2.5.2 Changes in Land Cover Since 1750
In 1750, 7.9 to 9.2 million km2 (6 to 7% of the global land surface) were under cultivation or pasture (Figure 2.15), mainly in Europe, the Indo-Gangetic Plain and China (Ramankutty and Foley, 1999; Klein Goldewijk, 2001). Over the next hundred years, croplands and pasture expanded and intensified in these areas, and new agricultural areas emerged in North America. The period 1850 to 1950 saw a more rapid rate of increase in cropland and pasture areas. In the last 50 years, several regions of the world have seen cropland areas stabilise, and even decrease. In the USA, as cultivation shifted from the east to the Midwest, croplands were abandoned along the eastern seaboard around the turn of the century and the eastern forests have regenerated over the last century. Similarly, cropland areas have decreased in China and Europe. Overall, global cropland and pasture expansion was slower after 1950 than before. However, deforestation is occurring more rapidly in the tropics. Latin America, Africa and South and Southeast Asia experienced slow cropland expansion until the 20th century, but have had exponential increases in the last 50 years. By 1990, croplands and pasture covered 45.7 to 51.3 million km2 (35% to 39% of global land), and forest cover had decreased by roughly 11 million km2 (Ramankutty and Foley, 1999; Klein Goldewijk, 2001; Table 2.8).
Overall, until the mid-20th century most deforestation occurred in the temperate regions (Figure 2.15). In more recent decades, however, land abandonment in Western Europe and North America has been leading to reforestation while deforestation is now progressing rapidly in the tropics. In the 1990s compared to the 1980s, net removal of tropical forest cover had slowed in the Americas but increased in Africa and Asia.
Figure 2.15. Anthropogenic modifications of land cover up to 1990. Top panel: Reconstructions of potential natural vegetation (Haxeltine and Prentice, 1996). Lower panels: reconstructions of croplands and pasture for 1750 and 1990. Bottom left: fractional cover of croplands from Centre for Sustainability and the Global Environment (SAGE; Ramankutty and Foley, 1999) at 0.5° resolution. Bottom right: reconstructions from the HistorY Database of the Environment (HYDE; Klein Goldewijk, 2001), with one land cover classification per 0.5° grid box.