La compréhension de la dynamique des forêts tropicales hyperdiverses a toujours été un défi en écologie. Historiquement les modèles se basant sur le concept de la niche ou la courbe logistique ont montré leurs limites lorsqu'il s'agissait d'expliquer la diversité d'espèces en forêt tropicale. L'arrivée des modèles neutres en écologie a permis d'exprimer dans un cadre mathématique l'échantillonnage des forêts tropicales, ouvrant de nouvelles perspectives. Ces modèles, très réduits en nombre de paramètres, ont été développés depuis la génétique des populations. Encore peu explorés, ces modèles considèrent les espèces comme étant fonctionnellement équivalentes entre elles. Pour commencer, nous réexaminerons les avancées récentes dans ce domaine extrêmement actif, pour discuter ensuite du développement futur de ces modèles. Dans un second temps, nous analyserons l'inférence des paramètres neutres, afin d'établir ce lien important entre modèles théoriques et données du terrain. De plus, nous introduirons un nouvel estimateur du paramètre décrivant la richesse d'espèces rencontrées dans ces forêts. Ces résultats seront mis en perspective par l'utilisation des données de terrain provenant des forêts sempervirentes des Ghâts Occidentaux d'Inde ainsi que des forêts humides autour du Canal du Panama. Nous testerons également ces approches sur des simulations variées. Finalement, nous essayerons d'évaluer la pertinence des estimations du paramètre de migration en les comparant avec les distances de dispersion des graines observées en forêt tropicale. / Understanding the dynamics of highly diverse communities such as tropical forests has always been a challenging task in ecology. Historically, simplified logistic models and complex niche theories have had a limited success in explaining the species diversity and composition in a tropical context. With the advent of neutral models, we have an original quantitative framework in terms of a sampling theory which opens new perspectives in the field of tropical community ecology. These parsimonious models originally developed from existing theories in population genetics, have a highly selective interpretation of niche theory defined as the functional equivalence of species which has been insufficiently explored. To begin with, we review recent advances of this extremely active field and provide insights into future developments of this theory. Further on, we provide a detailed account of parameter inference which is the crucial link between theoret ical models and field data. In addition, we improve on existing approaches by introducing a novel estimator for the parameter explaining the species richness found in these forests. These results are put into perspective by using field data from the wet evergreen forests of the Western Ghats region of India and the tropical rain forests around the Panama Canal Watershed. Our results are also rigorously tested using simulations of neutral community composition. Lastly, we provide insights into whether parameter inferences dealing with immigration correspond to the seed dispersal distances typically found in tropical forests.

La thèse analyse le rôle des organisations de conservation dans la contradiction croissante entre, d’une part, la formalisation continue d’un cadre politique - juridique - institutionnel - financier - médiatique pour la conservation de l’orang-outang de Sumatra et, d’autre part, le constat avéré du déclin continu de son habitat et de ses populations. Partant du niveau global, elle se concentre ensuite dans le contexte indonésien, porteur d’un conflit aigu autour de la transformation de la forêt de basse altitude -habitat de l’orang-outan de Sumatra- en culture de palmier à huile.Le rôle des organisations de conservation sont étudiées à travers quatre dimensions sociologiques : l’établissement des référentiels globaux de conservation, la construction scientifique des indicateurs de référence, la mise en œuvre du droit indonésien et l’application de l’accord volontaire du RSPO.La thèse a trouvé des réponses concluantes pour chaque dimension et transversalement. Sans minimiser le rôle de l'état et du secteur privé, les ONG jouent aussi un rôle décisif dans le maintien du problème. Deux constantes sont observées : l'une est leur difficulté à tenir compte de la société qui abrite les populations d'orangs-outans, l'autre est leur propension à privilégier leurs propres intérêts afin de perdurer dans le champ social au détriment de leur objectif initial de conservation. Se préoccuper à ces deux manquements est le défi contemporain de la conservation. Des pistes sont donc données dans la conclusion pour refondre la gouvernance internationale de la conservation et pour redéfinir stratégiquement le rôle des ONG de conservation. Cette thèse est basée sur près de vingt ans d'expérience dans la gestion de l'environnement - à la fois