Journal of Arid Environments (2002) 50: 205–218
doi:10.1006/jare.2001.0902, available online at http://www.idealibrary.com on
Carbon storage in grasslands of China
Jian Ni%wz
%
Max Planck Institute for Biogeochemistry, Carl Zeiss Promenade 10, P.O.
Box 100164, D-07701 Jena, Germany
wLaboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese
Academy of Sciences, Xiangshan Nanxincun 20, 100093 Beijing, China
(Received 15 September 2000, accepted 26 June 2001)
Carbon storage in grasslands of China was estimated by the carbon density
method and based on a nationwide grassland resource survey finished by
1991. The grasslands in China were classified into 18 types, which are
distributed mostly in the temperate region and on the Tibetan Plateau, and
scattered in the warm-temperate and tropical regions. Based on the median
estimate, vegetation, soil and total carbon storage of grasslands in China were
3?06, 41?03 and 44?09 Pg C, respectively. Vegetation had low carbon storage
and most carbon was stored in soils. Of the four types of regions that have
grasslands, alpine region (54?5%) and temperate region (31?6%) hold more
than 85% of the total grassland carbon (in both vegetation and soils) in
China. Considering specific types within these two regions, three grassland
types, alpine meadow (25?6%), alpine steppe (14?5%) and temperate steppe
(11%) constituted more than half of all carbon stored in China’s grasslands.
In general and regardless of regional vegetation types, steppes (38?6%) and
meadows (38?2%) made up more than 2/3 of total grassland carbon. The
carbon storage in alpine grasslands may have a significant and long-lived
effect on global C cycles. This study estimated more carbon storage in
vegetation and less in soils than previous studies. The differences of grassland
carbon between this study and two previous studies were due probably to
four reasons, i.e. different estimation methods, different classification systems
of grasslands, different areas of grasslands, and different carbon densities.
China’s grasslands cover only 6–8% of total world grassland area and have 9–
16% of total carbon in the world grasslands. They make a big contribution to
the world carbon storage and may have significant effects on carbon cycles,
both in global and in arid lands.
# 2002 Elsevier Science Ltd.
Keywords: carbon storage; carbon density; vegetation area; soil carbon;
alpine grasslands; temperate grasslands; China; arid lands
Introduction and literature
Grasslands are one of the most widespread vegetation types worldwide, covering 15
million km2 in the tropics and a further 9 million km2 in temperate regions, together
z Corresponding author. Tel: +49 3641 64 3743; Fax: +49 3641 64 3789; E-mail: [email protected]
0140-1963/02/020205 + 14 $35.00/0
# 2002 Elsevier Science Ltd.
206
J. NI
nearly one-fifth of the world’s land surface (Scurlock & Hall, 1998). Natural
grasslands both in tropical and in temperate regions play a significant role in the
regional climate and global carbon cycle (Hall & Scurlock, 1991; Hall et al., 1995;
Sala et al., 1996). Carbon storage and carbon sinks in the vegetation and soils of
grasslands in temperate and tropical regions were previously studied based upon
different data and methods at a regional to global scale, particularly within the context
of global change (e.g. Lieth, 1978; Hall & Scurlock, 1991; Long & Hutchin, 1991;
Thornley et al., 1991; Parton et al., 1993, 1995; Fisher et al., 1994, 1995; Hall et al.,
1995; Tate et al., 1995; Scurlock & Hall, 1998). However, carbon storage may have
been underestimated, especially in the soils and in the tropics (Scurlock & Hall,
1998). Recent studies of grassland carbon suggested that natural grass ecosystems
might be responsible for a substantial proportion (as much as 20% or more) of total
terrestrial production, and cautiously proposed that these biomes might already
constitute an annual sink of about 0?5 Pg carbon (Scurlock & Hall, 1998).
Grasslands in China cover vast, continuous areas of the northern temperate regions
with a continental arid climate, the Tibetan Plateau at very high elevations, and small,
disjunct areas of the warm temperate and tropical regions controlled by the monsoon
climate (Editorial Committee for Vegetation of China, 1980; Hou et al., 1982).
Several estimates of grassland distribution are now available at the national level, i.e.
