Soil Carbon
The Department of the Environment and Heritage, through the Australian
Greenhouse Office’s National Carbon Accounting System (NCAS), has worked with
State and Territory Governments and CSIRO to develop a capacity for analysing
changes in soil carbon. This is done primarily for the purpose of reporting greenhouse
gas emissions.
The NCAS soil carbon program is a hybrid of inventory and process model. The
inventory is used to define a ‘base’ condition with climate and management input
being primary drivers of modelled change to the base condition. The steps in
developing this capability were:

Provide a base map of soil type, clay content and soil carbon reflecting a
substantially unmodified condition. This required the development of a map
of boundaries of soil types to which clay and soil carbon content were
attributed (Webbnet Land Resource Services Pty. Ltd., 2002). While the
analytic measurement of clay is generally consistent, the analytic methods
(e.g. wet, chemical, dry combustion etc.) will yield different carbon contents.
To standardise the soil carbon maps, correlations of results to a single method
equivalent (dry combustion) were derived (Skjemstad et al., 2000).

Calibration and verification of the model was done in two stages. Initially
model calibrations for the RothC model (as used in the NCAS FullCAM model)
(Richards and Evans, 2004) were completed against a selection of research
sites (Skjemstad and Spouncer, 2002). Model sensitivity was then completed
and is reported in Janik et.al (2002). Subsequent verification was completed
across 88 ‘paired sites’ (before and after a land use change) across Australia
(Skjemstad and Spouncer, 2003).

Land use management data was compiled, corresponding to the mapped
soils units, to allow for the modelling of the handling of organic matter that
may or may not be incorporated in soil carbon. Data on crop growth was
also collected (Swift and Skjemstad, 2002).

Land cover change data is drawn from analysis of 14 (1972-2005) Landsat
Satellite images in time-series (Caccetta et al., 2003).

Monthly 1km ‘grids’ of climate conditions since 1970 was prepared to provide
the climate drivers to the model (Kesteven et al., 2004)
The national model is run at 25m resolution in monthly time-steps, taking input data
from the soils mapping, land use and management, land cover change and climate
datasets. Results are reported in terms of both greenhouse gas emissions and carbon
stock changes. Reporting is done through the National Greenhouse Gas Inventory
prepared under the Intergovernmental Panel on Climate Change Guidelines and
submitted under the United Nations Framework Convention on Climate Change.
Reporting categories include:






Forest land remaining Forest land
Land converted to Forest
Forest land converted to Cropland
Forest land converted to Grassland
Grassland remaining Grassland
Cropland remaining Cropland
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Testing has shown that it is only the Forestland conversion to Cropland and Grassland
that have significant impacts on soil carbon stocks. Australia reports ‘0’ emissions
against other categories. The Forest land conversion to both Cropland and Grassland
includes all deforestation on these land uses that has occurred since 1972, when the
land cover change record commenced. Table 1 shows the cumulative areas and soil
carbon stock changes in these areas of land since 1990.
Table 1
Year
Area Reported
C Stock Change in Soil
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
10,835,879
11,293,601
11,719,649
12,124,093
12,514,305
12,870,910
13,224,008
13,548,446
13,859,607
14,177,365
14,557,985
14,938,784
15,259,340
15,556,871
15,882,379
4,928,797
2,004,488
2,897,911
1,556,567
1,102,088
2,168,372
2,866,663
1,480,221
5,158,127
2,464,017
3,387,580
508,677
1,365,802
2,967,336
1,423,024
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Biomass
The Department of the Environment and Heritage, through the Australian
Greenhouse Office’s National Carbon Accounting System (NCAS), has worked with
the Australian National University and CSIRO to develop a capability for continental
monitoring of biomass stock and stock change (Richards and Brack, 2004). Biomass
stock changes are then used to calculate the associated carbon stock changes and
greenhouse gas emissions.
The analysis is through a method that is a hybrid of remote sensing, ecosystem
modelling and empiricism.

The age of the area of forest extent and change at a 25m resolution area
monitored through remote sensing (Landsat satellite) time-series (Caccetta et
al., 2003). Fourteen national snapshots are available to define the current
sequences of change. This information can also be used to determine the
age of forest areas, and therefore their rate of biomass accumulation.