pour des organisations de conservation et les Nations Unies - et 49 entretiens semi-directifs. / The thesis analyses the role of conservation organizations in the growing contradiction between, on the one hand a continuous and regular formalisation of a framework (political - legal - institutional - financial - media) for Sumatran orangutan conservation, and on the other hand, a proven report of the continuous decline of orangutan habitat and populations. Starting at the global level, the thesis then focuses on the Indonesian context that gives rise to an acute conflict centred on lowland primary tropical forest - the exclusive habitat of Sumatran orangutans - being converted into large-scale oil palm plantations. The role of conservation organizations has been studied through four sociological dimensions: i) the establishment of global paradigms for conservation, analysing in particular the Great Ape Survival Partnership - GRASP; ii) the "scientific" construction of reference indicators that characterise the orangutan; iii) the establishment and implementation of law at Indonesian level; and iv) the application of the voluntary agreement Roundtable on Sustainable Palm Oil - RSPO. The overall understanding of the role of NGOs is then given by the cross- analysis of the results under these four angles. The thesis has found articulated and conclusive answers for each dimension. Without underestimating the role of the state and the private sector, the cross-analysis shows that NGOs also play a decisive role in maintaining the problem of habitat loss and the decline of emblematic species, in particular the Sumatran orangutan. Two concomitant constants are observed. One is their difficulty to productively engage with the society that supports the wild orangutan populations. The other is their tendency to prioritize their own interests to perpetrate in the social and political sphere at the expense of their initial conservation objectives. To address these two structural shortcomings is the contemporary challenge for conservation. In the conclusion, suggested paths are given, both to reform international biodiversity governance and to strategically reorient the role of conservation organizations. The thesis is based on information gathered during twenty-years of experience in environmental protection - both in the United Nations and conservation organisations - and 49 semi-structured interviews.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第24111号 / 農博第2516号 / 新制||農||1093(附属図書館) / 学位論文||R4||N5402(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 北島 薫, 教授 井鷺 裕司, 准教授 東樹 宏和 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

As a strategy to conserve tropical rainforests of the East Usambara block of the Eastern Arc Mountains, Tanzania, I developed a set of models that can identify above-average tree species richness areas within the humid forests. I developed the model based on geo-referenced field data and satellite image-based variables from the Amani Nature Reserve, the largest forest sector in the East Usambara. I then verified the model by applying it to the Nilo Forest Reserve. The field data, part of the Tanzanian National Biodiversity Database, were collected by Frontier-Tanzania between 1999 and 2001, through the East Usambara Conservation Area Management Program, Government of Tanzania. The field data used are rapidly collectible by people with varied backgrounds and education. I gathered spectral reflectance values from pixels in the Landsat Enhanced Thematic Mapper (Landsat ETM) image covering the study area that corresponded to the ground sample points. The spectral information from different bands formed the satellite image-based variables in the dataset. The best satellite image logistic regression and discriminant analysis models were based on a single band, raw Landsat ETM mid-infrared band 7 (RB7). In the Amani forest, the RB7-based model resulted in 65.3% overall accuracy in identifying above average tree species locations. When the logistic and discriminant models were applied to Nilo forest sector, the overall accuracy was 62.3%. Of the rapidly collectible field variables, only tree density (number of trees) was selected in the logistic regression and the discriminant analysis models. Logistic and discriminant models using both RB7 and number of trees recorded 76.3% overall accuracy in Amani, and when applied to Nilo, 76.8% accuracy. It is possible to apply and adapt the current set of models to identify above-average tree species richness areas in East Usambara and other forest blocks of the Eastern Arc Mountains. Potentially, managers and researchers can periodically use the model to rapidly assess, monitor, update, and map the tree species rich areas within the forest. The same or similar models could be applied to check their applicability in other humid tropical forest areas. / Ph. D.

