Ce travail de doctorat a pour objectif de comprendre les mécanismes et les réponses régionales de la variabilité climatique Holocène en ciblant plus spécifiquement la Rade de Brest et la Baie de Douarnenez. Dans les environnements côtiers, la vulnérabilité des sociétés humaines face aux aléas climatiques est particulièrement élevée et les pressions anthropiques s’exerçant sur les écosystèmes sont de plus en plus fortes. Ainsi, il s’agit de discuter la part respective des forçages naturels de ceux liés aux activités humaines dans les différents signaux paléoenvironnementaux holocènes reconstruits. Pour cela, plusieurs séquences sédimentaires nous ont permis de renseigner différentes périodes au cours des 10 000 dernières années. Des études multiproxies principalement basées sur des analyses palynologiques (pollen et kystes de dinoflagellés) ont été conduites permettant de discuter en parallèle des signaux continentaux et marins. Les études polliniques permettent de caractériser l’évolution des paysages terrestres tandis que les dinokystes, dénombrés à partir des mêmes lames palynologiques que les grains de pollen et spores, permettent de discuter les conditions paléohydrologiques de surface. De plus, dans le but d’affiner la compréhension de l’enregistrement des palynomorphes dans les sédiments marins de la Rade de Brest, des échantillons de surface délivrant un message palynologique actuel ont été analysés en préambule de l’étude paléoenvironnementale Holocène. Cette thèse a mis en évidence la robustesse des études palynologiques pour l’étude des variations paléoenvironnementales à l’échelle régionale en milieu côtier, et a démontré la pertinence de l’outil pour mettre en évidence l’imbrication des influences humaines et naturelles. Ce travail apporte ainsi une contribution régionale à l’étude de la variabilité environnementale Holocène en Bretagne, fournissant des enregistrements palynologiques haute résolution sur les derniers 150 ans (résolution de 1 à 4 ans) ainsi que sur les derniers milliers d’années caractérisés par l’influence grandissante des sociétés humaines en lien avec l’accroissement de la déforestation et des pratiques agro-pastorales sur les bassins versants (résolution moyenne de 30 ans). / This PhD study aims at understanding mechanisms and regional responses of the Holocene climatic variability, targeting the Bay of Brest and the Bay of Douarnenez. In coastal environments, the vulnerability of human societies to climate hazards is particularly high and anthropogenic pressures on ecosystems are increasing. In this context, the respective part of natural forcings from those related to human activities can be discussed thanks to paleoenvironmental Holocene reconstructions carried out on sediment archives.Several sedimentary sequences allowed us to focus on different key periods across the last 10,000 years BP.Multiproxy studies mainly based on palynological analyzes (pollen and dinoflagellate cysts) allowed discussing continental and marine signals in parallel, and thus to better understand forcing mechanisms.Pollen studies are used to characterize terrestrial landscape evolutions while dinocysts, counted from the same palynological slides as pollen grains and spores, make it possible to discuss surface palaeohydrological conditions. In addition, in order to complete the understanding of our Holocene palynomorph records conducted on Bay of Brest marine sediments, Bay of Brest surface sediments were investigated so as to deliver a current palynological message.This work has demonstrated the robustness of palynological studies conducted at a regional scale and in a macro-estuarian environment, and also the relevance of our tools to highlight the intertwining of human and natural influences. This work therefore represents a regional contribution to the study of Holocene environmental variability in Brittany, providing high resolution palynological records over the last 150 years (resolution of 1 to 4 years) as well as over the last 9,500 years BP (averaged resolution of 30 years) characterized by the growing influence of human societies in relation to increased deforestation and agropastoral practices on watersheds.

