Land Use/Cover Change In Ulanbh Desert And Its Surrounding Region

Desertification is one of the world's most prominent problem of ecological environment, which directly affect 3.6 billion ha of land, and account for 70% of land area, to threat human survival and development. Desertification land in China are mainly distributed in the northern arid, semi-arid and partial sub-humid, to form a discontinuous arc-shaped distribution belt from Northeast to Northwest. Ulanbh Desert and its surrounding areas locate China's western region of farming-pastoral ecotone which has a typical fragility and transition of natural environment. As a result of climate change, the long-term integration of grassland culture and farming culture has formed nature landscape, which farm and sand stagger, and human landscape, which is chartistic of farmin-pastoral and mixed residence of Mongolians and Han Nationality so as to become typical region for study LUCC of fragile farming-pastoral ecotone.In this study,4 Landsat TM images of summer of 1985,1995,2000,2004, were chosen, which had better plant growth, and collected natural, socio-economic data, to study land use/land cover pattern, dynamics, change mechanism, with ERDAS IMAGE,Arc View GIS,Arcview,SPSS. The results are as follows:(1) Based on aridity index, geomorphology, soil, vegetation, hydrogeology and sand movement, human activity, and administrative division, the study area was divided into 4 sub-regions, that is, Hetao plain sub-region, Ordos pleatu sub-region, Yinchuan plain sub-region, Alashan plateau sub-region to represent different ecological environment types.(2) In the entire study area, grassland and unused land form matrix jointly, which accounted for 41.50～53.68%,36.11～48.07% respectively. From 1985 to 2004, number, edge density, mean patch edge, mean shape index, area weighted mean shape index decreased, while mean patch size, mean patch fractal dimension, area weighted mean patch fractal dimension, shannon diversity index and shannon evenness index increased to show patch integration, complexity of shape, balance of land use types, reducation of area difference. Relatively stable land use/land cover results from nature factor and human factor. Different sub-regions have drfferent land use pattern. Oasis landscape, such as, Hetao plain sub-region, Yinchuan plain sub-region, farmland and grassland are matrix, due to natural conditions and human factors. As desertification region, the matrix of Ordos pleatu sub-region and Alashan plateau sub-region is grassland and unused land, which landscape is increasingly controlled by a handful of patches. Not only total area of unused land increased but also patch area increased so as to be more and more unfavorable to desertification control.(3) In entire study area, farmland, forest land, resident land and unused land increased while grassland and water body reduced. In 3 time periods, the trend of LUCC is different. Farmland, water body and unused land reduced, and increased, and reduced. Forest land reduced continuously after increase. Grassland and resident land increased, and reduced, and increased. like results of sub-region, single land use dynamic degree in 1995-2000 was larger than that of the other two time periods, but change rate of entire area was far less than that of sub-regions, which show that, in general, land use change of entire area was small, and local change was large. On the one hand, it reflects that worsening desertification is related to deterioration of natural condition, on the other hand, in the short term, local human activities impact on land use frequently and strongly. Comprehensive land use dynamic degree in 1995-2000 was the biggest while that in 2000-2004 was the smallest, in line with single land use dynamic degree. As to land use transfer matrix, we can not simply consider transition probability, in the mean time, we must also consider transfer area, because small probability change of large matrix may lead to huge area change. From the point of transfer direction, conversion from farmland, forest land, resident land, unused land to grassland shows that initial result of local returning farmland to forest and grassland have been achieved, but conversion from grassland to unused land, which results in significant increase of unused land, shows that partial deterioration of desertification make the desertification control a long way to go. In oasis, increase of saline-alkali land coming from beach, gobi and farmland, which show seriousness of land salinization, should not be ignored in oasis construction. Overall LUCC is not as same as that in different time periods, along with relative fluctuation.(4)Through principal component analysis, local desertification factor is integration of natural factor and human factor. Natural factor include climate, soil and so on. Human factor include excessive population, excessive reclaim, overgrazing, unreasonable water resource use and policy mistake. Because of bad nature condition, self-reversal's possibility of desertification of arid desert is very small so that human being must take powerful measure to control desertification.(5) South Ordos pleatu was taken as a example to research near future desertification dynamics. From 1991 to 2004, non-desertification area maintained invariable. Mild desertification reduced largely. Moderate desertification and severe desertification increased. Simultaneously different desertification degree transformed frequently each other, and patch complexity of severe desertification reduced. The above result indicated that desertification degree of study area was being weaken, and the present desertification degree is in the moderate desertification. The primary cause which influence vegetation coverage has two points:First, natural factor, for example, increase of rainfall is advantageous to vegetation restoration and has lagging effect. Second, human factor, desertification control measures have improved local ecological environment positively. Moisture and vegetation in semi-arid area are fairly better than that in arid area. If human disturbance were eliminated, desertification would have self-reversal possibility, but the reversal would have repeatability.