「森林総合研究所研究報告」(Bulletin of FFPRI) Vol.11 No.4 (No.425) 207 - 221 December 2012

論 文（Original article）
Carbon stocks of dead wood, litter, and soil in the forest sector of Japan :general description of the National Forest Soil Carbon Inventory
Shin UGAWA1)*, Masamichi
TAKAHASHI2), Kazuhito
MORISADA2)3), Manabu TAKEUCHI1)4),
5)
6), Shuichiro YOSHINAGA, Makoto ARAKI, Nagaharu TANAKA,
Yojiro MATSUURA
1)
6)
1)
MIURA
,
Shigehiro
ISHIZUKA,
Masahiro
KOBAYASHI,
Shigeto IKEDA1), Satoru
1)1)1), Kazuki NANKO, Shoji HASHIMOTO,
Masahiro INAGAKI3)6), Akihiro IMAYA
7)
8)
9)
,
Shuhei AIZAWA9) , Keizo HIRAI10), Toru OKAMOTO , 1)Takeo MIZOGUCHI
Atsushi TORII , Hisao SAKAI , Yasuhiro OHNUKI , Shinji KANEKO1)
Abstract
The aims of this study were to report the C stocks of dead wood, litter, and soil at 0–30 cm in the forest sector ofJapan, to clarify the spatial distribution of those C stocks according to prefecture units and to determine the ratio of
soil C stock at 0–30 cm to that at 0–100 cm. To achieve these objectives, data collected by the National Forest Soil
Carbon Inventory Project, which surveyed the C stocks of dead wood, litter, and soil at 0–30 cm and at 0–100 cm
throughout the forest sector of Japan, were analyzed. The C stock (mean ± sample standard deviation) of dead wood,
litter, and soil at 0–30 cm was 0.42 ± 0.67, 0.49 ± 0.32, and 6.94 ± 3.25 kg m-2, respectively. This study did not detect
any clear tendency in the latitudinal distribution of the C stocks of dead wood and litter, although the litter C stock
was lower in prefectures with a higher annual mean temperature. On the other hand, the C stock of soil at 0–30 cm
was higher in northern Japan and lower in southern Japan. Exceptions to this pattern included a high C stock in some
prefectures in the volcanic regions of southern Japan. Thus, we suggest that the soil C stock at 0–30 cm is regulated
by a macroscale factor, i.e., temperature, as well as by the distribution of volcanic ash soils. The soil C stock at 0–100
cm was 14.29 ± 8.38 kg m-2 (mean ± sample standard deviation) and the ratio of the soil C stock at 0–30 cm to thatat 0–100 cm was 0.59 ± 0.31 (mean ± sample standard deviation), suggesting that the soil C stock at 0–30 cm in theforest sector of Japan accounts for a larger portion of that at 0–100 cm compared with worldwide average.
Key words : carbon stock, dead wood, litter, soil, national forest inventory, systematic sampling, Kyoto Protocol
1.Introduction

The main C pools in forest ecosystems are abovegroundThe carbon (C) stock of a forest is the basic datum

and belowground biomass, dead wood, litter, and soil

for evaluating the C sink function of the forest ecosystem.

(IPCC 2006). In Japan, measurement data on the C stock of

Therefore, the parties ratifying the United Nations

aboveground and belowground biomass have been collected

Framework Convention on Climate Change (UNFCCC)

throughout the entire forest sector (Forestry Agency ofwere asked to report the C stock in the forest sector of their

Japan 2012). On the other hand, the C stocks of dead woodcountries. The C stock of the total area of the forest sector

and litter have yet to be surveyed throughout the entire

is estimated using a model that describes the relationshipforest sector of Japan, although C stocks of dead wood

between actual measurement data and external data

and litter in forests dominated by major tree species wereprepared for the entire mesh area of the country. Thus,

summarized by Takahashi et al. (2010). The C stock of soil

recent, transparent, and verifiable measurement data should

was estimated by Morisada et al. (2004) throughout the

be collected throughout the entire forest sector of theentire forest land of Japan using soil profile data collected

country for accurate estimation of the C stock in the forestfrom 1950s to 1970s, but these soil profile data cannot be

sector of the country.

said to be recent. Therefore, measurement data for the C

原稿受付：平成 24 年 3 月 12 日 Received 12 March 2012
原稿受理：平成 24 年 8 月 22 日 Accepted 22 August 2012
1) Department of Forest Site Environment, Forestry and Forest Products Research Institute (FFPRI)
2) Department of Research Planning and Coordination, Forestry and Forest Products Research Institute (FFPRI)
3) Hokkaido Research Center, Forestry and Forest Products Research Institute (FFPRI)
4) Chubu Regional Forest Ofﬁce, Forestry Agency of Japan
5) Bureau of International Partnership, Forestry and Forest Products Research Institute (FFPRI)
6) Kyushu Research Center, Forestry and Forest Products Research Institute (FFPRI)
7) Tohoku Research Center, Forestry and Forest Products Research Institute (FFPRI)
8) Kiso Experiment Station, Forestry and Forest Products Research Institute (FFPRI)
9) Kansai Research Center, Forestry and Forest Products Research Institute (FFPRI)
10) Shikoku Research Center, Forestry and Forest Products Research Institute (FFPRI)* Department of Forest Site Environment, Forestry and Forest Products Research Institute (FFPRI), Matsunosato 1, Tsukuba, Ibaraki 3058687, Japan; e-mail: ushin@ffpri.affrc.go.jp

UGAWA, S. et al.

