the nutrient supply in forest soils strongly depends on their
natural environment (climate, parent material, vegetation,
etc.). From the aspect of climate condition, Andosols and
brown forest soils mainly appear in the forests of Central and
Southern Hokkaido under temperate and humid climate
regime. The soil pH in these forests is acidic (less than 6),
and the concentration of soil solution is very low compared
with that of greenhouse, upland, and grassland soils, for
which the input of fertilizer is common as a means of soil
management. Sodium and chlorine predominate in the soil
solution in forest soils, indicating the strong influence of sea
salts. As for the clay mineral compositions in the forest soils
of Hokkaido, illite and montmorillonite containing potassium and calcium are not so significant, but rather vermiculite is the dominant mineral, being produced from the
aforementioned clay minerals by the release of cations. The
clay mineral stability diagram determined from soil solution
shows that many forest soils are located in the stability area
of vermiculite, which indicates the progression of the cation
leaching process in Hokkaido (Satoh et al. 1982).
The evapotranspiration of Northern Hokkaido is very low
because of the cool summers and lack of sunshine. In terms
of soil geography, this area is a transition zone from acidified
brown forest soils to Podzols due to the strong leaching
potential. In the mountainous area of northwestern Hokkaido, heavy snowfall, which in some places exceeds more
than 1000 mm water equivalent per year, produces thick
accumulations of snow on the ground for more than
6 months of the year. The continuous downward movement
of soil water, which is caused by snowmelt under the
accumulated snow (about 0.5 mm/day) and during the
spring melt season, accelerates the annual leaching of
nutrients from the forest soil. Under such a strong leaching
process, extensive soil acidification occurs, with the pH of
forest soils in Northern Hokkaido becoming less than 4. In
this soil, the concentration of aluminum in the soil solution
increases, and Al-vermiculite is the dominant clay mineral in
the B horizons due to the leaching of aluminum from surface
horizons into the vermiculite clay sheets (Satoh et al. 1990).
(3) Forest soils on volcanic ejecta
Soils derived from volcanic ash that have strong phosphorus
absorptivity are distributed widely in the forests of Central
and Eastern Hokkaido. Because the input of fertilizer is not
essential for these forest soils, trees growing on Andosols
absorb the phosphorous supplied from the decomposition of
leaf litter. However, this phosphorous absorption is very
competitive in Andosols due to the presence not only of soil
microorganisms but also of amorphous aluminosilicate
minerals such as allophane with a high phosphorous-fixing
ability. In the Podzols of the Scandinavian Peninsula of
Northern Europe, the activity of soil microorganisms after
adding phosphorous is reported to be affected by the presence of amorphous iron and aluminosilicate (Giesler et al.
2004).
Additionally, dense broad-leaved forests develop on the
Volcanogenous Regosols in southwest Hokkaido. Despite
the fact that these Regosols are very poor in nutrients, the
growth of various broad-leaved trees is maintained by the
decomposition of litter by the earthworms living in the O
horizon.
(4) Forest soils on ultramafic rocks
Magnesian Eutrosols appear in the forests of Hokkaido on
ultramafic peridotite and serpentine rocks. These soils are
characterized by neutral soil pH, a high proportion of
exchangeable magnesium, and a soil base saturation of close
to 100%. These ultramafic soils are patchily distributed
around the line connecting Cape Erimo (southernmost
Hokkaido) with Cape Soya (northernmost Hokkaido), and
spruce forest (Picea glehnii) is representative of them. The
vegetation on serpentine rocks is generally considered to
become steppe or bare land, and forests occurring on serpentine are thus very valuable. Large amounts of precipitation plays an important role in the development of the
forests.
The reason why spruce trees precede other three species
on ultramafic soils is that, despite not being able to compete
with the other species, the spruce trees are able to tolerate
harsh environments such as ultrabasic rock, peatland, and
volcanic ash. An investigation into the mineral composition
of trees growing on serpentine rock in Northern Hokkaido
found that spruce did not absorb magnesium, unlike other
tree species, suggesting that this tree has some magnesium
excluding mechanism (Blandon et al. 1993). A symbiosis
between spruce and mycorrhizal fungi has also been reported, which may also play a role in the tolerance of spruce on
serpentine rocks (Kayama et al. 2006).
5.6.2 Material Cycling
(1) Winter snow cover and material export
In many forests in Hokkaido, snowfall dominates the annual
precipitation. For example, in Northern Hokkaido about
50% of the annual precipitation is supplied as snowfall.
