carbon stock in litter, deadwood and soil in japan’s forest sector and its comparison with carbon...

REVIEW

Carbon stock in litter, deadwood and soil in Japan’s forest sectorand its comparison with carbon stock in agricultural soils

Masamichi TAKAHASHI, Shigehiro ISHIZUKA, Shin UGAWA, Yoshimi SAKAI,Hisao SAKAI, Kenji ONO, Shoji HASHIMOTO, Yojiro MATSUURAand Kazuhito MORISADAForestry and Forest Products Research Institute, Ibaraki 305-8687, Japan

Abstract

Estimation of carbon sequestration in the forest sector should take into consideration changes in carbon stock in

all carbon pools, including above-ground and below-ground biomass, litter, deadwood and soil. In this review,

we discuss current knowledge of carbon stocks in litter, deadwood and soil in Japan’s forest sector. According

to data from published reports and nationwide surveys, the carbon stock in forest litter is less than that indicated

in the Intergovernmental Panel on Climate Change (IPCC) guidelines for temperate and cool temperate forests;

for example, coniferous species showed 4.4 Mg C ha)1 for Cryptomeria japonica and 3.1 Mg C ha)1 for Cha-

maecyparis obtusa, and broad-leaved species ranged from 3.5 Mg C ha)1 for Castanopsis spp. to

7.3 Mg C ha)1 for Fagus spp. For deadwood carbon stock, coniferous plantations with a record of non-com-

mercial thinning showed 17.1 Mg C ha)1 and semi-natural broad-leaved forests showed 5.3 Mg C ha)1 on

average, although only limited data were available. The black soil group (comparable to Andosols and Andisols)

showed large carbon stocks in soil layers 0–30 cm deep (130 Mg C ha)1). The brown forest soil group (Cambi-

sols and Inceptisols), occupying the most dominant area, showed a carbon stock of 87.0 Mg C ha)1 on average,

which was similar to the data shown in the IPCC guidelines. In a comparison of land use between the forest sec-

tor and the agricultural sector for the same soil group, the carbon stock in the agricultural soil was 21% lower

and in the grassland soil it was 18% higher than the stock in the forest soil. In this review, we also discuss issues

for improving the estimation method and inventory of carbon stock in litter, deadwood and soil in Japan.

Key words: cropland soil, dead organic matter, emission factor, forest soil, grassland soil.

INTRODUCTION

Global warming is a major concern in both the Japanese

domestic and international arena. According to the Inter-

governmental Panel on Climate Change (IPCC) Fourth

Assessment Report (IPCC 2007), continuous greenhouse

gas emissions at or above the current rates will cause fur-

ther warming and induce serious changes in the global

climate system in the 21st century. Although improved

sequestration of carbon dioxide is expected through inno-

vative engineering technology (e.g. Matysek et al. 2005),

forests play an important role as a cost-effective carbon

sink that absorbs carbon dioxide (Lal 2005; Stern 2007).

Soil is the largest carbon pool in the terrestrial ecosys-

tem. Global carbon storage in soil is estimated to be

1500–2000 Gt C, which is three–fourfold greater than

that in vegetation (Batjes 1996; Watson et al. 2000). In

forest ecosystems, dead organic matter, such as litter and

deadwood, forms specific carbon pools. Although there is

no doubt that growing trees function as an active carbon

sink, large emissions from dead organic matter and soil

would count as a reduction in the amount of sequestrated

carbon in the forest (Randerson et al. 2002). Thus, the

National Inventory Report and the Kyoto Protocol report

under the United Nations Framework Convention on Cli-

mate Change (UNFCCC) require that parties estimate the

carbon stock not only in above-ground and below-ground

biomass, but also in deadwood, litter and soil, separately.

Dead organic matter and soil carbon stock are influ-

enced by vegetation, site conditions and forest manage-

ment practices. For example, leaf litter from coniferous

species usually decomposes more slowly to accumulate

Correspondence: M. TAKAHASHI, Forestry and Forest ProductsResearch Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687,Japan. Email: [email protected]

Received 22 June 2009.Accepted for publication 2 October 2009.

� 2010 Japanese Society of Soil Science and Plant Nutrition

Soil Science and Plant Nutrition (2010) 56, 19–30 doi: 10.1111/j.1747-0765.2009.00425.x

thicker organic layers than broad-leaved species towing to

the higher lignin content (Berg and McClaugherty 2003;

IPCC 2006). Mesic and productive sites have thin organic

layers, referred to as mull-type humus, in temperate and

cool temperate forests (Green et al. 1993; Uchida 1959).

Deadwood stock is also influenced by forest type; old-

growth forests usually show large carbon stock in decay-

ing boles (Harmon and Hua 1991; Takahashi et al.

2000). Natural and anthropogenic disturbances, such as

typhoons and non-commercial thinning operations, result

in an immediate increase in deadwood stock (Harmon

et al. 1986). Regarding soil carbon, soil type and soil tex-

ture are the decisive factors for carbon stock level (IPCC

2003; Parton et al. 1994). Andosols, particularly those

with thick, fine-textured A horizons, sequestrate large

amounts of carbon in the soil (Morisada et al. 2004; Shoji

et al. 1993). Wide Andosol distribution is a unique char-

acteristic of the soil cover in Japan.