Forest areas by growth stage are linked to a time-series forest productivity
index that determines the forest ability to remove carbon from the
atmosphere via photosynthesis (Kesteven et al., 2004).

The pattern of biomass accumulation and maximum biomass carrying
capacity has been determined from available measurement data (Raison et
al., 2003).

Crop biomass is modelled using crop yield data that is converted to whole
plant estimates, and then subjected to crop management practices (e.g.
burning of stubble).
The national model is run at 25m resolution in monthly time-steps, taking input data
from the soils mapping, land use and management, land cover change and climate
datasets. Results are reported in terms of both greenhouse gas emissions and carbon
stock changes. Reporting is done through the National Greenhouse Gas Inventory
prepared under the Intergovernmental Panel on Climate Change Guidelines and
submitted under the United Nations Framework Convention on Climate Change.
Reporting for biomass change is done under the categories of Forest land remaining
Forest land, Land converted to Forest land, Forest land converted to Grassland and
Forest land converted to Cropland. Table 2 shows the changes in C stocks, and area
affected as accumulative total since 1990.
Table 2
Year
Area Reported
C Stock Change in Biomass
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
26,620,219
27,160,165
27,660,214
28,134,809
28,594,277
28,999,534
29,401,285
29,774,377
30,148,603
30,529,425
36,643,929
30,978,206
29,234,740
28,115,046
27,175,962
23,926,484
24,693,800
25,674,246
25,772,642
24,136,950
3
2000
2001
2002
2003
2004
30,988,634
31,448,020
31,888,435
32,269,017
32,665,985
24,033,414
25,858,923
26,711,204
22,291,346
26,275,041
References
Caccetta, P.A., Bryant, G., Campbell, N.A., Chia, J., Furby, S., Kiiven, H.J., Richards,
G.P., Wallace, J., Wu, X., 2003. Notes on Mapping and Monitoring Forest Change in
Australia Using Remote Sensing and Other Data. In, 30th International Symposium of
Remote Sensing and the Environment, Hawaii, October 2003.
Janik, L., Spouncer, L., Corell, R., Skjemstad, J., 2002. Sensitivity Analysis of the
Roth-C Soil Carbon Model (Ver. 26.3 Excel © ). National Carbon Accouting System
Technical Report 30, Australian Greenhouse Office.
Kesteven, J., Landsberg, J., URS Consulting, 2004. Developing a national forest
productivity model. National Carbon Accounting System Technical Report No.23,
Australian Greenhouse Office, Canberra, Australia.
Raison, R.J., Keith, H., Barrett, D., Burrows, W., Grierson, P.F., 2003. Spatial
Estimates of Biomass in 'Mature' Native Vegetation. National Carbon Accouting
System Technical Report 44, Australian Greenhouse Office, Canberra, Australia.
Richards, G., Brack, C., 2004. A continental biomass stock and stock change
estimation approach for Australia. Australian Forestry 67, 284-288.
Richards, G., Evans, D., 2004. Development of a carbon accounting model (FullCAM
Vers. 1.0) for the Australian continent. Australian Forestry 67, 277-283.
Skjemstad, J., Spouncer, L., 2002. Estimating Changes in Soil Carbon Resulting from
Changes in Land Use. National Carbon Accounting System Technical Report No. 36,
Australian Greenhouse Office, Canberra, Australia.
Skjemstad, J., Spouncer, L., 2003. Integrated Soils Modelling for the National Carbon
Accounting System. National Carbon Accounting System Technical Report No. 36,
Australian Greenhouse Office, Canberra, Australia.
Skjemstad, J., Spouncer, L., Beech, T.A., 2000. Carbon Conversion Factors for
Historical Soil Carbon Data. National Carbon Accounting System Technical Report
No. 15. Australian Greenhouse Office, Canberra, Australia.
Swift, R., Skjemstad, J., 2002. Agricultural Land Use and Management. National
Carbon Accounting System Technical Report 13, Australian Greenhouse Office,
Canberra, Australia.
Webbnet Land Resource Services Pty. Ltd., 2002. Pre-clearing Soil Carbon Levels in
Australia. National Carbon Accounting System Technical Report No. 12, Australian
Greenhouse Office, Canberra.
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