Soil organic carbon (SOC) is key player in the global carbon cycle. Afforestation on pastures potentially alters organic matter input and SOC sequestration. We investigated the effects of a Picea abies L. afforestation sequence (0 to 130 years) on a former subalpine pasture on SOC stocks and dynamics. We found no difference in the SOC stock after 130 years of afforestation and thus no additional SOC sequestration. SOC composition was altered due to a modified SOC input following afforestation.