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The development of a sustainable wood energy chain is an essential part of ecological and energy transition in Reunion Island (Indian Ocean), where Acacia mearnsii is the main potential wood energy resource identified to date. In order to assess future wood biomass supply chain strategies, a major first issue is to gain knowledge of the spatial distribution of this species forest stands.In this study, we assessed the potential of very high spatial resolution multispectral imagery for mapping the main forest stands in a study area located the Western Highlands region, where Acacia mearnsii expands alongside Acacia heterophylla, an endemic forest species and Cryptomeria japonica, an exotic forest stand. A reference database including 150 samples of seven classes (Acacia mearnsii (mature and non-mature), Acacia heterophylla (mature and non-mature), Cryptomeria japonica, ‘herbaceous areas’, and ‘bare soils’) was used to classify a Pleiades image acquired in May 2020. Spectral and textural indices were used in an incremental classification procedure using a random classifier.The best results (Kappa = 0.84, global accuracy = 84%) were obtained for the classification using all spectral and textural bands. The resulting map enables analyzing the spatial distribution of the different forest stands.

Forest-wood sector is a strategic sector for the mitigation of climate change, in particular through the production of fuelwood. However, the intensive harvesting of biomass can lead to a loss of forest soil fertility in the long term. The thesis work focuses on the sustainability of energy wood harvesting with (1) an environmental component, which concerns the assessment of nutrient returns by leaching during the pre-drying period, the characterization of exported biomass as well as the evaluation of dead wood on the ground (2) an economic component with an assessment of the economic impacts of a potential drop in productivity and their highlighting with the possible choices of cutting and silvicultural treatments.The Pre-drying operation of the trees proved to be unsatisfactory for an optimal return of nutrients contained in leaves and twigs. More than half of the nutrients remain exported from the forest after three months of pre-drying. The volumes of dead wood left on forests to maintain soil fertility and biodiversity were low (, La filière forêt-bois est un secteur stratégique pour l’atténuation des changements climatiques, notamment grâce à la production du bois-énergie. Toutefois, les récoltes intensives de biomasse peuvent induire à une perte de fertilité des sols forestiers sur le long terme. Le travail de thèse s’articule autour de la durabilité de la récolte de bois-énergie avec (1) un volet environnemental, qui concerne la quantification des retours d’éléments minéraux via la lixiviation pendant la phase de réessuyage, la caractérisation de la biomasse exportée ainsi que l’évaluation des bois morts au sol (2) un volet économique avec une évaluation des impacts économiques d’une potentielle baisse de productivité et leur mise en relief avec les choix possibles de coupe et de traitement sylvicoles.Le réessuyage des arbres s'est avéré insatisfaisant pour un retour optimal de nutriments contenus dans les feuilles et brindilles. Plus de la moitié de nutriments reste exportée de la forêt après trois mois de réessuyage. Les volumes de bois morts permettant de maintenir la fertilité des forêts et leur biodiversité étaient faibles (

International audience; Renewables’ industries position themselves at the heart of ecological transition strategies to justify their territorial insertion. This has not, however, protected them from criticism ongrounds of sustainability. Indeed, the government of these industries has come under attack, with opponents saying that industry actors have failed to address critical interdependencies necessary for sustainability to be achieved, including territorial ones. In this context, this article questions the functional argument of “spatial fit”, used by some analysts of ecological transition to explain the choice of regulatory scale. We do this by examining how actors use territorialresources to politicize the environmental government of these industries. Three case-studies are compared: salmon in Scotland, wind power in Quebec and wood energy in France. We show that the “spatial fit”, argument neither explains governing choices nor is sufficient for actors seeking to build legitimate regulation.; À l’heure de la » transition écologique », les industries qui misent sur des ressources renouvelables pour légitimer leur implantation dans de nouveaux territoires n’échappent pas à une critique sur leur durabilité. Les modalités mises en œuvre pour gouverner ces industries sont souvent attaquées, non seulement au nom d’interdépendances mal prises en compte qui mettraient en péril la durabilité, mais aussi au nom de valeurs. L’article s’interroge sur le lienfonctionnel entre l’échelle de régulation et l’enjeu à gouverner, et sur les autres sources de légitimité de la régulation, notamment institutionnelles et territoriales. Trois études de cas sont comparées : les saumons en Écosse, l’éolien au Québec et le bois énergie en France. Nous montrons à partir de ces trois exemples que l’argument fonctionnaliste ne suffit pas pour expliquer le choix des acteurs et n’est pas déterminant dans la construction d’une régulationlégitime.

