surface, but this does not affect the soil carbon balance. The
sum of the microbial (or heterotrophic) and root (or autotrophic) respiration is called soil respiration and is measured
at many forests in Japan. Lee et al. (2006) report that the
annual soil respiration rate in Japanese forests ranges from 2
to 14 Mg C ha
−1 yr
−1 , with an average rate of
6.47 ± 2.72 Mg C ha
−1 yr
−1 . The soil respiration rates of
forests in Hokkaido lie within this range, although the soil
respiration in forests with dense undergrowth of dwarf
bamboo tends to be near the upper maximum (>10 Mg C
ha
−1 yr
−1 ) of the range (Aguilos et al. 2014). This reflects the
high investment of the resources to the belowground organs
of this plant (i.e. root biomass and respiration). In Hokkaido,
soil respiration accounts for around 50–60% of total
ecosystem respiration (10–15 Mg C ha
−1 yr
−1 ) and microbial respiration for around 30–80% of the soil respiration,
with the contribution of microbial respiration decreasing
with an increase in the soil respiration.
Soil carbon balance and the carbon sink or source
strength can be estimated by accounting for the aforementioned inputs and outputs. However, because the annual
change in the soil carbon stock is considered to be less than a
few percent of the stock, having large uncertainty in the
estimation, many studies assume that carbon stock is constant during a certain period within several years.
(2) Effects of forest management or disturbances
Clear-cut harvesting decreases both the forest ecosystem
photosynthesis and respiration rates. However, because the
magnitude of the decrease is larger for the photosynthesis
rates, such harvesting usually turns forest into a carbon
source (Aguilos et al. 2014). Other serious disturbances,
such as typhoons, windthrows, and fires, cause a similar
change in the forest carbon balance. The change in the soil
respiration and soil carbon balance caused by harvesting and
these other disturbances strongly depends on the condition
of the vegetation after such disturbances. In Northern Hokkaido, an observed increase in the soil respiration rate after
clear-cut harvesting was mainly caused by an increase in the
biomass and root respiration of the undergrowth dwarf
bamboo resulting from better light conditions after the harvesting of overstory trees, while the increase in the biomass
slightly decreased the soil surface temperature and suppressed the increase in soil carbon decomposition by
microorganisms. Using a model and observed results,
Aguilos et al. (2014) simulated the effect of the clear-cut
harvesting on the forest carbon stock for each compartment
and showed that the increase in the soil respiration can be
explained by the increase in root respiration and in litter
(residuals such as stumps and branches) decomposition after
the harvesting. It is hard to recognize the change in the soil
carbon stock during the course of management (Fig. 5.7).
Soil carbon stock will decrease if such management or disturbance increases the soil temperature and enhances the
microbial decomposition under poor undergrowth conditions; however, it is hard to find studies on this in Hokkaido.
On the other hand, in Hokkaido, dense undergrowth and
surface soils are often removed after harvesting for the
plantation or natural regeneration of trees. Such practices
have a large effect on the soil carbon stock and cause the loss
of tens of Mg C ha
−1 .
(3) Effects of global warming
Recent global synthesis studies show that ecosystems in
cooler climates or with higher soil carbon stocks tend to lose
a larger amount of soil carbon by CO 2 emissions in warmer
conditions. Several soil warming experiments in black spruce
and Scots pine forests in Northern Europe and the USA have
shown that soil warming (3–6 °C temperature increase)
enhances soil respiration by 11–45% for several years, with
the limited temporal duration of the enhancement being due
to the rapid decrease in soil labile carbon content as a result of
warming. However, a soil warming experiment in a cool
temperate forested peatland in Northern Hokkaido showed
that warming (3.2 °C increase in the soil temperature at 5 cm
depth) enhances the soil carbon decomposition by an average
of 82% for the first 4 years (Aguilos et al. 2013), and that the
enhancement rate continues to increase for more than
10 years. This suggests that soils with high substrate availability and without severe water stress would lose a huge
amount of soil carbon in a future warmer environment, and
that the effect would last for more than a decade.
5.6.4 Biodiversity
(1) Importance and abundance of soil fauna in
Hokkaido
The organisms living in forest soils significantly influence
biogeochemical cycles and, consequently, ecosystem function. In particular, soil fauna impacts biogeochemical cycles
significantly via feeding on litter and coarse woody debris
and also plays a role in the modification of soil structure as
ecosystem engineers.
The study of soil fauna in the forest ecosystems of Hokkaido was begun by Yoshio Nakamura’s group in the 1970s.
