Optimal rotation length for carbon sequestration in Eucalyptus plantations in subtropical China

Most Eucalyptus plantations are intensively managed as short-rotation plantations and carbon (C) storage in plants and soils in stands older than 10 years is not well understood. We examined the changes in plant biomass C and soil organic C (SOC) storage across a chronosequence of E. urophylla × E. grandis forests (4-, 7-, 10-, 13-, and 21-year-old) in subtropical China. Biomass C stock significantly increased with stand age. SOC storage increased initially after afforestation, peaking in 10-year-old stands, and declined gradually. Ecosystem C pools in the five development stages were 111.76, 167.66, 234.04, 281.00, and 299.29 Mg ha⁻¹, respectively. Trees and soils were the dominant C pools across all stand ages with the contribution of tree biomass C storage significantly increasing and SOC storage decreasing with age. Eucalyptus plantations are still in vigorous growth phase and have great potential for C sequestration at the end of the current rotation length (within 7 years). Considering the sharp decrease of annual biomass C increment rate and the gradual loss of SOC storage in stands older than 13 years, we recommend the optimal length for one full Eucalyptus plantation cycle should be 12–15 years in subtropical China to maximize land-use value and carbon sink value.