355 million ha (DAHV & CISNR, 1994) and 399 including 354 million ha of major
17 grassland types (DAHV and GSAHV, 1996) according to the national grassland
resource survey, 360 million ha based on the Map of Grassland Resources in China at
1:4M scale (CISNR, 1996), 349 million ha by the Map of Land Use in China at 1:4M
scale (Wu, 1991), and 406 million ha by the Vegetation Map of China at 1:4M scale
(Hou et al., 1982). The areas of grasslands in China are similar regardless of the data
source, about 40% of the total territory of China (Chen & Fischer, 1998). The vast
area and wide distribution of Chinese grasslands implies that they would have
significant effects on regional climate and regional to continental carbon cycles.
There is relatively little research on carbon storage and carbon cycle in grasslands of
China (Fang et al., 1996; Feng et al., 2001; Ni, 2001). Some studies present carbon
estimates from all vegetation types in all of China, but they only included the carbon
storage in grasslands at the national level (Fang et al., 1996; Ni, 2001). Total biomass
(above- and below-ground) estimates of Chinese grasslands were calculated by Fang
et al. (1996) based on areal extent, the range of forage yield and above-below-ground
biomass ratio. However, carbon of grasslands estimated by the biomass method is not
completely accurate because of the lack of information on the biomass component of
grassland vegetation, especially below-ground biomass that was estimated only by the
ratio of above- to below-ground biomass (Fang et al., 1996). Ni (2001) also calculated
the carbon storage of Chinese ecosystems including grasslands using the carbon
density method, but the classification of grasslands derived from 1960 to 1970s
investigations is very simple. On the other hand, strong human activities in the last two
decades have had an impact on Chinese grasslands (distributions and areas). These
may influence the accuracy of the carbon estimation (Ni, 2001).
The areal extent of vegetation is a critical factor influencing the estimate of carbon
in terrestrial ecosystems, regardless of the method used. Ni (2001) has demonstrated
that different spatial resolutions of vegetation, and subsequently different estimated
vegetation areas could impact on the calculations of carbon storage within ecosystems.
Differences in vegetation classification also affect the calculation of area and
determination of carbon density (Ni, 2001). After the two phases of long-term
investigation of grassland resources in China from 1949 to 1978 and from 1979 to
1990s (Chen & Fischer, 1998), more detailed classification and more accurate
estimates of the areal coverage of grasslands in China are now available (DAHV &
CISNR, 1994; DAHV & GSAHV, 1996). Data on Grassland Resources in China
provided detailed descriptions and data on grasslands based on a nationwide grassland
CARBON STORAGE IN GRASSLANDS OF CHINA
207
resource survey in 1991 (DAHV & CISNR, 1994). Therefore, it is now possible to use
the carbon density method in combination with the improved classification scheme
and new estimates of grassland area to more accurately calculate carbon storage in
Chinese grasslands. Then, the ‘new and better’ carbon storage estimate of China’s
grasslands will be compared to previous studies, with a specific focus on temperate
and alpine grasslands.
Material and methods
Grasslands in China
Data on grassland type, total area, utilizable area, forage yield, dominant species and
distributions (Table 1) were obtained from a specialized statistical book Data on
Grassland Resources of China (DAHV & CISNR, 1994). These data were collected and
sorted systematically from all Chinese counties and provinces (autonomous regions
and municipalities) excluding Taiwan, based on a 10-year nationwide grassland
resource survey completed in 1991.
There are four grassland classification schemes in China, including (a) 18
vegetation types in the national grassland survey (DAHV & CISNR, 1994), (b) more
than 50 types in the Map of Grassland Resources in China (CISNR, 1996), (c) three
types in the Map of Land Use in China (Wu, 1991), and (d) more than 40 types in the
Vegetation Map of China (Hou et al., 1982). Chen & Fischer (1998) digitized and
simplified the Map of Grassland Resources in China at 1 : 4M scale (CISNR, 1996).
They used a 17-type grassland classification scheme, excluding the tropical dry shrubtussock with savanna, which covered only a very small area (Chen & Fischer, 1998).
In the current work, the DAHV & CISNR classification scheme of grasslands (18
types) was used (Table 1) for the following reasons. First, the 18 grassland types have
enough information to characterize Chinese grasslands. Second, they match the
grassland areas and other characteristics in the national grassland survey (DAHV &
CISNR, 1994). Finally, they are simplified from the more comprehensive Map of
Grassland Resources in China (CISNR, 1996).
