The Tropical savannas of central Brazil (cerrado) and the Everglades wetland (Florida) ecosystems are ideal systems to study landscape spatial mosaics and their interactions. Both ecosystems show a variety of plant physiognomies distributed within small spatial scales and elevation gradients. Such variety of plant physiognomies provide an opportunity to investigate the roles of climate, topography, nutrient availability and water table dynamics as determinants of plant physiognomic distributions, and their role in shaping regional systems. South Florida Wetlands and the tropical savannas of central Brazil are examples of hydrologically-controlled ecosystems. In hydrologically-controlled ecosystems water sources, the availability of nutrients, and the patterns of water movement play important roles in determining vegetation structure and function. The main objective of this study was to understand ecosystem level processes that shape different physiognomies in two hydrologically-controlled ecosystems. I conducted field work at the IBGE ecological reserve, a field experimental station located in Brasilia, Brazil. I also worked at the Everglades National Park in an area located near the south entrance of the Park in Homestead, Florida. I carried out three interconnected studies investigating water and nutrient dynamics: (1) In a Brazilian savanna I manipulated levels of litter input and measured changes to soil properties, organic matter decomposition and tree growth. I found that changes in litter input affect soil physicochemical properties and soil biochemical processes. I also found that litter dynamics influence tree growth through their effects on soil physicochemical properties. (2) I also studied the effect of water table depth and its temporal variation on spatial patterns of vegetation distribution in the cerrado landscape. I monitored diurnal and seasonal changes in water table depth along two tree-density and topographic gradients. In addition, I measured woody species composition, growth rates of four tree species, litter production, soil nutrients, and nutrient resorption efficiency along those two gradients. I found that water table depth has an important role in determining the spatial distribution of cerrado physiognomies; it also affects tree growth, species composition and nutrient resorption efficiency. (3) In the Everglades I studied patterns of underground water uptake by two vegetation types. I monitored seasonal and diurnal changes in water table depth in a Hammock forest, in a stand dominated by the invasive woody species Schinus terebinthifolius, as well as the water level in an adjacent lake. I estimated stand level transpiration using two different approaches: with sap flow measurements and diurnal oscillations in water table levels. Then, I calculated the total quantity of groundwater withdrawn by evapotranspiration for the wet and dry seasons in the Hammocks and in the exotic invaded site and then compared the results. I found that water uptake by Everglades trees is well coupled to diurnal changes in water table depth and that the amount of water withdrawn from the groundwater was larger during the wet season than during the dry season. Finally, I detected hydrological feedbacks between different vegetation types and nearby bodies of water. Results of this study contributes to the current knowledge of ecosystem level processes in tropical and subtropical ecosystems where water circulation and water availability play a dominant role in shaping vegetation structure and function.

Biomass energy is currently the largest renewable contributor to global energy supply and there is increasing demand for bioenergy feedstock. Consequently, the production of purpose-grown woody bioenergy crops, such as short rotation coppice (SRC) willow, is expected to proliferate. Although the economic and environmental benefits associated with SRC willow production are well documented, systematic assessments of nutrient cycling within these plantations are rare. The objective of this study was to examine biomass production and biogeochemical cycling of nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca), and magnesium (Mg) during an initial four-year rotation of six willow varieties grown at four plantations along a 500 km north-south pedoclimatic gradient within Saskatchewan, Canada. Nutrient budgets were also calculated after quantifying various nutrient inputs (e.g., atmospheric deposition, soil mineral weathering, and organic matter mineralization), outputs (e.g., above- and below-ground biomass, leaching, and denitrification), and transfers (e.g., canopy exchange, leaf litter decomposition, and fine root turnover) affecting the plant available soil nutrient pool. Total stem, leaf litter, and below-ground (primarily fine roots) biomass production after four years averaged 19.0, 7.1, and 12.5 Mg ha-1, respectively, with corresponding soil nutrient budget deficits of 17, 39, 112, 271, and 74 kg ha-1 of N, P, K, Ca, and Mg, respectively, but a soil S surplus of 60 kg ha-1. Despite willow’s relatively low nutrient-demanding nature, negligible leaching and denitrification losses, and substantial nutrient cycling from leaf litter, the nutrient export in harvested biomass over multiple rotations will require soil nutrient amendments, particularly N and P, to maintain plantation productivity. Given the apparent eventual need for supplemental fertility to support adequate willow growth over the 22-yr plantation life span, the fate of broadcast 15N-labelled fertilizer was also examined. Though the willow accumulated less than ⅓ of the applied fertilizer N after one year, the majority of the residual fertilizer N (51%) remained available for willow uptake in subsequent years. Further research is needed to track the fate of applied fertilizers over multiple rotations to better understand fertilizer dynamics for optimizing SRC willow agronomy; thus helping to promote its viability as a biomass energy feedstock option.

