Mixed-tree plantations can be a good silvicultural alternative to large-scale monoculture coniferous plantations
for climate change mitigation, which is facilitated by the sequestration of atmospheric carbon
dioxide. To evaluate the impacts of tree species compositions on the carbon storage capacity of plantation
ecosystems, we measured the above and belowground biomass, as well as the carbon content, in three
27-year old forest plantations of monoculture Castanopsis hystrix (CH stand), monoculture Pinus massoniana
(PM stand), and mixed C. hystrix and P. massoniana (mixed CH/PM stand) stands. We developed an
allometric equation to estimate tree carbon storage. The carbon storage levels of understory, litter, and
soil components were also estimated. Results show that biomass is positively correlated with carbon
storage. The ecosystem carbon storage of the mixed CH/PM stand (327.03 Mg ha1
) was higher than
those of the CH (314.59 Mg ha1
) and PM (293.60 Mg ha1
) stands. The majority of carbon storage was
found in the soil pool (84.73%, 63.54%, and 75.80% in the CH, PM and mixed CH/PM stands, respectively).
Almost 40% of soil carbon at a depth of 0–60 cm was stored in the upper 20 cm of the soil pool. Except for
the vegetation layer, each layer of the CH and mixed CH/PM stands consisted of a higher amount of carbon
than did the layers of the PM stand. These findings suggest that mixed CH/PM plantation stands or
valuable indigenous CH plantation stands more substantially improve carbon storage in litter, soil, and
ecosystems than do monoculture PM plantation stands. The results also imply that developing valuable
indigenous tree species is a good silvicultural option for enhancing carbon sequestration and valuable
timber cultivation in subtropical China.