Change in biomass carbon stocks aboveground biomass and belowground biomass

Plant biomass constitutes a significant carbon stock in many ecosystems. Biomass is present in both above-ground and below-ground parts of annual and perennial plants. Biomass associated with annual and perennial herbaceous (i.e., non-woody) plants is relatively ephemeral, i.e., it decays and regenerates annually or every few years. So emissions from decay are balanced by removals due to re-growth making overall net C stocks in biomass rather stable in the long term. Thus, the methods focus on stock changes in biomass associated with woody plants and trees, which can accumulate large amounts of carbon (up to hundreds of tonnes per ha) over their lifespan. Carbon stock change in biomass on Forest Land is likely to be an important sub-category because of substantial fluxes owing to management and harvest, natural disturbances, natural mortality and forest re-growth. In addition, land-use conversions from Forest Land to other land uses often result in substantial loss of carbon from the biomass pool. Trees and woody plants can occur in any of the six land-use categories although biomass stocks are generally largest on Forest Land. For inventory purposes, changes in C stock in biomass are estimated for (i) land remaining in the same land-use category and (ii) land converted to a new land-use category. The reporting convention is that all emissions and removals associated with a land-use change are reported in the new land-use category.

2.3.1.1 Land remaining in a land-use category

Equation 2.3 includes the five carbon pools for which stock change estimates are required. This section presents methods for estimating biomass carbon gains, losses and net changes. Gains include biomass growth in above-ground and below-ground components. Losses are categorized into wood fellings or harvest, fuelwood gathering, and losses from natural disturbances on managed land such as fire, insect outbreaks and extreme weather events (e.g., hurricanes, flooding). Two methods are provided for estimating carbon stock changes in biomass.

The Gain-Loss Method requires the biomass carbon loss to be subtracted from the biomass carbon gain (Equation 2.7). This underpins the Tier 1 method, for which default values for calculation of increment and losses are provided in this Volume to estimate stock changes in biomass. Higher tier methods use country-specific data to estimate gain and loss rates. For all tiers, these estimates require country-specific activity data, although for Tier 1, these data can be obtained from globally-compiled databases (e.g., FAO statistics).

Equation 2.7 Annual change in carbon stocks in biomass

IN LAND REMAINING IN A PARTICULAR LAND-USE CATEGORY (GAIN-LOSS METHOD)

Where:

ACb = annual change in carbon stocks in biomass (the sum of above-ground and below-ground biomass terms in Equation 2.3) for each land sub-category, considering the total area, tonnes C yr-1

ACg = annual increase in carbon stocks due to biomass growth for each land sub-category, considering the total area, tonnes C yr-1 ACl = annual decrease in carbon stocks due to biomass loss for each land sub-category, considering the total area, tonnes C yr-1

The changes in C stock in biomass for land remaining in the same land-use category (e.g., Forest Land Remaining Forest Land) are based on estimates of annual gain and loss in biomass stocks. Countries using any of the three tiers can adopt this method. This method can be used by countries that do not have national inventory systems designed for estimating woody biomass stocks. Default data are provided in land-use category chapters for inventory compilers who do not have access to country-specific data. Worksheets have also been developed using the methods and equations (Annex 1).

The stock-Difference Method requires biomass carbon stock inventories for a given land area, at two points in time. Annual biomass change is the difference between the biomass stock at time t2 and time t1, divided by the number of years between the inventories (Equation 2.8). In some cases, primary data on biomass may be in the form of wood volume data, for example, from forest surveys, in which case factors are provided to convert wood volume to carbon mass units, as shown in Equation 2.8.b.

Co2 Emission Factor Equations

Where:

AC = annual change in carbon stocks in biomass (the sum of above-ground and below-ground biomass

terms in Equation 2.3 ) in land remaining in the same category (e.g., Forest Land Remaining Forest Land), tonnes C yr-1

C t2 = total carbon in biomass for each land sub-category at time t2, tonnes C

C t1 = total carbon in biomass for each land sub-category at time t1, tonnes C C = total carbon in biomass for time t1 to t2

A = area of land remaining in the same land-use category, ha (see note below) V = merchantable growing stock volume, m3 ha-1 i = ecological zone i (i = 1 to n) j = climate domain j (j = 1 to m)

R = ratio of below-ground biomass to above-ground biomass, tonne d.m. below-ground biomass (tonne d.m. above-ground biomass)-1

CF = carbon fraction of dry matter, tonne C (tonne d.m.)-1

BCEFS = biomass conversion and expansion factor for expansion of merchantable growing stock volume to above-ground biomass, tonnes above-ground biomass growth (m3 growing stock volume)-1, (see Table 4.5 for Forest Land). BCEFS transforms merchantable volume of growing stock directly into its above-ground biomass. BCEFS values are more convenient because they can be applied directly to volume-based forest inventory data and operational records, without the need of having to resort to basic wood densities (D). They provide best results, when they have been derived locally and based directly on merchantable volume. However, if BCEFS values are not available and if the biomass expansion factor (BEFS) and D values are separately estimated, the following conversion can be used:

In applying the Gain-Loss or Stock-Difference Methods, the relevant area is clearly the area of land remaining in the relevant category at the end of the year for which the inventory is being estimated. Any other land will be in a conversion category (see Section 2.3.1.2). The length of time that land remains in a conversion category after a change in land use is by default 20 years (the time period assumed for carbon stocks to come to equilibrium for the purposes of calculating default coefficients in the 1996IPCC Guidelines and retained for GPG-LULUCF and used here also, though other periods may be used at higher Tiers according to national circumstances). Under default assumptions therefore land will be transferred from a conversion category to a remaining category after it has been in a given land use for 20 years. Some carbon stock changes will take place in the year of conversion, but nevertheless it is important to be consistent about the period for which land stays in the conversion category or the approaches to land area estimation described in the next Chapter will not work. Stock changes that are completed within 1 year after conversion will be related to the area converted annually and the relevant land areas may need to be treated as a sub-category within the conversion category but nevertheless should remain in the conversion category until the 20 year default or other conversion time period is completed.

The Stock-Difference Method will be applicable in countries that have national inventory systems for forests and other land-use categories, where the stocks of different biomass pools are measured at periodic intervals. The stock-difference method requires greater resources and many countries may not have national inventory systems for forests and other land-use categories. This method is suitable to countries adopting a Tier 3 and in some cases a Tier 2 approach, but may not be suitable for countries using a Tier 1 approach due to limitations of data. It is important to make sure that inventory system generates data on gains and losses of biomass carbon pools.

Either of the above two methods can be used for estimating biomass carbon stock changes for all land categories (e.g., Forest Land Remaining Forest Land, Grassland Remaining Grassland, and Cropland Remaining Cropland) where perennial woody biomass may be present. Figure 2.2 can be used to assist inventory agencies in identifying the appropriate tier to estimate changes in biomass carbon stocks.

Note that some biomass losses can lead to emissions of C other than as CO2, such as biomass consumption and emission as methane (CH4) by termites and wild mammals.2 Default Tier 1 methods for these sources have not been developed, and countries wishing to estimate and report these emissions should develop and employ a Tier 3 approach.

2 CO2 and non-CO2 losses of carbon associated with biomass burning are estimated such that carbon emissions are not double-counted.

Figure 2.2 Generic decision tree for identification of appropriate tier to estimate changes in carbon stocks in biomass in a land-use category.

Figure 2.2 Generic decision tree for identification of appropriate tier to estimate changes in carbon stocks in biomass in a land-use category.

Note:

1: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Note:

1: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

A. methods for estimating change in carbon stocks in

A.1 Estimating annual increase in biomass carbon stocks (Gain-Loss Method), A CG

This is the Tier 1 method that, when combined with default biomass growth rates, allows for any country to calculate the annual increase in biomass, using estimates of area and mean annual biomass increment, for each land-use type and stratum (e.g., climatic zone, ecological zone, vegetation type) (Equation 2.9).

Equation 2.9

Annual increase in biomass carbon stocks due to biomass increment in land remaining in the same land-use category

Where:

ACG= annual increase in biomass carbon stocks due to biomass growth in land remaining in the same land-use category by vegetation type and climatic zone, tonnes C yr-1 A = area of land remaining in the same land-use category, ha GTOTAL= mean annual biomass growth, tonnes d. m. ha-1 yr-1 i = ecological zone (i = 1 to n) j = climate domain (j = 1 to m)

CF = carbon fraction of dry matter, tonne C (tonne d.m.)-1

GTOTAL is the total biomass growth expanded from the above-ground biomass growth (Gw) to include below-ground biomass growth. Following a Tier 1 method, this may be achieved directly by using default values of GW for naturally regenerated trees or broad categories of plantations together with R, the ratio of below-ground biomass to above-ground biomass differentiated by woody vegetation type. In Tiers 2 and 3, the net annual increment (IV) can be used with either basic wood density (D) and biomass expansion factor (BEFi) or directly with biomass conversion and expansion factor (BCEFI) for conversion of annual net increment to above-ground biomass increment for each vegetation type. Equation 2.10 shows the relationships.

Equation 2.10 Average annual increment in biomass Tier 1

Gtotal = Z • (1 + R)} Biomass increment data (dry matter) are used directly

Tiers 2 and 3

Gtotal = • BCEFj • (1 + R)} Net annual increment data are used to estimate GW by applying a biomass conversion and expansion factor

Where:

Gtotal = average annual biomass growth above and below-ground, tonnes d. m. ha-1 yr-1

GW = average annual above-ground biomass growth for a specific woody vegetation type, tonnes d. m.

R = ratio of below-ground biomass to above-ground biomass for a specific vegetation type, in tonne d.m. below-ground biomass (tonne d.m. above-ground biomass)-1. R must be set to zero if assuming no changes of below-ground biomass allocation patterns (Tier 1).

Iv = average net annual increment for specific vegetation type, m3 ha- yr-

BCEFI = biomass conversion and expansion factor for conversion of net annual increment in volume (including bark) to above-ground biomass growth for specific vegetation type, tonnes above-ground biomass growth (m3 net annual increment)-1, (see Table 4.5 for Forest Land). If BCEFI values are not available and if the biomass expansion factor (BEF) and basic wood density (D) values are separately estimated, then the following conversion can be used:

Biomass Expansion Factors (BEFI)3 expand merchantable volume to total above-ground biomass volume to account for non-merchantable components of increment. BEFI is dimensionless.

Estimates for BCEFI for woody (perennial) biomass on non-forest lands such as Grassland (savanna), Cropland (agro-forestry), orchards, coffee, tea, and rubber may not be readily available. In this case, default values of BCEFI from one of the forest types closest to the non-forest vegetation can be used to convert merchantable biomass to total biomass. BCEFI is relevant only to perennial woody tree biomass for which merchantable biomass data are available. For perennial shrubs, grasses and crops, biomass increment data in terms of tonnes of dry matter per hectare may be directly available and in this case use of Equation 2.10 will not be required.

A.2 Estimating annual decrease in biomass carbon stocks due to losses (Gain-Loss Method), A Cl

Loss estimates are needed for calculating biomass carbon stock change using the Gain-Loss Method. Note that the loss estimate is also needed when using the Stock-Difference Method to estimate the transfers of biomass to dead organic matter when higher Tier estimation methods are used (see below). Annual biomass loss is the sum of losses from wood removal (harvest), fuelwood removal (not counting fuelwood gathered from woody debris), and other losses resulting from disturbances, such as fire, storms, and insect and diseases. The relationship is shown in Equation 2.11.

Equation 2.11

Annual decrease in carbon stocks due to biomass losses in land remaining in the same land-use category

= Lwood - removals + L fuelwood + Ldisturbance

Where:

ACl = annual decrease in carbon stocks due to biomass loss in land remaining in the same land-use category, tonnes C yr-1 Lwood-removais = annual carbon loss due to wood removals, tonnes C yr-1 (See Equation 2.12) Lfueiwood = annual biomass carbon loss due to fuelwood removals, tonnes C yr-1 (See Equation 2.13) Ldisturbance = annual biomass carbon losses due to disturbances, tonnes C yr-1 (See Equation 2.14)

Equation 2.11 and the following Equations 2.12 to 2.14 are directly applicable to Forest Land. These Equations (2.11 to 2.14) can also be used for estimating losses from Cropland and Grassland, if quantities of wood removal (harvesting), fuelwood removal, and loss due to disturbance are available for perennial woody biomass. In intensively managed as well as highly degraded croplands and grasslands, the perennial woody biomass loss is likely to be small. Default biomass carbon loss values for woody crop species are provided for the Tier 1 cropland methodology (see Table 5.1). It is important to note that wood-removal used in Equation 2.11 should be compared with the input to HWP in Chapter 12 for consistency.

The three terms on the right hand side of Equation 2.11 are obtained as follows:

Loss of biomass and carbon from wood removal (harvesting), Lwood-removals

The method for estimating the annual biomass carbon loss due to wood-removals is provided in Equation 2.12.

In some applications, BEFs are used to expand dry-weight of merchantable components or stem biomass to total biomass, excluding or including roots, or convert and expand merchantable or stem volume to above-ground or total biomass (Somogyi et al, 2006). As used in this document, biomass expansion factors always transform dry-weight of merchantable components including bark to aboveground biomass, excluding roots.

Equation 2.12 Annual carbon loss in biomass of wood removals

Where:

Lwood-removals annual carbon loss due to biomass removals, tonnes C yr-

H = annual wood removals, roundwood, m3 yr-1

R = ratio of below-ground biomass to above-ground biomass, in tonne d.m. below-ground biomass (tonne d.m. above-ground biomass)-1. R must be set to zero if assuming no changes of below-ground biomass allocation patterns (Tier 1).

CF = carbon fraction of dry matter, tonne C (tonne d.m.)-1

BCEFr = biomass conversion and expansion factor for conversion of removals in merchantable volume to total biomass removals (including bark), tonnes biomass removal (m3 of removals)-1, (see Table 4.5 for Forest Land). However, if BCEFR values are not available and if the biomass expansion factor for wood removals (BEFR) and basic wood density (D) values are separately estimated, then the following conversion can be used:

If country-specific data on roundwood removals are not available, the inventory experts should use FAO statistics on wood harvest. FAO statistical data on wood harvest exclude bark. To convert FAO statistical wood harvest data without bark into merchantable wood removals including bark, multiply by default expansion factor of 1.15.

Loss of biomass and carbon from fuelwood removal, Lfuelwood

Fuelwood removal will often be comprised of two components. First, removal for fuelwood of living trees and parts of trees such as tops and branches, where the tree itself remains in the forest, will reduce the carbon in the biomass of growing stock and should be treated as biomass carbon loss. The second component is gathering of dead wood and logging slash. This will reduce the dead organic matter carbon pool. If it is possible it is good practice to estimate the two components separately. The biomass carbon loss due to fuelwood removal of live trees is estimated using Equation 2.13.

Equation 2.13 Annual carbon loss in biomass of fuelwood removal

Lfuelwood = [{FGtrees • BCEFr • (1 + R)} + FGpart • D] • CF

Where:

Lfueiwood = annual carbon loss due to fuelwood removals, tonnes C yr-1

FGtrees = annual volume of fuelwood removal of whole trees, m3 yr-1

FGpart = annual volume of fuelwood removal as tree parts, m3 yr-1

R = ratio of below-ground biomass to above-ground biomass, in tonne d.m. below-ground biomass (tonne d.m. above-ground biomass)-1; R must be set to zero if assuming no changes of below-ground biomass allocation patterns. (Tier 1)

CF = carbon fraction of dry matter, tonne C (tonne d.m.)-1

BCEFr = biomass conversion and expansion factor for conversion of removals in merchantable volume to biomass removals (including bark), tonnes biomass removal (m3 of removals)-1, (see Table 4.5 for Forest Land). If BCEFR values are not available and if the biomass expansion factor for wood removals (BEFR) and basic wood density (D) values are separately estimated, then the following conversion can be used:

Biomass Expansion Factors (BEFR) expand merchantable wood removals to total aboveground biomass volume to account for non-merchantable components of the tree, stand and forest. BEFR is dimensionless.

If country-specific data on roundwood removals are not available, the inventory experts should use FAO statistics on wood harvest. It should be noted that FAO statistical data on wood harvest exclude bark. To convert FAO statistical wood harvest data without bark into merchantable wood removals including bark, multiply by default expansion factor of 1.15.

Wood harvest can comprise both wood and fuelwood removals (i.e., wood removals in Equation 2.12 can include both wood and fuelwood removal), or fuelwood removals can be reported separately using, both Equations 2.12 and 2.13. To avoid double counting, it is good practice to check how fuelwood data are represented in the country and to use the equation that is most appropriate for national conditions. Furthermore, the wood harvest from forests becomes an input to HWP (Chapter 12). Therefore, it is good practice to check for consistent representation of wood-harvest data in Equations 2.12 and 2.13 and those in Chapter 12.

Loss of biomass and carbon from disturbance, Ldisturbance

A generic approach for estimating the amount of carbon lost from disturbances is provided in Equation 2.14. In the specific case of losses from fire on managed land, including wildfires and controlled fires, this method should be used to provide input to the methodology to estimate CO2 and non-CO2 emissions from fires.

Equation 2.14 Annual carbon losses in biomass due to disturbances

Ldisturbance = {Adisturbance • BW • (1 + R) • CF • fd}

Where:

Ldisturbances = annual other losses of carbon, tonnes C yr-1 (Note that this is the amount of biomass that is lost from the total biomass. The partitioning of biomass that is transferred to dead organic matter and biomass that is oxidized and released to the atmosphere is explained in Equations 2.15 and 2.16).

Adisturbance = area affected by disturbances, ha yr-1

BW = average above-ground biomass of land areas affected by disturbances, tonnes d.m. ha-1

R = ratio of below-ground biomass to above-ground biomass, in tonne d.m. below-ground biomass (tonne d.m. above-ground biomass)-1. R must be set to zero if no changes of below-ground biomass are assumed (Tier 1)

CF = carbon fraction of dry matter, tonne C (tonnes d.m.)-1

fd = fraction of biomass lost in disturbance (see note below)

Note: The parameter fd defines the proportion of biomass that is lost from the biomass pool: a stand-replacing disturbance will kill all (fd = 1) biomass while an insect disturbance may only remove a portion (e.g. fd = 0.3) of the average biomass C density. Equation 2.14 does not specify the fate of the carbon removed from the biomass carbon stock. The Tier 1 assumption is that all of Ldisturbances is emitted in the year of disturbance. Higher Tier methods assume that some of this carbon is emitted immediately and some is added to the dead organic matter pools (dead wood, litter) or HWP.

The amounts of biomass carbon transferred to different fates can be defined using a disturbance matrix that can be parameterized to define the impacts of different disturbance types (Kurz et al., 1992). It is good practice, if possible, to develop and use a disturbance matrix (Table 2.1) for each biomass, dead organic matter and soil carbon pool, the proportion of the carbon remaining in that pool, and the proportions transferred to other pools, to harvested wood products and to the atmosphere, during the disturbance event. The proportions in each row always sum to 1 to ensure conservation of carbon. The value entered in cell A is the proportion of above-ground biomass remaining after a disturbance (or 1 - fd, where fd is defined in Equation 2.14). The Tier 1 assumption is that all of fd is emitted in the year of disturbance: therefore the value entered in cell F is fd. For higher Tiers, only the proportion emitted in the year is entered in cell F and the remainder is added to cells B and C in the case of fire, and B, C, and E in the case of harvest. It is good practice to develop disturbance matrix even under Tier 1 to ensure that all carbon pool transfers are considered, though all biomass carbon is assumed to be emitted in the year of land conversion. It is important to note that some of the transfers could be small or insignificant.

Table 2.1

Example of a simple matrix (Tier 2) for the impacts of disturbances on carbon pools

Harvested wood products

Atmosphere

Sum of row (must equal 1)

Table 2.1

Example of a simple matrix (Tier 2) for the impacts of disturbances on carbon pools

Harvested wood products

Atmosphere

Sum of row (must equal 1)

Enter the proportion of each pool on the left side of the matrix that is transferred to the pool at the top of each column. All of the pools on the left side of the matrix must be fully populated and the values in each row must sum to 1.

Impossible transitions are blacked out.

Enter the proportion of each pool on the left side of the matrix that is transferred to the pool at the top of each column. All of the pools on the left side of the matrix must be fully populated and the values in each row must sum to 1.

Impossible transitions are blacked out.

Note: Letters A to F are cell labels that are referenced in the text.

2.3.1.2 Land converted to a new land-use category

The methods for estimation of emissions and removals of carbon resulting from land-use conversion from one land-use category to another are presented in this section. Possible conversions include conversion from non-forest to Forest Land, Cropland and Forest Land to Grassland, and Grassland and Forest Land to Cropland.

The CO2 emissions and removals on land converted to a new land-use category include annual changes in carbon stocks in above-ground and below-ground biomass. Annual carbon stock changes for each of these pools can be estimated by using Equation 2.4 (ACB = ACG - ACL), where ACG is the annual gain in carbon, and ACL is the annual loss of carbon. ACB can be estimated separately for each land use (e.g., Forest Land, Cropland, Grassland) and management category (e.g., natural forest, plantation), by specific strata (e.g., climate or forest type).

METHODS FOR ESTIMATING CHANGE IN CARBON STOCKS IN BIOMASS (A cb)

i) Annual increase in carbon stocks in biomass, A Cg

Tier 1: Annual increase in carbon stocks in biomass due to land converted to another land-use category can be estimated using Equation 2.9 described above for lands remaining in a category. Tier 1 employs a default assumption that there is no change in initial biomass carbon stocks due to conversion. This assumption can be applied if the data on previous land uses are not available, which may be the case when land area totals are estimated using Approach 1 or 2 described in Chapter 3 (non-spatially explicit land area data). This approach implies the use of default parameters in Section 4.5 (Chapter 4). The area of land converted can be categorized based on management practices e.g., intensively managed plantations and grasslands or extensively managed (low input) plantations, grasslands or abandoned croplands that revert back to forest and should be kept in conversion category for 20 years or another time interval. If the previous land use on a converted area is known, then the Tier 2 method described below can be used.

ii) Annual decrease in carbon stocks in biomass due to losses, A Cl

Tier 1: The annual decrease in C stocks in biomass due to losses on converted land (wood removals or fellings, fuelwood collection, and disturbances) can be estimated using Equations 2.11 to 2.14. As with increases in carbon stocks, Tier 1 follows the default assumption that there is no change in initial carbon stocks in biomass, and it can be applied for the areas that are estimated with the use of Approach 1 or 2 in Chapter 3, and default parameters in Section 4.5.

iii) Higher tiers for estimating change in carbon stocks in biomass, (AC B )

Tiers 2 and 3: Tier 2 (and 3) methods use nationally-derived data and more disaggregated approaches and (or) process models, which allow for more precise estimates of changes in carbon stocks in biomass. In Tier 2, Equation 2.4 is replaced by Equation 2.15, where the changes in carbon stock are calculated as a sum of increase in carbon stock due to biomass growth, changes due to actual conversion (difference between biomass stocks before and after conversion), and decrease in carbon stocks due to losses.

Equation 2.15

Annual change in biomass carbon stocks on land converted to other land-use category (Tier 2)

ACb = ACg + ACconversion - ACl

Where:

AC = annual change in carbon stocks in biomass on land converted to other land-use category, in tonnes C yr-1

ACg= annual increase in carbon stocks in biomass due to growth on land converted to another land-use category, in tonnes C yr-1

AC = initial change in carbon stocks in biomass on land converted to other land-use category,

in tonnes C yr-1

ACl = annual decrease in biomass carbon stocks due to losses from harvesting, fuel wood gathering and disturbances on land converted to other land-use category, in tonnes C yr-1

Conversion to another land category may be associated with a change in biomass stocks, e.g., part of the biomass may be withdrawn through land clearing, restocking or other human-induced activities. These initial changes in carbon stocks in biomass (AC are calculated with the use of Equation 2.16 as follows:

CONVERSION

Equation 2.16

Initial change in biomass carbon stocks on land converted to another land category

ACCONVERSION = Z {(BAFTERi - BBEFOREi ) • AATO _ OTHERSi } • CF

Where:

AC = initial change in biomass carbon stocks on land converted to another land category,

CONVERSION tonnes C yr-1

BAFTERi = biomass stocks on land type i immediately after the conversion, tonnes d.m. ha-1 BBEFOREi = biomass stocks on land type i before the conversion, tonnes d.m. ha-1 AATO_OTHERSi = area of land use i converted to another land-use category in a certain year, ha yr-1 CF = carbon fraction of dry matter, tonne C (tonnes d.m.)-1 i = type of land use converted to another land-use category

The calculation of ACCONVERSION may be applied separately to estimate carbon stocks occurring on specific types of land (ecosystems, site types, etc.) before the conversion. The AAto others, refers to a particular inventory year for which the calculations are made, but the land affected by conversion should remain in the conversion category for 20 years or other period used in the inventory. Inventories using higher Tier methods can define a disturbance matrix (Table 2.1) for land-use conversion to quantify the proportion of each carbon pool before conversion that is transferred to other pools, emitted to the atmosphere (e.g., slash burning), or otherwise removed during harvest or land clearing.

Owing to the use of country specific data and more disaggregated approaches, the Equations 2.15 and 2.16 provide for more accurate estimates than Tier 1 methods, where default data are used. Additional improvement or accuracy would be achieved by using national data on areas of land-use transitions and country-specific carbon stock values. Therefore, Tier 2 and 3 approaches should be inclusive of estimates that use detailed area data and country specific carbon stock values.

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