Les prairies semi-naturelles constituent des espaces multifonctionnels susceptibles de rendre de nombreux services à la société. Ce sont en particulier des agro-écosystèmes favorables à l’expression d’une grande diversité floristique et faunistique permettant de concilier enjeux écologiques et agronomiques. Ce travail de thèse vise à analyser (i) l'influence des facteurs environnementaux sur l'assemblage des communautés in situ et (ii) les relations entre la structure fonctionnelle des assemblages (i.e. valeurs de traits agrégées et diversité fonctionnelle) et leurs performances (i.e. production de biomasse et digestibilité de cette biomasse). Cette étude s'appuie sur des approches expérimentales et de terrain dans les prairies humides pâturées du Marais Poitevin. Nos résultats montrent des réponses très différentes des traits aériens et racinaires étudiés aux gradients de stress et de perturbation rencontrés dans ces prairies. Ils ont également permis de mettre en évidence l'influence prépondérante des valeurs de traits agrégées sur la fourniture de services écosystémiques (i.e. productivité et digestibilité du fourrage), en accord avec la "Biomass ratio hypothesis" énoncée par Grime. L'influence du niveau de diversité fonctionnelle sur les services rendus par les assemblages varie selon le service considéré. Contrairement aux résultats attendus selon la "Diversity hypothesis" énoncée par Tilman, le niveau de diversité fonctionnelle est lié négativement à la productivité des assemblages. En revanche, un effet positif de la diversité fonctionnelle sur la digestibilité a été mis en évidence. Cette étude a par ailleurs permis de montrer un compromis entre la productivité des assemblages et la digestibilité de la biomasse produite dans ces prairies humides. Ce travail suggère que des outils de diagnostics de la valeur fourragère du couvert peuvent être construits sur la base de la structure fonctionnelle des assemblages, et ce avec un haut niveau de fiabilité. Il met également en avant les bénéfices agronomiques associés à l'hétérogénéité des couverts végétaux rencontrés dans ces prairies. / Semi-natural grasslands form multifunctional areas susceptible to serve the society from many aspects. Indeed, they are agro-ecosystems that promote expression of a large floristic and faunistic diversity, which allows conciliating ecologic and agronomic issues. This PhD work aims at analysing (i) influence of environmental factors on natural communities' assembly rules and (ii) the relationships between the functional structure of assemblages (i.e. community weighted mean trait values and functional diversity) and their performances (i.e. biomass production and its digestibility). This study is based on both experimental and field approaches in the Marais Poitevin wet grasslands. Our results show that the studied aerial and root traits display a wide diversity of answers to stress gradients and disturbances encountered in these grasslands. Our results also highlighted the crucial influence of community weighted mean trait values on provision of ecosystem services (i.e. forage productivity and digestibility), in agreement with the Biomass ratio hypothesis set out by Grime. The influence of the functional diversity level on services provided by the assemblages differs depending on the service considered. Contrary to the results expected according to the Diversity hypothesis of Tilman, the functional diversity level is negatively correlated with the productivity of the assemblages. However, our study points to a positive feedback between functional diversity and digestibility. Furthermore, this study demonstrated the existence of trade-off between the productivity of assemblages and the digestibility of biomass produced in these wet grasslands. This work suggests that highly reliable tools can be established, based on the functional structure of assemblages, to evaluate the feeding value of a vegetal cover. This work finally illustrates the agronomic benefits associated with heterogeneous vegetal covers encountered in these grasslands.

