Finally, the constitutive equations of a possible growth model dependent on wind are proposed and discussed.; Les tempêtes sont de loin la première cause de dégâts pour les arbres. Toutefois ceux-ci ne font pas que subir passivement le vent. Ils perçoivent leurs propres déformations sous l'effet du vent (comme de toute force externe) et y répondent en modifiant leur croissance et les propriétés mécaniques de leurs tissus. Mais ce processus, appelé thigmomorphogénèse, a surtout été étudié sur de très jeunes arbres en conditions contrôlées. Cette thèse vise à étendre pour la première fois cette étude à l'échelle d'un peuplement forestier afin de comprendre comment des arbres adultes s'acclimatent au vent en conditions naturelles en adaptant leur croissance. Elle s'appuie sur un dispositif expérimental mis en place dans un peuplement régulier de hêtre (Fagus sylvatica) non éclairci. La vitesse du vent, les déformations longitudinales et la croissance radiale de quinze paires d'arbres de dimension et d'exposition au vent contrastées (et regroupés selon leur statut social dominant ou dominé) ont été suivies pendant une année. En contrôlant l'intensité des déformations subies, par haubanage ou à l'aide de flexions artificielles, nous avons pu démontrer que les arbres ne répondent qu'à des stimulations mécaniques provoquées par des vents suffisamment forts ayant un temps de retour supérieur à la semaine. Cette réponse se traduit par contre par une très forte augmentation de leur croissance radiale et suit une loi de mécano-perception commune à l'ensemble des arbres, quelle que soit leur taille. Nous avons ensuite étudié les conséquences de la régulation des déformations sur le dimensionnement mécanique des arbres et leur risque d’endommagement. Il s'avère que malgré des dimensions et des expositions au vent contrastées, le régime de déformation reste uniforme entre les hêtres du peuplement, en accord avec l'hypothèse d'un dimensionnement mécanique optimal souvent inférée mais jamais validée dans son mécanisme. Finalement, les équations constitutives d'un possible modèle de croissance dépendant du vent sont proposées et discutées.

International audience; Beech (Fagus sylvatica L.) is a species of temperate broadleaved forests known to be very shade-tolerant. How does it manage to sustainably cope with very limited light resource? Processes must involve both C balance components (mainly photosynthesis vs. respiration) and efficient utilization/partitioning of the available C resource among the different sinks (mainly growth vs. reserve storage). We investigated them by combined experimental and integrated modelling approach.

National audience; La composition de la communauté végétale et l’abroutissement par les cervidés sont deux principaux facteurs limitant le recrutement des semis ligneux en forêt. Cette étude a examiné la possibilité d’un changement dans la nature des interactions entre un phénomène de compétition entre semis ligneux et végétation accompagnatrice en absence d’herbivore et un phénomène de facilitation indirecte des semis ligneux par la végétation accompagnatrice via l’abroutissement par les cervidés. Les changements de la communauté végétale (composition, couverture) et de la régénération ligneuse (nombre d’individus, hauteur moyenne) ont été suivis sur une période de 8 ans grâce à deux dispositifs appariés d’exclos (excluant le cerf, Cervus elaphus et le chevreuil, Capreolus capreolus) et de contrôle (accès libre aux cervidés) installés dans deux sites de la Réserve Nationale de Chasse et de Faune Sauvage (RNCFS) de La Petite-Pierre (Nord-Est de la France). Dans les deux sites d’étude, une espèce tolérante à l’ombre, tolérante à l’herbivorie et opportuniste a dominé la communauté dans l’exclos par le biais d’une stratégie de type “sit and wait”. Une année a suffi pour que la ronce Rubus sect. fruticosi (espèce à croissance rapide) domine la communauté végétale dans un des sites, alors que la domination du hêtre a été progressive dans l’autre site. Ces 8 années de suivi ont montrées que la présence des cervidés réduit la croissance des semis ligneux mais augmente la diversité de la communauté végétale. A l’inverse, la pose d’exclos a permis d’améliorer la croissance des semis de hêtre ou de la ronce au détriment de la diversité de la communauté. Par ailleurs, le développement d’un fort couvert de ronces en absence de cervidés empêche le recrutement des semis ligneux. Dans ces deux cas d’étude, l’abroutissement par les cervidés autant que la compétition par la strate herbacée peuvent poser problème pour l’établissement des semis ligneux. La combinaison éclaircie/ pose d’exclos a permis l’établissement des semis de hêtre. Cependant, le contrôle des espèces monopolistes à fort pouvoir colonisateur telle la ronce est également nécessaire pour favoriser la croissance des semis ligneux en absence de régénération préétablie. Nos résultats suggèrent que la forte densité de cervidés sur ces deux sites ne permet pas la facilitation indirecte et l’établissement des semis de ligneux via le contrôle de la croissance de la végétation de sous-bois contredisant notre hypothèse de départ.