Cette thèse étudie la dynamique de la végétation Holocène pour Burmarrad dans le NW Malte et fournit une reconstruction paléoclimatique quantitative à base de pollen pour cet archipel méditerranéen situé au centre. Le record de pollen donne un nouvel aperçu l'échange végétation 7280-1730 cal BP qui correspondent bien avec other régional dossiers. La reconstruction du climat fournit également forte corrélation avec les sites du sud (en dessous de 40oN) de la Méditerranée. L'interprétation suggère un paysage initialement ouvert au début du néolithique, se développer en un dense Pistacia brousse ca. 6700 calBP. Depuis environ 4450 calBP le paysage devient de nouveau ouvert, coïncidant avec le début de l'âge du bronze sur l'archipel. Cette période coïncide avec une instabilité accrue du climat (entre 4500 et 3700 calBP) qui est suivie par une diminution progressive de la disponibilité de l'humidité de l'été à la fin de l'Holocène. Durant la période romaine début de l'occupation (1972-1730 calBP) le paysage reste généralement ouvert avec une augmentation modérée de Olea. Cette augmentation correspond à des preuves archéologiques pour la production de l'huile d'olive dans la région, avec l'augmentation des taxons cultivés des cultures et des espèces rudérales associés, ainsi que d'une hausse des cas d'incendies. Cette thèse propose également une synthèse des résultats d'un autre noyau (BM1) provenant de la même zone de chalandise, ainsi que les résultats d'une étude préliminaire de la pluie de pollen de surface moderne. L'archipel fournit des indications sur la végétation, les impacts humains et les changements climatiques dans un contexte de l'île au cours de l'Holocène. / This thesis investigates the Holocene vegetation dynamics for Burmarrad in north-west Malta and provides a pollen-based quantitative palaeoclimatic reconstruction for this centrally located Mediterranean archipelago. The pollen record from this site provides new insight into the vegetation changes from 7280 to 1730 cal BP which correspond well with other regional records. The climate reconstruction for the area also provides strong correlation with southern (below 40oN) Mediterranean sites. The interpretation suggests an initially open landscape during the early Neolithic, surrounding a large palaeobay, developing into a dense Pistacia scrubland ca. 6700 cal BP. From about 4450 cal BP the landscape once again becomes open, coinciding with the start of the Bronze Age on the archipelago. This period is concurrent with increased climatic instability (between 4500 and 3700 cal BP) which is followed by a gradual decrease in summer moisture availability in the late Holocene. During the early Roman occupation period (1972 to 1730 cal BP) the landscape remains generally open with a moderate increase in Olea. This increase corresponds to archaeological evidence for olive oil production in the area, along with increases in cultivated crop taxa and associated ruderal species, as well as a rise in fire events. This thesis also provides a synthesis with the results from another core (BM1) taken from the same catchment area, as well as results of a preliminary modern surface pollen rain study. The Maltese archipelago provides important insight into vegetation, human impacts and climatic changes in an island context during the Holocene.

É apresentada aqui a revisão taxonômica das espécies de Viguiera Kunth que ocorrem no Brasil, com inclusão de descrições, ilustrações, mapas de distribuição e comentários. Também são providas chaves de identificação para grupos relacionados e para as espécies sul-americanas. O estudo da anatomia foliar forneceu novos subsídios para a delimitação de espécies ou grupo de espécies. As análises polínicas também apresentam informações parciais úteis à taxonomia. Foi elaborada uma investigação sobre Viguiera sensu lato, através de três análises envolvendo diferentes números de táxons terminais, com uso de dados morfológicos; a primeira visou o esclarecimento da real posição taxonômica de seus representantes e as duas últimas pleitearam uma melhor delimitação dos grupos de espécies no continente. A análise dos padrões de distribuição geográfica possibilitou a delimitação de dois grupos com características morfológicas distintas, além de um intermediário; o primeiro exclusivo da região dos Andes, o segundo extra-andino e o terceiro andino com pequenas intrusões em outras localidades. Os resultados também corroboram a hipótese de outros autores, de que a origem do gênero é recente no Brasil. Em relação às condições edáficas, existem dois grupos de espécies no Brasil; o primeiro encontrado em regiões com clima do tipo Cwa e o segundo no clima do tipo Aw, da classificação de Köpen; apenas 4 espécies ocorrem em clima Cfa, mas não são exclusivamente brasileiras. Não houve respaldo para a transferência das espécies sul-americanas para o gênero Rhysolepis. / This study presents a taxonomic review of the species Viguiera Kunth that occur in Brazil, and includes descriptions, illustrations, distribution maps and comments. Identification keys are also provided for related groups and to the South American species. The leaf anatomy study supplied new subsidies for the delimitation of the species or of species groups. The pollinic analysis either presents useful partial information in taxonomy. An investigation was elaborated on Viguiera sensu lato, through three analyses, involving different numbers of terminal taxa and using morphological data; the first one tried to explain the real taxonomic position of its representative members and the last two sought for a better delimitation of the groups of species in the Continent. The analysis of the patterns of geographic distribution made possible the delimitation of two groups with different morphological characteristics, and a intermediate one; the first group is exclusive from Andean region, the second not happens in the Andes, and the third do not occur in the Andes, with a few intrusions in other localities. The results also corroborate others author\'s hypothesis, that the origin of the genus is recent in Brazil. In relation of the edaphic conditions, there are two groups of species in Brazil: the first one is found in regions with climate of the type Cwa and the second in the climate of the type Aw, of the Köpen classification; only 4 species happen in climate Cfa, but they are not exclusively Brazilian. There was no support for the transfer of the South American species to the genus Rhysolepis.

