There is significant worldwide environmental concern related to the transportation of Invasive Aquatic Species (IAS) by ships ballast water into non-native environments. This has given rise to the development of a vast array of technological ballast water treatment systems. The complex environmental challenges and tight operational characteristics of marine vessels limits the scope of the technologies used for Ballast Water Treatment (BWT). As a result few technologies have progressed beyond the research and development stage; however one of the most promising technologies for ship board use is the cyclonic separator, or hydrocyclone. Despite the use of hydrocyclones in a wide variety of engineering applications they have yet to be successfully adapted towards the removal of suspended sediment and marine organisms from large volumes of ballast water. The following primary objectives of this study have been met: • Via critical review identify the technological solutions for treating ballast water best suited to onboard use. • Define the critical flow regimes evident within hydrocyclonic separators. • Establish a series of Computational Fluid Dynamics (CFD) simulations, evaluating standard turbulence models in order to determine the capacity for commercial CFD to model hydrocyclonic flow. This study has detailed the operational characteristics of ballast water hydrocyclones with the aim of enabling hydrocyclones to be optimised for individual ship configurations. Flow simulations have been conducted using CFD, and in particular the Detached Eddy Simulation (DES) turbulence model. Finally the DES model is shown to be a legitimate turbulence model for hydrocyclonic flow regimes, validated against empirical and experimental data.

Forest and forestland are important roles and sources of livelihood for the population living in or near forests and in mountainous areas of Vietnam. The objectives of this paper analysed the change in forest resource, and policy of forestry in Vietnam. In recent several years, forest area rapidly covered an average rate of 240,000 ha/year and had about 13.39 million hectares in 2010. It has contributed to the use of bare land, job creation and improvement of livelihoods for 25% of Vietnam’s population living in mountainous areas. Those results were the purpose of reforestation program and the production of wood industry in Vietnam. In this addition, government policies and regulations have provided a solid foundation for development of the forest plantations and conservation of forest ecosystems though forest land allocation and lease to organizations, households, and individuals. Therefore, the forest utilization has motivated by both environmental and commercial factors in Vietnam based on dividing into three forest categories special use, protection and production forests. However, the development strategy of forest management plan is the difficulties associated with conflicting land claims and boundary disputes due to the value of the established forest. / Rừng và đất rừng đóng vai trò quan trọng và là nguồn sinh kế cho người dân sống trong hoặc gần rừng ở các khu vực miền núi của Việt Nam. Mục tiêu của nghiên cứu này phân tích sự thay đổi về tài nguyên rừng và chính sách về lâm nghiệp. Trong một vài năm gần đây, diện tích rừng bao phủ nhanh với tốc độ trung bình 240.000 ha/năm và có khoảng 13,39 triệu ha trong năm 2010 này đã góp phần vào việc sử dụng đất trống, tạo việc làm và cải thiện đời sống cho 25% dân số sống ở khu vực miền núi của Việt Nam. Kết quả này là mục đích của chương trình trồng rừng và sản xuất gỗ công nghiệp tại Việt Nam. Bên cạnh đó, chính sách và các quy định của chính phủ đã cung cấp một nền tảng vững chắc cho việc phát triển diện tích trồng rừng và bảo tồn hệ sinh thái rừng mặc dù rừng và đất rừng đã được giao và khoán cho các tổ chức, hộ gia đình, cá nhân. Vì vậy, việc sử dụng rừng đã thúc đẩy bởi hai yếu tố môi trường và thương mại ở Việt Nam, dựa trên phân loại rừng: rừng đặc dụng, rừng sản xuất và rừng phòng hộ. Tuy nhiên, chiến lược kế hoạch quản lý phát triển rừng có những khó khăn liên quan đến xung đột khiếu nại đất và tranh chấp biên giới do giá trị của rừng được thành lập.