International audience; The phenotypic responses of functional traits in natural populations are driven by genetic diversity and phenotypic plasticity. These two mechanisms enable trees to cope with rapid climate change. We studied two European temperate tree species (sessile oak and European beech), focusing on (i) in situ variations of leaf functional traits (morphological and physiological) along two altitudinal gradients and (ii) the extent to which these variations were under environmental and/or genetic control using a common garden experiment. For all traits, altitudinal trends tended to be highly consistent between species and transects. For both species, leaf mass per area displayed a positive linear correlation with altitude, whereas leaf size was negatively correlated with altitude. We also observed a significant increase in leaf physiological performance with increasing altitude: populations at high altitudes had higher maximum rates of assimilation, stomatal conductance and leaf nitrogen content than those at low altitudes. In the common garden experiment, genetic differentiation between populations accounted for 0–28% of total phenotypic variation. However, only two traits (leaf mass per area and nitrogen content) exhibited a significant cline. The combination of in situ and common garden experiments used here made it possible to demonstrate, for both species, a weaker effect of genetic variation than of variations in natural conditions, suggesting a strong effect of the environment on leaf functional traits. Finally, we demonstrated that intrapopulation variability was systematically higher than interpopulation variability, whatever the functional trait considered, indicating a high potential capacity to adapt to climate change.

The economic decision model serving as an objective function in forest economics was conceived originally by Faustmann at the stand level. Nevertheless, the tree level seems to be an appropriate scale for analysis, especially for harvesting decisions and certain estimations both at tree and stand levels. However, the Faustmann formula cannot be directly applied to the tree level. The present research has provided certain tree-level formulations of the Faustmann formula, including, in particular, tree expectation value (TEV) and land expectation value (LEV). TEV and tree-level LEV formulas were developed by analyzing the Faustmann formula under deterministic conditions. Unlike previous tree-level decision models presented in the forest economics literature, TEV and tree-level LEV formulas incorporate the expectation value of the land occupied by trees and its variability over time as well as the interaction between trees and their trajectories (cutting age). The proposed formulas were then compared with the Faustmann formula using the first-order condition of optimal harvest age. The TEV and tree-level LEV formulas appeared to be absolutely compatible with the Faustmann formula. The utility of the proposed formulas was then illustrated with application examples, including target diameter, stand expectation value, TEV, LEV, and the value of damage to beech trees or stands in northeastern France.

International audience; Fagus crenata Blume is widely distributed throughout Japanese cool-temperate deciduous broad-leaved forests, but there are two divergent groups of populations in areas with contrasting winter climates separated by Japan’s Central Mountain Range. To facilitate investigations of adaptive genetic differentiation of the species using potentially functional genes, we have collected Expressed Sequence Tags and developed Simple Sequence Repeat markers using a cDNA library constructed from cambium and surrounding tissues. In total, 270 primer pairs were designed, and 87 of the corresponding loci showed polymorphism in 16 individuals, with 2–21 alleles per locus and expected heterozygosities ranging from 0.06 to 0.97. EST-SSR markers developed in the present study will be useful for genomic analyses of F. crenata populations.

