The Quality Of Agricultural Landscape In Xi'an And Its Response To Human Disturbance

With the impact of human beings, the landscape structure and pattern of the original agricultural landscape have changed greatly. The agricultural landscape system structure and its various functional values have undergone tremendous changes. Agricultural landscape area is narrowing and agriculture ecological system becomes fragile, which affects the sustainable development of agriculture. The comprehensive evaluation of agricultural landscape is especially important. At present, in the study process of agricultural landscape, more attentions are fixed on agricultural landscape types and patterns as well as ecological process, while the services of agricultural landscape for humans is always neglected. Based on the theories of landscape ecology and agricultural geography, the paper put forward the concept "agricultural landscape quality" and built a comprehensive evaluation index system in order to make a comprehensive assessment on agricultural landscape based on agricultural landscape output ability, multifunction service and its anti-interference ability. With RS, GIS and mathematical statistics, based on the 0.5 km×0.5 km grid dimension, appraised the agricultural landscape quality in Xi'an city of the year of 1999,2006 and 2013. The dynamic change and spatial difference of agricultural landscape quality were analyzed from the perspective of time and space. Meanwhile, the paper also analyzed the spatial and temporal changes on human impacts in two aspects of regional development and agricultural activities. It also discussed the way how human affects agricultural landscape and offered a case study taking Xi'an city as an example. The purpose of this study is to provide a new way and method for the comprehensive evaluation of agricultural landscape, which may deepen the theory system of agricultural landscape and provide the basis for agricultural development and plan.The main conclusions are:(1) The index of the agricultural landscape quality in Xi'an city from 1999-2013 showed a slow increased tendency and then a relatively a faster increased tendency. The faster increased tendency could be proved in the producing economy and social function value of the agricultural landscape. The landscape aesthetics value decreased before it increased. In addition, the ecological function and the landscape index of state both decreased.(2) The agricultural landscape quality in Xi'an city showed a tendency of first increasing and then decreasing from central areas to peripheral regions. The index of the agricultural landscape quality in 1999 was mainly intermediate-low and intermediate value. The index in 2006 intermediate and intermediate-high value. In 2013, intermediate and high value. The high value area had been keeping enlarging on the plains of the far outskirts, while the low value had enlarged in the suburbs. The producing economical functional value of agricultural landscape increased first and then decreased from suburbs to peripheral regions in which the lower value areas of producing economical function were enlarging, and that in far outskirts kept increasing. Social functional value was higher and increased faster in the north plains than that in south Qinling area. The value of ecological function and the landscape index of state showed lower in the north areas than that in the south, and the north areas kept enlarging around the city while the south kept lessening. Landscape aesthetics value index showed high in the north foot of Qinling area and the east bank of the Wei River. On the plains, the areas where the index shows high was constantly enlarging, while the situation in Qinling didn't change.(3) Complex activities of human being had an increasing impact on agricultural landscape in Xi'an. The regional population, GDP and the area of construction land from 1999 to 2013 kept increasing, which means the scale of regional development kept enlarging and its speed kept improving. The total power of agricultural machinery and the use of chemical fertilizer showed a tendency of increasing, which means the agricultural activities were being strengthened.(4) The interference index of regional development and the intensity of agricultural activities reflect the intensity of the human impacts on agricultural landscape. The interference index of regional development in Xi'an city spread decreasing progressively from the central urban area to near suburbs then to further outskirts. The interference index high value of Xi'an city in 1999 was in the main urban area while it extended to the near suburbs like Yanta, Weiyang and Baqiao in 2013, with the punctated distribution turning into a surface shaped one. However, the lower index transfered from mid-far outskirts to far outskirts. In terms of the agricultural activity intensity of Xi'an city, it showed a tendency of first increasing and then decreasing from central areas to outskirts. The agricultural activity intensity of the plains in mid-far outskirts was proved higher than that in Qinling area and the city's perimeter zones where the minimum value has extended in area during 1999-2013. The intensity on the plains decreased progressively from northeast part of Xi'an to southwest in 1999 and 2006, and the area of higher value extended to the plains in mid-far outskirts in 2013.(5) Human impacts include regional development and agricultural activities. The regional development affects the quality of agricultural landscape through changing the scale of agricultural landscape, agricultural landscape structure, agricultural landscape pattern and agricultural ecological environment. The quality of agricultural landscape can also be influenced by agricultural activities through changing the comprehensive productivity of agricultural landscape, changing farmers'income, changing its pattern, and changing the vegetation growth, soil's physical properties as well as the circles of C, N, P and poisonous substance. The adjustment of agricultural industry structure and agricultural science and technology investment will guide the human activities.(6) The interference index of regional development in Xi'an had a moderate negative correlation with the agricultural landscape quality index, an exceedingly weak positive correction with the agricultural landscape producing economic value and social value, an exceedingly weak negative correction with the landscape aesthetic value, a notable negative correction with landscape ecological value and landscape index of state. It meant the regional development of Xi'an had an obvious negative effect on the ecological function and state of the agricultural landscape. The intensity of Xi'an's agricultural activities had a moderate positive correction with the agricultural landscape quality index, a notable negative correction with the ecological function and state of the agricultural landscape, a weak correction with the landscape aesthetic value, and a notable positive correction with the agricultural landscape producing economic value and social value. It meant the agricultural activities had an obvious negative effect on the ecological function and state of the agricultural landscape, but a positive effect on the agricultural landscape producing economic function and social function.