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Les organisations non gouvernementales, en sigle ONG, sont des acteurs qui ont leur place dans le droit international des changements climatiques au même titre que les Etats et les organisations publiques internationales. Cette place a été conquise à la suite de durs efforts. C'est pourquoi, désormais, ces ONG, grâce à leur participation à l'élaboration des normes environnementales relatives au climat ainsi qu'à leur implication sur le terrain où prévalent les effets de ces changements climatiques, prouvent jour après jour qu'elles ont, dorénavant, un rôle incontournable dans la matérialisation de ce droit .

Tropical forests store more than half of the world's forest carbon and are particularly threatened by deforestation and degradation processes, which together represent the second largest source of anthropogenic CO2 emissions. Consequently, tropical forests are the focus of international climate policies (i.e. UN-REDD Programme) aiming at reducing forest-related CO2 emissions. The REDD initiative lies on our ability to map forest carbon stocks (i.e. spatial dynamics) and to detect deforestation and degradations (i.e. temporal dynamics) at large spatial scales (national, forested basin, global), with accuracy and precision. Remote-sensing is as a key tool for this purpose, but the numerous sources of error along the carbon mapping chain and the lack of sensitivity of traditional remote-sensing data to carbon stock variation in carbon-rich tropical forests makes meeting REDD criteria an outstanding challenge. In the present thesis, we assessed carbon (quantified through aboveground biomass, AGB) estimation error at the tree- and plot-level using a widely used pantropical AGB model, and at the landscape-level using a remote sensing method based on canopy texture features from very high resolution (VHR) optical data. Our objective was to better understand and reduce AGB estimation error at each level using information on large canopy tree structure, distribution and spatial organization.Although large trees disproportionally contributed to forest carbon stock and stock growth, they are dramatically under-represented in destructive datasets and subject to a systematic under-estimation error with the pantropical AGB model. We destructively sampled 77 very large tropical trees and assembled a large (pantropical) dataset to study how variation in tree form (through crown sizes and crown mass ratio) contributed to this error pattern. We showed that the source of bias in the pantropical model was a systematic increase in the proportion of tree mass allocated to the crown in canopy trees. An alternative –unbiased– AGB model accounting for this phenomenon was proposed. We also propagated the pantropical model error at the plot-level while explicitly accounting for this size-dependent systematic error and showed that the interaction between forest structure and AGB model error, although often overlooked, might in fact be substantial. We further analyzed the structural properties of crown branching networks in light of the assumptions and predictions of the Metabolic Theory of Ecology, which supports the power-form of the pantropical AGB model. Important deviations were observed, notably from Leonardo’s rule (i.e. the principle of area conservation), which, all else being equal, could support the higher proportion of mass in large tree crowns.A second part of the thesis dealt with the extrapolation of field-plot AGB via canopy texture features. Canopy texture properties emerge from the size distribution and spatial organization of apparent (canopy) trees in VHR optical data, notably. A major barrier for the development of a broad-scale forest carbon monitoring method based on canopy texture is that relationships between canopy texture and stand structure parameters (including AGB) vary among forest types and regions of the world. We investigated this discrepancy using a simulation approach: virtual canopy scenes were generated for 279 1-ha plots distributed on contrasted forest types across the tropics. We showed that complementing FOTO texture with additional descriptors of forest structure, notably on canopy openness and heterogeneity (from a lacunarity analysis) and tree slenderness (from a bioclimatic stress proxy) allows developing a consistent, steady inversion frame for forest AGB at large scale. Although the approach we proposed requires further empirical validation, a first case study on a forests mosaic in the Congo basin gave promising results. Overall, this work essentially increases our understanding of mechanisms behind AGB estimation errors at the tree-, plot- and landscape-level. It stresses the need to better account for variation patterns in tree structure (e.g. ontogenetic pattern of carbon allocation) and forest structural organization (across forest types, under different environmental conditions) to improve general AGB models, and in fine our ability to accurately map forest AGB at large scale.; Les forêts tropicales séquestrent plus de la moitié du carbone forestier mondial et sontparticulièrement menacées par les processus de déforestation et de dégradation, qui représentent ladeuxième source d’émissions anthropogéniques de CO2. De fait, les forêts tropicales sont au centre depolitiques climatiques internationales (i.e. Reducing emissions from deforestation and forest degradation,REDD) visant à réduire ces émissions. L’initiative REDD repose sur notre capacité à cartographier les stocksde carbone forestier (dynamique spatiale) et à détecter la déforestation et la dégradation (dynamiquetemporelle) à large échelle spatiale (e.g. nationale, bassin forestier), avec exactitude et précision. Dans cecadre, la télédétection apparait comme un outil crucial, mais les nombreuses sources d’erreur dans lachaîne de cartographie du carbone font des objectifs du REDD un challenge ambitieux. Dans cette thèse,nous avons évalué les erreurs associées aux estimations de carbone forestier (quantifié au travers de labiomasse épigée, AGB) (1) aux échelles de l’arbre et du peuplement en utilisant un modèle pantropicallargement employé et (2) à l’échelle du paysage en utilisant une méthode de télédétection basée sur lescaractéristiques texturales d’images optiques à très haute résolution spatiale. Notre objectif général étaitde mieux comprendre et de réduire l’erreur d’estimation de l’AGB à chaque échelle par une meilleure priseen compte de la structure, de la distribution et de l’organisation spatiale des arbres de canopée.Malgré l’importance des grands arbres dans la dynamique du carbone forestier, ils sont sous-représentésdans les jeux de données destructifs et soumis à un biais de sous-estimation dans le modèle d’AGBpantropical. Nous avons assemblé une base de données pantropicale et étudié l’influence de la forme del’arbre sur le patron d’erreur du modèle. Nos résultats montrent que la source de biais du modèle est uneaugmentation de la masse de l’arbre dans la couronne chez les arbres de canopée. Un modèle d’AGBprenant ce phénomène en compte a été proposé. Nous avons aussi propagé le biais du modèle à l’échelledu peuplement et montré que l’interaction entre la structure du peuplement et l’erreur du modèle, qui estsouvent négligée, peut en fait être substantielle. Une analyse des propriétés structurelles des couronnes aégalement été menée au regard des hypothèses de la Théorie Métabolique de l’Ecologie Des déviations ontété observées, notamment à la loi de Léonardo (i.e. principe de conservation des aires), qui, toutes choseségales par ailleurs, pourraient justifier la grande proportion de masse trouvée dans les couronnes desarbres de canopée.Une seconde partie de la thèse porte sur l’extrapolation des estimations d’AGB des parcelles de terrain viales caractéristiques de texture des canopées extraites par transformée de Fourier (i.e. méthode FOTO). Unobstacle majeur au développement d’une méthode d’estimation de l’AGB à large échelle basée sur latexture tient au fait que la relation texture – paramètres de structure du peuplement varie entre types deforêt et régions du monde. Nous avons investigué cette question en simulant des scènes de canopéesvirtuelles pour 279 parcelles de 1 ha établies dans des types de forêts tropicales contrastés. Nous montronsqu’en complémentant les indices de texture FOTO avec d’autres descripteurs structuraux, notamment surl’ouverture de la canopée (via une analyse de lacunarité) et l’élancement des arbres (via un proxybioclimatique), il devrait être possible de développer un cadre d’inversion stable de l’AGB à large échelle.Un premier cas d’étude empirique dans une mosaïque forestière du bassin du Congo a donné des résultatsprometteurs.Globalement, ce travail met en évidence le besoin de mieux prendre en compte les patrons de variation destructure de l’arbre (e.g. ontogénétique) et de la forêt afin d’améliorer les modèles génériques d’AGB.

