Dynamic Changes Of Landscape Pattern And Vegetation Coverage Loess Plateau For Nearly 20 Years

Located in the center of Loess Plateau, the Loess Plateau of Northern Shannxi Province is a special region suffering from the frailest ecological environment and the most serious soil and water loss in this area. Vegetation coverage is a comprehensive quantification index and important parameter to evaluate the eco-environment and ecosystem construction, so the study with the estimation, dynamic change and evolution of landscape pattern of the vegetation coverage has an important role in the effective control of soil and water conservation, ecological restoration and environmental construction.This thesis takes Loess Plateau of Northern Shannxi Province as its research area, and adopts three periods Landsat TM images around1990,2000, and2010as the remote sensing data sources. The vegetation coverage is estimated by using of modified dimidiate pixel model, and classified into different levels. On this basis, the dynamic change and evolution of landscape pattern of vegetation coverage in this research area are analyzed by the transfer matrix method, differential method, evolution of gravity center method and the landscape structure index, respectively. And the following results have been achieved:1. The vegetation coverage of Loess Plateau presents an increasing trend from1990to2010. In the first study period (i.e. from1990to2000), the vegetation was degraded seriously, and the decreased net area is38377km2. While in the second study period (i.e. from2000to2010), the vegetation was improved effectively, and the increased net area is47458km2. There are differences between transfer and change for all levels of vegetation coverage. The inferior and superior vegetation coverage changes mainly in quantity, and the second-inferior presents the transfer of position in space, while the medium and second-superior vegetation coverage has both the transfer in quantity and the change of position.2. The dynamic change of Loess Plateau vegetation coverage has different spatial distribution regions. In the first period, the regions with worse vegetation coverage are the loess ridge, hilly and gully region in the central research area, the loess hill and ridge region in the north, and the Baiyu mountain area in the west. While the regions with better vegetation coverage are the earth-rock low hilly region in the south, the loess tableland and ridge area in the east, and the area along the Great Wall in the north. And in the second period, the vegetation coverage of the areas both along the Great Wall in the north and the earth-rock low hilly region in south of research area gets worse, while the central area and its west become better. When it comes to the period from1990to2010, the area with obvious increasing vegetation coverage is concentrated in the middle research area, and the regions with dramatic decreasing vegetation coverage located in the counties of Fugu and Shenmu in the northern loess hill and ridge area.3. The gravity center of vegetation coverage with different levels (i.e. inferior, second-inferior, medium second-superior and superior) shifts from the high latitudes to the low latitudes gradually, and with different movements from1990to2010. It turns to the northeast for the less than40%vegetation coverage, and to the southwest for the more than60%vegetation coverage, and veers toward south for medium vegetation coverage, which forms a distribution with two directions expansion of southwest-northeast in space.4. The landscape pattern of Loess Plateau in North Shannxi presents lower degree of fragmentation, decreasing dominance of landscape patches, increasing trend of plaque extension and degree of aggregation, and homogenized trend of spatial distribution from1990to2010. All the evolutions of landscape pattern of forest zone, forest grass zone, dry and desert prairie zone show that the fragmentation of the whole landscape has reduced, the regional landscape diversity has decreased, the shape of patch has become more and more complicated, the aggregation distribution of each patch in space has increased, but the landscape diversity and evenness do not change significantly, In general, the vegetation system quality information,ecological environmental system, and the ecosystem services for three vegetation regions of the Loess Plateau can be express as forest zone> forest grass zone> dry and desert prairie zone. And this landscape pattern is the result of four elements such as topographic and geomorphic, climate conditions, vegetation type and human activity worked together.