Annual energy budgets of dominant benthic macro-invertebrates were examined during November 1973 to October 1974 from the benthos of a small pond ecosystem in north-central Texas. Estimates of annual secondary production (Hynes and Coleman 1968) were Procladius s. (Diptera, Chironimidae), 2.4 g m^-2 y^-1 (13 kcal m^-2 y^-1 ); Tendipes decorus (Diptera, Chironomidae), 6.0 g m^-2 y^-1 (40 kcal m^-2 y^-1 ); Brachycercus sp. (Ephemeroptera, Caenidae), 1.9 g m^-2 y^-1 (11 kcal m^-2 y^-1). Energy metabolism was measured in the laboratory at six seasonally encountered temperatures (5, 10, 15, 20, 25, and 30 C) on an acclimatization basis, and then extrapolated to the field. Estimates of annual energy metabolism are Procladius sp., 5.0 kcal m^-2 y^-1 ; Tendipes decorus, 17.2 kcal m^-2 y^-1 ; Brachycercus sp. 40.0 kcal m^-2 y^-1.

Coral reefs have one of the highest levels of biodiversity of all ecosystems in the world and are important for both human livelihood and food security throughout many tropical countries. However, due to increased anthropogenic pressure on marine ecosystems, especially during the last couple of decades, coral reefs have become critically over-fished, and many reefs are now in a degraded state and are facing additional future threats due to further over-exploitation, chemical pollution, sedimentation, and effects of climate change. The main aim of this PhD thesis was to understand effects of anthropogenic disturbances on tropical coastal ecosystems and fish connectivity for coastal management purposes. Therefore, linkages between anthropogenic disturbance and corals were investigated (Paper I), as well as interactions between coral reef habitat and associated fish assemblage (Paper II). Furthermore, connectivity between coral reefs and other tropical coastal ecosystems was explored (Paper III), as well as fish migration to reproduction sites (Paper IV), and evaluations of spatial ecology methods (Paper V). The result showed that coral reefs that are already exposed to disturbances, such as freshwater and nutrient run-offs, may be more sensitive to climate change, in terms of increased sea surface temperatures (Paper I). In addition, there were also clear linkages between coral reef quality, in terms of coral coverage, and fish assemblages, which displayed high spatial variability and suggesting patchy recovery after the 1997/1998 bleaching and subsequent coral mass mortality event (Paper II). This highlights the importance of understanding effects of disturbances on corals, especially in terms of synergistic effects between increased water temperatures and other coastal stressors such as decreased salinity and increased nutrients; and the indirect effects of habitat degradation on the fish community. Linkages between fish and different coastal habitats were further explored. The results showed that coral reefs were strongly connected with mangrove and seagrass beds, through ontogenetic migration of fish (Paper III). Migrations to spawning sites of groupers were related to lunar activities when thousands of fish gather for reproduction purposes during new moon, which increases the risk of over-exploitation (Paper IV). The results emphasises the importance of protecting key areas such as nursing grounds and reproduction sites. Furthermore, acoustic telemetry has become an increasingly common method in studies of fish movement, and the results showed that efficiency of acoustic arrays may increase depending on deployment strategies and habitat characteristics (Paper V). In conclusion, the results from this PhD thesis emphasises the importance of protecting coral reef habitats, as well as identifying related susceptible tropical coastal areas, such as nursing grounds and reproduction sites. Indeed, a better scientific understanding of coral reef ecology and indirect and direct effects on fish assemblages are needed for efficient and accurate coastal management decisions. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.</p>

