Carbon storage and sequestration rates in Leucaena leucocephala‑based silvopasture in Southern Mexico

Agroforestry practices that include trees on grazing lands could enhance atmospheric CO2 sequestration and storage. However, carbon sequestration rates and storage capacity of intensively grazed agroforestry systems vary due to the diversity in species composition, stand structure, system age, and management practices. The objective of this study was to evaluate carbon stocks and accrual rates in Leucaena leucocephala + Cynadon plectostachyus, and Brachiaria decumbens grass silvopastoral systems and compare them with conventional open grazing lands. The study was carried out in Chiapas in southern Mexico, one of the hotspots of deforestation driven by the expansion of livestock farming. We measured above- and belowground carbon stocks in 18 silvopasture (SP) plots, with the plantation age ranging from 2 to 10 years. Nine plots of adjacent conventional full-sun grasslands (open pasturelands) grazed rotationally were sampled for comparison. The average tree biomass stock in SP was 5.5 ± 1.9 Mg C ha−¹ and differed with SP age. Mean annual biomass accrual rates ranged from 0.25 to 2.57 Mg C ha−¹ year−¹, indicating that SP systems are CO2 sinks, excluding other sources of GHG such as methane emissions from enteric fermentation. The average soil organic carbon (SOC) sequestration rate of SP was 0.143 ± 0.043 Mg C ha−¹ year−¹ to 50 cm depth. The SOC sequestration rates correlated positively with SP age at the beginning and decreased after about 8 years. The results suggested that the age and lifespan of trees play a significant role in aboveground C sequestration through the Leucaena leucocephala SP, while SOC storage varied with soil properties. Further research on the relative response of active and stable SOC fractions along with soil CO2 fluxes could explain the results on the SOC storage potential of these agroforestry systems.