International audience; Renewables’ industries position themselves at the heart of ecological transition strategies to justify their territorial insertion. This has not, however, protected them from criticism ongrounds of sustainability. Indeed, the government of these industries has come under attack, with opponents saying that industry actors have failed to address critical interdependencies necessary for sustainability to be achieved, including territorial ones. In this context, this article questions the functional argument of “spatial fit”, used by some analysts of ecological transition to explain the choice of regulatory scale. We do this by examining how actors use territorialresources to politicize the environmental government of these industries. Three case-studies are compared: salmon in Scotland, wind power in Quebec and wood energy in France. We show that the “spatial fit”, argument neither explains governing choices nor is sufficient for actors seeking to build legitimate regulation.; À l’heure de la » transition écologique », les industries qui misent sur des ressources renouvelables pour légitimer leur implantation dans de nouveaux territoires n’échappent pas à une critique sur leur durabilité. Les modalités mises en œuvre pour gouverner ces industries sont souvent attaquées, non seulement au nom d’interdépendances mal prises en compte qui mettraient en péril la durabilité, mais aussi au nom de valeurs. L’article s’interroge sur le lienfonctionnel entre l’échelle de régulation et l’enjeu à gouverner, et sur les autres sources de légitimité de la régulation, notamment institutionnelles et territoriales. Trois études de cas sont comparées : les saumons en Écosse, l’éolien au Québec et le bois énergie en France. Nous montrons à partir de ces trois exemples que l’argument fonctionnaliste ne suffit pas pour expliquer le choix des acteurs et n’est pas déterminant dans la construction d’une régulationlégitime.

International audience; Since 2009 wood stumps are considered as one of the recognized sources of biomass to be used in the process of national energy transition in France. So far, stump harvesting has only been implemented in the Landes area in the southwestern part of the country. The aim of this paper is to identify the mechanisms underpinning this innovation. For this we used an analytical framework inspired by Science and Technology Studies. We show how the local pulp and paper industry has ensured the safety of its own supply agendas by promoting adjustments to renewable energy policies. These same firms took advantage of the two major storms which occurred in 1999 and 2009. Our study traces the development of a “local”wood energy policy aimed at consolidating well established firms and intensifying silvicultural management practices, which raise a number of questions regarding the true potential for energy transition gained from such a system; En France, les souches forestières font désormais partie des gisements de biomasse ligneuse identifiés pour contribuer à la transition énergétique. Mais la récolte de cette partie basse et souterraine des arbres est pour l'instant limitée à la forêt cultivée des Landes de Gascogne. Cet article se propose d'analyser les ressorts de cette innovation territoriale en mobilisant un cadre analytique et méthodologique issu du champ « sciences, technologies et société (STS) ». Les auteurs montrent ainsi que la valorisation de cette nouvelle ressource est portée par des industries de la filière bois-papier soucieuses de préserver leurs matières premières usuelles et d'ajuster le développement des politiques de soutien aux énergies renouvelables. Ils soulignent aussi que ce travail d'innovation a bénéficié du concours inattendu mais décisif de deux tempêtes majeures (1999 et 2009). Leur analyse dévoile in fine la construction d'une politique « locale » du bois-énergie qui, orientée vers le renforcement d'industries déjà bien établies et l'intensification des pratiques sylvicoles, questionne les potentialités associées à la transition énergétique.

