Short term effects of thinning on soil organic carbon fractions, soil properties, and forest floor in Cunninghamia lanceolata plantations

Forest management impacts on the soil carbon pool and soil properties. This study analyzed the changes of soil organic carbon (SOC) fractions, soil properties, and forest floor in a Chinese fir (Cunninghamia lanceolata) plantation after two years of thinning in Eastern China. The experiment consisted of three thinning treatments: unthinned, moderate thinned (stand stem density reduced by approximately 21%), and heavy thinned (stand stem density reduced by approximately 36%) stands. Concentrations of soil dissolved organic carbon (DOC), light fraction carbon (LFOC), and total SOC in the topsoil (0 to 20 cm) increased in the heavy thinned stands, and no significant effect for heavy fraction carbon (HFOC) was detectable in the soil profile. Some soil properties were also altered after thinning, which included a decrease in soil bulk density (BD), and an increase in soil temperature (ST), soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK), and pH. The change of these soil properties mainly occurred in the topsoil layers (0 to 20 cm) in the heavy thinned treatment. The SOC and soil labile carbon fractions were positively correlated with ST, TN, AN, AP, and AK. Moreover, the increase of SOC fractions and the availability of soil nutrients maybe due to the increased input from an abundant well-decomposed forest floor after thinning. These results suggest that a 36% of thinning operations had a marked impact on the soil labile carbon pool and soil fertility in the topsoil in a Chinese fir plantation during a short-time period. Thus, changes to soil carbon stability and soil fertility should be considered when developing forest management plans.