Among various groups of soil mesofauna, which largely
contribute to litter decomposition, Collembola (springtail)
communities are the most abundant and Oribatida communities the second most abundant. For soil macrofauna, centipedes (predator) and Enchytraeidae (detritus feeder) are the
156
T. Nakatsuji et al.
sum of the microbial (or heterotrophic) and root (or autotrophic) respiration is called soil respiration and is measured
at many forests in Japan. Lee et al. (2006) report that the
annual soil respiration rate in Japanese forests ranges from 2
to 14 Mg C ha
−1 yr
−1 , with an average rate of
6.47 ± 2.72 Mg C ha
−1 yr
−1 . The soil respiration rates of
forests in Hokkaido lie within this range, although the soil
respiration in forests with dense undergrowth of dwarf
bamboo tends to be near the upper maximum (>10 Mg C
ha
−1 yr
−1 ) of the range (Aguilos et al. 2014). This reflects the
high investment of the resources to the belowground organs
of this plant (i.e. root biomass and respiration). In Hokkaido,
soil respiration accounts for around 50–60% of total
ecosystem respiration (10–15 Mg C ha
−1 yr
−1 ) and microbial respiration for around 30–80% of the soil respiration,
with the contribution of microbial respiration decreasing
with an increase in the soil respiration.
Soil carbon balance and the carbon sink or source
strength can be estimated by accounting for the aforementioned inputs and outputs. However, because the annual
change in the soil carbon stock is considered to be less than a
few percent of the stock, having large uncertainty in the
estimation, many studies assume that carbon stock is constant during a certain period within several years.
(2) Effects of forest management or disturbances
Clear-cut harvesting decreases both the forest ecosystem
photosynthesis and respiration rates. However, because the
magnitude of the decrease is larger for the photosynthesis
rates, such harvesting usually turns forest into a carbon
source (Aguilos et al. 2014). Other serious disturbances,
such as typhoons, windthrows, and fires, cause a similar
change in the forest carbon balance. The change in the soil
respiration and soil carbon balance caused by harvesting and
these other disturbances strongly depends on the condition
of the vegetation after such disturbances. In Northern Hokkaido, an observed increase in the soil respiration rate after
clear-cut harvesting was mainly caused by an increase in the
biomass and root respiration of the undergrowth dwarf
bamboo resulting from better light conditions after the harvesting of overstory trees, while the increase in the biomass
slightly decreased the soil surface temperature and suppressed the increase in soil carbon decomposition by
microorganisms. Using a model and observed results,
Aguilos et al. (2014) simulated the effect of the clear-cut
harvesting on the forest carbon stock for each compartment
and showed that the increase in the soil respiration can be
explained by the increase in root respiration and in litter
(residuals such as stumps and branches) decomposition after
the harvesting. It is hard to recognize the change in the soil
carbon stock during the course of management (Fig. 5.7).
Soil carbon stock will decrease if such management or disturbance increases the soil temperature and enhances the
microbial decomposition under poor undergrowth conditions; however, it is hard to find studies on this in Hokkaido.
On the other hand, in Hokkaido, dense undergrowth and
surface soils are often removed after harvesting for the
plantation or natural regeneration of trees. Such practices
have a large effect on the soil carbon stock and cause the loss
of tens of Mg C ha
−1 .
(3) Effects of global warming
Recent global synthesis studies show that ecosystems in
cooler climates or with higher soil carbon stocks tend to lose
a larger amount of soil carbon by CO 2 emissions in warmer
conditions. Several soil warming experiments in black spruce
and Scots pine forests in Northern Europe and the USA have
shown that soil warming (3–6 °C temperature increase)
enhances soil respiration by 11–45% for several years, with
the limited temporal duration of the enhancement being due
to the rapid decrease in soil labile carbon content as a result of
warming. However, a soil warming experiment in a cool
temperate forested peatland in Northern Hokkaido showed
that warming (3.2 °C increase in the soil temperature at 5 cm
depth) enhances the soil carbon decomposition by an average
of 82% for the first 4 years (Aguilos et al. 2013), and that the
enhancement rate continues to increase for more than
10 years. This suggests that soils with high substrate availability and without severe water stress would lose a huge
amount of soil carbon in a future warmer environment, and
that the effect would last for more than a decade.
5.6.4 Biodiversity
(1) Importance and abundance of soil fauna in
Hokkaido
The organisms living in forest soils significantly influence
biogeochemical cycles and, consequently, ecosystem function. In particular, soil fauna impacts biogeochemical cycles
significantly via feeding on litter and coarse woody debris
and also plays a role in the modification of soil structure as
ecosystem engineers.
The study of soil fauna in the forest ecosystems of Hokkaido was begun by Yoshio Nakamura’s group in the 1970s.
Among various groups of soil mesofauna, which largely
contribute to litter decomposition, Collembola (springtail)
communities are the most abundant and Oribatida communities the second most abundant. For soil macrofauna, centipedes (predator) and Enchytraeidae (detritus feeder) are the
156
T. Nakatsuji et al.