Key message
This study presents a novel histologic approach to quantify the intra-annual dynamics of carbon sequestration in forming wood. This innovative approach, based on repeated measurements of ...xylem apparent density, is more direct, and more accurate than the previously published cellular-based approach. Moreover, this new approach, which was tested here on softwoods, is also applicable to hardwoods without any modification.
Context
Forest ecosystems are key players of the terrestrial carbon cycle. Indeed, wood represents the principal carbon pool of terrestrial biomass, accumulated in trees through cambial activity.
Aims
Here, we present a novel, simple, and fast approach to accurately estimate the intra-annual dynamics of aboveground woody biomass production based on image analysis of forming xylem sections.
Methods
During the 2015 growing season, we weekly collected wood samples (microcores) containing the forming xylem on seven Norway spruces (
Picea abies
(L.) Karst), grown in Hesse forest (North-East France). The microcores were prepared to allow the observation of the forming tissues with an optical microscope. Xylem apparent density and radial increment were then measured directly on images of the histological sections. In order to compare our “histologic approach” with the previously published “cellular approach,” we also counted the number of tracheids in each differentiation zones, and measured the tracheid dimensions all along the last-formed tree ring.
Results
The two approaches yielded comparable meaningful results, describing xylem size increase and aboveground woody biomass production as bell-shaped curves culminating in May and June respectively. However, the histologic approach provided a shorter time lag between xylem size increase and biomass production than the cellular one.
Conclusion
Better quantification of the shift between stem growth in size and in biomass will require addressing the knowledge gap regarding lignin deposition kinetics. Nevertheless, our novel histologic approach is simpler and more direct than the cellular one, and may open the way to a first quantification of intra-annual dynamics of woody biomass production in angiosperms, where the cellular approach is hardly applicable.
Oak (Quercus petraea and Quercus robur), an emblematic species in French forests, has a strong patrimonial value and plays a leading role in the forestry and forest-based industry. However, the ...industry appears to be confronted with major problems (e.g. supply to markets). We tried to better understand and analyse those problems by studying the oak chain in north eastern France (Alsace, Franche-Comté, Lorraine) through interviews conducted with public forest managers and players involved in primary processing. In order to survey a broad range of points of view and have a basis for comparison, the study area also included two Landers in south western Germany (Baden-Wurttemberg, Rhineland-Palatinate). A qualitative analysis of 25 interviews conducted on both sides of the Franco-German border enabled us to identify contrasting views and points of consensus about the issues relating to forest resources, the perception of the sector by the players and the entrepreneurial dynamic. Possible future developments could also be distinguished, some of which are already discussed in the literature while others were particular to this survey.
Le Chêne (Quercus petraea et Quercus robur), essence emblématique de la forêt française, a une valeur patrimoniale forte et joue un rôle majeur dans la filière forêt-bois. Néanmoins, cette filière semble être confrontée à des problèmes importants (par exemple au niveau de l’approvisionnement et des marchés) que nous avons cherché à mieux comprendre et à analyser. Notre étude s’intéresse plus particulièrement à la filière Chêne dans le nord-est de la France (Alsace, Franche-Comté, Lorraine) et se base sur des entretiens réalisés auprès de gestionnaires forestiers publics et d’acteurs de la première transformation. Afin d’obtenir une gamme large de points de vue et de disposer d’éléments de comparaison, la zone d’étude intègre également deux Länder du sud-ouest de l’Allemagne (Bade-Wurtemberg, Rhénanie-Palatinat). L’analyse qualitative de 25 entretiens, réalisés de part et d’autre de la frontière franco-allemande, a permis de dégager des avis divergents et des points de consensus au sujet de thématiques relatives à la ressource forestière, à la perception de la filière par les acteurs et aux dynamiques d’entreprise. Des perspectives d’évolution ont aussi pu être distinguées, comprenant des réflexions déjà évoquées dans la littérature et d’autres plus personnelles à cette étude.
