The thesis presents systematical study and taphonomical evaluation of fusite wood specimens collected in the middle bench of the main lignite seam in the Bilina mine. In the introduction part, there are a general characteristic of the Most Basin and its geological setting with respect to the main lignite seam. Consequently, the charcoal is described in detail. Generally, the charcoaled wood, which was produced during wildfires in the Tertiary forests, shows well preserved anatomical details. The final part resumes systematics and taphonomy of the charcoal specimens collected by the author.

Les tourbières stockent des quantités importantes de carbone (C) et jouent un rôle essentiel dans la dynamique globale du C, mais elles sont vulnérables aux changements globaux et aux perturbations humaines, notamment les perturbations linéaires telles que les routes non pavées (en gravier). La construction de ces routes et leur utilisation introduisent des quantités considérables de poussière de route dans les tourbières adjacentes, ce qui, combiné au dépôt de poussière atmosphérique, exerce une influence significative sur les tourbières qui est souvent négligée. L'objectif de cette recherche est d'étudier les effets de la poussière des routes sur la structure et les fonctions des tourbières, et plus particulièrement d'examiner les changements dans les assemblages de plantes et de thécamibiens, la chimie des tissus foliaires, de la tourbe et des eaux souterraines, ainsi que l'accumulation de C le long des gradients de dépôt de poussière. Pour ce faire, trois tourbières ombrotrophes ont été sélectionnées dans l'est du Québec, au Canada, qui sont exposées à des niveaux de dépôt de poussière de route variables et chimiquement distincts. Sur chaque site, un transect aligné sur la direction dominante du vent, commençant au bord de la route et perpendiculaire à celle-ci, a été échantillonné à des intervalles croissants jusqu'à 250 m de la route. Les résultats montrent que les dépôts de poussières de route affectent de manière significative les assemblages de plantes et de thécamibiens notamment en créant de l'ombrage physique et en bloquant les stomates, en apportant des cations basiques et en augmentant la disponibilité en nutriments. Plus précisément, les dépôts de poussières de route tendent à réduire la couverture des sphaignes et, dans le cas des amibes, l'abondance des espèces mixotrophes vivant en symbiose avec les algues et celles construisant des coquilles protéinées. Les dépôts de poussières routières réduisent les rapports stœchiométriques de C, d'azote (N) et de phosphore (P) dans la tourbe de surface et les tissus foliaires en réduisant la teneur nette en C et en fournissant des nutriments jusqu'à 200 m du bord de la route et à 15 cm de profondeur à partir de la surface. L'ampleur de cet impact dépend du niveau de dépôt et de la composition chimique de la poussière de route, ainsi que de la date de construction de la route. L'intensité des dépôts de poussières routières est nettement supérieure à celle des dépôts de poussières atmosphériques historiques, ce qui produit des effets contrastés sur les taux d'accumulation de C. Il a été démontré que les dépôts de poussières atmosphériques favorisent l'accumulation de C, tandis que les dépôts de poussières routières ont l'effet inverse, en réduisant le taux d'accumulation de C. Dans l'ensemble, notre étude met en évidence le rôle essentiel, mais encore méconnu, des dépôts de poussières routières dans la formation de la structure des communautés biologiques et dans la régulation de la fonction des tourbières adjacentes. L'étroite corrélation entre les dépôts de poussières routières et la composition des communautés microbiennes suggère l'utilisation possible des thécamibiens comme bioindicateurs des événements de poussières passés et présents. Les méthodes et les résultats de cette étude, qui ne se limitent pas aux effets des poussières routières sur les tourbières, peuvent être étendus aux effets similaires d'autres dépôts de poussières sur les écosystèmes voisins. / Peatlands store substantial amounts of carbon (C) and are of critical importance in global C dynamics, but are vulnerable to global changes and various forms of human disturbance, including linear disturbances such as unpaved (gravel) roads. The construction and use of these roads introduce considerable amounts of road dust into adjacent peatlands, which, combined with atmospheric dust deposition, exerts a significant influence on peatlands that is often overlooked. The objective of this research is to investigate the effects of road dust on peatland structure and function, specifically to examine changes in plant and testate amoeba assemblages; foliar tissue, peat, and groundwater chemistry; and C accumulation along road dust deposition gradients. To achieve this, three ombrotrophic