This thesis is missing page 57, this page is not in any of the other copies. -Digitization Centre / Scientists believe that the global climate is undergoing significant changes due to anthropogenic increases of carbon dioxide (CO2) and other Greenhouse gases. The relationship between climate and vegetation is not fully understood. Knowledge of the response of vegetation to past climate change aids in the understanding of potential vegetation responses to climatic changes due to the Greenhouse effect. The objectives of this thesis were to determine if vegetation in the lower Lena River Region has changed in the past, what were the factors which caused the changes and over what time scales did the changes occur. To address the objectives, the pollen, stomate and sediment stratigraphy of a core from a medium size lake, located in north-central Siberia, were analysed. Radiocarbon dating indicates that the record spans the last 12310 yr BP, and possibly the last 15000 yr BP. The early part of the fossil record was characterised by short rapid changes in the vegetation. The initial shrub tundra was quickly replaced by herb tundra with sparse vegetation cover. This was followed by a reversion to shrub tundra conditions at ~12000 yr BP. A clear Younger Dryas signal is found in this record between 11000 and 10000 yr BP, characterised by a shift from shrub tundra to herb tundra dominated by taxa with arctic affinities. The warming at the close of the Younger Dryas signalled the first appreciable climatic amelioration at this site. Following 10000 yr BP, Alnus became abundant in the pollen record and likely on the landscape. The dominance of Alnus was short lived however. At ~8500 yr BP arboreal vegetation, dominated by Larix dahurica, became abundant in the pollen and stomate record. The expansion of forests was the result of changes in the orbital parameters of the earth as predicted by Milankovitch cycles. Arboreal vegetation persisted in this region until-3500 yr BP when the modem shrub tundra vegetation was established. The use of a new technique, stomate analysis, proved extremely useful. Stomates accurately recorded the expansion and retreat of treeline across this region. This study clearly indicates the usefulness of this technique, especially for investigating fluctuations of treeline. / Thesis / Master of Science (MS)

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