Fast Net Carbon Balance Recovery After Clear-Cutting but Uncertain Long-Term Carbon Accumulation in Eucalyptus Plantations.

Forest plantations cover large areas globally, but their climate benefits remain unclear, hampering projections of the future land carbon (C) sink. Here, we combined an unprecedented 14-years series of eddy-covariance CO2 fluxes (net ecosystem productivity, NEP) with biometric measurements to explore C balance in a commercial Eucalyptus plantation in Brazil across three rotations. The plantation exhibited a 14-year average and maximum annual NEP of 9.8 and 20.2 MgC ha-1 y-1, respectively, which ranks among the highest documented forest productivity. The amount of time before the forest recaptures as much C as was emitted after harvest was substantially shorter than previously published values: 20 and 27 months, for first and second harvest, respectively. Time series of leaf area index, but not trunk biomass growth, were strongly related to NEP dynamics (> 75% of explained variance at annual and monthly scales) suggesting possible amenability to remote-sensing assessment in Eucalyptus plantations. Estimates of C accumulation in litter and below-ground stocks varied from positive to negative depending on the methodology used, and showed substantial differences across rotations. This indicates that long-term C accumulation in commercial Eucalyptus plantations is not guaranteed, despite their high productivity.