meteorological observations at the time of the arrival of the
Kosa, it was revealed that it originated from the Loess Plateau
and the desert in mainland China (Fig. 2.25: Ishizaka et al.
1981). Furthermore, oxygen isotope analysis of quartz in the
0.01–0.001 mm grain size fraction of volcanic ash showed
that the quartz originated not only from volcanic rocks, but
mainly from a wide range of wind-blown dust from China
(Mizota and Matsuhisa 1985; Mizota and Inoue 1988). It has
also been pointed out that a wide range of wind-blown dust,
including Kosa, is added to various sediments distributed
throughout Japan (see, e.g., Mizota and Matsuhisa 1985;
Inoue and Naruse 1987; Inoue and Mizota 1988.). The sedimentation rate of tropospheric dust on the Japanese Islands
after the last interglacial period has been approximately 10
0
–
10
−1 mg cm
−2 yr
−1 , and in cold periods (glacial period and
stadial) the rate has tended to increase by three to five times
compared with mild temperate periods (interglacial period,
interstadial, postglacial period) (Yoshinaga 1999).
2.2.5 Sediments of Plant Origin
as Landform-Covering Materials
(1) Peat
Peat is a sediment formed from plant tissue in anaerobic
environments, such as swamps and lakes, without the
decomposition of dead plant bodies. The Japanese peatlands
are concentrated in the alluvial plains and mountainous
region of the central and northern parts of Honshu and
Hokkaido, and very little in the southern part of Honshu,
Shikoku and Kyushu (Sakaguchi 1961; 1974; 1979; 1989;
Institute for Agro-Environmental Sciences, NARO 2019:
Fig. 2.26). In addition, most of the peatland in the mountainous area is distributed in the Late Cenozoic to Quaternary volcanic region, where depressions and flats with poor
drainage appear, and spring water is abundant.
Japanese peatlands are classified into three types
according to the relationship between the topographic type
and origin of water: (1) “terrestrisch peatland” by filling up
of waters (lake basin, lagoon and drowned valley by postglacial transgression), where basin becomes shallower by
sedimentation, (2) “telmisch peatland” by paludification of
dry land (back marsh of flood plain), which is formed by
periodical flood, and (3) “telmisch peatland” by paludification of dry land (valley head, slope and watershed), which is
formed by heavy snow, spring water, clouds and fog (Sakaguchi 1961, 1974, 1979, 1989: Fig. 2.26).
Peat deposits are also subdivided into “autochtonous
peat“, during the formation of which marsh plants die and
are deposited in situ, and “allochthonous peat,” where peat
separated by erosion is carried in running water and accumulates in another place. In Japan, the depositional rate of
autochtonous peat is approximately 0.5 to 1.5 mm/year
(Sakaguchi 1961, 1974). It is possible to reconstruct the
climate, hydrological situation and past vegetation at the
time of deposition from the change and decomposition
degree of the plants constituting the peat substance, as well
as from the compositions of pollen and diatoms in the peat.
(2) Opal phytolith
Opal phytoliths are structures composed of fine, amorphous
particles of silica, and are formed by hydrous silicic acid
being deposited in plant cells and tissue pores of gramineous
grasses and trees (Kondo 2010). The particle size is very
wide, from 5 to 200 lm. Although the particle size is small,
even after the plant body decomposes in the ground, it
remains in the soil accumulated by the deposition of air-fall
tephra and eolian dust, even under dry oxidizing conditions.
Generally, the content of opal phytolith in the humus layer
of Japanese volcanic ash soils is 0.3–17% (Kondo 2010).
Opal phytoliths provide useful information about the soil
formation environment, because they are left in the soil with
the deposition of volcanic ash and loess on the emerged
geomorphic surface (Sase et al. 1987; 2008: Fig. 2.8 in
Sect. 2.1.3).
2.3 Vegetation and Land Use
The vegetation of Japan is characterized by a large number
of species and a high percentage of endemic species. The
great variety of species is related to the geographical position
of the country. The Japanese archipelago is a group of hilly
and mountainous islands, located along the eastern end of
the Eurasian continent, which shows a large variation in
landscape and geology. The variation of climate from subtropical to subarctic along the archipelago is also considered
to be an important factor in the floral biodiversity. During
glacial periods, glacial cover developed in only high-altitude
areas, so forest vegetation remained in the glacial age in the
Pleistocene. It is thought that humans started living in the
Japanese archipelago in the Paleolithic age, 120,000 years
ago, and that rice cultivation was initiated in the Yayoi
period (800 BC–250 AD). Despite human influence, forest
vegetation persisted in the mountainous areas which cover
two-thirds of Japan’s territory; however, the area of the
original natural forests has gradually decreased and has been
replaced by early successional deciduous broad-leaved trees
38
K. Tamura et al.
Kosa, it was revealed that it originated from the Loess Plateau
and the desert in mainland China (Fig. 2.25: Ishizaka et al.
