Mesure des flux de CO2 et séquestration de carbone dans les écosystèmes terrestres ouest-africains (synthèse bibliographique)

CO2 measurement and carbon sequestration in West African terrestrial ecosystems. A review. Introduction. In West Africa, as elsewhere in other parts of the world, preserving terrestrial ecosystems has proven essential to any emissions mitigation policy for greenhouse gases, notably carbon dioxide. A meaningful assessment of the contribution of a given region to the global carbon cycle implies the need to think in terms of balance, taking into account the totality of the carbon export and import within the ecosystems. Literature. This review, based on the results of a small number of published and unpublished studies focusing on West African ecosystems, has as its main objective the assessment of the importance of carbon exchange. Carbon fluxes appear to be spatially highly variable in the West African region, mainly due to the variability of the types of vegetation, approaches to ecosystem management, and edaphic and climatic conditions. The mean annual precipitation appears to be the main factor controlling plant respiration and photosynthesis in this region. Annual cumulated NEE has been positively correlated with the rate of photosynthesis, and has been shown to account for 71% of its spatial variability at the annual scale. This paper also confirms the presence of carbon sink behavior for considered ecosystems in the West Africa with an annual average carbon sequestration of -2.0 ± 1.5 t C·ha-1 and highlights the need to improve understanding of factors or mechanisms controlling the carbon exchange between the ecosystems and the atmosphere. Conclusions. Based on these results, which were collected on a very limited number of sites, it appears necessary to continue with the measurement of carbon fluxes in the long term at the ecosystem scale in order to better appreciate the temporal and spatial variabilities, especially on a seasonal and inter-annual basis. This paper highlights the need to extend eddy covariance measurements to other vegetation types in this region in order to facilitate studies comparing the different ecosystems. This could be used as a basis for the recommendation of more sustainable management strategies favoring carbon sequestration while limiting emission levels.