Les écosystèmes forestiers constituent le principal réservoir à long terme de carbone. Toutefois, les dynamiques saisonnières de productions de cette biomasse ligneuse, en relation avec ...l'assimilation du carbone par l'écosystème et les déterminants environnementaux, restent peu étudiées, limitant notre compréhension du cycle du carbone et particulièrement sa sensibilité aux changements actuels du climat. Cette thèse a pour objectif de comprendre les relations entre le processus de séquestration du carbone dans le bois en formation, la physiologie de l’arbre, l’assimilation du carbone par le peuplement, et les conditions environnementales du site. L’étude porte sur trois sites instrumentés d’une tour à flux avec un peuplement constitué principalement par, respectivement l’épicéa à Tharandt en 2016, le hêtre à Hesse en 2015-2017, et le chêne à Barbeau en 2016. La formation du bois a été suivis par prélèvement hebdomadaire de microcarottes contenant, le phloème, le cambium et le xylème en formation sur des arbres dominants sélectionnés dans l’empreinte de mesure de la tour. La productivité primaire brute a été estimée par Eddy-Covariance, et les variables climatiques mesurés grâce aux dispositifs de la tour. En premier, nous avons mis au point une nouvelle approche histologique, plus rapide et plus précise que la méthode précédemment publiée sur les résineux, pour quantifier la dynamique intra-annuelle de la séquestration du carbone dans le bois en formation, basée sur des mesures répétées de la densité apparente du xylème, et applicable également aux angiospermes. Dans le 2nd chapitre, nous avons montré que l’occurrence en même temps du développement de la canopée et de la reprise de l’activité cambiale pouvait ralentir la croissance radiale du xylème, et favoriser la formation d’un xylème à porosité élevée mais rapidement fonctionnel. Dans le 3ème chapitre, nous avons démontré que le plan ligneux détermine la coordination temporelle entre la croissance en taille et en biomasse du tronc au cours de la saison de végétation, la séquestration du carbone dans le bois en formation étant toujours décalée derrière la croissance radiale du tronc due aux processus internes de la xylogenèse, avec une tendance croissance du décalage temporel pour l’épicéa et le hêtre, mais une tendance décroissante chez le chêne. Le 4ème chapitre démontre que indépendamment du peuplement, la dynamique d'assimilation du carbone présentait une courbe en cloche symétrique culminant en Juin, tandis que la dynamique saisonnière de la séquestration du carbone variait entre les 3 espèces. Le peuplement de hêtres a concentré la séquestration du carbone dans le tronc en Mai-Juillet, tandis que les peuplements d'épicéa et de chênes ont plutôt culminé en Juin-Août et ont concentré cette séquestration vers la 2ème partie de la saison de végétation. Dans le 5ème chapitre, grâce à un suivi de trois ans des flux de carbone, de la croissance des arbres, et des facteurs environnementaux dans le peuplement de hêtres matures, nous avons montré que le classement du bilan de carbone annuel n'était pas maintenu d'une année à l'autre, avec l’assimilation de carbone annuel la plus élevée en 2017, mais la production de biomasse ligneuse la plus élevée en 2016. Cela suggère que l'allocation du carbone de l'assimilation à la séquestration dans la tige ne suit pas une simple règle d’allométrie. Enfin, nous avons observé que, parallèlement à la formation d'un nouveau xylème, la teneur en amidon augmentait également durant la formation du bois. Cela suggère que le stockage de carbone et la croissance du tronc étaient étroitement liés, avec une proportion plus importante chez le chêne que chez l’épicéa et le hêtre. Ainsi, cette thèse a permis d'améliorer nos connaissances sur la dynamique de l'allocation du carbone dans l'arbre, de l'assimilation au niveau des feuilles à la séquestration à long terme dans le bois, et d'explorer leur sensibilité respective aux conditions climatiques.