Introduction and objectives In Vietnam, the forest resources have been declining and degrading severely in recent years. The degradation has decreased the natural forest area, changed the forest structure seriously and reduced timber volume and biodiversity. From 1999 to 2005, the rich forest area has decreased 10.2%, whereas the poor secondary forest has increased dramatically by 20.7%. Forest structure plays an important role in forestry research. Understanding forest structure will unlock an understanding of the history, function and future of a forest ecosystem (Spies, 1998). The forest structure is an excellent basis for restoration measures. Therefore, this research is necessary to contribute to improving forest area and quality, reducing difficulties in forest management. The study also enhances the grasp of forest structure, structure changes after harvesting and fills serious gaps in knowledge. In addition, the research results will contribute to improving and rescuing the poor secondary forest and restoring it, approaching the old-growth forest in Vietnam. Material and methods The study was conducted in Kon Ka Kinh national park. The park is located in the Northeastern region of Gia Lai province, 50 km from Pleiku city center to the Northeast. The park is distributed over seven different communes in three districts: K’Bang, Mang Yang and Đăk Đoa. Data were collected from 10 plots of secondary forests (Type IIb) and 10 plots of primeval forests (Type IV). Stratified random sampling was applied to select plot locations. 1 ha plots were used to investigate gaps. 2000 m2 plots were used to measure overstorey trees such as diameter at breast height, total height, crown width and species names. 500 m2 subplots were used to record tree positions. For regeneration, 25 systematic 4 m2 subplots were established inside 1 ha plots. After data were collected in the field, data analyses were conducted by using R and Excel. Firstly, some stand information, such as density, volume and so on, was calculated, and then descriptive statistics were computed for diameter and height variables. Linear mixed effect models were applied to analyze the difference of diameter and height and to check the effect of random factor between the two forest types. Diameter and height frequency distributions were also generated and compared by using permutational analysis of variance (PERMANOVA). Non-linear regression models were analyzed for diameter and height variables. Similar analyses were implemented for gaps. Regarding spatial point patterns of overstorey trees, replicated point pattern analysis techniques were applied in this research. For biodiversity, some calculations were run such as richness and biodiversity indices, comparison of biodiversity indices by using linear mixed models and biodiversity differences between two forest types tested again by permutational analysis of variance. In terms of regeneration, some analyses were implemented such as: height frequency distribution generation, frequency difference testing, biodiversity indices for the regeneration and spatial distribution checking by using a nonrandomness index. Results and discussion After analyzing the data, some essential findings were obtained as follows: Hypothesis H1 “The overstorey structure of secondary forests is more homogeneous and uniform than old-growth forests” is accepted. In other words, the secondary forest density is about 1.8 times higher than the jungle. However, the volume is only 0.56 times as large. The average diameter and height of the secondary forest is smaller by 5.71 cm and 3.73 m than the old-growth forest, respectively. Linear mixed effect model results indicate that this difference is statistically different and the effect of the random factor (Section) is not important. Type IIb has many small trees and the diameter frequency distribution is quite homogeneous. The old-growth forest has more big trees. For both forest stages, the height frequency distribution is positively skewed. PERMANOVA results illustrate that the frequency distribution is statistically different between the two forest types. Regression functions are also more variant and diverse in the old-growth forest, because all standard deviations of the parameters are greater there. Gap analysis results indicate that the number of gaps in the young forest is slightly higher, while the average gap size is much smaller. The gap frequency distribution is statistically different between the two types. In terms of the spatial point pattern of overlayer trees, the G-test and the pair correlation function results show that trees distribute randomly in the secondary forest. In contrast, the spatial point patterns of trees are more regular and diverse