Estimation of emissions from deforestation .1 Disturbance matrix documentation

Land-use conversion, particularly from forests to non-forests, can involve significant transfers of carbon among pools. The immediate impacts of land conversion on the carbon stocks for each forest stratum can be summarized in a matrix, which describes the retention, transfers, and releases of carbon in and from the pools in the original land-use due to conversion (Table 2.4.2). The level of detail on these transfers will depend on the decision of which carbon pools to include, which in turn will depend on the key category analysis (see Table 2.3.2 in Section 2.3). The disturbance matrix defines for each pool the proportion of carbon that remains in the pool and the proportions that are transferred to other pools. Use of such a matrix in carbon estimating will ensure consistency of estimating among carbon pools, as well as help to achieve higher

39Although in theory the stock-difference approach could be used to estimate stock changes in both mineral soils and organic soils, this approach is unlikely to be used in practice due to the expense of measuring soil carbon stocks. The IPCC has adopted different methodologies for soil carbon, which are described below.

accuracy in carbon emissions estimation. Even if all the data in the matrix are not used, the matrix can assist in estimation of uncertainties.

Table 2.4.2. Example of a disturbance matrix for the impacts of deforestation on carbon pools (Table 5.7 in the AFOLU Guidelines). Impossible transfers are blacked out. In each blank cell, the proportion of each pool on the left side of the matrix that is transferred to the pool at the top of each column is entered. Values in each row must sum to 1.

To From

Above-ground biomass

Below-ground biomass

Dead

wood Litter Soil organic matter

Harvested wood products

Atmo-sphere

Sum of row (must equal 1) Abovegrou

nd biomass Belowgroun d biomass Dead wood Litter Soil organic matter

2.4.5.2 Changes in carbon stocks of biomass

The IPCC methods for estimating the annual carbon stock change on land converted to a new land-use category include two components:

 One accounts for the initial change in carbon stocks due to the land conversion, e.g., the change in biomass stocks due to forest clearing and conversion to say cropland.

 The other component accounts for the gradual carbon loss during a transition period to a new steady-state system and the carbon gains due to vegetation regrowth, if any.

For the biomass pools, conversion to annual cropland and settlements generally contain lower biomass and steady-state is usually reached in a shorter period (e.g., the default assumption for annual cropland is 1 year). The time period needed to reach steady state in perennial cropland (e.g., orchards) or even grasslands, however, is typically more than one year. The inclusion of this second component will likely become more important for future monitoring of the performance of REDD+ as countries consider moving into a Tier 3 approach and implement an annual or bi-annual monitoring system.

The initial change in biomass (live or dead) stocks due to land-use conversion is estimated using a stock-difference approach in which the difference in stocks before and after conversion is calculated for each stratum of land converted. Equation 2.4.3 (below) is the equation presented in the AFOLU Guidelines for biomass.

Equation 2.4.3

Initial Change in Biomass Carbon Stocks on Land Converted to New Land-Use Category (Stock-Difference Type Method)

 

 B B A  CF

C





 



 

Where:

∆CCONV =initial change in biomass carbon stocks on land converted to another land-use category (t C yr^-1)

BAFTERi =biomass stocks on land type i immediately after conversion (t dry matter/ha) BBEFOREi =biomass stocks on land type i before conversion (t dry matter/ha)

∆Ai = area of land type i converted (ha) CF = carbon fraction (t C /t dm) i = stratum of land

The Tier 1 default assumption for biomass and dead organic matter stocks immediately after conversion of forests to non-forests is that they are zero, whereas the Tier 2 method allows for the biomass and dead organic matter stocks after conversion to have non-zero values. Disturbance matrices (e.g., Table 2.4.2) can be used to summarize the fate of biomass and dead organic matter stocks, and to ensure consistency among pools.

The biomass stocks immediately after conversion will depend on the amount of live biomass removed during conversion. During conversion, aboveground biomass may be removed as timber of fuelwood, burned and the carbon emitted to the atmosphere or transferred to the dead wood pool, and/or cut and left on the ground as deadwood; and belowground biomass may be transferred to the soil organic matter pool (See Ch 2.3.5).

Estimates of default values for the biomass stocks on croplands and grasslands are given in the AFOLU Guidelines in Table 5.9 (croplands) and Table 6.4 (grasslands). The dead organic matter (DOM) stocks immediately after conversion will depend on the amount of live biomass killed and transferred to the DOM pools, and the amount of DOM carbon released to the atmosphere due to burning and decomposition. In general, croplands (except agroforestry systems) and settlements will have little or no dead wood and litter so the Tier 1 ‘after conversion’ assumption for these pools may be reasonable for these land uses.

A two-component approach for biomass and DOM may not be necessary in REDD+

estimating. If land-use conversions are permanent, and all that one is interested in is the total change in carbon stocks, then all that is needed is the carbon stock prior to conversion, and the carbon stocks after conversion once steady state is reached. These data would be used in a stock difference method (Equation 2.4.1), with the time interval the period between land-use conversion and steady-state under the new land use.

2.4.5.3 Changes in soil carbon stocks

The IPCC Tier 2 method for mineral soil organic carbon is basically a combination of a stock-difference method and a gain-loss method (Equation 2.4.4). (The first part of Equation 2.4.4 [for ∆CMineral] is essentially a stock-difference equation, while the second part [for SOC] is essentially a gain-loss method with the gains and losses derived from the product of reference carbon stocks and stock change factors). The reference carbon stock is the soil carbon stock that would have been present under native vegetation on that stratum of land, given its climate and soil type.

Equation 2.4.4

Annual Change in Organic Carbon Stocks in Mineral Soils

 

D