Em suas várias nuanças a geografia se apresenta como uma ciência interdisciplinar, com interface em muitos segmentos do conhecimento. As ramificações geográficas fazem com que esta ciência seja plural na tradicionalidade acadêmica, nos permitindo trabalhar questões cronológicas, biológicas, humanas e da natureza, como será apresentado nesta tese. A questão que fundamenta este trabalho pauta-se na necessidade de compreender os fatores externos e internos que alteram a vida do ser humano no ecossistema manguezal do Rio Jordão sob a hipótese de que, a ausência de políticas públicas gera problemas ambientais e sociais. O que será realizado ao detectar da comunidade suas correlações com o manguezal em cena. A ação degradadora do homem vai aniquilando aos poucos o ecossistema do manguezal, isso nos faz perceber que as peculiaridades inerentes ao povo vivente desta comunidade também perde sua especificidade. Consequentemente, a atividade pesqueira perde força porque a comunidade local vai sendo removida, comprometendo assim a conservação de sua cultura. O pescador passa para a condição de cidadão, usuário urbano, um simples morador a somar-se ao sistema vicioso da cultura uniformizada, característica dos centros urbanos. O eixo da tese trata inicialmente de compreender a localização da área de pesquisa e da ocupação territorial do estado envolvendo o tema; tem consequência com a realização da caracterização do manguezal em questão e do ser humano nele habitante; apresentação da análise bibliográfica; justificativas, finalidades, metodologia do trabalho, identificar as externalidades e internalidades relacionadas ao ecossistema em questão e as alterações que os moradores do manguezal em estudo sofrem/causam. Com a caracterização da bacia hidrográfica do Rio Jordão, não foi apenas delimitada a área de estudo, mas interpretou-se também a dinâmica no sistema de bacia, neste caso, possibilitou-se conhecer melhor o entorno do rio, o manguezal e focar-se especificadamente nas questões relacionadas com as comunidades quando detectamos a correlação em que os moradores percebem entre o ecossistema do manguezal e suas próprias vidas. Contudo, os capítulos desta tese expressam uma vontade, a de trazer da população habitante da bacia do rio Jordão, informações tributárias a este ecossistema. / Geography, presented here as an interdisciplinary science, with interface in a lot of segments of the knowledge. Its branches make this science a plural science in the academic traditionalism. It allows us to work issues on chronologic, biologic, human and nature as it will be presented in this study. A question that bases this work line is the theory of the necessity to understand the external and internal factors that change lives of the people and the mangrove ecosystems of Jordan River that can be detected from the community and its correlations with the mangrove. The degenerating action of the man is destroying the mangrove ecosystem and this makes us realize that the inherent peculiarities of those people also lose their individualization. Consequently the fish activity loses the strength because the local community is forced to change their life styles, committing the upkeeping of their culture. The fisherman becomes a city citizen, a urban user, an ordinary person who comes to add to the vicious cycle of the unifying culture, what is a characteristic of the urban centres. The main idea of this study is to deal initially with the understanding the location of the area in study, and the territorial occupation of the state involving this subject. It has consequence with the practice of the mangrove characteristics and its inhabitants. A presentation of a bibliographic analysis, justification, purpose, methodology of the study, identification of the internal and external factors related to the ecosystem and the changes that the inhabitants from the mangrove have to deal with. With the characterization of hydrographical basin of the Jordan river, it wasnt only marked the area of study but it was also interpreted the dynamics of the basin system and in this case, the possibility of knowing the river better and to focus on questions connected with community when we detected the correlation between the inhabitants and the ecosystem and the mangrove, and their own existence. However, the chapters of study express a strong will of bringing to the population who live in the Jordan River basin, information about this ecosystem.

