Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s

Abstract

Global demand for agricultural products such as food, feed, and fuel is now a major driver of cropland and pasture expansion across much of the developing world. Whether these new agricultural lands replace forests, degraded forests, or grasslands greatly influences the environmental consequences of expansion. Although the general pattern is known, there still is no definitive quantification of these land-cover changes. Here we analyze the rich, pan-tropical database of classified Landsat scenes created by the Food and Agricultural Organization of the United Nations to examine pathways of agricultural expansion across the major tropical forest regions in the 1980s and 1990s and use this information to highlight the future land conversions that probably will be needed to meet mounting demand for agricultural products. Across the tropics, we find that between 1980 and 2000 more than 55% of new agricultural land came at the expense of intact forests, and another 28% came from disturbed forests. This study underscores the potential consequences of unabated agricultural expansion for forest conservation and carbon emissions.

Fig. 1.

Map of major tropical regions with locations of the 117 randomly sampled Landsat sites shown as red squares. (All Landsat sites were used except in four cases where inherent errors or missing data could not be corrected.) Each Landsat sampling unit is ∼3 million hectares in size, comparable to a district or province, and is shown to scale. Percent forest cover estimated from moderate-resolution imaging spectroradiometer (MODIS) data for the year 2000 is shown by background shading.

Fig. 2.

The origins of new agricultural land, 1980–2000. Bars show the average proportion of land sources comprising new agricultural land in major tropical regions.

Fig. 3.

Sources for newly expanded agricultural land in tropical America during the 1980s and 1990s. The pie charts show the relative proportions of land sources across broad regions and for individual Landsat sites, which are scaled according to the size of the agricultural land expansion (Fig. S1 shows unscaled pie charts).

Fig. 4.

Sources for newly expanded agricultural land in tropical Africa during the 1980s and 1990s. The pie charts show the relative proportions of land sources across broad regions and for individual Landsat sites, which are scaled according to the size of the agricultural land expansion (Fig. S2 shows unscaled pie charts).

Fig. 5.

Sources for newly expanded agricultural land in tropical Asia during the 1980s and 1990s. The pie charts show the relative proportions of land sources across broad regions and for individual Landsat sites, which are scaled according to the size of the agricultural land expansion (Fig. S3 shows unscaled pie charts).