Silvopastoral systems reduce soil CO2 emissions, enhance carbon stocks, and regulate the micro-environment in tropical grazing lands

Soil carbon dioxide (CO₂) flux is a fundamental component of the global carbon cycle and can be regulated by land use and management practices. Silvopastoral systems, livestock agroforestry that includes trees in grazing lands, can increase carbon storage and reduce soil CO₂ fluxes, yet their relationship with micro-climate, soil properties, and vegetation attributes has not been studied well. The objective of this research was to evaluate carbon storage and soil CO₂ fluxes and decipher the linkage between micro-climatic variables, soil properties, and vegetation characteristics in three silvopastoral systems: 1) dispersed trees in pasturelands, 2) grazing under forest plantations, and 3) live fences around pastureland, and 4) full-sun pastureland. Soil CO₂ fluxes were measured in situ using an EGM-5 gas analyzer connected with a soil respiration chamber (PP Systems, USA) over twelve months. Structural equation modeling was used to untangle the relative contribution of vegetation characteristics, soil properties, and micro-climatic variables on soil CO₂ fluxes. Soil CO₂ flux varied significantly between silvopastoral systems and full-sun pasturelands (p < 0.01), ranging from 0.59 to 0.87 g m⁻² hr⁻¹, with the full-sun pastureland having the highest flux, followed by live fences around pastureland, dispersed trees in pasturelands, and grazing under forest plantations. Silvopastoral systems reduced 12 – 32 % of soil CO₂ fluxes compared to the full-sun pasture. Soil organic carbon stocks to 100 cm depth were 12 % and 29 % higher in grazing under forest plantations (187 Mg C ha⁻¹) and dispersed tree silvopastoral systems (215 Mg C ha⁻¹), respectively, than in full-sun pasturelands (167 Mg C ha⁻¹). Soil temperature, air temperature, and relative humidity also differed significantly between pastoral systems, with the full-sun pasture (grass monoculture) having the highest temperature and the lowest relative humidity. In a structural equation model, soil CO₂ flux showed a negative path coefficient (-0.82, p = 0.03) with vegetation attributes that include the number of trees per hectare and biomass stocks, which covaried significantly with the micro-climatic variables. The soil properties construct was not a strong predictor of CO₂ flux but covaried positively with vegetation, including plant biomass and litter stocks. While further studies on soil microbial activities may help better understand the patterns of soil CO₂ fluxes among these livestock agroforestry systems, this study shows that the presence of trees modifies micro-environmental conditions in grazing lands, thereby reducing soil CO₂ emissions and enhancing carbon sequestration. The results have important implications in designing climate-smart and environment-friendly livestock production systems.