Pollen and packrat midden data from the Great Basin indicate that the Pleistocene vegetation of the region was a combination of subalpine conifers on coarse substrates and steppe plants on finer valley bottom soils. While some of the modern dominants of the woodland zone were apparently absent from this region, other woodland and montane plants apparently persisted through the late Pleistocene. Some features of the Pleistocene environment, such as the large pluvial lakes, apparently disappeared by 12,000 yr B.P., while subalpine plants remained well below their modern elevational limits after 11,000 yr B.P. Limber pine and Rocky Mountain juniper apparently did not retreat from the lower mountain slopes until after 6500 yr B.P. Montane and woodland conifers, rare or absent in the region during the Wisconsin, dispersed across the region in the Middle Holocene. Other plants apparently did not reach their modern geographic limits until after 3000 yr B.P. The low elevational occurrences of subalpine species suggest that the late Pleistocene climate of the Great Basin was characterized by summer temperatures that were as much as 10°C cooler than those of today, and that there was some augmentation in the level of mean annual precipitation. The vegetational records provide no evidence of greater than modern levels of summer precipitation. While the persistence of montane plants at relatively low elevations implies cool or moist conditions through the Early Holocene, evidence from lacustrine systems suggests that there was a trend toward increasingly dry conditions during this period. The main period of migrations of woodland plants seems to slightly postdate the warmest and/or driest part of the Holocene, and these migrations may have been related to relatively high levels in summer temperatures, summer precipitation, and/or winter temperatures. Pollen data from a high elevation site, in conjunction with changes in water level in lower elevational lakes, suggest a return to cooler and/or moister conditions after 4000 yr B.P.

This thesis examines the role of autogenic and allogenic forces in determining the timing and development of blanket peat initiation and how the occurrence and growth of blanket peat subsequently constrains human activities. A number of factors involved in the formation of blanket peat have been defined in the literature, in particular the roles of climate change, soil processes and anthropogenic effects, tested in this thesis from a typical peat-covered upland in south west Scotland. Tests are developed from a multi-proxy approach and by comparing peat-stratigraphic and palaeoecological records from a series of nine 14C dated peat profiles from a single hillside. A detailed examination of the sequence and timing of blanket peat initiation in the Holocene Epoch is presented from a case study from the head of the Glen App valley, Lagafater, south west Scotland. The evidence was taken from a total of nine peat transects at 215m OD, 300m OD and 400m OD where agricultural, hydrological and micro-climatic effects are expected to have differed and had different impacts on soils and vegetation. Samples were retrieved from the top, middle and bottom of a gently undulating slope at each altitude. This has allowed a localised picture of peat initiation to be obtained from each locality and with changes in altitude, allowed for an analysis of the factors responsible up and down slope and the identification of synchronous autogenic forces. A number of analytical techniques have been used. Pollen analysis was undertaken as the principal method of vegetation reconstruction at all sites, particularly through the initiation horizon. Variations in mire-surface wetness, determined through dry bulk density and humification analysis, were also employed to generate a record of probable changes in effective precipitation and the effect these may have had on the accumulation rate of the blanket peat. In order to attempt to answer the question of when blanket peat was initiated and to establish the synchroneity of changes, twenty nine AMS 14C dates were obtained. The evidence suggests that blanket peat developed during the Mesolithic period, through to the early Bronze Age. It substantiates an anthropogenic forcing factor for palaeohydrological changes, with early landscape management and cereal cultivation accelerating the process of blanket peat initiation. With progressive changes in precipitation interacting with factors such as weathering of bedrock and vegetation cover, the local landscape at Lagafater was covered by blanket peat by the early Bronze Age. The radiocarbon chronology obtained from the multi-proxy records allowed the synthesis of these data sets and the definition of Holocene vegetation change, climate change and the history of human impact throughout the early prehistoric era across this landscape.

The long-term climatic and environmental history of Southeast Asia is still fragmentary. This thesis therefore aims at studying lake sediment/peat sequences using a multi-proxy approach to reconstruct the environmental history and the impact of past changes in monsoon variability and intensity on lake ecosystems in Thailand. The study focuses on two lakes located in northeast Thailand: the larger Lake Kumphawapi and the smaller Lake Pa Kho. The comparison of multiple sediment sequences and their proxies from Kumphawapi suggests a strengthening of the summer monsoon between c. 10,000 and 7000 cal yr BP. Parts of the lake had been transformed into a wetland/peatland by c. 7000 cal yr BP, while the deeper part of the basin still contained areas of shallow water until c. 6600 cal yr BP. This gradual lowering of the lake level can point to a weakening of the summer monsoon. Paleoenvironmental information for the time interval between 6200 and 1800 cal yr BP is limited due to a several thousand-year long hiatus. This new investigation demonstrates that arguments using the phytolith and pollen record of Lake Kumphawapi to support claims of early rice agriculture in the region or an early start of the Bronze Age are not valid, because these were based upon the assumption of continuous deposition. The lithostratigraphy and multi-proxy reconstructions for Pa Kho support a strengthened summer monsoon between 2120-1580 cal yr BP, 1150-980 cal yr BP, and after 500 cal yr BP; and a weakening of the summer monsoon between 1580-1150 cal yr BP and between 650-500 cal yr BP. The increase in run-off and higher nutrient supply after AD 1700 can be linked to agricultural intensification in the region. Conclusively, the Holocene records from northeast Thailand add important paleoclimatic information for Southeast Asia and allow discussing past monsoon variability and movements of the Intertropical Convergence Zone in greater detail. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted. Paper 5: Manuscript.</p>