L'hétérogénéité spatiale est aujourd'hui reconnue comme un facteur primordial pour la diversité et le fonctionnement des écosystèmes prairiaux, mais reste souvent négligée dans l'analyse de l'impact de différents modes d'utilisation pastorale. Les communautés prairiales subalpines sont des milieux hautement diversifiés, au cœur d'enjeux écologiques, socio-économiques et culturels. Depuis plusieurs décennies, des changements d'usage, notamment l'extensification conduisant parfois à l'abandon du pâturage, affectent ces prairies dans de vastes régions des Alpes. Connaitre la réponse spatiale de ces communautés à ces changements d'usage peut constituer un enjeu important pour mieux prédire les conséquences en termes de valeurs écologiques et agronomiques. L'objectif général de ce travail est d'identifier l'organisation spatiale de composantes spécifiques et fonctionnelles de communautés prairiales subalpines dans des situations contrastées d'usage : pâturage traditionnel et abandon sur le moyen terme (~20 ans), de comprendre les mécanismes liés au pâturage influençant cette organisation spatiale et d'explorer les conséquences potentielles de l'organisation spatiale des composantes spécifiques et fonctionnelles sur les valeurs d'usage de ces milieux. Ce travail révèle que l'arrêt du pâturage conduit à des modifications importantes de l'organisation spatiale à la fois des espèces et de traits fonctionnels aériens. La variabilité spatiale de ces composantes est systématiquement augmentée à différentes échelles spatiales en situation d'abandon révélant un grain plus grossier d'hétérogénéité spatiale, lié à une plus faible coexistence locale des espèces et des traits et à une convergence fonctionnelle plus forte que sous l'effet diversificateur à échelle fine du pâturage traditionnel. D'autres part, même si une réponse en termes de patrons spatiaux est également observée, celle-ci n'est pas systématique, indiquant l'absence d'une action structurante forte du pâturage qui agit donc surtout sur la variabilité. Une expérimentation in situ montre en effet que la formation de patrons spatiaux marqués en réponse à une action de défoliation sélective semble limitée dans ces prairies relativement peu productives. De plus, une faible structuration spatiale du couvert en termes de valeurs d'usage fourragère a été observée, pilotée dès des échelles très fines par la variabilité spatiale à un grain fin des assemblages d'espèces et de traits dans les zones pâturées. Ces résultats suggèrent ainsi l'expression d'un pâturage peu sélectif exprimé par les troupeaux ovins dans ces milieux peu productifs, et la prépondérance du filtre abiotique dans la détermination des assemblages spatiaux des espèces et des traits. La formation de patchs très contrastés et très structurés spatialement en réponse au pâturage est plus probable dans des milieux très productifs où la compétition est plus intense et la repousse de la végétation favorisée. La prise en compte de la variabilité autour de la réponse moyenne des communautés se révèle donc un élément essentiel pour analyser l'évolution des prairies subalpines en réponse au changement d'usages pastoraux. Une des perspectives fortes suite à ce travail est l'analyse de la synergie entre la réponse de l'hétérogénéité spatiale du couvert et celle du compartiment souterrain (traits racinaires, mycorhization, diversité microbienne…). / Spatial heterogeneity is now widely recognized as a key component for diversity and functioning of grazed plant communities but is still often neglected for the analysis of the impact of different pastoral uses. Subalpine grassland communities are species-rich habitats of high conservative, economic and cultural values. In large regions of the Alps, these grasslands have experienced a decrease in pastoral use and even abandonment, in the last decades. The investigation of the spatial response of these communities to these changes in pastoral use can be a key issue to better predict ecological and agronomical consequences of such changes. The main objective of this study is to identify the spatial organization of species and traits of subalpine grassland communities in contrasted situations of pastoral use: traditional grazing and abandonment (~20 years), to understand grazing-induced mechanisms influencing this spatial organisation and to explore the potential consequences of the spatial organization of species and traits on the pastoral value of these grasslands. This work reveals that grazing cessation leads to strong modifications of the spatial organization of both species and aerial functional traits. The spatial variability of these components are systematically increased at different spatial scales following grazing abandonment which revealed a coarser grain of spatial heterogeneity in relation to a lower species and trait local coexistence and to a stronger functional convergence than under the fine-scale diversifying action of traditional grazing. Besides, despite we also observed a response in terms of spatial patterns, this one is not systematic which indicates the absence of strongly structuring action of grazing that especially acts on variability. An in situ experiment indeed showed that spatial pattern creation in response to selective defoliation is limited in these relatively low productive grassland communities. In addition, we also evidenced that pastoral values (forage quality) exhibited poor spatial heterogeneity in these grasslands in relation to the fine grained spatial variability of species and plant traits in grazed areas. These results suggest the expression of a low selective grazing promoted by sheep herds grazing and low productivity of subalpine communities and the predominance of the abiotic filter in the determination of spatial assemblages of species and traits. Pronounced spatial patterns in response to grazing may be expected in more productive environments where competitive interactions between species are more intense and species regrowth promoted. Therefore, the consideration of the spatial variability in addition to the mean response of community components appeared to be essential in the analysis of subalpine grassland community dynamics in response to land use changes. One of the strong perspective following this work is to analyse the association between spatial responses of vegetation components and those of belowground components (root traits, microbial diversity…).

