Vegetation changes in the south of the Russian Far East in the middle and late Holocene

Abstract

The results of biostratigraphic analysis of bottom sediments of the Karas’e, Utinoe, Krugloe lakes as well as loose sediments of accumulative plains at the mouths of the Tumannaya and Poima rivers in the south of the Far East are presented. Natural conditions were recovered and periodicity of vegetation changes in the foothills of the East Manchurian Mountains and in the coastal plains of the Peter the Great Bay in the Middle and Late Holocene were reconstructed by the complex of data. The synchronicity of both the development of vegetation formations and changes of sedimentation conditions with global climatic variations were revealed. The first, Middle Holocene stage proceeded in the conditions of general planetary increase of average annual temperatures, accompanied by flooding of lowland plains of the coast of the Sea of Japan by sea waters. The distribution and species diversity of broad-leaved plants in spurs of the East Manchurian Mountains increased. In the Holocene Optimum, the polydominant forests with richer composition of species than that of the present time were formed and vegetation on the foothill accumulative plains was represented with sedge and mixed meadows. The second, Late Holocene stage was characterized by a decrease in average annual temperatures and series of climatic changes. Its beginning was marked by the cooling, during which the coastal lowlands were freed from sea waters. Climate deterioration caused expansion of dark coniferous and small-leaved plants in the East Manchurian Mountains, as well as reduction of polydominant forests. On the foothills near the coast of the Peter the Great Bay sedge meadows were developed, sometimes there were thickets of shrubby birch (Betula sect. Nanae) and sphagnum swamps. At the end of the Late Holocene the warming occurred again. On the slopes of the East Manchurian Mountains, the vegetation formations with the dominance of Mongolian oak (Quercus mongolica Fisch. ex Ledeb.) and dentate oak (Quercus dentataThunb.), needle fir (Abies holophylla Maxim.), Korean pine (Pinus koraiensis Siеbold et Zucc.) and with the presence of birches began to dominate. The dissemination of pine (Pinus densiflora Siebold et Zucc.), elm (Ulmus sp.), hornbeam (Carpinus cordata Blume) and maple (Acer sp.) has increased. On the foothill lowlands the sedge-reed meadows with different grass dominated.