in the old-growth forest. The spatial point pattern difference is not significant, and this is proved by a permutational t-test for pair correlation function (pcf). Envelope function results indicate that the variation of pcf in young forests is much lower than in the primary forests. Hypothesis H2 “The overstorey species biodiversity of the secondary forest is less than in the old-growth forest” is rejected. Results show that the number of species of the secondary forest is much greater than in the old-growth forest, especially richness. The richness of the secondary forest is 1.16 times higher. The Simpson and Shannon indices are slightly smaller in the secondary forest. The average Simpson index for both forest stages is 0.898 and 0.920, respectively. However, the difference is not significant. Species accumulation curves become relatively flatter on the right, meaning a reasonable number of plots have been observed. Estimated number of species from accumulation curves in two forest types are 105 and 95/ha. PERMANOVA results show that number of species and proportion of individuals in each species are significantly different between forest types. Hypothesis H3 “The number regenerating species of the secondary forest is less and they distribute more regularly, compared to the old-growth forest” is rejected. There are both similarities and differences between the two types. The regeneration density of the stage IIb is 22,930 seedlings/ha, greater than the old forest by 9,030 seedlings. The height frequency distribution shows a decreasing trend. Similar to overstorey, the richness of the secondary forest is 141 species, higher than the old-growth forest by 9 species. Biodiversity indices are not statistically different between two types. PERMANOVA results indicate that the number of species and the proportion of individuals for each species are also not significantly different from observed forest types. Nonrandomness index results show that the regeneration distributes regularly. Up to 95% of the plots reflect this distribution trend. Hypothesis H4 “Restoration measures (with and without human intervention) could be implemented in the regenerating forest” is accepted. The investigated results show that the secondary forest still has mother trees, and it has enough seedlings to restore. Therefore, restoration solutions with and without human intervention can be implemented. Firstly, forest protection should be applied. This measure is relevant to national park regulations in Vietnam. Rangers and other related organizations will be responsible for carrying out protection activities. These activities will protect forest resources from illegal logging, grazing and tourist activities. Environmental education and awareness-raising activities for indigenous people is also important. Another measure is additional and enrichment planting. It should focus on exclusive species of the overstorey in Type IIb or exclusive species of the primary forest. Selection of these species will lead to species biodiversity increase in the future. This also meets the purpose of the maximum biodiversity solution. Conclusion Forest resources play a very important role in human life as well as maintaining the sustainability of ecosystems. However, at present, they are under serious threat, particularly in Vietnam. Central Highland, Vietnam, where forest resources are still relatively good, is also threatened by illegal logging, lack of knowledge of people and so on. Therefore, it needs the hands of the people, especially foresters and researchers. Through research, scientists can provide the knowledge and understanding of the forest, including the structure and forest restoration. This study has obtained important findings. The secondary forest is more homogeneous and uniform, while the old-growth forest is very diverse. Biodiversity of the overstorey in the secondary forest is more than the primary. The number of regenerating species in the secondary forest is higher, but other indices are not statistically different between two types. The regeneration distribute regularly on the ground. The secondary forest still has mother trees and sufficient regeneration, so some restoration measures can be applied here. Findings of the study contribute to improve people’s understanding of the structure and the structural changes after harvesting in Kon Ka Kinh national park, Gia Lai. That is a key to have better understandings of the history and values of the forests. These findings and the proposed restoration measures address rescuing degraded forests in Central Highland in particular and Vietnam in general. And further, this is a promising basis for the management and sustainable use of forest resources in the future.

