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We conducted particle size and pollen analyses on two cores extracted from Lake Baikal to investigate the response of vegetation to climate change and to assess the differences in vegetation changes between the northern and southern regions of Lake Baikal over the last 350 kyr. Vegetation changes in the Lake Baikal region corresponded well to the fluctuations in median particle size, which are indicators of the climate changes in this region. Forest, which was mainly composed of Pinus and Picea, spread widely during the interglacials/interstadials of MIS 9, 7, 5, and 1, and open forest or desert covered most areas during the glacial/stadial substages. However, the responses of vegetation to climate changes differed between the northern and southern regions. Generally, vegetation expansion was restricted around the northern region. During the interglacial substages equivalent to MIS 9.3, 7.5, and 5.5, forest spread widely around both the northern and southern regions. However, sparsely vegetated (poor) desert/open forest covered the northern region during MIS 5.3 and 5.1, while forest extended around the southern region in these substages. Moreover, during glacial periods, open forest, composed mainly of Artemisia, Chenopodiaceae/Amarantaceae, Betula, and Alnus, covered the southern region, while poor desert/open forest covered the northern region. These different vegetation responses are considered to have been caused by the geographical characteristics of the regions, i.e., the mountains around the northern region and the plains around the Selenga River in the southern region.

バイカル湖の湖底から得られた5.1Maをカバーする全長200mコア(BDP96-1)のうち,第四紀に相当する上部の深度80m以浅についての花粉分析を行い,植生変遷について考察した.産出した化石花粉・胞子のうち51種類を同定したが,マツ科針葉樹が70～80%を占め,その産出状況に特色がみられた.すなわち,大量の化石花粉・胞子の産出する多産層(間氷期,湿潤期)と,草本花粉・胞子がごくわずかに産出するだけの稀産層(氷期,乾燥期)が交互に現れている.上部80mの2Maに32回のサイクルが認められ,δ18O曲線とほぼ調和的な環境変動を記録している.また,マツ科のツガ属と落葉広葉樹のクマシデ属,コナラ亜属,クリ属,ニレ科,ハシバミ属,カエデ属は第四紀前半に絶滅してしまい,後半以降のバイカル湖周辺のタイガはマツ科針葉樹とカバノキ属を中心とした比較的単純な植生からなる森林が継続した.

Accelerator mass spectrometry (AMS) radiocarbon dating and paleoecological analysis of slope deposits at Mt Raizan provided seven 14C dates indicating that landslides occurred in that area at 6.0 to 6.3 cal ka BP and 6.5 cal ka BP. Plant macrofossils, pollen grains, and spores point to a mixed forest at that time, consisting of conifers and broad-leaved trees. On the other hand, insect fossil indicates slightly colder climate than that of the flora. This difference may be attributed to varied sensitivities of each proxy to climatic changes.

A palynological study was conducted on samples taken from the bottom sediments of Lake Baikal. The pollen records from 600-m to 400-m depth of the BDP-98 core show that the vegetation consisted mainly of broad-leaved tree forests composed of Fagaceae, Ulmaceae, and Juglandaceae in the lower part of the core. In the middle and upper parts of the core, the vegetation consisted mainly of coniferous tree forests and deciduous broad-leaved tree forests. The coniferous tree forests were composed of Pinus and Picea accompanied by Tsuga and Larix, and the deciduous broad-leaved tree forests were mainly composed of Betula and Alnus. A major reduction in palynological diversity and abundance was found at 8.6 Ma. In addition, a drastic change in the Steppe/forest index (SFI; Traverse 1988) was detected, reflecting the intensification of dry conditions. After the change, Betula and Alnus became more important elements of the deciduous broad-leaved tree forests, suggesting that a cool continental climate prevailed.

Publisher Summary The watershed of Lake Baikal constitutes the southern portion of the Siberian taiga and the northern part of the Mongolian steppe, and it is located at a high-latitude (51–56 N), far from the ocean. The paleoclimatic history of the Baikal region sensitively reflects past global changes, such as warm-cold and dry-moist oscillations of climate. Paleovegetational reconstruction of the region is indispensable to understanding how the Siberian taiga forest responded in timing and magnitude to past global changes. However, there are few palynological studies for paleovegetational reconstruction of the past million years in the region. This chapter presents a palynological study on the BDP96 Hole 1 core drilled by a Russian scientific drilling team in 1996. The results obtained in this study prove that the forest-desert alternations are closely related to global glacial–interglacial cycles during the Pleistocene. Considerable forest retreats are visible for relatively long periods during the late Pliocene, and a remarkable desert prevailing period during the early and middle Pliocene preceded the forest dominant period. The work in the Baikal area has also shown that these forest-desert alternations are more sensitive to global paleoclimate changes than those found in other continental region records.