Tropical forests store more than half of the world’s forest carbon and are particularly threatened by deforestation and degradation processes, which together represent the second largest source of anthropogenic CO2 emissions. Consequently, tropical forests are the focus of international climate policies (i.e. Reducing emissions from deforestation and forest degradation, REDD) aiming at reducing forestrelated CO2 emissions. The REDD initiative lies on our ability to map forest carbon stocks (i.e. spatial dynamics) and to detect deforestation and degradations (i.e. temporal dynamics) at large spatial scales (e.g. national, forested basin), with accuracy and precision. Remote-sensing is as a key tool for this purpose, but numerous sources of error along the carbon mapping chain makes meeting REDD criteria an outstanding challenge. In the present thesis, we assessed carbon (quantified through aboveground biomass, AGB) estimation error at the tree- and plot-level using a widely used pantropical AGB model, and at the landscape-level using a remote sensing method based on canopy texture features from very high resolution (VHR) optical data. Our objective was to better understand and reduce AGB estimation error at each level using information on large canopy tree structure, distribution and spatial organization.Although large trees disproportionally contributed to forest carbon stock, they are under-represented in destructive datasets and subject to an under-estimation bias with the pantropical AGB model. We destructively sampled 77 very large tropical trees and assembled a large (pantropical) dataset to study how variation in tree form (through crown sizes and crown mass ratio) contributed to this error pattern. We showed that the source of bias in the pantropical model was a systematic increase in the proportion of tree mass allocated to the crown in canopy trees. An alternative AGB model accounting for this phenomenon was proposed. We also propagated the AGB model bias at the plot-level and showed that the interaction between forest structure and model bias, although often overlooked, might in fact be substantial. We further analyzed the structural properties of crown branching networks in light of the assumptions and predictions of the Metabolic Theory of Ecology, which supports the power-form of the pantropical AGB model. Important deviations were observed, notably from Leonardo’s rule (i.e. the principle of area conservation), which, all else being equal, could support the higher proportion of mass in large tree crowns.A second part of the thesis dealt with the extrapolation of field-plot AGB via canopy texture features of VHR optical data. A major barrier for the development of a broad-scale forest carbon monitoring method based on canopy texture is that relationships between canopy texture and stand structure parameters (including AGB) vary among forest types and regions of the world. We investigated this discrepancy using a simulation approach: virtual canopy scenes were generated for 279 1-ha plots distributed on contrasted forest types across the tropics. We showed that complementing FOTO texture with additional descriptors of forest structure, notably on canopy openness (from a lacunarity analysis) and tree slenderness (from a bioclimatic proxy) allows developing a stable inversion frame for forest AGB at large scale. Although the approach we proposed requires further empirical validation, a first case study on a forests mosaic in the Congo basin gave promising results.Overall, this work increased our understanding of mechanisms behind AGB estimation errors at the tree-, plot- and landscape-level. It stresses the need to better account for variation patterns in tree structure (e.g. ontogenetic pattern of carbon allocation) and forest structural organization (across forest types, under different environmental conditions) to improve general AGB models, and in fine our ability to accurately map forest AGB at large scale.; Les forêts tropicales séquestrent plus de la moitié du carbone forestier mondial et sont particulièrement menacées par les processus de déforestation et de dégradation, qui représentent la deuxième source d’émissions anthropogéniques de CO2. De fait, les forêts tropicales sont au centre de politiques climatiques internationales (i.e. Reducing emissions from deforestation and forest degradation, REDD) visant à réduire ces émissions. L’initiative REDD repose sur notre capacité à cartographier les stocks de carbone forestier (dynamique spatiale) et à détecter la déforestation et la dégradation (dynamique temporelle) à large échelle spatiale (e.g. nationale, bassin forestier), avec exactitude et précision. Dans ce cadre, la télédétection apparait comme un outil crucial, mais les nombreuses sources d’erreur dans la chaîne de cartographie du carbone font des objectifs du REDD un challenge ambitieux. Dans cette thèse, nous avons évalué les erreurs associées aux estimations de carbone forestier (quantifié au travers de la biomasse épigée, AGB) (1) aux échelles de l’arbre et du peuplement en utilisant un modèle pantropical largement employé et (2) à l’échelle du paysage en utilisant une méthode de télédétection basée sur les caractéristiques texturales d’images optiques à très haute résolution spatiale. Notre objectif général était de mieux comprendre et de réduire l’erreur d’estimation de l’AGB à chaque échelle par une meilleure prise en compte de la structure, de la distribution et de l’organisation spatiale des arbres de canopée.Malgré l’importance des grands arbres dans la dynamique du carbone forestier, ils sont sous-représentés dans les jeux de données destructifs et soumis à un biais de sous-estimation dans le modèle d’AGB pantropical. Nous avons assemblé une base de données pantropicale et étudié l’influence de la forme de l’arbre sur le patron d’erreur du modèle. Nos résultats montrent que la source de biais du modèle est une augmentation de la masse de l’arbre dans la couronne chez les arbres de canopée. Un modèle d’AGB prenant ce phénomène en compte a été proposé. Nous avons aussi propagé le biais du modèle à l’échelle du peuplement et montré que l’interaction entre la structure du peuplement et l’erreur du modèle, qui est souvent négligée, peut en fait être substantielle. Une analyse des propriétés structurelles des couronnes a également été menée au regard des hypothèses de la Théorie Métabolique de l’Ecologie Des déviations ont été observées, notamment à la loi de Léonardo (i.e. principe de conservation des aires), qui, toutes choses égales par ailleurs, pourraient justifier la grande proportion de masse trouvée dans les couronnes des arbres de canopée.Une seconde partie de la thèse porte sur l’extrapolation des estimations d’AGB des parcelles de terrain via les caractéristiques de texture des canopées extraites par transformée de Fourier (i.e. méthode FOTO). Un obstacle majeur au développement d’une méthode d’estimation de l’AGB à large échelle basée sur la texture tient au fait que la relation texture – paramètres de structure du peuplement varie entre types de forêt et régions du monde. Nous avons investigué cette question en simulant des scènes de canopées virtuelles pour 279 parcelles de 1 ha établies dans des types de forêts tropicales contrastés. Nous montrons qu’en complémentant les indices de texture FOTO avec d’autres descripteurs structuraux, notamment sur l’ouverture de la canopée (via une analyse de lacunarité) et l’élancement des arbres (via un proxy bioclimatique), il devrait être possible de développer un cadre d’inversion stable de l’AGB à large échelle. Un premier cas d’étude empirique dans une mosaïque forestière du bassin du Congo a donné des résultats prometteurs.Globalement, ce travail met en évidence le besoin de mieux prendre en compte les patrons de variation de structure de l’arbre (e.g. ontogénétique) et de la forêt afin d’améliorer les modèles génériques d’AGB.