Termites are important ecosystem engineers in tropical and sub-tropical terrestrial regions where they influence ecosystem processes by altering the physical and chemical structure of the habitat. Termites affect nutrient availability by decomposition and comminution (shredding) of organic matter and act as agents of bioturbation as they re-work substrates during the construction of nests, tunnels and runways. At present we have a relatively good understanding of termite diversity patterns in the tropics through the extensive use of the standardised transect sampling protocol by Eggleton et al. (1995). These diversity data suggest that there is a functional difference in termite assemblage structure, and potentially in termite abundance and biomass, among comparable habitats across continents. However due to the lack of comparable abundance and biomass data from South America this has not previously been confirmed. In this thesis I, therefore, collected extensive data on termite taxonomic and functional assemblage structure in a South American site in Peru. The data were used to compare termite abundance and biomass from two comparable sites in Africa (Cameroon) and south east Asia (Malaysia) in order to gain better understanding of the role termites play in ecosystem processes. I found that there was an intercontinental difference in the abundance and biomass of termite feeding-groups mainly due to the dominance of soil-feeding termites in Cameroon and the absence of fungus-growing termites from Peru. The impact of certain lineages on the intercontinental differences suggests that the differences may be due to biogeographical evolution. Moreover, Eggleton et al. (1998) show that larger-bodied soil-feeding termites in Cameroon process more energy per unit area than predicted by their body size. Due to the need for an examination of the allometric relationships in termite assemblages outside Africa and the development of a more sophisticated feeding-group classification I explore the findings in Eggleton et al. (1998) further using population density - body mass relationships in three termite feeding-groups among the three continental sites in Cameroon, Peru and Malaysia. I found that large-bodied soil-feeding termites in Cameroon and large-bodied wood-feeding termites in Peru had higher population densities than expected by their body masses. As the population density - body mass relationship is inverse to that of the energy - body mass relationship the results suggest that the two feeding-groups also use more energy than expected by their body masses. Further, we have a relatively good understanding of the role termites play as ecosystem engineers e.g. in nutrient cycling and distribution, however, compared with our understanding of wood and litter decomposition in tropical forests quantitative data on the impact of termites in soil processes is poorly understood. In this thesis I conducted, to our knowledge, the first in situ soil macrofauna exclusion experiment using translocated soil in Peru to examine the impact of termites on soil C and N loss. I found that termites promote soil C and N loss which may be linked to the increase in microbial activity due to the passage of soil through the termite gut as well as the affect termites have on bioturbation and nutrient distribution. To conclude, in this thesis I present the first intercontinental comparison of abundance and biomass as well as the first in situ soil macrofauna exclusion experiment to date. The link between termite ecology, biogeography and evolution is discussed as well as the contribution of this thesis to the field of termite ecology.

No description available.

Documenting life history characteristics of populations, especially of herbivorous insects such as butterflies, is fundamental to the ecological study of tropical rainforests. However, we know relatively little about tropical forest butterflies. Here, I combine information gathered using the mark-release-recapture (MRR) approach with manipulative and observational experiments in a natural environment to explore aspects of the population biology of three closely-related species of Costa Rican fruit-feeding understory butterflies (Cithaerias pireta, Dulcedo polita, and Pierella helvina), specifically: vertical stratification, attraction to and persistence in fruit-baited traps, relative abundance and distribution, movement patterns, probabilities of recapture and daily survival, and factors that affect those probabilities. Among the three focal species there were differences in capturability, recapturability, spatial distribution, and degree of vertical stratification. Males appear to fly within smaller home ranges than females, and P. helvina can traverse the entire forest reserve in a single day. These findings have implications for the genetic diversity of these populations and for the risk of local extinction in the face of changing ecological conditions.

