Effect of cropland occupation and supplement on light-temperature potential productivity in China from 2000 to 2008

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There are more people but less land in China, so food safety has always been a most important issue government concerned. With continuous population increase, economic development and environment protection, cropland occupation and supplement are unavoidable. It not only leads to the variation of cropland area, but also makes the light-temperature potential productivity per unit area different due to regional climate differentiation, therefore impacts the total potential productivity and food output eventually. So, it is necessary to analyze the climate differentiation between occupation and supplement cropland areas and to study its impact on total potential productivity, which is significant to reasonably develop natural resources and instruct agricultural arrangement. This study firstly discussed the variation and distribution of occupation and supplement croplands in China from 2000 to 2008, then analyzed the climate differentiation between occupation and supplement cropland areas and its effect on light-temperature potential productivity. The results demonstrate: 1) From 2000 to 2008, the cropland variation presented occupation in the south and supplement in the north, but overall decreased. Supplement cropland was mainly from ecological reclamation (77.78%) and was mainly distributed in Northeast China and Northwest China with poor climatic and natural conditions. Occupation cropland was mainly used for construction (52.88%) and ecological restoration (44.78%) purposes, and was mainly distributed in the Huang-Huai-Hai Plain, and the middle and lower reaches of the Changjiang (Yangtze) River with better climatic and natural conditions. 2) The climate conditions were quite different in supplement and occupation cropland areas. The annual precipitation, annual accumulated temperature and average annual temperature were lower in the supplement cropland area, and its average potential productivity per unit was only 62% of occupation cropland area, which was the main reason for the decrease of total potential productivity. 3) Cropland occupation and supplement led to the variation of total potential productivity and its spatial distribution. The productivity decreased in the south and increased in the north, but had a net loss of 4.38315×107 t in the whole country. The increase of cropland area was at the cost of reclaiming natural forest and grassland resources, and destroying natural ecological environment, while the decrease of cropland area was mainly due to a lot of cropland occupied by urban-rural construction, which threatened the sustainable use of cropland resources.