Effects And Scenario Simulation Of Cropland Displacement

The strictest policies have been implemented to protect croplands as a foundation for food security in China.Hence,lost croplands may be compensated by new croplands at other locations to fulfill policy requirements.In fact,large amounts of cropland have been spacially displaced since the requisition and the compensation.However,few studies focus on cropland displacement.Emphasizing changes in the quantity of cropland while ignoring changes of cropland location may result in a serious bias in the analysis of related policies and the effects of cropland changes,including the impacts on food production and ecological environment.In this context,the extent of cropland displacement and its effects at four administrative levels of China during a past decade was estimated,and the changes for the future was simulated by this study as well.We hope this study can contribute to better implementation of Chinese cropland protection.The main lines and results of this study are presented as following:1)analyzing the spatial distribution of cropland displacement and its contribution to cropland change at national level,provincial level,municipal level,and county level of China,based on land use data for the year 2000 and 2010.Cropland displacement has significant impact on Chinese cropland change.China has experienced a net decrease of cropland with 3.7×10~3 km~2,accounting for 0.21%of the total cropland area in the year 2000.However,6.4×10~4 km~2 of cropland was displaced,and made a contribution of 94%to cropland change.In addition,cropland displacement dominated cropland change at 58%,56%,and 59%of administrative units at provincial level,municipal level and county level,respectively.During the decade,cropland loss was mainly attributed to the requisition of built-up in East China,while cropland gain was mainly from the compensation by forest and grassland in North China.Therefore,cropland change of China in this period can be briefly characterized as a dynamic balance of cropland quantity through cropland displacement from the East to the North.2)Furthermore,using the dataset of cropland potential productivity to estimate the contribution of cropland displacement to the changes of crop production potential at multi-levels.The difference of production effects of cropland displacement was explicit.Between 2000 and2010,Chinese crop production potential has decreased by 7.9×10~6 t at national level.Among which,cropland displacement led to a decrease of 6.2×10~6t,while cropland net change led to a decrease of 1.6×10~6 t.The contribution of cropland displacement on the change in crop production potential is 79%.However,cropland displacement dominated the change of crop production potential only at 10%,9%,14%of the administrative units of provincial level,municipal level,and county level,respectively.From the view of spatial distribution,the decrease of crop production potential of China was mainly attributed to the displacement of requisitioning high-quality cropland in the East while compensating low-quality cropland in the North.Combined with the analysis of cropland change,the national level presented a uniformity of spatial matching that both the cropland change and the change of crop production potential were dominated by cropland displacement.However,as for the provincial level,municipal level,and county level,61%,56%,and 51%of the administrative units presented a spatial mismatching that cropland displacement dominated the cropland change while cropland net change dominated the change of crop production potential.3)analyzing the impact of cropland displacement on the loss of ecological lands,with the compasion of urban expansion.The ecological effect of cropland displacement far exceeded that of urban expansion.China witnessed a net decrease of ecological lands with 7.0×10~4 km~2during 2000-2010.Among which,cropland displacement resulted in a loss of 6.3×10~4 km~2 in ecological lands,while urban expansion resulted in a loss of 0.7×10~4 km~2.Thus,the ecological land loss index(ELI)at the national level was 9.26.The results of sub-national levels indicate that the units which has a relatively low ELI are mainly centred in the East as great urban expansion,and in the units both few built-up expansion and cropland compensation.The units which have a relatively high ELI are mainly centred in the North as large amounts of cropland compensation.4)using LANDSCAPE(LAND System Cellular Automata model for Potential Effects)model to simulate the changes of cropland displacement and its effects on food production and environment at multi-levels,respectively targeting the balances of cropland quantity and cropland production potential.Under the scenario of balance of cropland quantity,cropland displacement at national level would have more negative impact on crop production potential.From 2010 to 2030,cropland displacement due to the balance of cropland quantity would lead to decreases in crop production potential,with 2.45×10~5 t at national level,1.15×10~5 t at provincial level,9.59×10~4 t at municipal level,and 9.90×10~4 t at county level.At the same time,cropland displacement would lead to a most loss in unused land at national level,and a most loss in forest at county level.Under the scenario of balance of crop production potential,cropland displacement at national level would lead to more loss of ecological lands.From 2010 to 2030,cropland displacement due to the balance of crop production potential would lead to decreases in crop production potential,with 5951 km~2 at national level,1474 km~2 at provincial level,3005 km~2 at municipal level,and 4158 km~2 at county level.Thus,cropland displacement at provincial level would cost the least cropland to fulfill the balance of crop production potential.At the same time,cropland displacement at national level would result in the most loss of ecological lands,especially forest and unused land.Based on the results above,the implications for Chinese cropland protection include:Firstly,cropland displacement,especially its negative effects,needs more attentions.Secondly,the balance of cropland quantity is still the basic target of Chinese cropland protection for the foreseeable future.The changes of cropland quantity at provincial level need to be strengthened,especially for the cropland with high productivity.Thirdly,using least cropland to keep the balance of crop production potential is the key for achieving the balance of cropland quality.The direction of cropland displacement needs to be strictly controlled.Finally,the protection of ecological lands is also a essential part of cropland protection.Loss of ecological lands through cropland compensation at ecologically vulnerable area needs to be avoided.