Impacts of deforestation and reforestation on soil organic carbon storage and CO2 emission

Soil organic carbon (SOC) storage and CO2 flux into the atmosphere can be influenced by land use change, especially re/deforestation. The impacts of conversion of primary deciduous (PF) to secondary coniferous (SF) forest and deforestation of PF land to abandoned rangeland (AR) on various soil properties, SOC storage, and soil CO2 emission were investigated on the selected sites (Neshat and Garakpass) in Kelardasht region, northern Iran. The highest SOC storages were determined in coniferous forest land uses (SF1=255.00 and SF2=237.90 Mg C ha^−1) followed by deciduous forest (PF1=216.74 and PF2=159.12 Mg C ha^−1) and abandoned rangeland (AR1=185.31 and AR2=151.60 Mg C ha^−1). Land use changes showed significant impacts on soil CO2 efflux. The significant positive correlations, with exponential and linear relationships were observed between the monthly CO2 emissions; the minimum air temperature and the cumulative precipitation in the last week ended to CO2 measurement time. The highest recorded soil CO2 efflux in a wide range of land uses were obtained in August to October due to more suitable temperature and rainfall distribution. Based on lower CO2 emission in abandoned rangelands, lesser soil organic carbon is related to lower input to soil. The higher C: N ratios in litter and some of mineral horizons (SF2) and lower CO2 emissions by the higher lignin and polyphenol concentrations (SF1) in coniferous forests compared to deciduous forests have probably caused increasing SOC storage.