CHANGES IN THE LANDSCAPE OF LATIN-AMERICA BETWEEN 1850 AND 1985 .2. NET RELEASE OF CO2 TO THE ATMOSPHERE

The net release of carbon to the atmosphere from deforestation in Latin America was calculated for the period 1850-1985. Changes in the area of forests were described in a companion paper. Here, the stocks of carbon in vegetation and soils of major ecosystems, and changes in these stocks of carbon as a result of disturbance, were used to calculate the net annual flux of carbon. The total net release of carbon between 1850 and 1985 was about 30 x 10(15) g (range 17-35 x 10(15) g). The land uses responsible for the emissions of carbon were increased areas of pastures (42% of the total emissions), croplands (34%), degraded lands (19%), and shifting cultivation (5%). Logging and the establishment of plantations contributed or accumulated negligible amounts of C over this 135-year period. The annual releases of C to the atmosphere increased over the period 1850-1985; half of the total release occurred after 1960. By 1985 the net release was 0.67 x 10(15) g C year-1 (range 0.39-0.82 x 10(15) g C). The relative contributions of different land uses to this flux were different from those over the long-term. The greatest single source of C in 1985 resulted from increases in the area of degraded lands (37% of the net flux), and the importance of shifting cultivation increased to almost 20%. The range of estimates calculated here for the current net flux of C is lower than earlier estimates of the range. The range results from uncertainties in the rates of land-use change, in the types of ecosystems cleared and the stocks of C in these ecosystems, and in the rates of decay and regrowth of organic matter associated with land-use change.