208

stocks of dead wood, litter, and soil should be collected

C is also stored in deeper soil layers, and this C storage isthroughout the entire forest sector of Japan, and the mean C

related to the C sink function of forest ecosystems. Soil C

stocks of the three pools in the forest sector of Japan shouldstock generally decreases with depth as a result of C influx

be determined.

from decomposing litter and dead roots in the upper soil

As a subsequent step, the heterogeneity of the C stocks

layer and low decomposition rates in the lower soil layer.

of the three pools should be determined because C stocks

Moreover, the vertical distribution of soil C stock variesof the total area of the forest sector are estimated using awith climate, soil type, vegetation type, and volcanic ash

model that explains this heterogeneity. The heterogeneity ofcontent (Batjes 1996, Jobbágy and Jackson 2000, Yang

C stocks is a result of many factors of site environment andet al. 2010, Imaya et al. 2010a, b). Thus, the verticaltree community. Thus, the factors that strongly influence

distribution of soil C stock indicates the character of soil C

the C stocks should be delineated. Many of these factors

accumulation in the forest sector of Japan.

can be classified as macroscale factors such as temperature

The goals of this study were to (i) report the C stocks

or microscale factors such as forest management.

of dead wood, litter, and soil to a depth of 30 cm in the

Therefore, it is prudent to determine whether a macroscale

forest sector of Japan, (ii) clarify the spatial distribution

factor strongly influences the C stocks, that is, whether aof the C stocks of the three pools at a prefecture level, andmacroscale pattern exists in the spatial distribution of the(iii) determine the ratio of the㡫ᖜ
soil C stock in the 0–30-cm

C stocks. This study focused on the heterogeneity amonginterval to that in the 0–100-cm interval. To achieve these

prefectures to detect any spatial patterns throughout theobjectives, measurement data collected by the National

entire forest sector of Japan.

Forest Soil Carbon Inventory Project, which surveyed C

The UNFCCC requests reporting of the C stock of soil
from the soil surface to a depth of 30 cm. However, soil

stocks of dead wood, litter, and soil at 0–30 cm and 0–100
cm in FY2006–2010, were analyzed.

Fig. 1 Location of survey plots (solid circles) in forest sector (green area) of Japan. Forest sector isshown according to National Land Numerical Information provided by the National and Regional
Planning Bureau of the Ministry of Land, Infrastructure, Transport and Tourism.

森林総合研究所研究報告 第 11 巻 4 号 , 2012

Carbon stocks of dead wood, litter, and soil in the forest sector of Japan:
general description of the National Forest Soil Carbon Inventory

209

2.Materials and Methods

intersected a line (see below), were defined as dead wood

The C stock of dead wood, litter, and soil was surveyed

because non-commercial thinning felled stunted trees,in the National Forest Soil Carbon Inventory Project using

which usually are <10 cm in diameter in plantation forest of

the survey methods described below.

Japan (Sakai et al. 2008).
In each survey plot, a north–south line and an east–west line were established, and their horizontal lengths were

Survey Plot
The 4×4-km grid points over the forest sector of Japanmeasured (Fig. 2). Dead wood that intersected the lines atwere systematically selected for the Forest Resourcesheights between 0 and 150 cm was divided into four species

Monitoring Survey, in which tree censuses were conductedcategories: conifer, broadleaved, unidentified woody, andduring FY1999–2003 (Forestry Agency of Japan 2012).

bamboo. Then, the decay class of each piece of dead wood

One-fifth of these survey sites were selected in the National

was determined according to appearance using Tables 1 andForest Soil Carbon Inventory Project, giving a total of 2919

2, and the diameter at the point where it intersected a line2

grid points (Fig. 1). A 1000-m circular plot was establishedẁ⤌ᖜ

was measured (Fig. 3).

in each grid point (Fig. 2), and the C stock of dead wood,

The C stock of dead wood was calculated for eachlitter, and soil at 0–30 cm was surveyed in each plot. The

species category and decay class by Formula 1 using thesoil C stock at 0–100 cm was surveyed in 992 of the survey

line intersect method (Warren and Olsen 1964, Van Wagner

plots, which were selected from every third survey plot on a1968, Brown 1974), where D (cm) is the diameter of deadnorth–south grid line.

