Objective  The restoration progress of forest ecosystems could be reasonably evaluated by the analyses of variations in soil quality and soil organic carbon (SOC) stability with forest stand age.

  Method  Four forest stands of Pinus tabuliformis at different ages (20 years, 40 years, 80 years and 110 years) were selected to analyze the soil physical quality and SOC stability and their determinants. The soil from these stands were analyzed for SOC fraction, clay content, root biomass and extracellular enzyme activities; soil quality was defined by the ratio of SOC to clay, and the stability of SOC was delineated by the ratio between recalcitrant carbon and labile carbon.

  Result  The biophysical properties, i.e., soil moisture content, soil hydrolase activity, and iron and aluminum oxides were modified along a chronosequence of P. tabuliformis forests. Simultaneously, both of the soil quality and SOC stability increased with forest stand age. During the soil depth of 0 to 10 cm, soil quality increased from 0.12 in the 40 years stand to 0.40 in the 110 years stand, and the SOC stability changed from 2.69 in the 40 years stand to 6.72 in the 110 years stand. A significant and positive correlation was found between soil quality and SOC stability across different forest stands.

  Conclusion  The iron and aluminum oxides contribute more to sustaining the SOC stability, and the soil quality was modified more by soil moisture content, root biomass, and soil extracellular enzyme activities.