Post on 27-Mar-2017
Forest biomass carbon sinks in East Asia, with specialreference to the relative contributions of forest expansionand forest growthJ INGYUN FANG1 , 2 , ZHAOD I GUO1 , 3 , HU I FENG HU2 , TOMOMICH I KATO4 ,
H IROYUK I MURAOKA5 and YOWHAN SON6
1Department of Ecology, College of Urban and Environmental Science, and Key Laboratory for Earth Surface Processes of the
Ministry of Education, Peking University, Beijing, 100871, China, 2State Key Laboratory of Vegetation and Environmental
Change, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China, 3National Satellite Meteorological Center,
China Meteorological Administration, Beijing, 100081, China, 4Laboratoire des Sciences du Climat et de l’ Environnement, IPSL,
CEA-CNRS-UVSQ, Orme des Merisiers, Gif sur Yvette, 91191, France, 5Institute for Basin Ecosystem Studies, Gifu University,
1-1 Yanagido, Gifu, 501-1193, Japan, 6Division of Environmental Science and Ecological Engineering, Korea University,
Anam-dong, Sungbuk-ku, 136-701, Seoul Korea
Abstract
Forests play an important role in regional and global carbon (C) cycles. With extensive afforestation and reforestation
efforts over the last several decades, forests in East Asia have largely expanded, but the dynamics of their C stocks
have not been fully assessed. We estimated biomass C stocks of the forests in all five East Asian countries (China,
Japan, North Korea, South Korea, and Mongolia) between the 1970s and the 2000s, using the biomass expansion fac-
tor method and forest inventory data. Forest area and biomass C density in the whole region increased from
179.78 9 106 ha and 38.6 Mg C ha�1 in the 1970s to 196.65 9 106 ha and 45.5 Mg C ha�1 in the 2000s, respectively.
The C stock increased from 6.9 Pg C to 8.9 Pg C, with an averaged sequestration rate of 66.9 Tg C yr�1. Among the
five countries, China and Japan were two major contributors to the total region’s forest C sink, with respective contri-
butions of 71.1% and 32.9%. In China, the areal expansion of forest land was a larger contributor to C sinks than
increased biomass density for all forests (60.0% vs. 40.0%) and for planted forests (58.1% vs. 41.9%), while the latter
contributed more than the former for natural forests (87.0% vs. 13.0%). In Japan, increased biomass density domi-
nated the C sink for all (101.5%), planted (91.1%), and natural (123.8%) forests. Forests in South Korea also acted as a
C sink, contributing 9.4% of the total region’s sink because of increased forest growth (98.6%). Compared to these
countries, the reduction in forest land in both North Korea and Mongolia caused a C loss at an average rate of 9.0 Tg
C yr�1, equal to 13.4% of the total region’s C sink. Over the last four decades, the biomass C sequestration by East
Asia’s forests offset 5.8% of its contemporary fossil-fuel CO2 emissions.
Keywords: biomass density, biomass expansion factor, carbon sink, China, East Asia, forest area, forest inventory, Japan,
Mongolia, North Korea, South Korea
Received 14 June 2013 and accepted 15 November 2013
Introduction
As the largest part of terrestrial ecosystems, forests
occupy around 30% of the global land surface with
about 4.2 9 109 ha (Kramer, 1981; Bonan, 2008). It is
estimated that over 80% of terrestrial vegetation carbon
(C) is stored in forests (Pan et al., 2011), and the annual
C flux between forests and the atmosphere through pho-
tosynthesis and respiration accounts for 50–90% of the
total annual flux of terrestrial ecosystems (Winjum et al.,
1993; Malhi et al., 2002). Because of their capacity for C
storage and high productivity, forest ecosystems play a
dominant role in the global C cycle (IPCC, 2007; Pan
et al., 2011). The Kyoto Protocol, which was approved in
the 1997 United Nations (UN) meeting on climate
change, clearly suggested increasing C sequestration
through afforestation and reforestation to meet green-
house gas emission targets (Brown et al., 1999). There-
fore, estimation of forest biomass C sinks or sources and
their spatial and temporal distributions is both of scien-
tific and of political importance (Watson et al., 2000;
Fang et al., 2001; Janssens et al., 2003; Nabuurs et al.,
2003; Birdsey et al., 2006; McKinley et al., 2011).
Since the early 1970s, regional and national forest
inventories have been carried out across the world and
provide data for estimating forest biomass on a regional
Correspondence: Jingyun Fang, tel. + 86 10 6276 5578, fax +86 10
6275 6560, e-mails: jyfang@urban.pku.edu.cn;
fangjingyun@ibcas.ac.cn
© 2014 John Wiley & Sons Ltd 2019
Global Change Biology (2014) 20, 2019–2030, doi: 10.1111/gcb.12512
Global Change Biology
or national scale (e.g., Brown & Lugo, 1984; Kauppi
et al., 1992; Turner et al., 1995; Schroeder et al., 1997;
Fang et al., 1998, 2001, 2005, 2007; Brown & Schroeder,
1999; Choi et al., 2002; Goodale et al., 2002; Liski et al.,
2003; Li et al., 2010; Pan et al., 2011). Using forest inven-
tory data and long-term ecosystem C studies, Pan et al.
(2011) recently estimated that the current C stock in the
world’s forest ecosystems was 861 � 66 Pg C (1
Pg = 1015 g), with 363 � 28 Pg C (42%) in above- and
belowground live biomass. Global forests have func-
tioned as a significant C sink over the last two decades,
but there exists a large regional and temporal difference
in the magnitude of that sink (Pan et al., 2011). There-
fore, detailed assessment of regional forest C sinks/
sources and their spatial and temporal distributions is
necessary for understanding the dynamics, processes,
and mechanisms of the terrestrial C cycle (Goodale
et al., 2002; Birdsey et al., 2006; Fang et al., 2010;
McKinley et al., 2011). During the past decade, several
key regional programs such as the North American
Carbon Program, Carbon Europe Integrated Project,
and African Carbon Project have been established to
clarify regional C budgets and have greatly contributed
to knowledge of the C cycle in their respective regions
(Fang et al., 2010; http://www.globalcarbonproject.
org/carbontrends).
