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Forest systems cover more than 4.1 x 10 sup 9 hectares of the Earth's land area. Globally, forest vegetation and soils contain about 1146 petagrams of carbon, with approximately 37 percent of this carbon in low-latitude forests, 14 percent in mid-latitudes, and 49 percent at high latitudes. Over two-thirds of the carbon in forest ecosystems is contained in soils and associated peat deposits. In 1990, deforestation in the low latitudes emitted 1.6 +/- 0.4 petagrams of carbon per year, whereas forest area expansion and growth in mid-and high-latitude forest sequestered 0.7 +/- 0.2 petagrams of carbon per year, for a net flux to the atmosphere of 0.9 +/- 0.4 petagrams of carbon per year. Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem productivity, could conserve or sequester significant quantities of carbon. Future forest carbon cycling trends attributable to losses and regrowth associated with global climate and land-use change are uncertain. Model projections and some results suggest that forests could be carbon sinks or sources in the future.
The emission of the greenhouse gas CO sub 2 to the atmosphere by fossil fuel combustion and land-use change continues to escalate, and its global dynamics and regulation are inadequately understood (1). Recent estimates for annual emissions of CO sub 2 by fossil fuel combustion and land-use change for 1980 to 1989 are 5.4 +/- 0.5 Pg of C per year (1 Pg = 10 sup 15 g = 1 Gt) and 1.6 +/- 1.0 Pg of C per year, respectively (I). Global oceans are estimated to absorb 2.0 +/- 0.8 Pg of C per year, and ==3.2 0.1 Pg of C per year remains in the atmosphere. This calculation leaves an amount of 1.8 +/- 1.4 Pg of C per year unaccounted for. Low-latitude and mid-latitude terrestrial ecosystems, particularly forests, have both been proposed to be significant repositories of this missing C or the imbalance in the C budget (2).
Globally, forests cover ==4.1 billion hectares of the Earth's land surface with ==13% of the forests protected by governments and less than 10% actively managed (Table 1). (Table 1 omitted) The largest area of forests (42%) is in low latitudes, where more than half are in tropical America. Mid-latitude...