Research Of Vegetation Change And The Potential Degradation Risk Evaluation Of Marsh Wetland In The Mt. Qomolangma National Nature Reserve

The Qomolangma National Nature Reserve was established on 18 March 1989, On March 2005, it was listed in the global biosphere protected area network. The domestic studies on its vegetation cover change are less,and marsh wetland is very important to the environment of this region.Based on the project that the international scientific and technological cooperation project between China and Belgium that The Nature and Cultural Heritage Resources Information System in Tibet (2008-2009, 2008DFA11020) , this paper accomplished two aspects of research. On the one hand, using MODIS NDVI data from 2000 to 2009, the spatial distribution and variation of vegetation cover on the south slope and the north slope in the Mt. Qomolangma Nature Reserve were studied based on the linear trend analysis on the growing season NDVI peak value of each pixel by pixel level. The results showed that: (1) For significantly improved area and slightly improved area of vegetation cover, average annual growth rates of NDVI-Max are 3.06% and 1.25% respectively; For significantly degraded area and slightly degraded area of vegetation cover, average annual reduction rates of NDVI-Max are 2.82% and 1.09% respectively. (2)The vegetation cover of the south slope of the Mt. Qomolangma Nature Reserve showed an increasing trend on the whole from 2000 to 2009, and 22.59% of research area improved greatly, 19.05% improved lightly, 24.75% kept stable; while in the north slope, the vegetation cover showed a decreasing trend on the whole, and 19.5% of research area degenerated greatly, 24.43% degenerated lightly, 38.12% kept stable; (3) Among the eight landuse types covered with vegetation in the south slope, the vegetation cover of dry farmland in mountain area showed a decreasing trend, and the others showed an increasing trend; while within the ten landuse types covered with vegetation in the north slope, all of the vegetation cover showed a decreasing trend.On the other hand, taking the Mt. Qomolangma National Nature Reserve as the study area, selecting all 23 MODIS NDVI images of 2009, using the HANTS algorithm based on Fourier transform to remove the interference of the cloud and reconstruct NDVI time series images. The Spectral angle mapper(SAM) was used to extract marsh wetland of the study area according to the different phenological characters between marsh wetland and other surface features. The area of marsh wetland is 2481.13km2, which account for 6.88% of total study area; Its distribution in Tingri was the most abundant, which account for 36.85% of the total marsh wetland area; followed by Dingjie, Nyalam and Geelong, the propotions are 25.79%, 24.5% and 12.86% respectively. According to the characteristics of the study area, we evaluated the potential degradation risk of marsh wetland in the study area by selecting annual mean temperature linear trend as natural risk factor, influences of settlements and roads as artificial risk factors which are based on distance decay theory. This paper divided general risk assessed results mainly into five grades, that is, the lowest risk, lower risk, moderate risk, higher risk, and the highest risk, the proportions of the total marsh wetland area in the study area are 7.39%, 13.61%, 24.72%, 31.43% and 22.84% respectively.