| Land resources are the bases of human survival and development. With the rapid growth of population and the rapid development of industrialization and urbanization, land ecological degradation affects human health and restricts the socio-economic development seriously. Therefore, land ecological security has become one of the research frontiers and hot research topics now. However, at present, the theory and method of land ecological security research are still in the exploratory stage, and many problems need to be resolved. GuanZhong area which including different geomorphologic patterns is the economic and cultural center of western China. Land use changes such as urbanization and replacing farmland with forest are typical in GuanZhong area. With the accelerating of Western development, the pressures loading on the land here increase, and the structure and function of its land ecosystem have been changed violently. Studying the process and mechanism which these changes affect land ecological security here has important significance for keeping land resources of GuanZhong area sustainable and deepening the theory and method of land ecological security.Relying on the National Natural Science Foundation of China(No.40771019), Based on remote sensing images, fieldwork data, climate data, soil data, LUCC data, environmental and economic data, using the theory of geographic information images and supported by RS and GIS, choosing total soil production potential, vegetation cover index, ecosystem services value, and ecological risk intensity index as the evaluation index of land ecological security, the author has analyzed their temporal-spatial changes in different scales such as grid units, terrain units, slope units, and administrative units of GuanZhong area from1986 to 2007. Then assigning the weight for each evaluation index by entropy method and using principal component analysis to remove relevance of the weighted evaluation index, the author synthesized a comprehensive evaluation index of land ecological security by euclidean distance and revealed temporal-spatial changes of land ecological security of GuanZhong area in different scales betweenl986 and 2007. The results show that:1) From 1986 to 2007, the area of cultivated land, grassland, waters and unused land decreased, while the area of construction and forest land increased in GuanZhong area and the change accounts was about 5.70% of the total area. There are 29 categories of changes; and the 3 main kinds of changes whose area was 81.52% of the total changes were the transformation from cultivated land to forest land, from grassland to forest land and from cultivated land to construction. The largest change in plain and loess plateau was cultivated land converted into construction, while largest change in mountains, loess mountain ridge and loess tableland, was cultivated land converted into woodland. Fragmentation, diversity and dispersion degree of the landscape increased. Land use degree belonged to the period of development from1986 to 2000, and the period of adjustment between 2000 and 2007.2) Between 1986 and 2007, it decreased for the total productive potential of agricultural land in GuanZhong area, in which the total soil potential of the cultivated land and grassland decreased by about 6.64% and 5.20% while that of forest land increased by about 12.55%. It declined in general in all geomorphologic patterns for the total productive potential of agricultural land, which shrank the fastest in plain and the slowest in mountains. It decreased in slope zones from 0 to 20 degree for the total productive potential of agricultural land, which reduced with the slope increasing. It declined in all cities of GuanZhong area for the total productive potential of agricultural land, whose deceleration order as follows:Xi'an city>Xianyang city> Weinan city>Tongchuan city> Baoji city. There are five counties whose total potential of the agricultural land increased slightly while the others reduced.3) In 1986-2007, the vegetation coverage of forest and grass in GuanZhong area increased by 15.25%, and the growth rate of the vegetation coverage in 2000-2007 was as about 2.60 times fast as that in 1986-2000. The vegetation coverage in all geomorphologic patterns increased, and the order of the growth rate as follows:mountains> loess mountain ridge> loess tableland> loess plateau >plain. The vegetation coverage in all slope zones increased, whose growth rate expanded with the slope increasing. The vegetation coverage in all cities raised, and the order of the growth rate as follows:Xi'an city>Weinan city>Xianyang city>Tongchuan city> Baoji city. The vegetation coverage in all counties grew.4) From 1986 to 2007, the total ecosystem service value (ESV) of GuanZhong area increase by 10.09%; and the growth rate of the total ESV in 2000-2007 was as approximately 33.65 times fast as that in 1986-2000. Among five geomorphologic units of GuanZhong, the total ESV of plain reduced and the total ESV of the other four geomorphologic units increased, in which both the largest increment and the fastest growing took place in mountains. The total ESV of the slope zones between 0 and 3 degree declined, but the total ESV of the slope zones whose slope was more than 3 degree expanded, and both increment and growth rate increased with the slope raising. The total ESV of all cities of GuanZhong area expanded, and both the largest increment and the fastest growing took place in Baoji city. There are 11 counties whose total ESV increased in GuanZhong area in the research period.5) During 1986-2007, the land ecological risk index (ERI) reduced generally in GuanZhong area. Among five geomorphologic patterns, the land ERI of plain and loess plateau raised; but that of mountains, loess mountain ridge and loess tableland decreased. Among all slope zones, the land ERI of the slope zones between 0 and 3 degree increased, but the land ERI of the slope zones whose slope was more than 3 degree reduced generally. Among all cities, there was biggest land ERI in Weinan city and the smallest in Baoji city, while the land ERI rose generally in Weinan city and Xi'an city, but the land ERI reduced generally in Baoji city, Tongchuan city and Xianyang city. Among all counties, there were 17 counties whose land ERI rose.6) Between 1986 and 2007, the land ecological security situation improved generally in GuanZhong area, and there were more improvement in 2000-2007 than in 1986-2000. The land ecological security situation improved generally in all geomorphologic patterns, slope zones, cities and counties (except Urban area of Xi'an city) of GuanZhong area during 1986-2007,but during 1986-2000, the land ecological security situation deteriorated in plain and loess plateau, slope zones between 0 and 3 degree, Xianyang city and Weinan city, as well as 22 counties. Land use/cover change resulted in the temporal-spatial changes of land ecological security of GuanZhong area, and replacing farmland with forest helped the land ecological security situation here better.There may be following innovative in this research:1) Using land-use map and equivalent value per unit area of ecosystem services in China to obtain distribution map of equivalent value per unit productivity of ecosystem services, and then multiplying it with the distribution map of soil production potential which was revised with slope and vegetation index, by which the spatial heterogeneity issue of land ESV assessment was solved at the grid scale. This method made up a major flaw of land ESV assessment relying on equivalent factor.2) Overlaying the distribution map of land-use changes and the distribution map of land production potential, we can obtain the distribution map of land production potential transfer which includes information about the changes of land quality. This method made up the deficiency that land-use change can not reflect land quality erosion, and offer a workable approach for further improving the dynamic balance policy of arable land quantity.3) Supported by RS and GIS, multi-scale dynamic analysis was done in the research from grid cell to terrain patters, slope zones and administrative units. This method can help us get a deeper understanding on land ecological security situation and its conversion in different scales.4) Established a new evaluation index system of land ecological security. The indicator system is simple and universal. Each indicator means clear and has good comprehensive and representation.
|
PDF Full Text Request