Mapping soil carbon stocks of Central Africa using SOTER

Little is known about the soil carbon stocks of Central Africa although such baseline data are needed for research and policy development on soil carbon changes. Estimates are presented based on a 1:2 million scale soil and terrain (SOTER) database for Burundi, the Democratic Republic of Congo, and Rwanda (hereafter referred to as Central Africa). Each SOTER map unit consists of up to six soil components, characterized by a representative soil profile extracted from survey data. Gaps in the measured soil analytical data were filled using consistent, taxonomy-based pedotransfer procedures. Natural variation in individual soil components was simulated to put bounds on regional-scale carbon stocks rather than a single figure. The 95% confidence interval for the median stock of soil organic carbon (SOC) to 1 m is 19.3 to 19.6 Pg C; this corresponds with some 11% of African and about 1% of worldwide SOC stocks to that depth. The area-weighted SOC content is largest in the cool, humid mountains (22.1–22.7 kg C m− 2) in part due to the presence of soils formed on volcanic parent materials, and smallest for the warm savannah region (7.6–7.7 kg C m− 2). Local differences in SOC content are related to type and texture of parent material, soil drainage conditions, and land use/vegetation. Less than 1% of the region consists of soil units that contain secondary carbonates (~ 0.19 Pg C), accounting for ~ 0.8% of the total carbon stock to 2 m in the soils of Central Africa. About 45% of the SOC stock to 2 m is held in the upper 30 cm; much of this would be released to the atmosphere as CO2 upon forest clearance.