This thesis explored the impacts of forest harvesting on gaseous elemental mercury emissions from forest soils in both field and laboratory studies, through novel use of enriched mercury isotope tracers. Forest floor Hg emissions, sourced from legacy deposition, increased proportionally to the vegetation quantity removed, with biomass harvesting most exacerbating emissions. Contemporary Hg deposition did not appear to be influenced by harvesting. Some of the tracer was rapidly lost to the atmosphere (~8%), but most was sequestered within the soil. Two regimes facilitating Hg emissions were observed in low-light conditions. Under extremely dry conditions deeper Hg sources (> 2cm depth) were as equally susceptible to emission as shallower sources. Following wetting to field capacity, emissions were elevated only from shallow sources, likely as a result of upward capillary transport. Impacts of vegetation removal and dry fluxes are previously uncharacterized and may constitute large additional sources to regional atmospheric Hg cycling.

This thesis explored the impacts of forest harvesting on gaseous elemental mercury emissions from forest soils in both field and laboratory studies, through novel use of enriched mercury isotope tracers. Forest floor Hg emissions, sourced from legacy deposition, increased proportionally to the vegetation quantity removed, with biomass harvesting most exacerbating emissions. Contemporary Hg deposition did not appear to be influenced by harvesting. Some of the tracer was rapidly lost to the atmosphere (~8%), but most was sequestered within the soil. Two regimes facilitating Hg emissions were observed in low-light conditions. Under extremely dry conditions deeper Hg sources (> 2cm depth) were as equally susceptible to emission as shallower sources. Following wetting to field capacity, emissions were elevated only from shallow sources, likely as a result of upward capillary transport. Impacts of vegetation removal and dry fluxes are previously uncharacterized and may constitute large additional sources to regional atmospheric Hg cycling.

No description available.

Apesar dos habitats de restinga representarem aproximadamente 5.000 km da costa brasileira, o conhecimento disponível sobre a composição da fauna de anuros nestes habitats ainda é restrito a poucas áreas. Estes habitats encontram-se sob intensa pressão imobiliária, com uma densidade demográfica cinco vezes maior do que a média do país, levando a uma ocupação descomedida, degradação e eventual perda destes importantes habitats. Isso é especialmente preocupante para as populações de vertebrados terrestres endêmicos e ameaçados de extinção, devido à dificuldade de recuperação da vegetação das restingas. Atualmente, os remanescentes de restinga ao longo da costa brasileira são representados por fragmentos completamente isolados. Esta é a primeira aproximação da lista de anfíbios da restinga de Grumari, inserida no Parque Natural Municipal de Grumari (PNMG), município do Rio de Janeiro, sudeste do Brasil. É também a primeira pesquisa a analisar a comunidade de anuros de folhiço, e a obter dados de densidade, para as restingas brasileiras. A área está situada no Domínio da Mata Atlântica. O estudo foi conduzido de maio de 2009 a dezembro de 2010 utilizando dois métodos de amostragem: parcelas grandes ou plots de 16 m (4x4 m) e transecções visuais/acústicas. Registramos 22 espécies de anfíbios anuros distribuídas em seis famílias: Leptodactylidae (3), Craugastoridae (1), Bufonidae (1), Strabomantidae (1), Microhylidae (2) e Hylidae (14). Ocorreram dez espécies de anuros de folhiço em 2560 m de chão de floresta amostrados com a metodologia de parcelas grandes durante o estudo. Na zona fechada de pós-praia ocorreram apenas sete espécies de anuros de folhiço, enquanto na mata de restinga ocorreram as dez espécies registradas para a restinga. A densidade geral estimada de anuros de folhiço para a restinga de Grumari foi