with the body weight of Lumbricidae earthworms. Together,
these facts indicate that the difference in calcium concentration among soil types is an important determinant of the
geographical variation of earthworm distribution. At a larger
spatial scale, Uchida et al. (2004) reported that the density
and biomass of earthworms in Central Hokkaido were far
larger than in temperate forests in the Kanto region. However, little is known about the nationwide variation in the
abundance of soil fauna and its diversity, or about the driver
of the variation, and further nationwide comparative studies
are therefore required.
In Hokkaido, many soil fauna groups show clear seasonal
changes in their abundance. Their abundance peaks in the
middle of autumn, and later the group of overwintering soil
fauna moves to a deeper part of the soil profile to avoid the
cold temperature (Nakamura et al. 1970). In Hokkaido, air
temperature sometimes drops between −20 and −30 °C in
the middle of winter. The deep snowpack in Northern
Hokkaido insulates the soil from the cold air temperature,
and soil does not freeze. As a result, some soil fauna groups
can manage overwintering without suffering the damage
caused by soil frost. In forests with a cold biome, the soil
nitrogen availability for trees is the limiting factor affecting
the primary production of forests (Aber 1989). In Hokkaido,
the influence of earthworms is more predominant in summer
compared with winter, which suggests seasonality in the
relationship between soil fauna and its influence on biogeochemical cycles (Hishi et al. 2014). Species of Lumbricidae, which is the major earthworm group in boreal Eurasia,
are more abundant in Northern Hokkaido than in Southern
Hokkaido, which is consistent with the fact that forest vegetation in Northern Hokkaido is in the transient zone
between temperate forests to boreal forests.
(3) Human activity and soil fauna
Artificial factors such as land use change can influence the
soil faunal community. In Central Hokkaido, the soil faunal
abundance was found to be greater in natural mixed-conifer
broad-leaved forests than in artificial forests of Abies
sachalinensis (Nakamura et al. 1970). Among artificial forests, those of non-native Picea abies have a lower abundance
of soil faunal than that of native A. sachalinensis because of
the poor understory vegetation in P. abies forests. This study
suggests that the proper management of understory vegetation can maintain the diversity and abundance of the soil
faunal community in artificial forests. On the other hand,
little is known about the influence of silvicultural practices
other than plantation (e.g. scarification of understory dwarf
bamboo), and further studies are necessary.
In high-latitude areas such as Hokkaido, the influence of
climate warming on organisms is predicted to be predominant.
Based on experimental studies and latitude gradient studies
(e.g. Fujii et al. 2018), climate warming is predicted to change
the soil faunal contribution to litter decomposition and consequently the plant growth. Although winter climate influences
the structure and function of forest communities, the magnitude of change in temperature has been greater in winter than
in summer. In Northern Hokkaido, the snow cover period has
become shorter due to the warming climate. In future studies,
the influence of characteristic climate change in Hokkaido (e.g.
advancing snowmelt) on the biodiversity and the associated
biogeochemical cycle should be clarified by utilizing the
long-term monitoring data obtained by the Japan Long-term
Ecological Research (JaLTER) and Monitoring 1000 research
programs being conducted by the Japanese Ministry of the
Environment.
5.7 Agriculture and Environment
5.7.1 Environmental Burden and Conservation
As a result of the material cycling through the soil, agricultural environmental burden extends to the aquasphere and
atmosphere. In Hokkaido, in particular, the NO 3 -N contamination of groundwater is a problem. Figure 5.8 shows
the results of an investigation of the concentration of NO 3 -N
in well water across the whole of Hokkaido (Hokkaido
2013). A large number of wells were contaminated with
NO 3 -N in upland fields of Andosols and livestock areas,
especially in the Abashiri area. The environmental standard
(10 mg N L
−1 ) was exceeded in 5.7% of cases (for details,
see Sect. 5.7.2). Based on the results of this survey, it is
thought that the groundwater pollution was derived from
nitrogen fertilization, and efforts have been made to improve
fertilization methods. In particular, the upper limit of the
nitrogen fertilizer application for producing crops is set in
accordance with the nitrogen environmental capacity which
is the sum of the amount of nitrogen taken up by the crop
and the allowable remaining amount of NO 3 –N in soil
(Matsumoto and Tou 2006). The nitrogen environmental
capacity (kg ha
−1 yr
−1 ) was 157 ± 19 for paddy fields
218 ± 39 for grasslands and 169 ± 30 for upland fields in
Hokkaido. The groundwater NO 3 –N concentration increased
in proportion to the difference between the nitrogen fertilizer
application rate and the nitrogen environmental capacity in
all plots, and in upland fields where the nitrogen fertilizer
application rate was above the nitrogen environmental
capacity, the groundwater NO 3 –N concentration was higher
than 10 mg N L
−1 . It is recommended to account for surplus
nitrogen in soil in previous cultivation by implementing a
three-crop rotation, for example, sugar beet, azuki bean, and
spring wheat. This is because surplus nitrogen easily exceeds
158
T. Nakatsuji et al.
these facts indicate that the difference in calcium concentration among soil types is an important determinant of the
geographical variation of earthworm distribution. At a larger
spatial scale, Uchida et al. (2004) reported that the density
and biomass of earthworms in Central Hokkaido were far
larger than in temperate forests in the Kanto region. However, little is known about the nationwide variation in the
abundance of soil fauna and its diversity, or about the driver
of the variation, and further nationwide comparative studies
are therefore required.
