A mixed-forest in Northern Japan, which had been a weak carbon sink (net ecosystem exchange (NEE): -0.44 tC ha^-1 yr^-1) was disturbed by clearcutting and was replaced with hybrid larch plantation. In order to predict the impact of such disturbance and determine the length of time to reach the carbon compensation point after harvest, a 10-year (2001-2010) eddy covariance measurements of CO₂ fluxes coupled with the biomass change evaluation were employed. When trees in the study site of 13.7 ha were clearcut in 2003, the ecosystem abruptly became a large carbon source but attained an almost balanced NEE of 28 tC ha^-1 yr^-1 in 2009. Finally in 2010, the ecosystem gained back its status as carbon sink (NEE, -0.49 tC ha^-1 yr^-1). Total GPP, RE, and NEE during 7 years after the disturbance (2003-2009) were 64.5, 79.2, and 14.7 t C ha^-1, respectively. The total NEE value could be as much as 77% of the carbon transferred out of this ecosystem as timbers in 2003 (19 t C ha^-1). Considering the biomass increment during this period, these results also indicate that soil (including roots and residuals after tree harvesting) had been a large carbon emitter (ca. 31.9 t C ha^-1) during the period.