No description available.

L’objectif de ce mémoire est de déterminer si l’unicité écologique des communautés végétales est un critère approprié pour prioriser l’allocation des efforts de conservation dans les milieux humides lacustres. Pour répondre à cette question, j’ai utilisé des données d’inventaire végétal dans deux emplacements géographiques situés dans le sud du Québec et pour trois types de milieux humides (i.e., frênaies, aulnaies, tourbières). J’ai d’abord identifié les milieux humides statistiquement uniques en calculant leur contribution locale à la diversité bêta (LCBD). J’ai ensuite mesuré le degré d’association relatif entre les valeurs d’unicité écologique et plusieurs autres critères couramment employés pour déterminer les priorités de conservation, et ce, à l’aide de corrélations de Pearson et de partitionnements hiérarchiques. Les tourbières uniques avaient une grande valeur de conservation dans les deux régions étudiées, alors que les aulnaies et frênaies uniques montraient des signes d’altération de leur composition en espèces. La composition en espèces des sites uniques devrait donc être examinée pour en déterminer la valeur de conservation, puisqu’elle pourrait être affectée par le niveau d’intégrité du paysage. La proportion d’espèces rares ainsi que la présence d’espèces spécialistes sensibles aux perturbations étaient corrélées de façon importante et congruentes avec l’unicité dans les deux régions étudiées. Au contraire, la richesse spécifique était négativement corrélée avec l’unicité, ce qui suggère la nécessité d’un compromis. Une combinaison de critères complémentaires devrait donc être utilisée en plus de l’unicité afin d’identifier l’ensemble optimal de sites à protéger dans un contexte donné. / This study aimed to determine whether plant composition uniqueness is an adequate criterion for assessing conservation priorities in lake-edge wetlands. To answer this question, I used vegetation data from two large datasets of lake-edge wetlands located in southern Québec, which encompassed three wetland types (i.e., ash-dominated swamps, alder-dominated swamps, peatlands). I first identified statistically unique wetlands by computing their local contribution to beta diversity (LCBD). I then measured the relative association between ecological uniqueness values and other criteria commonly used to assess conservation priorities using Pearson correlations and hierarchical partitioning. Unique peatlands had a high conservation value in both study regions, while ash- and alder-dominated swamps showed more signs that their species composition had been altered. The species composition of unique sites should thus be examined closely to determine its conservation value, as it could be affected by the overall integrity of the landscape. The proportion of rare species and the presence of disturbance-sensitive specialist species were appreciably correlated and congruent with uniqueness in both study regions. On the other hand, species richness was negatively correlated with uniqueness, suggesting that there was a trade-off. A combination of complementary criteria should therefore be used in conjunction with uniqueness in order to identify the optimal set of sites to protect in a given context.

Light is essential component of forest ecosystem, as limited light availability in forest-floor restricts herb and tree seedlings growth. Importance of light availability for maintaining plant species diversity and community structure wasn't sufficiently evaluated in the Czech Republic. This study focus on the ecological relevance of light availability on both landscape and local scale. Relationship of light to cover, diversity and species composition was quantified in the thesis. Dominant tree species affected light availability and its spatial variability. Light availability was along the soil reaction and slope most influential factor for large-scale species diversity. Within-site light variability affected plant diversity more than soil reaction variability. Measuring light by means of hemispherical photography seems to be an appropriate for studies like this. Light availability influnence on community compostition is weak in comparison with other environmental gradients.

Semi-natural grasslands of the eastern Moravia have big potential to host species-rich plant communities. However, changes in land-use during the second half of the last century were rapid and vast and many grasslands had been ploughed over. In the early 80s some arable lands were sown with low diversity clover-grass mixture and transferred back to grassland. Restoration of grasslands on former arable fields is a major challenge. Their colonisation by grassland species may be complicated by initial seeding productive low diversity seed mixtures. The aim of this study was to estimate differences in species composition and species diversity between ex-arable artificially seeded grasslands and fragments of grasslands with continuity over 70 years in the north part of White Carpathian Mts., SE Czech Republic and identify species traits limiting species ability to colonize the ex-arable grasslands. Target plant species (total of 137) were surveyed on 66 grasslands. Surveyed grasslands were according to continuity and type of management. Coordinates of centroids from each polygon (i. e. surveyed grassland) were used to treat the spatial correlation of the surveyed grasslands. The effect of continuity on species composition and diversity was tested after accounting for differences in the management and...

This thesis is the first of its kind that evaluates the species composition, species richness and species abundance of zooplankton in littoral samples of 90 Tatras lakes (Western and High Tatras of Slovakia and Poland) collected in September 2004 in the context of environmental parameters of lakes and spatial relationships of individual lakes. The most frequently occurring species in the Tatras lakes in 2004 were also evaluated in terms of their occurrence in the lakes a century ago (Minkiewicz 1914, 1917 and Lityński 1913, 1917), during the period of acidification (Ertl & Vranovský 1964, Ertl et al. 1965, Hrbáček et al. 1974, Stuchlík et al. 1985) and during the period of recovery of the lakes from acidification (Hořická et al. 2006, Sacherová et al. 2006). Relationships between variables were analysed using Poisson regression, cluster analysis with multinomial regression, canonical correspondence analysis, Mantel tests and multiple negative binomial regression. Using analyses, lakes were divided into four clusters (A, B, C, D). Each cluster consisted of lakes with the same environmental and spatial factors and similar species composition. Thirteen zooplankton species (Acanthocyclops vernalis, Acroperus harpae, Alona affinis, Arctodiaptomus alpinus, Ceriodaphnia quadrangula, Cyclops abyssorum...

