Analysis of Spatial Variations in Grain Yield and Relevant Driving Forces in Rapid Urbanization Regions: A Case Studyon Shunyi in Beijing

The authors examined characteristics of variations in grain yield in Shunyi District, Beijing City,since the reform and opening-up.During the period,the district has shifted from a main production district to a new satellite city of Beijing,with showing that arable land has been increasingly exploited for other purposes.Meanwhile,the level of both the means of production input and the crop breeding continued to be improved greatly.As a result,over the past 31 years, Shunyi District and Beijing have reached their highest level of total grain output in 1994 and 1993, in succession,which were 8.02 and 4.89 times of that in 2003,the lowest total grain output.A "Shunyi grain yield variation spatial cluster-diffusion degree model"and a"spatial center of gravity of different yield levels model"were developed in the present work.On the basis of the two models,spatial changes in grain yield over the recent 12 years were quantified carefully. Taking into account regional,social and economic development,a grey integrated connection grade was utilized to explore driving forces of such changes.Results indicated that 1)the "cluster-diffusion degrees"of all spatial grain production units in 1996 were larger than 0.85, showing a dispersedly distributed characteristic.In contrast,it was found that high-level and non-food production areas explicitly converged to the lower"cluster-diffusion degrees"index in 2008;2)the grain production gravity center deviated progressively from the regional center during 12 years.In general,the gravity center of the high-level production areas showed a displacement of 8.06 kilometers towards the northeast.Also,a displacement of 5.17 kilometers towards the southwest for the non-food production areas was observed;and 3)the grain planting area,net income per capita of farmers,and financial revenue were positively correlated with the change in the grain yield,which were considered major driving forces in Shunyi District.In addition,eight factors(e.g.,the agricultural population and the secondary industry GDP)were found to be moderately correlated with the change.The order of the correlation degree for the eight factors was ρ2ρ4ρ3ρ7ρ10ρ9ρ5ρ1.Overall,there exist a decreasing trend in grain production and a transfer of grain-production regions to regions far away from urban areas and the industry development center.Similar to the pattern at the national scale,with decreases in the grain yield,the food production areas are moving from developed southeastern areas to developing western regions.