A biogeografia estuda a distribuição dos organismos em relação ao espaço e ao tempo, favorecendo a compreensão dos mecanismos que geram e mantém a diversidade, especiação, extinção e dispersão das espécies. Dentre as florestas tropicais, a Mata Atlântica constitui um mosaico vegetal de grande diversidade, onde a filosfera representa um dos habitats mais comuns para os microrganismos. O objetivo do presente trabalho foi avaliar a estrutura e diversidade da comunidade bacteriana da filosfera de Maytenus robusta no Parque Estadual Carlos Botelho, Parque Estadual Ilha do Cardoso e Estação Ecológica de Assis, no estado de São Paulo, Brasil. As folhas foram coletadas em duas épocas do ano, seca e chuvosa. A estrutura da comunidade bacteriana foi avaliada através de PCR-DGGE da região V3 do gene rRNA 16S e a diversidade por sequenciamento da região V1-V3 do mesmo gene. A similaridade entre a estrutura de comunidades de Bacteria foi determinada com base na presença ou ausência das bandas detectadas no gel após PCR-DGGE. O agrupamento hierárquico gerado com o coeficiente de Jaccard e o método UPGMA mostrou a existência de comunidades bacterianas distintas na filosfera de M. robusta nas áreas amostradas. A existência de padrões biogeográficos foi determinada através de análises de regressão, usando os dados de similaridade da estrutura das comunidades bacterianas e os de distância geográfica entre as árvores amostradas. A correlação negativa observada nas avaliações fornece evidências para suportar a hipótese de que a similaridade entre as comunidades bacterianas da filosfera de plantas da mesma espécie diminui com o aumento da distância entre as árvores, dentro de um mesmo bioma. A avaliação espaço temporal da composição da comunidade bacteriana, realizada pela análise NMDS, demonstrou que houve efeito espacial mas no temporal na estrutura das comunidades bacterianas da filosfera de M. robusta. A afiliação taxonômica de 1.470 sequências de clones do gene rRNA 16S de Bacteria, obtidas da filosfera de M. Robusta, nas diferentes áreas e épocas, e a comparação múltipla das bibliotecas, mostraram que as comunidades bacterianas na filosfera foram distintas umas das outras, sendo os filos Proteobacteria e Acidobacteria os mais frequentes. Somente 1% das Unidades Taxonômicas Operacionais foram comuns entre os indivíduos avaliados. Com base nos resultados obtidos, pode-se inferir que, em cada bioma, plantas da mesma espécie possuem comunidades bacterianas únicas, sugerindo a existência de endemismo, altos níveis de especiação e baixa dispersão das comunidades bacterianas nas áreas avaliadas. / Biogeography studies the distribution of organisms in relation to space and time, favoring the understanding of the mechanisms that generate and keep the diversity, speciation, extinction and dispersion of species. Among the tropical forests, the Atlantic Forest constitutes a highly diverse vegetation mosaic, in which the phyllosphere represents one of the most common habitats for microorganisms. The goal of this work was to evaluate the structure and diversity of the bacterial community from the phyllosphere of Maytenus robusta in the Carlos Botelho State Park, Ilha do Cardoso State Park and Assis Ecologic Station, São Paulo state, Brazil. The leaves were collected in two different seasons of the year, dry season and rainy season. The structure of the bacterial community was evaluated through PCR-DGGE of the 16S rRNA gene V3 region, and the diversity by sequencing of the V1-V3 region of the same gene. The similarities between the structures of the bacterial community were determined based on the presence or absence of bands detected in the gels after PCR-DGGE. The hierarchical clustering generated using the Jaccard coefficient and the UPGMA method showed the existence of distinct bacterial communities in the M. robusta phyllosphere of the sampled areas. The existence of biogeographic patterns was determined through regression analyses, using the community structure similarity data geographic distance among the sampled trees. The negative correlation observed in most of the cases provides evidence to support the hypothesis that the similarity between the bacterial communities from phyllosphere of plants of the same species decreases as the distance among trees increased, within the same biome. The spacial-temporal evaluation of the structure of the bacterial communities, performed by the NMDS analyses, showed the occurrence of spacial but not temporal effects on the structure of the bacterial communities of M. robusta phyllosphere. The taxonomic affiliation of 1,470 bacterial 16S rRNA gene clones obtained from the M. robusta phyllosphere, in different areas and seasons, as well as the multiple comparisons of libraries showed that the bacterial communities in the phyllosphere were distinct from each other, and that Proteobacteria and Acidobacteria phyla were the most frequent. Only 1% of the bacterial Operational Taxonomic Units were common among the individuals evaluated. Based on the results obtained it is possible to conclude that, in each biome, plants of same species have unique bacterial communities, suggesting the existence of endemism, high levels of speciation and low dispersal of bacterial communities in the evaluated areas.

