百原 新

Among the Early Pleistocene fluvial sediments in Japan that yield plant macrofossils, the Uonuma Group in the Niigata sedimentary basin provides the most continuous profile without any conspicuous hiatuses and is therefore suitable for high-resolution reconstructions of environmental and vegetation histories based on tephro-and magneto-stratigraphy. Based on the species composition of plant macrofossil assemblages, along with previously reported results on sedimentary environments and pollen records, we performed a reconstruction of changes in paleovegetation and paleotemperatures between MIS 63 and 53. Macrofossil assemblages identified from 33 samples include 89 arboreal and 88 herbaceous taxa in total, of which 9 taxa are extinct from Japan. Assemblages from the peat deposits in fluvial backmarshes during glacial stages are composed mainly of wetland herbaceous plants, whereas those from the sandy channel-fill deposits are characterized by a higher diversity in life forms and habitat preferences. During the interval from MIS 63 to 53, paleotemperatures fluctuated between a coldest-month mean temperature of -4.6 degrees C and - 0.9 degrees C and between a mean annual temperature of 6.6 degrees C and 11.0 degrees C, which is within the present range for cool-temperate, deciduous broad-leaved forests in Japan. MIS 60 was the coldest of the glacial stages with temperatures nearly equivalent to those during the last glacial maximum. Major plant extinctions in and around MIS 60 were not recorded in the sedimentary basin in response to the temperature decline. The relatively indistinct floral changes in and around MIS 60 are attributed to easier recovery of flora by migration from glacial refugia in the southern basins after termination of the glacial stage. Interglacial temperatures during MIS 57, 55, and 53 were higher than during MIS 63, 61, and 59. The presence of a maritime environment during the interglacial periods between MIS 57 and 53 may have resulted from a greater extent of marine transgression and heat provided by the Tsushima Warm Current flowing into the Sea of Japan after MIS 59. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

Paleovegetation and climatic conditions in the Last Glacial Maximum (LGM; ca. 24.4 and 20.1 ka) were reconstructed based on plant macrofossils and pollen assemblages deposited in a sandy channel out-cropped in the Hanamuro River, Ibaraki Prefecture, central Japan. The plant macrofossil assemblages were composed of 31 arboreal and 76 herbaceous taxa. Occurrence of plants with various habitat preferences exhibited distribution patterns of highly diverse vegetation types depending on geo-morphology and humidity in and around the drainage of the Hanamuro River. Rich aquatic and wetland flora indicates an expansion of backmarsh mosaic environments along the river channel in the bottom of the valley. Wetland forests composed of Picea sect. Picea assignable to Picea koyamae, and riparian forests dominated by Alnus inokumae, are well represented in the macrofossil assemblages. Pinaceous conifers were dominant in mesic or dry places with Betula and the other deciduous broadleaved trees. Macrofossils and pollen indicates that Abies veitchii was distributed in mesic locations, Larix kaempferi and Picea jezoensis var. hondoensis were on the upper slopes, and Pinus koraiensis was dominant on the plateau. Dominant Selaginella remotifolia and the other drought-intolerant understory herbs indicate closed canopy of mesic coniferous forests, while many kinds of meadow and/or ruderal plants were indicative of open vegetation along the river and slopes. Annual mean temperature of the fossil site based on occurrence of Selaginella remotifolia was 8.1 degrees C, which is observed in present cool temperate zones where deciduous broad-leaved trees are dominant. This indicates that the distribution limit of subarctic conifers shifted to warmer temperature conditions than at present. The overlapping distribution of temperate and subarctic plants occurred widely in the lowlands in the distribution ranges of temperate trees, south of around 38 degrees N in Japan. In the LGM, with lower precipitation, dryness was an important environmental factor that controlled plant distribution along with temperature. Water stress confined temperate broadleaved trees to the humid valley bottoms and relieved conifers from competition against broad-leaved trees to promote their expansion to warmer regions. Macrofossils indicate the persistence of temperate plants in humid inland and/or northern refugia during the LGM, locations conducive to Paleolithic human occupation. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.

In the present study, the plant macrofossil stratigraphy of the Plio-Pleistocene sedimentary basins of Japan is reviewed, and the process of development of modern flora is discussed. Taxa endemic to the modern flora of central and south China became extinct, while plants that have been dominant in the recent cool-temperate and subarctic zones of Japan increased and/or emerged after the Late Pliocene. The floral change was stepwise, and the events were concentrated in transition periods of climatic fluctuation and/or in a downward shift of the glacial climate. These events are represented by the last occurrence of exotic taxa at 3.35 Ma, 2.9 Ma, 2.7-2.5 Ma, 1.2 Ma, 0.9 Ma, 0.5 Ma, and in the Late Pleistocene. Local extinctions occurred earlier in northern and inland basins, and the first appearance of plants dominant in modern cool-temperate and subarctic forests was dependent on the topography of mountains surrounding the basin. Geomorphological changes that were accompanied by mountain uplifts and sea level changes occurred in and around sedimentary basins during stage of floral changes. These alterations, along with climate changes, likely changed the habitats and migration routes of plants, which ultimately resulted in their extinction. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.