Forest ecosystems are the major and most perennial terrestrial carbon pool. However, the seasonal dynamics of production of this woody biomass, in relation to the ecosystem carbon uptake remain poorly studied, limiting our understanding of the carbon cycle and particularly its sensitivity to current climate changes. This thesis aimed to better understand the underlying process of carbon sequestration within forming wood, as related to tree physiology, stand carbon assimilation and site environmental conditions. The study was conducted on three instrumented site with a flux tower, the stand is dominated respectively by spruce in Tharandt in 2016, by beech in Hesse in 2015-2017, and by oak in Barbeau in 2016. To monitor wood formation, wood samples containing phloem, cambial zone, and developing xylem were collected weekly on dominant trees within the tower footprint. Flux tower measurements were used to estimate the daily GPP of the stand, and record the climatic conditions. In the 1st chapter, we developed a novel histologic approach, to quantify the intra-annual dynamics of carbon sequestration in spruce forming wood. This approach, based on repeated measurements of xylem apparent density, is easier, faster, and more accurate than the previously available method, and is applicable also to angiosperm species. In the 2nd chapter, we showed that simultaneous occurrence of the canopy development and the resumption of cambial activity slowed down xylem radial growth, and might entail the formation of xylem with high porosity but functional at early growing season. In the 3rd chapter, we demonstrated that the tree-ring structure determined the temporal coordination between stem growth in size and in biomass along the growing season, with carbon sequestration in forming wood always lagging behind stem radial growth due to inner processes of xylogenesis. Indeed, we showed an increasing timelag ranging from ten days to nearly one month for spruce and beech, but a decreasing timelag from nearly three to one week for oak trees. In the 4th chapter, we observed that regardless of the stand, carbon assimilation followed a large and symmetric bell curve peaking in June, while seasonal dynamics of carbon sequestration differed among the three species. The beech trees concentrated carbon sequestration in stem in May-July, while the spruce and oak trees rather peaked in June-August, and completed stem growth towards the second part of the growing season. In the 5th chapter, based on a three-year monitoring of carbon fluxes, trees growth and environmental factors in the mature beech stand, we showed that ranking of annual carbon balance was not maintained from one year to another, with higher carbon assimilation during the hottest year, but higher woody biomass production in the wettest year. This suggests that allocation of carbon from assimilation to sequestration in stem is not following a simple allometric rule. In the last chapter, we observed that parallel to formation of a new xylem, starch content also increased in forming wood, suggesting that storage and stem growth were tightly connected along the growing season, with higher allocation to storage for sessile oak, compared to spruce and beech. This thesis has improved our knowledge about the dynamics of carbon allocation in the tree, from assimilation at the leaf level to long-term sequestration into the wood, and allowed to explore their respective sensitivity to climate conditions. A better quantification of the shift between stem growth in size and in biomass will require to disentangle the kinetics of cellulose and lignin deposition. However, our work contributed to a better understanding of the intra-annual dynamics of stem radial growth and carbon sequestration, which could help to improve modelling of forests net primary productivity, in the context of current global warming.
In wood machining operations, target surfaces are chosen to achieve technical functions (gluing, finishing), or aesthetic functions (raw wood, varnishing) in order to produce a surface which ...consumers will appreciate. Although the literature often refers to the optimization of cutting conditions to improve the surface quality, there is currently no specific criterion to define what good surface quality is. The purpose of this study was to investigate quantitative criteria related to consumer preferences and to find an acceptability threshold for each criterion in order to determine the best cutting conditions. To this end, 32 surfaces from
Chrysophilum boivinianum
(Sapotaceae) were machined in various cutting conditions which yielded surfaces ranging from very rough to smooth. The primary surface profile, roughness and waviness parameters, and machining defects (raised grain, torn grain, chip marks, cutting traces) were measured on each surface. Visual and visuo-tactile tests were then carried out with a panel of 174 consumers. The results show that touch allowed better appreciation of surface defects than a simple visual observation. Consumers like smooth surfaces without visible defects and less visible peaks of waviness. The acceptability thresholds of surface parameters correlated with consumer preferences were determined. The rotational speed and the feed speed affect the most the surface quality. To obtain good surface quality for consumers, the rotation speed should be greater than 5000 rpm, with a maximum feed rate per tooth of 0.5 mm, and a maximum average chip thickness of 0.18 mm. This knowledge will help industries to better optimize the cutting of wood.
