Four new pollen sections tracing the Holocene vegetational development of the southern part of the West Siberan Lowland

In the southeast of Western Siberia within the zone of birch and pine forests in the Ob'-Tom' interfluve area, four new pollen diagrams from sites in different landforms (interfluve, terraces, floodplain, and ancient drainageways) with sandy and clay soils were correlated with two published pollen diagrams. Two main types of pollen stratigraphy are characteristic for areas with clay and sandy soils, reflecting different vegetational developments during the Holocene that were controlled by changes in climate and soil properties. Open birch forest-steppe with Artemisia and Chenopodiaceae was widespread in the Ob'-Tom' interfluve during the early Holocene, whereas the young floodplains had flooded meadows and willow scrub. The principal vegetation change from open steppe and forest-steppe to dense forest took place about 7000 yr BP, after which forest vegetation has prevailed. On sandy soils the dominant tree species was Pinus sylvestris throughout, but on clay Pinus sibirica and Abies sibirica together with Betula pendula had more important roles, alternating periodically with Pinus sylvestris. Expansion of Pinus sibirica and Abies sibirica in this area started about 4500-4000 yr BP, but in some places they declined markedly during recent centuries due to human influence. Based on the vegetational development, the climate in the southeast of Western Siberia changed from colddry to warm-dry (9500 yr BP) then to warm-wet (7000 yr BP), and finally to cool-wet (4000 yr BP).