Estima-se que atualmente 80% dos remanescentes florestais de Mata Atlântica estejam localizados em propriedades particulares, o que torna evidente a necessidade da conservação dessas áreas por entidades engajadas. A avaliação e o monitoramento das florestas restauradas são essenciais para o aperfeiçoamento das técnicas de restauração, contribuindo dessa forma para a manutenção e a permanência da biodiversidade nessas áreas. O presente estudo teve como objetivo avaliar a influência do tempo de restauração florestal em áreas plantadas com espécies arbóreas nativas e suas características estruturais sobre a riqueza e abundância da anurofauna de serapilheira. Os dados da presente pesquisa foram obtidos entre abril de 2011 e fevereiro de 2012, em parcelas de 5 × 5 m dispostas em 12 fragmentos localizados em três áreas de vegetação nativa e uma cronossequência (cinco meses e quatro e 11 anos de idade) de áreas restauradas, totalizando três fragmentos por idade. Em cada fragmento foram instaladas seis unidades amostrais, cada uma composta por quatro parcelas, perfazendo 288 parcelas de esforço amostral. Além da contagem de anuros, em cada parcela, com a intenção de caracterizar os micro-habitats disponíveis para os anuros dentro das diferentes florestas, foram medidas as seguintes variáveis abióticas: temperatura e umidade relativa do ar aprisionado na serapilheira, profundidade da serapilheira e cobertura do dossel. Observouse a presença de cinco espécies distribuídas em cinco famílias. A maior riqueza de espécies e abundância foram registradas nos fragmentos com 11 anos de restauração, seguida pela área de floresta nativa e pelo fragmento com cinco meses de idade. Na área com quatro anos de restauração nenhum indivíduo foi capturado. A análise de correlação de Spearman indicou que a riqueza foi significativamente correlacionada com a profundidade de serapilheira e a cobertura do dossel. Foi observada correlação positiva entre as variáveis cobertura do dossel e profundidade de serapilheira e correlação negativa entre umidade relativa do ar e temperatura relativa do ar. O teste de Kruskal-Wallis indicou diferença significativa entre os diferentes tipos de fragmentos avaliados. O teste de Wilcoxon revelou que os fragmentos de cinco meses e quatro anos não diferiram entre si, mas foram significativamente diferentes dos fragmentos de 11 anos e de floresta nativa. Ressalta-se, no entanto, a necessidade de estudos de médio e longo prazo para que se possa melhorar a compreensão dos processos envolvidos na sucessão ecológica e da ocupação desses habitats pelas espécies de anuros. / It is estimated that currently 80% of the remaining Atlantic forest are located on private properties, which makes evident the need for conservation of these areas by engaged entities. Evaluation and monitoring of restored forests are essential to improve restoration techniques, thereby contributing to the maintenance and persistence of biodiversity in these areas. The present study aimed to evaluate the influence of time of forest restoration in areas planted with native tree species and their structural characteristics on the richness and abundance of leaf litter frogs. The data set of this study was obtained between April 2011 and February 2012, on 5 × 5 m plots arranged in 12 fragments located in three areas of native vegetation and a chronosequence (five months, and four and 11 years old) of areas restored with native species, totaling three fragments by age. Four sampling stations with six sampling units were installed in each fragment, totaling 288 plots of sampling effort. In addition to counting the frogs in each plot the following abiotic variables were measured: temperature and relative humidity of the air trapped in the litter, litter depth and cover canopy. Five anuran species belonging to five families were recorded. The highest species richness and abundance were obtained in forested fragments with 11 years old, followed by the native forest area and the fragment with five months old. No individual was captured at the four years old area. The Spearman correlation analysis indicated that anuran richness was significantly correlated with the depth of leaf litter and canopy cover. Canopy cover and litter depth were positively correlated, and relative humidity and temperature of the air were negatively correlated. The Kruskal-Wallis test indicated a significant difference among different types of fragments evaluated. The Wilcoxon test revealed that five old months and four years old fragments did not differ, but they were significantly different from 11 years old and native forest fragments. It should be noted, however, the need for medium and long term studies to improve our understanding about processes involved in ecological succession and occupation of these habitats by anurans.