In Hokkaido, many soil fauna groups show clear seasonal
changes in their abundance. Their abundance peaks in the
middle of autumn, and later the group of overwintering soil
fauna moves to a deeper part of the soil profile to avoid the
cold temperature (Nakamura et al. 1970). In Hokkaido, air
temperature sometimes drops between −20 and −30 °C in
the middle of winter. The deep snowpack in Northern
Hokkaido insulates the soil from the cold air temperature,
and soil does not freeze. As a result, some soil fauna groups
can manage overwintering without suffering the damage
caused by soil frost. In forests with a cold biome, the soil
nitrogen availability for trees is the limiting factor affecting
the primary production of forests (Aber 1989). In Hokkaido,
the influence of earthworms is more predominant in summer
compared with winter, which suggests seasonality in the
relationship between soil fauna and its influence on biogeochemical cycles (Hishi et al. 2014). Species of Lumbricidae, which is the major earthworm group in boreal Eurasia,
are more abundant in Northern Hokkaido than in Southern
Hokkaido, which is consistent with the fact that forest vegetation in Northern Hokkaido is in the transient zone
between temperate forests to boreal forests.
(3) Human activity and soil fauna
Artificial factors such as land use change can influence the
soil faunal community. In Central Hokkaido, the soil faunal
abundance was found to be greater in natural mixed-conifer
broad-leaved forests than in artificial forests of Abies
sachalinensis (Nakamura et al. 1970). Among artificial forests, those of non-native Picea abies have a lower abundance
of soil faunal than that of native A. sachalinensis because of
the poor understory vegetation in P. abies forests. This study
suggests that the proper management of understory vegetation can maintain the diversity and abundance of the soil
faunal community in artificial forests. On the other hand,
little is known about the influence of silvicultural practices
other than plantation (e.g. scarification of understory dwarf
bamboo), and further studies are necessary.
In high-latitude areas such as Hokkaido, the influence of
climate warming on organisms is predicted to be predominant.
Based on experimental studies and latitude gradient studies
(e.g. Fujii et al. 2018), climate warming is predicted to change
the soil faunal contribution to litter decomposition and consequently the plant growth. Although winter climate influences
the structure and function of forest communities, the magnitude of change in temperature has been greater in winter than
in summer. In Northern Hokkaido, the snow cover period has
become shorter due to the warming climate. In future studies,
the influence of characteristic climate change in Hokkaido (e.g.
advancing snowmelt) on the biodiversity and the associated
biogeochemical cycle should be clarified by utilizing the
long-term monitoring data obtained by the Japan Long-term
Ecological Research (JaLTER) and Monitoring 1000 research
programs being conducted by the Japanese Ministry of the
Environment.
5.7 Agriculture and Environment
5.7.1 Environmental Burden and Conservation
As a result of the material cycling through the soil, agricultural environmental burden extends to the aquasphere and
atmosphere. In Hokkaido, in particular, the NO 3 -N contamination of groundwater is a problem. Figure 5.8 shows
the results of an investigation of the concentration of NO 3 -N
in well water across the whole of Hokkaido (Hokkaido
2013). A large number of wells were contaminated with
NO 3 -N in upland fields of Andosols and livestock areas,
especially in the Abashiri area. The environmental standard
(10 mg N L
−1 ) was exceeded in 5.7% of cases (for details,
see Sect. 5.7.2). Based on the results of this survey, it is
thought that the groundwater pollution was derived from
nitrogen fertilization, and efforts have been made to improve
fertilization methods. In particular, the upper limit of the
nitrogen fertilizer application for producing crops is set in
accordance with the nitrogen environmental capacity which
is the sum of the amount of nitrogen taken up by the crop
and the allowable remaining amount of NO 3 –N in soil
(Matsumoto and Tou 2006). The nitrogen environmental
capacity (kg ha
−1 yr
−1 ) was 157 ± 19 for paddy fields
218 ± 39 for grasslands and 169 ± 30 for upland fields in
Hokkaido. The groundwater NO 3 –N concentration increased
in proportion to the difference between the nitrogen fertilizer
application rate and the nitrogen environmental capacity in
all plots, and in upland fields where the nitrogen fertilizer
application rate was above the nitrogen environmental
capacity, the groundwater NO 3 –N concentration was higher
than 10 mg N L
−1 . It is recommended to account for surplus
nitrogen in soil in previous cultivation by implementing a
three-crop rotation, for example, sugar beet, azuki bean, and
spring wheat. This is because surplus nitrogen easily exceeds
158
T. Nakatsuji et al.