Comparison of changes in land use and land cover in China and the USA over the past 300 years

Comparative studies of changes in land use and land cover between different countries over a long time-scale are helpful in understanding the processes and driving forces of these changes in different situations. We compared and analyzed the temporal and spatial characteristics of cropland, forest and grassland between China's mainland and the conterminous USA over the past 300 years. We found that, over the past 300 years, the area of cropland showed an overall increasing trend both in China and in the USA. In China, the area of cropland increased by about 79.46x10(4) km(2) from 1661 to the 1980s, and the per capita cropland decreased from 0.37x10(4) m(2) in 1685 to 0.10x104 m(2) in 2000. For the USA, the area of cropland increased by 190.87x10(4) km(2) between 1700 and 1950. The per capita cropland area of each time slice for the past 300 years was greater than 0.60x10(4) m(2) and the maximum value was 2.01x10(4) m(2) in 1890. As a result of the expansion in land reclamation, the forest and grassland areas of the USA have decreased by about 136.98x10(4) km(2) and 136.98x104 km(2), respectively, over the past 300 years; the corresponding values for China are about 89.73x10(4) km(2) and 40.00x10(4) km(2), respectively. In terms of the spatial patterns, the expansion in cropland in China mainly occurred in the border areas (including the northeast, southwest and Inner Mongolia) and in the hilly areas. Cropland expansion in the USA mainly occurred in the mid-west regions. In China, population growth is the most important driving factor in changes in land use and land cover, whereas in the USA, government policy plays the most significant role.