International audience; Analysis of volatile compounds and gases emitted as smoke at the welding interface during rotational wood dowel welding of a hardwood (beech) and of a softwood (Norway spruce) has shown that the compounds in such a smoke are water vapour, CO2, degradation compounds from wood polymeric carbohydrates and from amorphous lignin, as well as some volatile terpenes, these latter only for the softwood used, Norway spruce. The main carbohydrates contributing to the volatile compounds are xylans for beech and glucomannans for spruce. Numerous compounds, in very small proportions derived from the degradation and rearrangement reactions of lignin, have also been identified. The proportion of CO2 emitted is very low, and neither CO nor methane is emitted due to the relatively low temperature of dowel welding. Experiments at temperature slightly higher than that of dowel welding but prolonged in time have shown that the main component of the smoke produced during welding appears to be water vapour.

National audience

National audience; Establishing mixed species, uneven-aged forests by relying on natural regeneration is increasingly encouraged. Nonethless, it is difficult to achieve in practice particularly when it comes to controlling the composition of regeneration by managing exposure to light. With a view to providing forest managers with guidance, we tracked the growth of 27 regenerations of sessile oak (Quercus petraea (Matt.) Liebl.) or beech (Fagus sylvatica L.) in Ardenne (Belgium) and used a simulator to test the effect of various shelterwood systems on available light for regeneration. One of our conclusions is that exposure to light for the purpose of regeneration can be achieved either by small-scale progressive shelterwood cuts or by thinning from below if the removals justify the latter. However, in some cases, adequate management of light is not enough to guarantee the development of the least shade-tolerant species.; Le traitement en futaie irrégulière et mélangée utilisant la régénération naturelle est de plus en plus encouragé. Pourtant, son application reste délicate notamment lorsqu’il est question de la gestion de l’éclairement pour contrôler la composition de la régénération. Afin d’apporter de nouveaux points de repères aux gestionnaires forestiers, nous avons suivi la croissance de 27 régénérations de Chêne sessile (Quercus petraea (Matt.) Liebl.) ou de Hêtre (Fagus sylvatica L.) en Ardenne (Belgique) et utilisé un simulateur pour tester l’effet de différentes modalités de coupes sur l’éclairement disponible pour la régénération. Nous en concluons notamment que l’éclairement disponible pour la régénération peut aussi bien s’effectuer en ouvrant de petites trouées ou avec des coupes par le bas si l’intensité du prélèvement est adaptée. Cependant, dans certains cas, une bonne gestion de l’éclairement n’est pas une condition suffisante pour garantir le développement de l’espèce la moins tolérante à l’ombre.

International audience; In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66% of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver .r (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary to cause failure was measured. The energy (Efail) required to break or uproot a tree was then calculated. Most .r trees failed in the stem and spruce usually failed through uprooting. Beech was either uprooted or broke in the stem and was twice as resistant to failure as .r, and three times more resistant than spruce. Efail was strongly related to stem diameter in European beech only, and was signi.cantly higher in this species compared to Norway spruce. Results suggest that beech would be a better species to plant with regards to protection against rockfall. Nevertheless, all types of di.erent abiotic stresses on any particular alpine site should be considered by the forest manager, as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches. In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66% of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver .r (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary to cause failure was measured. The energy (Efail) required to break or uproot a tree was then calculated. Most .r trees failed in the stem and spruce usually failed through uprooting. Beech was either uprooted or broke in the stem and was twice as resistant to failure as .r, and three times more resistant than spruce. Efail was strongly related to stem diameter in European beech only, and was signi.cantly higher in this species compared to Norway spruce. Results suggest that beech would be a better species to plant with regards to protection against rockfall. Nevertheless, all types of di.erent abiotic stresses on any particular alpine site should be considered by the forest manager, as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches.

