| The Remote sensing and Geographical Information System inside and out of the country were simply introduced. The general natural and social situation was illuminated. The TM type and the theories and methods to judge the type were introduction.It gave a detailed introduction about the classification process of Erhai watershed land use supported by Erdas 9.2 software with the resource of Landsat TM 1990 and 2008. Used method of supervised to get two pictures of land use dynamic about 1990 to 2008, the total classification accuracy was 79.37%, Kappa analysis was 0.76 for 1990, the total classification accuracy was 77.69%, Kappa analysis was 0.74 for 2008. It shows that building increase by 102.97km2, brushwood increase by 50.17 km2, agricultural land increase by 29.90km2, grass decrease by 109.14 km2, and other types(including others, water and woodland) were not obvious in last 18 years. Analyzing from the degree of change, building changed greatly with 140.232%,then was the type of other with 72.84%(but must ignore in this thesis), the third was grass and brushwood 25.28% and 9.06%,ther showed limited change. Correlation analysis between population index of economical development and change of land use showed that population, gross national product were negatively correlated with area of farm land, and positively with building area from 1990 to 2007 in Dali City. So, population growth leaded farm land to decrease for Dali city with a relatively high rate of urbanization, but the growth of population may result in the increase of farm land,due to their demandin Erhai Watershed with high rate of agriculture. Rapid development of urbanization and growth of population were main reasons for change of land use during eighteen years.Although protected areas are generally believed to be the cornerstones of biodiversity conservation and safest strongholds of wilderness, human encroachments and threats are still very common in many protected areas. The Cangshan-Erhai National Nature Reserve often was disturbed by human economic activities, such as tourism, so we selected three typical small watersheds at eastern slope of Cangshan Mt. based on land use classification with the resource of Landsat TM 1990 and 2008of Erhai Watershed, combining with data of population, economy, industrial structure around area to discuss human impacts on ecosystem. The change of land use at eastern slope of Cangshan Mt. was similar to Erhai watershed. Percentage of building area increased from 5.61% to 15.05%, percentage of agricultural land declined from 31.83% to 21.51%, percentage of forest land increased from37.98% to 44.46%., the change of other types was not obvious in last 18 years. Although percentage of forest increased in-total, forest percentage of Xieyang Watershed and Yingle Watershed nearing city declined, percentage of building obviously increased contrarily at two watersheds. Percentage of forest above 2000m altitude increased, especially between 2200-2600m inside reserve was obvious, meanwhile it decreased below 2000m, wasn't obvious. Farm land and building were Main land types below 2200m, percentage of building increased sharply, correspondingly, there was a big decrease of farm land during eighteen years. Although ecosystem of reserve was suffering negative influence of human activities, construction of reserve had positive significance to protect forest, even maintain economical function of area.
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