wood, L ns (m) is the horizontal length of the north–southline, L ew (m) is the horizontal length of the east–west line,
M (g cm−3) is the wood density of each species category andDead Wood C Stock
According to the IPCC guidelines (IPCC 2006), deaddecay class (Table 3), CC (kg kg −1) is the C concentration

wood includes coarse woody debris, dead coarse roots,of the dry wood (equal to 0.5), and the subscript i indicatesand standing dead trees ≥10 cm in diameter. However,individual dead wood, respectively. The dead wood C stocks

in this project, fallen boles and branches, stumps, andof all species categories and decay classes were summed

inclined dead stems ≥5 cm in diameter at the point where it

to give the dead wood C stock in a survey plot, althoughdead wood C stock was not calculated for survey plots withmissing data.
Dead wood C stock for each species category and decay

1class (kg m−2)
π 2 × Σ D i2=i

8×(Lns + Lew)

×M×CC×10-1[Formula 1]

Litter C Stock:(The IPCC guidelines define litter an organic horizon(all leaves, twigs, small branches, fruits, flowers, roots, andbark) on the mineral soil surface (IPCC 2006), although
the term litter differs in soil science, where its meaning is
restricted to fallen dead leaves (e.g., Wild 1971). However,in this study, litter was defined as an organic horizon that6is divided into four litter types: fine woody debris, whichP

includes fallen boles, branches, twigs <5 cm maximum

Fig. 2 Two lines (solid lines) for surveying dead wood C stockand four points (solid circles) for measuring C stock oflitter and soil at 0–30 cm in a survey plot (dotted line).
The diameter of the circular plot is a horizontal distanceof 35.68 m. Dead wood C stock was surveyed along
the north–south and the east–west lines using the line
intersect method, and the C stocks of litter and soil at
0–30 cm were measured at four points, in the northern,eastern, southern, and western parts of the plot.

layer and the humus layer. We defined the humus layer as

diameter, strobilus, and bark; fresh leaves; the fermentation
continuously stocked humus ≥1 cm in depth.
In each survey plot, slope inclination was measured atfour points, one each in the northern, eastern, southern, andwestern parts of the plot (Fig. 2). At each point, a sample ofeach litter type was taken from a 0.5-m square (Fig. 4).
These samples were oven dried at 70°C for 48 h, andweighed. Then, the samples of the same litter type wereBulletin of FFPRI, Vol.11, No.4, 2012

UGAWA, S. et al.

210

Table 1 Criteria determining the decay class of dead wood for
conifer and broadleaved species'HFD\FODVV $SSHDUDQFHRIGHDGZRRG
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Fig. 3 Field survey for dead wood C stock. The diameter ofdead wood was measured where it intersected a line
(white tape).

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Table 3 Wood density (g cm-3) of dead wood in each species category and decay class. These
values were determined by data from Forestry Agency of Japan (2007) and Sakai et al.
(2008)'HFD\FODVV

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森林総合研究所研究報告 第 11 巻 4 号 , 2012

Carbon stocks of dead wood, litter, and soil in the forest sector of Japan:
general description of the National Forest Soil Carbon Inventory211

repeated measurement values as long as the values met therequirements of Table 4.
Water content (%) =Wbefore–Wafter
×100
Wbefore–Wbottle

C concentration (kg kg−1) =WcarbonWC
1+
100
Wsample([Formula 2])[Formula 3]

We calculated the C stock of each sampling point using
Formula 4, where W (kg) is dry weight of the sample, CC(kg kg −1) is the C concentration, θ (radians) is the slope
inclination, S (m2) is the sampling area (equal to 0.25), andFig. 4 Litter stock in a sampling point. Litter samples weretaken from a 0.5-m square.

the subscript i indicates the litter type. Then, the mean C
stock across sampling points was calculated to obtain thelitter C stock for a survey plot. Sampling points containing
a litter sample with missing data or anomalous data weremixed across all sampling points of a survey plot andexcluded from the calculations (see Quality Control of Data

ground into fine particles (≤0.25 mm) using a cutting mill

section).

and mortar. A portion of the fine particles (0.4–0.6 g) was

Litter C stock at each sampling point (kg m−2)

put into a weighing bottle, and the bottle was weighed.
The weighing bottle was then oven dried at 70°C for 24 h
and weighed again. The water content of the fine particles

= Σ
i

(

Wi
×CCi
(S×cos θ))[Formula 4]

was determined using Formula 2, where W bottle (g) is theweight of the weighing bottle, and W before (g) and Wafter

Soil C Stock at 0–30 cm(g) are the weights of the weighing bottle containing fine

Soil C stock at 0–30 cm㡫ᖜ
was surveyed at the same

particles before and after oven drying, respectively. If

points where litter was sampled, i.e., the northern, eastern,

the resulting water content was >20%, the sample was air

southern, and western parts of each survey plot (Fig. 2). At

dried, and the water content was measured again. These

each point, a soil profile of >30 cm depth was made andsteps were repeated until the water content was ≤20%.

then divided into three soil layers, 0–5, 5–15, and 15–30 cm

The C content was measured from a different portion of(Fig. 5). For each soil layer, the ratio of gravel area to thethe fine particles by the dry-combustion method usingarea of soil profile was recorded, and a volumetric sample

elemental analyzers. The C concentration was calculated

and also a sample for analyzing C concentration were taken.

using Formula 3, where W carbon (kg) is C content, W sample

For the volumetric samples, a 400-cm 3 cylindrical core(kg) is sample weight, and WC (%) is water content. The(height, 4 cm; area, 100 cm2) was sampled from a soil layer

C concentration was measured for more than two splits of

having low gravel content, whereas the soil sample wasfine particles, and the C concentration of a mixed sample

taken from a cuboid space (including gravels) in a soil layer

was determined by obtaining an intermediate value of two

having high gravel content (Fig. 5).