To study the dynamics of pine plantations, three stands were selected, which had matured from a pure pine plantation to a mixed broadleaved-pine forest. Microclimatic conditions inside the stands were monitored: air temperature, soil temperature, air relative humidity and global radiation. A reference station was installed in an open area nearby. Forest cover has a weak effect on temperatures: air and soil temperatures are warmer in the mixed broadleaved-pine stand and the coldest under the pine plantation. No difference in relative humidity (h, %) or vapour pressure deficit (D, Pa) was observed across the forest maturing stages, but a strong effect of forest cover in general was observed. Radiation was highly attenuated beneath the canopy and was the most heterogeneous variable between and within stands. These variations were significantly and negatively related to the local basal area or canopy cover; the exact shape of the relationship could not be assessed because of too few spatial data.

International audience; Soil respiration was measured for six years from June 1996 to December 2001 in order to investigate both seasonal and interannual variations in a young beech forest in North Eastern France (Hesse forest). Soil respiration exhibited pronounced seasonal variations that clearly followed the seasonal changes in soil temperature (T) and soil water content (W). An exponential function (y = AWeBT) fitted the data well, and including a linear effect of soil water content on soil respiration strongly improved the predictive capacity of the model. However, the increase in residuals when plotted against the date of measurements clearly evidenced that changes in soil temperature or soil water content failed to predict the increase in soil respiration with time, highlighting that the interannual variation in soil respiration was not solely due to direct climate effects. When fitted against single year data, the temperature sensitivity coefficient (B) was very close for both years while the pre-exponential factor (A) for 1997 was half of those for 2001. The model was further run over the entire data set, allowing A to vary from one year to another. There was a close agreement between predicted and observed soil respiration and A exhibited a linear trend with time with a high value for 1999 after thinning.; Variation interannuelle de la respiration du sol dans une hêtraie au cours de six années de mesure. La respiration du sol a été mesurée pendant six années de juin 1996 à décembre 2001 pour analyser les variations saisonnières et interannuelles dans une jeune hêtraie du nord-est de la France (forêt de Hesse). La respiration du sol montrait des variations saisonnières marquées, reflétant clairement les changements saisonniers de la température (T) et du contenu en eau du sol (W). Une fonction exponentielle (y = AWeBT) s'ajustait correctement sur les données, et le fait d'inclure un effet linéaire du contenu en eau du sol augmentait considérablement les capacités prédictives du modèle. Néanmoins, l'augmentation des résidus lorsqu'ils étaient tracés en fonction de la date de mesure montrait clairement que les changements de température et de contenu en eau du sol ne permettaient pas de prédire les variations de respiration du sol au cours du temps, soulignant le fait que les variations interannuelles de la respiration du sol n'étaient pas uniquement dues à des effets directs du climat. Lorsqu'ils étaient ajustés sur les données d'une seule année, le coefficient de sensibilité à la température (B) était très proche pour les deux années de mesures alors que le facteur pré-exponentiel (A) était deux fois plus faible en 1997 qu'en 2001. Lorsque le modèle est appliqué sur l'ensemble du jeu de données, en permettant à A de varier d'une année sur l'autre, la respiration prédite était très proche de la respiration mesurée, et A montrait une augmentation linéaire avec le temps, avec une valeur élevée en 1999 après une éclaircie.

