The 1300-Year Dynamics of Vegetation Cover in the Lake Shira Depression (Khakassia, Siberia, Russia) Reconstructed on the Basis of Bottom Sediments

摘要

The Late Holocene bottom sediments of Lake Shira (Khakassia, Southern Siberia, Russia) have been for the first time analyzed by quantitative spore—pollen analysis in order to assess the vertical distribution of a wide range of plant species. Five pollen zones have been distinguished in the examined time span of 1300 years with the help of factor analysis. The major arboreal components of the spore—pollen spectrum (SPS) over the entire examined section are the pollen of Pinus sylvestris and Betula sect. Albae in the arboreal group and representatives of the families Astereaceae and Poaceae in the nonarboreal group. In the arboreal group, the prevalence of B. sect. Albae during the time period studied (1300 years) has been gradually replaced by theprevalence of P. sylvestris, reflecting an increasing aridization of Siberian area in the Middle—Late Holocene. This is also confirmed by elimination of fir and spruce pollen from SPS approximately 600 years ago and almost complete disappearance of Juniperus s.l., B. sect. Nanae, and Salix pollen by the 1600s. According to the obtained chronicle, the overall vegetation cover surrounding the lake belongs to a boreal-steppe type, with its steppe ecotope increasing over the past 600 years. These results suggest climate aridization in the area of the Northern Minusinsk Depression during the last millennium. Further studies of deeper bottom sediment layers will allow the reconstruction of the vegetation dynamics (and, correspondingly, climate dynamics) over a more extended period.