Table 4 Accuracy criteria for measuring carbon concentrations in litter and soil samples. The criteria
were applied to two repeated measurements,QWHUPHGLDWHYDOXH$FFXUDF\FULWHULD

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Bulletin of FFPRI, Vol.11, No.4, 2012

UGAWA, S. et al.

212

The volumetric samples were oven dried at 105°Cẁ⤌ᖜ
for 24 h and then weighed. The soil particles in a sample
were washed out through a sieve (2-mm mesh) using water.

D

The remaining gravels and plant roots were oven dried at
105°C for 24 h and weighed. Bulk density was calculatedusing Formula 5, where W t (g) is the total weight of thevolumetric sample, Wg (g) is the weight of gravels, Wr (g) is
the weight of plant roots, and V (cm3) is the spatial volumeof the volumetric sample, i.e., 400 cm 3 of cylindrical coreor the volume of a cuboid space that included gravel.
Bulk density (Mg m−3) =Wt–Wg–Wr[Formula 5]
V

The samples for analyzing C concentration were air
dried and sieved (2-mm mesh). The soil particles ≤2 mm indiameter were ground into fine particles (≤0.25 mm) usingE

an agate mortar. A split of the fine particles (2–3 g) was
put into a weighing bottle, and the bottle was weighed. The
weighing bottle then was oven dried at 105°C for 24 h andweighed again. Then, the water content of the fine particles
was determined using the same methods as described earlier(see Litter C Stock section). The C concentration of a soil
sample was also determined using the same methods as
described in Litter C Stock section.
The C stock of each soil layer was calculated using
Formula 6, where BD (Mg m −3 ) is bulk density, T (cm)is the thickness of the soil layer, CC (kg kg −1 ) is the C
concentration, G (%) is the ratio of gravel area to the areaof soil profile. The ratio of gravel area is taken as 0% forF

the soil layers from which we took the volumetric sample
from a cuboid space containing gravels to avoid double
counting of gravel content. Additionally, we considered
the soil C stock as 0 kg m −2 for a soil layer from which asoil profile could not be obtained due to bedrock or a large
boulder. The C stock of each soil layer was summed foreach sampling point, and the mean C stock across sampling
points was calculated to give the soil C stock at 0–30 cm ina survey plot. Sampling points containing a soil layer withmissing data, anomalous data, or outlier data were excluded
from the calculations (see Quality Control of Data section).
Soil C stock in each soil layer (kg m−2)

Fig. 5 Field survey for soil C stock. A soil profile of >30 cm
depth was made (a). For the volumetric sample, a 400cm 3 cylindrical core was sampled from a soil layer
having low gravel content (b), whereas the soil sample
was taken from a cuboid space in a soil layer having
high gravel content (c).

( 100)= BD×T×CC× 1– G ×10[Formula 6]

Soil C Stock at 0–100 cm
Soil C stock at 0–100 cm was surveyed in the
representative soil profile of >100 cm depth. A
representative soil profile was made at a point with

森林総合研究所研究報告 第 11 巻 4 号 , 2012

Carbon stocks of dead wood, litter, and soil in the forest sector of Japan:
general description of the National Forest Soil Carbon Inventory

213

significant microtopography and vegetation cover after anbulk density of sandy loam compacted by heavy traffic, i.e.,observation of the survey plot. For the representative soil

1.9 Mg m−3, is considered extreme in the forestry field (Lalsurvey, a soil profile was divided into generic soil horizons

2002). According to Soil Survey Staff (1999), mineral soil

(e.g., A1, A2, B1, B2, and C horizons). The thickness ofcontains <20% organic carbon. However, in this study, aeach soil horizon and the ratio of gravel area to the areasoil C concentration >0.25 kg kg−1 is considered anomalousof the soil profile were obtained. A volumetric sample andbecause a C concentration of >0.2 kg kg−1 is often observeda sample for analyzing C concentration were taken fromin Andosols, which are distributed widely in the forest land

each soil horizon and bulk density, and C concentrations ofof Japan.

these samples were determined using the same methods as
described earlier (see Soil C Stock at 0–30 cm section).

For soil samples at 0–30 cm, outlier data were
determined statistically. Outlier values of bulk density

The C stock of each soil horizon was calculated using

were detected among the values in a survey plot using

the same methods as described in the Soil C Stock at 0–30

the Smirnov–Grubbs outlier test (upper-tail probability

cm section and these were then summed to give the soil

≤0.005) and taken as outlier data of bulk density. Outlier

C stock of a representative soil profile. Representativevalues of C concentration among the values in a survey plot

soil profiles containing a soil horizon with missing or

were also detected with the Smirnov–Grubbs test (upper-

anomalous data were excluded from the calculation (seetail probability ≤0.005), and outlier values in soil layers

Quality Control of Data section).

of 5–15 cm and 15–30 cm are considered outlier data of C
concentration because the soil layer at 0–5 cm is frequently
disturbed, and the C concentration varies largely.