Competition between species is believed to lead to patterns of either competitive exclusion or limiting similarity within ecological communities; however, to date the amount of support for either as an outcome has been relatively weak. The two classes of null model commonly used to assess co-occurrence and limiting similarity have both been well studied for statistical performance; however, the methods used to evaluate their performance, particularly in terms of type II statistical errors, may have resulted in the underreporting of both patterns in the communities tested. The overall purpose of this study was to evaluate the efficacy of the negative co-occurrence and limiting similarity null models to detect patterns believed to result from competition between species and to develop an improved method for detecting said patterns. The null models were tested using synthetic but biologically realistic presence-absence matrices for both type I and type II error rate estimations. The effectiveness of the null models was evaluated with respect to community dimension (number of species × number of plots), and amount of pattern within the community. A novel method of subsetting species was developed to assess communities for patterns of co-occurrence and limiting similarity and four methods were assessed for their ability to isolate the species contributing signal to the pattern. Both classes of null model provided acceptable type I and type II error rates when matrices of more than 5 species and more than 5 plots were tested. When patterns of negative co-occurrence or limiting similarity were add to all species both null models were able to detect significant pattern (β > 0.95); however, when pattern was added to only a proportion of species the ability of the null models to detect pattern deteriorated rapidly with proportions of 80% or less. The use of species subsetting was able to detect significant pattern of both co-occurrence and limiting similarity when fewer than 80% of species were contributing signal but was dependent on the metric used for the limiting similarity null model. The ability of frequent pattern mining to isolate the species contributing signal shows promise; however, a more thorough evaluation is required in order to confirm or deny its utility.

A identificação de atributos funcionais de colêmbolos associada com sua caracterização taxonômica responde aos impactos causados por mudanças de uso e manejo, além de terem um efeito sobre os processos funcionais do solo. Além disso, a descrição de atributos funcionais visa também atender o crescente interesse de investigar mecanismos relacionados com os processos de montagem de comunidade, tais como a convergência e divergência de atributos funcionais. Este trabalho teve três objetivos: 1) investigar a composição e estrutura de comunidades de colêmbolos em relação a alterações de uso do solo e diferentes ofertas de forragem através de uma abordagem funcional e taxonômica; 2) avaliar a existência de filtros ambientais e diferenciação de nichos dentro das comunidades; 3) avaliar o efeito de diferentes grupos funcionais dos colêmbolos no funcionamento do solo. Para isto, foram realizamos três estudos, sendo avaliados no primeiro estudo diferentes usos do solo (mata, campo e eucalipto) e no segundo estudo quatro níveis de ofertas de forragem. Como resultado principal de ambos os estudos, observamos que os de índices taxonômicos, tais como riqueza e diversidade de espécies, podem apresentar padrões diferentes dos índices funcionais, porém ambas as abordagens foram sensíveis aos tratamentos avaliados. De modo geral, o aumento da riqueza e diversidade de colêmbolos não é diretamente relacionado com o aumento da diversidade funcional. Também foi observado em ambos os estudos que a composição e estrutura das comunidades de colêmbolos foram afetadas significativamente pela existência de um filtro ambiental e pela diferenciação de nicho ecológico, uma vez que observamos convergência e divergência de atributos funcionais significativamente relacionados com os gradientes estudados. O terceiro estudo, realizado em condições de microcosmos, consistiram em 6 tratamentos e um controle, sendo os tratamento a combinação de diferentes grupos funcionais de colêmbolos. De modo geral, os resultados mostram que a presença de colêmbolos não afetou significativamente o tamanho da comunidade microbiana do solo, porém estimulou a mineralização de C e N. A presença de apenas um grupo funcional de colêmbolos estimulou a atividade microbiana, sendo estes significativamente diferentes do tratamento controle. Estas diferenças são ainda maiores quando há duas e três grupos funcionais no mesmo microcosmo. O estímulo sobre a comunidade microbiana possivelmente deve-se aos diferentes nichos ocupados pelos colêmbolos dentro do solo, pelas modificações na composição microbiana e pela redistribuição de nutrientes no interior do solo. Palavra-chave: colêmbolos; filtro ambiental; interação biológica; regras de montagem; campos; uso do solo; grupo funcional; atributo funcional; convergência de atributos; divergência de atributos. / Traits-based approach (functional traits) associated with taxonomical description in collembolan communities can response to environmental changes and have a directly effect on soil functioning. Furthermore, trait-based approach also aims to attend the growing interest in investigating mechanisms that are related to assembly process in communities, such as trait-convergence and trait-divergence assembly patterns. This work was three objective: 1) investigating the