Spelling suggestions: "subject:"bodenvegetation relationships"" "subject:"polstervegetation relationships""
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Pollen productivity estimates and pollen-based reconstructions of Holocene vegetation cover in Norhtern adn temperate China for climate modellingLi, Furong January 2016 (has links)
Model projections of future climate change require that coupled climate-vegetation models are developed and validated, i.e. these models should be able to reproduce past climate and vegetation change. Records of pollen deposited in lake bottoms and peat bogs can provide the information needed to validate these models. The aim of this thesis was i) to explore the modern relationships between pollen and vegetation in northern and temperate China and estimate pollen productivity of major plant taxa, and ii) to use the results of i) to produce the first reconstruction of plant cover in China over the last 10 000 years for the purpose of climate modelling. A study of the modern pollen-vegetation-climate relationships was performed in northwestern China (Paper I). Pollen productivity for 18 major plants of cultural landscapes in central-eastern China was estimated (Paper II). Based on a synthesis and evaluation of all existing estimates of pollen productivity in the study region, a standard dataset of pollen productivity for 31 plant taxa is proposed (Paper III). This dataset was used to achieve pollen-based REVEALS reconstructions of plant cover over the last 10 000 years in 35 regions of northern and temperate China (Paper IV). The major findings can be summarized as follows. Paper I: Annual precipitation (Pann) is the major climatic factor influencing pollen assemblages, followed by July precipitation (PJul). The shared effect of combinations of two climatic factors explains a larger portion of the variation in pollen data than individual variables. Paper II: Of the 16 reliable pollen productivities estimated, the estimates for 8 taxa are new, Castanea, Cupressaceae, Robinia/Sophora, Anthemis type/Aster type, Cannabis/Humulus, Caryophyllaceae, Cruciferae, and Galium type. Trees have in general larger pollen productivity than herbs. Paper III: Of the total 31 taxa for which estimates of pollen productivity are available in China, 13 taxa have more than 1 value. All or most of these values are similar for Artemisia, Cyperaceae, Larix, Quercus and Pinus. Eight taxa have very variable estimates. Paper IV: The REVEALS plant percentage-cover strongly differs from the pollen percentages, and they provide new important insights on past changes in plant composition and vegetation dynamics.
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Modélisation de la végétation holocène du Nord-Ouest de la France : reconstruction de la chronologie et de l’évolution du couvert végétal du Bassin parisien et du Massif armoricain / Holocene vegetation cover of the North-Western France : reconstrution of the chronology and evolution of the vegetation cover from the Paris Basin and the Armorican MassifDavid, Rémi 04 April 2014 (has links)
Comprendre la complexité des relations entre nature et sociétés a toujours constitué un défi pour les recherches dans le domaine de l'environnement. A l'ère de la compilation de données dans de nombreuses disciplines, la modélisation constitue l'une des options les plus attractives pour comprendre et traduire les évolutions du milieu naturel. Les objectifs principaux de ce travail de recherche sont 1) de restituer la structure du couvert végétal régional et d'en retracer les évolutions au cours de l'Holocène au sein de deux régions du nord-ouest de la France, le Bassin parisien et le Massif armoricain, et 2) de les interpréter en termes de relations entre les sociétés pré- et protohistoriques et leur milieu naturel. Pour cela, nous avons mis en place une démarche méthodologique visant à 1) redéfinir le cadre chronologique des séquences polliniques rassemblées pour les deux régions, 2) tester, adapter puis appliquer un modèle de reconstitution quantitative du couvert végétal, 3) définir une histoire de la végétation estimée relative à chaque aire géographique modélisée, 4) comparer ces histoires régionales et 5) les confronter aux informations disponibles en matière de densités de sites archéologiques et de proximité de ces sites aux points de sondages polliniques. Des cadres structurant l'évolution du couvert végétal pour chacune des deux régions étudiées ressortent les grandes étapes de la mise en place des paysages au cours de l'Holocène. Des spécificités régionales ont cependant pu être identifiées, tant en matière de chronologie de l'évolution de la végétation estimée qu'en matière de proportions relatives des taxons présents. Une certaine singularité doit donc être reconnue à l'évolution des paysages holocènes de chacune de ces deux parties du nord-ouest de la France. On remarque notamment des dynamiques et des niveaux d'anthropisation tout à fait distincts entre Bassin parisien et Massif armoricain de la fin du Mésolithique à celle du Néolithique. A l'inverse, on retrouve de part et d'autre une certaine similarité entre les proportions estimées des taxons marqueurs d'anthropisation entre la fin du Néolithique et celle de l'âge du Bronze. Des liens évidents entre les variations de l'impact anthropique enregistré et celles de la densité des occupations reconnues ont par ailleurs pu être observés. / Understanding the complex relationship between nature and societies has always been a challenge for environmental sciences. With the growing impact of databases in many disciplines, the modelling appears as one of the most attractive methods for understanding and describing environmental changes. The main objectives of this research work are 1) to reconstruct the structure of the regional vegetation cover and to determine its trends during the Holocene in two regions of north-western France, the Paris Basin and the Armorican Massif, and 2) to interpret them in terms of relationships between the pre- and proto-historic societies and their environment. Thus, we set up a methodological approach aimed at 1) redefining the chronological framework of pollen sequences collected for both regions, 2) testing, adapting and then applying a model in order to produce quantitative estimates of vegetation cover, 3) defining a history of the estimated vegetation for each area modelled, 4) comparing these regional results and 5) confronting them to the available informations in terms of densities of archaeological sites and proximity of these sites to the pollen samples locations. From the general framework structuring the vegetation cover changes for both study areas stand out the major steps of the development of natural landscapes during the Holocene. Nevertheless, regional distinctive features were identified; both in terms of chronology of the vegetation cover changes, than in terms of relative proportions of taxa in the vegetation estimates. Some singularity must be recognized in the Holocene landscape evolution for each of these two parts of north-western France. We noticed distinct rates and rhythms, concerning the anthropogenic impact on the Paris Basin and the Armorican Massif estimated vegetation covers, from the late Mesolithic to the late Neolithic. On the other hand, we found similarities between both areas concerning the estimated proportions for anthropogenic markers taxa between the late Neolithic and the late Bronze Age. Clear links between changes observed in human impact on the vegetation cover estimates and those recorded in the density of archaeological sites were also noticed.
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