International audience; The effects of shading levels, comparable to the light quantity and quality below the canopy of a Norway spruce (Picea abies [L.] Karst.) stand on one year old European beech (Fagus sylvatica L.) and pendunculate oak (Quercus robur L.) were tested. The treatments were: shading of plants exposed to "natural shade" by using green synthetic nets (PAR reduced to 32.6%, R/FR-ratio 1.04), shading of plants exposed to "neutral shade" by using black nets (PAR reduced to 24.7%, R/FR-ratio 1.13), no shading (control, PAR 100%, R/FR-ratio 1.15). Beech seedlings showed a strong decrease in height, diameter, stem-, branch-, leaf- and root dry mass with decreasing light quantity. Neither growth rates nor total yield indicated an impact of slightly changed light quality (R/FR-ratio 1.04) on growth and biomass partitioning of beech. Relative growth rate of the main stem dry mass of oak was considerably higher for the seedlings of the shade treatment with the reduced R/FR-ratio than for the control and the other shade treatment whereas branch dry biomass exposed to changed light quantity and quality was reduced disproportional, resulting in the lowest branch-stem-ratio. The tallest oak seedlings were found under the green nets (treatment with reduced light quantity and quality), whereas the control showed the shortest seedlings.; Répartition de la croissance et de la biomasse de plants de Fagus sylvatica L. et de Quercus robur L. soumis à ombrage et à de faibles changements du rapport R/FR de radiation. On a testé l'effet sur des plants de un an de hêtre (Fagus sylvatica L.) et de chêne pédonculé (Quercus robur L.) de différents niveaux d'ombrage, reproduisant les conditions de lumière en quantité et qualité d'un couvert de peuplement d'épicéa (Picea abies Karst.). Les traitements furent les suivants : plants soumis à une "ombre naturelle" en utilisant des filets synthétiques verts (réduction du PAR à 32,6 %, rapport R/FR 1,04) ; plants soumis à une "ombre neutre", en utilisant des filets noirs (réduction de PAR à 24,6 %, rapport R/FR 1,13) ; pas d'ombrage (témoin PAR 100 %, rapport R/FR 1,15). Pour les plants de hêtre, la réduction de la quantité de lumière s'est traduite par une forte diminution de la hauteur et du diamètre, ainsi que du poids sec des tiges, branches, feuilles et racines. Un faible changement de la qualité de la lumière (rapport R/FR de 1,04) n'a pas d'effet sur la croissance et la répartition de la biomasse. En ce qui concerne les plants de chêne, la croissance en matière sèche de la tige principale est proportionnellement plus élevée pour le traitement ombrage avec rapport R/FR réduit que pour le témoin ou l'autre traitement d'ombrage. Un changement en quantité et qualité de la lumière induit donc une réduction du rapport branche/tige. On obtenait les plants de chêne les plus grands sous filet vert (traitement avec réduction en quantité et qualité de la lumière) alors que les plus petits étaient dans le témoin.

Master

This stage took place in the LERMaB and among the CoolWood project that aims to develop an innovative process of log preservation at low temperatures. Yet, there are only few studies on drying wood at such temperatures. This internship aimed to characterize the migration of vapor water among the bark of three trees : spruce (Picea abies), oak (Quercus ) and beech (Fagus sylvatica), and also to study the drying of little spruce logs with or without bark at temperatures around 10°C. A 1m3 cooling chamber has been used, a humidifier built during this study within, for the drying experiments. The sorption isotherms of each species' bark are relatively close. The diffusion coefficients of water vapor in the bark are in the order of 10-13m²/s for spruce, and 10-11m²/s for oak. The reduced diffusivities of bark are in order of 10-8 for spruce and for 10-6 oak. Those coefficients have not been estimated for beech bark. The drying of spruce logs is possible yet slow; it can be accelerated if the bark is removed. The extrapolation of the results to simulate drying of entire logs could be done with the TransPore code.; Ce stage a été réalisé au sein du LERMaB et s'inscrit dans le projet CoolWood qui vise à développer un procédé innovant de préservation des grumes à basses température. Or, il existe très peu d'études sur le séchage du bois à de telles températures. Le but de ce stage était la caractérisation de la migration de la vapeur d'eau au travers de l'écorce de trois essences : l'épicéa (Picea abies), le chêne (Quercus) et le hêtre (Fagus sylvatica), ainsi que l'étude de la cinétique de séchage de petits billons d'épicéa avec ou sans écorce à des températures autour de 10°C. Une enceinte réfrigérante de 1m3 pourvue d'un humidificateur construit durant ce stage a été utilisée pour les expériences de séchage. Les isothermes de sorption de l'écorce de chacune des trois essences testées sont relativement similaires. Les coefficients de diffusion de la vapeur d'eau dans l'écorce sont d'un ordre de grandeur de 10-13m²/s pour l'épicéa et de 10-11m²/s pour le chêne. L'ordre de grandeur des diffusivités réduites sont de 10-8 pour l'épicéa et de 10-6 pour le chêne. Ces coefficients n'ont pas été estimés pour l'écorce de hêtre. Le séchage des billons d'épicéa est possible, quoique lent; il peut être accéléré en écorçant l'échantillon. L'extrapolation des résultats afin de simuler le séchage de grumes entières pourra se faire grâce au code TransPore.