composition and structure of Collembola communities regarding environmental changes in soil and litter induced by land-use and grassland management using both taxonomic and functional approaches; 2) assessing the existence of environmental filtering and biotic interaction within collembolan communities; 3) evaluating the effect of three collembolan life-form on soil functioning. To this, we carried out three studies to investigate these objectives which two of them was carried out in three land-uses types (study 1) and four herbage allowance (study 2).The results of the studies 1 and 2 showed that taxonomic indices such as richness and taxonomical diversity and functional indices can have different patterns in collembolan communities, but both approaches are sensitive to the treatments evaluated. In general, increasing the richness and diversity of collembola was not directly related with the increase of the functional diversity. We also observed in both studies the composition and structure of Collembolan communities are significantly affected by the existence of an environmental filtering and biotic interaction, since we observed significantly trait-convergence and trait- divergence related to ecological gradients tested. Our findings show that functional traits provide a better understanding of the response of communities to biotic and abiotic changes. The third study was carried out in microcosm conditions and consisted of 6 different combinations of collembolan life-form. Overall, our results showed that collembolan life-forms did not significantly affect microbial biomass but collembolan life-forms affected microbial activities. The presence of only one life-form stimulated C and N mineralization regarding to their CO2 and enzymatic activities, but these stimulations were higher when there was two or three life-forms in the same microcosm. We suggest that stimulation on the microbial community is due to different niches occupied by each collembolan life-form, the changes on microbial composition and redistribution of nutrients in the soil.

A identificação de atributos funcionais de colêmbolos associada com sua caracterização taxonômica responde aos impactos causados por mudanças de uso e manejo, além de terem um efeito sobre os processos funcionais do solo. Além disso, a descrição de atributos funcionais visa também atender o crescente interesse de investigar mecanismos relacionados com os processos de montagem de comunidade, tais como a convergência e divergência de atributos funcionais. Este trabalho teve três objetivos: 1) investigar a composição e estrutura de comunidades de colêmbolos em relação a alterações de uso do solo e diferentes ofertas de forragem através de uma abordagem funcional e taxonômica; 2) avaliar a existência de filtros ambientais e diferenciação de nichos dentro das comunidades; 3) avaliar o efeito de diferentes grupos funcionais dos colêmbolos no funcionamento do solo. Para isto, foram realizamos três estudos, sendo avaliados no primeiro estudo diferentes usos do solo (mata, campo e eucalipto) e no segundo estudo quatro níveis de ofertas de forragem. Como resultado principal de ambos os estudos, observamos que os de índices taxonômicos, tais como riqueza e diversidade de espécies, podem apresentar padrões diferentes dos índices funcionais, porém ambas as abordagens foram sensíveis aos tratamentos avaliados. De modo geral, o aumento da riqueza e diversidade de colêmbolos não é diretamente relacionado com o aumento da diversidade funcional. Também foi observado em ambos os estudos que a composição e estrutura das comunidades de colêmbolos foram afetadas significativamente pela existência de um filtro ambiental e pela diferenciação de nicho ecológico, uma vez que observamos convergência e divergência de atributos funcionais significativamente relacionados com os gradientes estudados. O terceiro estudo, realizado em condições de microcosmos, consistiram em 6 tratamentos e um controle, sendo os tratamento a combinação de diferentes grupos funcionais de colêmbolos. De modo geral, os resultados mostram que a presença de colêmbolos não afetou significativamente o tamanho da comunidade microbiana do solo, porém estimulou a mineralização de C e N. A presença de apenas um grupo funcional de colêmbolos estimulou a atividade microbiana, sendo estes significativamente diferentes do tratamento controle. Estas diferenças são ainda maiores quando há duas e três grupos funcionais no mesmo microcosmo. O estímulo sobre a comunidade microbiana possivelmente deve-se aos diferentes nichos ocupados pelos colêmbolos dentro do solo, pelas modificações na composição microbiana e pela redistribuição de nutrientes no interior do solo. Palavra-chave: colêmbolos; filtro ambiental; interação biológica; regras de montagem; campos; uso do solo; grupo funcional; atributo funcional; convergência de atributos; divergência de atributos. / Traits-based approach (functional traits) associated with taxonomical description in collembolan communities can response to environmental changes and have a directly effect on soil functioning. Furthermore, trait-based approach also aims to attend the growing interest in investigating mechanisms that are related to assembly process in communities, such as trait-convergence and trait-divergence assembly patterns. This work was three objective: 1) investigating the composition and structure of Collembola communities regarding environmental changes in soil and litter induced by land-use and grassland management using both taxonomic and functional approaches; 2) assessing the existence