East Asia, which includes the five countries of China,
Japan, Democratic People’s Republic of Korea (hence-
forth referred to North Korea), Republic of Korea
(South Korea), and Mongolia, is located at the eastern
margin of the Eurasian Continent and the western coast
of the Pacific Ocean (Fig. 1). This area has a population
of more than 1.5 billion and covers about 1.2 9 109 ha
land area, of which 22% (254.6 9 106 ha) is occupied
by forests (FAO, 2010a; Table S1). As one of the most
active regions in the global economy, it is of great
importance both in scientific understanding of the
region’s forest C cycle and in the use of appropriate for-
est management strategies. Characterized by a warm-
humid climate that is under the influence of the Asian
monsoon, East Asia has abundant forest types that
range from tropical rainforests and evergreen broadleaf
forests in the south to boreal forests in the north, pro-
viding a model for exploring heterogeneity of ecologi-
cal attributes of C cycle.
East Asia has experienced extensive afforestation and
reforestation activities over the past several decades,
with about 34.2% of the global plantations located
in this region (90.2 9 106 ha in East Asia and
264.1 9 106 ha in the globe in 2010) (FAO, 2010a). This
abundance of plantations could provide insight into the
effect of forest management on the dynamics of forest
C stocks and C sinks or sources (Fang et al., 2010).
Using a process-based model of the terrestrial C cycle,
Ito (2008) conducted the first regional estimation of the
C budget of terrestrial ecosystems in East Asia and esti-
mated that 73.1 Pg C was stored in vegetation and soil
with an average C sequestration rate of 98.8 Tg C yr�1
(1 Tg = 1012 g) in East Asian forests during 2000–2005.Since the mid-1990s, using national forest inventory
data, several studies have estimated forest biomass C
stocks in China (e.g., Fang et al., 1998, 2001, 2007; Guo
et al., 2010), Japan (Fang et al., 2005) and South Korea
(Choi et al., 2002; Li et al., 2010), and these studies
Fig. 1 Locations of the five East Asian countries in this study.
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
2020 J . FANG et al.
conclude that forests in all these countries have
functioned as C sinks since the late 1970s. However, a
long-term study that uses consistent methods and well-
qualified data sets to evaluate changes in biomass C
stocks and the size of C sinks or sources for East Asian
forests is lacking. This study uses statistically sound
inventory data from the 1970s to the 2000s to estimate
forest biomass C stocks and C sinks or sources for the
entire East Asia region using the biomass expansion
factor (BEF) method and forest inventory data (for
China, Japan, and South Korea) and FAO (Food and
Agriculture Organization of the United Nations) data
(for North Korea and Mongolia). Furthermore, we dis-
cuss the relative contributions of forest areal expansion
and increased biomass C density to explore the possible
mechanisms for forest C dynamics in this region over
the last four decades.
Materials and methods
Forest inventory data
In recent decades, China, Japan, and South Korea have period-
ically conducted national-level forest resource inventories.
These inventories provide information on forest area and tim-
ber volume for each forest type for each administrative unit
(e.g., Fang et al., 2005, 2007; Li et al., 2010).
China’s forest inventory data used in this study included
seven periods: 1973–1976, 1977–1981, 1984–1988, 1989–1993,
1994–1998, 1999–2003, and 2004–2008 (Chinese Ministry of
Forestry, 1977, 1983, 1989, 1994, 2000, 2005, 2010). In the inven-
tories, China’s forests were classified into three categories:
stands (including natural and planted forests), economic for-
ests (woods with the primary objective of production of fruits,
edible oils, drinks, flavorings, industrial raw materials, and
medicinal materials), and bamboo forests. In this study, ‘for-
est’ only refers to ‘forest stands’ with canopy coverage ≥ 20%
and therefore excludes economic and bamboo forests (Fang
et al., 2007). For each forest stand, the inventories documented
detailed information on forest type, age class, area, and
volume at the provincial level.
Japan’s forest inventory data included seven periods: 1966–
1975, 1976–1980, 1981–1985, 1986–1990, 1991–1995, 1996–2000,
and 2001–2005, and were compiled from Japan’s Forest
Resources Statistics for 1975, 1980, 1985, 1990, 1995, 2000, and
2005 (Japan Agency of Forestry, 1978, 1982, 1987, 1992, 2000,
2003, 2008). In the inventories, forest is defined as land with
≥20% canopy coverage for government-owned lands and
>30% canopy coverage for community- and privately owned
lands (Fang et al., 2005; Wang et al., 2011).
South Korea’s forest inventory data included five periods:
1972–1974, 1975–1982, 1983–1992, 1993–2000, and 2001–2007,
and were compiled from the Agriculture and Forestry Statisti-
cal Yearbooks for 1974, 1982, 1992, 2000, and 2007 (Korean
Ministry of Agriculture & Forestry, 1975, 1983, 1993, 2001,
2008). In the inventories, forest was defined as land with ≥30%canopy coverage for government-, community-, and privately
owned lands (Li et al., 2010).
Due to the lack of forest inventory data in North Korea and
Mongolia, FAO statistics were used to estimate total forest
area and timber volume for these two countries in 1990, 2000,
2005, and 2010 (FAO, 2006, 2010a). According to the FAO
report on Global Forest Resource Assessment 2010, forest was
defined as land spanning more than 0.5 hectares with trees tal-
ler than 5 meters and a canopy cover >10%, or trees able to
reach these thresholds in situ. The thresholds for tree height
and the areal extent for a forest are similar in the FAO criteria
to that of inventories in China, Japan, and South Korea, but
that for canopy cover is smaller than the other inventories and
may result in relatively higher estimates of forest area for
North Korea and Mongolia. We obtained the information on
the forest area and timber volume for North Korea in 1970
from Lee (2006), and for Mongolia in 1974 from Persson (1974)
and the Mongolian Ministry of Environment, Nature & Tour-
ism (2009). Forest area and timber volume in 1980 for these
two countries were estimated by assuming linear relationships
of each variable between the 1970s and 1990.