Nitrogen ( N) is an essential element for plants but is limited in most forest ecosystems. The main source of N for trees comes from the decomposition of litter. The fate of litter N on the long term (ten years) in beech forest was followed using one cohort of litter enriched in nitrogen-15 (15N) in ten sites in Europe. 15N in the soil profile showed a low incorporation of litter-derived N deeper than 10 cm. Leaf 15N dynamics illustrate the litter N availability and then its stabilization in the soil aggregates.The use of litter derived N in the tree depends on the needs of N by trees but also on the type of humus. At moder humus sites, trees are able to mine the litter-derived N directly from the organic horizon. Approximately 25 % of the total N requirement of the trees are covered by the N reallocation, and 75 % comes from soil N uptake., L’azote (N) est un élément indispensable pour les végétaux mais reste limitant dans la majorité des écosystèmes forestiers. La source principale de N pour les arbres provient de la décomposition des litières. Afin d’étudier le devenir du N des litières dans l’écosystème forestier, une expérience de marquage d’une cohorte de litière enrichie en azote 15 (15N) a été mise en place dans dix hêtraies européennes. Sur le moyen terme (une décennie), les profils 15N dans le sol montrent une faible incorporation du marqueur en profondeur (>10cm). Dans les feuilles, la dynamique d’incorporation du 15N par l’arbre témoigne de la mise à disposition du N des litières puis de sa stabilisation dans les agrégats du sol. L’utilisation du N dérivé des litières par l’arbre dépend des besoins en N des arbres mais aussi du type d’humus. Les arbres sous moder sont capable d’utiliser le N dérivé des litières directement depuis l’horizon organique. Environ 25 % des besoins totaux en N de l’arbre sont couverts par la réallocation du N, et 75 % sont issus du prélèvement du N dans le sol.

Nowadays, adhesively reconstituted products made of beech timber appear to be of increasing interest for structural purposes due to its high strength/stiffness properties as compared to the most soft-wood species. Furthermore, beech timber is not recognized by most standards for structural uses and restricted to service class 1 and only the furniture, interior joinery and do-it-yourself sectors are still the major users. The French market shows great increasing imports of adhesively reconstituted structural products from Germany and Austria. Moreover, the use of local species, like beech, for the production of reconstituted structural elements could be better for the carbon balance, since it reduces import transportation. However, despite the high mechanical performance of beech timber, adhesively reconstituted products need to meet some requirements, such as the performance of finger-joints. This thesis presents experimental and numerical approaches to deal with the mechanical behaviour of adhesively reconstituted beech beams, for structural purposes. Two-layer and three-layer beams with or without finger-joints have been considered and successfully studied. In addition, a parametrical study has been undertaken to study the influence of several parameters on the mechanical resistance of finger-joints. We, finally, proposed an optimization of the finger-jointing geometry in order to increase the resistance of finger-joints, Les produits structuraux (poutres, poteaux…etc) en bois de hêtre reconstitué par collage, notamment le Bois Massif Reconstitué (BMR) présentent un fort potentiel tant au niveau de la performance mécanique que de la ressource disponible par comparaison aux essences résineuses. Par ailleurs, les normes européennes actuelles sont rédigées pour les essences résineuses et l’usage du bois de hêtre en structures est limité à la classe de service 1 et aux produits d’intérieur et d’ameublement. Le marché français montre une forte augmentation de l’importation de produits structuraux en bois reconstitué par collage, principalement d’Allemagne et d’Autriche. Au-delà du potentiel de résistance mécanique du hêtre, son utilisation comme bois d’œuvre contribuera positivement au bilan carbone pour l’environnement, par la réduction des transports des bois d’importation. Cependant, pour un usage structural, les produits en hêtre reconstitué par collage nécessitent de passer par une évaluation de leur performance, notamment la fiabilité des aboutages. Cette thèse présente une méthodologie expérimentale et numérique permettant l’analyse du comportement mécanique des poutres en BMR. La démarche a été appliquée avec succès dans le cadre de poutres constituées de 2 à 3 lamelles avec ou sans aboutages. Dans ce contexte, nous avons également réalisé une étude paramétrique pour étudier l’influence de plusieurs paramètres sur la résistance des aboutages. En fin, nous avons formulé le problème d’optimisation de la géométrie de l’enture multiple afin d’augmenter la résistance des aboutages et donc la résistance globale des poutres en BMR

