Soil carbon balance in a clonal Eucalyptus plantation in Congo: effects of logging on carbon inputs and soil CO₂ efflux

Soil CO₂ efflux was measured in clear-cut and intact plots in order to quantify the impact of harvest on soil respiration in an intensively managed Eucalyptus plantation, and to evaluate the increase in heterotrophic component of soil respiration because of the decomposition of harvest residues. Soil CO₂ effluxes showed a pronounced seasonal trend, which was well related to the pattern of precipitation and soil water content and were always significantly lower in the clear-cut plots than in the intact plots. On an annual basis, soil respiration represented 1.57 and 0.91 kgC m⁻² yr⁻¹ in intact and clear-cut plots, respectively. During the first year following harvest, residues have lost 0.79 kgC m⁻² yr⁻¹. Our estimate of heterotrophic respiration was calculated assuming that it was similar to soil respiration in the clear-cut area except that the decomposition of residues did not occur, and it was further corrected for differences in soil water content between intact and clear-cut plots and for the cessation of leaf and fine root turnover in clear cut. Heterotrophic respiration in clear-cut plots was estimated at 1.18 kgC m⁻² yr⁻¹ whereas it was only 0.65 kgC m⁻² yr⁻¹ in intact plots (41% of soil respiration). Assumptions and uncertainties with these calculations are discussed.