Table 1 summarizes the periods of inventory data or FAO
reports that were used to estimate the forest biomass C stocks
for the five countries from the 1970s to the 2000s.
Estimation of forest biomass C stocks
Because forest inventories only report forest area and timber
volume, but do not provide detailed information on forest bio-
mass, it is necessary to develop allometric relationships
between forest biomass and forest timber volume for each
forest type (Fang et al., 1998, 2001; Brown & Schroeder, 1999).
The BEF, which is defined as the ratio of stand biomass to
timber volume (Mg m�3) (1 Mg = 106 g), is used to convert
timber volume from forest inventory to biomass (e.g., Fang
et al., 2001, 2005; Guo et al., 2010; Li et al., 2010). Previous
studies have suggested that BEF is not constant, but var-
ies with forest age, site class, stand density, and site quality
(e.g., Brown & Lugo, 1992; Schroeder et al., 1997; Fang et al.,
1998, 2001, 2005; Brown & Schroeder, 1999; Brown et al., 1999).
Fang et al. (1996, 1998, 2001, 2005), Fang and Wang (2001)
derived a simple reciprocal equation from direct field
Table 1 Periods of inventory data or FAO reports used for estimating biomass C stocks for the five countries
Decade China Japan North Korea South Korea Mongolia
1970s 1973–1976; 1977–1981 1966–1975; 1976–1980 1970; 1980 1972–1974; 1975–1982 1974; 1980
1980s 1984–1988 1981–1985; 1986–1990 1980; 1990 1983–1992 1980; 1990
1990s 1989–1993; 1994–1998 1991–1995; 1996–2000 1990; 2000 1993–2000 1990; 2000
2000s 1999–2003; 2004–2008 2001–2005 2000; 2005; 2010 2001–2007 2000; 2005; 2010
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
FOREST BIOMASS C SINKS IN EAST ASIA 2021
measurements to express the BEF-timber volume relationship
by forest type in China and Japan:
BEF ¼ aþ b=x ð1Þ
where x is the timber volume per unit area (m3 ha�1), and a
and b are constants for each specific forest type. In Eqn (1),
when timber volume is very large (such as mature forest), BEF
will approach to a constant parameter, a, while it will be extre-
mely large when timber volume is quite small (such as young
forest). This simple mathematic relationship fits for almost all
forest types. With this simple BEF approach, one can easily
calculate regional or national forest biomass based on direct
field measurements and forest inventory data. For detailed
information about the BEF method, see Fang et al. (1998, 2001,
2007) and Guo et al. (2010) for China, Fang et al. (2005) for
Japan, and Li et al. (2010) for South Korea. Parameters of the
BEF equations for major forest types in China, Japan, and
South Korea are listed in Table S2.
In this study, we used the BEF method with parameters for
each forest type from Guo et al. (2010) and Fang et al. (2005) to
calculate forest biomass in China and Japan, respectively, from
the 1970s to the 2000s. It should be mentioned that the forest
inventory data from 1973 to 1976 for China included only total
forest area and timber volume at the provincial level. Fang &
Chen (2001) established an empirical, linear relationship
between mean biomass and mean volume at the provincial
level using China’s forest inventory data between 1977 and
1998. We used recent forest inventory data and an updated
robust linear relationship to calculate provincial forest bio-
mass in China from 1973 to 1976:
BD ¼ 0:704VDþ 19:953ðR2 ¼ 0:968; n ¼ 211Þ ð2Þ
where BD and VD are biomass density (Mg ha�1) and volume
density (m3 ha�1), respectively.
Before 1994, forest was defined as land with >30% canopy
coverage in China (Fang et al., 2001). The 1994–1998 inventory
data provided both criteria (20% and 30% canopy coverage),
and Fang et al. (2007) found that there existed robust linear
relationships for the forest area and biomass C stock between
the two criteria at the provincial level. In this study, we modi-
fied their equations with power function relationships to
obtain more accurate conversions:
AREA0:2 ¼ 1:290AREA0:9950:3 ðR2 ¼ 0:996; n ¼ 30Þ ð3Þ
CARBON0:2 ¼ 1:147CARBON0:9960:3 ðR2 ¼ 0:998; n ¼ 30Þ ð4Þ
where AREA and CARBON are forest area (104 ha) and
biomass C stock (Tg C) in a province, respectively; subscripts
0.3 and 0.2 stand for the criterion of >30% and ≥20% canopy
coverage, respectively.
As a result, the provincial forest areas and biomass C stocks
with the new criterion in China in 1973–1976, 1977–1981,
1984–1988, and 1989–1993 were calculated based on Eqns (3)
and (4), and corresponding forest C densities were hence
obtained.
For South Korea, we adopted the results of forest biomass
from the 1970s to the 2000s estimated by Li et al. (2010), who
used the same BEF method as Fang et al. (1998, 2001) for three
major forest types (coniferous, deciduous, and mixed forests)
in South Korea.
According to the recent report on Global Forest Resources
Assessment 2010 from FAO, major forest types in North Korea
were oak (Quercus), pine (Pinus), and larch (Larix) (FAO,
2010b), and major forest types in Mongolia were Siberian larch
(Larix sibirica), Siberian pine (Pinus sibirica), Scots pine (Pinus
sylvestris), and Betula (Betula platyphylla) (FAO, 2010c). There
were no direct field measurement data for these two countries
and therefore we could not establish BEF functions, but the
forest types in these two countries are very similar to those in
the northeast and north China. Therefore, similar to Eqn (2),
we used the data in the northeast and north China and estab-
lished empirical relationships between provincial mean bio-
mass and mean volume for North Korea [Eqn (5)] and
Mongolia [Eqn (6)], to estimate forest biomass for these two
countries from the 1970s to the 2000s:
BD ¼ 0:969VDþ 12:800ðR2 ¼ 0:953; n ¼ 178Þ ð5Þ
BD ¼ 0:898VDþ 19:311ðR2 ¼ 0:965; n ¼ 122Þ ð6Þwhere BD and VD are the same as Eqn (2).
We used a factor of 0.5 to convert biomass to C stock in this
study (Fang et al., 2001, 2005).
