| Land desertification is one of the most important problems about the issue of environment, social and economy in the world. The desertification land in China is mainly distributed in the arid, semi-arid and some of the semi-humid areas in the north. The area of desertification land is very large and it is widely distributed. And it has a very serious impact on the environment and others. The interleaving area of agriculture and pasture, grassland and the edge of desert are the most serious areas of desertification. There are eight large deserts and four large sandlots in China. The area of Keerqin Sandlot is biggest of the four sandlots. And it lies in the west part of northeast China, the transition zone of inner Mongolia Plateau and Northeast Plain, and is the transition areas of Daxingan Mountain knap zone and west Liao River Plain, the interleaving section of agriculture and pasture in east China.The paper is mainly based on geography, ecology, sight ecology, region location theory and system theory. By interpreting the MSS remote sensing image of 1970s and the TM remote sensing image of 1980s and the end of 1990s in Keerqin Sandlot based on background database and expert information, we have achieved the three periods vector data of land desertification of the research area, then we have disposed the data property by using the powerful spatial analysis function of Arc/info and achieved the information extraction and analysis supported by Arcview and Erdas Imagine. Thus the rule of temporal and spatial variation of land desertification in Keerqin Sandlot is researched and the blueprint and countermeasures of the prevention and treatment of land desertification in Keerqin Sandlot are put forward.1. In this paper, the background database of geography data, social economic data, midway data during the research course, and the research results database are established, which are needed for the land desertification research. The desertification land is classified as latency desertification land, gently desertification land, medium desertification, severe desertification land and theinseverest desertification land. The desertification distributing scope and degree of the research area in 1970s, 1980s and the end of 1990s are evaluated, based on the desertification research area and the collected remote sensing information, using the TM and MSS data, the background database of desertification research and the method of man-computer interactive identification based on knowledge system.2. The main technical module of processing GIS spatial information of land desertification is designed, which can carry out the spatial overlay of vector data in three periods, extract as well as process attributative information and transform the spatial vector data into visualizing data. The GIS database of land desertification is established.3. The overall temporal variation characteristics of land desertification in the recent 30 years in Keerqin Sandlot are that: the main types of land desertification are changed from medium and severest desertification types to gently and medium desertification types. The area of gently desertification land is increasing. The area of severe desertification is decreasing.The overall temporal and spatial variation trends in the recent 30 years are that: The total area of desertification land is increasing. The reverse trend of land desertification is greater than the evaluative trend. The proportion of gently reversion and distinctively reversion is equivalent.4. The driving cause of the formation and change of land desertification in Keerqin Sandlot is analyzed from the nature and society aspects based on field investigation and former research. The research indicates that the climate character which is the temporal coupling of aridity, lack of rain and excessive wind, together with the thick sand matter sediment of the west Liao River system, lead to the frangibility of environment in Keerqin Sandlot. In the recent years, there is a seriously lack of water resources...
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