Grazing Affects Soil Organic Carbon Stocks Directly and Indirectly Through Herbaceous Species Diversity in Sahelian Savanna Ecosystems

Abstract

The impact of livestock grazing on soil organic carbon (SOC) stocks in the Sahel has been poorly documented due to a lack of data from different grazing intensities. This study evaluated SOC stocks under four grazing intensities within 0–30 cm soil depth in dry savanna ecosystems of Senegal. It also examined possible indirect relationships between grazing and SOC through herbaceous species diversity, herbaceous biomass, and carbon–nitrogen ratio. Four sites representing high, moderate, light, and no grazing intensity levels were selected. Transect survey methods were used for sampling soil and vegetation data within each of the sites. Data were analyzed using mixed-effects models and piecewise structural equation modeling (pSEM). SOC stocks were significantly different among the four grazing intensities, and higher stocks were observed with increased intensity. Furthermore, high-intensity grazing was shown to reduce the carbon–nitrogen ratio by negatively affecting the diversity of herbaceous species, which indirectly promoted SOC stocks. In conclusion, this study found that increased grazing intensity promoted SOC stocks both directly and indirectly through herbaceous species diversity.