de 13,1 indivíduos por 100m, superior a cinco de seis estudos publicados com dados de densidade de anuros de folhiço na Mata Atlântica. A biomassa total estimada foi de 13131 g/ha, podendo ser considerada a maior biomassa de anurofauna de folhiço globalmente. Não houve diferença estatisticamente significativa entre as zonas quanto aos parâmetros da comunidade (riqueza, densidade e biomassa), mesmo havendo diferença entre os parâmetros ambientais mensurados nas duas zonas. Os fatores que melhor explicaram a riqueza, a densidade e a biomassa na restinga de Grumari durante a estação chuvosa foram, respectivamente, a temperatura, o diâmetro das árvores/arbustos e o número de árvores/arbustos. A presença de espécies ameaçadas de extinção e endêmicas para o estado do Rio de Janeiro e Mata Atlântica evidencia que a restinga de Grumari é uma área essencial para a conservação da anurofauna dos remanescentes deste habitat no Brasil. Além disso, Grumari é a restinga com maior riqueza de espécies do estado e a segunda maior entre todas as áreas de restinga estudadas até o momento, quanto à anurofauna. / Although restinga habitats represent approximately 5000 km of the Brazilian coast, the information available about the composition of the anuran fauna present on those habitats are restricted to relatively few areas. Nowadays restinga habitats are under intense set of pressures as result of a demographic density five times higher than the average for the country leading to the occupation, degradation and eventual loss of such habitats. This is especially alarming for the threatened endemic populations of terrestrial vertebrates due to the difficulty of vegetation recovery after clearings. Presently, the remnants of these habitats along much of the eastern Brazilian coast are represented by completely isolated fragments. Herein we present the first approximation to the list of the amphibians from the restinga of Grumari, inserted in the Parque Natural Municipal de Grumari (PNMG), municipality of Rio de Janeiro, Rio de Janeiro state, southeastern Brazil. The area is situated in the Atlantic Rainforest Biome. Its also the first study on the community of litter anuran fauna, obtaining density data, for the Brazilian restinga. The study was carried out from May 2009 to December 2010 using two sampling methods: quadrant plots (4x4 m) and acoustic/visual transects. We recorded 22 species of anuran amphibians distributed in six families: Leptodactylidae (3), Craugastoridae (1), Bufonidae (1), Strabomantidae (1), Microhylidae (2) and Hylidae (14). We found ten species of litter frogs in 2560 m of sampled forest floor with the methodology of large plots. In the closed post-beach zone, there were only seven species of anuran leaf litter, while the restinga forest zone present the ten species recorded for the restinga. The overall density of litter frogs at the restinga of Grumari was 13.1 individuals per 100m, more than five of six published studies on the density of litter frogs in the Atlantic Rainforest. The estimated total biomass was 13131 g/100m, being currently the area with highest litter frog biomass on the planet. There was no statistically significant difference between the zones regarding community parameters (richness, density and biomass), even though there is difference between the environmental parameters measured in both zones. The factors that best explained the richness, density and biomass in the restinga of Grumari during the rainy season were, respectively, temperature, diameter of the trees/shrubs and the number of trees/shrubs. The presence of endangered and endemic species indicates that the restinga of Grumari is an important area for conservation of the anuran fauna in remnants of these habitats in the Rio de Janeiro state, being currently the richest known area in terms of amphibian species of all restinga areas in the state, and the second richest of the Brazilian restingas studied up to now.