No description available.

The life of bryophytes is closely connected with their surrounding environment. Changes in atmospheric conditions on the microscale directly affect the physiological functions of bryophytes, which in turn determine their distribution. The current development of technologies allows us to measure the microclimate affecting bryophytes directly in the field. Nevertheless, there have not been many studies published examining the response of bryophytes to in situ measured microclimate. This diploma thesis is one of the first in Europe to provide data from continuous field microclimatic measurement performed on a scale relevant to bryophytes. It deals with the influence of the microclimate on the bryophyte species richness and community composition within a single gorge in the Bohemian Switzerland National Park. For 17 months, 38 HOBO Pro v2 Onset dataloggers were recording air temperature and air humidity 10 cm above the ground. I performed detailed bryological survey on two differently sized plots (circle with a radius of 1 or 2 m) around each of the dataloggers. The microclimate is influenced by the topography and character of the vegetation, therefore I derived topographical data from a digital terrain model (resolution of 1 m), calculated the canopy openness using hemispherical photographs and...

No description available.

No description available.

Les écosystèmes herbacés méditerranéens, caractérisés par une importante biodiversité, ont subi de considérables changements d‟usage. Désormais, leur conservation est devenue insuffisante au regard de l‟augmentation des dommages causés par les activités humaines. La restauration écologique apparaît donc comme un outil approprié pour participer à leur préservation. Des recherches préalables sur les différents compartiments de l‟écosystème ainsi que sur les facteurs responsables de l‟assemblage de leurs communautés avant et après dégradations sont donc nécessaires afin de mettre en place des méthodes de restauration adaptées à ces écosystèmes. Ainsi, en utilisant comme modèle biologique les Coussouls de Crau et leurs friches post-culturales (Bouches-du-Rhône, France), représentatif de nombreux écosystèmes steppiques méditerranéens, nous avons choisi de déterminer et d‟étudier les principaux filtres potentiellement responsables de l‟organisation de cette communauté végétale. Le pâturage ovin, les changements trophiques du sol, les phénomènes de compétition et la capacité de reproduction et/ou de dispersion des espèces, identifiés lors d‟une première étude sur la régénération de la steppe, ont ainsi été étudiés dans trois expérimentations différentes. Deux protocoles de restauration écologique in situ (transfert de foins et semis d‟espèces structurantes) et un protocole d‟expérimentation ex-situ testant les interactions d‟une sélection d‟espèces de la steppe ont permis de réaliser ces recherches. Nos principaux résultats montrent que les filtres de reproduction/dispersion, le niveau trophique du sol, la compétition et le régime de perturbations récurrentes lié au pâturage ovin ont un rôle déterminant dans les changements de la composition et de la structure de la communauté et ils expliquent ainsi en partie le ralentissement de sa dynamique successionnelle vers la steppe de référence. Nous avons également pu démontrer que ces filtres interagissaient entre eux. Au niveau de la recherche appliquée, les protocoles testés favorisent le retour de la végétation steppique, néanmoins la composition des parcelles restaurées reste toujours très différente de l‟écosystème de référence à très court terme (deux à trois années après la restauration). Cela démontre que même si nous comprenons mieux aujourd‟hui les facteurs expliquant l‟organisation de cette communauté, il est cependant toujours difficile de la restaurer dans son intégralité car il n‟est pas aisé de manipuler et de trouver un équilibre entre l‟action de ces différents facteurs. Il est donc désormais plus que nécessaire de poursuivre ces recherches fondamentales et appliquées notamment au niveau des processus de maturation et de structuration des vieilles communautés végétales herbacées. / Mediterranean herbaceous ecosystems which are characterized by a high biodiversity have been submitted to a lot of changes in use. Their conservation is not sufficient enough and ecological restoration seems to be an adapted solution to improve conservation efforts as it can mitigate damages induced by human activities. To develop restoration methods adapted to these ecosystems, preliminary researches on the different communities composing an ecosystem and the filters which are responsible for community assemblage before and after disturbance are necessary. Representative of numerous Mediterranean steppe ecosystems, the “Coussouls de Crau” and their ex-arable-fields (Bouches-du-Rhône, France) are the biological models used to identify and study the principal filters potentially responsible for organizing the plant communities. Sheep grazing, trophic changes, competition and reproduction and /or species dispersal, were identified in a first study on steppe regeneration; these filters were then the core of the following three research experiments. We carried out two in-situ restoration protocols (hay transfer and sowing foundation species) and one ex-situ experiment testing interactions between a selection of steppe species. The main results show that reproduction, seed dispersal, soil trophic level, competition, extensive sheep grazing are filters which have a determinant role in structuring the communities, in determining plant composition and partly in explaining the slow dynamics towards the reference steppe. Also, we show that filters interact between them. For applied restoration, the tested methods promote steppe vegetation come back, but in the short term (two or three years after restoration), the composition of restored areas remains different to the reference ecosystem. Even if we understand better the different factors which explain community organization, these results demonstrate that it is difficult to restore it integrally because it is not easy to manipulate and find an equilibrium between the different filters actions. Now it is necessary to continue these fundamental and applied researches, in particular on the maturation and structure of the old herbaceous plant communities.