Effects of Forest Management on Soil Organic Carbon Stability and Dynamics in Chinese Fir Plantation

Chinese fir is a very important timber tree species specific in subtropical China, and it has been extensively planted for timber production through conversion of natural evergreen broadleaf forest. A large amount of biomass carbon sequestration and timber production have been periodically gained at the expense of soil organic carbon (SOC) loss and subsequently the soil fertility decline. Generally, the mineral SOC pool slightly decreased from the young stand to the middle-aged stand and then rapidly increased to a maximum in the mature stand. Litter, either from aboveground or belowground, is one of the major sources of the SOC in Chinese fir plantation; the quality and quantity of litter affects the stock and stability of SOC. Chemical components of the litter are the key to regulate the decomposition rate and the remaining to be added in soil in the form of SOC. In addition, litter decomposition and/or rhizosphere deposition imparts SOC stock and stability through priming effects. Harvest residues are another important source of SOC; relatively higher quality with no nutrient retranslocation harvest residues are preferable for soil organic carbon accumulation. The SOC in Chinese fir plantation can be recovered to the level at planted trees if the rotation extends over 27 years; therefore, a promising practice suggested to manage SOC in Chinese fir plantation is to extend the rotation so that a certain amount of SOC to be sequestered in a longer enough period of time. An alternative practice for the sustainable management of this conifer plantation is to plant mixed plantation to mitigate the decrease of SOC, or to enhance SOC sequestration.