Land-use changes and fossil fuel combustion are two important anthropogenic factors that have contributed to the increase of atmospheric CO₂ concentrations since the Industrial Revolution in the mid-18th century. The influence of land management on the C content in soils and biomass is well documented worldwide [1] [2]. Land-use changes not only affect C sources and sinks, but also impact methane (CH₄) and nitrous oxide (N₂O) emissions. However, little information is available on aspects of C sequestration in agroecosystems located in the temperate areas of the Southern Hemisphere, and especially those on volcanic soils.

This study was undertaken to model C sequestration potentials in three predominant ecosystems: 1) Pinus ponderosa-based silvopastoral systems arranged in strips (SPS), 2) 18-year-old managed exotic plantations (PPP) and 3) natural prairie (PST), in Patagonia, Chile. The C contents of trees and pasture were determined by destructive sampling and dry combustion. Litterbags were used to measure decomposition of organic material. Soil respiration was quantified with the in situ soda-lime technique. Soil samples were taken at 0-5, 5-20, 20-40 cm depths to determine soil C.

For PPP and SPS, total tree C was 64% and 69% of the total system, respectively. Total above and belowground C pools were 224, 199 and 177 Mg C ha^-1 in SPS, PPP and PST, respectively. The aboveground: belowground C pool ratio was 1:10, 1:5 and 1:177 for SPS, PPP and PST, respectively. Total soil respiration decreased in the order PST > SPS > PPP, and leached C decreased in the order PPP > PST > SPS. Estimated system net C flux was +1.8, +2.5 and –2.3 Mg C ha^-1 y^-1 for SPS, PPP and PST, respectively [2]. Based on this study and to attain C neutrality, a land area of approximately 481 km² or 0.33% of the Chilean Patagonia territory under silvopastoral systems (SPS) with cattle would be sufficient to offset all C losses (CO₂, CH₄ and N₂O) from cattle-based livestock systems [3]. 

Given that large, deforested areas are currently subject to soil erosion coupled with poor and inferior quality pasture production, the adoption of SPS over large tracts of grazing lands should not be a problem in Patagonia nor a threat to other types of land uses. As the Prairie is acting as a C source, pine-based SPS could contribute enormously towards Chilean strategies to mitigate climate change.