Apesar dos habitats de restinga representarem aproximadamente 5.000 km da costa brasileira, o conhecimento disponível sobre a composição da fauna de anuros nestes habitats ainda é restrito a poucas áreas. Estes habitats encontram-se sob intensa pressão imobiliária, com uma densidade demográfica cinco vezes maior do que a média do país, levando a uma ocupação descomedida, degradação e eventual perda destes importantes habitats. Isso é especialmente preocupante para as populações de vertebrados terrestres endêmicos e ameaçados de extinção, devido à dificuldade de recuperação da vegetação das restingas. Atualmente, os remanescentes de restinga ao longo da costa brasileira são representados por fragmentos completamente isolados. Esta é a primeira aproximação da lista de anfíbios da restinga de Grumari, inserida no Parque Natural Municipal de Grumari (PNMG), município do Rio de Janeiro, sudeste do Brasil. É também a primeira pesquisa a analisar a comunidade de anuros de folhiço, e a obter dados de densidade, para as restingas brasileiras. A área está situada no Domínio da Mata Atlântica. O estudo foi conduzido de maio de 2009 a dezembro de 2010 utilizando dois métodos de amostragem: parcelas grandes ou plots de 16 m (4x4 m) e transecções visuais/acústicas. Registramos 22 espécies de anfíbios anuros distribuídas em seis famílias: Leptodactylidae (3), Craugastoridae (1), Bufonidae (1), Strabomantidae (1), Microhylidae (2) e Hylidae (14). Ocorreram dez espécies de anuros de folhiço em 2560 m de chão de floresta amostrados com a metodologia de parcelas grandes durante o estudo. Na zona fechada de pós-praia ocorreram apenas sete espécies de anuros de folhiço, enquanto na mata de restinga ocorreram as dez espécies registradas para a restinga. A densidade geral estimada de anuros de folhiço para a restinga de Grumari foi de 13,1 indivíduos por 100m, superior a cinco de seis estudos publicados com dados de densidade de anuros de folhiço na Mata Atlântica. A biomassa total estimada foi de 13131 g/ha, podendo ser considerada a maior biomassa de anurofauna de folhiço globalmente. Não houve diferença estatisticamente significativa entre as zonas quanto aos parâmetros da comunidade (riqueza, densidade e biomassa), mesmo havendo diferença entre os parâmetros ambientais mensurados nas duas zonas. Os fatores que melhor explicaram a riqueza, a densidade e a biomassa na restinga de Grumari durante a estação chuvosa foram, respectivamente, a temperatura, o diâmetro das árvores/arbustos e o número de árvores/arbustos. A presença de espécies ameaçadas de extinção e endêmicas para o estado do Rio de Janeiro e Mata Atlântica evidencia que a restinga de Grumari é uma área essencial para a conservação da anurofauna dos remanescentes deste habitat no Brasil. Além disso, Grumari é a restinga com maior riqueza de espécies do estado e a segunda maior entre todas as áreas de restinga estudadas até o momento, quanto à anurofauna. / Although restinga habitats represent approximately 5000 km of the Brazilian coast, the information available about the composition of the anuran fauna present on those habitats are restricted to relatively few areas. Nowadays restinga habitats are under intense set of pressures as result of a demographic density five times higher than the average for the country leading to the occupation, degradation and eventual loss of such habitats. This is especially alarming for the threatened endemic populations of terrestrial vertebrates due to the difficulty of vegetation recovery after clearings. Presently, the remnants of these habitats along much of the eastern Brazilian coast are represented by completely isolated fragments. Herein we present the first approximation to the list of the amphibians from the restinga of Grumari, inserted in the Parque Natural Municipal de Grumari (PNMG), municipality of Rio de Janeiro, Rio de Janeiro state, southeastern Brazil. The area is situated in the Atlantic Rainforest Biome. Its also the first study on the community of litter anuran fauna, obtaining density data, for the Brazilian restinga. The study was carried out from May 2009 to December 2010 using two sampling methods: quadrant plots (4x4 m) and acoustic/visual transects. We recorded 22 species of anuran amphibians distributed in six families: Leptodactylidae (3), Craugastoridae (1), Bufonidae (1), Strabomantidae (1), Microhylidae (2) and Hylidae (14). We found ten species of litter frogs in 2560 m of sampled forest floor with the methodology of large plots. In the closed post-beach zone, there were only seven species of anuran leaf litter, while the restinga forest zone present the ten species recorded