Evaluation On The Function Of Agricultural Ecological Service In Xi'an

As the requirement of the quality of living environment increasing in urban areas and the quality of city environment sharply deteriorating, ecological environment deterioration has become one of the key problems affecting the development of cities. As an important part of urban ecosystem, urban agriculture has a great value in ecosystem services and sustainable development of the city. It provides urban residents with a lot of things or non-food products or services. Especially, many kinds of ecological service play a very important role in effectively improving the urban environment, maintaining the urban ecological health and sustainable development.Based on the theories of ecological economics, land resources and landscape ecology, this paper defines the urban agriculture and urban agriculture ecosystem, using the land use status data and social and economic statistical data of1999,2004,2010and2012, according to the nature and human attributes of urban agriculture, make up for the calculation model to measure the value of carbon sequestration, water conservation, water conservation of soil and environmental purification of urban agriculture in Xi’an. Furthermore, this paper summarizes the urban agriculture ecological service value in Xi’an, and compares and analyses it from two aspects of time and space for urban agriculture,different land types and each single function, sums up the characteristics and temporal and spatial evolution law of Xi’an urban agriculture ecological service. This study aims to provide the assessment of urban agriculture ecological service with a train of thought and method, to enrich and deepen the theoretical system of the urban agriculture, to provide a reference for the development and planning of urban agriculture, to provide theoretical guidance for Xi’an urban agriculture planning.Through the research and analysis, the main conclusions are as follows:1. The characteristics of Xi’an urban agriculture ecological function:(1) Xi’an urban agriculture ecological service value is7.46×1010yuan in1999, Xi’an urban agriculture ecological service value is5.45×1010yuan in2004, Xi’an urban agriculture ecological service value is5.71×1010yuan in2010, Xi’an urban agriculture ecological service value is5.33×1010yuan in2012;(2) The total ecological service value and ecological service value per unit area is different due to the difference of agricultural land use types. From the total, woodland> cultivated land> garden land> grass. From the perspective of per unit area ecosystem service, woodland> garden land> grassland> cultivated land;(3) Each individual function value of the urban agriculture is different obviously, carbon sequestration and soil and water conservation service value is bigger, water conservation service value comes second, the purification service value is minimum;(4) The spatial pattern of Xi’an urban agriculture ecological service is higher in south and lower in north.2. The temporal evolution characteristics of Xi’an urban agriculture ecosystem service:(1)1999-2012, Xi’an agricultural ecological service value continues to decline;(2) From the point of land use types,1999-2012, garden land and grassland ecological service value shows a trend of increasing, cultivated land and forest land is declining;(3) In space, the damping of the south districts and counties of the area in urban agriculture ecological service is greater than that of the northern districts and counties;(4)1999-2012, the individual function value appears various degrees reduction, including soil and water conservation function’s damping is biggest, environment purification function’s damping is smallest.3. The spatial evolution characteristics of Xi’an urban agriculture ecosystem service:(1) The continuous decrease area of ecological service value is mainly concentrated in the southern Qinling mountain, rendering narrowed down, but the damping showed a trend of increase;(2) From the point of land use types, ecological function value’s change of cultivated land is relatively concentrated, less and shows a trend of decrease; The variations of forest ecological service value is large and showed a trend of decrease, the damping of forest ecosystem service value in southeastern of Lantian county is the largest, followed by south and central of zhouzhi county. The southern of Chang’an and Hu county, northern district of Jingyang county and a small number of parts of southern Lintong county’s is smallest. Garden land and grassland area is lesser, the trend is not obvious, largely increase;(3) The individual function value is different obviously in space:carbon sequestration function’s damping presents increasing trend from the center of Xi’an to the surrounding counties; The changes of water conservation function is regional difference, damping larger areas are mainly distributed in Lantian county, Zhouzhi county and Hu county,increasing bigger areas are mainly distributed in northern of Zhouzhi county, Hu county and Chang’an county. Soil and water conservation function value’s damping is uniformly, the increasing regional distribution function value is scattered and small size. The increasing areas of Environmental purification value are mainly distributed in Xi’an around, the reducing areas of function value is located in the edge of the area, namely suburb located away from the city proper, and damping gradually increases.