The forest transition describes a reversal or turnaround in long-run land-use trends for a country or region from a period of net forest area loss to net gain. Such forest recovery has occurred in high-income economies, and increasingly in developing countries. Although this process has been studied extensively by geographers, social scientists and historians, only recently has it been analyzed by economists. This contribution has focused on how competing land use values result in changing patterns of use that lead to an increase or decrease in forest cover. A simple model of forest transition is developed to illustrate this approach in the literature. Empirical applications attempt to explain the underlying economic factors, including governance and institutions, which determine the long-run transition in land use values and patterns. The various findings of these analyses have important policy implications, including for REDD + and other forest recovery programs.

Tropical forests, which provide important ecosystem functions and services, are increasingly threatened by anthropogenic pressures. This has resulted in an urgent need to understand tree species diversity of those forests. Where knowledge of that diversity is largely from the botanical surveys and local ecological studies, data must inevitably be up-scaled from point observations to the landscape and regional level if a holistic perspective is required. This thesis explores aspects of the spatio-temporal heterogeneity of canopy reflectance patterns over the forests of French Guiana, in order to assess whether this information could help defining an ecologically consistent forest typology. To gain insight into both the spatial and temporal heterogeneity of French Guiana’s forests, instrumental artefacts affecting the satellite data first had to be addressed. Data used in this study represent the spectral response of forest canopies, and the way in which such data are captured makes them susceptible to the ‘bi-directional reflectance distribution function’ (BRDF). BRDF indicates that objects do not reflect light in equal proportions in all directions (isotropically). Thus, forest canopies will reflect light anisotropically depending on factors including canopy roughness, leaf optical properties and inclination, and the position of the sun relative to the sensor. The second chapter of this thesis examines how BRDF affects the canopy reflectance of forests in French Guiana, and how not correcting for BRDF affects spectral classifications of those forests. When monthly reflectance data corrected for the artefact are examined, these suggest seasonally-occurring changes in forest structure or spectral properties of French Guiana’s forests.The third chapter of this thesis thus examines temporal effects of BRDF, and used cross-regional comparisons and plot-level radiative transfer modelling to seek to understand the drivers of the monthly variation of the forests’ canopy reflectance. For the latter, the Discrete Anisotropic Radiative Transfer (DART) model was used along with aerial laser scanning (ALS) observations over different forest structures, indicating that the observed variation in reflectance (and derivatives known as vegetation indices) could not be explained by monthly variations in solar direction. At the regional scale, it was also demonstrated that forests in the Guiana Shield possess temporal variation distinct from forests in central Africa or northern Borneo, forests also lying just above the Equator. Had the observed temporal variation in vegetation indices been the result of BRDF, it would have been expected that the forests in the three zones would have similar patterns of variation, which they did not. Central African forests appear to have their greening synchronized with rainfall, whereas forests in the Guianas appear synchronized with the availability of solar radiation.Further analysis of the vegetation index time-series of observations also indicated that different types of forests in French Guiana possess distinct patterns of temporal variation, suggesting that tropical forest types can be discriminated on the basis of their respective “temporal signatures.” That was exploited in the fourth chapter of the thesis, which maps forests in French Guiana based on their combined spatio-temporal canopy reflectance patterns and by so doing presents a novel way of addressing forest typology, based on ecologically meaningful information.The thesis presented demonstrates that it is possible to adequately address remote sensing data artefacts to examine patterns of spatial and temporal variation in tropical forests. It has shown that phenological patterns of tropical rainforests can be deduced from remote sensing data, and that forest types can be mapped based on spatio-temporal canopy reflectance patterns. It is thus an important contribution to understand the ecology of tropical forests in French Guiana and to improve the toolbox of scientists dealing with the identification of spatio-temporal patterns observable in forests at the landscape level.; Les forêts tropicales fournissent des services écosystémiques globaux mais sont de plus en plus menacées par la pression anthropique. Il en résulte un besoin pressant de mieux caractériser la diversité biologique (taxonomique et fonctionnelle) de ces milieux. La connaissance accumulée à travers les inventaires botaniques et les études écologiques à l’échelle stationnelle peut être utilement complétée par une approche spatiale intégrative à l’échelle du paysage ou de la région. Cette thèse explore certains aspects de l’hétérogénéité spatiale et temporelle des canopées forestières de Guyane telle que caractérisée par différents capteurs satellitaires en vue de proposer une typologie forestière écologiquement pertinente.La première