for the restinga. The overall density of litter frogs at the restinga of Grumari was 13.1 individuals per 100m, more than five of six published studies on the density of litter frogs in the Atlantic Rainforest. The estimated total biomass was 13131 g/100m, being currently the area with highest litter frog biomass on the planet. There was no statistically significant difference between the zones regarding community parameters (richness, density and biomass), even though there is difference between the environmental parameters measured in both zones. The factors that best explained the richness, density and biomass in the restinga of Grumari during the rainy season were, respectively, temperature, diameter of the trees/shrubs and the number of trees/shrubs. The presence of endangered and endemic species indicates that the restinga of Grumari is an important area for conservation of the anuran fauna in remnants of these habitats in the Rio de Janeiro state, being currently the richest known area in terms of amphibian species of all restinga areas in the state, and the second richest of the Brazilian restingas studied up to now.

In tropical forests, ants are numerous, diversified and ecologically important, being present from forest floor to upper canopy and exploiting a wide variety of diets. Nearly half of the ant species are directly in contact with the ground stratum, including the leaf-litter and the underlying soil, for nesting or foraging. The main factors known to influence ant distribution and abundance can be environmental (e.g. heterogeneous distribution of microhabitat size, nutrient availability, microclimate, soil properties) or biotic (e.g. inter- and intraspecific competition, prey availability). Some of these factors, such as leaf-litter volume or prey availability, may also vary seasonally. Also, the Ecuadorian Andes are known as being a hotspot of biodiversity for a large array of organisms, but it was not documented until now if this is also the case for ants.<p><p>The general aim of the PhD project was to identify, by both descriptive and experimental approaches, the factors determining the structure of a ground-dwelling ant assemblage at a small-spatial scale and its temporal variation in an evergreen premontane tropical forest of the Ecuadorian Andes.<p><p>In the descriptive part of the project, we studied both horizontal (along a transect) and vertical (across ground layers) species diversity and distribution of ground-dwelling ants. To attempt to explain the observed patterns, we measured a series of environmental factors varying at small spatial scale and/or seasonally: canopy openness, leaf-litter quantity, slope, and a series of soil physico-chemical properties (e.g. texture). The ant assemblage richness appeared to be at least as high as in the Amazonian Basin, with up to 33 species per m². The heterogeneity of species spatial distribution at small spatial scale was high, with distinct species composition (average Jaccard index = 0.2 ± 0.08 SD) and abundance (up to 40 fold) in contiguous plots. We observed a strong seasonal effect on the ant assemblage structure. The higher ant diversity and abundance found at the surface and in the mineral soil during the dry season suggested a seasonal peak of activity on the ground surface and the seasonal migration of drought-sensitive species downwards in the soil. Ant diversity was related to distinct environmental factors according to the ground layer considered. We found strong correlations between litter amount and dominant ant distribution in the leaf-litter layer, while we found no correlation with any factor in the soil layer. The low amount of negative association between dominant species suggested a low interspecific competition.<p><p>In the experimental part of the project, our aim was to identify experimentally the relative importance of habitat size vs. prey availability in structuring the leaf-litter ant assemblage. We studied the response of various ant trophic groups to an increased nutrient availability which boosted the decomposition of their leaf-litter habitat and enhanced the abundance of their prey. Bottom-up effect on the ant fauna (and other predaceous arthropods) regarding species composition and dominance was also studied. Stable isotope analysis was used to distinguish trophic groups among ants and mesofauna. Ants responded differentially according to their trophic group: despite increased prey availability, predatory species were negatively affected by nutrient supply, while other ant trophic group densities did not change. Our results showed that predatory ants are limited by habitat size rather than by prey availability, and that these ants are more affected by habitat loss than their prey, other ant trophic groups and other macrofauna taxa. Furthermore, a taxonomic shift occurred within each ant trophic group, leading to the replacement of dominant genera in fertilized plots.