Global soil organic carbon stock changes after afforestation with different plant types

Background/Question/Methods: Afforestation contributes to Soil Organic Carbon (SOC) sequestration and alleviate soil degradation. The objectives of this paper are to investigate the main effects of, and interactions among, plantation age, previous land use and plant types on SOC storage changes, and the main factors influencing SOC sequestration rates for different plant types at three soil layers (0-20 cm, 20-40 cm, 40-60 cm). A meta-analysis of 90 studies evaluates the influences of afforestation on SOC change dynamics. We perform a multi-way ANOVA to test the effects of various factors on SOC, and the influences of previous land use and plant age group on different plant classifications. We use stepwise regression analysis to analyse the relationship between ∆Cs following afforestation and average annual temperature (T), average annual precipitation (P), plantation age (A) and initial Cs (I) for different plant classifications. We use Pearson correlation analysis to study the relationship between SOC sequestration rates following afforestation and T, P and I of all data.

Results/Conclusions: This synthesis suggests an average SOC change rate of 0.3 Mg ha^-1 yr^-1 at the soil layer of 0-20 cm, with the increase of SOC stocks starting after 7 years of afforestation. However, SOC stock changes in deeper soil layers were less significant. The results indicate that the interactions among previous land use, plant types and plantation age can significantly change the SOC sequestration potential of afforestation. For instance, the afforestation of cropland generally leads to significantly greater SOC accumulation rates than the afforestation of grassland, yet the differences were not significant in the first 10 years or after 30 years of afforestation, pointing to an important temporal effect. Deciduous hardwood showed a quicker and more stable accumulation of SOC stock after afforestation, with an increase of SOC stock starting from the third year of afforestation. The SOC sequestration capacity of different plant types varied across different afforestation time periods; in the first 20 years, the SOC sequestration rates increased in the following order: evergreen softwood < evergreen hardwood < deciduous hardwood; after that, evergreen hardwood sequestered more SOC. High initial SOC stocks negatively influence SOC sequestration rates of evergreen plants, but positively influence that of deciduous hardwood; the effects of temperature and precipitation on SOC stock changes were minimal.