The grasslands of China are generally and mainly distributed in the temperate and
alpine regions in north and west China, respectively. The temperate meadow–steppe,
steppe, desert–steppe, as well as part of lowland and mountain meadow are
distributed in the northern region (Table 1). Some extend to north-eastern (temperate
meadow) and north-western (temperate steppe–desert and desert) regions. The
Tibetan Plateau has unique alpine meadow–steppe, steppe and desert–steppe types,
which are quite different from the temperate meadow, steppe and desert (Table 1). In
east and south parts of China, the warm-temperate and tropical tussocks, shrubs and
savannas are sparsely distributed, and deciduous and evergreen forests dominate
(Table 1).
Carbon density
Biomass carbon densities from Olson et al. (1983) and soil carbon densities from
Zinke et al. (1984) were used in this paper to give a range of low, median and high
carbon densities for every grassland type (Table 2). These values were multiplied by
the utilizable areas to obtain the carbon storage of grasslands in China (Table 2).
Areas of sediment, road, bare land and river have been excluded from the estimate of
utilizable area (DAHV & CISNR, 1994), and therefore more accurately reflect the
total utilizable grassland areas in China.
Utilizable
area (ha)
Forage yield
(kg1 ha)
Ecosystem complexes
(Olson et al., 1983)
Dominants
Temperate
meadow–
steppe
14,519,331
12,827,411
1465
Cool grassland
Temperate
steppe
41,096,571
36,367,633
889
Cool grassland
Temperate
desert–steppe
18,921,607
17,052,421
455
Cool grassland
6,865,734
6,011,528
307
41,623,171
35,439,220
284
Very cold Tibet
meadows and
parklands
Cool grassland
Leymus chinense, Stipa
baicalensis, Filifolium
sibiricum, Carex, Festuca,
Artemisia, Lespedeza
Leymus chinense, Stipa
grandis, Stipa Krylovii, Stipa
bungeana, Agropyron
cristatum, Cleistogenes
squarrosa, Artemisia frigida,
Artemisia, Caragana, Ephedra
Stipa klemenzii, Stipa brevifolia, Stipa glareosa, Stipa
goboca, Artemisia, Caragana
Stipa purpurea, Stipa capillacea, Festuca, Carex
9,566,006
7,752,078
195
Alpine desert
Alpine
meadow–
steppe
Alpine steppe
Alpine
desert–steppe
Stipa purpurea, Festuca subsessiliflora var. basiplumosa,
Poa, Artemisia, Carex
Stipa glareosa, Stipa purpurea, Caragana, Artemisia, Ceratoides compacta
Distribution
North-east
and northwest China
North China
North and
north-west
China
West China
West China
West China
J. NI
Area (ha)
Grassland
208
Table 1. Information on grasslands in China (from DAHV & CISNR, 1994). Grassland was defined as coverage of steppe community greater
than or equal to 5%; canopy index of tree community less than or equal to 0?3; and canopy index of shrub community less than or equal to 0?4.
The grassland area was summarized by areas measured from the grassland map at a 1:50,000 or 1:100,000 scale, differing from region to region.