étape de ce travail a été d’identifier et de corriger certains artefacts instrumentaux dans les données de télédétection utilisées. L’anisotropie de la réflectivité des couverts forestiers affecte les mesures spectrales. Cette anisotropie est caractérisée par la fonction de distribution de réflectivité directionnelle dont l’acronyme en anglais est la BRDF (‘bi-directional reflectance distribution function’). La BRDF des couverts forestiers est complexe et dépend notamment de la rugosité de la canopée, des propriétés optiques des feuilles et de leur orientation. Le second chapitre traite de l’importance des effets de BRDF dans les images multispectrales utilisées et des conséquences de leur non prise en compte sur les classifications ultérieures. L’analyse des données mensuelles de réflectance corrigée des effets de BRDF suggère que des changements saisonniers affectant la structure ou les propriétés spectrales intrinsèques de la canopée sont à l’œuvre.Le troisième chapitre examine plus spécifiquement la contribution d’éventuels effets artefactuels résiduels dans les variations temporelles de réflectance corrigée des effets de BRDF. Deux études sont menées l’une comparative à l’échelle régionale et l’autre sur base de simulation du transfert radiatif. L’étude comparative à l’échelle de la ceinture équatoriale montre des patrons temporels distincts sur le bouclier guyanais, en Afrique centrale et sur l’ile de Bornéo. Le « verdissement » des forêts d’Afrique centrale semble synchronisé avec la pluviométrie alors qu’il semble être en phase avec l’évolution du rayonnement solaire disponible en Guyane. Les variations temporelles de géométrie capteur-soleil étant les mêmes pour les différents sites celles-ci ne peuvent être responsables des patrons temporels discordants observés. Dans la seconde étude un modèle de transfert radiatif, DART (‘Discrete Anisotropic Radiative Transfer’), est utilisé pour simuler des images multispectrales pour les différents mois de l’année à partir de scène forestières reconstituées par analyse de levés lidar aérien. Les variations temporelles de géométrie capteur-soleil ne permettent pas de retrouver les variations temporelles observées dans les images réelles, conduisant encore à la conclusion que le signal de variation saisonnière de la réflectance est bien réel.Le quatrième chapitre explore l’intérêt de l’introduction de la variation temporelle de la réflectance de la canopée dans la classification des forêts. L’analyse spatio-temporelle de l’indice de végétation amélioré (EVI) indique que les patrons saisonniers varient spatialement à l’échelle de la Guyane. Une classification basée sur la signature temporelle est proposée et discutée. L’introduction de la signature temporelle saisonnière dans les classifications des couverts forestiers sempervirens ouvre des perspectives nouvelles pour la typologie des forêts tropicales humides.Cette thèse montre qu’il est possible de se prémunir des artefacts instrumentaux liés à la réflectivité directionnelle anisotrope des couverts pour tirer parti des variations saisonnières de la réflectance des canopées tropicales. L’introduction de cette caractéristique du fonctionnement des forêts dans le processus de classification devrait permettre à la fois de raffiner et de renforcer la pertinence des typologies des couverts forestiers tropicaux.

Agricultural expansion is the main deforestation driver, while forest degradation is due to non-sustainable poaching and harvesting of forest products. Policies to reduce emissions from deforestation and forest degradation (REDD) thus focus on agricultural expansion and illegal harvesting. The feedbacks between these two policy instruments are rarely discussed. Does reduced deforestation indire ctly decrease or enhance forest degradation? How does better control on illegal har vesting influence deforestation? Using a simple household model, we assess the impact of a P ayment for Environmental Services (PES) on both deforestation and illegal harvesting, and the impact of increasing the control on illegal harvesting on deforestation. We show that when land and labor are substitutes, both policies have positive feedbacks and win-win potential. Conversely, when production factors are complements, they have negative feedbacks and need to be taken into account by the public policies. Further, we demonstrate that the production factors can become substitutes if distance costs are high, making a win-win situation more likely.

International audience

International audience

SUMMARYEcosystems services have become a key concept in understanding the way humans benefit from ecosystems. In Costa Rica, a pioneer national scheme of payment provides compensation for forest conservation that is assumed to jointly produce services related to biodiversity conservation, carbon storage, water and scenic beauty, but little is known about the spatial correlations among these services. A spatial assessment, at national scale and with fine resolution, identified the spatial congruence between these services, by considering the biophysical potential of service provision and socioeconomic demand. Services have different spatial distributions but are positively correlated. Spatial synergies exist between current policies (national parks and the payment scheme) and the conservation of ecosystem services: national parks and areas receiving payments provide more services than other areas. Biodiversity hotspots have the highest co-benefits for other services, while carbon hotspots have the lowest. This finding calls for cautiousness in relation to expectations that forest-based mitigation initiatives such as REDD (reducing emissions from deforestation and forest degradation) can automatically maximize bundled co-benefits for biodiversity and local ecosystem services.