Related to the effects of human activity in terrestrial

ecosystems, land-use category is a key factor for determin-

ing the equilibrium level of carbon stock in the soil (Paul

et al. 2002; Post and Kwon 2000). In general, forests and

grasslands show high soil carbon stock as a result of the

high input of dead organic matter from the vegetation.

The conversion of forest land to agricultural land usually

reduces the soil carbon stock and this has been a major

source of carbon dioxide (CO2) emission throughout

human history (Houghton 2003), although the applica-

tion of organic manure and no-till farming maintain or

enhance the soil carbon level (Lal 2004). Thus, we need to

understand the steady-state carbon level in the land-use

categories for each soil type.

Since 2007, the Japanese government has submitted an

annual National Inventory Report (NIR) and Kyoto Pro-

tocol (KP) report to the UNFCCC secretariat (Ministry of

the Environment, Japan 2008). The accounting methods

for estimating the emission and removal (absorption or

uptake) of greenhouse gases (GHG) in Japan’s forest sec-

tor can be referenced in previous reports (Fang et al.

2005; Matsumoto et al. 2007). In the present paper, we

review the characteristics of litter, deadwood and soil car-

bon stock in the forest sector using data from the NIR and

KP reports (Ministry of the Environment, Japan 2008)

and data from other sources (e.g. Morisada et al. 2004;

Takahashi 1995). Among the GHG, we focus on CO2

emission and removal in the present review; non-CO2

gases, such as methane and nitrous oxides, have been

reported elsewhere (Ishizuka et al. 2009; Morishita et al.

2007). To understand the effect of changing land use on

the carbon balance in ecosystems, a comparison of soil

carbon stock is made between agricultural land and forest

land. We also discuss methods for improving the estima-

tion of carbon stock in dead organic matter and soil in the

forest sector.

LAND-USE CATEGORIES

Intergovernmental Panel on Climate Changeguidelines and reporting format

Annex I Parties of the UNFCCC are required to submit

information on their national inventory of carbon emis-

sion and removal every year using the common reporting

format provided by the UNFCCC office. To assist this

process, the IPCC has prepared several guidelines: the

Revised 1996 IPCC Guidelines for National Greenhouse

Gas Inventories for Land Use, Land-Use Change and For-

estry (IPCC 1996), the Good Practice Guidance for Land

Use, Land-Use Change and Forestry (IPCC 2003) and the

2006 IPCC Guidelines for National Greenhouse Gas

Inventories for Agriculture, Forestry and Other Land Use

(IPCC 2006). Using these guidelines, most parties can cal-

Table 1 Land-use categories, their definitions and a comparison of areas and area percentages between 1990 and 2005 in Japan

Land-use

categories Contents of land use

Area (kha)

in 1990

(%)†

Area (kha)

in 2005

(%)†

Forest land Forests under Forest Law Articles 5 and 7.2 24,950 (66.1) 24,992 (66.1)

Cropland Rice fields, crop fields and orchards 4,596 (12.2) 4,061 (10.7)

Grassland Pasture land and grazed meadow land 660 (1.7) 638 (1.7)

Wetland Bodies of water (such as dams), rivers and waterways 1,320 (3.5) 1,340 (3.5)

Settlement Urban areas that do not constitute forest land, cropland,

grassland or wetlands

Urban green areas that are all wooded and planted areas

that do not constitute forest land

2,750 (7.3) 3,170 (8.4)

Other land Any land that does not belong to the above land-use categories 3,493 (9.2) 3,588 (9.5)

Total 37,769 (100) 37,789 (100)

†Percentage of area in total for Japanese land is shown in parentheses. Definitions and area data are cited from the National Inventory Report (Ministry ofthe Environment, Japan 2008).


20 M. Takahashi et al.

culate CO2 emission and removal in agriculture, forestry

and other land-use sectors if they at least have data on the

areas of the land-use categories (see below). In this review,

the CO2 accounting methods are not explained, but the

referenced IPCC guidelines can be downloaded from the

UNFCCC website (http://unfccc.int/; June 2009).

Land-use categories and changes

All land in Japan is classified into six land-use categories

(Forest Land, Cropland, Grassland, Wetland, Settlement

and Other Land; Table 1) (IPCC 2006), and the emission

and uptake of CO2 are calculated for each land-use cate-

gory. These categories are further subdivided into land

remaining in the same category and land converted from

one category to another (Table 2). As the conversion of

land-use often leads to high emissions of CO2, particu-

larly, for example, in forest clearing for agricultural use

(Guo and Gifford 2002; Houghton 2003; Murty et al.

2002), estimating the area of land-use change is the first

step in the accounting procedure for CO2 emission and

uptake (IPCC 2006).