The late Holocene flood history and associated channel changes were reconstructed for the Escalante River in south-central Utah. Analyses of flood deposits at 8 sites in the bedrock canyon indicate that the frequency of large floods was at a maximum 1100 to 900 yrs BP and in historic times in a 2000 year record. The largest flood occurred approximately 900 to 1000 yrs BP and was 7 times the largest flood recorded at a gaging station. The paleoflood discharges were close to the "maximum expected flood" derived from a regional flood envelope curve, and the 100-yr flood was increased 220% to 800 cubic meters per second (cms) with the addition of four historic flood discharges. Possible nonstationarity in the distribution due to channel changes and climatic shifts reduced the reliability of statistical flood-frequency analyses. The additional parameters of the "largest recorded flood" in 2000 years of paleoflood record -- 720 ems -- and the "maximum expected flood" -- 1180 cms -- were added to the flood-frequency summary. Channel changes in the upstream alluvial channel were related to flood-frequency changes. Valley-margin stratigraphy representing 1600 years of deposition indicated that after 1100 yrs BP, a time of increased frequency of large floods, a marshy floodplain was converted to a dry, fire-swept meadow and an arroyo 24-m wide and 2.5-m deep formed. This arroyo quickly filled with sediments between 500 and 400 yrs BP and a smaller channel then formed and persisted until settlement of the basin. Floods between 1909 and 1940 transformed the small channel into an arroyo up to 100-m wide and 17-m deep. The cause for flood-frequency and consequent channel changes on the Escalante River is complicated. Land-use practices caused pronounced changes in watershed and floodplain conditions. A subtle shift in climate increased the amount of summer precipitation and intensity of storms. The inability to test either the land-use practices or climatic shift hypotheses independently precludes the determination of a regional cause for arroyos.

Accelerated glacial recession and downwasting of glaciers in the Bowser River Watershed of the northern British Columbia Coast Mountains have exposed subfossil wood remains and laterally contiguous wood mat layers. To develop an understanding of Holocene glacial fluctuations in this region, field investigations were conducted in 2005, 2006 and 2013 at Frank Mackie, Charlie, Salmon and Canoe glaciers. These wood remains represent periods of Holocene glacier advance, when glaciers expanded and overwhelmed downvalley forests. Dendroglaciology and radiocarbon analyses revealed five intervals of glacial expansion: (1) a mid-Holocene advance at 5.7-5.1 ka cal. yr BP; (2) an early Tiedemann advance at 3.6-3.4 ka cal. yr BP; (3) a late Tiedemann advance at 2.7-2.4 ka cal. yr BP; (4) a First Millennium AD Advance at 1.8-1.6 ka cal. yr BP; and, (5) three advances during the Little Ice Age at 0.9-0.7, 0.5 and 0.2-0.1 ka cal. yr BP. These results provide new evidence for mid-Holocene glacier activity in northern British Columbia, as well as supporting previous research that Holocene glacier advances were episodic and regionally synchronous. / Graduate / 0368

The Mediterranean has long been recognised as an area that is particularly sensitive to climate change. It is also an area that has been impacted by human activity for millennia. Disentangling climatic and anthropogenic influences on the history of vegetation change in the Mediterranean remains an important challenge. As a contribution to this ongoing debate, this thesis explores the late Holocene environment of part of the coast in Central Italy using a multiproxy approach to investigate the archives of change preserved in dune slack deposits. Distinguishing between natural and anthropogenic signals presents a real challenge in most environmental reconstruction work; however, due to the extensive archaeological research carried out at Castelporziano, it is possible to examine human-environmental interactions in some detail. In order to understand these interactions part of the thesis examines how management has affected recent environmental changes and the current vegetation and whether there is a legacy of Roman landuse at the Castelporziano estate. The key findings of the thesis showed that dune slacks are suitable for palaeoenvironmental reconstruction with proxies such as plant macrofossils, ostracods, molluscs and bryozoans statoblasts. However, the pH and seasonality of the slacks meant proxies such as pollen were badly preserved or absent, and diatoms did not preserve due to the high levels of carbonate on site. Overall the results show the impact of the Romans on site in terms of localised eutrophication and increased fires, but with abandonment, came the formation of wet woodlands.

