Long-term continuity of mixed-species broadleaves could reach a synergy between timber production and soil carbon sequestration in subtropical China

Tree species and forest age are two key variables affecting timber production and carbon sequestration in forest ecosystems. In this study, in Jiangxi province of eastern China, by a thorough investigation of 179 subtropical forest stands in a 16.7 x 10(6) ha area with similar climatic conditions and past land-use history, we systematically examined biomass of live aboveground tree, forest floor litter, shrub and herb as well as soil organic carbon (SOC) content (0-10, 10-30 and 30-100 cm depths) to compare differences among five major vegetation types (Chinese fir, masson pine, single-species broadleaves, mixed conifers-broadleaves, and mixed-species broadleaves), and between age classes (below vs above 30 years of stand age). Tree species and stand age both had significant effects. Among the five forest types, mixed-species broadleaved forests had remarkably highest timber productivity, SOC content and storage in the 0-100 cm depth and total C store in the age group of above 30 years. Coniferous stands had generally higher forest floor biomass than broadleaved stands in the age group of below 30 years; this trend was opposite for mineral soil C in the age group of above 30 years. Stand age significantly affected aboveground timber production for all the tree species; this effect was weaker on belowground soil C, as broadleaves exhibited increases in SOC content with stand age while conifers did not. Our results suggest that long-term continuity ( > 30 years) of mixed-species broadleaves could be an optimal strategy for forests in subtropical region of China. This study contributes to a better understanding of the effects of management practices on forest ecosystems.