As a definition of land-use categories is not provided by

the IPCC guidelines, parties need to establish their own

definition (IPCC 2006). This may cause some discrepancy

in reported estimates among parties, but it is a practical

solution for implementing the UNFCCC process. In

Japan, forest land is defined by the following criteria: min-

imum area 0.3 ha, minimum tree crown cover 30%, mini-

mum tree height 5 m and minimum width of forest land

20 m (Ministry of the Environment, Japan 2008). The

area fulfilling these criteria covers 24,992 kha, which is

66.1% of Japan’s total land area (Table 1). Following for-

est land is cropland, covering 10.7% in 2005. The large

forest cover over Japanese land means that the forests are

expected to function as a national carbon sink. As conver-

sion of land use has not been active in modern Japan, the

proportion of land-use change was very small between

1990 and 2005, although land-use changes occurred

between most land-use categories (Table 2). In fact, it has

been reported that significant land-use change has not

occurred in more than 100 years (Himiyama 1995). These

data suggest that the emission and uptake of CO2 under

afforestation, reforestation and deforestation (ARD)

activities set out in Article 3.3 of the KP as significant

causes of change in soil carbon stock (Watson et al.2000), do not become weighty values in Japan com-

pared with newly industrializing and developing

countries.

DEAD ORGANIC MATTER AND SOILCARBON STOCK

Definition of litter, deadwood and soil

Dead organic matter is composed of litter and dead-

wood. Although the IPCC guidelines imply that litter is

organic layers on the mineral soil surface, the term ‘‘lit-

ter’’ is equivocal in soil science because it is restricted to

freshly fallen dead leaves (Wild 1971). Soil science con-

ventionally describes decomposing dead leaves as humus

(organic) layers, for example, an A0 layer consisting of

L, F and H layers (Forest Soil Division 1976) or an O

layer consisting of Oi, Oe and Oa layers (Soil Survey

Staff 2006). There is no analytical definition for these

layers and the boundary between ‘‘litter’’ and mineral

soil can sometimes be ambiguous in the field, particularly

when the site has an H (Oa) layer, even though the

carbon content usually exceeds 20% of the weight (IUSS

Working Group WRB 2006; Takahashi 1998). In

Japan’s forest sector, ‘‘litter’’ includes the L, F and H

layers on the mineral soil.

Deadwood, often referred to as coarse woody debris

(CWD) (Harmon et al. 1986), is defined as non-living

woody biomass and includes dead boles, stumps and

snags. In Japan, the minimum size of deadwood is defined

as 5 cm in diameter, which is smaller than the criteria

(10 cm) indicated in the IPCC guidelines (IPCC 1996,

2003, 2006), because non-commercial thinning fall

stunted trees which are usually smaller than 10 cm in

diameter in Japan’s forest plantation (Sakai et al. 2008).

Table 2 Matrix of land-use change areas between 1990 and 1991

1991

Forest land Cropland Grassland Wetland Settlement Other land

1990

Forest land 23,632 167 51 57 375 69

Cropland 102 4,118 62 18 928 404

Grassland 17 10 289 3 111 67

Wetland IE 9 2 1,241 IE IE

Settlement IE IE IE 1 1,367 IE

Other land 1,188 251 258 0 IE 2,981

IE, included elsewhere in the inventory instead of the expected category (Ministry of the Environment, Japan 2008).


Soil and dead organic carbon stock in Japan 21

In Japan, carbon stock in the soil is defined as the

organic carbon in the mineral soil from a depth of 0 to

30 cm. The stipulated thickness of the soil is rather shal-

low if we consider that a large carbon stock exists in deep

soil layers (Batjes 1996); however, this value is in accor-

dance with the IPCC guidelines. In addition, a uniform

thickness among all land-use categories is indispensable

for calculating soil carbon in the case of land-use change.

In Japan’s forest sector, organic soil, such as peat, is not

an important pool for carbon storage because peat soil

exists in only 0.3% of the forest sector (Morisada et al.

2004).

Carbon stock in litter

The dry weight of litter in Japan’s forests has been com-

piled from various published and unpublished reports

(Ono et al. 2001; Takahashi 1995). In cases where data

on the carbon content of the litter were not available, a

conversion equation was applied to obtain the carbon

content from the dry weight (Takahashi 2005). Statistics

on the major tree species are shown in Table 3. According

to the IPCC guidelines (IPCC 2003, 2006), coniferous spe-

cies have a carbon stock of 22 Mg C ha)1 and broad-

leaved species have a carbon stock of 13 Mg C ha)1 on

average in warm temperate moist climates. However,

most Japanese tree species, including conifers, have litter

pools with a low carbon stock of less than 10 Mg C ha)1.

The widely planted coniferous species Cryptomeria japon-

ica (Japanese cedar, Sugi) and Chamaecyparis obtusa

(Japanese cypress, Hinoki) show quite low litter stocks of

4.35 and 3.11 Mg C ha)1, respectively. As C. japonica

plantations are selected from among sites with moist and

fertile soils (Hirai et al. 2006; Mashimo 1960), litter

decomposition would be quick. For C. obtusa, fragments

of decomposing litter are easily eroded on slopes (Miura

2000) or incorporated into mineral soil (Sakai et al. 1987;

Tsukamoto 1991). Moreover, C. obtusa and C. japonica

are planted in warm temperate areas and not in cool tem-

perate zones, such as Hokkaido Island and high subalpine

mountains. These environmental conditions and species

characteristics of the litter appear to result in the accumu-

lation of a small amount of litter in Japanese coniferous

plantations. In cool temperate zones, however, coniferous

species, including both natural and planted stands, show a

larger carbon stock, 9.49 Mg C ha)1 for Abies and

11.53 Mg C ha)1 for Picea spp.

Carbon stock variations in broad-leaved species are also

influenced by climatic conditions. Evergreen broad-leaved

species such as Castanopsis spp., distributed in warmer

climate areas, have lower carbon stock (5.11 Mg C ha)1),

whereas deciduous species show relatively larger stock,

particularly for Fagus spp. (10.0 Mg C ha)1) and Betula

spp. (9.0 Mg C ha)1), in cool climates. The low carbon

stock in the litter appears to be reflected in the quick litter

decomposition rate, probably because of the warm and

humid climatic conditions in Japan (Takeda et al. 1987).

