Carbon fluxes over two contrasting types of vegetation in West Africa: the case of forest and savannah sites under a Sudanian climate in northern Benin

Abstract:

Continuous CO₂, water vapour and sensible heat fluxes were measured during eighteen months (from July 2008 to December 2009) using an eddy-covariance technique over a Savannah and a Forest. Both sites were under a Sudanian climate and located in Benin. All data was computed following the standard procedure. Flux responses to the main environmental factors were studied and discussed during the year within four periods. Water was found to be the main factor controlling the ecosystem dynamic. During dry season, while the CO₂ assimilation was limited for the Savannah, it was reduced for the Forest. The respiration was always constantly higher for the Forest than Savannah sites. No clear relationships were found between nighttime fluxes and soil temperature, but the soil moisture appeared to be the main factor controlling the respiration at the two sites. At the seasonal scale, both CO₂ assimilation and quantum efficiency were higher within each period at the Forest than Savannah sites. During the dry periods, the Forest acted as a carbon sink while the Savannah was clearly a carbon source. Annually, Forest and Savannah sequestered 0.64 ± 0.05 and 0.19 ± 0.04 kg C m^-2, respectively. Besides, the difference of the two sites in land-use strategies and species, the drought could have a big impact on the carbon fluxes dynamics in West Africa.