As part of the AGATCO ANR project (Turbine Advance GAz for cogeneration), which began at the end of 2012, the design of a micro-cogeneration generating 1.5 kW of electricity and 10 kW of heat was started and presented in this manuscript. Based on the technology of an externally fired gas turbine, this micro-CHP uses the combustion of pellets coupled to a heat exchanger and a micro-turbine. This technology requires the design of a new fireplace (burner and combustion chamber) suitable to produce fumes at high temperatures (1200°C). The challenge is significant because the desired smoke flow is important (27 g/s) and the fuel power is low (15 kW). Two solutions are proposed to solve the problem, the first uses fresh air at ambient temperature and the second uses recycled hot fumes. The high temperature of the fumes makes it possible to obtain a turbine inlet temperature of 1100°C after the transfer of heat into the exchanger. Experimental and numerical simulation characterization of the exchanger makes it possible to verify its performances. The micro-turbine uses a new technology using channel instead of blades allowing it to have small dimensions for the desired performance. The work carried out made it possible to highlight several results: the realization of the high temperature combustion in very unfavorable conditions, the very interesting performances of the heat exchanger while proposing improvements to optimize the exchanges and the improvements to be brought to the turbine; Dans le cadre du projet ANR AGATCO (Advance GAz Turbine for COgeneration) qui a débuté fin 2012, la conception d’un micro-cogénérateur aux granulés de bois permettant de produire 1,5 kW électrique et 10 kW thermique a été entrepris et est présentée dans ce manuscrit. Basé sur la technologie d’une turbine à air chaud à combustion externe, ce micro-cogénérateur utilise la combustion des granulés couplés à un échangeur de chaleur et une micro-turbine. La technologie demande la conception d’un nouveau foyer (brûleur et chambre de combustion) adapté pour la production de fumées à haute température (1200°C). Le défi est grand car le débit de fumées souhaité est important (27g/s) et la puissance de combustible est faible (15kW). Deux solutions sont proposées pour répondre à la problématique, la première utilise de l’air frais à température ambiante et la deuxième utilise le recyclage des fumées chaudes. La haute température des fumées permet d’obtenir une température d’entrée turbine de 1100°C après le transfert de chaleur dans l’échangeur. La caractérisation expérimentale et par simulation numérique de l’échangeur permet de vérifier ses performances. La micro-turbine utilise une technologie nouvelle de canaux hélicoïdaux à la place d’aubes qui lui permettent d’avoir des dimensions faibles pour les performances souhaitées. Les travaux effectués ont permis de mettre en valeur plusieurs résultats : la réalisation de la combustion haute température dans des conditions fortement défavorables, les performances très intéressantes de l’échangeur de chaleur tous en proposant des améliorations pour optimiser les échanges et les améliorations à apporter à la turbine

As part of the AGATCO ANR project (Turbine Advance GAz for cogeneration), which began at the end of 2012, the design of a micro-cogeneration generating 1.5 kW of electricity and 10 kW of heat was started and presented in this manuscript. Based on the technology of an externally fired gas turbine, this micro-CHP uses the combustion of pellets coupled to a heat exchanger and a micro-turbine. This technology requires the design of a new fireplace (burner and combustion chamber) suitable to produce fumes at high temperatures (1200°C). The challenge is significant because the desired smoke flow is important (27 g/s) and the fuel power is low (15 kW). Two solutions are proposed to solve the problem, the first uses fresh air at ambient temperature and the second uses recycled hot fumes. The high temperature of the fumes makes it possible to obtain a turbine inlet temperature of 1100°C after the transfer of heat into the exchanger. Experimental and numerical simulation characterization of the exchanger makes it possible to verify its performances. The micro-turbine uses a new technology using channel instead of blades allowing it to have small dimensions for the desired performance. The work carried out made it possible to highlight several results: the realization of the high temperature combustion in very unfavorable conditions, the very interesting performances of the heat exchanger while proposing improvements to optimize the exchanges and the improvements to be brought to the turbine, Dans le cadre du projet ANR AGATCO (Advance GAz Turbine for COgeneration) qui a débuté fin 2012, la conception d’un micro-cogénérateur aux granulés de bois permettant de produire 1,5 kW électrique et 10 kW thermique a été entrepris et est présentée dans ce manuscrit. Basé sur la technologie d’une turbine à air chaud à combustion externe, ce micro-cogénérateur utilise la combustion des granulés couplés à un échangeur de chaleur et une micro-turbine. La technologie demande la conception d’un nouveau foyer (brûleur et chambre de combustion) adapté pour la production de fumées à haute température (1200°C). Le défi est grand car le débit de fumées souhaité est important (27g/s) et la puissance de combustible est faible (15kW). Deux solutions sont proposées pour répondre à la problématique, la première utilise de l’air frais à température ambiante et la deuxième utilise le recyclage des fumées chaudes. La haute température des fumées permet d’obtenir une température d’entrée turbine de 1100°C après le transfert de chaleur dans l’échangeur. La caractérisation expérimentale et par simulation numérique de l’échangeur permet de vérifier ses performances. La micro-turbine utilise une technologie nouvelle de canaux hélicoïdaux à la place d’aubes qui lui permettent d’avoir des dimensions faibles pour les performances souhaitées. Les travaux effectués ont permis de mettre en valeur plusieurs résultats : la réalisation de la combustion haute température dans des conditions fortement défavorables, les performances très intéressantes de l’échangeur de chaleur tous en proposant des améliorations pour optimiser les échanges et les améliorations à apporter à la turbine