This dissertation presents the results of late Holocene insect fossil analysis from six raised bogs in the Irish Midlands. A distribution and taphonomic study was performed on a sequence of samples across a 1-km transect from the lagg (margin) to the dome (centre) of Ballykean Bog, County Offaly, Ireland. The purpose of this study was to detect any patterns in the taphonomy of the insect fossil assemblages, through the development of the bog and across ancient bog surfaces. This study also investigated how vegetation changes and taphonomy influence beetle assemblages from different locations across the bog surface and to test whether fossil assemblages reflect these changes. The insect faunal assemblages from the transect did not show any clear spatial or temporal patterns in fossil abundance or taxonomic diversity. However, the study demonstrated the benefit of the analysis of multiple sampling points in a bog. Multiple sampling site analysis appears to be critical in the development of a comprehensive reconstruction of key intervals of peat deposition and in providing a greater understanding of the local bog surface habitats. Insect fossil records were analysed across six raised bogs as part of a multi-proxy environmental archaeology project focusing on seven trackways, a wooden platform and a habitation structure. The archaeology dates from the early Bronze Age (1569±9 BC) at Kinnegad Bog to the Christian period (AD 900 to 1160) at Lullymore Bog. This study demonstrates that insect records associated with the minor structures, such as trackways and platforms, contained less diverse assemblages comprising of mainly generalist taxa. In comparison, the major habitation structure at Ballykean Bog had a strong anthropogenic signal. While the reasons behind the construction of the trackways and platforms remains unsolved on the basis of the multi-proxy environmental analysis, it was possible to suggest reasons for their construction based on structure directionality and historical context.

For the first time, Mid-Late Holocene insect fossil assemblages were studied from inland northern Sweden, producing new evidence relating to both natural environmental changes and human impacts. The insect fossil assemblages from natural deposits indicated extensive woodland with old and dead wood and a deep litter layer of decaying matter. Human impacts became apparent from the 1st millennium AD, when the landscape around many sites became more open, with elements of heath. It is difficult to determine whether these changes were driven purely by human activity, indicating subtle landscape change as a result of periodic exploitation, or if natural influences were significant in creating this landscape structure. If connected with human use, then the impacts of periodic exploitation can be seen to be subtle and localised, but notable enough to leave tell-tale signs in the insect fossil record. These relatively subtle changes in the environment can be compared with the more severe effects found during periods of historically known permanent settlement, where extensively open and disturbed habitats are suggested in the insect fossil record. Species associated with arable and pasture land are restricted to the last few hundred years, in association with settled occupation. The climate signal in the insect fossil record has been weak, and use of the Mutual Climatic Range method (MCR) has not revealed evidence of climatic fluctuations during the Late Holocene period.

Changes in monsoon patterns not only affect ecosystems and societies but also the global climate system in terms of heat energy and humidity transfer from the equator to higher latitudes. However, understanding the mechanisms that drive monsoon variability on longer timescales remains a challenge, partly due to sparse paleoenvironmental and paleoclimatic data. This thesis, which contributes new hydroclimate data sets for the Asian monsoon region, seeks to advance our understanding of the mechanisms that contributed to Southeast Asian summer monsoon variability in the past. Moreover, it explores how past climatic conditions may have impacted societies and ecosystems. In this study lake sediment and peat sequences from northeastern and southern Thailand have been investigated using organic geochemistry, and more specifically the stable carbon and hydrogen isotopic composition of specific biomarkers (n-alkanes, botryococcenes, and highly branched isoprenoids). The hydrogen isotopic composition of leaf waxes (δDwax) in Thailand was shown to relate to the amount of precipitation and the extent of the El Niño Southern Oscillation.  Higher values of δDwax can be interpreted as reflecting relatively dry climatic conditions, whereas lower values relate to wetter conditions. The hydroclimate reconstruction for northeastern Thailand, based on the sedimentary record of Lake Kumphawapi, suggests higher moisture availability between ca. 10,700 cal. BP and ca. 7,000 cal. BP likely related to a strengthened early Holocene summer monsoon. Moisture availability decreased during the mid-Holocene, but seems to have increased again around 2,000 years ago and has fluctuated since. The high-resolution Lake Pa Kho peat sequence, which allows for a sub-centennial reconstruction of moisture availability, indicates that the wettest period occurred between ca. 700 and ca. 1000 CE whereas driest intervals were from ca. 50 BCE to ca. 700 CE and from ca. 1300 to ca. 1500 CE. Hydroclimate comparison of Pa Kho’s δDwax record with other paleoclimate records from the Asian-Pacific region suggests that El Niño-like conditions led to Northeastern Thailand being wetter, whereas La Niña-like conditions led to drier conditions. Regional hydroclimate variability also greatly influenced the Angkor Civilization, which flourished between ca. 845 and ca. 1450 CE. The shift from drier to wetter conditions coincided in time with the rise of the Angkor Civilization and likely favored the intense agriculture needed to sustain the empire. The gradual decline in moisture availability, which started after ca. 1000 years CE, could have stretched the hydrological capacity of Angkor to its limit. It is suggested that Angkor’s population resorted to unconventional water sources, such as wetlands, as population growth continued, but summer monsoon rains weakened. The 150-year long record of Lake Nong Thale Prong in southern Thailand offers insights into decadal-scale hydroclimatic changes that can be connected to the instrumental record. δDwax-based hydroclimate was drier from ~1857 to 1916 CE and ~1970 to 2010 CE and wetter from ~1916 to 1969 CE. Drier climatic conditions between ~1857 and 1916 CE coincided with oligotrophic lake waters and a dominance of the green algae Botryococcus braunii. Higher rainfall between ~1916 and 1969 CE concurred with an increase in diatom blooms while eutrophic lake water conditions were established between ~1970–2010 CE. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript.</p> / Monsoon project

