| Loess Plateau has an important strategic position in China's regional economic development, and it has serious soil erosion, bad ecological environment, and poor land use management which exacerbated the degradation of land resources and the poverty of people living. Southern Ningxia is a typical representative of the Loess Plateau. How to restore the ecological environment and get rid of poverty is an important subject for Southern Ningxia and the whole Loess Plateau. Carrying out the study on land use change and its effect on the ecological environment in Southern Ningxia and proposing the ecological function zoning is crucial for rational use of land and improving the eco-environment and people's living standards. Studies on land use in Southern Ningxia focused on the small watershed scale. It is of a great thoretical and practical significance to develop the township scale land use change in order to promote and verify the results of optimizating small watershed land use, make up for the limitations of small watershed scale in space, form a law of "Village - Township - County" multi-scale comprehensive land use dynamic changes, and solve the problem of rational use of regional land fundamentally.In this dissertation, taking Hechuan Town in Guyuan City, Ningxia Hui Autonomous Region as an example, using 1:10000 topographic maps and remote sensing image, under the guidance of the technology of GIS and the theory of land resource science and landscape ecology science, and topographic maps, the change of land use pattern, its driving mechanism and ecological effects, suitability and optimized model of land resources, and ecological function zoning at town scale are studied roundly. The main results and conclusions of this paper are as follows:(1) Change of land use pattern Analysis on change of land use pattern was conducted between the time period of 1982 to 2002 and the time period of 2002 to 2008 in Hechuan Town. Results indicated that the most significant change from 1982 to 2002was the increase of arable land and the decrease of grassland, and that the most significant change from 2002 to 2008 was the increase of forest land and the decrease of arable land. Throughout the study period, the orchard was increasing which reflects its important role in agricultural development in Hechuan Town. The residential area was increasing slowly, indicating that the region's social and economic was poor and its development was slow. In addition, unused land was declining and water area change little. The main types of land use conversion from 1982 to 2002 and from 2002 to 2008 were transferring grassland to arable land and transferring arable land to forest land or grassland, respectively. The degree of land use increased because of the blindfold and excessive grassland reclamation before the Grain for Green project and declined because of the Grain for Green project. With the Geo-informatic Tupu method, the Tupu on land use change and arasing and falling series of land use change was established, from which the characteristics of the increase or decrease of some land use type, the conversion type, and their spatial distribution can be obtained exactly and intuitionisticly.(2) Driving forces of land use changeThe distribution of land use pattern has a certain regularity with topographic change: arable land are located in medium altitude and 0°-15°slope, the shrub land are located at high altitudes, 15°-35°slope, the orchards and residential are located at 0°-8°slope and low altitude, and the grassland are located at slope greater than 25°.The characteristics of the socioeconomic driving forces on land use change: in 1982-2002, the main driving force of the increase of arable land and the grassland degradation was economic, the main driving forces of the increase on forest land were science, policy and technology, the main driving force of increasing orchards were technology, policy and economy. In 2002-2008, the main driving force of the decline of arable land and the increase of shrub land was policy; the main driving force of increasing orchards was economy.(3) Landscape change and its ecological effectsThe landscape pattern of Hechuan Town from 1982 to 2008 experienced an"arable land and grassland dominated - arable land dominated - coordination of forest, grassland, arable land in propotion"process. The landscape dominance declined, and the diversity increased. The landscape structure developed in the direction of sustainability on the whole. The value of ecosystem services increased from 19,284,300 yuan to 32,956,100 yuan. The landscape patterns and the ecosystem services value existed regional differences. For example, the counties distributed by the flat land, such as Luotuohe, Shanghuang, Mingchuan and Zaiwa, had higher landscape fragmentation, diversity and ecological services value.(4) Effect of land use on soil carbon and nitrogenLand use is an important factor on the distribution of soil carbon and nitrogen content and carbon density. The characteristic of soil carbon and nitrogen content and organic carbon density under different land uses are as follows: the carbon and nitrogen under shrub land and natural grassland was significantly greater, the carbon and nitrogen under arable land was significantly lower, and the carbon and nitrogen under grassland and arable land were in same level. The organic carbon density under shrubland, natural grassland, artificial grassland, cropland, abandoned cropland, and orchards were 6.74, 6.32, 4.05, 5.69, 4.11, 4.65 kg m-2, respectiveily. The organic carbon density in Hechuan Town was 5.67 kg m-2, slightly higher than the average level of the Loess Plateau, and the total carbon storage was 1,148,541.66 tons. Rational land use pattern change is of a great significance on the increasing soil organic carbon storage. Shrub land and grassland are the most effective land uses to increase carbon sequestration and control soil erosion. The Grain for Green project plays an important role on the increase of soil carbon stocks.(5) Suitability evaluation of land resourcesThe six indicators, including altitude, slope, aspect, soil organic matter, soil erosion and water conditions, were selected as the land suitability evaluation factors. In accordance with the order of agriculture, forestry and stockbreeding, the study area was divided into five categories of land resources, including the land highly suitable for agriculture, the land moderately suitable for agriculture, the land suitable for forestry, the land suitable for both forestry and stockbreeding, and the land suitable for stockbreeding, accounting for 4.86%, 16.73%, 3.98%, 53.77% and 20.67%, respectively.(6) Ecological function zoning of land useUnder the Ecological Economic Zone Liupanshan Planning Framework, according to the land use pattern analysis and the results evaluation of ecosystem services and land use suitability evaluation, Hechuan Town was divided into three functional regions: soil and water conservation eco-environmental protection region in north mountain district, high efficiency ecological agriculture region in flat district, and dry farming region in south mountain district. Soil and water conservation eco-environmental protection region in north mountain district areas 13820.53ha, accounting for 64.13% of total area with broken terrain and severe soil erosion, the direction of land use in this region is to restore the vegetation, conserves the soil and water. High efficiency ecological agriculture region in flat district areas 4627.91ha, accounting for 21.46%. The land is flat with good water and fertilizer conditions. The land use direction is to develop the efficient ecological agriculture. Dry farming region in south mountain district areas 3110.45ha, accounting for 14.4 %. The land use direction is to construct basic dry farming land and ensure the food production. |
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