International audience; This chapter explores the role of spatiality and how it is constructed in energy transition processes. Space is part of different operations for channelling, assessing and controlling material flows to turn them into energy resources and ensure a predictable production. The chapter proposes the idea of a ‘politics of volumes’ to describe how an energy volume is calculated, delineated and controlled, how sharing it and living together within it is made possible, and how it is (re-)configured when being connected to a pre-existing large sociotechnical assemblage (such as an electrical grid). These explorations offer new insights about the strategic combinations of energy and non-energy volumes, the influence of social and spatial heritage in the making of energy volumes, and the power relationships at work.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM [ADD1_IRSTEA]Bioéconomie territoriale; International audience; Energy transition is fundamentally acknowledged as a geographical process that happens in particular places, transforms landscape features, produces uneven development and, more generally, entails reconfiguring current spatial patterns of economic and social activities. The way in which spatial processes shape new energy technologies and influence their capacity for transformation, however, has rarely been a focus of analyses. To investigate further the role of space in the energy transition, this chapter proposes to take into account the diffuse materiality of renewable energy resources. Our aim is to contribute to an emerging agenda about the spatialities of energy resources and their political issues at the crossroad of materiality and space. The chapter is divided into four sections. The first briefly presents the field of the geography of energy resources and explains the approach of renewable energy resources as a 'turbulent' materiality. The second proposes theoretical elements inspired by works on the vertical dimension of space to study the processes through which space is configured as a manageable 'volume' for controlling energy material flows. The third examines five case studies from France, Germany and Tunisia. Finally, a discussion about emerging politics of 'volume' in the energy transition aims at providing a critical geographical appraisal of the current development of renewable energies

International audience; Since 2009 wood stumps are considered as one of the recognized sources of biomass to be used in the process of national energy transition in France. So far, stump harvesting has only been implemented in the Landes area in the southwestern part of the country. The aim of this paper is to identify the mechanisms underpinning this innovation. For this we used an analytical framework inspired by Science and Technology Studies. We show how the local pulp and paper industry has ensured the safety of its own supply agendas by promoting adjustments to renewable energy policies. These same firms took advantage of the two major storms which occurred in 1999 and 2009. Our study traces the development of a “local”wood energy policy aimed at consolidating well established firms and intensifying silvicultural management practices, which raise a number of questions regarding the true potential for energy transition gained from such a system; En France, les souches forestières font désormais partie des gisements de biomasse ligneuse identifiés pour contribuer à la transition énergétique. Mais la récolte de cette partie basse et souterraine des arbres est pour l'instant limitée à la forêt cultivée des Landes de Gascogne. Cet article se propose d'analyser les ressorts de cette innovation territoriale en mobilisant un cadre analytique et méthodologique issu du champ « sciences, technologies et société (STS) ». Les auteurs montrent ainsi que la valorisation de cette nouvelle ressource est portée par des industries de la filière bois-papier soucieuses de préserver leurs matières premières usuelles et d'ajuster le développement des politiques de soutien aux énergies renouvelables. Ils soulignent aussi que ce travail d'innovation a bénéficié du concours inattendu mais décisif de deux tempêtes majeures (1999 et 2009). Leur analyse dévoile in fine la construction d'une politique « locale » du bois-énergie qui, orientée vers le renforcement d'industries déjà bien établies et l'intensification des pratiques sylvicoles, questionne les potentialités associées à la transition énergétique.

Because of its energy and mechanical properties, babassu shell is a promising energy crop for the future. Its production potential in Brazil is estimated at 6.8 million tons of fruits/year. The aim of this study was to evaluate the effects of torrefaction on the main energy and mechanical properties of Orbignya speciosa (Babassu). Three different torrefaction temperatures (220, 250, and 280°C) and two different durations (15 and 30 minutes) were employed. The influence of sample orientation was taken into account. The results showed that the energy properties of babassu are greatly improved during heat treatment. Torrefaction also led to uniform resistance to babassu shell compression. It was found that low temperature treatment was sufficient to envisage grinding and babassu use in pulverulent form.