Cet article est un résumé élargi du volume 1 d'une habilitation à diriger des recherches (HDR) soutenue en décembre 2012 à l'université du Maine . Les recherches qui ont donné lieu à ce volume portent sur deux mécanismes qui ont émergé dans le cadre de la convention cadre des nations unies sur le changement climatique, complétée par le protocole de Kyoto. Il s'agit d'une part du mécanisme pour un développement propre (MDP), et d'autre part du mécanisme de réduction des émissions de gaz à effet de serre résultant de la déforestation et de la dégradation des forêts dans les pays en développement (REDD). La préoccupation centrale qui a sous-tendu les recherches effectuées était de " géographier " le MDP et la REDD, c'est à dire, au sens de Postel-Vinay (1998), scruter la dimension spatiale de la construction de ces deux mécanismes afin de démontrer l'ordonnancement du monde et l'organisation géopolitique qui en résultent. Il s'agissait de mener des investigations scientifiques pour répondre à plusieurs questions : comment le MDP et la REDD sont-ils devenus objets de relations Nord-Sud ? Quelles sont les échelles et qui sont les acteurs de la construction et du déploiement de ces relations ? Quels enseignements, en termes de connaissances pratiques et théoriques, tirer de la coopération qui se déroule entre les pays développés et les pays en développement en vue d'un développement dit propre et de l'évitement de la déforestation ? S'agissant d'une recherche en géographie, certes dans le champ des relations internationales , l'objectif était de démontrer et d'expliquer comment des acteurs, tant étatiques que non étatiques, participent au déploiement du MDP et de la REDD, et contribuent à mettre en œuvre ces mécanismes en tissant des relations ou en menant des activités qui s'inscrivent dans une perspective Nord-Sud. Les recherches menées se sont focalisées sur le rôle et l'action des différents acteurs, et sur les dimensions territoriales et environnementales associées aux échelles de déploiement du MDP et de la REDD. Après avoir présenté la filiation épistémologique de ces recherches, cet article explicite l'approche méthodologique utilisée. Les principaux résultats sont ensuite exposés, et les perspectives scientifiques sont énoncées dans la conclusion.

International audience

Bioprospection is, largely, meant to help reducing deforestation and, the other way around, stopping deforestation enhances the prospects of bioprospection. The need for a global agreement to the problem of tropical deforestation has led to the REDD (Reducing Emissions from Deforestation and Degradation) scheme, which proposes that developed countries pay developing countries for CO2 emissions saved through avoided deforestation and degradation. The remaining issue at stake is to definer the rules defning payments to countries reducing their deforestation rate. This article develops a game-theoretic bargaining model, simulating the on-going negotiation process which is currently taking place within the Convention of Climate Change, after the Copenhagen agreement of December 2009. It shows that the conditions under which developing countries are left to bargain over the allocation of the global forest fund may lead to an ineffective system of incentives. Below a given level of contributions from the North, the mechanism fails to curb the deforestation. Beyond this level, it induces perverse effects: the larger the North's contribution, the larger the deforestation rate. Consequently, the mechanism is most effective only at a specifc threshold level which, given the unobservability of countries'preferences, can only be found by a repeated "trial and error" implementation process.

Tropical forests contain an important proportion of the carbon stored in terrestrial vegetation, but estimated aboveground biomass (AGB) in tropical forests varies two-fold, with little consensus on the relative importance of climate, soil and forest structure in explaining spatial patterns. Here, we present analyses from a plot network designed to examine differences among contrasting forest habitats (terra firme, seasonally flooded, and white-sand forests) that span the gradient of climate and soil conditions of the Amazon basin. We installed 0.5-ha plots in 74 sites representing the three lowland forest habitats in both Loreto, Peru and French Guiana, and we integrated data describing climate, soil physical and chemical characteristics and stand variables, including local measures of wood specific gravity (WSG). We use a hierarchical model to separate the contributions of stand variables from climate and soil variables in explaining spatial variation in AGB. AGB differed among both habitats and regions, varying from 78 Mg ha−1 in white-sand forest in Peru to 605 Mg ha−1 in terra firme clay forest of French Guiana. Stand variables including tree size and basal area, and to a lesser extent WSG, were strong predictors of spatial variation in AGB. In contrast, soil and climate variables explained little overall variation in AGB, though they did co-vary to a limited extent with stand parameters that explained AGB. Our results suggest that positive feedbacks in forest structure and turnover control AGB in Amazonian forests, with richer soils (Peruvian terra firme and all seasonally flooded habitats) supporting smaller trees with lower wood density and moderate soils (French Guianan terra firme) supporting many larger trees with high wood density. The weak direct relationships we observed between soil and climate variables and AGB suggest that the most appropriate approaches to landscape scale modeling of AGB in the Amazon would be based on remote sensing methods to map stand structure.