La dégradation de la forêt est un changement de sa structure et de la composition floristique et faunistique, ce qui conduit à une perte de biodiversité, de production de biens et de services et à un accroissement de la vulnérabilité aux aléas climatiques et aux incendies. Elle concerne de vastes espaces en zone tropicale particulièrement dans les régions de fronts pionniers plus ou moins consolidés où la forêt primaire est soumise à l’extraction de bois, aux incendies et à la fragmentation. Pour évaluer son ampleur et son intensité, il est nécessaire de recourir à la télédétection. Mais les méthodologies disponibles restent encore insuffisantes.L’enjeu scientifique est de développer des méthodes adaptées à de grandes surfaces afin d’analyser l’effet de différentes perturbations sur les trajectoires suivies par le couvert forestier. Il s’agit également de distinguer différentes intensités de dégradation suite à l’accumulation de perturbations. C’est un préalable indispensable pour définir et mettre en œuvre des plans de gestion adaptés. Le premier axe de ce travail a pour objectif de cartographier annuellement l’ampleur des perturbations, d’identifier les principaux types de perturbations et de caractériser la trajectoire de restauration de l’activité photosynthétique. Il est réalisé à partir de séries temporelles d’images Landsat traitées au moyen du progiciel CLASlite. L’agrégation des couvertures annuelles résultant des traitements avec CLASlite a également permis de constituer un indicateur de dégradation résultant du cumul de processus de perturbations sur plusieurs années. / The forest degradation is a change of the structure and the composition of flora and fauna, which leads to a loss of biodiversity, of production of goods and services and an increased vulnerability to weather hazards and fires. This process concerns large areas in the tropics, particularly in agricultural frontier where primary forest is subject to timber extraction, fire and fragmentation. Remote sensing is used to assess the magnitude and the extent of forest degradation. However, the methodologies available are still insufficient. The scientific challenge is to develop methods adapted to large areas to analyze the effect of different disturbances on the trajectories followed by the forest cover. It is also to identify different intensities of degradation following disturbances events. This is a prerequisite for defining and implementing appropriate management plans. The first axis of this work aims to map annually the extent of the disturbances, to identify the main types of disturbances and to characterize the restoration trajectory of the photosynthetic activity. This work is based on time series of Landsat images processed using CLASlite software. The aggregation of the annual coverages resulting from treatments with CLASlite also made it possible to constitute an indicator of degradation resulting from the accumulation of disturbance processes over several years. The second axis aims to evaluate the evolution of the forest sensitivity to drought as a function of its degradation and to build a degradation indicator. The approach uses MODIS images and TRMM precipitation data. This work is implemented in the municipality of Paragominas (state of Pará, Brazil).

Depuis plus de 150 l’exploitation aurifère en Guyane française bouleverse le paysage en entrainant une déforestation massive des concessions minières. Les conséquences sont multiples, aussi bien pour l’environnement que pour la santé humaine. Pendant des décennies l’utilisation du mercure dans le processus d’extraction a entrainé une contamination du réseau hydrique et de la chaine trophique. Afin d’inscrire l’exploitation aurifère dans une optique de développement durable le code minier impose depuis 1998 une obligation de réhabilitation des sites exploités. Des méthodes de revégétalisation utilisant différentes essences végétales ont donc été adoptées afin d’accélérer les successions écologiques. Le contrôle de la qualité de restauration écologique est néanmoins difficile à mettre en œuvre et il est nécessaire d’avoir des outils de bio-géo-indications fiables et peu couteux pour estimer le recouvrement des fonctionnalités des écosystèmes et apprécier le risque de mobilités des éléments traces toxiques. Dans ce contexte, les objectifs de ce travail de thèse ont été d’évaluer la qualité de restauration écologique de sites miniers en Guyane française à travers une caractérisation des activités microbiennes, du fonctionnement des cycles biogéochimiques d’éléments majeurs (C,N,P) et de la dynamique du mercure. L’originalité de ce travail réside dans l’évaluation dans le temps et dans l’espace des interactions entre couvert végétal – propriétés physico-chimiques du sol – activités microbiennes – spéciation du mercure après revégétalisation et en faire un outils diagnostic de la réussite de cette restauration. Dans ce but, plusieurs campagnes d’échantillonnages ont été réalisées en Guyane sur un panel de sites miniers réhabilités, avec différents types de couverts végétaux. Des échantillons de sols ont été prélevés sur des sites revégétalisés avec des espèces de fabacées, et sur des sites non revégétalisés. Nous avons évalué les fonctionnalités des communautés microbiennes de ces sites avec plusieurs bio-marqueurs de la qualité du sol. Afin d’estimer le devenir du mercure, des mesures du mercure total ainsi que des spéciations opérationnelles et environnementales ont été réalisées. Ce travail de thèse a permis de mettre en évidence un effet positif de la revégétalisation sur la densité et les activités des communautés microbiennes telluriques. Les sites restaurés ont montré une biomasse microbienne, des taux de minéralisation des macroéléments (C,N,P), une diversité catabolique plus