Carbon stock in deadwood

Deadwood dynamics are closely related to forest manage-

ment, such as thinning and harvesting operations. After

pre-commercial and non-commercial thinning, living trees

immediately change to deadwood and litter. Similarly,

tree harvesting produces deadwood as stumps and slashes.

According to the root ⁄ shoot ratio (R), which is also called

the below-ground ⁄ above-ground biomass ratio (IPCC

2006), 1 ⁄ 4 to 1 ⁄ 3 of the total living biomass turns to

deadwood after harvesting. This is the largest event creat-

ing deadwood carbon in plantation forestry.

The Forestry Agency of Japan conducted a survey on

the amount of deadwood carbon stock in plantations with

a record of non-commercial thinning (Sakai et al. 2008;

Takahashi and Sakai 2006). Plantations that had been

Table 3 Statistics on carbon stock in litter of major tree species (Mg C ha)1)

Tree species n Range Mean SD Median

Cryptomeria japonica 634 0.49–47.1 5.15 3.84 4.35

Chamaecyparis obtusa 281 0.32–55.4 5.25 6.39 3.11

Larix kaempferi 188 0.13–23.5 6.74 4.45 5.62

Pinus spp. 127 0.67–62.6 7.84 7.01 6.23

Abies spp. 147 0.86–30.0 9.49 6.10 8.24

Picea spp. 24 1.59–35.2 11.53 8.35 8.55

Quercus spp. 70 1.57–18.0 6.74 3.80 6.15

Castanopsis spp. 23 1.24–12.5 4.21 2.33 3.49

Fagus spp. 47 1.96–37.8 10.00 8.14 7.28

Alnus spp. 11 2.39–20.8 6.05 4.94 4.15

Betula spp. 22 0.32–71.5 9.00 15.15 3.60

Deciduous broad-leaved 184 0.32–71.5 7.50 7.67 5.27

Evergreen broad-leaved 55 1.24–18.9 5.11 3.69 4.00

Data were compiled from Takahashi (1995) and from an acid rain monitoring project by the Forestry Agency of Japan. In cases where the carbon contentwas not analyzed, the carbon stock was calculated from its dry weight using a conversion equation (Takahashi 2005). SD, standard deviation.



thinned over the previous 20 years had a carbon stock

ranging from 6.7 Mg C ha)1 for Larix kaempferi (Japa-

nese larch) to 22.3 Mg C ha)1 for Cryptomeria japonica

on average (Takahashi and Sakai 2006)(Table 4). Owing

to large variation in the size of the stands and the intensity

of thinning, no clear relationship was found between

deadwood carbon stock and years after thinning. It can be

concluded that plantations sometimes show large carbon

stock in the deadwood carbon pool, particularly after

non-commercial thinning.

Several reports have examined deadwood accumulation

in natural and semi-natural forests of Japan (Matsuura

et al. 2001; Jia et al. 2002; Jomura et al. 2007; Kawagu-

chi and Yoda 1986; Yoneda 1982) (Table 4), although

the measurement methods used differed among the stud-

ies; for example, the smallest size of deadwood measured

ranged from >1 cm to >10 cm and standing snags and

stamps were sometimes ignored. Coniferous old-growth

forests tend to show large carbon stock, such as Hokkaido

Island’s Picea and Abies forests (24.7 Mg C ha)1)

(Takahashi 1995) and a C. japonica forest in southern

Yakushima Island (19.4 Mg C ha)1) (Yoneda 1982).

Broad-leaved species usually show carbon stock lower

than 10 Mg C ha)1. These field data indicate that the car-

bon stock in deadwood is generally smaller than that indi-

cated in the IPCC Good Practice Guidance (IPCC 2003).

Sakai et al. (2008) suggested that the warm and humid

climate, which induces quick decomposition of dead-

wood, and small deadwood size may result in low accu-

mulation of deadwood carbon in Japan’s forests.

It should also be noted that windblown disturbances

caused by the many typhoons that occur around Japan

and monsoon Asia can have a drastic effect on dead

organic matter dynamics (Harmon and Hua 1991; Sato

2004; Takahashi et al. 2000) and can result in the unpre-

dictable accumulation of deadwood in the stands. Dead

and broken boles are usually withdrawn from plantation

stands after several years (Yamaguchi et al. 1963), but in

a natural forest on Hokkaido Island deadwood carbon

still remained at 24.7 Mg C ha)1 42 years after a

typhoon event (Takahashi 1995).