of environmental filtering and biotic interaction within collembolan communities; 3) evaluating the effect of three collembolan life-form on soil functioning. To this, we carried out three studies to investigate these objectives which two of them was carried out in three land-uses types (study 1) and four herbage allowance (study 2).The results of the studies 1 and 2 showed that taxonomic indices such as richness and taxonomical diversity and functional indices can have different patterns in collembolan communities, but both approaches are sensitive to the treatments evaluated. In general, increasing the richness and diversity of collembola was not directly related with the increase of the functional diversity. We also observed in both studies the composition and structure of Collembolan communities are significantly affected by the existence of an environmental filtering and biotic interaction, since we observed significantly trait-convergence and trait- divergence related to ecological gradients tested. Our findings show that functional traits provide a better understanding of the response of communities to biotic and abiotic changes. The third study was carried out in microcosm conditions and consisted of 6 different combinations of collembolan life-form. Overall, our results showed that collembolan life-forms did not significantly affect microbial biomass but collembolan life-forms affected microbial activities. The presence of only one life-form stimulated C and N mineralization regarding to their CO2 and enzymatic activities, but these stimulations were higher when there was two or three life-forms in the same microcosm. We suggest that stimulation on the microbial community is due to different niches occupied by each collembolan life-form, the changes on microbial composition and redistribution of nutrients in the soil.

Les zones humides sont des écosystèmes dynamiques en perpétuel changement, dans le temps et dans l'espace et demeurent parmi les plus menacés au monde. Ce travail de thèse est une contribution à la connaissance et la conservation des zones humides. Nous avons étudié la végétation de différents milieux, appartenant à un réseau de zones humides de Gironde, allant des landes humides aux prairies alluviales. Nous les avons choisies pour leur intérêt patrimonial et les enjeux de gestion qu'elles représentent dans le département. Nous avons utilisé plusieurs approches descriptives et expérimentales. La première partie vise à étudier l’organisation des communautés des deux grands systèmes, les landes humides et les prairies alluviales, le long de gradients environnementaux. Dans un deuxième temps, une approche combinant données anciennes et récentes, nous a permis de caractériser les changements de végétation à long terme selon différentes stratégies d’étude de la végétation. La troisième partie, par une approche expérimentale a été conduite sur une communauté végétale à fort enjeu patrimonial : les prairies à Molinie (code 6410 de la Directive Natura 2000). Cette troisième partie a permis de mettre en évidence la part respective des filtres stochastiques (dispersion de graines) et déterministes (compétition) dans une communauté soumise à de fortes contraintes environnementales (inondation). Enfin, dans une analyse prospective, nous avons considéré les enjeux de biodiversité ainsi que les services écosystémiques, cette fois, à l'échelle du département. Cette analyse envisage les outils à développer pour une approche multi-taxon et multi-services sur l'ensemble des zones humides de Gironde. L’ensemble de ce travail a permis de construire un dispositif de suivi de la biodiversité végétale au niveau départemental. Les résultats de ce travail contribuent aujourd’hui à considérer la gestion de ces communautés végétales de façon intégrée et proposent des outils d’aide à la décision pour la gestion de ces espaces. / Wetlands are dynamic ecosystems, constantly changing in time and space, and remaining among the most threatened ecosystems in the world. This thesis contribute to wetland knowledge and conservation. We studied the vegetation of different communities belonging to a network of wetlands in Gironde and ranging from wet heathlands to alluvial meadows. Wetlands were selected from the department council historical interest and management issues. We used several descriptive and experimental approaches. The first part aims to study the organization of the communities of the two major systems, heathlands and alluvial grasslands, along environmental gradients. Then, in a second time, an approach combining old and recent data allowed us to characterize long-term vegetation changes according to different strategies of vegetation study. The third part was conducted on a plant community with a strong conservation issue: Molinia caerulea wet meadow (Code 6410 of the Natura 2000 Directive) with an experimental approach. We highlight here the importance of stochastic filters (seed dispersion) and deterministic filters (competition) in a community controlled by environmental constraints (flooding). Finally, within a prospective analysis, we considered biodiversity issues and supply in ecosystems services at the departmental level. This analysis investigate tools to develop for a multi-taxon and multi-service approach in any Gironde wetlands. This work allowed us to create a monitoring device for plant biodiversity in the department. These results lead to consider nowadays the management of these plant communities in an integrated way and offer tools of decision support for the management of these communities.