Composition of pollen pellets foraged by honeybees, sampled in Degernäs and Tavelsjö, Västerbotten County, during early summer 2020, is used to explore if honeybees are monofloral or polyfloral. Samples from different days and different colours were evaluated by light microscopy. Each unique pollen species in each pellet was morphologically identified with help of an international pollen database (PalDat) and a common bee plant document, using light microscopy and scanning electron microscope photographs. A selection of pollen species were identified down to species level and were used to explore which wild pollinators can also pollinate these plant species, to speculate around possible competition scenarios between them and honeybees. SEM and DNA extraction were performed with a selection of the pollen pellets and with the extracted DNA, different PCR primers targeting different plant gene markers were tested to see which ones worked with pollen from northern Sweden. More detailed pictures of the pollen grains were seen in SEM which helped ease the species identification of some of them. The results showed that only a few of the pollen pellets had only one detected plant species while the rest had 2 or more plant species in them. Thus, these data indicate that the honeybees in Degernäs and Tavelsjö are polyfloral, at least for the samples studied in this bachelor thesis. Methods are evaluated and the findings were that a combination of morphological and molecular biology studies are both needed to be able to establish a new updated pollen database for northern Sweden.

The Gray Fossil Site, northeastern Tennessee, is formed by multiple karst sub-basins filled with lacustrine sediments. The oldest sediments found were recently dated as Paleo-Eocene by palynological means, whereas the youngest sediments are considered Mio-Pliocene based on their faunal assemblage. In this study, we examined the Mio-Pliocene lacustrine sediments from the Gray Fossil Site to determine the Late Neogene floral characteristics of a site within the southern Appalachian Mountains. The Mio-Pliocene lacustrine sinkhole fill preserves a unique fossil assemblage, which includes invertebrate, vertebrate, and floral remains. Floral remains are represented by wood, seeds, leaves, and pollen grains. Forty-seven palynological samples from six different test-pits were analyzed. All pits exhibit a low pollen yield, a result of basic pH levels, drought, and fire events that occurred during deposition. The palynofloral assemblage has a low to moderate diversity and is largely dominated by a Quercus-Carya-Pinus assemblage (~ 90% of the palynoflora). The presence of Pterocarya grains supports a Late Neogene age for these lacustrine sediments. Comparison with modern pollen-based floras from North America suggests that: (1) examined pits can be discriminated into two separate groups based on their palynofloral signatures, (2) the Mio-Pliocene vegetation at the site ranged between a closed to open woodland setting, depending on the intensity and frequency of drought and fire events, and (3) the fossil palynofloral assemblage is comparable to what would be expected in the modern North American Mesophytic Forest region.

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Pollen analysis of two surface transects of modern soil samples and four stratigraphic sections from the central Sierra Nevada of California have provided a climatic record covering the time interval since the recession of the last glaciers of the Wisconsin glaciation. Two separate warm intervals are recognized between the recession of the Wisconsin glaciers and the reappearance of glaciers in the Sierra during the Little Ice Age.