Data of NDVI and forested area
Remotely sensed normalized difference vegetation index
(NDVI) data are not only an indicator of land cover and vege-
tation growth (e.g., leaf area index and net primary produc-
tion) but also used as a surrogate of growing conditions for
vegetation (i.e., the physical environment for plant growth,
such as soil conditions, moisture, temperature, and light avail-
ability) (Potter et al., 1993; Field et al., 1995; Fang et al., 2003).
Because we do not have direct measures of growing condi-
tions at a national scale, we use NDVI and its trend over time
to compare the growing conditions of forested areas among
East Asian countries. In general, a large NDVI value and a
positive NDVI trend imply good site quality and favorable
growing conditions for vegetation.
The NDVI data used in this study come from the third ver-
sion of the AVHRR NDVI archive, provided by the Global
Inventory Monitoring and Modeling Studies group at a spatial
resolution of 8 9 8 km2 over 15 day intervals for the period of
1982 to 2011 (Beck et al., 2011). This data set is one of the most
accurate products with which to assess the change in vegeta-
tion growth over time and is used widely to depict long-term
change in global and regional vegetation cover (Fensholt &
Proud, 2012). To eliminate spurious NDVI trends caused by
winter snow, our analysis focused on the interannual changes
in the forested areas during the growing season (May to
September) for East Asia.
In addition, we used the global land cover data set with a
resolution of 8 9 8 km2, generated by University of Maryland
(http://glcf.umiacs.umd.edu/data/landcover/; Hansen et al.,
1998, 2000), to document forest area for each East Asian coun-
try, except Mongolia because of data unavailability.
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
2022 J . FANG et al.
Calculation of change rates of forest area, C density, andC stock
We used the concept of Forest Identity, proposed by Kauppi
et al. (2006) and Waggoner (2008), to explore the relative con-
tribution of changes in forest area and biomass C density
(biomass C stock per area) to the C sink for China, Japan, and
South Korea. According to the Forest Identity concept, forest
area (A, ha), biomass C density (D, Mg C ha�1), and total bio-
mass C stock (M, Tg C) can be linked using Eqn (7), and their
change rates (a, d, and m) over time (t) can be linked with
Eqns (8) and (9). By calculating these attributes, we can assess
the relative contribution of changes in forest area and bio-
mass C density to the change in total biomass C stock (i.e., C
sink):
M ¼ A�D ð7Þ
Because ln (M) = ln (A) + ln (D),
the change rates (m, a, and d) of M, A and D should be:
1
M
dM
dt¼ 1
A
dA
dtþ 1
D
dD
dt; or
d lnðMÞdt
¼ d lnðAÞdt
þ d lnðDÞdt
ð8Þ
Let
m � d lnðMÞdt
; a � d lnðAÞdt
; d � d lnðDÞdt
Then, m ¼ aþ d (9)
where M, A, and D represent total biomass C stock (Tg C, or
Pg C), forest area (ha), and biomass C density (Mg C ha�1) at
the national level, respectively; and m, a, and d depict the
corresponding derivatives (or change rate) of these attributes
over time. This identity combines the values of forest area
with the biomass density into the changing biomass C stock
(i.e., C sink).
Results
Changes in forest area
In East Asia, forest area increased by 9.4% from
179.78 9 106 ha in the 1970s to 196.65 9 106 ha in the
2000s, with most of this increase in China (Table 2).
The forest area in China increased by 21.88 9 106 ha,
from an initial area of 127.31 9 106 ha to 149.19 9
106 ha by the 2000s, which accounted for 129.7% of the
total area increment in the East Asian region. Forest
area in North Korea and Mongolia decreased by
3.08 9 106 and 1.86 9 106 ha over the study period,
respectively, representing 32.8 and 14.1% of the respec-
tive country’s forest area in the 1970s. There was a
slight decrease of 0.18 9 106 ha in Japan and a slight
increase of 0.11 9 106 ha in South Korea (Table 2).
Changes in forest biomass C density, total C stock, and Csink
The biomass C density in the region had dramatically
increased from 38.6 Mg C ha�1 in the 1970s to 45.5 Mg
Table 2 Forest area, C stocks, and C sinks for each country in East Asia from the 1970s to the 2000s
Period East Asia China Japan North Korea South Korea Mongolia
Area (106 ha)
1970s 179.78 127.31 23.82 9.38 6.10 13.17
1980s 183.14 131.69 23.79 8.59 6.29 12.78
1990s 185.62 136.06 23.60 7.57 6.26 12.13
2000s 196.65 149.19 23.64 6.30 6.21 11.31
Net change 16.87 21.88 �0.18 �3.08 0.11 �1.86
C stock (Tg C)
1970s 6937 4719 954 339 51 874
1980s 7301 4885 1173 311 106 826
1990s 7989 5395 1395 274 157 768
2000s 8944 6145 1615 232 240 712
Net change 2007 1426 661 �107 189 �162
C density (Mg C ha�1)
1970s 38.6 37.1 40.1 36.1 8.4 66.4
1980s 39.9 37.1 49.3 36.2 16.9 64.6
1990s 43.0 39.7 59.1 36.2 25.1 63.3
2000s 45.5 41.2 68.3 36.8 38.6 63.0
Net change 6.9 4.1 28.3 0.7 30.3 �3.4
C sink (Tg C yr�1)
1970s–1980s 36.4 16.6 21.9 �2.8 5.5 �4.8
1980s–1990s 68.8 51.0 22.2 �3.7 5.1 �5.8
1990s–2000s 95.5 75.0 22.0 �4.2 8.3 �5.6
1970s–2000s 66.9 47.5 22.0 �3.6 6.3 �5.4
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
FOREST BIOMASS C SINKS IN EAST ASIA 2023
C ha�1 in the 2000s (Table 2). Among the five countries,
the largest increase in biomass C density (30.3 Mg
C ha�1) was in South Korea, with an initial biomass C
density of 8.4 Mg C ha�1 and a biomass C density of
38.6 Mg C ha�1 by the 2000s. Biomass C density
increased in Japan and China from 40.1 and 37.1 Mg
C ha�1 in the 1970s to 68.3 and 41.2 Mg C ha�1 in the
2000s, with a net increase of 28.3 and 4.1 Mg C ha�1,
respectively. It did not change much (ranging from 36.1
to 36.8 Mg C ha�1 over the four decades) in North
Korea and had a slight decrease of 3.4 Mg C ha�1 in
Mongolia (66.4 Mg C ha�1 in the beginning to 63.0 Mg
C ha�1 in the 2000s).