élevées que des sites non restaurés. Nos résultats confirment également que la restauration influence les activités des communautés microbiennes anaérobies. En effet, les travaux portant sur les communautés bactériennes ferri-réductrices (BFR) et sulfato-réductrices (BSR) montrent des activités variantes entre les modalités de revégétalisation. Ces différences sont à mettre en relation avec les propriétés physiques et chimiques du sol ainsi qu’avec la nature et la densité du couvert végétal. Les communautés BFR sont actives sur les sites réhabilités alors que les communautés BSR seraient davantage actives sur les sites faiblement restaurés. Ces différences ont des conséquences sur la mobilité du mercure. Nos travaux montrent également que si dans les sites revégétalisés le mercure est associé à des phases stables du sol alors que dans les sites non restaurés il est sous des formes solubles mobilisable dans le réseau hydrique, biodisponible pour les organismes de la chaine trophique. Pour conclure, l’approche interdisciplinaire proposée dans ce travail a permis d’identifier certains processus d’écologie microbienne fondamentaux impactant le recouvrement des fonctionnalités des écosystèmes miniers dégradés. Ce travail offre un outil d’évaluation de la qualité de la restauration écologique original, appliqué et prometteur, qui pourra intéresser les décisionnaires responsables de la réhabilitation des sites miniers en Guyane française / For more than 150 years, gold mining in French Guiana has disrupted the landscape by causing massive deforestation of mining concessions. The consequences are multiple, both for the environment and human health. Indeed, for decades the use of mercury in the extraction process has led to pollution of aquatic systems, contaminating the food chain. In order to ensure that gold mining is carried out in a sustainable development perspective, the Mining Code has imposed an obligation since 1998 to rehabilitate the sites operated. Several revegetation methods using different plant species have been adopted to accelerate ecological succession. However, quality control of ecological restoration is difficult to implement and it is necessary to have reliable and inexpensive bio-geo-indication tools to estimate the recovery of the functionalities of anthropized ecosystems and assess the risk of mobility of toxic metallic elements.In this context, the objectives of this thesis work were to evaluate the quality of ecological restoration of mining sites in French Guiana through a characterization of microbial activities, the functioning of biogeochemical cycles of major elements (C,N,P) and the dynamics of mercury. The originality of this work lies in the evaluation over time and space of the interactions between vegetation cover - physico-chemical properties of the soil - microbial activities - mercury speciation after revegetation and making it a diagnostic tool for the success of this restoration. To this end, several sampling campaigns were carried out in French Guiana on a panel of rehabilitated mining sites, with different types of vegetation cover. Soil samples were taken from replanted sites with fabaceous species (A. mangium and C. racemosa), and from non-restored sites. We then evaluated the main functionalities of the microbial communities of these sites through the use of several soil quality bio-markers. In order to estimate the fate of mercury, measurements of total mercury as well as operational and environmental specimens were carried out. This thesis work revealed a positive effect of revegetation on the density and activities of soil microbial communities. Sites restored with fabaceous species have thus shown microbial biomass, macro-element mineralization rates (C,N,P), and catabolic diversity significantly higher than sites that have not been restored. The associations of fabaceous plants show more conclusive results than the use of monoculture in terms of microbial functionalities. While the activities of aerobic microorganisms have been impacted by the return of vegetation, our results confirm that restoration influences the activities of anaerobic microbial communities. Indeed, work on iron-reducing (IRB) and sulfate-reducing (SRB) bacterial communities shows varying activities between revegetation modalities. These differences are related to the physical and chemical properties of the soil and the nature and density of the vegetation cover. BFR communities are more active on rehabilitated sites while SRB communities are more active on poorly restored sites. These differences in activities have consequences on mercury mobility and methylation. Our work also shows that while mercury in re-vegetated sites is associated with stable phases of the soil, including iron oxides, in non-restored sites it is in soluble forms that can potentially be mobilized in the water network, bioavailable and assimilated by organisms in the food chain.In conclusion, the interdisciplinary approach proposed in this work made it possible to identify certain fundamental microbial ecological processes that impact the recovery of the functionalities of degraded mining ecosystems. This work provides an original, applied and promising tool for assessing the quality of ecological restoration that may be of interest to decision-makers responsible for the rehabilitation of mining sites in French Guiana