The dark kangaroo mouse, Microdipodops megacephalus, is a sensitive species in the Great Basin Desert. This thesis explores the structure of desert rodent communities of the Great Basin to better understand M. megacephalus' place in the community and the conditions that promote large and stable populations. To determine community structure, I used nestedness analysis to evaluate 99 communities of nocturnal granivorous rodents. I found that the community structure was non-random, indicating the existence of assembly rules and ecological constraints. I also found that M. megacephalus was the second most vulnerable species in the community. To explore the correlation between species diversity and relative abundance, I performed regression analyses on M. megacephalus and five commonly co-occurring species of the nocturnal granivore guild: Perognathus longimembris (little pocket mouse), Perognathus parvus (Great Basin pocket mouse), Dipodomys ordii (Ord's kangaroo rat), Dipodomys microps (chisel-toothed kangaroo rat), and Peromyscus maniculatus (deer mouse). Results showed a positive correlation between rodent species diversity and relative abundance for M. megacephalus, P. longimembris, P. parvus, and D. microps, and a negative correlation for D. ordii and P. maniculatus. To further understand community composition, I ran interspecific association analyses based on presence-absence data for the six species using chi-square to determine strength of interspecific associations. I found positive interspecific associations between M. megacephalus and P. parvus, between P. longimembris and P. parvus, between P. longimembris and D. microps, and between D. microps and P. maniculatus, and a negative association between P. longimembris and P. maniculatus. A species cluster dendogram with respect to sites in common further supports the interspecific association results. A site cluster dendogram with respect to species abundances implies that dune habitat promotes diversity but not uniformity. All results indicate that M. megacephalus is more abundant and stable at sites with high species richness. The results also provide evidence for the existence of assembly rules, competition, and niche partitioning in desert rodent communities.

No description available.

A legislação ambiental brasileira obriga a maioria das propriedades rurais a ter Áreas de Preservação Permanente (APPs), que são áreas naturais protegidas devido à fragilidade física e ecológica, e Reserva Legal (RL), cuja função é a conservação da biodiversidade e a exploração sustentável. Em vista do passivo ambiental nas propriedades rurais brasileiras, no que se refere à RL, há uma demanda por estudos que buscam discutir estratégias para a recuperação dessas áreas. A possibilidade de exploração da RL gera uma expectativa de retorno econômico, ao mesmo tempo que essas áreas prestarão serviços ecossistêmicos importantes para a sociedade. Avaliações da regeneração natural sob plantios florestais homogêneos têm demonstrado que florestas plantadas para fins comerciais podem atuar como catalisadoras da regeneração natural a depender do manejo. Contudo, poucos estudos avaliaram a regeneração sob plantios puros de espécies nativas em regiões tropicais. Nesse contexto, para dar suporte à seleção de modelos que possam ser implementados na RL, em áreas cuja vegetação original seja de fisionomia florestal, testamos o \"modelo de mosaico\", que seria composto por pequenos talhões puros. Para tanto, utilizamos parâmetros de estrutura, riqueza, diversidade funcional e potencial econômico para avaliar plantios homogêneos (PH) de espécies nativas. No capítulo 1 comparamos PH com i) plantios mistos de espécies nativas e ii) com florestas nativas de referência em diferentes graus de conservação, visando avaliar se os PHs podem, em longo prazo, promover a conservação de biodiversidade e manutenção de processos ecológicos. No capítulo 2 avaliamos se a sucessão ecológica em PH é condicionada pelos atributos da espécie plantada ou por atributos abióticos, para identificar fatores que possam limitar o sucesso desses plantios. No capítulo 3 avaliamos se a exploração sustentável de madeira em RL a partir de PHs, que não foram manejados, é uma atividade economicamente viável frente a outros tipos de investimentos de longo prazo e outras opções de compensação de RL. Do ponto de vista ecológico, verificamos que PH com espécies nativas, que não sofreram manejo, podem, em longo prazo, promover a restauração das comunidades vegetais características de florestas semideciduais, tanto no aspecto estrutural, quanto na biodiversidade e funcionalidade. Os plantios homogêneos estudados apresentaram valores semelhantes para esses atributos ecológicos em relação a florestas de referência, inclusive às florestas maduras, que seriam a meta ideal de restauração. Em longo prazo, a estrutura (densidade e área basal) e o nível de riqueza das comunidades de plantas lenhosas sob esses plantios são muito pouco influenciados por filtros bióticos ou abióticos. O ritmo de crescimento da espécie plantada foi o único atributo que explicou parcialmente a riqueza e a densidade de indivíduos adultos nos plantios, embora não tenha exercido influência sobre a composição de espécies na comunidade em regeneração. Do ponto de vista econômico, verificamos que PHs de espécies nativas que não tiveram tratos silviculturais ao longo do