Allometric models are necessary for estimating biomass in terrestrial ecosystems. Generalized allometric relationship exists for many tropical trees, but species- and region-specific models are often lacking. We developed species-specific allometric models to predict aboveground biomass for 11 native tree species of the Sudanian savannawoodlands. Diameters at the base and at breast height, with species means ranging respectively from 11 to 28 cm and 9 to 19 cm, and the height of the trees were used as predictor variables. Sampled trees spanned a wide range of sizes including the largest sizes these species can reach. As a response variable, the biomass of the trees was obtained through destructive sampling of 4 754 trees during wood harvesting. We used a stepwise multiple regression analysis with backward elimination procedure to develop models separately predicting, total biomass of the trees, stem biomass, and biomass of branches and twigs. All speciesspecific regression models relating biomass with measured tree dimensions were highly significant (p < 0.001). The biomass of branches and twigs was less predictable compared to stem biomass and total biomass, although their models required fewer predictors and predictor interactions. The best-fit equations for total above-ground biomass and stem biomass had R2 > 0.70, except for the Acacia species; for branches including twig biomass, R2-values varied from 0.749 for Anogeissus leiocarpa to 0.183 for Acacia macrostachya. The use of these equations in estimating available biomass will avoid destructive sampling, and aid in planning for sustainable use of these species.

International audience; Si les énergies renouvelables offrent des opportunités de développement aux territoires ruraux, leur déploiement dépend d'orientations technologiques, économiques et politiques qui engagent une pluralité d'échelles et fluctuent dans le temps. Afin de questionner leurs modalités de territorialisation, cet article propose de suivre les assemblages construits autour du bois-énergie en Aquitaine. Inspirée des approches sociotechniques, la grille d'analyse permet d'appréhender la persistance de trajectoires de développement diversifiées plus de trente ans après les premières initiatives. Elle souligne le rôle des héritages territoriaux dans le dimensionnement des projets mais aussi la fragilité de certaines expériences rurales face à l'emprise croissante des référentiels énergétiques. Au final, elle invite à définir les territoires de l'énergie comme des ensembles instables naviguant entre processus de stabilisation et redéfinition de leurs contours et composants.

Climate changes result in hydrological cycle alterations, with impacts on distribution and quantity of rainfall affecting forest plantations in the tropics and subtropics. Trees minimize water stress effects by leaf osmotic adjustments which are dependent on K ions. Eucalyptus plantations were established in tropical and subtropical soils especially poor in K. Fertilization by substitution of K by Na is a potential alternative way, at lower cost and greater availability, that is especially suitable for smallholder plantations. For these reasons, we studied respective K and Na fertilization effects on growth and basic wood density of Eucalyptus grandis plantations with different objectives (domestic energy, timber). Significant differences in volume of trunk and wood density were observed on 8-year-old E. grandis trees fertilized with Na vs. K and the control. Trees with Na fertilization showed a significantly higher volume with Na vs. the control and a lower volume vs. K. Wood density and radial variability were significantly lower compared to trees with K and the control. In this paper we discuss the advantages of Na fertilization both to minimize the drought stress effect due to global climate change and to optimize economically the wood production of smallholder plantations. (Texte intégral)

Eucalyptus is the most widely planted species in Madagascar. Eucalyptus robusta is the most common species (225 000 ha) because it is well adapted and has multipurpose wood uses (energy, pole, and timber). Although this species has been naturalized for more than a century, little is known about the introduced genetic diversity. Previous research leads us to assume that it has a narrow genetic base. A study of genetic variability and genotype by environment interaction for E. robusta growth was therefore conducted. This study concerns two provenance trials (24 provenances from Australia, 1 from Madagascar) and three progeny trials established in two bioclimatic regions, regularly monitored for >10 years. In both sites, results showed strong provenance effects and genotype by environment interactions for growth. However, the Malagasy provenance was the poorer performer for growth, compared to the Australian. This could be attributed to its origin, mainly to inbreeding depressions due to the narrow genetic base introduced. Due to climate change, this low diversity, which will be confi rmed by ongoing molecular genetic studies, may represent biological and economical risks. These will help forest managers to capitalize on the genetic resources existing in Madagascar for a better future. (Texte intégral)