The utilizable area equals total grassland area minus areas of sediment, road, bare land and river. The forage yield is a mean value of the 10-year
production, estimated by measuring above-ground standing crops in fresh weight in the field during the highest yield period in summer and
autumn. The fresh weight was converted to dry weight based on grassland type-based dry/fresh weight ratio (DAHV & CISNR, 1994). Every
grassland classification was assigned to an ecosystem complex (from Olson et al., 1983) in order to obtain their carbon densities in vegetation and
soils (Olson et al., 1983; Zinke et al., 1984). More details can be found in Data on Grassland Resources of China (DAHV & CISNR, 1994)
10,673,418
9,140,926
465
Cool semi-desert
Temperate
desert
45,060,811
3,060,4131
329
Desert and semidesert
Alpine desert
7,527,763
5,592,765
117
Warm-temperate tussock
6,657,148
5,853,667
1643
Sand desert: scrub/
herb or barren
Warm/hot grassland
Warmtemperate
shrub-tussock
11,615,910
9,773,518
1769
Warm/hot grassland
with relatively more
shrub, trees
Tropical tussock
14,237,195
11,419,999
2643
Warm/hot grassland
Stipa glareosa, Salsola abrotanoides, Ceratoides latens,
Reaumuria soongarica,
Caragana, Artemisia
Sympegma regelii, Iljnia regelii, Ephedra, Nitraria sibirica,
Haloxylon, Artemisia, Caragana, Zygophyllum, Calligonum, Halocnemum
strobilaceum
Ceratoides compacta, Ajania,
Artemisia
Spodiopogon sibiricus, Bothriochloa ischaemum, Themeda
triandra var. japonica, Eulalia
pallens, Carex, Artemisia
Bothriochloa ischaemum, Themeda triandra var. japonica,
Miscanthus sinensis, Vitex
negundo var. heterophylla,
Ziziphus jujuba, Lespedeza,
Carex, Artemisia
Miscanthus floridulus,
Miscanthus sinensis, Heteropogen contortus, Cymbopogon
distans, Imperata cylindrica
var. major, Arundinella hirta,
Ischaemum ciliare, Dicranopteris dichotoma
North-west
China
North-west
China
West China
Central east
and central
south China
Central east
and central
south China
Central south
and south
China
CARBON STORAGE IN GRASSLANDS OF CHINA
Temperate
steppe–desert
209
210
Table 1Fcontinued.
Grassland
Area (ha)
Utilizable
area (ha)
Forage yield
(kg ha)
Tropical
17,551,276
shrub-tussock
13,447,569
2527
Tropical dry
863,144
shrub-tussock
with savanna
Lowland
25,219,621
meadow
639,429
2719
21,038,409
1730
16,718,926
14,923,439
1648
Alpine meadow
63,720,549
58,834,182
882
Swamp
2,873,812
2,253,714
2183
Warm/hot grassland
with relatively more
shrub, trees
Dominants
Miscanthus floridulus, Miscanthus sinensis, Heteropogen
contortus, Imperata cylindrica
var. major, Arundinella hirta,
Ischaemum ciliare, Rhododendron, Melastoma
Warm/hot grassland
Heteropogen contortus, Pinus
with relatively more
yunnanensis, Acacia
shrub, trees
farnesiana, Flacourtia indica
Heath and moorland,
Calamagrostis angustifolia,
maritime scrub with
Achnatherum splendens,
meadows
Sanguisorba officinalis, Carex,
Deyeuxia angustifolia, Aeluropus littoralis var. sinensis
Maritime/montane grass Festuca ovina, Deyeuxia arundinacea, Arundinella chenii,
Stipa aliena, Carex, Poa
Kobresia pygmaea, Kobresia
Very cold Tibet
meadows and parklands humilis, Kobresia capillifolia,
Kobresia schoenoides, Kobresia
littledalei, Festuca rubra,
Polygonum macrophyllum,
Polygonum viviparum, Carex,
Rhododendron
Carex muliensis, Phragmites
Swamps/shrub/herb
marshes
australis, Scirpus triqueter,
Kobresia
Distribution
Central south
and south
China
South China
Whole China
J. NI
Mountain
meadow
Ecosystem complexes
(Olson et al., 1983)
North and
west China
West and
south-west
China
North, west
and central
China
Table 2. Carbon density (from Olson et al., 1983; Zinke et al., 1984) and carbon storage (low: L, median: M and high: H) in vegetation and