Total forest biomass C stocks in the region increased
by 28.9%, from 6937 Tg C in the 1970s to 8944 Tg C in
the 2000s, resulting in a net accumulation of 2007 Tg C.
The increase was attributed to increases in China,
Japan, and South Korea: over the four decades, the C
stocks increased by 1426, 661, and 189 Tg C in China,
Japan, and South Korea, respectively, from initial stocks
of 4719, 954, and 51 Tg C to the stocks of 6145, 1615,
and 240 Tg C by the 2000s, which accounted for 71.1,
32.9, and 9.4% of the total accumulation. On the other
hand, the C stocks in North Korea and Mongolia
decreased from initial stocks of 339 and 874 Tg C to 232
and 712 Tg C by the 2000s, with an accumulated C loss
of 107 and 162 Tg, respectively.
Across the entire East Asian region, biomass C sinks
increased from 36.4 Tg C yr�1 during the 1970s–1980sto 95.5 Tg C yr�1 during the 1990s–2000s, at an average
rate of 66.9 Tg C yr�1 over the four decades. Not sur-
prisingly, among the five countries, the largest C sink
occurred in China. Over the study period, China’s for-
ests contributed 47.5 Tg C yr�1 (71.1%) to the total
region’s C sink and increased from an initial value of
16.6 Tg C yr�1 to 75.0 Tg C yr�1 during the 1990s–2000s. Forests in Japan and South Korea also functioned
as C sinks, with an average C gain of 22.0 Tg yr�1 in
Japan and 6.3 Tg yr�1 in South Korea, accounting for
32.9% and 9.4% of the total region’s C sink, respec-
tively. North Korea and Mongolia showed C losses of
3.6 and 5.4 Tg yr�1 averaged over the last 40 years,
respectively.
Relative contributions of forest area and biomass densityto C sinks
To quantitate the relative contribution of areal expan-
sion and increased regrowth (biomass density) to the
total C sink of forests in the three countries (China,
Japan, and South Korea) with C sinks, we calculated
the relative change rates of forest area (a) and biomass
C density (d) for all, planted, and natural forests in
China and Japan, and for all forests in South Korea in
each period and over the four decades, using the con-
cept of Forest Identity (Kauppi et al., 2006; Waggoner,
2008) (Fig. 2; Table S3).
For all forests, the mean change rates of forest
area and biomass density were 0.264% yr�1 and
0.175% yr�1 in China, respectively, with a larger contri-
bution of the former than that of the latter (60.0% vs.
40.0%) to the C sink over the last 40 years (Fig. 2a).
These rates and relative contributions were very much
different from those in Japan and South Korea. In those
two countries, forest area either decreased slightly (for
Japan, with a = �0.013% yr�1) or did not change much
(for South Korea, with a = 0.030% yr�1), and thus their
contribution of areal expansion to the C sink was very
small or negative. However, the biomass density of
(a)
(b)
Fig. 2 Mean change rates of forest area and biomass density
and their relative contributions to changes in total biomass C
stock (i.e., C sink) for China, Japan, and South Korea over the
40 years. (a) For all forests in the three countries; and (b) for
planted and natural forests in China and Japan. Numbers above
bars are relative contributions (%) of forest area and biomass
density to the total C sink over the four decades. The minus
value for the change rate of forest area in Japan shows that for-
est area has shrunk and made its negative contribution to the C
sink. The change rates were only calculated for all forests in
South Korea because data were not available for planted and
natural forests or a small area of natural forests in the country.
For details, see text and Table S3.
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
2024 J . FANG et al.
these countries increased remarkably, with respective
average rates of 0.869 and 2.148% yr�1 that contributed
almost all of their C sinks (101.5% for Japan and 98.6%
for South Korea) (Fig. 2a). The minus value for the
change rate of forest area in Japan reveals that the area
of forests has shrunk by a rate of �0.013% yr�1 and
thus exerted a negative influence (�1.5%) on C gain,
acting as a C source over the four decades.
For planted forests (Fig. 2b), areal expansion made a
larger contribution to the C sink than did the change in
biomass density (58.1% vs. 41.9%) in China, with a
change rate of 1.249 and 0.902% yr�1, respectively.
Compared with those in China, Japan’s forests showed
much different patterns: increased biomass density
dominated the C sink with a contribution of 91.1%
(d = 1.235% yr�1) and the areal expansion only contrib-
uted 8.9% (a = 0.120% yr�1) of the C sink.
In contrast to planted forests, increased biomass den-
sity of natural forests (Fig. 2b) in China was a greater
contributor to the C sink than was areal expansion
(87.0% vs. 13.0%), with d and a of 0.217 and
0.032% yr�1, respectively. In Japan, increased biomass
density was responsible for all the C sink (123.9%),
while the area of natural forests has shrunk by 6.4%
over the last 40 years (a = �0.110% yr�1) (also, see
Table 3).
We calculated the change rates of forest area and bio-
mass density and their relative contributions to the C
sink for each period for the three countries (Table S3).
In general, the change rate (m, or C sink) of the total C
stock tended to increase in China, but decrease in Japan
and South Korea, suggesting that the C sink strength
increased in China’s forests, but declined in the other
two countries. For example, for all forests in China, the
m value increased from 0.173% yr�1 during the 1970s–1980s to 0.650% yr�1 during the 1990s–2000s, whereas
it decreased from 1.030% yr�1 to 0.731% yr�1 in Japan
and from 3.521% yr�1 to 2.089% yr�1 in South Korea,
respectively (Table S3). However, this trend was not
very evident in the different periods for planted and
natural forests because of their contrasting patterns of
changes in forest area and biomass density.
