To know plants utilized by prehistoric man, plant remains from archaeological sites should be identified. Plant remains found on house floors directly reflect plant usage of prehistoric people, but are mostly incinerized and carbonized. Identification of small carbonized cereals such as millet grains was very difficult, especially when only light microscopy was available. Gramineous plants including cereals accumulate silica in the epidermis, and their silica skeletons detected from their ash were found to have specific characteristics. The spodograms or Aschenbild were the only method of identification with light microscopy for ash or carbonized grains found on prehistoric house floors. When the scanning electron microscopy (SEM) began to be applied to the observation of carbonized remains, various kinds of useful plants other than Gramineae came to be identified, such as Perilla (Labiateae) and Brassica (Cruciferae). However, a limited number of researchers have tried identification of carbonized grains or detection of cereals from ash in Japan, probably because great efforts and time are needed for the collection and observation of extant comparative specimens.
Vegetation history since the Late Glacial was reconstructed by means of pollen analysis and radiocarbon measurement for sediments obtained from Habomai Bog and Ochiishi Cape Bog, Nemuro Peninsula, eastern Hokkaido. Four tephra layers, Ko-c2, Ko-d1, Ta-c1, and Ma-f1, were discriminated in Habomai Bog in the descending order. Two layers, a mixed one of Ko-c2 and Ta-a and one of Ta-c1, were also discriminated in Ochiishi Cape Bog. In Habomai Bog, high bog has developed since 12,000 yr B.P. Taiga composed mainly of Larix gmelinii with Picea jezoensis and/or Picea glehnii and a few Abies sachalinensis and Pinus pumila was distributed between 11,000 and 12,000 yr B.P. Between 10,000 and 11,000 yr B.P., open Larix taiga was distributed under an extremely cold and dry climatic condition. We named this period “Habomai Stadial”, which probably correspond to the Younger Dryas. After disappearance of Larix gmelinii at 7000 yr B.P., Picea jezoensis and/or Picea glehnii survived there till 5200 yr B.P. A broad-leaf forest composed mainly of Quercus was established at 5200 yr B.P. and has existed there to the present. The dry condition caused by the strong local wind prohibited the distribution of conifer trees. In Ochiishi Cape Bog, peat has been deposited since 4600 yr B.P. A Picea glehnii forest mixed mainly with Abies sachalinensis and Quercus has developed around the bog till present. Fluctuations in forest components around the bog might be caused by changes of the underground water level.
Pollen analytical studies were made on materials collected from two sites in a mire developed on Yururi Island to clarify the vegetation history of Nemuro Peninsula in easternmost Hokkaido since the Late Glacial. A landscape consisting of grassland and poor birch forests existed around this area ca. 12,000 years ago. Thereafter, a larch forest began to invade and formed a boreal forest on this island. Picea glehnii forests began to increase in this area ca. 10,000 years ago. The larch forest was extinct ca. 8000 years ago, but Picea glehnii forests continuously occupied this area until ca. 4500 years ago. After this period woody vegetation never developed on Yururi Island. Though coniferous forests deteriorated due to climatic warming, cool temperate oak forests have not developed fully in Nemuro Peninsula because of the cool and wet climate of the summer season. Boreal birch forests gradually developed in this area, and boreal coniferous forests began to increase in the western part of Nemuro Peninsula during the last 2500 years. However, coniferous forests has not developed fully in the eastern part yet.
To identify species of fossil Lagerstroemia pollen common in interglacial sediments of Japan, we studied and described the morphology of long and short stamen pollen grains of modern L. indica, L. subucostata, and L. subucostata var. fauriei using light and scanning electron microscopy. Among L. indica, L. subcostata, and L. subcostata var. fauriei, long stamen pollen grains were similar to each other, but short stamen pollen grains were distinguishable. Pollen grains of L. subcostata and L. subcostata var. fauriei were smaller and had thicker pollen walls in the polar area than those of L. indica. Fossil Lagerstroemia pollen grains obtained from interglacial sediments at four localities in Honshu, Japan, inclusive of Last Interglacial sediments, were mostly short stamen pollen grains, and long stamen pollen grains were few. Short stamen pollen grains of fossil Lagerstroemia were morphologically similar to those of modern L. subcostata and L. subcostata var. fauriei. Considering the plant macrofossil record in Japan and the pollen morphology of modern Chinese species, Lagerstroemia distributed widely in central Honshu during Pleistocene interglacial stages is referable to L. subcostata or L. subcostata var. fauriei.