Snowfall accumulates as snowpack in forests during winter
and then is removed as water to streams during the short
snowmelt season. Therefore, the leaching of material from
soil, which is a significant component of material cycling,
occurs during the snowmelt period. Since nutrient uptake by
154
T. Nakatsuji et al.
natural environment (climate, parent material, vegetation,
etc.). From the aspect of climate condition, Andosols and
brown forest soils mainly appear in the forests of Central and
Southern Hokkaido under temperate and humid climate
regime. The soil pH in these forests is acidic (less than 6),
and the concentration of soil solution is very low compared
with that of greenhouse, upland, and grassland soils, for
which the input of fertilizer is common as a means of soil
management. Sodium and chlorine predominate in the soil
solution in forest soils, indicating the strong influence of sea
salts. As for the clay mineral compositions in the forest soils
of Hokkaido, illite and montmorillonite containing potassium and calcium are not so significant, but rather vermiculite is the dominant mineral, being produced from the
aforementioned clay minerals by the release of cations. The
clay mineral stability diagram determined from soil solution
shows that many forest soils are located in the stability area
of vermiculite, which indicates the progression of the cation
leaching process in Hokkaido (Satoh et al. 1982).
The evapotranspiration of Northern Hokkaido is very low
because of the cool summers and lack of sunshine. In terms
of soil geography, this area is a transition zone from acidified
brown forest soils to Podzols due to the strong leaching
potential. In the mountainous area of northwestern Hokkaido, heavy snowfall, which in some places exceeds more
than 1000 mm water equivalent per year, produces thick
accumulations of snow on the ground for more than
6 months of the year. The continuous downward movement
of soil water, which is caused by snowmelt under the
accumulated snow (about 0.5 mm/day) and during the
spring melt season, accelerates the annual leaching of
nutrients from the forest soil. Under such a strong leaching
process, extensive soil acidification occurs, with the pH of
forest soils in Northern Hokkaido becoming less than 4. In
this soil, the concentration of aluminum in the soil solution
increases, and Al-vermiculite is the dominant clay mineral in
the B horizons due to the leaching of aluminum from surface
horizons into the vermiculite clay sheets (Satoh et al. 1990).
(3) Forest soils on volcanic ejecta
Soils derived from volcanic ash that have strong phosphorus
absorptivity are distributed widely in the forests of Central
and Eastern Hokkaido. Because the input of fertilizer is not
essential for these forest soils, trees growing on Andosols
absorb the phosphorous supplied from the decomposition of
leaf litter. However, this phosphorous absorption is very
competitive in Andosols due to the presence not only of soil
microorganisms but also of amorphous aluminosilicate
minerals such as allophane with a high phosphorous-fixing
ability. In the Podzols of the Scandinavian Peninsula of
Northern Europe, the activity of soil microorganisms after
adding phosphorous is reported to be affected by the presence of amorphous iron and aluminosilicate (Giesler et al.
2004).
Additionally, dense broad-leaved forests develop on the
Volcanogenous Regosols in southwest Hokkaido. Despite
the fact that these Regosols are very poor in nutrients, the
growth of various broad-leaved trees is maintained by the
decomposition of litter by the earthworms living in the O
horizon.
(4) Forest soils on ultramafic rocks
Magnesian Eutrosols appear in the forests of Hokkaido on
ultramafic peridotite and serpentine rocks. These soils are
characterized by neutral soil pH, a high proportion of
exchangeable magnesium, and a soil base saturation of close
to 100%. These ultramafic soils are patchily distributed
around the line connecting Cape Erimo (southernmost
Hokkaido) with Cape Soya (northernmost Hokkaido), and
spruce forest (Picea glehnii) is representative of them. The
vegetation on serpentine rocks is generally considered to
become steppe or bare land, and forests occurring on serpentine are thus very valuable. Large amounts of precipitation plays an important role in the development of the
forests.
The reason why spruce trees precede other three species
on ultramafic soils is that, despite not being able to compete
with the other species, the spruce trees are able to tolerate
harsh environments such as ultrabasic rock, peatland, and
volcanic ash. An investigation into the mineral composition
of trees growing on serpentine rock in Northern Hokkaido
found that spruce did not absorb magnesium, unlike other
tree species, suggesting that this tree has some magnesium
excluding mechanism (Blandon et al. 1993). A symbiosis
between spruce and mycorrhizal fungi has also been reported, which may also play a role in the tolerance of spruce on
serpentine rocks (Kayama et al. 2006).
5.6.2 Material Cycling
(1) Winter snow cover and material export
In many forests in Hokkaido, snowfall dominates the annual
precipitation. For example, in Northern Hokkaido about
50% of the annual precipitation is supplied as snowfall.
Snowfall accumulates as snowpack in forests during winter
and then is removed as water to streams during the short
snowmelt season. Therefore, the leaching of material from
soil, which is a significant component of material cycling,
occurs during the snowmelt period. Since nutrient uptake by
154
T. Nakatsuji et al.