Quality Control of Data
Criteria have been established to detect anomalous data
for C concentration of a litter sample, bulk density, and C

Results

concentration of a soil sample at 0–30 cm and at 0–100 cm.

㡫ᖜlitter, and soil at 0–30
Carbon stock of dead wood,

Criteria have also been established to detect outlier data forcm were determined in 2438, 2432, and 2404 survey plots,

bulk density and C concentration of a soil sample at 0–30

respectively. The C stock could not be surveyed in 457

cm and at 0–100 cm.

survey plots (Table 5), and the C stock of dead wood, litter,

The C concentration of a litter sample is considered−1

and soil at 0–30 cm could not be calculated in 24, 30 and 58

because organic

survey plots, respectively, due to missing, anomalous, andmaterial is defined as having a C concentration ≥0.2 kg

outlier data. The C stock (mean ± sample standard deviation)

anomalous if the value is <0.2 kg kg
kg−1(Soil Survey Staff 1999). For soil samples, a bulk

density >2.0 Mg m −3 is considered anomalous because afor dead wood, litter, and soil at 0–30 cm was 0.42 ± 0.67,
0.49 ± 0.32, and 6.94 ± 3.25 kg m−2, respectively (Table 6).

Table 5 Reasons for failure to complete survey and the breakdown in the number of plots. The number of plots
included in soil survey at 0-100 cm is shown in parentheses

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Bulletin of FFPRI, Vol.11, No.4, 2012

UGAWA, S. et al.

214

Table 6 Carbon stocks of dead wood, litter, and soil at 0-30 cm and 0-100 cm&DUERQSRRO

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The C stocks of dead wood, litter, and soil at 0–30 cm± 8.38 kg m −2 (mean ± sample standard deviation) acrossin each prefecture (and each district) are shown in Table

the 676 survey plots (Table 6). The ratio of soil C stock

7. These C stocks are classified into four groups: <25that 0–30 cm to that at 0–100 cm could be calculated in 667

percentile; ≥25th percentile and < median; ≥ median andsurvey plots and was 0.59 ± 0.31 (mean ± sample standard<75th percentile; and ≥75th percentile, as shown in Fig. 6.

deviation).

The C stock for dead wood in each prefecture ranged from0.08 kg m −2 of Kagawa Prefecture to 0.66 kg m −2 of Akita
Prefecture. Dead wood C stock was high in the Hokkaido

Discussion
Dead Wood C Stock

District, the central highland of the Chubu District, and

The mean dead wood C stock, 0.42 kg m −2 (Table 6),

the northern part of the Kinki District, but dead wood C

was within the mean values of forests dominated by thestock was low in the eastern part of the Tohoku District, themajor tree species of Japan, 0.42–2.47 kg m −2 (Takahashi

Hokuriku area of the Chubu District, and the Shikoku andet al. 2010). The mean C stock of dead wood ≥10 cm in

Kyushu Districts. The C stocks for litter in each prefecture

diameter was estimated to be 0.69 kg m −2 in Asia (FAO

ranged from 0.25 kg m −2 of Kanagawa and Okinawa

2006). This value would be higher if dead wood ≥5 cm inPrefectures to 0.63 kg m −2 of Wakayama Prefecture. Litter

diameter were included. We therefore suggest that deadC stock was high in the Hokkaido District, the central

wood C stock in the forest sector of Japan ranks low inhighland of the Chubu District, the southern part of theAsia.

Kinki District and the Chugoku District, but low in the

Dead wood C stock is higher in regions with higher

southern part of the Kanto District, the Hokuriku area of thealtitude or higher latitude because of lower temperature

Chubu District, and the Kyushu District. The C stock for(Woodall et al. 2008). In this study, high C stock was−2

observed in some regions with low temperature, includingof Kagawa Prefecture to 9.16 kg m−2 of Ibaraki Prefecture.

the Hokkaido District and the central highland of Chubu

High C stock was observed in the Hokkaido, Tohoku, andDistrict; low C stock was observed in regions with

Kanto Districts, whereas low values were observed in thehigh temperature, including the Shikoku and Kyushu

Kinki, and Shikoku Districts. Soil C stock was also highDistricts (Fig. 6 and Table 7). However, some exceptionalin some prefectures located in the volcanic regions of thecircumstances were observed. These include low C stock

Chugoku and Kyushu Districts, such as Tottori, Shimane,in the eastern part of the Tohoku District and the Hokuriku

Nagasaki, Oita, and Kagoshima Prefectures.

area of the Chubu District and high C stock in the northernsoil at 0–30 cm in each prefecture ranged from 2.95 kg m