Key message
In order to record the seasonal changes in aboveground biomass production (trunk and branches) in a forest, changes in wood density must be taken into account. A 60
-
year-old beech ...forest displayed a large intra-annual variability in its aboveground woody biomass production efficiency. This variation followed a seasonal trend with a maximum during the summer while gross primary production was rather low.
Context
In the current context of land use and climate change, there is a need to precisely quantify the carbon (C) balance of forest ecosystems, and more specifically, of C allocation to tree compartments.
Aims
We quantified the seasonal changes in the aboveground biomass production (aBP) of a beech forest growing on two different soils: an alocrisol and a calci-brunisol. In addition, for the alocrisol ecosystem, we assessed the existence and degree of intra-annual variability in the ratio of wood aBP to gross primary production (GPP), i.e., the wood aBP efficiency.
Methods
The study site is a 60-year-old beech forest in northeastern France. An eddy covariance tower records continuously net ecosystem exchange. To investigate the temporal changes in aBP, mini-cores were drilled and diameter at breast height measurements were taken on a monthly basis from 45 trees for both stands studied over 2014.
Results
A clear difference in aBP was observed between the two soils with the alocrisol being more productive than the calci-brunisol. For the alocrisol, both woody aBP and GPP changed over the course of the year, reaching peak values during June (6 and 12.5 gC m
−2
day
−1
, respectively). Wood applied bias photon-to-current efficiency aboveground Biomass Production Efficiency (aBPE) also showed important intra-annual variations, ranging from 0.09 in September to 0.58 in July. Wood density varied throughout the year, and not taking it into account would have led to an overestimation of aBP by as much as 20% in April and May.
Conclusion
Our study highlights the importance of taking wood density into account for intra-annual studies of aBP. Wood aBPE cannot be considered as constant as it fluctuated from 0.09 to 0.58 throughout the year for an annual value of 0.34. The potential error in wood aBPE stemming from not taking these changes into account amounts to 15%.
Oak (Quercus petraea and Quercus robur), an emblematic species in French forests, has a strong patrimonial value and plays a leading role in the forestry and forest-based industry. However, the ...industry appears to be confronted with major problems (e.g. supply to markets). We tried to better understand and analyse those problems by studying the oak chain in north eastern France (Alsace, Franche-Comté, Lorraine) through interviews conducted with public forest managers and players involved in primary processing. In order to survey a broad range of points of view and have a basis for comparison, the study area also included two Landers in south western Germany (Baden-Wurttemberg, Rhineland-Palatinate). A qualitative analysis of 25 interviews conducted on both sides of the Franco-German border enabled us to identify contrasting views and points of consensus about the issues relating to forest resources, the perception of the sector by the players and the entrepreneurial dynamic. Possible future developments could also be distinguished, some of which are already discussed in the literature while others were particular to this survey.
Le Chêne (Quercus petraea et Quercus robur), essence emblématique de la forêt française, a une valeur patrimoniale forte et joue un rôle majeur dans la filière forêt-bois. Néanmoins, cette filière semble être confrontée à des problèmes importants (par exemple au niveau de l’approvisionnement et des marchés) que nous avons cherché à mieux comprendre et à analyser. Notre étude s’intéresse plus particulièrement à la filière Chêne dans le nord-est de la France (Alsace, Franche-Comté, Lorraine) et se base sur des entretiens réalisés auprès de gestionnaires forestiers publics et d’acteurs de la première transformation. Afin d’obtenir une gamme large de points de vue et de disposer d’éléments de comparaison, la zone d’étude intègre également deux Länder du sud-ouest de l’Allemagne (Bade-Wurtemberg, Rhénanie-Palatinat). L’analyse qualitative de 25 entretiens, réalisés de part et d’autre de la frontière franco-allemande, a permis de dégager des avis divergents et des points de consensus au sujet de thématiques relatives à la ressource forestière, à la perception de la filière par les acteurs et aux dynamiques d’entreprise. Des perspectives d’évolution ont aussi pu être distinguées, comprenant des réflexions déjà évoquées dans la littérature et d’autres plus personnelles à cette étude.
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