Os manguezais são ecossistemas complexos tipicamente encontrados na interface entre a terra e o mar. Apesar de sua grande importância ecológica estes ambientes estão em risco, devido à proximidade de áreas com elevada exposição a poluentes, como hidrocarbonetos policíclicos aromáticos (HPAs) liberados em derramantos de petróleo. Em nosso trabalho nós exploramos a diversidade e abundância taxonômica e funcional de bactérias em três manguezais localizados sob diferentes estágios de preservação no Estado de São Paulo. Os resultados mostraram que a concentração total de HPAs nos sedimentos foram diferentes entre todos os pontos de amostragem, com o sedimento de manguezal apresentando as concentrações mais elevadas. Genes <font face=\"Symbol\">a-ARHDs foram encontrados em todos os locais de amostragem, revelando a presença de enzimas envolvidas no metabolismo do bifenilo, naftaleno, dibenzofurano, 3-fenilpropanoato e benzeno. A PCR em tempo real demonstrou um maior número de cópias do gene <font face=\"Symbol\">a-ARHD e 16S rRNA nas áreas contaminadas. A análise das seqüências obtidas pelo sequenciamento do gene 16S rRNA mostrou estruturas de comunidades distintas para todas as amostras. O filo mais frequente foi Proteobacteria e o número de Unidades Taxonômicas Operacionais (OTUs) detectadas nas amostras da área preservada foi superior às daárea contaminada. A análise das seqüências obtidas para o pirosequenciamento do gene bph indicou um maior número de Famílias Proteicas Operacionais (FPOs) no ambiente com atividade antrópica. Em conclusão, os resultados permitiram acessar e identificar uma extensa diversidade de bactérias, incluindo os genes ARHD, 16S rRNA e bph. Tais dados podem oferecer novas abordagens para melhorar a recuperação de tais ambientes. / Mangroves are complex ecosystems typically found at the interface between land and sea. Despite its great ecological importance, these environments are at risk due to the proximity of areas with high exposure to pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs) released by oil spill. In our work we explore the diversity and taxonomic and functional abundance of bacteria in three mangroves under different stages of preservation located in the state of São Paulo. The results showed that the total concentration of PAHs in sediments were different between all the sampling sites, with mangrove sediment having the higher concentrations. <font face=\"Symbol\">a-ARHDs genes were found in all the sampling sites, revealing the presence of enzymes involved in the metabolism of biphenyl, naphthalene, dibenzofuran, 3-phenylpropanoate and benzene. The real-time PCR demonstrated an increased number of copies of the <font face=\"Symbol\">a-ARHD and 16S rRNA genes in the contaminated areas. The analysis of the sequences obtained by pyrosequencing of 16S rRNA gene showed distinct communities structures for all samples. The phylum Proteobacteria was more frequent and the number of Operational Taxonomic Units (OTUs) detected in pristine samples area was higher than contaminated area. The analysis of the sequences obtained for pyrosequencing of bph gene indicated a greater number of Operational Protein Families (OPFs) in the environment with human activity. In conclusion, the results allow to access and identify a wide variety of bacteria, including ARHD genes, 16S rRNA and bph. Such data may provide new approaches for improving the recovery of such environments.

