The Towada-a (To-a) Tephra from A.D. 915 allowed reconstruction of the local and regional vegetation at and near Ohse-yachi Mire from pollen samples taken just below the tephra. In earlier studies the tephra was dated from ~4C data, stratigraphy at archaeological sites and a historical record. Twelve cores along two perpendicular transects yielded pollen from modern and pre-tephra samples. The modern pollen data were compared with the modern vegetation, and used to interpret the pollen data from A.D. 915. Ericaceae, Drosera, Sanguisorba, other Rosaceae, and Sphagnum were concluded to be local elements. Ohse-yachi Mire was a wet Sphagnum bog in A.D. 915, with Sphagnum dominating the central part of the mire. The present stand of scrub was not yet established, but there was a stand of Pinus pumila scrub. The bog subsequently became drier and changed to the present-day mixed Moliniopsis-Sphagnum bog.
The use of data for present‐day vegetation, modern and pretephra pollen have, together, allowed reconstruction of the spatial pattern of the vegetation of an oligotrophic mire, Shimo‐kenashi Mire, in AD 915. The modern pollen data were compared with the surrounding vegetation, showing that pollen of Ericaceae, Rosaceae (excluding Sanguisorba), Sphagnum and Liliaceae, together with trees and shrubs, which form scrub or thicket, indicate the limits of the mires. Shimo‐kenashi Mire was narrower in AD 915 and had more islands and peninsulas of scrub. Subsequently, the mire margin has advanced and the scrub islands and peninsulas have disappeared at some sites. The fact that the mire is spreading implies that conditions are wetter since AD 915, caused by changes in local hydrology. This history of vegetation at the site will contribute to the conservation and management of the mire as trends in vegetational change provide the basic information for conservation strategy.
The late Quaternary vegetation and climatic history at high altitude in eastern Nepal was studied through stratigraphy, radiocarbon dating and pollen analysis. The Thulo Pokhari lake (27°41′ N, 87°43′ E, ca. 3980 m a.s.l.) is just above the subalpine Abies spectabilis–Betula utilis forest zone and surrounded by Rhododendron scrub. The climate in the studied area is very humid under the influence of the monsoon. Silty sediments suggesting lake conditions prevailed at the lower part of the sediment samples, whereas the upper part consisted mainly of herbaceous peat indicating a mire condition. The pollen record extends back to ca. 11000 yr bp. Although the absence of major changes between the pollen assemblages of the Pleistocene and those in the Holocene was attributed to the situation of the sampling plot above the forest limit, the results suggest the following history. (1) The abundance of Pinus pollen around 11000 yr bp represents expansion of the area unoccupied by late successional trees and/or a drier condition. Significant occurrence of Picea pollen is noteworthy, since this genus is absent in eastern Nepal at present in spite of its wide distribution throughout the neighbouring areas of the Himalayas. (2) The increase in abundance of Quercus pollen and the decline in Pinus pollen in the latest Pleistocene represent climatic amelioration favourable to late successional mesophytes. (3) The climate was most moist and mild in the SP‐III, although the absolute age of the pollen zone is not distinct. The percentages of broadleaved trees such as Alnus, Betula, Carpinus and Corylus were increased at the expense of Quercus and coniferous pollen types. Sedimentation was interrupted by lake level decline and/or glacial advance during the period from ca. 11000–1600 yr bp. (4) The increase in abundance of coniferous pollen types such as Pinus, Abies and Tsuga indicates that the climate became drier and cooler, and the present subalpine forest zone composed of A. spectabilis, T. dumosa and Betula utilis was established around 1600 yr bp. The formation of bog or alpine meadow vegetation during the period was shown by the 14C dates of the peat and the increase in Rosaceae and herbaceous pollen. (5) The increase in abundance of Ericaceae and Alnus pollen in the SP‐V indicates that the present alpine Rhododendron scrub zone has been established since ca. 940 yr bp as a result of human influence on the original vegetation. This interpretation is supported by the decline in the proportion of arboreal pollen. Since the age of the initiation of human influence varies with the altitude and region, further study will be necessary to determine the accurate age.
Although the most crucial factor shaping vegetation history is temperature, snowfall regime is also important in regions of heavy snow. Pollen analysis in a mire in a snowy mountainous region of central Japan revealed histories of vegetation and precipitation regimes since the latest Pleistocene. The abundance of pinaceous pollen during the latest Pleistocene indicates a subalpine regional coniferous forest and cooler conditions; moreover, sandy sediment and significant occurrence of pollen from Artemisia along with several alpine elements suggest local plant communities of poor vegetation cover in an erosive environment. The increase in Betula and Quercus subgen. Lepidobalanus pollen and the decline in pinaceous pollen in 13,550 cal. yr BP indicates climatic amelioration favourable to temperate trees, and the invasion of sedges and Reynoutria to the small basin and the onset of peat deposition suggest an increase in summer rain. The increase in Fagus crenata pollen after 11,130 cal. yr BP and onwards indicates that the present heavy snowfall regime induced by inflow of the Tsushima Current has been established since that age. The climatic amelioration delayed establishment of the heavy snowfall regime for more than 2400 years. In addition, the retreat of sedges and subsequent invasion of several species of drier habitat after 11,130 cal. yr BP indicate a drier mire condition caused by increased summer temperatures. The recovery of sedges after 3740 cal. yr BP indicates the wettest mire conditions induced by climatic deterioration. A general increasing tendency of conifers in this period supports this interpretation.
Chuh YONEBAYASHI2)Three pollen diagrams of Komado-Ohyachi Moor in Fukushima Prefecture were compared. Data for the same period (from the climatic optimum in the Holocene to the present) were available from the three sites, which indicated that Fagus crenata forest was predominant over the whole Komado area, and at the same time one site (K12) was dominated by a Quercus mongolica var. grosseserrata stand and the other (JIMBO and SHIODA, 1980) was dominated by a community dominated by Cyperaceae in the latest Pleistocene and changed into a Moliniopsis japonica-Sphagnum community, a Fraxinus mandshurica var. japonica forest, a Osmundastrum cinnamomeum var. fokiense community, a Ilex crenata scrub, a Moliniopsis japonica-Osmundastrum cinnamomeum var. fokiense community and a Moliniopsis japonica-Cyperaceae community, in that order.
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