soils of grasslands in China. Every grassland type was assigned to an ecosystem complex (see Table 1) described in Olson et al. (1983), and then
the carbon density in vegetation and soils of each ecosystem complex at three levels (low, median and high) was obtained from Olson et al. (1983)
and Zinke et al. (1984). The carbon densities multiplied by the utilizable area (see Table 1) give the carbon storage of grasslands in China
Grassland
M
H
Vegetation
carbon
storage (Pg C)
L
M
H
9?5
11?2
13?3
L
M
H
Soil carbon
storage
(Pg C)
Total carbon
storage
(Pg C)
L
M
H
L
M
H
0?13 0?19 0?26
1?22
1?44
1?71
1?35
1?63 1?96
1
1?5
2
0?5
0?5
0?5
0?5
0?5
0?3
0?2
0?02
0?5
1
1
1
1
1
0?8
0?6
0?4
0?05
1
1?6
2
2
4
2
1?5
1
1
0?2
2
3
11?6
7?2
15?7
14
14
7
4?1
14
10
10
12?3
8?7
18?2
17
17
8
6?2
17
13
13
13
10?2
20?7
19
19
9
8?3
19
14
14
0?18
0?09
0?03
0?18
0?04
0?03
0?06
0?00
0?03
0?10
0?73
0?34
0?24
0?71
0?12
0?09
0?31
0?01
0?12
0?29
4?22
1?23
0?94
4?96
1?09
0?64
1?25
0?78
0?59
0?98
4?47
1?48
1?09
6?02
1?32
0?73
1?90
0?95
0?76
1?27
4?73
1?74
1?24
6?73
1?47
0?82
2?54
1?06
0?82
1?37
4?40
1?31
0?97
5?14
1?12
0?67
1?32
0?78
0?61
1?08
4?84
1?65
1?15
6?38
1?38
0?79
2?02
0?95
0?82
1?43
0?5
1
1
1
1?6
1?6
2
3
3
11
11
6?7
14
14
7?3
15
15
7?9
0?06 0?11 0?23
0?13 0?22 0?40
0?01 0?01 0?02
1?26
1?48
0?04
1?60
1?88
0?05
1?71
2?02
0?05
1?31
1?61
0?05
1?71 1?94
2?10 2?42
0?06 0?07
1
0?5
0?5
1?5
0?64
1?5
1
1
3
1?15
2
2
4
6
2?37
9?5
15?7
15?7
11?6
11?02
11?2
18?2
18?2
12?3
13?16
13?3
20?7
20?7
13
14?73
0?21
0?07
0?29
0?03
1?67
0?36
0?17
0?06
0?35
0?06
0?05
0?12
0?00
0?06
0?16
0?32
0?15
0?59
0?07
3?05
5?46
2?08
1?48
7?44
1?59
0?91
2?85
1?07
0?94
1?66
CARBON STORAGE IN GRASSLANDS OF CHINA
L
0?42 2?00 2?36 2?80 2?21 2?67 3?22
0?30 2?34 2?72 3?09 2?42 2?87 3?39
2?35 9?24 10?71 12?18 9?53 11?30 14?53
0?14 0?26 0?28 0?29 0?30 0?34 0?43
7?08 34?52 41?03 46?37 36?18 44?09 53?44
211
Temperate
meadow–steppe
Temperate steppe
Temperate desert–steppe
Alpine meadow–steppe
Alpine steppe
Alpine desert–steppe
Temperate steppe-desert
Temperate desert
Alpine desert
Warm-temperate tussock
Warm-temperate
shrub-tussock
Tropical tussock
Tropical shrub-tussock
Tropical dry shrub-tussock
with savanna
Lowland meadow
Mountain meadow
Alpine meadow
Swamp
Mean carbon density
and total carbon
Soil carbon
density
(kg m2)
Vegetation
carbon density
(kg m2)
212
J. NI
Results
According to the carbon densities in vegetation and soils (Table 2) and the utilizable
areas (Table1), the low, median and high values of carbon in vegetation, soils and total
carbon storage for each grassland type are given in Table 2. Based on the median
estimate, vegetation, soil and total carbon of grasslands in China were 3?06, 41?03 and
44?09 Pg C, respectively. Vegetation has low carbon storage and most carbon is
stored in soils (Table 2). The alpine meadow has the highest carbon storage both
in vegetation and in soils, covering 25?6% of total carbon in grasslands of China
(Table 2). The alpine steppe (14?5%) and temperate steppe (11%) also have higher
carbon storage (Table 2). Together, these three grassland types make up more than
half of all of the carbon being stored in China’s grasslands. This is due to these three
grasslands having the highest utilizable areas and higher carbon densities (Table 1).
The warm temperate and tropical tussocks as well as swamp, however, have the lowest
carbon because of their small areas and lower carbon densities (Table 2).
In terms of the grassland type, steppe has the highest carbon storage in vegetation
and soils, totaling 17?03 Pg C (38?6%), with meadows storing 16?83 Pg C (38?2%).
