Conversion of a natural broad-leafed evergreen forest into pure plantation forests in a subtropical area: Effects on carbon storage

For the last several decades, native broad- leafed forests in many areas of south China have been converted into plantations of more productive forest species for timber use. This paper presents a case study examining how this forest conversion affects ecosystem carbon storage by comparing 33 year- old plantations of two coniferous trees, Chinese fir (Cunninghamia lanceolata, CF) and Fokienia hodginsii (FH) and two broadleaved trees, Ormosia xylocarpa (OX) and Castanopsis kawakamii (CK), with an adjacent relict natural forest of Castanopsis kawakamii (NF, similar to 150 year old) in Sanming, Fujian, China. Overall estimates of total ecosystem carbon pools ranged from a maximum of 399.1 Mg ha(-1) in the NF to a minimum of 210.6 Mg ha(-1) in the FH. The combined tree carbon pool was at a maximum in the NF where it contributed 64% of the total ecosystem pool, while the OX had the lowest contribution by trees at only 49%. Differences were also observed for the carbon pools of undergrowth, forest floor and standing dead wood, but that these pools together represent at the most 5% of the ecosystem C stock. Total C storage in the surface 100 cm soils ranged from 123.9 Mg ha(-1) in the NF to 102.3 Mg ha(-1) in the FH. Significant differences (P < 0.01) in SOC concentrations and storage between native forest and the plantations were limited to the surface soils (0 - 10 cm and 10 - 20 cm), while no significant difference was found among the plantations at any soil depth (P > 0.05). Annual aboveground litterfall C ranged from 4.51 Mg ha(-1) in the CK to 2.15 Mg ha(-1) in the CF, and annual belowground litterfall (root mortality) C ranged from 4.35 Mg ha(-1) in the NF to 1.25 Mg ha(-1) in the CF. When the NF was converted into tree plantations, the vegetation C pool (tree plus undergrowth) was reduced by 27 - 59%, and the detritus C pool (forest floor, standing dead wood, and soils) reduced by 20 - 25%, respectively. These differences between the NF and the plantations may be attributed to a combination of factors including more diverse species communities, more C store types, higher quantity and better quality of above- and belowground litter materials under the NF than under the plantations and site disturbance during the establishment of plantations.