543 
The LANDSAT-based estimates on the order of 21 x10 3 sq.km/year for 
the past decade, or 26x10 3 sq.km/year for 1989, represent the most reliable 
values at present for the forest clearing rate in Brazilian Amazonia. 
We emphasize that the average rate for 1978/1989 does not imply 
that the pace of deforestation was constant over this period. Although the data 
for intermediate years reported by other Brazilian agencies are not as complete 
as those for the end-points, they suggest that the rate increased through about 
1987, after which it tapered off (in part due to heavy rainfall during the 1989 
burning season). This confirms subjective impressions of deforestation activity 
in the region over this period. 
Translating information on deforestation rates into releases of 
greenhouse gases requires knowledge of the spatial distribution of the clearing, 
the corresponding spatial distribution of vegetation types and their respective 
biomasses and the biomass of replacement vegetation, as well as the fate of 
biomass and soil carbon under prevailing agricultural and ranching practices in 
cleared areas (Fearnside, 1990b). Studies of these factors indicate annual 
carbon releases on the order of 0.3 gigatons (Fearnside, nd-b). 
Although deforestation rates in Brazilian Amazonia are much lower 
than some have believed, the pace of forest loss remains high. Among other 
impacts, Amazonian deforestation makes a significant contribution to the global 
greenhouse effect. 
ACKNOWLEDGMENTS 
We thank Joao Roberto dos Santos and Eliana Maria Kalil Mello for 
reanalysis of the 1978, 1988 and 1989 datasets, Alberto Waingort Setzer for 
comments on the manuscript, and Marcio Nogueira Barbosa for critically 
reviewing the manuscript and, in particular, for pointing out the special 
difficulties associated with the skewed distribution of dates in the 1988 data set.