Discussion
Forest C sinks in East Asia and the relative contributionsof forest area and biomass density
Over the last four decades, East Asia’s forests have
functioned as a persistent C sink, with a peak of 95.5 Tg
C yr�1 in the 2000s (Table 2). This sink was attributed
to increased C stocks in China, Japan, and South Korea;
however, the mechanisms underlying the C sinks in
these three countries were quite different.
In China, areal expansion and forest regrowth (i.e.,
increase in biomass density) were the major contribu-
tors to this C sequestration and have made a respective
contribution of 60.0% and 40.0% to the C sink for all for-
ests (Fig. 2a; Table S3). Among a total of 1426 Tg C
sequestration within China’s forests, planted and natu-
ral forests have almost equal contributions (703 and 723
Tg C, respectively) (Tables 2 and 3), but were driven by
different mechanisms (Fig. 2b). For planted forests,
areal expansion and biomass density made a respective
contribution of 58.1% and 41.9% to the C sink (Fig. 2b).
During the study period, 90% of the forest area incre-
ment was from planted forests, mainly because of the
implementation of national afforestation and reforesta-
tion projects since the 1970s (Fang et al., 2001; Lei,
2005). As a result, the area of planted forests dramati-
cally increased from 16.44 9 106 ha to 36.15 9 106 ha
in the 2000s, and its proportion to the total forest area
Table 3 Forest area, C stocks, and C densities for planted and natural forests in China and Japan from the 1970s to the 2000s
Period
Planted forests Natural forests
Area
(106 ha)
C stock
(Tg C)
C density
(Mg C ha�1)
Area
(106 ha)
C stock
(Tg C)
C density
(Mg C ha�1)
China
1970s 16.44 249 15.1 110.87 4470 40.3
1980s 23.47 418 17.8 108.22 4467 41.3
1990s 27.95 584 20.9 108.11 4811 44.5
2000s 36.15 952 26.3 113.04 5193 45.9
Net change 19.71 703 11.2 2.17 723 5.6
Japan
1970s 9.61 346 36.0 14.22 608 42.8
1980s 10.23 497 48.6 13.56 676 49.9
1990s 10.34 668 64.6 13.26 727 54.8
2000s 10.33 810 78.4 13.31 805 60.5
Net change 0.72 464 42.4 �0.91 197 17.7
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
FOREST BIOMASS C SINKS IN EAST ASIA 2025
increased from 12.9% to 24.2% in the 2000s (Table 3).
Meanwhile, the regrowth of these young forests also
made a significant contribution to the C gain: the bio-
mass C density of planted forests increased by 11.2 Mg
C ha�1, from an initial density of 15.1 Mg C ha�1 to
26.3 Mg C ha�1 in the 2000s. For natural forests, how-
ever, forest area had a slight increase (2% increment),
but the biomass C density increased remarkably, with a
net gain of 5.6 Mg C ha�1 (13.9%). Therefore, regrowth
of existing forests was found to be the dominant factor
related to C sequestration (87.0% vs. 13.0% for biomass
density vs. area) (Fig. 2b).
Japan’s forest is the second largest C sink with a total
C sink of 661 Tg C over the four decades. However, for-
est area was reduced by 0.18 9 106 ha, indicating that
increased biomass density contributed the entire C sink
for all forests in Japan (Fig. 2a; Tables 2 and S3). Within
Japan’s forests, over 70% of the total biomass C accu-
mulation (464 Tg C) was derived from planted forests
(Table 3). During the study period, biomass C density
of planted forests increased by 42.4 Mg C ha�1 and
the area of planted forests slightly increased by
0.72 9 106 ha (Table 3). Therefore, the regrowth of
planted forests dominated this large C sink with a con-
tribution of 91.1% (Fig. 2b). Despite a decrease
(0.91 9 106 ha) in forest area over the four decades,
total biomass accumulation of 197 Tg C was found in
natural forests. Therefore, the C sink was due entirely
to the regrowth of natural forests, with a net increase of
17.7 Mg C ha�1 of biomass C density during the study
period (Fig. 2b; Table 3).
In South Korea, total forest biomass C stocks
increased by 189 Tg C over the four decades mainly
due to the regrowth of existing forests. There was a net
increase in biomass C density of 30.3 Mg C ha�1, or 3.6
times, from an initial density of 8.4 Mg C ha�1 to a den-
sity of 38.6 Mg C ha�1 in the 2000s. As a result,
increased biomass density was largely responsible for
this C sink (98.6%) and areal expansion made a small
contribution (1.4%) due to a slight increase in total
forest area over the four decades (0.11 9 106 ha or
2% increment) (Fig. 2a; Tables 2 and S3).
In contrast, forests in both North Korea and Mongo-
lia acted as C sources because of deforestation, but the
mechanisms causing the C loss were different in these
two countries. In North Korea, land-use change (con-
verting forests to croplands) and harvest of firewood
were major causes of the decrease in forest area (Lee,
2006), while in Mongolia, the combined effects of tim-
ber cutting, forest fires, pests, and diseases had
resulted in the decrease in forest area and biomass C
density (United Nations Environmental Programme
and Mongolian Ministry of Nature and Environment,
2002).
Factors affecting C sink strength among the countries
As shown in Tables 2 and 3, China’s forest has been the
largest C sink (1426 Tg C) over the last four decades,
followed by that of Japan (661 Tg C) and South Korea
(189 Tg C). Compared with China’s much larger forest
area, however, forests in Japan and South Korea
showed greater C sink strength (C sink per area), with
0.35, 0.93, and 1.01 Mg C ha�1 yr�1 in China, Japan,
and South Korea, respectively. This may be attributed
to two major factors: forest age structure and growth
conditions. We discuss these factors below, focusing on
the forests of China and Japan because information was
not available for South Korea.
First of all, the age structures of forests (especially for
planted forests) are much different in the two countries.
