Carbon stock and sequestration potential of traditional and improved agroforestry systems in the West African Sahel

Carbon (C) sequestration potential of agroforestry systems has attracted worldwide attention following the recognition of agroforestry as a greenhouse gas mitigation strategy under the Kyoto Protocol. Our knowledge on this topic from the arid and semiarid regions such as the West African Sahel (WAS) is, however, very limited. To address this problem, a study was undertaken in the Ségou region of Mali (annual temperature: 29°C; annual rainfall: 300-700mm in 60-90 days; soils: Haplustalfs (USDA Soil Taxonomy)/Lixisol (FAO classification), loamy sand, low in fertility) on five land-use systems in farmers' fields (two traditional parkland systems with Faidherbia albida and Vitellaria paradoxa as the dominant tree species, two improved agroforestry systems (live fence and fodder bank), and a so-called abandoned land, i.e., land that was previously under cultivation but was abandoned after it became unproductive). Carbon stock in the biomass was estimated by allometric equations and soil C stock was determined at three depths (0-10cm, 10-40cm and 40-100cm). Biomass C stock ranged from 0.7 to 54.0MgC/ha, and total C stock (biomass C+soil C, 0-100cm depth) from 28.7 to 87.3MgC/ha, indicating that a major portion of the total amount of C in the system is stored in the soil. Traditional parkland agroforestry systems had relatively larger C stock than the improved systems, but they seemed to have only limited potential for sequestering additional C. On the other hand, the improved systems showed higher potential for sequestering C from the atomsphere. The results show that soil C is a substantial component of the total C stock of the system, suggesting the importance of considering soil C in C sequestration calculations, which at present is not recognized by Kyoto Protocol. Carbon sequestration benefit is a promising incentive for introducing agroforestry practices and contributing to sustainable land-use in the WAS.