Assessment and measurement issues related to soil carbon sequestration in land-use, land-use change, and forestry (LULUCF) projects under the Kyoto protocol

Mitigating the potential large negative impacts of a change in the earth's climate will require strong and definite actions in the different economic sectors, particularly within agriculture and forestry. Specifically, soils deserve a close examination due to their large carbon mitigation potential. The Kyoto protocol establishes the possibility for crediting greenhouse gas emission reductions from forestry and agriculture activities. In most circumstances, particularly those regarding developing countries, greenhouse gas mitigation activities will be carried out through projects. These projects will have to meet a series of criteria, for the carbon benefits to be measurable, transparent, verifiable and certified. These criteria include: establishing credible baselines (without-project or reference scenario), additionality, permanence, quantifying and reducing potential leakage of greenhouse gases across project borders, coping with natural or human induced risks, accurately measuring changes in carbon stocks using carbon accounting techniques, and-in the case of the Clean Development Mechanism-resulting in sustainable development benefits. In this paper we describe the methods and approaches that have been developed to cope with the different criteria and discuss their implications for carbon sequestration in soils. Soil carbon represents the largest carbon pool of terrestrial ecosystems, and has been estimated to have one of the largest potentials to sequester carbon worldwide. However, getting credits from soil carbon sequestration through project activities presents several challenges: the need to monitor small incremental changes in soil carbon content relative to large carbon pools, long-time periods to accrue the full carbon benefits, high local variability of soil carbon content, and relatively costly soil carbon measurement procedures. Also, the responses of soil C stocks to forestry and agriculture activities are complex and need careful attention. Specifically, the time dynamics of soil C responses to land use changes, the diversity of soil types, soil-plant interactions, and the availability of accurate soil C inventories, should be considered to successfully implement LULUCF projects.