Soil organic carbon (SOC) plays a vital role in ecosyste
m function, deter
mining soil fertility, water holding capacity and susceptibility to land degradation. In addition, SOC is related to at
mospheric CO
2 levels with soils having the potential for C release or sequestration, depending on land use, land
manage
ment and cli
mate. The United Nations Convention on Cli
mate Change and its Kyoto Protocol, and other United Nations Conventions to Co
mbat Desertification and on Biodiversity all recognize the i
mportance of SOC and point to the need for quantification of SOC stocks and changes. An understanding of SOC stocks and changes at the national and regional scale is necessary to further our understanding of the global C cycle, to assess the responses of terrestrial ecosyste
ms to cli
mate change and to aid policy
makers in
making land use/
manage
ment decisions. Several studies have considered SOC stocks at the plot scale, but these are site specific and of li
mited value in
making inferences about larger areas. So
me studies have used e
mpirical
methods to esti
mate SOC stocks and changes at the regional scale, but such studies are li
mited in their ability to project future changes, and
most have been carried out using te
mperate data sets. The co
mputational
method outlined by the Intergovern
mental Panel on Cli
mate Change (IPCC) has been used to esti
mate SOC stock changes at the regional scale in several studies, including a recent study considering five contrasting eco regions. This ‘one step’ approach fails to account for the dyna
mic
manner in which SOC changes are likely to occur following changes in land use and land
manage
ment.
A dynamic modelling approach allows estimates to be made in a manner that accounts for the underlying processes leading to SOC change. Ecosystem models, designed for site scale applications can be linked to spatial databases, giving spatially explicit results that allow geographic areas of change in SOC stocks to be identified. Some studies have used variations on this approach to estimate SOC stock changes at the sub-national and national scale for areas of the USA and Europe and at the watershed scale for areas of Mexico and Cuba. However, a need remained for a national and regional scale, spatially explicit system that is generically applicable and can be applied to as wide a range of soil types, climates and land uses as possible. The Global Environment Facility Soil Organic Carbon (GEFSOC) Modelling System was developed in response to this need. The GEFSOC system allows estimates of SOC stocks and changes to be made for diverse conditions, providing essential information for countries wishing to take part in an emerging C market, and bringing us closer to an understanding of the future role of soils in the global C cycle.