In Japan, large-scale plantation and restoration of natu-
ral forests had been conducted since the late 1950s and
early 1960s (after World War II) (Japan Agency of For-
estry, 2000), while afforestation campaigns have been
occurring in China since the end of 1970s (Fang et al.,
2001; Xiao, 2005). As a result, Japan’s forests are about
20 years older than China’s forests, suggesting that
Japan’s forests are mostly in the middle- to premature-
aged growing stage in which trees grow fast, while for-
ests in China are young- to mid-aged stands. Although
we do not have detailed information on forest age for
each study period for both countries, we have some data
to support this. In China, national inventories report
timber volume for each age class for some forest types
and forests were divided into five age classes: young,
middle, premature, mature, and overmature-aged clas-
ses (Xiao, 2005). In this classification, the age span
changes with forest types, but at the national level, this
could be generalized as: young- (<20 years), mid- (20–35 years, or 20–40 years), premature- (35–60 years), and
mature-aged forests (>60 years) (for practically, we
combined mature and overmature-aged classes into a
single mature-aged class for comparison of the two
countries). In China’s planted forests in 2000, the area of
young-, mid-, premature-, and mature-aged forests was
40.2%, 37.2%, 13.7%, and 8.9% of the total forest area,
respectively (China State Administration of Forestry,
2005). In comparison, the respective numbers were
12.8%, 35.0%, 43.7%, and 8.6% (Japan Agency of For-
estry, 2003), suggesting that a majority of forest stands
were in the mid- and premature-aged classes in Japan.
The younger age structure of China’s forests likely
contributed to lower biomass C densities and smaller C
sink strength when compared with Japan’s forests.
Table 3 shows this clearly. The area in planted forests
in China increased by 19.71 9 106 ha over the
study period, from 16.44 9 106 ha in the 1970s to
36.15 9 106 ha in the 2000s; likewise, the area of natural
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
2026 J . FANG et al.
forests increased by 2.17 9 106 ha. In comparison, the
area of Japan’s plantations fluctuated between
10.23 9 106 ha and 10.34 9 106 ha during the 1980s–2000s, and the area of natural forests showed a slight
decrease (Table 3). With such changes in forest age
structure, China’s forests have much lower biomass C
density than that of Japan’s forests. For example, bio-
mass C density of planted forests in China was only
15.1 Mg C ha�1 in 1970s and 26.3 Mg C ha�1 in the
2000s, while that in Japan was 36.0 and 78.4 Mg C ha�1,
respectively.
Growing conditions (or site quality) differ consider-
ably among East Asian countries. Japan has a typical
oceanic climate, with abundant precipitation and warm
temperature that favor the relatively fast growth for
forests as compared with China and other countries
(Kira, 1991; Fang et al., 2005, 2010). Consequently, bio-
mass density of both planted and natural forests in
Japan generally increases faster than that in the other
countries, even at the same forest ages. Because we do
not have direct measurements of growing conditions
and because remotely sensed NDVI data can be a surro-
gate to indicate integrative growing conditions (Potter
et al., 1993; Field et al., 1995; Fang et al., 2003), we used
the NDVI time series data set to compare integrative
growing conditions for forests among the different
countries. Specifically, we explored possible causes of
the large biomass C density and high productivity of
Japan’s forests relative to the other countries. In gen-
eral, a large NDVI value and a positive NDVI trend
over time imply good site quality and favorable grow-
ing conditions for forests.
Figure 3 shows interannual variation in growing sea-
son NDVI (May to September) of forested areas in
China, Japan, South Korea, and North Korea (data for
Mongolia were not available). Table 4 lists statistics for
the NDVI attributes. Japan had the largest 30 years
averaged NDVI (0.672 units), followed by South Korea
(0.638), China (0.606), and North Korea (0.583)
(Table 4). The NDVI trends also showed a similar order
as did the averaged NDVI (but Japan and South Korea
showed a similar value of the trend, or 9.59 9 10�4 vs.
9.61 9 10�4). Together, these suggest that Japan has the
best growing conditions for forests, followed by South
Korea, China, and North Korea. This order is the same
as that of biomass C density and C sink (Table 2), sug-
gesting that NDVI and its change over time can not
only indicate the growing conditions for forests but also
act as good measures to show biomass C density and
vegetation production (or C sink strength). Note that
the NDVI in North Korea did not exhibit an increasing
trend (R2 = 0.000, P = 0.938) and coincidently did not
show an increase in biomass C density (ranging from
36.1 to 36.8 Mg C ha�1) over the last 40 years.
Implications of forest C sinks in East Asia
Although we estimated the changes in forest biomass C
accumulation in East Asia over the last four decades,
we could not estimate the total C budget for this region
because we lacked the estimates for the four other
important C pools of the forest system: dead wood, lit-
ter, soil organic C, and harvested wood products (Pan
et al., 2011). Here, we use the ratios of different C pools
in US forests to make an approximate account for the C
budget of the whole forest sector in East Asia. Similar
to forest of the United States, those of East Asia have
experienced a long history of forest clearing, agricul-
tural expansion, and subsequent abandonment; cur-
rently, forests are still recovering from such activities
(Perlin, 1991; Brown et al., 1997; Fang et al., 2005; Li
et al., 2010; Pan et al., 2011). The ratio of net change
among different C pools of the forest sector in the Uni-
ted States was 0.49: 0.11: 0.01: 0.02: 0.37 for living vege-
tation: dead wood: litter: soil organic C: harvested
forest products (Woodbury et al., 2007). By applying
these ratios to our data, we obtained an average C sink
rate of 136.5 Tg C yr�1 for the whole forest sector in
East Asia over the four decades.
Table 4 Statistics for NDVI attributes over 30 years between
1982 and 2011 for forested areas in East Asian countries
Country Mean � SD
Trend
(910�4) R2 P value
China 0.606 � 0.124 7.49 0.163 0.027
Japan 0.672 � 0.124 9.59 0.164 0.027
North Korea 0.583 � 0.065 0.26 0.000 0.938
South Korea 0.638 � 0.069 9.61 0.173 0.022
Fig. 3 Interannual variation in growing season NDVI of for-
ested area for four countries (China, Japan, North Korea, and
South Korea) in East Asia from 1982 to 2011. Other than North
Korea, all countries show a significant NDVI increase. Mongolia
was not included because data were not available.
