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Reduction in the area of forests in Latin America between 1850 and 1985 was estimated from changes in the major uses of land, including permanent croplands, pastures, shifting cultivation, logging, and degradation. Changes in croplands were documented through historical statistics. The types of forests and other natural ecosystems converted to croplands were estimated from a comparison of maps of natural vegetation with maps of agriculture. Changes in the area of pastures were inferred from changes in the number of cattle and stocking rates. Estimates of the rate of deforestation for shifting cultivation were available only in recent years. Before 1940 the area in shifting cultivation was assumed constant; between 1940 and 1985 the increase in area was assumed to accelerate. In recent decades, the area of forests has decreased more rapidly than increases in the areas of croplands and pastures. This additional loss of forests is thought to have resulted from the replacement of degraded agricultural land, and was estimated to have occurred historically according to different assumptions.

The results showed that, between 1850 and 1985, about 370 x 10(6) ha of forest (28% of the forest area in 1850) were replaced by some other type of ecosystem. Most of this reduction of forest area was due to the expansion of pastures (44% of the reduction), croplands (25%), degraded lands (20%), and shifting cultivation (10%). The use of alternative data and assumptions gave estimates of total deforestation that ranged between 313 and 412 x 10(6) ha (25-30% of the area in 1850). The largest uncertainties were related to historical rates of degradation and shifting cultivation, and to the types of ecosystems converted to human uses. Use of satellite imagery can eliminate most of these uncertainties after 1975.