Soil C stock at 0–100 cm was determined in 676 survey

part of the Kinki District. Additionally, the dead woodplots. The soil C stock at 0–100 cm could not be surveyed

C stock was not related to annual mean temperature andin 156 survey plots (Table 5) and could not be calculated

annual precipitation in the prefectures (Fig. 7; p = 0.069

in 160 survey plots due to missing and anomalous data.

and p = 0.893, respectively) when the data in Table 7 were

The representative soil profile did not reach 100 cm in 136

analyzed using the Spearman rank correlation coefficient.

survey plots due to bedrock or a large boulder. The digging

Dead wood occurs not only by natural disturbance but also

depth in these plots was 62 ± 22 cm (mean ± sample

by forest management (e.g., Fridman and Walheim 2000,

standard deviation). The soil C stock at 0–100 cm was 14.29

Siitonen 2000, Gibb et al. 2005, Lombardi et al. 2008).

森林総合研究所研究報告 第 11 巻 4 号 , 2012㡫ᖜ

Carbon stocks of dead wood, litter, and soil in the forest sector of Japan:
general description of the National Forest Soil Carbon Inventory

215

Table 7 Climate condition and carbon stocks (kg m-2) of dead wood, litter, and soil at 0-30 cm in each prefecture'LVWULFW

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216

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森林総合研究所研究報告 第 11 巻 4 号 , 2012

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Carbon stocks of dead wood, litter, and soil in the forest sector of Japan:
general description of the National Forest Soil Carbon Inventory

217

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Fig. 7 Carbon stocks of dead wood, litter, and soil at 0–30 cm in each prefecture with annual mean
temperature and annual precipitation of the forest sector. The annual mean temperature and annual
precipitation are the mean values for 1971–2000, which were calculated using data from Japan
Meteorological Agency (2002). The C stocks of litter and soil at 0–30 cm decreased with increasing
annual mean temperature (Spearman rank-correlation coefficient: p = 0.004 and p < 0.001,
respectively).

The amount of dead wood also varies among stands with

Litter is decomposed easily in regions with highdifferent dominant tree species (Takahashi et al. 2010).

temperature but is decomposed with difficulty in regions

Thus, we speculate that the dead wood C stock is influenced

with low temperature (Coûteaux et al. 1995, Aerts 1997,

by microscale factors such as tree community structure andTrofymow et al. 2002). This pattern is consistent with

forest management rather than by macroscale factors suchthe high C stock in the Hokkaido District and the central

as temperature.

highland of the Chubu District and also with low C stockin the Kyushu District (Fig. 6 and Table 7). Moreover, thelitter C stock was lower in prefectures with a higher annual

Litter C Stock−2(Table 6), wasmean temperature (Fig. 7; p = 0.004). These results imply

within the mean values of forests dominated by the majorthat the litter C stock is influenced to some extent by a

The mean litter C stock, 0.49 kg m
−2

(Takahashi et al.

macroscale factor, i.e., temperature. On the other hand,2010). The mean litter C stock was estimated to be 0.29 kg

some exceptional instances were noted. These include

tree species of Japan, 0.42–1.15 kg m
−2

m in Asia (FAO 2006). We therefore suggest that the litter

low C stock in the southern part of the Kanto District

C stock in the forest sector of Japan ranks high in Asia.

and the Hokuriku area of the Chubu District and high C

Bulletin of FFPRI, Vol.11, No.4, 2012

UGAWA, S. et al.

218

stock in the southern part of the Kinki District and theyears (Machida and Arai 2003). Soil derived from volcanic

Chugoku District. Litter C stock varies among dominantash (i.e., Andosols) is known to accumulate large amounts

tree species (Takahashi et al. 2010). The exceptionalof organic C (Shoji et al. 1993, Morisada et al. 2004). This

results in the spatial distribution of litter C stock may

indicates that the exceptional instance of high C stock can

be caused by microscale factors such as tree community

be explained by the existence of volcanic ash soils.

structure (Takahashi et al. 2010). Further study is needed todetermine these microscale factors precisely.

Ratio of Soil C Stock at 0–30 cm to Soil C Stock at 0–100 cm
The mean soil C stock at 0–100 cm, 14.29 kg m−2 (Table

Soil C Stock at 0–30 cm

6), was lower than the value of 18.8 kg m −2 reported by

The mean soil C stock at 0–30 cm, 6.94 kg m−2 (Table

Morisada et al. (2004), and the mean ratio of soil C stock6), was lower than the value of 9.0 kg m −2 estimated by

at 0–30 cm to that at 0–100 cm, 0.59, was higher than 0.48,

Morisada et al. (2004), who compiled soil profile data

the value estimated by Morisada et al. (2004). However, as

collected from 1950s to 1970s in national forest soil survey

discussed in an earlier section (Soil C Stock at 0–30 cm),

projects. In previous studies, the soil survey point was

the survey methods may explain the difference in the soilchosen by surveyors as a representative soil profile in

