Vegetation history and climate changes in Lithuania during the Late Glacial and Holocene, according to pollen and diatom data

Six types of pollen diagram are distinguished for the Late Glacial and Holocene in Lithuania, and the net-like method suggested earlier by the author (Kabailiene, 1969) is used to obtain a reconstruction of the different phases of forest history. The cold Pre-Allerod climate favoured a tundra and forest-tundra vegetation, and the Bolling warming was neither very marked nor of any great duration. Considerable warming took place in this area in the Allerod, however, especially during the second half of the period, so that the first half is characterized by the prevalence of birch, while pine evidently became dominant in the second half. The cooling of the climate during the Younger Dryas gave rise to a forest-tundra vegetation. During the Preboreal and the first half of the Boreal the climate was warm and dry and the forests were dominated by pine and birch, while the second half of the Boreal was warmer, with higher precipitation, marked by the spread of pine and hazel. The Atlantic was the warmest post-glacial climatic period, and the most humid, so that broad-leaved forests and alder flourished. The amounts of broad-leaved trees and spruce decrease during the Subboreal, but pine and birch spread, suggesting a moderately warm, dry climate. The Subatlantic is marked by a spread of dense alder and spruce forests indicating greater humidity. A further important approach is the study of fluctuations in lake water quality by means of planktonic, epiphytic and benthic diatom data. It is benthic and littoral planktonic diatoms that prevail in the Late Glacial deposits, suggesting that the lakes were of the oligotrophic type. The water level in the lakes dropped in the Preboreal and the first half of the Boreal, and most of the lakes underwent eutrophication, the shallow ones becoming completely overgrown with plants. Only the deep lakes retained an oligotrophic regime. Although the water level in the lakes rose in the second half of the Boreal and during the Atlantic,