Le mécanisme financier de la Réduction des émissions dues à la déforestation et à la dégradation des forêts (Redd) intéresse les pays du bassin du Congo, qui disposent de peu de données précises sur les stocks de carbone en forêt. Les principales équations allométriques pantropicales disponibles ont pour paramètres : le diamètre, la hauteur et la densité spécifique du bois ; mais aucun des arbres mesurés ne provient de forêts africaines. Les rares équations établies en Afrique s'avèrent insuffisantes, notamment par déficit d'échantillon en arbres de grande taille. Ainsi, pour pallier cette carence, 55 arbres de 10 à 120 cm de diamètre, appartenant à 23 espèces, ont été mesurés en forêt dense semidécidue du Sud-Est du Cameroun. Après abattage, les arbres tronçonnés ont été mesurés jusqu'à la découpe d'un centimètre de diamètre. Cet échantillon a permis de relier le diamètre et le volume total de bois des arbres via des modèles polynomiaux et non linéaires (additif et multiplicatif). La biomasse des arbres pourra être alors déduite par l'utilisation de la densité spécifique et un facteur correctif pour le feuillage. Dans la perspective de cette étude, afin d'affiner les mesures, l'échantillon sera augmenté lors d'une prochaine campagne de mesures, pour mieux estimer le volume total des gros arbres., The REDD mechanism (Reducing Emissions from Deforestation and forest Degradation) is of interest to the Congo Basin countries, but they have few precise data on their forest carbon stocks. The parameters for the main pan-tropical allometric equations are tree height and diameter and specific timber density, but none of the trees measured are from African forests. The few equations established for Africa turn out to be insufficient, in particular because large trees are not sufficiently represented in the samples measured. To address this data deficit, we measured 55 trees with a diameter of 10 to 120 cm, from 23 different species in a dense semi-deciduous forest in south-eastern Cameroon. After felling, the logs were cross-cut and measured until the one centimetre in diameter cutting. The sample was used to link the diameter and total timber volume of the trees via polynomial non-linear models (addition and multiplication). Then tree biomass should be deduced by applying the specific density and a correction factor for foliage. In order to refine these measurements, the sample will be enlarged during a further measurement campaign to produce a closer estimation of the total volume of huge trees., El impacto de una explotación forestal en términos de emisión de carbono ha sido raramente contemplado en trabajos de investigación reales en África Central. Sin embargo, en el marco de los mecanismos REDD (Reducción de Emisiones por la Defo- restación y la Degradación), este problema plantea importantes desafíos con el incre- mento del número de concesiones sujetas a ordenación y la creciente importancia de las técnicas de aprovechamiento de bajo impacto. Este estudio constituye un ensayo de metanálisis que incluye las distintas experiencias procedentes de la literatura existente. Los datos así obtenidos se apli- caron a una hipotética explotación para elaborar un balance teórico del impacto en las reservas de carbono. Los resultados ponen de manifiesto que, con las hipótesis adoptadas, la ordenación de un bosque permitiría una reducción de la décima parte de las pérdidas de carbono, para una extracción por hectárea de 10 a 20 m 3 de madera de construcción; todo ello compa- rado con una concesión forestal convencio- nal sin manejo planificado. La parte funda- mental en el ahorro del carbono procedería sobre todo del aumento de los diámetros mínimos de aprovechamiento. Por otra parte, los beneficios que podrían impulsar la práctica de un aprovechamiento de bajo impacto serían los derivados de la mejora del trazado de pistas y carreteras, esto es: del 5 al 8% de las pérdidas de carbono debidas al aprovechamiento convencional. Estos beneficios son superiores al error constatado en la medición de biomasa por tala total, la más cerca de la realidad, hecho en Guayana francesa. Sin embargo, dichos beneficios son muy inferiores a los errores calculados en la estimación de la biomasa en varios estudios disponibles en la literatura científica. En cualquier caso, la implementación de la ordenación en una concesión forestal y el uso de técnicas de aprovechamiento de bajo impacto son capaces de generar una diferencia favora- ble de las reservas de carbono en el bos- que denso.

International audience; The Reduction of greenhouse gas Emissions due to Deforestation and forest Degradation (REDD) is a mechanism preached in international negotiations for the elaboration of a protocol which is supposed to replace the Kyoto protocol after 2012. In these negotiations, remote sensing is requested to provide solutions to methodological difficulties relating to REDD implementation. It indeed raises the question to know how to measure avoided deforestation and the quantities of greenhouse gas not emitted in the atmosphere thanks to deforestation avoidance. This paper presents knowledge related to this question starting from a review of recent scientific publications in remote sensing of deforestation and forest logging in tropical areas. Bibliographical review shows that measurement of reduction in forest cover is made at several levels (global, regional, national, local) with images provided by various sensors. Countries, like Brazil or India, have national systems of monitoring by remote sensing, which allows a follow-up of deforestation at national level. Remote sensing of forest logging is not current and is still mainly in research, like measurement of greenhouse gas emissions due to land cover and land use changes (deforestation/forest degradation). The paper underlines the great variability of quantifications by remote sensing, with many statistical inaccuracies which forecast a difficult use of remote sensing in the REDD framework. Additional methodological research is needed for an efficient use of remote sensing to support REDD implementation.; La Réduction des Emissions de gaz à effet de serre (GES) dues à la Déforestation et à la Dégradation forestière (REDD) est un mécanisme prôné dans les négociations internationales pour l'élaboration du protocole censé remplacer le protocole de Kyoto après 2012. Dans ces négociations, la télédétection est sollicitée pour fournir des solutions aux difficultés méthodologiques relatives à la mise en œuvre de la REDD. Il se pose la question de savoir comment mesurer la déforestation et la dégradation forestière évitées ou réduites, ainsi que les quantités de GES associées à cette déforestation et à cette dégradation forestière évitée ou réduite. Cet article fait le point sur cette question à partir d'une revue des publications scientifiques récentes en télédétection de la déforestation et de l'exploitation forestière dans la zone intertropicale. La recherche bibliographique effectuée montre que la mesure de la diminution du couvert forestier est faite à plusieurs niveaux (global, régional, national, local) grâce aux images fournies par différents capteurs. Des pays, comme le Brésil ou l'Inde, disposent de systèmes nationaux de monitorage par télédétection, ce qui permet un suivi de la déforestation au niveau national. La télédétection de l'exploitation forestière n'est pas courante et relève encore en grande partie de la recherche, tout comme la mesure des émissions de GES en lien avec les changements d'occupation du sol (déforestation/dégradation forestière). L'article rend compte de la grande variabilité des quantifications par télédétection, avec de nombreuses imprécisions statistiques qui augurent d'une difficile utilisation de la télédétection dans l'optique de la REDD, ce qui souligne la nécessité de recherches méthodologiques complémentaires.

Tropical deforestation is a major driver of climate change accounting for ∼12% of global anthropogenic CO2 emissions. A mitigation strategy named Reduction Emission from Deforestation and forest Degradation (REDD) has been developed to tackle emissions due to forest loss in developing countries. REDD will be the core instrument in any post-2012 climate agreement according to the final document of the 15th UN Conference of the Parties. Nonetheless, REDD's implementation presents several political and scientific challenges. A review of current and future deforestation estimates in terms of forest surface change, carbon densities, and carbon fluxes is under preparation to aid the scientific community. REDD mitigation potential estimates and a case study have also been examined. Preliminary results of this review are presented.