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
FOREST BIOMASS C SINKS IN EAST ASIA 2027
We used national fossil-fuel CO2 emissions data pro-
vided by the Oak Ridge National Laboratory of the
United States Department of Energy (Boden et al., 2012)
to estimate average CO2 emissions from fossil fuels in
each country and the entire region over the last four
decades (Table 5). The C sink rate averaged 47.5, 22.0,
and 6.3 Tg C yr�1 in living forests of China, Japan, and
South Korea over the last four decades, respectively,
which offsets 6.3, 7.5, and 8.9% of total fossil-fuel CO2
emissions of the respective countries over the study
period (Table 5). However, over the same period, living
biomass of forests in North Korea and Mongolia
released 3.6 and 5.4 Tg C yr�1, equaling to 9.2% and
270.0% of total fossil-fuel CO2 emissions of these two
countries, respectively. Overall, the net C sink (66.9 Tg
C yr�1) in living biomass in East Asian forests has off-
set 5.8% of the total fossil-fuel CO2 emissions in this
region over the last 40 years. If the four other C pools
mentioned above were also included in the account,
then the forest sector in this region could offset 11.8%
of its contemporary fossil-fuel CO2 emissions.
Uncertainty of estimations
The most important uncertainty may come from the
quality of forest area and timber volume data from the
forest inventories and FAO. For China, Japan, and
South Korea, forest inventory data used in our study
specified the precision requirement in the sampling
design: in China, the forest area and timber volume pre-
cision were required to be >90% in almost each province
(>85% in Beijing, Shanghai, and Tianjin) (Xiao, 2005); in
Japan, the error of timber volume in the inventories at
the national level was <3% (Japan Agency of Forestry,
2000); and in South Korea, the error in total timber
volume at the provincial and national levels was <5%(Li et al., 2010). For Mongolia, data on forest area and
timber volume for 1990–2010 were collected from sev-
eral official documents (Enkbayar, 1997; GOM, 2004,
2009). Although the quality of the data source was
ranked moderate by FAO, we could still obtain reason-
able information. For North Korea, the main source of
data was the publication ‘State of the Environment
2003-DPR Korea’ by the United Nations Environment
Programme. Although the quality of the data source for
the country was ranked high by FAO, large uncertainty
in estimating forest area and timber volume still existed.
Uncertainty may also arise from the estimation of
national biomass stocks using the BEF method. The R
square values of the BEF equations used to convert tim-
ber volume to biomass for most dominant tree species
or forest types were above 0.8, 0.9, and 0.7 for China,
Japan, and South Korea, respectively (Table S2). The
empirical relationships with high R square values in
China were applied to convert timber volume to bio-
mass at the provincial level for North Korea and Mon-
golia because of the lack of detailed information on
forest area and timber volume for major forest types in
these two countries. Therefore, the method used in this
study has relatively high precision. Previous studies
have reported that the estimation error of biomass
stocks at the national level should be less than 3% in
China (Fang et al., 1996) and ranged from �2.8% to
4.3% in Japan (Fang et al., 2005).
In conclusion, forest biomass C accumulation in East
Asia has increased from 36.4 Tg C yr�1 in the 1970s to
95.5 Tg C yr�1 in the 2000s, with an average of 66.9 Tg
C yr�1 over the last four decades. Among the five coun-
tries, China, Japan, and South Korea each contributed
to the region’s forest C sink by 71.1%, 32.9%, and 9.4%,
respectively, although the mechanism driving the
increased C differed among the countries. In China,
areal expansion was the major contributor to the C
sinks for all (60.0%) and planted (58.1%) forests, while
increased biomass density was the major contributor
for natural forests (87.0%). In Japan, increased biomass
density dominated the contribution of C sink for all
(101.5%), planted (91.1%), and natural (123.8%) forests.
In South Korea, increased biomass density contributed
98.6% of the total forest C sink during the study period.
Relative to these three countries, shrinking forests in
both North Korea and Mongolia caused a C loss at an
average rate of 9.0 Tg C yr�1, equal to 13.4% of the total
region’s forest C sink.
Acknowledgements
This publication was a product of the A3 foresight program oncarbon cycle in terrestrial ecosystems in East Asia jointly sup-ported by the three funding agencies, National Natural ScienceFoundation of China (NSFC), Japan Society for the Promotion ofScience (JSPS), and National Research Foundation of Korea(NRF). We are grateful to the subject editor and four anony-mous reviewers for their insightful comments and suggestions
Table 5 The percentage of the national fossil-fuel CO2 emis-
sions offset by East Asia’s living forests during the 1970s–
2000s
Region
C sink
(Tg C yr�1)
Fossil-fuel
emission
(Tg C yr�1)*
Offset
percent
(%)
China 47.5 749 6.3
Japan 22.0 292 7.5
North Korea �3.6 39 �9.2
South Korea 6.3 71 8.9
Mongolia �5.4 2 �270.0
East Asia 66.9 1153 5.8
*The mean fossil-fuel emission during 1970s–2000s.
© 2014 John Wiley & Sons Ltd, Global Change Biology, 20, 2019–2030
2028 J . FANG et al.
on an earlier version of this manuscript. We thank X. Zhao forassistance in NDVI data analysis. We also thank Benjamin O.Knapp for his editing on the manuscript. This study was alsopartly supported by the National Basic Research Program ofChina on Global Change (2010CB950600), National Natural Sci-ence Foundation of China (31321061 and 31330012), StrategicPriority Research Program of the Chinese Academy of Sciences(XDA05050300), and State Forestry Administration of China.
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Supporting Information
Additional Supporting Information may be found in theonline version of this article:
Table S1. Forest area and its proportion in 2010 for eachcountry in East Asia. Data are provided by FAO (2010a).Table S2. Parameters of the BEF equation for major foresttypes in China, Japan, and South Korea.Table S3. Change rates of forest area, biomass C density,and total C stock, and their relative ratio to the changes oftotal C stock (C sink) for all, planted, and natural forests inChina and Japan, and for all forests in South Korea, from1970s to 2000s.
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