Contrasted seasonal balances in a Sahelian pastoral ecosystem result in a neutral annual carbon balance

Abstract This paper explores an original approach in which greenhouse gas (GHG) emissions and carbon (C) accumulation are assessed monthly and at landscape scale to account for the highly seasonal monsoon climate and the mobility of pastoralherds that characterize West African pastoralecosystems. The study was conducted in northern Senegal, in the service area of the Widou Thiengoly borehole, a circular zone of 706 km 2 centered on the borehole. The C balance was calculated using an ecosystem approach, i.e. taking allmain sources of GHG emissions and C sinks of the ecosystem, not only anthropogenic sources, into account. The annual C balance of the pastoralecosystem was −0.04 ± 0.01 tC-eq.ha −1 .year −1 , showing that total GHG emissions were mitigated by C accumulation in trees, soil and livestock. The C balance varied considerably with the seasons, with a positive monthly balance in the wet season, from July to October (+0.58 tC-eq.ha −1 .month −1 ) and a negative monthly balance in the cold dry seasonfrom November to February and the hot dry seasonfrom March to June (−0.57 and −0.05 tC-eq.ha −1 .month −1 respectively). Care should be taken when generalizing these results, which were obtained in a dry year, because of strong inter-annual variations in rainfall.