International audience; Although 2010 was a make-or-break year for international climate change negotiations, delegates arrived in Cancún for the 16th Conference of the Parties (COP 16) to the United Nations Framework Convention on Climate Change (UNFCCC) without much enthusiasm and with few expectations. After the disappointing outcomes of the previous COP in Copenhagen (COP 15), many feared that the UNFCCC would not be able to recover from yet another failure. But as the final hours of the Cancún conference ended in standing ovations and loud cheers, there was a collective sigh of relief symbolizing faith restored in the UNFCCC process and an overall acknowledgment that significant progress had been made. The Cancún Agreements garnered support from all but one of the Convention's 194 parties. This can largely be attributed to the COP president, Patricia Espinosa - Mexico's Secretary of Foreign Affairs, who focused first and foremost on building an effective, transparent and inclusive international process. Her skilful diplomacy was praised by both delegates and media, who rewarded her with deafening applause as the conference came to a close. The Cancún Agreements delivered two decisive texts, one on Long-Term Cooperative Action (LCA) and one on the future of the Kyoto Protocol, following the two negotiating tracks. The agreements materialized after much compromise by both developed and developing country parties and are considered as marking a "new era of international cooperation on climate change", as Mexican President Felipe Calderón emphasized. Even though technical details and legal issues - notably on a global goal for reducing global emissions by 2050 and a second commitment period for the Kyoto Protocol - have been deferred to further negotiations, the Cancún Agreements contain key political decisions which will guide and catalyze comprehensive work programmes and substantive discussions in 2011. But do they really constitute a step forward or are they just a rushed deal stemming from the pressure to reach a successful outcome? We look into this question here, focusing primarily on the outcomes for tropical forests and adaptation.

International audience; Reducing greenhouse gas Emissions from Deforestation and forest Degradation (REDD) is an emerging initiative which aims at integrating tropical forests in the struggle against climate change. This paper synthesizes knowledge on this mechanism using literature review and discussions with NGO leaders and scientists involved in its implementation. Recommendations for REDD implementation suggest that it is a mechanism with an important commercial base for a purpose which does not appear obvious: avoid or reduce deforestation in order to mitigate climate change. Differences between REDD proposals and projects, added to the difficulties of quantifying and compensating financially deforestation and forest degradation really avoided, do not forecast a coherent functioning of this initiative. Emerging REDD pilots projects seem to simplify or minimize deforestation causes and processes; there also consider that deforestation can be stopped or reduced at the cost of rewards or financial compensations. Nevertheless, REDD has been integrated in the Copenhagen Agreement elaborated in December 2009 at the end of the United Nations Conference on climate change.; La Réduction des Emissions de gaz à effet de serre dues à la Déforestation et à la Dégradation forestière (REDD) est une initiative récente qui vise à intégrer les forêts tropicales dans la lutte contre les changements climatiques. Cet article synthétise les connaissances sur ce mécanisme à partir d'une recherche bibliographique complétée par des entretiens avec des responsables d'ONG et avec des chercheurs qui participent à l'expérimentation de la REDD. L'analyse des préconisations de mise en œuvre de la REDD suggère qu'il s'agit d'un mécanisme à fondement essentiellement marchand pour une finalité qui ne parait pas évidente : éviter ou réduire la déforestation et atténuer le changement climatique. Les divergences entre les propositions et les projets REDD, ajoutées aux difficultés de quantification et de rémunération de la déforestation et de la dégradation forestière réellement évitées, n'augurent pas d'une cohérente mise en œuvre de cette initiative. Les projets pilotes qui émergent montrent que la REDD simplifie ou minimise les causes et les processus de déforestation et considère que cette déforestation peut être enrayée ou réduite au prix de récompenses ou de compensations financières. Le Mécanisme a néanmoins été intégré dans l' « Accord » de Copenhague élaboré en décembre 2009 à l'issue de la conférence des Nations unies sur le changement climatique.

International audience; The development of tree allometric equations is crucial to accurate forest carbon assessment. However, very few allometric equations exist for sub-Saharan Africa and as a result generalized allometric equations, often established for forests in other continents, are used by default. The objectives of this study were (1) to propose a sampling methodology and calculation procedures to assess biomass for tropical tree species of contrasted tree shapes in Africa, (2) to identify factors affecting within and between trees wood density, (3) to propose an allometric model that integrates these factors and (4) to evaluate the reliability of using generalized allometric equations in this type of forests. Models were developed to predict wood density and phytomass of the trees based on the harvesting of 42 trees from 16 species, representing three guild status in the wet evergreen forest of Boi Tano in Ghana. Results indicated that the wood density was highly influenced by the tree species, guild status, size of the tree and pith to bark distance. Dry mass of a tree was influenced by diameter at breast height, crown diameter and wood density. The wood density depends on the position of the wood within the tree and the guild status considered. The use of generalized allometric models in literature is limited by the specific climate zone, the consideration of tree height and species specific wood density. In considering those factors, using generalized allometric equations could result in an error of 3%. Further research should better consider the bigger trees and the influence of the topography and ecosystem history.

International audience; The widely debated mechanism "avoided deforestation" (REDD), would benefit developing countries that reduce their deforestation rates, thereby generating at least two positive impacts : (i) a greater effectiveness of the global climate change mitigation efforts, and (ii) expected positive side effects on, e.g., biodiversity conservation. Several proposals were designed for the mechanism, which implementation is challenging: firstly, sophisticated tools available to measure the reduction of emissions (e.g. remote sensing) might be ineffective when combined with national baselines; secondly, predictive baselines lack accuracy because of insufficient knowledge concerning the causes of deforestation, and the unpredictable evolution of key variables (e.g. agricultural commodity prices); thirdly, historical baselines lack legitimacy because they only refer to past trends; and fourthly, a reduction in deforestation rates is hardly connectable to specific public policies. Based on our analysis, we recommend not promoting any mechanism within the Kyoto Protocol based on financial rewards for assumed national emissions reductions from deforestation. Two reasons justify our perspective: not only would the mechanism probably generate fake reductions ("hot air"), but undesirable side effects would also appear. Instead, we encourage use of funds made available as carbon finance (broadly speaking) for reinforcing multi- and bilateral instruments that relate to forest management in developing countries, with a focus on the correction of governance deficiencies. In addition, we support any initiative that mitigates perverse incentives from public policies in tropical and industrialized countries.

