Late Holocene (Meghalayan) palaeoenvironmental evolution inferred from multi-proxy-studies of lacustrine sediments from the Dayan Nuur region of Mongolia

Abstract

The ‘Altai Tavan Bogd’ National Park, located between 2000 m and 4000 m a.s.l. in the north-western part of the Mongolian Altai, is a forest-steppe ecosystem in Central Asia which is noticeable because of its extreme continental and high-altitude conditions. Its vegetation is very sensitive to environmental changes and impact by nomadic people. To reconstruct the dynamics of this forest-steppe ecosystem, a broad approach was taken employing multi-proxy analyses including the analysis of pollen, spores, non-pollen palynomorphs, charcoal and diatoms, as well as XRF scanning of a lacustrine sediment core of a small and shallow lake located south of Dayan Nuur. Five radiocarbon dates indicate a record spanning the last 4375 years.Between 4310 and 1040 cal yr BP, the vegetation was characterized by a mixture of alpine meadow and moist true steppe communities as well as forested areas with Larix sibirica, Pinus sibirica and Picea obovata stands. Starting around 2350 cal yr BP, a substantially greater and/or denser forest occurrence can be inferred. A marked forest decline after 1040 cal yr BP and the loss of Pinus sibirica and Picea obovata near the study area proceeded in accordance with a significantly higher abundance of large herbivores and a strong indication of nomadic people in the area as inferred from coprophilous fungi. One period of markedly increased fire activity is found from 640 to 550 cal yr BP. For the latest Holocene period, the records of non-pollen palynomorphs and diatoms suggest a rise of the lake water level. These contrasting trends of forest decline despite higher water availability may reflect the considerable human impact of the nomadic population and their cattle on the ecosystem in the ‘Altai Tavan Bogd’ National Park and Central Asia in general.