These two types constitute more than 2/3 of the total carbon stored in grasslands of
China (Fig. 1). Other three grassland types, desert, tussock and swamp have a carbon
storage of only 10?22 Pg C, less than 1/3 of the total carbon of grasslands in China
(Fig. 1). Based on regional grassland distribution, the alpine region has the highest
carbon storage, 24?03 Pg C, making up 54?5% of the total carbon (Fig. 2; Table 2).
The temperate region also has a large area and therefore a high carbon storage of
13?94 Pg C (31?6% of total carbon) (Fig. 2). Together, these two regions constitute
more than 85% of all the carbon stored in grasslands of China (Fig. 2). In warmtemperate and tropical regions, however, the grasslands have very low carbon storage
(Fig. 2).
Discussion
Grasslands play a very important role in modeling the biospheric feedbacks of
atmospheric CO2 increase and climate changes (Hall et al., 1995; Thornley &
Cannell, 1997). It has long been suggested that the majority of the ‘missing sink’ for
carbon in the global CO2 balance may be located in temperate and tropical regions
(e.g. Tans et al., 1990). Therefore, the role of grasslands, with large area both in
tropics and in temperate regions, should not be overlooked in global biogeochemical
cycles (Hall & Scurlock, 1991; Thornley et al., 1991; Parton et al., 1993, 1995; Fisher
et al., 1994, 1995; Hall et al., 1995; Tate et al., 1995; Scurlock & Hall, 1998).
In China, grasslands are mostly distributed in temperate regions (the semi-arid and
arid north China) and in alpine regions (the high and cold west China) (Hou et al.,
1982; DAHV & CISNR, 1994). The largest proportion of carbon is stored in alpine
and temperate grasslands (Table 2; Fig. 2). The importance of temperate grassland
carbon storage is well known (e.g. Thronley et al., 1991; Hall et al., 1995; Tate et al.,
1995; Sala et al., 1996), but the importance of alpine carbon storage is less
appreciated. In grassland ecosystems carbon is stored mostly in soils, where C
turnover times of the bulk soil carbon are relatively long (Hall et al., 1995; Tate et al.,
1995; Matthews, 1997). 95% of the carbon stored in alpine grasslands of China are
stored in soils (Table 2), which is 55?6% of the total carbon storage in China’s
grassland soils (Fig. 2). Similar to high-latitude tundra ecosystems (Hobbie et al.,
2000), the high elevation of alpine regions results in low temperature and low evapotranspiration in alpine region. Therefore, soil carbon is difficult to decompose and
mostly remains in soils for a long time. If climate change and CO2 increase were to
would impact on soil carbon, especially in cooler regions (Hall et al., 1995), changes of
CARBON STORAGE IN GRASSLANDS OF CHINA
213
Figure 1. Utilizable areas and median carbon stored in grasslands of China by grassland
type. Steppe includes temperate meadow–steppe, temperate steppe, temperate desert–steppe,
alpine meadow–steppe, alpine steppe and alpine desert–steppe. Desert includes temperate
steppe–desert, temperate desert and alpine desert. Tussock includes warm-temperate tussock,
warm-temperate shrub-tussock, tropical tussock, tropical shrub-tussock and tropical dry
shrub-tussock with savanna. Meadow includes lowland meadow, mountain meadow and alpine
meadow. Swamp includes swamp grassland.
alpine grassland carbon storage may have a significant and long-lived effect on global
C cycles.
Fang et al. (1996) and Ni (2001) calculated the grassland carbon of China based on
the biomass and organic carbon matter method and the carbon density method,
respectively, when they estimated carbon storage of terrestrial ecosystems in China
(Table 3). Compared to the carbon storage of grasslands in this paper, considering the
meadow and tussock as steppe ecosystems (Table 3), the sort for vegetation carbon is
Fang o this paper o Ni and that for soil carbon is this paper oNi oFang. In total,
the carbon storage in grasslands of China estimated by this study was lower than those
calculated by Ni (2001) and Fang et al. (1996). The differences of grassland carbon
between this study and two previous studies are probably due to the following four
reasons.
First, the classification of grasslands was quite different. Fang et al. (1996) used a
very coarse classification of eight types (Table 3). Ni (2001) classified the grasslands
214
J. NI
Figure 2. Utilizable areas and median carbon stored in grasslands of China by region.