seu desenvolvimento apresentaram valores para a taxa interna de retorno inferiores à poupança e valor presente líquido negativos. A compensação da RL por meio de arrendamento foi mais vantajosa do que a recomposição, mesmo considerando a venda de madeira. Destacaram-se os plantios de Handroanthus heptaphyllus, Myracrodruon urundeuva e Anadenanthera colubrina var. colubrina, cujo rendimento conseguiu superar os custos da recomposição, mesmo sem manejo adequado. Este estudo demonstrou que plantios de espécies nativas, ainda que homogêneos, podem ser utilizados para fins de recomposição de reserva legal, como proposto no \"modelo de mosaico\", pois conseguem recuperar a biodiversidade e garantir a funcionalidade dos ecossistemas em longo prazo, ainda que a composição de espécies seja distinta de florestas maduras, como tem sido observado também em plantios heterogêneos. A exploração da madeira, mesmo em áreas não manejadas, contribui para o aumento da rentabilidade de propriedades de pecuária e agricultura em longo prazo. A incorporação de tratos silviculturais adequados pode impulsionar a rentabilidade dessa atividade na RL, desde que sejam respeitadas as especificidades de exploração na RL, de modo a conciliar a produção de madeira com a conservação da biodiversidade. / Environmental legislation in Brazil states that most properties must have Permanently Protected Areas (PPA), which are natural protected areas due to its physical and ecological frailty, and also Legal Reserves (LR), aiming at biodiversity conservation and sustainable management. There is a huge demand for studies on strategies to recover and to manage LR due to environmental liability on rural private properties. Sustainable timber management is allowed in LR, and this may, potentially, provide economic return to the stakeholders, in addition to important ecosystem services to society as a whole. Reviews of natural regeneration under pure forest plantations have shown that planted forests can catalyse natural regeneration. However, few studies have evaluated the regeneration under pure stands of native species in tropical regions. In this context, aiming to support the selection of models that may be implemented in LR in areas which forest was the original vegetation, we tested the \"mosaic model\", which is comprised of small pure stands. We analysed the structure, richness, functional diversity and economical potential of homogeneous stands (HS) of native species. In chapter 1 we compared HSs with i) mixed plantations of native species and ii) reference ecosystems with distinct conservation status, aiming to verifiy if HS can, in the long term, foster biodiversity conservation and sustain ecological processes. In chapter 2 we analysed if ecological succession in HS is constrained by the species planted traits or by abiotic traits, in order to identify which attributes could restrict this type of planting in order to achieve the LR purposes. In chapter 3 we evaluated if sustainable timber exploitation from homogeneous stands, without silviculture practices, in LR is a viable economical activity in comparison with other types of long term investiments and other options for LR compensation. In the long term, from the ecological perspective, homogeneous stands with native species, without management except for the seedlings cultivation during three years after planting, can foster the restoration of seasonal forest plant communities in terms of structure, biodiversity and functionality. The homogeneous stands analysed had similar values for those ecological attributes when compared with reference ecosystems, including pristine forests which is the ultimate goal of restoration projects. In the long term, structure (density and basal area) and woody species richness under these stands are barely influenced by biotic or abiotic filters. Growth rate of the species planted was the only attribute that explained, in part, the richness and density of adult individuals in the stands, although it had no influence over species composition. From the economic perspective, homogeneous stands of native species without silviculture practices throughout their development had internal rates of return lower than saving and negative net present values. Compensation of LR through leasing was most profitable for the property revenue than restoration, even when timber exploitaition was included in the property income. Significant yields were assessed at stands of Handroanthus heptaphyllus, Myracrodruon urundeuva and Anadenanthera colubrina var colubrina, that exceeded the restoration costs, without any silviculture practices. This study demonstrates that native species plantations, even with only a single species, can be considered for the restoration of legal reserve, such as the \"chessboard model\", since they can foster biodiversity recovery and assure ecosystem functioning in the long term, even though species composition are distinct from pristine forests, which has been observed also in mixed plantations. In addition, timber exploitation, even in unmanaged areas, contributes for agriculture and livestock properties revenue in the long term. The incorporation of silviculture practices can bolster timber exploitation yield in the LR, as long as it considers the specificities for this activity in LR, in order to balance timber production with biodiversity conservation.

