| The ecological service function is the prevent windstorms and fastens sand in sensitive areas of the land desertification. It is important to the government to solve national ecological security and the contradiction between people and land of regional. To effectively Prevention and control of desertification, we must carry out monitoring and evaluation of sandy change. The method of traditional map has the following disadvantages, difficult, long cycle, lacking of evaluation on the time sequence and on a regional scale. Remote sensing technology provides methods of the macroscopic, dynamic, real-time monitoring for the sand control. Mean while, it also provide multi-source, multi temporal and spatial scale, multiple factors data for sandy evaluation. It provides a variety of ways for the sand surface change process. We applied the remote sensing, geographic information system technology and the theory and method of landscape ecology. Three elements are selected as the main research object, which is sandlot, vegetation, vegetation net primary productivity. The three elements all are closely related to development and change of sand. Using different temporal and spatial scales data of the Landsat M/ETM+, SPOT NDVI, NPP, we analysis and simulate temporal and spatial change and process of the sandy on the southeastern margin of Mu Us Sand land from 1991 to 2013. Mean while we monitors and evaluates effect of sand control.(1) This study analysis the shifting sandy land spatial and temporal change in Yulin city by use of TM/ETM+ data(30m×30m), and assessment the change on the scale of 1km×1km. The results showed: shifting sandy land only distributes in the six countries which are Yuyang, Shenmu, Hengshan, Jingbian, Dingbian and Fugu according to size of area of the shifting sandy land. The shifting sandy land annual change rate is about-2.36% in the Yulin city from 1991 to 1999.But it is about-3.91% during 1999 to 2007. The larger patch number and average area of the shifting sandy land is on the decrease and the spatial distribution of density values decrease continuously. Consequently, the desertification is under the control and the governance, the shifting sandy land fixing in Yulin city. The results of desertification control are better in Shenmu and weaker in Yuyang. The methods of transform grid scale don’t influence the shifting sandy land area. The shifting sandy land density and spatial distribution values can be used as indicators of desertification monitoring. The values can expression the aggregation degree of shifting sandy land with detailed, clear and intuitive. Through the grid expression of the shifting sandy land and extract density features, we can better evaluation of it’s the development and changes on the regional scale.(2) Taking the Dingbian County as a sample area, we study the pattern characteristics of vegetation and the change by using the TM/ETM data. The results showed that: the vegetation landscape pattern is multi-core modes. And the distribution of vegetation of core outline has the gradient. The different cores are connected by the intermediate degree vegetation. The core of sandy area is mostly no vegetation and the core of hilly is coverage by good vegetation. In the different periods, the vegetation pattern is same. But the area, shape of core and type convert to the advantage type. The 1999 is the turning point of the vegetation landscape structure change from 1999 to 2007. The two regions have the same trend, but the degrees are different. The first period is deterioration and the second period is significantly improved. With Vegetation landscape changing, the modes remain unchanged. However, the core area, the shape of patch and patch type is change. The desert landscape was partly replaced by the vegetation landscape in the western wind sand region. The vegetation was largely recovered from 1999.(3) By using of the data 1km×1km SPOT NDVI, We study transfer process of the five levels of vegetation in Yulin City. The results showed that: there are 3 stages of vegetation succession in Yulin city from 1998 to 2007: rapid degradation from 1998 to 1999, fast restoration from 2000 to 2002 and stable restoration from 2003 to 2007. In stage of rapid degradation, negative transition of many types and large amplitude is among different vegetation classifications, the lowest vegetation covers over half of the research area. In stage of fast restoration, positive transition of vegetation classifications accelerates, classification of main vegetation promotes. In stage of stable restoration, speed of positive transition slows down, classification of main vegetation stays the same, and coverage of higher vegetation adds while lower vegetation reduces. This indicated that the efforts to vegetation reconstruction and recovery are strong. The land desertification prevention degree is enhanced and the function of ecological service is improved.(4) We analysis vegetation spatial heterogeneity of NDVI and coupling with sand distribution based on SPOT NDVI from 1998 to 2013. The results showed that: NDVI spatial autocorrelation is significant in Yulin city during 1998-2013. There are four cluster regions. Low-low region concentrates in the northwest of the desert area with a wide distribution. High-high region scattered around the three hot spots in the southeastern where vegetation cover is high. Low-high region and high-low region distributed band like, low-high region is on the skirts of low-low region and high-low region is round high-high region. Low-low region goes through four stages which are degradation(1998- 1999), recovery(1999- 2002), stable(2002-2007) and cyclic degradation(2007-2013). At the same time, High-high also region goes through four stages which are degradation(1998-1999), recovery(1999-2003), stable(2003-2007) and improve(2007-2013). In the past 16 years, it is significant correlation between the annual rainfall and the NDVI value between 0.2-0.3 pixel frequencies of the low-low region, at the 0.05 level, the correlation coefficient is 0.502. Low-low region and the spatial distribution of sandy area is with strong coupling by study the cluster of average NDVI from 1998 to 2007.The impacts of annual precipitation on the less vegetation cover regions are larger. By analyzing the regional NDVI spatial autocorrelation, we can delineate ecologically fragile areas in the region.(5) We Study on the NDVI change of Yulin city on the pixel scale. The results showed that: The vegetation growth is 1.3%/a, 0.96%/a in Sandy region and 1.47%/a in Non sand region in Yulin in recent 16 years. All counties NDVI distribution heterogeneity is strong. At the same time, heterogeneity is high and poor stability in south-east region. Heterogeneity is the lower and strong stability in the north-west region. The NDVI appear on increasing on the whole and local reduction. The vegetation in south-east region shows the increase trend and worsen trend. Therefore, the restoration and reconstruction of the vegetation is very difficult in desert areas. The government must take effective measures to ensure the achievements and get the better development.(6) We analysis of spatial and temporal variation characteristics of NPP in Yulin City by Markov transfer matrix and Spatial overlay analysis based on the 2000, 2005 and 2010 NPP data. The results showed relusts. The Npp distributes from the northwest to the southeast gradually increasing in Yulin City. The annual NPP showed a significant upward trend from 2000 to 2010 in Yulin City. The NPP increased area is about 95%, which was larger than 300 g C/(m2 ?a) accounted for 47.22%,mainly distributed in the north and South Area from 2000 to 2005.Meanwhile,The NPP increased area is about 94%, which was larger than 300 g C/(m2 ? a) accounted for 54.10%, mainly distributed in the Southeast from 2005 to 2010. It indicates that the land productivity is restoring with the desertification governance.We can conclude that the land desertification is under control, governance and improves in Yulin from the shifting sandy land spatial and temporal, vegetation and Vegetation net primary productivity change. Meanwhile, the land productivity is restoring continued. But results of prevention and control of desertification is very different indifferent stages and difference of regional. |
PDF Full Text Request