Carbon stock in the soil

All soil in Japan’s forest sector has been classified by the

Japanese Forest Soil Classification System (Forest Soil

Division 1976). Morisada et al. (2004) compiled data on

the soil survey reports used to calculate soil carbon stock

in Japan’s forests. There is wide variation among the soil

groups, ranging from 39 (immature soil group) to

172 Mg C ha)1 (peat soil group) in soil layers 0–30 cm

deep on average. The predominant soil group is brown

forest soil, which covers 70% of the forest sector and has

a carbon stock of 87 Mg C ha)1 (Table 5). Japanese

brown forest soils are often strongly influenced by volca-

nic ash (Imaya et al. 2007) and are classified as Andisols

in some cases (Soil Survey Staff 2006), but the mean value

of all soil groups (90 Mg C ha)1) is not as high as we

expected and is similar to the value (88 Mg C ha)1) indi-

cated in the IPCC guidelines (IPCC 2006). Morisada et al.

(2004) also reported that variation exists in the carbon

stock in the brown forest soil group among soil types:

drier soil moisture types, for example, dry brown forest

soils, have a lower soil carbon stock compared with soil in

moist sites, for example, slightly wet brown forest soils.

Table 4 Carbon stock in deadwood in Japanese forests (Mg C ha)1)

Species No. stands Range Mean SD Median

Years after

thinning

Coniferous plantations with a record of non-commercial thinning†

Picea glehnii 8 1.4–20.7 8.9 6.7 8.0 1–7

Abies sachalinensis 8 2.5–41.8 12.2 13.1 8.5 1–11

Larix kaempferi 16 0.6–29.4 6.7 7.1 3.5 1–14

Cryptomeria japonica 34 0.4–71.5 22.3 16.8 19.6 1–20

Chamaecyparis obtusa 36 1.5–68.7 19.6 15.4 15.6 1–20

Total 102 0.36–71.5 17.1 15.3 12.4

Natural and semi-natural forests

Broad-leaved spp.

Fagus crenata‡ 6 2.9–5.4 4.2 0.9 4.3

Evergreen broad-leaved forests§ 4 3.8–18.5 9.2 6.9 n.d.

Deciduous broad-leaved forests¶ 3 1.1–9.3 5.0 4.2 n.d.

Total 13 1.1–18.5 5.3 4.8 3.8

Coniferous spp.

C. japonica†† 1 19.4

Abies-Picea forests‡‡ 3 18.3–36.8 24.7 10.5 n.d.

†Takahashi and Sakai (2006). ‡Kawaguchi and Yoda (1986) and Yoneda (1982). §Yoneda (1982) and Sato (unpubl. data ). ¶Jomura et al. (2007), Jia et al.(2002) and Matsuura et al. (2001). ††Yakushima Island, Yoneda (1982). ‡‡Takahashi (1995) and unpublished data (M. Takahashi).



Black soil, referred to mainly as Andisols in Soil

Taxonomy (Soil Survey Staff 2006) or Andosols in the

World Reference Base (WRB) (IUSS Working Group

WRB 2006), covers the second largest area in the forest

sector. This is because Japanese soil is distinctively influ-

enced by volcanic activity (Shoji et al. 1993; Takahashi

et al. 2001; Wada 1986). The black soil group, derived

from fine-textured volcanic ash, shows a large amount

of soil carbon (130 Mg C ha)1), and this is far larger

than the value of 80 Mg C ha)1 indicated by the IPCC

guidelines for volcanic soil. This might be the result of

humus characteristics, for example, characteristics of

humus considered to be derived from charred plant

materials (Shindo et al. 2004) and the low decompos-

ability of the humus through the formation of alumino-

humus bindings in weathering volcanic ash (Shirato

et al. 2004).

With regard to volcanic soil, part of the immature soil

group also derived from volcanic materials, such as

slightly weathered pumice and scoria, is distributed

around the mouths of active volcanoes. These soils con-

tain only a small amount of carbon in the surface soil, for

instance 31.9 Mg C ha)1 on Hokkaido Island (Sanada

et al. 1995), although they often have a buried A horizon

under the deposits of volcanic materials. This means that

the influence of volcanic activity varies widely in the soil

carbon stock, ranging from a minimum to a maximum

influence, according to the deposition thickness and parti-

cle size of the volcanic products.

Another major soil type in the immature soil groups is

eroded soil (weathered granite soil), which is distributed in

western Japan where forest resources have been inten-

sively used for several centuries (Totman 1999; Tsukimori

et al. 1992). The other soil groups (podzol, red yellow soil,

gley soil and peat soil) have minor distributions in Japan.

Distributions of soil carbon stock were depicted using

1 km · 1 km resolution maps in Hokkaido (Hakamata

et al. 2000; Takahashi 2000) and in the forest sector of

Japan (Morisada 2004). According to these maps, we con-

clude that wide variations in carbon stock and in the het-

erogeneity of the soil types in the mountainous landscape

have created a diverse soil carbon distribution in Japan’s

forest sector.

FOREST AND AGRICULTURALSECTORS IN THE SAME SOIL GROUP

For soil comparisons between the forest and agricultural

sectors, data on agricultural soil were obtained from the

National Greenhouse Gas Inventory Report (Ministry of

the Environment, Japan 2008); data were calculated from

countrywide monitoring of soil characteristics in arable

land conducted by the Ministry of Agriculture, Forestry

and Fisheries of Japan and cooperating prefectural gov-

ernments since 1979 (Nakai and Obara 2003). Monitor-

ing sites were selected according to the area proportion of

the soil groups and the number of sites totaled approxi-

mately 20,000 and covered the entire agricultural sector

in Japan. Therefore, the average features of the agricul-

tural soils could be represented using the monitoring data-

set. For the Kyoto Protocol, the soil carbon stock in each

land-use category of the agricultural sector was calculated

using data surveyed around 1990, which is the base year

of the Kyoto Protocol.

