Soil CO2 and N2O emissions in Sahelian Silvopastoral systems: spatial distribution and annual budget estimation

Silvopastoral systems (SPS) are one of the most common livestock production systems in the Sahel. They are composed of a mix of trees, pastures, and livestock in the same area. Known for providing several beneficial services compared to traditional pastures, SPS can release or absorb greenhouse gases. So far, our understanding of the magnitude and spatial distribution of greenhouse gas emissions in Sahelian SPS is subject to many uncertainties. This is mainly due to a lack of experimental and modelling studies focused on the region.

We use a process-based model, STEP-GENDEC-N₂O, that couples vegetation growth, biogeochemistry, and gas emissions to investigate the spatial and temporal pattern of carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from soil and estimate their annual budget in the Sahelian SPS. After model validation using in-situ data collected at the Dahra site (north-western Senegal), simulations were performed on the entire Sahelian area (latitude: 13°N to 18°N; longitude: 18°W to 20°E) divided into 18271 grid cells of 0.1° x 0.1°, from 2010 to 2021. Input variables were extracted from different datasets available at global or regional scales.

We found that the spatial pattern of CO₂ and N₂O emissions from soils in Sahelian SPS can be mainly explained by the spatial distribution of soil properties (soil temperature, soil sand, and clay content), climate, and animal load. The overall estimated CO₂ and N₂O emissions from Sahelian SPS during the 2010-2021 period were 0.054 ± 0.005 Tg C yr^-1 (1 Tg = 10¹² g) and 0.046 ± 0.008 Tg N yr^-1, respectively. These values are relatively low compared to other estimates for grazing and cropping systems in other regions. Mapping CO₂ and N₂O emissions from soils in SPS at the Sahel-wide scale helps identify emission hotspots in order to establish more effective mitigation strategies and management policies for Sahelian SPS.