Soil carbon and plant diversity distribution at the farm level in the savannah region of Northern Togo (West Africa)

In western Africa, soil organic matter is a source of fertility for food provision and a tool for climate mitigation. In the Savannah region, strong soil degradation linked to an increase in population threatens organic matter conservation and agricultural yield. Soil degradation is also expected to impact biodiversity and, with it, increase the vulnerability of ecosystem goods and services, including the storage of soil organic carbon. Studies of land use, plant species composition and soil fertility were conducted for a conservation project at a demonstration farm in Northern Togo (West Africa), host to various management regimes. Results showed a low organic matter content of the surface soil horizons, often around 0.5%. The highest values were found in a sacred forest within the farm (2.2%). Among crops, rice had the highest soil organic matter, around 1%. In a survey of grasslands, pastures showed the highest organic matter content, with vegetation composition differing from grazed fallows and abandoned grasslands. Plant species richness showed a positive relationship with soil organic matter (R2adj=41.2%), but only by the end of the wet season, when species richness was also highest. Sampling date had a strong effect on vegetation composition. Results showed a strong influence of human activity on soil formation and distribution, and also on plant diversity. The soil characteristics found under the permanent forest suggest a high potential of the soils of the region for improvement of both agricultural yields and as a potential carbon sink relevant to global change policies.The authors want to thank Anna Comellas and Josep Miquel Ubalde for their help in field work and sample processing, and to the Centre de Formation Rurale de Tami in Togo and his director Felipe Garc´ıa for invaluable help in all areas; this work would not have been possible without his collaboration. Funding from the Universitat de Lleida, PROIDE and 15 the Agencia Espan˜ola de Cooperacio´n Internacional para el Desarrollo made the work possible. APPLUS-Agroambiental S.A. provided soil analyses. Work within the CARBOPAS (REN2002- 04300-C02-01) and CARBOAGROPAS (CGL2006-13555-C03-01/BOS) projects, both from the Spanish Science Foundation (FECYT), and the PASTUS-INTERREG (I3A-4-147-E) project from the EU programme INTERREG III-A contributed to the development of ideas in this paper