The IPCC Guidelines (e.g. IPCC 2006) recommend that

where land-use change has occurred, carbon stock change

is to be calculated in accordance with the linear change in

carbon stock in a land-use category compared with that in

the other land-use categories over a transition period of

20 years. However, a direct comparison of carbon stock

between pre-land-use and post-land-use categories is not

appropriate because the dominant soil type in each land-

use category is biased. As shown in Table 6, the dominant

soil types differ between the forest sector and the agricul-

tural sector (Ministry of the Environment, Japan 2008).

Brown forest soil is the main soil type in the forest sector,

whereas lowland soil and gley soil dominant paddy fields,

and Andosols dominant in cropland and grassland. In this

mountainous country, agricultural lands have long been

concentrated on flat land and on gentle slopes (Himiyama

1995). Grassland in Japan is mostly managed as grazing

Table 5 Soil carbon stock and distribution area of forest soilgroups in Japan calculated from data in Morisada et al. (2004)

Soil group†Area

(kha)

Carbon stock

(Mg C ha)1)‡Carbon stock

(Mg C)

Podzols

(Spodosols ⁄ Podzols)

990 106 104,940

Brown forest soils

(Inceptisols, Andisols ⁄Cambisols, Andosols)

17,230 87 1,499,010

Red-yellow soils

(Ultisols, Inceptisol ⁄Acrisols, Cambisol)

510 69 35,190

Black soils

(Andisols ⁄ Andosols)

3,230 130 419,900

Gley soils

(Inceptisols ⁄ Gleysols)

407 92 37,444

Peat soils

(Histisols ⁄ Histosols)

74 172 12,728

Immature soils

(Entisols ⁄ Regosols)

1,852 39 72,228

Total 24,293 90 2,181,440

†Indicates the dominant soil groups classified by the Japanese forest soilclassification system (Forest Soil Division 1976) and international systemsin parentheses (Soil Taxonomy [Soil Survey Staff 2006] ⁄ the World Refer-ence Base (WRB) [IUSS Working Group WRB 2006] equivalent in thatorder). Note that several exceptions exist because these classifications arenot interchangeable. ‡Soil type and subgroup area weighted average.



land and is very small in area; 1.7% of the total land area

in 2005 (Table 1).

Carbon stock data were prepared for each soil group

present in every land-use category, that is, Andosols,

brown forest soils, red-yellow soils, dark red soils, gley

soils and peat soils (Table 7). These soil groups cover

77.5–87.7% of each land-use category, except for rice

fields, suggesting that the results of the comparison can

be applied to most cases of land-use conversion from

forest to agriculture in Japan. In rice fields, the soil

groups for comparison cover 51.8% of the total area

because the most dominant group, lowland soil, is not

included.

EMISSION FROM LAND-USE CHANGE

The emission factor is the emission or removal of CO2

after conversion of land-use by human activities. To

understand the effects of land-use change from forest to

agriculture on soil carbon stock, the emission factor was

determined by calculating the relative amounts of soil car-

bon stock in the agricultural sector to that in the forest

sector. Table 7 shows that rice fields, croplands and orch-

ards have a lower carbon stock than forest land in most

soil groups and that the emission factors are similar irre-

spective of the soil group. This suggests that forest land in

the soil groups compared contains similar proportions of

labile and active soil carbon pools (Leifeld and Kogel-

Knabner 2005; Parton et al. 1994), which could be

considered easily decomposing organic carbon by distur-

bances for agricultural land use. The emission factor for

rice fields was the lowest, 0.76, followed by crop fields

and orchards. Converting from forest to agriculture land

use, the area-weighted average of the emission factor was

0.79, meaning that 21% of the carbon stock in the soil

would be released after the conversion. In contrast, the

conversion to grassland accumulated carbon in the soil

and its increment rate relative to forest soil was 1.18.

Although dark red soil and peat soil showed a somewhat

different trend, which may have resulted from statistics

based on a small number (n = 9 for dark red soil and

n = 3 for peat soil), the narrow distribution of the dark

red soil and peat soil groups did not have a significant

effect on the weighted average of the emission factor.

Land-use change from forest to agriculture usually

results in large carbon emissions from dead organic matter

and soil (Guo and Gifford 2002). Murty et al. (2002)

reported that the change in soil carbon after land-use con-

version from forest to agriculture was 22%. This rate is

comparable to the reduction rate (21%) in our analyses.

