Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A bacia do rio Branco abrange uma região com grande diversidade de ambientes e elevada diversidade biológica. Apesar da importância ecológica e biogeográfica do rio Branco, as pesquisas ornitológicas começaram mais intensamente apenas na última década, e existem poucas informações sobre as espécies de aves que ocorrem nas florestas sob seu domínio. Neste estudo, forneço dados detalhados sobre a composição e distribuição das aves do rio Branco. Amostrei a avifauna através de levantamentos acústicos conduzidos em 362 pontos, alocados sistemanticamente ao longo de todo o rio, da nascente à sua foz (~550 km). Análises de riqueza, abundância e padrões de distribuição foram obtidas com dados qualitativos e quantitativos, através de extrapolações de riqueza, análise de agrupamento e identificação de barreiras biogeográficas. Nos censos padronizados, registrei 297 espécies e 6.866 indivíduos, distribuídos em 53 famílias e 202 gêneros. Incluindo dados de observações esporádicas, este número chega a 360 espécies, o que representa boa parte da comunidade. Utilizando estimadores não paramétricos de riqueza, o número de espécies de aves nas florestas do rio Branco deve ultrapassar 350. Dados de riqueza total e abundância não revelaram uma variação espacial ao longo do rio. A maioria das espécies registradas nos censos padronizados foi encontrada distribuída ao longo de todo o rio (167 espécies, ~55%). Por outro lado, 38 (~13%) ocorreram apenas nas florestas do alto curso do rio ( pontos 1 a 4), e outras 92 (~32%) exclusivamente no baixo rio Branco (pontos 5 a 12). Análises de ordenação e agrupamentos sugerem fortes congruências e mudanças na composição da comunidade entre as savanas e florestas ao longo do rio Branco, sugerindo a existência de duas comunidades de aves diferentes. Estes resultados mostram que o rio Branco é bastante atrativo para estudos sobre padrões de distribuição, diversidade e evolução de aves amazônicas de florestas ripárias, por apresentar uma comunidade diferenciada ao longo do rio, e em ambas as margens, separando aves de terra firme do Escudo das Guianas. Documentei a presença, e ampliei a distribuição de espécies típicas de várzeas, especialistas de rios de águas brancas e com populações isoladas no rio Branco. Atualmente, o rio Branco está sob forte pressão dos planos do governo federal em utilizar seu potencial hidrelétrico, o que causará efeitos sem precedentes em toda a bacia. / The rio Branco basin covers an area with an immense variety of environments and biological diversity. Despite the ecological and biogeographical importance of the rio Branco, the ornithological research began more intensely in the last decade, and theres little information about the species of bird found in the rio Branco forests. In this study, I provide detailed data about the composition and distribution of the birds in rio Branco. I sampled the avifauna through acoustic surveys conducted in 362 points, systematically allocated along entire river, from the source to the mouth ( ~ 550 km). Analysis of richness, abundance and distribution patterns were obtained with qualitative and quantitative data through extrapolations, cluster analysis, and identification of biogeographical barriers. On standardized surveys, recorded 297 species and 6.866 individuals, distributed in 53 families and 202 genera. Including data from sporadic observations, this number reaches 360 species, which represents a large part of the community. Using non-parametric estimators of richness, the number of birds species on the rio Branco forests can exceed 350. Data of total richness and abundance revealed no spatial variation along the river. Most of the species registered on standardized census were found distributed over the whole river (167 species, ~55%). However, a large number of species occurs in one region of the river: 38 (~13%) occurred only in points 1 to 4, and other 92 species (32%) exclusively in points 5 to 12. Sorting and grouping analyzes suggest strong congruence and changes in the bird community composition between savannas and forests along the rio Branco, suggesting the existence of two different avian communities. These results show that the rio Branco is very attractive for studies on distribution patterns, diversity and evolution of flooded forests birds, by presenting a differentiated community along the river, and on both sides, separating birds of terra firme forest from the Guiana Shield. I documented the presence and widened the distribution of species typical of the lowland, white-water rivers specialists and with isolated populations in the rio Branco. Currently, the rio Branco is under threat from the Federal Government plans to use its hydropower potential, which may cause unprecedented negative effects throughout the basin.

L’objectif de ce travail était de caractériser la variabilité saisonnière des échanges gazeux des arbres de la canopée en forêt tropicale humide guyanaise confrontés à des saisons sèches.L’étude s’est orientée sur la mesure des flux de carbone et d’eau au cours des saisons sèches dans deux habitats contrastés du point de vue hydrique, afin de préciser leur sensibilité et réponse à la sècheresse. Nos résultats montrent qu’une proportion non négligeable d’arbres ne subit pas de sécheresse marquée en saison sèche, malgré la forte diminution de la teneur en eau du sol en surface. Nous faisons l’hypothèse que ces arbres possèdent alors des racines en profondeur qui leur permettent d’accéder aux horizons qui restent humides malgré la faible pluviométrie. Durant les longues saisons sèches, nous observons une diminution de l’assimilation nette de CO2 foliaire, de l’efflux de CO2 des troncs ou de la densité de flux de sève, et dans une moindre mesure de la respiration foliaire. Cette diminution concerne un nombre plus important d’arbres, quand l’intensité de la sécheresse est plus forte (2008 par rapport à 2007). Néanmoins, de grandes différences de réponse à la sècheresse du sol ont été observées, suggérant des sensibilités et des mécanismes de réponse différents entre ces arbres. En habitat de bas-fond, nous montrons une plus faible diminution des flux carbonés et hydriques en saison sèche, suggérant un accès pour ces arbres aux horizons humides, proches de la nappe phréatique. Par ailleurs, nos résultats suggèrent pour certains arbres un effet négatif des conditions d’anoxie sur ces flux en saison des pluies.Si l’accentuation de l’intensité des saisons sèches en forêt tropicale humide Amazonienne se confirme, comme suggérée par les modèles climatiques, ce travail suggère des modifications rapides de la composition spécifique des forêts, au profit des espèces plus résistantes aux contraintes hydriques / The aim of this work was to characterize the seasonal variations in leaf and trunk gas exchange of tropical rainforest canopy trees exposed to dry seasons. This study focused on measuring gas exchange (CO2 and H2O) at the leaf and trunk level during dry seasons in a Terra firme forest and in a seasonally flooded forest in order to specify their sensitivity and response to drought.Our results showed that part of the studied trees do not encounter a large reduction in soil water content during dry seasons, suggesting that they display deep rooting systems.During long dry periods, we recorded a decrease in leaf photosynthesis, trunk CO2 efflux or sap flow density, and foliar respiration to a lesser extent, for a majority of the trees. Nevertheless, large differences among trees in their response to these conditions were observed, suggesting distinct sensitivities and response to soil drought among trees. Furthermore, these variations were greatest when soil drought was highest (2008 as compared to 2007).In seasonally flooded forest, the decrease in gas exchange was less, suggesting that these trees do have access to wet layers during the dry season, close to the groundwater. However, during wet seasons, we observed a negative effect of anoxia for some trees, whereas others did not display any response, suggesting large differences in tolerance to anoxia among trees abundant in these seasonally flooded forests.We conclude that would seasonal soil droughts increase over the next decades, large vegetation changes might occur because of the large differences among trees in their functional response to soil drought conditions