C stock at 0–100 cm and in the ratio of soil C stock at 0–30

which genetic soil horizons were typical in the survey plot

cm to that at 0–100 cm between the result in this study(Government Forest Experiment Station 1955). Thus, well-and that reported by Morisada et al. (2004). On the otherdeveloped soils with high C stock may have been selected

hand, the mean ratio of soil C stock at 0–30 cm to that at

in the soil survey, resulting in a higher mean value for soil

0–100 cm was estimated to be 0.52 in Cambisols and 0.44

C stock in previous studies than in our study. Additionally,in Andosols worldwide (Batjes 1996), and these two soil

the methods used to measure gravel content, soil mass, andtypes are distributed dominantly in the forest land of JapanC concentration are different between the previous work

(Morisada et al. 2004). Therefore, the ratio of soil C stockand our study. Therefore, it is not necessarily appropriate

at 0–30 cm to that at 0–100 cm in the forest sector of Japanto suggest that the difference in soil C stock reflects theis higher than the world average, that is, the C stock of soil

passage of time. Careful discussion is needed to interpret

at 0–30 cm accounts for a larger portion of that at 0–100

the difference in soil C stock.

cm compared with ratios worldwide. Jobbágy and Jackson

We suggest that the soil C stock at 0–30 cm in the(2000) reported that the ratio of soil C stock at 0–20 cm

forest sector of Japan ranks slightly high in Asia because

to that at 0–100 cm increased with increasing annual

the mean soil C stock at 0–30 cm was estimated to beprecipitation. The high ratio of soil C stock at 0–30 cm may

6.61 kg m −2 in Asia (FAO 2006). Soil C stock at 0–30

reflect the monsoon climate and high humidity of Japancm tends to be higher in regions with higher altitude or(Kottek et al. 2006).

higher latitude because of the lower temperature (e.g.,
Batjes 2002, Liski et al. 2002). The results of this study

Organic Soilare generally consistent with this pattern. Soil C stock at

I n t h i s s t u d y, w e e x c l u d e d a s o i l l a y e r w i t h C

0–30 cm was high in northern Japan, i.e., in the Hokkaido,

concentration >0.25 kg kg −1 from the calculations of soil

Tohoku, and Kanto Districts, and low in southern Japan,

C stock due to anomalous data resulting from a mistakei.e., in the Kinki and Shikoku Districts (Fig. 6 and Table 7).

in the field survey. However, according to the criteria,

This tendency was also supported by the lower soil C stocksome organic soils were probably excluded from ourin the prefectures with higher annual mean temperature

count, which may have decreased the mean soil C stock(Fig. 7; p < 0.001). Thus, we suggest that the soil C stock

at 0–30cm. Organic soils are not common in the forest

is regulated by a macroscale factor, i.e., temperature.

sector of Japan: the soil C stock of the Peaty Soil Group

Exceptions to this pattern included high C stock observed(Forest Soil Division 1976), corresponding to Histosols,in Tottori and Shimane Prefectures of the Chugoku District,

was estimated to be 13 Tg at 0–30 cm depth and occupied

and Nagasaki, Oita, and Kagoshima Prefectures of thejust 0.6% of total C stock in the forest sector. On the other

Kyushu District. Active volcanoes (i.e., Mt. Daisen, Mt.

hand, Histosols are a major global soil type; the total extent

Sanbesan, Mt. Unzendake, Mt. Sakurajima, and Mt. Aso)of Histosols is estimated to be 325–375 million ha, and they

are located in Tottori, Shimane, Nagasaki, and Kagoshima

are mainly observed in the boreal, subarctic, and low arctic

Prefectures, and at the southwest border of Oita Prefecture,regions of the northern hemisphere (IUSS Working Group

respectively, and have supplied volcanic ash in the last 20

WRB 2006). We therefore need to identify organic soils

森林総合研究所研究報告 第 11 巻 4 号 , 2012

Carbon stocks of dead wood, litter, and soil in the forest sector of Japan:
general description of the National Forest Soil Carbon Inventory

219

using a description of the soil profile and evaluate the C

Forestry Agency of Japan (2007) Implementation report of thestock of organic soils in the forest sector of Japan in future

National Forest Carbon Inventory in FY2007. Forestry

studies.

Agency of Japan, Tokyo, 39–59. (In Japanese)
Forestry Agency of Japan (2012) "Forest Resources
Monitoring Survey in 1999–2008", http://www.rinya.

Conclusion
In this study, we found that the C stock of dead wood,
litter, and soil in the forest sector of Japan was 0.42 ± 0.67,−2

maff.go.jp/j/keikaku/monitar/index.html, (accessed 201203-07).

