| Under instructions of agricultural location theory and sustainable development theory, taking Beijing plain area as a case study, this paper analyzed the characteristics and evolution mechanism of farmland in space and time process, with land use data obtained from remote sensing imageries of 2004, 2011 and 2014. Then, urban landscape limitations in the economic and policy were analyzed taking natural resources and the ecological environment of Beijing into consideration, and the design of agricultural land layout adjustment was proposed, which was more accordance with agriculture function in post-industrial age and different spatial planning of Beijing. At last, ecological system services value system was constructed and the gap between optimized agricultural land layout and current agricultural land layout in ecological system services value was calculated. This study can provide scientific support for achieving the sustainable development, cultivated land reasonable utilization and protection in Beijing. The main conclusions were as follows:â‘ Land use change was dramatically, and circle layer structure in agriculture land use was obvious in Beijing plain area.The general trend of land use change was that an amount of cultivated land was transformed into construction land and forest land in Beijing plain area from 2004 to 2014. Among agriculture land types, cropland was translated into forestland and facility vegetable land; and this phenomenon has distinct differentiation in spatial.In other words, the nearest and farthest regions to the central city, cropland was transformed into forestland mainly, and cropland in transition zone located between suburbs and outer suburbs was transformed into forestland, facility vegetable land and open-air vegetable land. Cultivated land loss was induced by building land expansion and urban greening. Responding to market demand, agricultural production structure was upgraded by farmers and cropland was transformed into vegetable land.Circle layer structure in agriculture land use was obvious in Beijing plain area. Forest land circle layer, rather than vegetable land circle layer, was nearest to the main urban area. From main urban area to outer suburbs, mixed circle layer of vegetable land-crop land-forest land and mixed circle layer of forest land and crop land were appear in order. Furthermore, Forest land circle layer next to the main urban area was become more contiguous and larger. This condition that vegetable land was replaced by forest land and forest land distributed continuously in suburbs was promoted by the "invisible hand" of the government which aimed at improving the ecological environment by conducting greening projects. But, cultivated land was mostly used as vegetable land in suburb and cultivated land was mostly used as crop land in outer-suburb in outer-suburb from 2004 to 2014. This was meeting to the agriculture location theory. At the same time, it resulted from the agricultural planting structure adjustment by farmers at the background of urban expansion.â‘¡ Layout and utilization of farmland should make full use of farmland ecosystem service functions.Ecological problem, such as water resource shortage, heat island effect, air pollution, green space insufficient, became the new restricting factors of urban sustainable development. Ecological services of agricultural land should be taken into fully consideration in agricultural land use in Beijing plain area. Targeting "livable city" of Beijing, "three circle layers+ one belt" optimized spatial layout of agricultural land was put forward, namely, city garden agricultural circle layer, eco-leisure agricultural circle layer, intensive and efficient agriculture circle layer, and eco-leisure agricultural belt. Based on the existing farmland use problems in 4 agricultural circle layers,5 agricultural land adjustment types were proposed, including urban beautification type, green and ecology type, green and safe type, eco-leisure type, intensive and efficient type. Details and time sequence of agriculture land adjustment were formulated from aspects of planting structure, farmland infrastructure construction and agromelioration.Landscape pattern was measured in current agricultural land use and optimized agricultural land use. Changes in landscape pattern indicating that farmland landscape became concentration and connectivity from the state of fragmentized and scattered. And optimization degree of landscape in suburb was more obvious than that in outer-suburb. Thus, the proposed agricultural land layout adjustment is beneficial for landscape and ecology which were the demands of metropolises.â‘¢ Ecological service function value of optimized agricultural land layout was higher than that of current agricultural land layout.In combination with the ecological environment characteristics of Beijing plain area and the reliability and availability of data, an ecosystem service value assessment system was established which included 8 indicators, namely organic matter production, gas regulation, nutrient circulation, clean environment, water conservation, biodiversity maintenance, landscape and leisure.The descending order of ecological system service values of Beijing plain area in 2014 was: organic production value, landscape and leisure value, gas regulation value, nutrient circulation value, biodiversity maintenance value, water conservation value, clean environment value. Forest land and crop land made the most contribution to the regional ecological service values. Ecosystem service value has the increasing trend from the urban area to outer suburbs in spatial. Low ecological service area, which was construction land mostly in Beijing plain area, appeared the ring and radial high ecosystem service value area. This was the result of green belts along roads and river.Ecological service value of agricultural land increased after agricultural land layout optimized. Thus, this paper proposed optimized agricultural land layout project could increase ecological service value. This conformed to the agriculture land function orientation at the background of "livable city" construction of Beijing and it was beneficial to ease the regional ecological environmental problem.â‘£According to the analysis of "One million mu afforestation in Beijing plain area", we got conclusions as follows. The success of "One million mu afforestation in Beijing plain area" was relied on the powerful finance of Beijing Municipal Government. And this put great pressure on the government financial. Furthermore, Fiscal expenditure on afforestation was much higher than the improved ecological service value. Due to the rare unused land in Beijing plain area, afforestation was on cultivated land mostly, which broke through the basic responsibility of protecting basic farmland and cultivated land.Taking economic feasibility, ecological service value, national cultivated land protection policy into comprehensive consideration, farmland ecological function should be fully used in urban landscape and ecological construction in metropolitan area. This can satisfy demands of cultivated land protection and ecological construction. |
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