peatlands were selected in eastern Québec, Canada, which are exposed to chemically distinct and varying levels of road dust deposition. At each site, a transect aligned with the dominant wind direction, starting at and perpendicular to the roadside, was sampled at increasing intervals up to 250 m away from the road. The results show that road dust deposition significantly affects plant and testate amoeba assemblages with a diverse array of factors involved, mainly including physical shading and stomatal blockage, base cation inputs, and increased nutrient availability. Specifically, road dust deposition tends to reduce the coverage of Sphagnum mosses, and in the case of amoebae, the abundance of mixotrophic species living in symbiosis with algae and those constructing proteinaceous shells. Road dust deposition reduces the stoichiometric ratios of C, nitrogen (N), and phosphorus (P) in surface peat and foliar tissues by reducing the net C content and supplying nutrients up to 200 m away from the roadside and 15 cm deep from the surface. The extent of this impact depends on the deposition level and the chemical composition of the road dust, as well as the age of the road. The intensity of road dust deposition is markedly greater than that of historical atmospheric dust deposition, yielding contrasting effects on C accumulation rates. Atmospheric dust deposition has been demonstrated to promote C accumulation, while road dust deposition has the opposite effect, reducing the rate of C accumulation. Overall, our study highlights the pivotal yet unacknowledged role of road dust deposition in peatlands on shaping their structure of biological communities and regulating their function. The close correlations between road dust deposition and microbial community composition suggest the possible use of testate amoebae as bioindicators of past and present dust events. The methods and findings of this study, which are not limited to its scope of road dust effects on peatlands, can be extended to similar effects of dust from other proximate sources on neighbouring ecosystems.

This study focuses on the vegetation of the African city of Bujumbura, Burundi. Urban flora is detailed according to the origin of the species (native or introduced), their life form, the use of these species by the local population and their behaviour (invasive or not). <p>The correlation between different natural and anthropogenic environmental factors and the composition of plant communities has been demonstrated through the analysis of vegetation plots. Three types of green areas were studied: spontaneous vegetation on terra firma, wetlands <p>and domestic gardens.<p><p>The main ecological factor correlated to the composition of the spontaneous vegetation of terra firma is the degree of urbanization. From the suburb to the city centre, savannah species typical for the region are replaced by alien invasive species, mostly ruderals. The latter generally have a large distribution, often on several continents. The physiognomy of the vegetation also changes, with hemicryptophytes and phanerophytes in the outskirts and the dominance of therophytes and chamaephytes in the city centre.<p><p>In most of wetlands, a large proportion of the plant species are natives, but some wetlands are almost totally invaded by alien species. Soil type is the main environmental factor correlated with <p>the variability of the vegetation.<p><p>The flora of domestic gardens is mainly composed of introduced species used as ornamental, food or medicinal plants. The socio-economical status of the neighbourhood is the main factor correlated with the variability of the garden flora. In high standing neighbourhoods, most species are onamental, with many trees and shrubs. In popular neighbourhoods, the flora is mainly utilitarian (vegetables and fruits), with a significant proportion of native species, and composed mainly of annual species. <p>A small proportion of the alien species cultivated in gardens has become invasive in the semi-natural vegetation of the city and its surroundings. Many other species cultivated in the gardens could become invasive, based on their ecology and their invasive behaviour in other regions with a climate similar to that of Bujumbura.<p><p>Overall, the city of Bujumbura has a diverse flora, with many useful species (vegetables and fruits, traditional medicine, construction of fences and roofs, material for mats and art objects.). The vegetation also hosts wildlife: birds, fishes, hippos, crocodiles etc… <p><p>In conclusion, the vegetation of Bujumbura contributes to biodiversity conservation and provides services to the urban population, but the expansion of alien invasive species and the consequent homogenization of the vegetation is a challenge for the future.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished