Choice of method

The general method for biomass carbon stock change in Settlements Remaining Settlements follows the approach in Equation 2.7 in Chapter 2. This method estimates changes in biomass carbon stocks, accounting for gains in carbon stocks in biomass as a result of growth minus losses in carbon stocks as a result of pruning and mortality. Depending on the relative magnitudes of the increment and loss terms, the average annual changes in biomass carbon stocks in settlements may be positive or negative.

Biomass change in Settlements Remaining Settlements is the sum of biomass change in three components: trees, shrubs, and herbaceous perennials (e.g., turfgrass and garden plants), as described in Equation 8.1.

Equation 8.1

Annual carbon change in live biomass pools in settlements remaining settlements

ACb = ACTrees + ACshrubs + ACHerbs

Where:

ACb = annual carbon accumulation attributed to biomass increment in Settlements Remaining Settlements, tonnes C yr-1

ACTrees = annual carbon accumulation attributed to biomass increment in trees in Settlements Remaining Settlements, tonnes C yr-1

ACShrubs = annual carbon accumulation attributed to biomass increment in shrubs in Settlements Remaining Settlements, tonnes C yr-1

ACHerbs = annual carbon accumulation attributed to biomass increment in herbaceous biomass in

Settlements Remaining Settlements, tonnes C yr-1

Depending on the availability of relevant activity data and appropriate emission factors, any of the methodological tiers described below can be used. Figure 2.2 in Chapter 2 also provides guidance for the identification of the appropriate tier to estimate changes in carbon in biomass.

Tier 1

Tier 1 assumes no change in carbon stocks in live biomass in Settlements Remaining Settlements, in other words, that the growth and loss terms balance. If the category Settlements Remaining Settlements is determined to be a key category, then a country should collect appropriate activity data and/or develop emission factors appropriate to the region and adopt Tier 2 or 3.

Tier 2

There are two options for Tier 2 estimation of changes in biomass in Settlements Remaining Settlements. Tier 2a uses changes in carbon stocks per unit of plant crown cover area as a removal factor, and Tier 2b uses changes in carbon stocks per number of plants as a removal factor. The choice of method will depend on availability of activity data. Tier 2a and Tier 2b both provide methods for estimating ACG in Equation 2.7 (Gain-Loss Method). This is appropriate for countries lacking a continuous inventory in Settlements Remaining Settlements.

The main perennial types are trees, shrubs, and herbaceous perennials (such as turfgrass and garden plants). The methods as presented here set the change in biomass of herbaceous annuals to zero in Settlements Remaining Settlements on the basis that growth of herbaceous biomass (whether perennial or annual herbaceous vegetation) is equal to loss from harvest or mortality. Countries may choose to define tree and woody perennial types as appropriate and each types may be further divided into classes defined according to species, climate zone, seasonality, or other criteria as appropriate and if data are available.

Tier 2a: Crown cover area method

This method is represented by Equation 8.2 and should be used when data are available on total area of crown cover in perennial types (j) and their classes (i) in Settlements Remaining Settlements.

Equation 8.2

Annual biomass increment based on total crown cover area

Where:

ACg = annual carbon accumulation attributed to biomass increment in Settlements Remaining Settlements, tonnes C yr-1

ATy = total crown cover area of class i in woody perennial1 type j, ha

CRWij = crown cover area-based growth rate of class i in woody perennial type j, tonnes C (ha crown cover)-1 yr-1

Tier 2b: individual plant2 growth method

The method is represented by Equation 8.3 and should be used where data on the number of woody plants by broad species class in Settlements Remaining Settlements are available. It is possible, when making estimates for trees, to convert between the methods used in Tiers 2a and 2b by assuming that an individual tree in an urban area covers approximately 50 m2 crown area when mature (cf. Akbari, 2002).

Equation 8.3

Annual biomass growth based on number of individual woody plants in broad classes

Where:

ACg = annual carbon accumulation due to live biomass increment in Settlements Remaining Settlements, tonnes C yr"1

NTjj = number of individuals of class i in perennial type j

Cij = annual average carbon accumulation per class i of perennial type j, tonnes C yr"1 per individual

1 References to woody perennials include trees unless otherwise specified.

2 References to plants include trees unless otherwise specified.

Tier 3

Tier 3 approaches can be based either on Tier 2 methods above (Equations 8.2 and 8.3) with more detailed measurements of parameters at disaggregated level for different settlement systems such as parks, rural or urban residential areas, avenues, etc., or on a stock difference approach based on Equation 2.8. Changes in carbon stocks are estimated at two points in time, where the changes account for biomass carbon gains and losses. The generic approach for this method calls for forest-specific biomass expansion factors (BEFs) which do not apply to settlements. Countries wishing to use the stock difference method to estimate biomass change in Settlements Remaining Settlements should consider using allometric methods such as those based on individual tree diameter at breast height (dbh) (Jenkins et al, 2004), adjusted for open-grown trees as described above, rather than forest specific BEFs for estimating tree biomass.

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