| Western Sichuan Prov is located in upper reaches of the Yangtze River, it’s the birthplace of the key river system and belongs to the fragile eco-regions in China The balance of the eco-system directly affected the ecological security of the lower-middle reaches of Yangtze River. The fragile eco-environment is sensitivity in this region and mainly reflected the effect and influence of the human activities by the change of the pattern of land use. This study refers to the western Sichuan region consists mainly of the Ganzi Tibetan Autonomous Prefecture in Sichuan Province, the specific scope of the study three typical county of Ganzi Tibetan Autonomous Prefecture, analysis of the structure of the land use in recent15years is benefit to the responses of the environment to human activities and initiate the changing driving forces and the whole region. Grassland is one of the most important segments of the ecological barrier in western Sichuan and the basis of the pasture development. There exits conflict between the needs of economic development and maintance of ecological equilibrium in this region. With the development of economics and increasing population, pressure will increase to the resources of vegetation and pasture in this region. Herdsman Settlement Project is a method to decrease this pressure mainly by changing the lifestyle of the herdsman, and the ultimate goal is to harmonize man and land and balance the development of the population and resources. But most of the present research of the settlement of the herdsman focus on qualitative analysis, it’s neither to embodied the benefits of the project in scientific and visualized, nor provide scientific basis and guide to the Continuing to implement this project.Firstly, three representative typical counties were selected from the whole study areas, and then based on remote sensing interpretation, the paper got the landuse structure change facts of the three typical study areas under three different periods.Secondly, based on the previous interpreted landuse data of the typical areas in three different periods, with a combination of different regional problems and the landues strcture change themselves, the author describes the driving force factors that caused the regional problems of Shiqu County, Derong County, and Yajiang County, which are located respectively in western Sichuan Three Rivers Source, dry-hot valley (DHV) area, and Longitudinal Rang-gorge Region, from the following three aspecs:land desertification, landscape pattern evolution, and urban center sprawl.Finally, the paper applies system dynamic method for the first time to study on herdsmen settlement engineering, and a case study of Shiqu County which has the most prominent contradiction between man and land and the most sensitive fragile eco-environment, develops landuse system dynamic model. Through the simulation of the interactions as well as mutual influence among various land types and socio-economic factors, the author concludes the the regional landuse structure change characteristics and make a quantitative description of how herdsmen settlement engineering works to alleviate the pressure on the grassland ecosystem.The result is as the following:(1) The area of arable land in the three typical study regions has been decreasing while that of building land has been growing, speed of which is faster in the past10year compared with that in the former5years. This demonstrates that the social economy of these regions has been developing rapidly with the support of national macropolicy, and the rapid expanding of construction land has been taking over part of the arable land. Except that of Shiqu county the area of forest land in Yajiang county and Derong county has kept a downtrend, which demonstrates that the result of carrying out the "Grain for Green Project" and " Natural Forest Protection Programme" varies in different places due to the differences of human factor in these regions. To illustrate, Shiqu county, located in the origin of three rivers, is effected by little human activity. Therefore its forests has recovered well, area of which has been increasing in the mass. The area of pasture in Shiqu county has been growing, but the quality has got worse as the high coverage pasture has been turning to moderate coverage pasture. the area of high coverage pasture of Shiqu county shows an increasing trend in general but has been decreasing in the past ten years.(2) The land types and emphasis of land use of Shiqu county shows dramatically differences in years of1994,2001and2009. The problem of desertification is sever, deserted lands, desertification degree of which is mainly in low grade and middle grade, have taken27.49%area of the land of the county. Among these deserted lands, most are arable lands or pasture. The desertification degree in low-grade and middle grade of construction land and arable land is higher that other land types. By analyzing the level index of plaque type in Derong county locate in dry hot valley, it is concluded that the degree of separation and breakage of construction land and water area is high, while the separation degree of arable land and pasture has got a downtrend first but a uptrend later due to macropolicy and the strong interface of human. The analysis of the index of landscape level demonstrates that the landscape structure of Derong county was getting broken but turning to gather afterward, which means that the heterogeneity of landscape there was rising in the beginning then declined. However, the lands of this county are developing in the direction of diversification and homogenization in general. The construction land of the town and county is expanding along the river, butt which should be turned to "satellite town facet expand mode". From1994to2009, patch density, marginal density, Shannon’s diversity index and Shannon evenness index of the concentration part of the developing area of city, town and village have been decreasing while the CONTAG(Contagion Index) and polymerization degree index have been increasing, which means that this region has got dramatically build-up effect, landscape structure has been becoming simpler and the degree of landscape heterogeneity has been getting lower in general.(3)Through the scenarios simulation A(standard or criteria development type)and B(restrained type of herdsman settlement) of landuse dynamic model, we know that the grassland area change indicates a more obvious trend in degradation of the study areas, while the herdsman settle engineering can curb this tendency to a certain extent. The simulation results of scenarios B let us see clearly that the grassland area will be significantly restored during the period our country plan to apply the herdsman settle engineering. The grassland area of scenarios B will be more than that of scenarios A by480.00hectares, besides both grass yield and grassland vegetation coverage degree will gain a growth, which also show that herdsman settle engineering realize its ecological benefits in particular, to the restoration of grassland eco-system. |
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