4.9.3 Correlation with International
Classification Systems
Most Brown Forest soils with cambic horizons are classified
as Cambisols in the WRB (IUSS Working Group WRB
2015) and as Inceptisols in the USDA Soil Taxonomy (Soil
Survey Staff 2014). Brown Forest soils with argic horizons
are classified as Acrisols, Alisols, Luvisols, or Lixisols in the
WRB and as Ultisols in the USDA Soil Taxonomy. The soils
of the Anthraquic subgroup are classified as Stagnosols in
the WRB. As described above, in the Soil Classification
System of Japan the Brown Forest soil great group corresponds to soils which are classified as different soil great
groups in other soil classification systems.
In the Soil Classification System of Japan (2017), soils
which correspond to Cambisols/Inceptisols include Cambic
Red-Yellow soils and Brown Forest soils. Cambic
Red-Yellow soils cannot be classified into soil orders which
have argic horizons, such as Acrisols or Ultisols, because
these soils do not have argic horizons in the control section.
Brown Forest soils may have reddish cambic horizons while
Cambic Red-Yellow soils have cambic horizons with
red-yellow property, which are identified by soil color and
SOC content. As is the case for Brown Forest soils,
Red-Yellow soils contain an Argic group, which corresponds to Acrisols and Cambic group which corresponds to
Cambisols in the WRB system. Soils having argic horizons
and soils having cambic horizons coexist in the great groups
of Brown Forest soils and Red-Yellow soils in the Japanese
classification system, which strongly reflects the specificity
of soil genesis in mountainous regions of Japan. On the
slope, the movement of the clay fraction along the slope
surface stronger than ones downward in the solum, even if
the current climatic condition tends to cause clay illuviation.
Therefore, both the overlying coarser-textured horizon and
the underlying horizon with illuvial accumulation of clay are
hard to develop in Japan. However, even for those soils
without an argic horizon, weathering progressed. These soils
have a reddish or yellowish color due to the presence of iron
oxide consisting of goethite and hematite produced by the
oxidation and dehydration of free iron by weathering.
Moreover, these soils do not store significant amounts of soil
organic matter and have a pale and thin A horizon as a result
of an increase in the amount of low-activity clay minerals.
4.9.4 Distribution
(1) Distribution of the Brown Forest soil group
Brown Forest soils are distributed in a rather wide range of
temperate and warm temperate zones in humid (high
precipitation) climates. These are zonal soils which are formed
between the zones of “podzols” and “red-yellow soils” (Forest
Soils Division 1976). Brown Forest soils are mainly distributed in sloping land in hills and mountainous regions,
between areas below the subalpine zone where Podzols are
distributed and the alluvial fan, basin, and plain areas where
Fluvic soils are distributed. However, on steeper slopes,
Regosols are distributed more widely than Brown Forest soils.
Because Japan contains many volcanoes, the soils in most
areas of Japan are affected by volcanic ash. The soils classified into the Andosol great group are distributed near
volcanoes, and on flat and gently sloping land. In neighboring areas, Brown Forest soils are mixed with Andosols.
From the eastern sides of volcanoes, the distribution ratio of
Andosols increases, and the ratio of Brown Forest soils
relatively decreases because the volcanic ash was blown by
the westerlies and deposited in eastern sides from the volcano on the Japanese archipelago. The area classified into
the Brown Forest soil group accounts for around 30% of the
area in the Hokkaido, Tohoku, Tokai–Hokuriku, and
Kyushu–Okinawa regions, and a little over 20% of the area
in the Kanto region. In contrast, Brown Forest soils cover
47% of the area in the Kinki–Chugoku–Shikoku region
(Table 2.1 in Sect. 2.5).
(2) Distribution of each soil subgroup
The soils of the Anthraquic subgroup are distributed in
paddy fields in sloping lands in hilly and mountainous areas.
The soils of the Andic subgroup are distributed in marginal areas to the soils of the Andosol great group. In areas
that do not contain Andosols, soils of the Andic subgroup
are distributed in flat and gently sloping land affected by
widespread tephra.
The soils of the Podzolic subgroup are distributed close to
boundaries between Podzols and Brown Forest soils under a
cold moist climate. The soils which correspond to dry
slightly podzolic soils are distributed around locations which
are susceptible to drying, such as crests, ridges, the upper
parts of convex slopes, and the shoulders of plateaus. Such
soils are derived from acidic parent materials, have a sandy
texture, and are developed under forests of hiba (Thujopsis
dolabrata) and Japanese umbrella pine (Sciadopitys verticilata) in subalpine and alpine zones. The soils which correspond to wet iron slightly podzolic soils are distributed
around dull ridges, peneplains, and volcanic mudflow plateaus with heavy clayey and dense materials under natural
forest vegetation (e.g., Sakhalin Spruce (Picea glehnii),
Abies mariesii, Japanese white pine (Pinus parviflora var.
parviflora), Japanese Thuja (Thuja standishii), Japanese
cypress (Chamaecyparis obtusa), and Japanese Beech
(Fagus crenata) from upper temperate to subalpine zones in
120
Y. Takata et al.
Classification Systems
Most Brown Forest soils with cambic horizons are classified
as Cambisols in the WRB (IUSS Working Group WRB
2015) and as Inceptisols in the USDA Soil Taxonomy (Soil
Survey Staff 2014). Brown Forest soils with argic horizons
are classified as Acrisols, Alisols, Luvisols, or Lixisols in the
WRB and as Ultisols in the USDA Soil Taxonomy. The soils
of the Anthraquic subgroup are classified as Stagnosols in
the WRB. As described above, in the Soil Classification
System of Japan the Brown Forest soil great group corresponds to soils which are classified as different soil great
groups in other soil classification systems.
