Holocene vegetational and climatic changes in the forest zone of Western Siberia according to pollen records from the extrazonal palsa bog Bugristoye

Pollen stratigraphy of an extrazonal palsa bog in the middle taiga of the W est Siberian Plain is dated by radiocarbon at five levels. Local pollen ass emblage zones (LPAZ) are the basis for palaeogeographical reconstructions. Tundra-steppe plant communities with shrub birch (Betula nana) dominated in the latest Pleistocene. Warming after 10 000 C-14 yr BP caused the local t hawing of permafrost, forming shallow lakes. Larix and then Picea spread al ong river valleys and depressions. Steppe plant communities existed on the dry interfluves. Further climatic warming and drying caused Picea to retrea t, and Betula forest-steppe dominated 9500-8900 yr BP. Dense Pinus sylvestr is and Pinus sibirica forests then spread over the whole area, and steppe c ommunities decreased about 8300 yr BP. The Holocene climatic optimum (6000- 5000 yr BP) was characterized by warm and wet conditions and Abies was wide spread. Cooling then caused retreat of Abies forests to the south and the e xpansion of Pinus sibirica forests on clay soils and Pinus sylvestris fores ts on sandy soils. Cooling about 4300 yr BP caused the pear to freeze and t he palsa to form by bulging. Feat accumulation on the Bugristoye bog stoppe d at this time.