Phenological behavior of a cultivated savannah and an open clear forest in a tropical humid climate in West Africa derived Eddycovariance fluxes.

CO2 fluxes observations and associated annual budgets are essential to understand the functioning of ecosystems and the sequestration capacities of continental areas. On a global scale, scarcity of carbon fluxes and stocks on the African continent has been identified by the carbon community as a source of uncertainty for climate models. At the local scale, ecosystem/atmosphere exchanges in terms of water and carbon are poorly documented in the equatorial belt, making it difficult to implement sustainable strategies for land use planning and agricultural systems, which are necessary for adaptation to global changes.

We present one of the largest CO2 measurement series for two tropical ecosystems in Benin, under a Sudanese climate: a light forest and an agricultural area. The series cover the period 2008-2024. Processing these data has revealed specificities in terms of qualification, selection, and gap-filling procedures. In particular, temperature models are inefficient for calculating respiration due to the low seasonal variability of daily temperatures. Ecophysiological parameters (dark respiration, quantum light efficiency, maximum CO2 assimilation rate) show more intense activity for the forest than for the agricultural area. The seasonality of phenology also contrasts between the two sites, with a rapid increase in Amax associated with leafing before the rainy season for the forest and a steady increase with the onset of the rainy season for the agricultural area.

These measurements, carried out as part of the AMMA-CATCH observatory, contribute to a regional dynamic led by the WAF-Net collective, which brings together scientist involved in measuring carbon and water flows in West Africa.