<p><p>As a conclusion, our results emphasize the importance of distinguishing layers among the ground matrix, since both ant faunas and their response to environmental factors vary vertically and seasonally. The distribution of ground-dwelling ants was only weakly explained by both the environmental factors measured and by biotic interactions, at a small spatial scale. Also, our results emphasize the importance of distinguishing trophic groups among the ant assemblage, since the response of these groups under changing conditions was different. In this regard, stable isotope analysis was a useful tool for investigating the trophic ecology of various leaf-litter taxa, and it was successfully used for the first time to assess the diet of leaf-litter ants and their position in the Brown Food Web relative to other taxa. Also, the isotopic approach allowed us to increase the knowledge about the biology of a rare and cryptic ant species, by revealing its top-predatory position. The outstanding local species richness that we observed confirms that the Ecuadorian Andes are also a biodiversity hotspot for ants. / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

Il est de plus en plus clair que nos écosystèmes sont liés les uns aux autres de façons multiples et parfois complexes. De plus en plus nous identifions de nouvelles façons dont deux systèmes échangent des ressources et de l’énergie. Le rôle de ces échanges et transferts est encore difficile à quantifier. Nous en savons relativement peu sur les interactions de ceux-ci avec des processus locaux et spatiaux, ainsi que sur leur importance relativement à ces processus locaux et régionaux plus connus. À travers ce projet, nous cherchons à éclaircir l’importance relative des subsides particulaires de feuilles (et particulièrement de leur stoechiométrie) sur les communautés littorales d’invertébrés benthiques. Nous avons récolté des invertébrés et des feuilles mortes sur 23 sites à travers 7 lacs relativement isolés de l’influence humaine et avons comparé l’influence de la stoechiométrie de ces subsides à l’influence de facteurs locaux de qualité de l’eau et de facteurs spatiaux. Les résultats suggèrent que l’importance de la qualité nutritive (i.e. stoechiométrie) est secondaire aux facteurs locaux de qualité de l’eau dans des milieux naturels. L’importance des subsides particulaires de feuilles semble être grandement dépendante du contexte et pourrait gagner en importance dans des contextes de fortes perturbations. Les résultats indiquent que la qualité nutritive des subsides de feuilles, leur contenu relatif en azote et phosphore, est associée avec de plus grande abondance de plusieurs taxons. La richesse spécifique n’étant pas affecté, c’est à travers l’équitabilité (i.e. une distribution des abondances plus stable) que la qualité nutritive des feuilles pourrait promouvoir une plus grande biodiversité d’invertébrés benthiques. / It is clear now, more than ever before, that our ecosystems are linked to one another in multiples and sometimes complex ways. The role of these exchanges and transfers is still hard to quantify. We know little of the interactions of these fluxes with local and spatial processes happening in ecosystems, as well as their relative importance compared to local and regional drivers of ecosystem functions and community structure. With this project, we aim to untangle the relative importance of particulate subsidies of leaves (and specifically their stoichiometry) on littoral communities of benthic invertebrates in lakes. We collected invertebrates and leaf litter on 23 sites across 7 lakes somewhat isolated from human influence and compared the influence of leaf litter stoichiometry to the influence of local water quality and spatial variables. Results suggest that nutritive quality of leaf litter (i.e. stoichiometry) is secondary to water quality. Importance of leaf subsidies appears to be context dependant and could gain in importance in systems with higher degrees of disturbances. Results that nitrogen and phosphorus content of leaf subsidies is associated with higher abundances of several taxonomic groups. Species richness being unaffected, it is through higher evenness (i.e. even distribution of abundances) that higher quality of leaves may promote higher biodiversity of benthic invertebrates.

No description available.