10113_2016_948_MOESM1_ESM

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10113_2016_948_MOESM1_ESM
Electronic Supplementary Material
Table S1. Variable Definition
Variable
SOC density
Description
Density of soil organic carbon in the layer of
top 30 cm (kg/m2)
Source
Global Soil Organic Carbon
Estimates (Hiederer and Köchy
2012)
Land use database generated by the
Chinese Academy of Sciences (Liu
and Buheaosier 2000; Liu et al.
2003; Liu et al. 2010)
Land use
Land use classes for four time periods (the
mid-1980s, the mid-1990s, the late 1990s, the
middle year of the 2000‒10 decade, including
paddy, dry farmland, woodland, dense
grassland, medium grassland, sparse grassland,
water area, urban land, and unused land
Soil class
Default IPCC soil classes (Batjes 2010),
including high activity (HAC, 79%), low
activity (LAC, 9%), sandy (SAN, 9%); the
remaining miscellaneous units are lumped
together in a class named “others” (OTR, 2%)
Harmonized World Soil Database
version 1.1
(FAO/IIASA/ISRIC/ISS-CAS/JRC
2009)
Climate
classification
Six major climate zones, including desert
(BW, 18%), steppe (BS, 8%), warm temperate
with fully humid (Cf, 14%), warm temperate
with dry winter (Cw, 17%), snow (D, 24%),
and tundra (ET, 19%)
Köppen-Geiger climate
classification map (Kottek et al.
2006)
Note: SOC density, land use, and soil class are available at a spatial resolution of 1 km (~30 arc-second). We resampled the original
climate data from 0.5 degree to 30 arc-second using the nearest neighbor assignment.
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Table S2. The Classification System of Land Use Category in This Study
Land use category
Paddy
Dry farmland
Woodland
Dense grassland
Medium grassland
Sparse grassland
Water area
Urban
Unused land
Explanations
Land equipped for irrigation to grow aquatic crops, such as rice paddy, locus root, etc.
Land used for growing non-aquatic crops, including rainfed uplands, land equipped for irrigation
to grow dry crops, and land used for growing vegetables.
Natural or planted forests with canopy covers greater than 30%; land covered by trees less than 2
meters high with a canopy cover greater than 40%; land covered by trees with canopy cover
between 10% and 30%; land used for tea-gardens, orchards and nurseries.
Natural and improved grasslands and rangeland, with coverage greater than 50%.
Natural and improved grasslands with coverage between 20% and 50%.
Natural grassland with coverage between 5% and 20%.
Land covered by natural water bodies or land with facilities for irrigation and water reservation,
including rivers, canals, lakes, permanent glaciers, beaches and shorelines, and bottomland.
Land used for urban and rural settlements, industry, and transportation.
The rest of all other lands, including sandy desert, Gobi desert, salinized land, bare soil, bare rock,
and tundra.
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Table S3. Summarized Changes in Land Use Area and SOC Stock
Land use
1985
Paddy
Dry farmland
Woodland
Grass_D
Grass_M
Grass_S
Water
Urban
Unused
Total
45.6
133.3
234.0
98.1
111.3
91.5
12.9
4.5
193.7
925.1
Land area (Mha)
Change
1985–1995 1995–2000
-0.1
0.3
-2.3
5.2
1.9
-3.3
-21.9
21.4
-14.9
13.5
32.0
-32.6
-0.3
0.3
1.2
0.2
4.3
-5.0
-
2000–2005
-0.0
1.4
2.9
-6.6
0.6
-3.4
-0.6
1.5
4.2
-
SOC stock for the 0–30 cm layer (PgC)
1985
Change
1985–1995 1995–2000 2000–2005
1.976
0.013
0.017
-0.000
5.210
-0.074
0.214
0.068
10.399
0.085
-0.147
0.126
5.308
-1.246
1.265
-0.303
5.634
-1.024
0.903
0.011
4.165
1.885
-1.893
-0.103
0.633
-0.013
0.010
-0.033
0.164
0.045
0.004
0.061
6.492
0.320
-0.361
0.178
39.982
-0.010
0.013
0.004
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Figure S2: Spatial distribution of land use in China, 1985
Figure S1: Spatial distribution of farmland changes, 1985‒2005
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Figure S4: The IPCC soil class map
Source: Harmonized World Soil Database (version 1.1)
(FAO/IIASA/ISRIC/ISS-CAS/JRC 2009)
Figure S3: Spatial distribution of topsoil carbon density in
China
Source: Global Soil Organic Carbon Estimates (Hiederer and
Köchy 2012)
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Figure S5: Köppen-Geiger Climate Classification
Figure S6: Boxplots of SOC density by land use, climate
classification, and soil type Classification map
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Heilongjiang
Inner Mongolia
Inner Mongolia
Loess Plateau
Figure S7: Estimated cost of restoration of dense grassland
Figure S8: Estimated cost of converting dry farmland to dense
grassland
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Description of original soil and climate data
The IPCC soil class map is derived from HWSD version 1.1. Soils are classified into
12 categories in HWSD, including high activity (HAC), low activity (LAC), sandy (SAN),
land ice (GG), organic (ORG), spodic (POD), rock outcrops (RK), salt flats (ST),
volcanic (VOL), wetland (WET), water bodies (WR), and no data (ND).
Boundary of climate zones used in this study is from Köppen-Geiger climate
classification map. Kottek et al. (2006) update the map using temperature data from
Climatic Research Unit of the University of East Anglia and precipitation data from the
Global Precipitation Climatology Centre for the period 1951–2000 on a regular 0.5
degree latitude/longitude cell (approximately 55 × 55 km at the equator). Kottek et al.
(2006) identified five broad climate regions: equatorial (A), arid (B), warm temperate (C),
snow (D), and polar (E), which are further divided into 31 subclasses subjected to
subsequent precipitation and temperature conditions.
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Methods for calculating the variance of SOC change estimates
Disaggregate estimates of SOC change:
For each land unit i, SOC density change induced by land use conversion from j to k can
be expressed as
,
where
, representing the stock change factor; s is the index of soil-
climate block. For convenience, we denote the variance of
as
. By definition,
, which can be estimated from the
empirical model.
Assumptions: For each land unit i, error of SOC changes caused by land use conversion
is associated with the estimated stock change factors δjks. The error is uncorrelated with
errors of other land units and is independent across time period. This assumption is
consistent with the assumption made in the empirical estimation in the paper.
For the period of 1985‒1995,
is a non-stochastic variable and
variance of
is a nonlinear function of random term
. The
can be estimated by using the delta method:
,
The variance of SOC density in 1995 equals
.
For the period of 1995‒2000,
is a nonlinear function of random terms
and
. Applying the delta method
yields
.
The variance of SOC density in 2000 is equal to
.
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Likewise, for the period of 2000‒2005,
,
and
.
Aggregate estimates of SOC change:
We denote the aggregate change in SOC stock induced by land use conversion from j to k
as
.
For the period of 1985‒1995,
.
By definition,
,
which can be directly estimated from the empirical results.
For the period of 1995‒2000,
.
Likewise, for the period of 2000‒2005,
.
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