Vegetation and climate change as well as human impact during the last 1200 years in the Dayan Nuur region, Mongolian Altai

The Mongolian Altai Mountain range in Central Asia has an extreme continental and sensitive climate. The Altai Tavan Bogd National Park at elevations of 2000 m above sea level in the southeastern part of the mountain range near Lake Dayan belongs to the high mountain subalpine forest-steppe ecosystem. It is characterized by rich plant diversity and is sensitive to impacts of human activities. Paleoecological research by pollen and charcoal analysis has been carried out on sediments deposits from a small lake to reconstruct past environmental changes in this area. Four radiocarbon dates indicate that the record spans back to the last 1180 cal yr BP years (since AD 770). Four periods have been identified.During the first recorded period from 1180 – 720 cal yr BP (AD 770-1230), the area was covered by mountain forest-steppe. The small areas of forests in the region were pseudo-taiga forests dominated by Larix sibirica and some Picea obovata. The little occurrence of Betula reflects a close forest. Palynological data suggest relatively humid climatic conditions due to the presence of Picea obovata, but due to the lower lake level of the studied lake, conditions might be not so humid. The rare occurrence of dung spores suggests low influence of grazing. During the period from 720 – 210 cal yr BP (AD 1230-1750), conditions shifted from pseudo-taiga to a subalpine forest with less Picea obovata and more open forests. Increasing lake levels suggest more wetter conditions. Moderate grazing was also detected by the increase of dung spores. During the following period from 210 – (-40) cal yr BP (AD 1750-1990), the area was subalpine vegetation, characterized by a forest openness and intensive grazing. Higher lake levels reflect wetter conditions. During the period (-40) cal yr BP (AD 1990 to the present), the subalpine forest was more open. Marked higher lake levels indicate more humid conditions. High grazing activity is also recorded. This study shows that vegetational changes were caused climate changes and by human activities. The more recent increase in the water level of the thermokarst lake is suggested to be the melting of glaciers and snow that has resulted from global warming as well as the degradation of permafrost.