0.49 ± 0.32, and 6.94 ± 3.25 kg m , respectively. For dead

Forest Soil Division (1976) Classification of forest soil inwood and litter, this study detected no latitudinal tendency

Japan. Bull. Gov. For. Exp. Sta., 280, 1–28. (In Japanesein the distribution of C stocks throughout Japan. However,with English summary)soil C stock at 0–30 cm was generally higher in northern

Fridman, J. and Walheim, M. (2000) Amount, structure,

Japan and lower in southern Japan. This is supported by theand dynamics of dead wood on managed forestland inlower soil C stock in prefectures with a higher annual mean

Sweden. For. Ecol. Manag., 131, 23–36.

temperature. On the other hand, high C stock was observed

Governmental Forest Experiment Station (1955) The manualin some prefectures of the volcanic region of southern

for forest soil survey in the national forest. Governmental

Japan. We thus suggest that the soil C stock is regulated

Forest Experiment Station of Japan Forest Agency,

by macroscale factors, i.e., temperature, as well as by the

Tokyo, 47 pp. (In Japanese)

distribution of volcanic ash soils. Additionally, our results

Gibb, H., Ball, J. P., Johansson, T., Atlegrim, O., Hjältén, J.

indicate that the soil C stock at 0–30 cm in the forest sector

and Danell, K. (2005) Effects of management on coarseof Japan accounts for a larger portion of that at 0–100 cm

woody debris volume and composition in boreal forests

compared with forest soils around the world.

in northern Sweden. Scand. J. For. Res., 20, 213–222.
Imaya, A., Yoshinaga, S., Inagaki, Y., Tanaka, N. and Ohta, S.

Acknowledgements(2010a) Proposal for advanced classification of brown

We are grateful to researchers of the prefectural forest

forest soils in Japan with reference to the degree of

research institutes for collecting field data and samples.

volcanic ash additions. Soil Sci. Plant Nutr., 56, 454–

We also thank the members of the Department of Forest

465.

Site Environment and the Bureau of Climate Change

Imaya, A., Yoshinaga, S., Inagaki, Y., Tanaka, N. and Ohta,of the Forestry and Forest Product Research InstituteS. (2010b) Volcanic ash additions control soil carbon

for supporting this study. This study was a result of theaccumulation in brown forest soils in Japan. Soil Sci.

National Forest Soil Carbon Inventory managed by the

Plant Nutr., 56, 734–744.

Forestry Agency of Japan.

IPCC (2006) 2006 IPCC Guidelines for National Greenhouse
Gas Inventories. The Institute for Global Environmental

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221

日本の森林における枯死木、堆積有機物、土壌の炭素蓄積量：
森林土壌インベントリの第 1 報
鵜川 信 1)*、高橋 正通 2)、森貞 和仁 3)、竹内 学 4)、松浦 陽次郎 5)、吉永 秀一郎 6)、
荒木 誠 1)、田中 永晴 1)、池田 重人 1)、三浦 覚 1)、石塚 成宏 6)、小林 政広 1)、
稲垣 昌宏 6)、今矢 明宏 1)、南光 一樹 1)、橋本 昌司 1)、相澤 州平 3)、平井 敬三 7)、
岡本 透 8)、溝口 岳男 9)、鳥居 厚志 9)、酒井 寿夫 10)、大貫 靖浩 1)、金子 真司 1)
要旨
本研究では、日本の森林における枯死木、堆積有機物および土壌（深さ 0–30 cm）の炭素蓄積量を明らかにすること、 炭素蓄積量の空間分布を都道府県単位で示すこと、 深さ 0–100 cm の土壌炭素蓄積量に占める深さ 0–30 cm の土壌炭素蓄積量の割合を示すことを目的とした。これらの目的を達成するため、 2006–2010 年度に実施した林野庁森林吸収源インベントリ情報整備事業 ( 日本全国の森林における枯死木、 堆積有機物および土壌の炭素蓄積量調査 ) のデータを解析した。 枯死木、堆積有機物および土壌（深さ 0–30 cm）の炭素蓄積量（平均 ± 標本標準偏差）は、それぞれ 0.42 ±0.67、0.49 ± 0.32、6.94 ± 3.25 kg m-2 であった。各都道府県の枯死木および堆積有機物の炭素蓄積量は、
緯度方向の分布傾向を示さなかった。しかしながら、統計解析では、年平均気温が高い都道府県ほど堆積有機物炭素蓄積量が低くなる傾向が検出された。土壌炭素蓄積量は、北日本で高く、南西日
本で低くなる傾向がみられ、年平均気温が高い都道府県ほど土壌炭素蓄積量が低くなることが確認された。他方、火山帯に位置する南西日本の都道府県で土壌炭素蓄積量が高くなる傾向がみられた。
このことから、深さ 0–30 cm の土壌炭素蓄積量は、気温のみならず、火山灰の分布によっても規定されることが窺われた。加えて、深さ 0–100 cm の土壌炭素蓄積量は 14.29 ± 8.38 kg m-2 （平均 ± 標
本標準偏差）であり、これに占める深さ 0–30 cm の土壌炭素蓄積量の割合は 0.59 ± 0.31 （平均 ± 標
本標準偏差）であった。この割合は、世界の平均値よりも高かった。
キーワード：炭素蓄積量、枯死木、堆積有機物、土壌、インベントリ、システマティックサンプリ
ング、京都議定書

1) 森 林 総 合 研 究 所 立 地 環 境 研 究 領 域
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茨 城 県 つ く ば 市 松 の 里 1 e-mail: ushin@ffpri.affrc.go.jp