L’étude des interactions sociétés-milieux sur la longue durée, à l’origine de la construction des paysages de l’Aubrac et du Lévezou, a été menée à partir d’une démarche largement pluridisciplinaire dans laquelle la palynologie constitue l’outil principal. La constitution d’un référentiel actuel a conduit, dans un premier temps, à discriminer les principaux taxons polliniques représentatifs des activités humaines et d’en préciser la représentativité spatiale et fonctionnelle. L’étude multi-proxy de six séquences sédimentaires, étayées par 24 datations radiocarbones, a, dans second temps, permis de retracer l’histoire de la végétation et de l’anthropisation, notamment par l’identification des rythmes, des seuils et des ruptures durant l’Holocène. L’évolution des paysages en lien avec le développement des déboisements et des activités agricoles a pu être appréhendée à une échelle locale grâce aux apports combinés des pollens, des macrocharbons, des microfossiles non polliniques, de la confrontation avec les données archéologiques disponibles et de l’examen des sources archivistiques. Les premiers indices tangibles de fréquentation du massif de l’Aubrac apparaissent au cours du Néolithique moyen et les pratiques semblent se généraliser au Néolithique final sur l’Aubrac et le Lévezou. L’âge du Fer et le début de l’Antiquité marquent les premiers déboisements importants sur le plateau de l’Aubrac, concomitants d’une hausse de la pression agropastorale observée dans tous les sites. Enfin, les périodes médiévales et modernes contribuent à ancrer les formes du paysage esquissées aux époques plus anciennes. L’ensemble de ces dynamiques suggère avant tout l’importance des variabilités territoriales qui renvoient à des modes d’occupation temporaires jusqu’à l’âge du Bronze et à une grande mobilité des pratiques. Ces territoires présentent également des tendances communes qui répondent pour une part aux grandes trajectoires de colonisation des espaces montagnards. A l’examen de ces dynamiques d’anthropisation, le forçage climatique ne semble pas avoir été un facteur limitant et pourrait constituer un stimulus positif favorisant le développement de nouvelles stratégies adaptatives. / Based upon a multidisciplinary approach centered on palynology, the aim of our study was to better understand the long-term interaction in human/vegetation processes in the Aubrac and Levezou mountainous regions (Massif Central, France). In a first step, the relationships between present pollen deposition, vegetation and land-uses have been studied using a comparative approach. The main pollen taxa representative of human activities have been isolated and their spatial and functional representativeness have been assessed. Secondly, six sedimentary records, supported by 24 radiocarbon dates, have been studied with a multi-proxy approach combining pollen, macro charcoals, non-pollen palynomorphs, archeological and historical data. The analysis has allowed us to characterize vegetation history and local human impact on the landscape, in particular rhythms, breaks and thresholds concerning anthropisation’s dynamics According to our analysis, the first signs of human impact on the vegetation appear in Aubrac during the middle Neolithic period, while evidence of human activities seem to extent during the Late Neolithic. The Iron Age and early Antiquity periods are characterized by large scale deforestation correlated to the increase of the agro-pastoral pressure. Our analysis further suggests that the medieval and modern periods consolidate the types of landscape that have been created in earlier periods. The dynamics that have been highlighted in this study suggest an important degree of spatial variability of land use. The analyzed territories present common trends that correspond to colonization trajectories generally encountered in mountain areas. Relative to anthropisation’s dynamics, climate forcing seems to have not been a limiting factor for human settlements and may even have been a positive stimulus promoting the development of new adaptive land use strategies.