In rice fields, organic matter under anaerobic conditions is

often considered to be recalcitrant (Kilham and Alexander

1984; Shirato 2006). Indeed, soil monitoring of Japan’s

arable land has shown that the soil carbon concentration

Table 6 Soil group composition (%) and land area in the land-use categories

Area in each land-use type (kha)

Land-use category

Forest† Paddy field‡ Cropland‡ Orchard‡ Grassland‡

24,294 2,887 1,832 403 23

Soil group§

Black soils and Kuroboku soils

(Andisols ⁄ Andosols)

13.3 11.9 50.5 22.0 50.8

Brown forest soils

(Inceptisols, Andisols ⁄ Cambisols, Andosols)

70.9 0.2 15.7 36.9 17.5

Upland soils (Inceptisols, Ultisols, Entisols ⁄ Anthrosols,

Gleysols, Planosols)

0.0 4.1 4.1 1.6 9.6

Red-yellow soils and dark red soils

(Ultisols, Alfisols, Inceptisols ⁄ Acrisols, Cambisols, Luvisols)

2.1 5.1 8.8 25.3 6.4

Lowland soils (Inceptisols, Entisols ⁄ Anthrosols, Fluvisols) 0.0 41.5 16.7 11.2 12.3

Gley soils (Inceptisols, Entisols ⁄ Anthrosols, Fluvisols) 1.7 30.8 0.7 0.5 0.0

Podzols

(Spodosols ⁄ Podzols)

4.1 0.0 0.0 0.0 0.0

Immature soils

(Entisols ⁄ Regosols)

7.6 0.0 1.6 2.4 0.6

Peat soils

(Histisols ⁄ Histosols)

0.3 6.4 1.9 0.1 2.8

†Calculated from data in Morisada et al. 2004;. ‡Statistics of the Ministry of Agriculture, Forestry and Fisheries, Japan (Ministry of the Environment,Japan 2008). §Indicates the dominant soil groups classified by the Japanese forest soil classification system (Forest Soil Division 1976), the classification sys-tem of cultivated soils (Classification Committee of Cultivated Soils 1995) and international systems in parentheses (Soil Taxonomy [Soil Survey Staff2006] ⁄ WRB [IUSS Working Group WRB 2006] equivalent in that order). The Japanese names for the soil groups were identified by referring to the Japa-nese version of the National Inventory of Greenhouse Gas of Japan (Ministry of the Environment, Japan 2008).



in the rice fields has been stable for 25 years in most soil

groups, whereas that in cropland decreased with time

(Nakai 2008). However, the emission factor for conver-

sion from forest to paddy field is similar to that for crop

fields in our analyses. This may be the result of the long-

term use of land for rice or the artificial effects of soil

dressing by land improvement activities in rice fields.

Nakai (2008) suggested that some monitoring sites were

influenced by soil dressing over the plowed layer (Ap hori-

zon).

In grassland, there are large variations in carbon stock

among soil groups, but appropriate management of

grassland appears to result in the accumulation of soil

carbon. Increased rates for soil carbon in grasslands are

similar to the rates observed in forests (Post and Kwon

2000). Moreover, the maximum potential carbon stock

in grassland and pasture soil is often larger than that in

forest soil (Cerri et al. 2003; Halliday et al. 2003). In

New Zealand, conversion from pasture to pine planta-

tion could result in a 15% reduction of mineral soil

carbon, except in high clay activity soils (Scott et al.

1999). As in New Zealand, Japan’s grassland manage-

ment system appears to have the potential to increase the

soil carbon stock.

The difference in carbon stock between the forest and

agricultural sectors in this comparison would mostly be

the maximum potential carbon emission or removal after

the land-use change because soil carbon in each land-use

category is considered to have almost reached equilibrium

under continuous land use for several decades or centuries

under the usual management system. However, soil car-

bon stock in agricultural soil varies with changes in man-

agement. Soil monitoring in the agricultural sector has

revealed that some properties in the top layer have chan-

ged over the past 25 years (Nakai and Obara 2003; Obar-

a 2000; Obara and Nakai 2003, 2004). A large input of

organic manure in tea soil and greenhouse soil tended to

accumulate carbon in the soil (Nakai 2008). It has also

been suggested that the soil carbon concentration in orch-

ard soil tends to increase, probably as a result of no-tillage

management. Thus, agricultural soils have the potential to

accumulate soil carbon through an improved soil manage-

ment system and the emission factors in Table 7 may need

to be revised in future.

Table 7 Average carbon stock (0–30 cm) in the soil groups, the percentage area of soil type in each land-use type and the emissionfactor

Land-use categories

Forest soil Rice field Crop field Orchard Grassland

Soil group (area of soil type in each land-use category (%))

