In spite of an intensive work of nearly thirty years, no satisfying explanation is given for the existence/nonexistence of tundra and/or forest tundra in eastern and northern Hokkaido during the last glacial maximum. To supply basis for the reconstruction of past vegetation in this area, pollen transfer and deposition were examined in a mire on Yururi Island, a small, unforested island 3 km off the Nemuro peninsula. Modern pollen assemblages obtained from Sphagnum-polsters were compared with the surrounding vegetation. On average, 34.8 (19.7–54.5)% of pollen and fern spores were thought to be derived from outside the island, and tree pollen accounted for 90% of such transported pollen. An average of 20% of tree pollen was transported from the south, such as southern Hokkaido or Honshu and were mainly derived from Pinus subgen. Diploxylon and Cryptomeria. Pollen is carried to Yururi Island mainly by the summer monsoon and is deposited there. When sampling is made in a large unforested area, long-distance pollen is supplied from an extensive area and affects pollen spectra. If percentages of pollen transported over long distances and those of non-tree pollen from a local vegetation can be estimated reasonably, past woodland can possibly be distinguished from past grassland.
Forests buried by latest Pleistocene tephra layers from Asama volcano were studied in the Minami-Karuizawa basin, Nagano Prefecture. A number of tephra layers were deposited since ca. 25,000 yBP in the Minami-Karuizawa basin, and peat, peaty sediments, and soil were deposited between them. Buried forests were found from below Asama-Kumoba pumice flow deposit (As-Kb) to above an unnamed tephra layer (MK-15) and were especially extensive below Asama-Itahana yellow pumice (As-YP) dated at 13,320±130 to 13,710 ± 130 yBP. Buried forests below As-YP were dominated by Picea and Pinus cf. pumila, accompanied by Juniperus, and were more developed on herbaceous peat than on moss peat. At localities or horizons where Picea and Pinus cf. pumila were not dominant, Picea, Abies, and Larix dominated. In the Minami-Karuizawa basin, coniferous forests similar to the present subalpine ones seem to have grown in drier areas, whereas open Picea sect. Picea–Pinus pumila forests seem to have grown in wetter areas. Contemporaneous fossil wood assemblages buried by As-YP in the Maebashi area was dominated by Picea, accompanied by Larix and Pinus subgen. Haploxylon, and coniferous forests seem to have had an extensive distribution at this period.
In northern Hokkaido, sediments of the early half of the last glacial include several tephra layers from Mt. Rishiri. Those tephra layers are important keys for the geological correlation and the study of environmental changes during this period. We made a palynological study of peaty sediments including Rishiri-Acharu (Rs-Ac) at Toyotomi to determine the timing of Rs-Ac and to clarify the environmental changes. This tephra has been tephrochronologically positioned between Toya and Aso-4. Fossil pollen assemblages from the peaty sediments changed with the fall of Rs-Ac1, and assemblages rich in deciduous broadleaf tree pollen changed to those dominated by spruce pollen, suggesting environmental change to a colder and drier climate. After the fall of Rs-Ac2, Larix pollen increased, which indicated further environmental change to a cold and dry climate. Correlating these pollen spectra at Toyotomi to those at Haboro and Tomamae which intercalate Toya and Aso-4, Rs-Ac1 and Rs-Ac2 were repectively estimated to have fallen at the beginning of the marine isotope stage (MIS) 5b and just before the peak of MIS 5b.