International audience; Climate change mitigation would benefit from Reduced Emissions from Deforestation and Degradation (REDD) in developing countries. The REDD mechanism, still in discussion, would be in charge of distilling the right incentives and promoting the right policies for fostering forest conservation. The estimation of reduced emissions induced by the mechanism has been raised as an issue, either for issuing the proper amount of carbon credits or for providing appropriate compensations of foregone revenues and other costs to host countries. This estimation would be based on the gap between observed deforestation and a counterfactual value. Although any prediction of deforestation rates (i.e. business-asusual scenarios) is challenging, and any negotiated target is subject to obvious political influence, these two ways have been prioritirized so far to determine the counterfactual value. In other words proposals focused on a results-based approach, the relevance of which is questionable because estimations of avoided deforestation are hardly reliable. With this approach, issuance of carbon credits and distribution of financial compensations could threaten respectively environmental integrity of the scheme and equity outcomes. Rather than considering overall deforestation (predicted and observed), we argue that a REDD mechanism would gain from linking distribution of carbon finance to real efforts (opposed to “results”) that developing countries implement for slowing deforestation rates. This would provide strong incentives to design and enforce suitable policies and measures. The methodology we present to measure these efforts (labeled Compensated Successful Efforts) is based on the rationale that overall deforestation is partly due to structural factors, and to domestic policies and measures. This typology differs from others presented in the literature such as proximate/underlying causes, or economic/institutional factors. Using an econometric model, our approach estimates efforts that are (i) independent of structural factors (economic development, population, initial forest area, agricultural export prices), (ii) estimated ex post at the end of the crediting period, and (iii) relative to other countries. In order to illustrate the methodology we apply the model to a panel of 48 countries (Asia, Latin America, Africa) and four periods between 1970 and 2005. We conclude on the feasibility to estimate avoided deforestation using the Compensated Successful Efforts approach.

Ce rapport est disponible dans : Climate Report, 14; Tropical deforestation is responsible for 15-20% of total man-made emissions of greenhouse gases. In December 2007, at the international conference of Bali, the United Nations acknowledged that a viable solution to climate change must include a mechanism to limit deforestation and forest degradation. Today, the most widely used economic tool to reduce emissions is carbon markets: caps on emitters, and trade allowed between emitters and reducers, drive a price signal on carbon and provide incentives to control emissions. This report examines the different possibilities to broaden the range of this tool so that it helps reduce emissions from deforestation. The three main possibilities presented are a tax-based fund, the use of auctions revenues, and the issuance of tradable credits. The report does not discuss other instruments unrelated to carbon-related payments. We first summarize existing information on the causes of deforestation, and the impact forest loss has on the global climate. To the contrary of a commonly held view, we find that farmers, more than loggers, are driving deforestation. Some, mostly in Africa, cut the forest to grow staple crops, while others, especially in South America, do so in response to the increasing demand for commercial crops and cattle. Building on this analysis, we describe the different possibilities to link carbon markets to the fight against deforestation. In the latter case of the issuance of tradable credits, we find that while carbon markets could substantially increase the amount of funding available to develop projects and programs that reduce deforestation, demand for carbon credits must keep up with this potential new source of supply, probably around one billion ton of CO2 per year. As an analysis conducted by EDF shows, the emission caps currently advocated by the European Commission for Europe and by the Lieberman-Warner bill for the US would create enough demand to generate a price signal around 20 €/tCO2. Other solutions such as reserve prices in auctions or credits banking have been put forward to mitigate the risk of too many deforestation credits flooding carbon markets. In any case, reducing deforestation and maintaining a high price signal on carbon markets are like conjoined twins in the fight against climate change. Their link can be both a source of strength and vulnerability, but they eventually are both essential to achieve the ultimate goal of stabilizing the climate.

L’evaluation de la survie du saumon Atlantique entre la ponte et l’emergence des alevins hors des graviers est realisee dans le bassin de la Nivelle dans les domaines accessible (trois troncons) et non accessible (trois troncons) aux geniteurs. Pour ce faire, des capsules d’incubation de 12 cm 3 , contenant des œufs fraichement fecondes, sont inserees dans des frayeres artificielles et naturelles. Le debit et la temperature de l’eau de surface, l’oxygene dissous des eaux de surface et interstitielle et les caracteristiques granulometriques du substrat des frayeres sont controles pendant toute la duree de l’experience. La survie, de 28,6 % en moyenne dans l’ensemble des sites, est plus elevee dans les troncons de l’amont (52,7 % dans la Tres Haute Nivelle et son affluent, le Lapitxuri) que dans les autres sites, dont ceux actuellement colonises par l’espece (21,5 %). Il n’est pas observe de difference de survie entre les frayeres artificielles et naturelles. Les mortalites interviennent essentiellement lors des episodes de crues avant l’eclosion. Une correlation positive forte existe entre la saturation en oxygene de l’eau interstitielle et la survie. Pour une saturation minimum en oxygene au-dessous de 62 %, la survie reste inferieure a 27 %. En revanche, la composition granulometrique du substrat ne semble pas agir directement sur la survie. Ce facteur n’etant pas correle avec l’oxygene dissous, ceci suggere que dans ce cours d’eau, le flux circulant dans les frayeres ne provient pas uniquement de l’eau de surface, mais aussi de la nappe alluviale pauvre en oxygene dissous.

International audience; The Ninth Conference of the Parties (COP-9) decided to adopt an accounting system based on expiring carbon credits to address the problem of non-permanent carbon storage in forests established under the Clean Development Mechanism (CDM). This article reviews and discusses carbon accounting methods that were under consideration before COP-9 and presents a model which calculates the minimum area that forest plantation projects should reach to be able to compensate CDM transaction costs with the revenues from carbon credits. The model compares different accounting methods under various sets of parameters on project management, transaction costs, and carbon prices. Model results show that under current carbon price and average transaction costs, projects with an area of less than 500 ha are excluded from the CDM, whatever accounting method is used. Temporary crediting appears to be the most favorable approach to account for non-permanent carbon removal in forests and also for the feasibility of smaller projects. However, lower prices for credits with finite lifetimes may prevent the establishment of CDM forestry projects. Also, plantation projects with low risk of unexpected carbon loss and sufficient capacity for insuring or buffering the risk of carbon re-emission would benefit from equivalence-adjusted average carbon storage accounting rather than from temporary crediting.