Andosols 13.3 11.9 50.5 21.9 50.8

Brown forest soils 70.9 0.2 15.7 36.9 17.5

Red-yellow soils 1.6 5.0 7.2 23.7 3.4

Dark red soils 0.2 0.1 1.6 1.5 3.0

Gley soils 1.4 30.8 0.7 0.0 0.0

Peat soils 0.3 3.8 1.8 0.0 2.8

Other soil groups 12.3 48.2 22.5 16.0 22.5

Mean carbon stock (Mg C ha)1)†

Andosols 130 112.5‡ 112.3‡ 118.6‡ 154.3‡

Brown forest soils 87 59.5 65.2 68.4 101.3

Red-yellow soils 69 63.2§ 46.2¶ 64.3¶ 74.4§

Dark red soils 89 56.3 45.2 54.6 54.6

Gley soils 92 64.8 65.9

Peat soils 172 115.0 184.9 325.2

Emission factor††

Andosols 1.00 0.87 0.86 0.91 1.19

Brown forest soils 1.00 0.68 0.75 0.79 1.16

Red-yellow soils 1.00 0.92 0.67 0.93 1.08

Dark red soils 1.00 0.63 0.51 0.61 0.61

Gley soils 1.00 0.71 0.72

Peat soils 1.00 0.67 1.08 1.89

Weighted average emission factor 1.00 0.76 0.82 0.86 1.18

0.79‡‡

†The carbon stock in the forest soils was calculated from Morisada et al. (2004) and the carbon stock in agricultural soil was calculated from Chapter 7,Land Use, Land-Use Change and Forestry in the National Greenhouse Gas Inventory Report of Japan, which was provided by Dr Makoto Nakai of theNational Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki, Japan (Ministry of the Environment, Japan 2008). ‡Area weighted average ofAndosols, Wet Andosols and Gleyed Andosols. §No red soils are distributed. ¶Area weighted average of Red soils and Yellow soils. ††Carbon stock incroplands and grasslands relative to forest soil for each soil type. ‡‡Area weighted average emission factor for rice fields, crop fields and orchards.



IMPROVEMENT IN THE ESTIMATINGMETHODS AND INVENTORY

The forest data analyzed were collected from published

and unpublished reports on soil surveys conducted

mainly in the late 20th century (Morisada et al. 2004).

For the following reasons, caution should be used when

evaluating these data. First, the data that we collected

from representative soil profiles in the soil map reports

might have been overestimated or underestimated

because the representative soil pit was often selected at

a point that had the most typically developed soil pro-

file around the area. The soil profile of the representa-

tive pit was often emphasized by developing soil layers

and characteristics compared with the average features

of the soil around the area. Second, the soil carbon bal-

ance might have changed from the noontide period of

the soil survey (1950s–1970s) because broad-leaved

natural forests have been converted to coniferous plan-

tation forests in a large area of Japan’s forest sector

over the past 40 years (Handa 1988). The equilibrium

of carbon stock under plantations could still be shifting

even now. Third, the evaluation of gravel and stone

content was not quantitative in the soil mapping survey,

and this appears to influence accurate calculation of soil

carbon stock.

Similar issues, such as biased site selection, can be

pointed out when the carbon stock in litter is evaluated.

For deadwood, nationwide data must be collected from a

wide range of forest vegetation and management prac-

tices. As shown in Table 4, deadwood stock, which would

be large carbon stock in managed forests under Article 3.4

in the Kyoto Protocol, is sometimes large and varies with

the management methods of the forest. These issues

would be solved by systematic and uniform sampling pro-

tocols. In 2006, a soil carbon inventory under a strategic

soil survey project was launched to evaluate soil carbon

stock in Japan’s forest sector (Takahashi and Moridasa

2008). We expect to be able to update the values on car-

bon stock in soil and dead organic matter in the future. In

addition, repeated sampling should be organized using the

same sampling protocols to monitor the effect of global

warming on soil carbon stock in Japan.

To evaluate land-use change, we should establish long-

term monitoring sites in each land-use category under dif-

ferent climate conditions. Soil carbon stocks in settlement

and other land are still rather limited in Japan. Compari-

sons will need to be drawn between land influenced and

not influenced by volcanic soil. Plantation forests should

be included to detect changes in carbon balance in accor-

dance with the management system. The modeling

approach would also be highly variable (Liski et al. 2005;

Parton et al. 1994). To understand the full flux of CO2

and carbon stock in all pools in the forest ecosystems, con-

tinuous efforts must be made in the future.

Conclusions

We reviewed the data on carbon stock in deadwood, litter

and soil in Japan’s forest sector. The carbon stock in dom-

inant coniferous plantation species litter, such as Crypto-

meria japonica and Chamaecyparis obtusa, is small

compared with that indicated in the IPCC guidelines

(IPCC 2003, 2006). Deadwood accumulation is low in

semi-natural forests, generally <10 MgC ha)1. Deadwood

carbon stock in natural forests is also small, although

plantations sometimes have large carbon stock after pre-

commercial thinning. The black soil group has high car-

bon stock, 130 MgC ha)1 in layers 0–30 cm deep,

although the brown forest soil group, which is the pre-

dominant soil type in the forest sector, has a carbon stock

(87 MgC ha)1) comparable to the values indicated in the

IPCC guidelines. Soil carbon stock in the agricultural sec-

tor is 21% lower than that in the forest sector except for

grassland, which is 18% higher in soil carbon compared

with forests. These values should be revised by systematic

survey and monitoring in the future.

ACKNOWLEDGMENTS

This study was funded by the Forestry Agency of Japan,

the Ministry of the Environment Japan (Global Environ-

ment Research Fund B082 and Global Environment

Research Account for National Institute) and the Ministry

of Agriculture, Forestry and Fisheries of Japan (the Evalu-

ation, Adaptation and Mitigation of Global Warming

11070). We thank Dr Masahiro Amano, Dr Mitsuo Mat-

sumoto, Dr Yoshiyuki Kiyono and Dr Tamotsu Sato for

their invaluable support and suggestions. We also thank

Dr Hiroshi Obara of the National Institute for Agro-Envi-

ronmental Sciences for his valuable guidance on arable

soils in Japan.

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carbon stock in litter, deadwood and soil in japan’s forest sector and its comparison with carbon...

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