In the Soil Classification System of Japan (2017), soils
which correspond to Cambisols/Inceptisols include Cambic
Red-Yellow soils and Brown Forest soils. Cambic
Red-Yellow soils cannot be classified into soil orders which
have argic horizons, such as Acrisols or Ultisols, because
these soils do not have argic horizons in the control section.
Brown Forest soils may have reddish cambic horizons while
Cambic Red-Yellow soils have cambic horizons with
red-yellow property, which are identified by soil color and
SOC content. As is the case for Brown Forest soils,
Red-Yellow soils contain an Argic group, which corresponds to Acrisols and Cambic group which corresponds to
Cambisols in the WRB system. Soils having argic horizons
and soils having cambic horizons coexist in the great groups
of Brown Forest soils and Red-Yellow soils in the Japanese
classification system, which strongly reflects the specificity
of soil genesis in mountainous regions of Japan. On the
slope, the movement of the clay fraction along the slope
surface stronger than ones downward in the solum, even if
the current climatic condition tends to cause clay illuviation.
Therefore, both the overlying coarser-textured horizon and
the underlying horizon with illuvial accumulation of clay are
hard to develop in Japan. However, even for those soils
without an argic horizon, weathering progressed. These soils
have a reddish or yellowish color due to the presence of iron
oxide consisting of goethite and hematite produced by the
oxidation and dehydration of free iron by weathering.
Moreover, these soils do not store significant amounts of soil
organic matter and have a pale and thin A horizon as a result
of an increase in the amount of low-activity clay minerals.
4.9.4 Distribution
(1) Distribution of the Brown Forest soil group
Brown Forest soils are distributed in a rather wide range of
temperate and warm temperate zones in humid (high
precipitation) climates. These are zonal soils which are formed
between the zones of “podzols” and “red-yellow soils” (Forest
Soils Division 1976). Brown Forest soils are mainly distributed in sloping land in hills and mountainous regions,
between areas below the subalpine zone where Podzols are
distributed and the alluvial fan, basin, and plain areas where
Fluvic soils are distributed. However, on steeper slopes,
Regosols are distributed more widely than Brown Forest soils.
Because Japan contains many volcanoes, the soils in most
areas of Japan are affected by volcanic ash. The soils classified into the Andosol great group are distributed near
volcanoes, and on flat and gently sloping land. In neighboring areas, Brown Forest soils are mixed with Andosols.
From the eastern sides of volcanoes, the distribution ratio of
Andosols increases, and the ratio of Brown Forest soils
relatively decreases because the volcanic ash was blown by
the westerlies and deposited in eastern sides from the volcano on the Japanese archipelago. The area classified into
the Brown Forest soil group accounts for around 30% of the
area in the Hokkaido, Tohoku, Tokai–Hokuriku, and
Kyushu–Okinawa regions, and a little over 20% of the area
in the Kanto region. In contrast, Brown Forest soils cover
47% of the area in the Kinki–Chugoku–Shikoku region
(Table 2.1 in Sect. 2.5).
(2) Distribution of each soil subgroup
The soils of the Anthraquic subgroup are distributed in
paddy fields in sloping lands in hilly and mountainous areas.
The soils of the Andic subgroup are distributed in marginal areas to the soils of the Andosol great group. In areas
that do not contain Andosols, soils of the Andic subgroup
are distributed in flat and gently sloping land affected by
widespread tephra.
The soils of the Podzolic subgroup are distributed close to
boundaries between Podzols and Brown Forest soils under a
cold moist climate. The soils which correspond to dry
slightly podzolic soils are distributed around locations which
are susceptible to drying, such as crests, ridges, the upper
parts of convex slopes, and the shoulders of plateaus. Such
soils are derived from acidic parent materials, have a sandy
texture, and are developed under forests of hiba (Thujopsis
dolabrata) and Japanese umbrella pine (Sciadopitys verticilata) in subalpine and alpine zones. The soils which correspond to wet iron slightly podzolic soils are distributed
around dull ridges, peneplains, and volcanic mudflow plateaus with heavy clayey and dense materials under natural
forest vegetation (e.g., Sakhalin Spruce (Picea glehnii),
Abies mariesii, Japanese white pine (Pinus parviflora var.
parviflora), Japanese Thuja (Thuja standishii), Japanese
cypress (Chamaecyparis obtusa), and Japanese Beech
(Fagus crenata) from upper temperate to subalpine zones in
120
Y. Takata et al.