During the last decade, the academic interest for Earth’s natural carbon sinks and their role concerning climate change has increased. Today, many scientists around the world are trying to calculate different ecosystem’s potential to sequester and store carbon dioxide from the atmosphere. As a newcomer to the scientific arena, the term ‘blue carbon’ has been well received by scientists in the field. ‘Blue carbon’ highlights the carbon captured and stored by productive ecosystems along the world’s coasts. The term refers to coastal wetlands – such as mangrove forests, salt marshes and seagrass meadows – and it came to life as the scientific community recognized these ecosystems’ significant potential as effective carbon sinks. New research indicates that these ecosystems’ complex and vertical root systems can store much larger amounts of carbon in the soil than any other terrestrial ecosystem. By studying this subject, scientists are trying to understand how these ecosystems can help us in the quest of removing excessive carbon dioxide from the atmosphere. The goal of this thesis is to conduct a literature review, aiming to analyse and compile the new research on ‘blue carbon’ that has been published during the last 10 years. The paper aims to investigate whether the ecosystem’s potential as carbon sinks differ from each other, and what threats they will face in the future. It will additionally review if scientists have been able to unite around any predictions about what the future for ‘blue carbon’ – and its role in mitigating climate change – will look like. / Under det senaste decenniet har intresset kring naturliga kolsänkors potential och roll i att mildra klimatförändringar ökat. Idag är det många forskare som arbetar med att beräkna mängden kol som olika ekosystem runt om världen kan lagra i sin biomassa och i jorden under dess rötter. Som en nykomling på den vetenskapliga arenan, har termen ’blue carbon’ blivit väl mottaget av forskare inom området. ’Blue carbon’ syftar på det kol som fixeras och lagras av de produktiva ekosystemen längs världens kuster. Termen refererar till kustbelägna våtmarker – så som mangroveskogar, saltträsk och sjögräsbäddar – och introducerades efter att den vetenskapliga världen erkänt deras imponerande potential som kolsänkor. Ny forskning tyder på att deras avancerade och vertikala rotsystem kan lagra mer koldioxid i marken än vad vanliga terrestra skogar kan. Genom att studera detta ämne försöker forskare att förstå hur dessa ekosystem kan hjälpa oss att avlägsna överskottet av koldioxid från atmosfären. Målet med denna uppsats är att utföra en litteraturstudie och analysera, samt sammanställa den nya forskningen om ’blue carbon’ som publicerats de senaste 10 åren. Uppsatsen kommer undersöka hur stor skillnad det är mellan de olika ekosystemen och vilka hot de står inför i framtiden. Dessutom kommer den undersöka ifall forskare kommit närmre i att enas kring förutsägelser om framtiden för ’blue carbon’, och hur dess roll i att mildra klimatförändringarna kommer se ut.

Les écosystèmes forestiers jouent un rôle clé en régulant des cycles du carbone (C) et des nutriments et l’érosion en cours de la biodiversité peut affecter ces fonctions écosystémiques. Ces deux dernières décennies, un effort de recherche important a cherché à comprendre comment la biodiversité affecte la productivité primaire. Le processus inverse de minéralisation du C pendant la décomposition de la matière organique est en revanche beaucoup moins étudié. Dans cette thèse, j’ai cherché à démêler les différents mécanismes par lesquels la diversité des arbres et de leurs litières foliaires affecte la décomposition des litières dans les écosystèmes forestiers d’Europe, à travers trois approches.En utilisant un réseau de placettes forestières contenant des gradients de diversité dans six types de forêts à travers l’Europe, j’ai étudié les effets de la diversité des arbres sur la décomposition de la litière via (i) des modifications de l’environnement de décomposition et (ii) les conséquences directes de la diversité des litières foliaires, avec deux expériences en sachets de litière. A travers tous les sites, alors que la richesse spécifique des arbres a eu un effet limité, la fermeture de la canopée a positivement affecté la décomposition par une modification potentielle des conditions microclimatiques. De plus, les traits moyens de qualité physique et chimique de la chute de litière et la dissimilarité de traits entre les litières d’espèces différentes ont influencé les communautés de décomposeurs permettant dans une certaine mesure de prédire la décomposition de substrats standards. Une fois ces effets pris en compte, la qualité des litières en décomposition a eu un impact supplémentaire mais relativement plus faible sur la décomposition. Ces résultats suggèrent que les effets indirects de la diversité des arbres sur la modification des conditions microenvironnementales sont plus importants pour la décomposition que les effets directs de la qualité intrinsèque des litières en décomposition.J’ai ensuite exploré le rôle des composés solubles lessivés à partir de litière d’espèces différentes sur les processus microbiens du sol par une expérience en microcosmes. Les lessivats de litière d’arbres décidus étaient qualitativement et quantitativement différents