Temperate region includes temperate meadow–steppe, temperate steppe, temperate desert–
steppe, temperate steppe–desert, temperate desert, lowland meadow and swamp. Warmtemperate region includes warm-temperate tussock and warm-temperate shrub-tussock?
Tropical region includes tropical tussock, tropical shrub-tussock and tropical dry shrub-tussock
with savanna. Alpine region includes alpine meadow–steppe, alpine steppe, alpine desert–
steppe, alpine desert, mountain meadow and alpine meadow.
into 11 types (Table 3) based on the vegetation map of China (Hou
et al., 1982). In this study, however, 18 grassland types were used based on the
nationwide grassland survey (DAHV & CISNR, 1994). The differences in
classification result in the differences in area and carbon density, subsequently carbon
stored in grasslands of China.
Second, authors used the different areas of grasslands, i.e. 569?9 million ha (Fang
et al., 1996), 405?87 million ha (Ni, 2001) and 355?3 million ha (298?97 for the
utilizable area) in this study. This is a very important factor that influences
the estimation of carbon (Ni, 2001). The live vegetation area of grasslands of
Fang et al. (1996) was derived from statistics of land use resources and an agricultural atlas of China from the 1980s. The soil area was calculated from all soils
in which grasslands are able to grow (Fang et al., 1996). Clearly, the live grassland
area was not accurate enough and soil area was overestimated. Thus, Fang’s
grassland area is much higher than those of other calculations (Table 3).
The grassland area from Ni (2001) was calculated from The Vegetation Map of China
CARBON STORAGE IN GRASSLANDS OF CHINA
215
Table 3. Areas and carbon storage in Pg C of grasslands in China estimated by
different authors
Grassland
Total
Area Vegetation Soils
carbon carbon
(106 ha) carbon
Steppe*
430?66
1?02
63?44
Desert
Swamp
Subtotal
128?24
11?00
569?90
0?01
0?20
1?23
3?52
7?78
74?74
Steppe z
220?11
2?66
32?78
Desert}
152?57
Swamp11
33?19
Subtotal
405?87
1?12
0?87
4?66
16?86
4?08
53?72
Steppe
115?45
1?20
15?83
Meadow
Tussock
Subtotal
94?80
41?13
251?38
1?05
0?55
2?81
Desert
Swamp
Subtotal
45?34
2?25
298?97
0?18
0?07
3?06
Estimated
method
Reference
64?46 Biomass and organic Fang et al.,
carbon matterw
(1996)
3?53
7?98
75?97
35?45 Carbon density,
median estimatez
17?98
4?95
58?38
Ni (2001)
This study
15?78
5?56
37?17
17?03 Carbon density,
median estimate
16?83
6?11
39?98
3?58
0?28
41?03
3?76
0?34
44?09
*Meadow–steppe, typical steppe, desert–steppe, alpine steppe, tussock, savannas and grasslands in desert
area.
zArid shrublands/steppe, temperate savannas (grass-scrub), temperate steppe, temperate deserted steppe,
alpine steppe and alpine meadows.
}Temperate desert, tundra and alpine desert.
8Bogs/mires of cool or cold climate, wetlands, swamps and marshes.
wFang et al. (1996) classified the grasslands in China into eight types: Meadow-steppe, typical steppe,
desert–steppe, alpine steppe, tussock, savannas and grasslands in desert regions, desert, and swamp. They
used the biomass multiply areas to product vegetation carbon, and the soil organic carbon content, areas,
mean depth and mean voluminal weight to product the soils carbon.
zNi (2001) used the same method as this study (carbon densities multiply vegetation areas) to obtain the
vegetation and soils carbon in grasslands of China, but the grassland classification and carbon density of
every type were quite different.
(Hou et al., 1982). This value was derived from the 1970s grassland distributions and
therefore potentially overestimates the actual grassland area compared with today
because of long-term human disturbances. The utilizable area used in the current
study excluded areas of sediment, road, bare land and river from the total grassland
area (DAHV & CISNR 1994). It is more accurate than other areal calculations such as
the statistical data from provinces (Fang et al., 1996) and the potential area of
grasslands from the vegetation map of China (Ni, 2001). If the relatively accurate
grassland area of this study (355?3 million ha) was used with methods of Fang et al.
