THE CARBON-CYCLE AND GLOBAL FOREST ECOSYSTEM

Attempts to account for the fluxes by quantifying C sources and sinks have provided evidence of a missing C sink (Detwiler and Hall, 1988), which may be located somewhere in the temperate region of the northern hemisphere (Tans et al., 1990). Until recently, most estimates have concluded that the temperate forest is a small C source. Two recent papers (Sedjo, 1992; Kauppi et al., 1992) provided evidence that the temperate forests are substantial C sinks. This paper combines these earlier findings on temperate forest carbon sequestration with a new estimate of the annual C releases due to tropical deforestation, 1.7 Gt, which is obtained using the FAO estimates of the rate of deforestation in the tropics over the decade of the 1980s and conservative estimates of C releases associated with this deforestation. Finally, to this is added the crude estimate of C export by the global river system found in Hall et al. (1992). Applying these estimates of the C sink function of both temperate and tropical forests to Detwiler and Hall's alternative C budgets largely eliminates the ''missing C'' hypothesized by Detwiler and Hall, and Tans et al.