From our meta-analysis of worldwide data, soil carbon decreased following land use change from pasture to conifer plantation. A paired site (a native pasture with Themeda triandra dominant, and a 16 year old Pinus radiata plantation) study is set up at Kowen Forests, ACT, Australia to assess the soil carbon reduction and the possible reason for the reduction, such as the change of fine root dynamics (production and mortality). Soil analysis has shown that soil carbon stocks were significantly less under the pine plantation than under the native pasture. Hence, soil carbon decreased after pine trees planted, especially in the top 10 cm). From fine root dynamics monitored via minirhizotrons, much less fine roots were produced and deceased much slower under the pine plantation than under the native pasture. Therefore, the soil carbon reduction after land use change from pasture to conifer plantation could be caused by the change of fine root dynamics, at least partly.