1981). Furthermore, oxygen isotope analysis of quartz in the
0.01–0.001 mm grain size fraction of volcanic ash showed
that the quartz originated not only from volcanic rocks, but
mainly from a wide range of wind-blown dust from China
(Mizota and Matsuhisa 1985; Mizota and Inoue 1988). It has
also been pointed out that a wide range of wind-blown dust,
including Kosa, is added to various sediments distributed
throughout Japan (see, e.g., Mizota and Matsuhisa 1985;
Inoue and Naruse 1987; Inoue and Mizota 1988.). The sedimentation rate of tropospheric dust on the Japanese Islands
after the last interglacial period has been approximately 10
0
–
10
−1 mg cm
−2 yr
−1 , and in cold periods (glacial period and
stadial) the rate has tended to increase by three to five times
compared with mild temperate periods (interglacial period,
interstadial, postglacial period) (Yoshinaga 1999).
2.2.5 Sediments of Plant Origin
as Landform-Covering Materials
(1) Peat
Peat is a sediment formed from plant tissue in anaerobic
environments, such as swamps and lakes, without the
decomposition of dead plant bodies. The Japanese peatlands
are concentrated in the alluvial plains and mountainous
region of the central and northern parts of Honshu and
Hokkaido, and very little in the southern part of Honshu,
Shikoku and Kyushu (Sakaguchi 1961; 1974; 1979; 1989;
Institute for Agro-Environmental Sciences, NARO 2019:
Fig. 2.26). In addition, most of the peatland in the mountainous area is distributed in the Late Cenozoic to Quaternary volcanic region, where depressions and flats with poor
drainage appear, and spring water is abundant.
Japanese peatlands are classified into three types
according to the relationship between the topographic type
and origin of water: (1) “terrestrisch peatland” by filling up
of waters (lake basin, lagoon and drowned valley by postglacial transgression), where basin becomes shallower by
sedimentation, (2) “telmisch peatland” by paludification of
dry land (back marsh of flood plain), which is formed by
periodical flood, and (3) “telmisch peatland” by paludification of dry land (valley head, slope and watershed), which is
formed by heavy snow, spring water, clouds and fog (Sakaguchi 1961, 1974, 1979, 1989: Fig. 2.26).
Peat deposits are also subdivided into “autochtonous
peat“, during the formation of which marsh plants die and
are deposited in situ, and “allochthonous peat,” where peat
separated by erosion is carried in running water and accumulates in another place. In Japan, the depositional rate of
autochtonous peat is approximately 0.5 to 1.5 mm/year
(Sakaguchi 1961, 1974). It is possible to reconstruct the
climate, hydrological situation and past vegetation at the
time of deposition from the change and decomposition
degree of the plants constituting the peat substance, as well
as from the compositions of pollen and diatoms in the peat.
(2) Opal phytolith
Opal phytoliths are structures composed of fine, amorphous
particles of silica, and are formed by hydrous silicic acid
being deposited in plant cells and tissue pores of gramineous
grasses and trees (Kondo 2010). The particle size is very
wide, from 5 to 200 lm. Although the particle size is small,
even after the plant body decomposes in the ground, it
remains in the soil accumulated by the deposition of air-fall
tephra and eolian dust, even under dry oxidizing conditions.
Generally, the content of opal phytolith in the humus layer
of Japanese volcanic ash soils is 0.3–17% (Kondo 2010).
Opal phytoliths provide useful information about the soil
formation environment, because they are left in the soil with
the deposition of volcanic ash and loess on the emerged
geomorphic surface (Sase et al. 1987; 2008: Fig. 2.8 in
Sect. 2.1.3).
2.3 Vegetation and Land Use
The vegetation of Japan is characterized by a large number
of species and a high percentage of endemic species. The
great variety of species is related to the geographical position
of the country. The Japanese archipelago is a group of hilly
and mountainous islands, located along the eastern end of
the Eurasian continent, which shows a large variation in
landscape and geology. The variation of climate from subtropical to subarctic along the archipelago is also considered
to be an important factor in the floral biodiversity. During
glacial periods, glacial cover developed in only high-altitude
areas, so forest vegetation remained in the glacial age in the
Pleistocene. It is thought that humans started living in the
Japanese archipelago in the Paleolithic age, 120,000 years
ago, and that rice cultivation was initiated in the Yayoi
period (800 BC–250 AD). Despite human influence, forest
vegetation persisted in the mountainous areas which cover
two-thirds of Japan’s territory; however, the area of the
original natural forests has gradually decreased and has been
replaced by early successional deciduous broad-leaved trees
38
K. Tamura et al.