National audience; Régénérer naturellement le chêne apparaît très délicat en Ardenne et cela se traduit déjà par un déficit marqué de jeunes chênes au niveau régional. Afin de rechercher des solutions sylvicoles à ce problème, vingt-sept régénérations naturelles de hêtre et de chêne ont été suivies entre 2007 et 2011. L’analyse montre clairement les besoins en lumière des chênes par rapport aux hêtres et, surtout, l’importance d’effectuer des nettoiements afin de réduire les effets de la compétition des hêtres sur les chênes.

Nitrogen ( N) is an essential element for plants but is limited in most forest ecosystems. The main source of N for trees comes from the decomposition of litter. The fate of litter N on the long term (ten years) in beech forest was followed using one cohort of litter enriched in nitrogen-15 (15N) in ten sites in Europe. 15N in the soil profile showed a low incorporation of litter-derived N deeper than 10 cm. Leaf 15N dynamics illustrate the litter N availability and then its stabilization in the soil aggregates.The use of litter derived N in the tree depends on the needs of N by trees but also on the type of humus. At moder humus sites, trees are able to mine the litter-derived N directly from the organic horizon. Approximately 25 % of the total N requirement of the trees are covered by the N reallocation, and 75 % comes from soil N uptake., L’azote (N) est un élément indispensable pour les végétaux mais reste limitant dans la majorité des écosystèmes forestiers. La source principale de N pour les arbres provient de la décomposition des litières. Afin d’étudier le devenir du N des litières dans l’écosystème forestier, une expérience de marquage d’une cohorte de litière enrichie en azote 15 (15N) a été mise en place dans dix hêtraies européennes. Sur le moyen terme (une décennie), les profils 15N dans le sol montrent une faible incorporation du marqueur en profondeur (>10cm). Dans les feuilles, la dynamique d’incorporation du 15N par l’arbre témoigne de la mise à disposition du N des litières puis de sa stabilisation dans les agrégats du sol. L’utilisation du N dérivé des litières par l’arbre dépend des besoins en N des arbres mais aussi du type d’humus. Les arbres sous moder sont capable d’utiliser le N dérivé des litières directement depuis l’horizon organique. Environ 25 % des besoins totaux en N de l’arbre sont couverts par la réallocation du N, et 75 % sont issus du prélèvement du N dans le sol.

Radial variations in wood mineral element concentrations (N, P, Ca, Mg, K, Mn, Al) were investigated in 5 oak trees (a ring-porous species with typical heartwood) and 5 beech trees (a diffuse-porous to semi-ring porous wood species lacking typical heartwood) growing on an ochreous brown earth in the Belgian Ardennes. Differences in concentration profiles were consistent with the difference in wood structure. Specifically, oak had markedly higher concentrations in sapwood, suggesting that nutrients are actively resorbed from senescing wood rings, resulting in very low elemental concentrations in heartwood. Similarities between the two species, including outwardly decreasing cation concentrations and a recent increase in Al concentration, might be ascribed to a common environmental influence, i.e. soil leaching by acid rain. However, the decrease in Mn concentration in both species is not consistent with a scenario of decreasing soil pH. Alternative explanations are discussed., info:eu-repo/semantics/published