de ceux des litières de conifères et ont induit une respiration microbienne du sol plus importante. Le mélange de lessivats des différentes espèces a donné lieu à des effets non-additifs sur les processus microbiens du sol, associés à la dissimilarité de stochiométrie des lessivats. Le lessivage étant un processus dominant pendant la phase initiale de décomposition, l’identité et la diversité des lessivats peut contribuer au contrôle du recyclage du C et des nutriments.Par une troisième approche, mon but a été de mieux comprendre les mécanismes qui sous-tendent les forts effets observées des détritivores du sol sur la décomposition des litières et les effets de diversité. J’ai cherché à comprendre si la transformation de litière en fèces par le détritivores Glomeris marginata stimulait les décomposeurs microbiens, et si cette stimulation dépendait de la qualité de la litière ingérée. L’activité microbienne était stimulée pour les fèces issues de litières récalcitrantes, mais pas pour les fèces issus de litières de meilleure qualité initiale. Ainsi, les conséquences de la transformation de litière en fèces de macroarthropodes pour les décomposeurs microbiens dépend de l’espèce de litières et peut contribuer aux effets de diversité des litières.Les données collectées durant cette thèse montre que la diversité fonctionnelle des arbres peut affecter la décomposition des litières à travers plusieurs mécanismes à différentes étapes de la décomposition. Du fait de cette complexité, les conséquences des changements de diversité pour le cycle du C et des nutriments dans les forêts d’Europe peuvent être importantes, mais sont actuellement difficiles à prédire et à généraliser. / Forest ecosystems play a key role in regulating the global carbon (C) and nutrient cycles, and the ongoing erosion of biodiversity is susceptible to modify these ecosystem functions. Over the past two decades, a strong research effort was put into the understanding of how changing biodiversity impacts primary productivity. The reverse process of respiratory C loss during organic matter breakdown however, remained much less studied. In this PhD thesis, I aimed at teasing apart the different mechanisms of how tree and associated leaf litter diversity may affect litter decomposition in European forest ecosystems using three distinct approaches.First, using a network of forest plots with tree diversity gradients in six major forest types across Europe, I studied the effects of tree diversity on litter decomposition through (i) modifications of the decomposition environment and (ii) the direct consequences of leaf litter diversity, with two litterbag experiments. Across all sites, while tree species richness had only a limited effect, forest canopy closure affected decomposition positively by potentially improving microclimatic conditions. In addition, mean chemical and physical quality traits of the litterfall, and trait dissimilarity in leaf litter from different species influenced decomposer communities in a way that decomposition of the common substrates was predictable to a reasonable degree. Once these effects were accounted for, the quality of decomposing litter showed an additional, but comparatively small impact. Collectively, these results suggest that the indirect effects of tree diversity on decomposition through microenvironmental controls are more important than the direct effects of the inherent quality of decomposing litter.With a second approach using microcosms under controlled-conditions, I aimed at assessing the role of soluble compounds leached from decomposing litter of different species for microbial-driven soil processes. Leachates from litter of broadleaved deciduous species differed in composition and quantity and induced stronger soil microbial respiration than those from litter of coniferous species. When the species-specific leachates were mixed, I observed non-additive mixing effects on soil microbial processes associated to the dissimilarity in leachate stoichiometry. Since leaching is the dominant process during the initial stage of decomposition, litter leachate identity and diversity may significantly contribute to the control of carbon and nutrient cycling.Finally, in a third approach my goal was to better understand the underlying mechanisms of the observed strong effects of soil detritivores on litter decomposition and diversity effects. I investigated whether the transformation of litter into feces by the detritivore Glomeris marginata stimulated microbial decomposers, and whether this stimulation depended on the quality of the ingested litter. Microbial activity was stimulated in feces derived from recalcitrant litter, but not in feces derived from litter of higher initial quality. In conclusion, the consequences of litter transformation into macroarthropod feces for microbial decomposers is litter species-specific which may further contribute to litter diversity effects.The data collected during my PhD thesis shows that the functional diversity of trees can affect litter decomposition through various mechanisms during different stages of decomposition. As a result of this complexity, the consequences of changes in biodiversity for the carbon and nutrient cycles in European forests can be substantial, but are presently difficult to predict and to generalize.