Spatial + Temporal Scope [MGD Sections]

REDD+ Activities [MGD Sections]

Forest Definition [MGD Sections]

Carbon Pools [MGD Sections]

5.2.3   Soil organic carbon Previous topic Parent topic Child topic Next topic

IPCC provides Tier 1 methods for estimating CO2 emissions and removals on mineral soils associated with the transitions from
  • forest to non-forest land uses that sum to deforestation,
  • other land uses to forest.
The Tier 1 method assumes that mineral soil carbon stock density on land that has been forest for at least 20 years will be equal to the mineral soil carbon stock density under native vegetation for the relevant climate and ecosystem type and that where there are transitions to or from another land use, the mineral soil carbon stock density on the other land use in question will be that value times a relative carbon stock change factor depending on the land use, the level of management and the climate. Following transition between land uses carbon is emitted or removed over a 20 year transition period at which time the new carbon value is assumed to be achieved.
At Tier 1 IPCC assumes that mineral soil carbon stocks do not change for land remaining in forest land use. For drained organic soils IPCC provides emission/removal factors which depend on climate and ecosystem and will produce emissions so long as the land is drained and organic carbon remains. The relevant tables in the IPCC guidance are summarised in Table 15 and Table 16.
Where soil-related emissions are key (Chapter 2, Section 2.2.3) countries should aim to apply higher Tier methods. Developing estimates of temporal change in soil carbon stocks using repeated field sampling is challenging. This is because soil carbon stocks are large and spatially variable so that it is almost impossible to detect changes which are usually small (generally only a few % of the total stock) unless intensive and expensive sampling is undertaken. Instead, for Tier 1 default reference carbon stocks (i.e. carbon stocks under native vegetation and default soil C change factors (multipliers capturing the effect of management practices and land uses) are applied. At Tier 2, the method is the same, but default values are replaced by country-specific values. Tier 3 methods employ detailed modelling of soil C dynamics, requiring detailed calibration and validation data and large and long-term investment for their development.
Whatever approach is used, soil maps are required in combination with soil carbon change factors or more complex models. Some maps may already be held by Agriculture and Forestry agencies, but their spatial resolution may need to be enhanced based on further soil survey before they can be applied to REDD+ activities. For many inaccessible tropical forest areas soil maps may not exist, or have poor spatial resolution. This is especially so for peat and other carbon-rich soils, which are important sources of carbon emissions due to biological oxidation or fire following forest disturbance. Barthelmes et al., (2015) provide valuable advice on how existing maps combined with remote sensing which can provide useful vegetation and topographic surrogates for soils, and new ground surveys can be effectively integrated to map organic soils under tropical forests at scales useful for management decision making.
At Tier 1, the IPCC 2013 Wetlands Supplement Opens in new window provides default emission/removal factors for non-CO2 greenhouse gases associated with the processes shown in Table 16 below:
Under some conditions nitrous oxide (N2O) can be released from soils. Emissions can be either direct (derived from local soil management processes) or indirect (resulting either from atmospheric deposition of N or inputs of N from leaching or run-off from elsewhere). Emissions of N2O are increased following the addition of N fertilizers, or by any forest management practices that increase the availability of inorganic N in soils. IPCC(1) provides guidance on how to estimate emissions of N2O from managed soils which is cross-referenced in the guidance in GPG2003 (see Table 17 below).
N2O emissions would not usually represent a key category for forests unless lands have had heavy application of N fertilizer; this combined with the complexity of estimating emissions of N2O means most countries will use Tier 1 approaches unless they have undertaken replicated field studies to demonstrate that the IPCC default factors are inappropriate for their circumstances.
The activity data needed to implement the Tier 1 approach are the quantity of N fertilizer used and other organic amendments added, and an estimate of the area of land to which the management activity has been applied. The IPCC provides Tier 1 emissions factors for both direct and indirect emissions from the identified area of management (i.e. activity data).

Table 15: IPCC emissions and removal factors associated with soil carbon stocks

2003 Good Practice Guidance
2006 Guidelines
2013 Wetlands Supplement
Mineral Soil Organic Carbon reference carbon stocks
Relative carbon stock change factors
Drained and rewetted organic soil emission/removal factors
Change due to fires
Soil carbon stocks in mangroves
Notes: a) emission/removal factors in Table 2.2 of the wetlands supplement Opens in new window are for estimating emissions of CO2 from waterborne carbon arising from drained and rewetted organic soils. b) Removals and emissions factors in Table 3.1 of the wetlands supplement Opens in new window are for rewetted organic soils. c) This table provides undisturbed soil carbon densities. Carbon in extracted soil is assumed by default to be oxidized in the year of extraction.

Table 16: IPCC emission and removal factors associated with non-carbon dioxide emissions from the soil

Location in 2013 Wetlands Supplement
CH4 emissions and removals from drained and rewetted inland organic soils
N2O emissions and removals from drained inland organic soils
CO and CH4 emissions and removals from fires on drained inland organic soils
CH4 and N2O from mangroves
N2O from aquaculture in mangroves
CH4 from rewettted inland wetland mineral soils

Table 17: IPCC emission and removal factors associated with direct and indirect nitrous oxide emissions from soil

2003 Good Practice Guidance
2006 Guidelines
Emission/removal factors related to direct N2O emissions from managed soils
1.25 % of applied N
Emission/removal factors related to indirect N2O emissions from managed soils