La description des gradients spatiaux ainsi que la documentation des dynamiques temporelles de la biodiversité sont des piliers centraux de l'écologie moderne, en particulier dans le contexte actuel des changements globaux auquel l'intérêt porté est croissant depuis les dernières décennies. Les communautés écologiques sont désormais reconnues comme des entités issues de la sélection d'espèces à partir d'un pool régional, sélection déterminée par différents processus appelés règles d'assemblage. Les deux règles d'assemblage principalement reconnues sont les filtres environnementaux, sélectionnant des espèces similaires adaptées à un milieu, et la limite à la ressemblance, sélectionnant des espèces dont les caractéristiques n'induisent pas de compétition trop forte et permettent la coexistence. Les objectifs de ma thèse ont été de (i) comprendre les patrons spatiaux de la diversité des communautés piscicoles à large échelle, (ii) comprendre la dynamique temporelle de cette diversité et (iii) d'appréhender la dynamique temporelle des processus sous-jacents à la structuration des communautés. Pour ce faire, des données de communautés piscicoles ont été analysées, d'une part à l'échelle continentale (i.e. européenne), et d'autre part à l'échelle nationale (i.e. France) pour laquelle la dimension temporelle est également disponible (i.e. séries temporelles depuis 1966 jusqu'à 2012). La description de la diversité piscicole européenne a permis de mettre en évidence la complémentarité des facettes phylogénétique, morphologique et écologique de la diversité. De plus, le climat, et en particulier la saisonnalité des conditions climatiques, est apparu comme un déterminant majeur de la distribution spatiale de la diversité. A une échelle plus locale et en tenant compte de la temporalité des communautés, il a été mis en évidence que les communautés piscicoles françaises connaissaient actuellement une réorganisation taxonomique due aux déclins de populations et menant à une homogénéisation taxonomique globale. Bien qu'une réorganisation fonctionnelle de ces mêmes communautés ait été observée, résultant des variations démographiques des espèces d'eau chaude et de bas niveau trophique, les conséquences à large échelle restent à explorer. De plus, depuis les années 90, les filtres environnementaux se sont renforcés dans leur rôle structurant des communautés. Finalement, les travaux de cette thèse ont permis de valider des hypothèses usuellement associées aux patrons spatiaux de la diversité, comme mécanismes en lien avec les variations temporelles de la diversité. L'hypothèse de prédominance du stress (au travers des changements de saisonnalités des températures) et de préadaptation des espèces non-natives ont notamment permis de comprendre les dynamiques temporelles de diversité ainsi que des règles d'assemblage sous-jacentes à la structuration des communautés. / The description of spatial patterns as well as temporal dynamics of diversity has been a major cornerstone in modern ecology, especially in the contemporary context of global changes for which a growing concern is notable during last decades. Ecological communities are now acknowledged as the result of species that are sorted by selection from the regional pool. This selection of species is determined by several processes, namely the assembly rules. The two main assembly rules are the habitat filtering, selecting species that are able to inhabit in a given set of abiotic conditions, and the limiting similarity, selecting species for which ecological features are dissimilar in order to avoid a too strong competition and to coexist. The goals of my thesis were to (i) understand spatial patterns of freshwater fish community diversity at large scale, (ii) understand temporal dynamic of this diversity and (iii) describe temporal dynamics of the processes underlying the structuration of communities. In order to do this, data of freshwater fish communities has been analyzed first at continental scale (i.e. European) and then at national scale (i.e. France) for which temporal dimension of the data was also available (time series from 1966 to 2012). Based on the European freshwater diversity, we highlighted that phylogenetic, morphological and ecological facets were complementary. Moreover, climatic conditions, and especially their seasonality, seem to be a major driver of the spatial distribution of diversity. At finer scale and by taking into account the temporality of communities, we found that French freshwater communities experienced taxonomic reorganization due to population declines that ultimately leads to taxonomic homogenization of freshwater diversity in France. Although functional homogenization has been observed due to demographic fluctuations of warm water-dweller and low trophic level species, consequences at large scale remained to be explored. Moreover, since the 90s, habitat filtering increased as structuring force for freshwater fish communities. Finally, this thesis allowed us to validate hypothesis usually associated to spatial patterns of diversity, as mechanisms related to temporal variations of diversity. The stress dominance hypothesis (through temporal trends in temperature seasonality) and preadaption hypothesis (related to non-native species) have been used to understand temporal dynamics of diversity as well as of the assembly rules underlying structuration of communities.