(1996) and Ni (2001) to recalculate the carbon storage in grasslands of China, the
new estimates would both be lower than those estimated by the two previous studies.
In other words, Fang et al. (1996) and Ni (2001) overestimated the carbon storage in
China’s grasslands.
Third, the biomass field measurements had many uncertainties and were not
accurate because they were averaged from only a few samples in grasslands (Fang
et al., 1996). Specifically, the measurements of below-ground biomass were very few
and were calculated by the ratio of above- to below-ground biomass (Fang et al.,
216
J. NI
1996). This approximation may lead to very low values of vegetation carbon in
grasslands of China estimated by Fang et al. (1996), compared with the other two
estimates (Tables 2 and 3).
The fourth cause of differences in carbon storage estimates relates to carbon
density. In this paper and also in Ni (2001), carbon densities in vegetation
and soils were estimated using common values from global ecosystems (Olson
et al., 1983; Zinke et al., 1984). Although these values have general global averages
and are used largely by ecologists studying carbon of terrestrial ecosystems,
they are not perfectly suited to Chinese grasslands. However, more accurate
carbon densities in vegetation and soils of Chinese grasslands have not been
available till now. Only soil organic carbon of some grassland types in some places
was reported (Fang et al., 1996; Feng et al., 2001). The common carbon
densities worldwide, therefore, are still the useful values in estimating grassland
carbon at present.
In summary, Fang et al. (1996) underestimated the vegetation carbon
and overestimated the soil carbon of grasslands in China. Ni (2001) also
overestimated both the vegetation and soil carbon. The two previous studies
also overestimated the total carbon storage in grasslands of China. The estimation
of carbon in this study might be more credible because of more accurate grassland areas and more reasonable vegetation classification scheme than the two
previous studies.
What proportion do China’s grasslands contribute to the world grassland carbon
storage? It is not easy to answer this question because estimates of the amount of
grassland carbon worldwide vary, specifically with respect to soil carbon (Hall et al.,
1995; Scurlock & Hall, 1998). The grassland ecosystem complexes (cold and
warm grass/shrub, desert and semidesert, swamps, marshes and bogs/mires,
alpine ecosystems) have 50?4 Pg C in vegetation in the area of 5155 million ha,
based on the carbon densities (Olson et al., 1983). The temperate thorn steppe,
cool temperate steppe, tropical desert bush, warm desert, cool desert and
wetlands have 435?7 Pg C in soils in the area of 3510 ha, based on soil surveys
(Post et al., 1982). From these estimates, China’s grassland carbon is 6?1% of
the world grassland live carbon, 9?4% of the global grassland soil carbon, and 9?1%
of total grassland carbon. By comparison, China’s grasslands constitute 5?8–8?5%
of world grassland area. Prentice et al. (1993) also estimated the present world
grassland carbon when they modeled global terrestrial carbon storage using the
carbon density method from Olson et al. (1983) and Zinke et al. (1984). The
warm grass/shrub, cool grass/shrub, hot desert and semidesert combined have
27?9 Pg C in vegetation, 250?5 Pg C in soils and 279 Pg C in total carbon, with a
total area of 4160 million ha (Prentice et al., 1993). Using these estimates, carbon
storage in China’s grasslands is 10?9% of the world grassland live carbon, 16?4%
of the world grassland soil carbon and 15?8% of the total grassland carbon in ca.
7?2% of the total world grassland area. Therefore, China’s grasslands cover only 6–8%
of the total world grassland area and have 9–16% of the total carbon in the world
grasslands. They make a big contribution to the world carbon storage and may have
significant effects on carbon cycles, both in global and in arid lands within a global
context.
The research was funded by the National Natural Science Foundation of China (NSFC No.
39970154), the China Ministry of Science and Technology (G1999043507), the Alfried Krupp
von Bohlen und Halbach-Stiftung, the Max-Planck Society (MPS) and the Max-PlanckInstitute for Biogeochemistry (MPI-BGC), Germany. The author would like to thank two
anonymous reviewers for their thoughtful comments and useful information on an earlier
version of the manuscript. Thanks are also due to Dr Karen E. Kohfeld for her improvement of
English language of this paper.
CARBON STORAGE IN GRASSLANDS OF CHINA
217
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