Carbon Inventory Under Baseline and Project Scenarios

The main goal of carbon inventory for carbon mitigation projects is to estimate the incremental or additional biomass and soil carbon stocks gained because of project activities. Estimation of incremental or additional carbon benefit or stock gain requires monitoring of carbon stocks of a given area and over a given period under the "without-project" or "baseline scenario" as well as changes in stocks for the project area over the same period as a result of implementation of project activities under the "project scenario". Carbon inventory methods are required in a project cycle during project proposal development, post-project implementation and monitoring phases. This chapter describes the broad approaches, methods and steps for estimating carbon stock changes at two levels:

• Under baseline and project scenarios

• At project development and monitoring phases of the project cycle

These approaches and methods are also applicable to non-carbon land-based projects, such as roundwood production. Detailed methodologies for measurement, calculation, projection and monitoring of different carbon pools are described in the later chapters.

7.1 Broad Approaches to Estimating Carbon Stocks

Three broad approaches to estimation of carbon stocks and changes under baseline and project scenarios are those based on:

(i) Default value

(ii) Cross-sectional field studies

(iii) Modelling

7.1.1 Approach Based on Default Value

Default values used in estimating carbon stocks are values obtained from databases, published literature or previous studies of similar land-use systems in similar environments. Default values of carbon stock and growth rate are available in the literature (IPCC 2003, 2006, www.fao.org and www.efdb.int). The approach based on default values does not involve any field studies and measurements of biomass and soil carbon pools but involves the following steps:

• Defining the physical and biological conditions of the project location, namely rainfall, soil type and topography

• Defining the land-use category, namely forest land, degraded forest land, degraded grassland, cropland, shrub land and plantations of different species

• Identifying the vegetation type, namely forest type, plantation type, dominant tree or grass or shrub species, age of the stand and crop grown

• Identifying management practices such as grazing, thinning, fertilizer application and irrigation

• Defining the land category for which default data are required, e.g. land-use category, rainfall, soil type, gradient, forest type or plantation species, age of the stand, density of trees and grazing practice

• Searching published literature and databases as well as local or regional studies or measurements conducted earlier

• Selecting relevant carbon pools

• Selecting an appropriate default value for the carbon pool for the land category defined for the project location, based on expert judgement

Baseline scenario Default data are required for biomass and soil carbon pools for degraded forest, cropland and grassland areas proposed for, say, afforestation, which are subjected to different levels of grazing, biomass extraction and degradation. Very few sets of default values are available for such land-use conditions for the baseline scenario. Avoided deforestation projects may require default biomass and soil carbon data for the forest stand; these values are, however, available.

Project scenario Default values for stocks and growth rates of above-ground biomass, below-ground biomass, soil carbon, litter and deadwood are available for forests, plantations, grasslands and agroforestry systems. The stocks and growth rates of different carbon pools vary not only among different land-use categories (e.g. forests, grassland and cropland), vegetation types (e.g. grassland, eucalyptus plantations and savannah), but also significantly within a given vegetation type (e.g. evergreen forests, savannah, eucalyptus plantation) under different rainfall, soil and temperature regimes. Carbon stocks or growth rates may vary even for a given tree plantation (e.g. eucalyptus or pine) or agroforestry system, depending on management practices, such as irrigation or fertilizer application. Therefore, default values should be evaluated considering the physical (soil and rainfall) and vegetation conditions (e.g. dominant species and variety) and management practices (fertilizer or irrigation application). Management practices vary often, and the default values may not be available for a given species-mix or soil condition and, even when available, may not be suitable for a given location, such as a village forest or a patch of grazing land. Expert judgement is required in using a default value from a global or regional database. The uncertainty could be very high if the default value is not available for location-specific conditions. Default values are required, particularly during the project development stage, for calculating carbon stock in both baseline and project scenarios.

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