| In recent years, with the rapid development of urbanization and industrialization, regional economy has improved. But a series of problems have appeared, such as the population explosion, city environmental deterioration, the per capita consumption of resources reduction and the gap between urban and rural areas increase. The problems seriously hinder the sustainable development of the city. Due to human well-being is closely related to agricultural ecosystem services, the agricultural multi-functionality is gradually taken seriously by people. At present, study on the agricultural multi-functionality has become the focus of the scholars both at home and abroad. However, there are few studies for the value evolution and driving force of the agricultural functions. In the process of urbanization, the influence mechanism of the change of agricultural functions has not been fully recognized. The spatial accuracy of the agricultural multi-functionality research is not high and can not fully reveal the spatial variation of the agricultural functions.Based on the urban geography, agricultural geography and theory of human geography, the TM image of 1999,2006 and 2013 and used the existing agricultural function evaluation model for reference, this paper took Xi’an Metropolitan zone as the study area, calculated its agricultural value of 1999,2006 and 2013 of 30 km×30 km grid scale and analyzed the space-time evolution of the agricultural value. Also this paper discussed the influence mechanism of the change of agricultural functions in the process of urbanization and researched the driving factors of the evolution of agricultural value by using the logistic regression model. This paper enriched the theory of the agricultural multi-functionality, was conducive to the rational distribution of agricultural industrial structure and provided a new method for the driving factor research of the agricultural multi-functionality. It had important significance for the farmers’ employment and income, the integration of urban and rural areas, enhancing people’s consciousness of environment protection and improving the living environment of the residents.Through the research, the following conclusions are obtained:(1) In 1999,2006 and 2013, the agricultural value respectively were 219.032×108 yuan,301.816×108 yuan and 572.930×108 yuan and showed a rising trend. The agricultural value of cultivated land was the maximum and grassland was the minimum. The value of the production function was the highest. The tourism and leisure function and water conservation function were the lowest. The agricultural functions showed obvious spatial differences. The production function and tourism and leisure function showed a decreasing trend from the city center to periphery. The general agricultural function and employment function of Qinling area were the lowest, and the plain area showed the trend of increasing outward from the city center area. The carbon fixation and oxygen release function and water conservation function showed a decreasing trend from south to north.(2) The agricultural value increased 82.784×108 yuan from 1999 to 2006 and increased 271.114×108 yuan from 2006 to 2013. In two stages, the added values of agricultural function of the cultivated land were the maximum and the added values of the grassland were the minimum. In terms of the single function of agriculture, the value of the agricultural production function, employment function and tourism and leisure function increased constantly, the carbon fixation and oxygen release function increased at first then decreased and the water conservation function had been decreased. In two stages, the variations of the production function value were the maximum and respectively were 58.12x 108 yuan and 208.95×108 yuan. The variations of the water conservation function value were the minimum.(3) From 1999 to 2013, the space changes of the general agricultural function value were mainly in the slight increase areas and the significant increase areas gradually increased. The spatial evolution characteristics of different agricultural functions were different. The space changes of the production function value were mainly in the slight increase areas, the significant increase areas distributed less, the significant decrease areas concentrated in the suburban areas. The space changes of the agricultural employment function value were mainly with slight increase areas, the significant decrease areas distributed in suburban areas and the distribution range had expanded. The slight decrease areas were located in the slight increase areas. The space changes of the agricultural tourism and leisure function value were mainly with slight increase areas and slight decrease areas. From 2006 to 2013, the scope of significant increase areas was rapid expansion and distributed in suburban areas. From 1999 to 2006, the space changes of the carbon fixation and oxygen release function value were mainly with slight increase areas and the significant decrease areas were less. From 2006 to 2013, the space changes of the carbon fixation and oxygen release function value were mainly with slight decrease areas and the slight increase areas were significantly reduced. The space changes of the agricultural water conservation function value were mainly with slight decrease areas, followed by the significant decrease areas. The increase areas were located in the decrease areas.(4) The change of agricultural function value was influenced by population and social factors, and the main driving factors were cultivated area, construction land area and population density. From 1999 to 2013, the main driving factors of the agricultural production function, employment function and tourism and leisure function were the human driving factors. In two stages, the biggest contribution rate factor of production function was the cultivated area. The biggest contribution rate factors of employment function were the rural per capita net income and total fixed asset investment. Social and economic development was the fundamental driving force for the improvement of agricultural employment function. The biggest contribution rate factors of the tourism and leisure function was population density. The greater the population density was, the higher the function of agricultural tourism and leisure. The driving factors of the agricultural carbon fixation and oxygen release function and water conservation function were the natural driving factors and human driving factors. In two stages, the biggest contribution rate factor of the carbon fixation and oxygen release function was urbanization rate. The biggest contribution rate factors of the water conservation function were the afforestation area and precipitation. The greater the area of forest land was, the higher the ability of plant interception, the stronger of the agricultural water conservation function. |
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