| Vegetation which refers to surface of plant community in general, is an important part of the land ecosystem and the foundation of the existence. And it is also connected to the natural "bond" of soil, air and moisture. Vegetation coverage and its change offer important information for the change of ecological environment, and has important significance to hydrology, ecology, global change. The upper reaches of the Dadu River, located in the eastern edge of Hengduan Mountains, west plateau of Sichuan and Sichuan Basin transition zone, farming animal husbandry distribution in China, belongs to the important forest area of the Southwest and is also an important national corridor. All of this has the significant meaning about the study of the vegetation coverage on the research area. The article selected the Danba in upper reaches of the Dadu River as the research area, and depended on the data of remote sensing imagines in three periods of1989,2000and2009. Based on software platform of ERDAS IMAGINE9.2and ARCGIS9.3, this paper extracted the vegetation coverage information with the help of dimidiate pixel model. The vegetation coverage was divided into five grades:low coverage (<15%), medium low (15%～40%), coverage (40%-60%), medium high coverage (60%～75%) and high coverage (>75%). Temporal and spatial variation characteristics of the vegetation coverage, from1989to2009, was analyzed in this paper. Besides, Combined with DEM data, vegetation distribution and its change characteristic in different elevation, slope and aspect was also analyzed. Main roads and settlements in study area as object to the establishment of three level buffers, this paper analyzed the influence of highway and population distribution to vegetation coverage of the study area. The main conclusions listed as follows:(1) As a whole, vegetation canopy in the study area was well, which the area of high-level and medium high-level vegetation accounted for above50%. Area of low-level and medium low-level vegetation accounted for34.28%. In space distribution characteristic, the vegetation above the medium level was mainly distributed river valley with relatively low elevation and better water and heat condition, the vegetation below the medium level was presented a characteristic that distributed along the ridge. Less Vegetation canopy in Daduhe river valley in east-north area due to the frequent human activity.(2) From1989to2009, vegetation coverage in the study area overall increased. But it showed different trends at different stages. From1989to2000, with the degradation of low and low medium vegetation, the dimension of the vegetation coverage area increased in1221.74hm2and1524.37hm2, and the dimension of the high and the medium high vegetation coverage area reduced by7614.23hm2and109.39hm2. In the period of2000-2009, the dimension of the high and the medium high vegetation coverage area increased by11116.08hm2and2540.44hm2; the low and the low medium vegetation coverage area the reduced by15311.89hm2and1595.82hm2.(3) Large difference of the vegetation cover exited in different sea levels, slope and aspect area. In the point of elevation view, in1741to2500m range, human activity is relatively frequent, which low vegetation cover exit in general, the proportion of low and in low vegetation coverage area was46.05%, while high and high vegetation coverage area was only21.42percent, high vegetation coverage area counted only5.84%; in the range of2500-4500m high area ratio of more than50%and high vegetation coverage in the main, high vegetation coverage area ratio of35.75%. It shared a relatively small area ratio of37.98%in low vegetation coverage region. In the range of4500～5429m, vegetation cover was low for it was affected by the altitude and heat conditions, and area ratio of low vegetation coverage was up to67.56%, while the high vegetation coverage area was only0.04%. From the point of the slope, in the region of0°～15°, the slope is relatively flat, and frequently of human activities, vegetation cover mainly to low and low vegetation coverage,57.17percent about the area ratio, and high vegetation coverage area, compared to just29.91%. in the region of15°to45°, and high vegetation coverage area ratio was above41.11%, the relative0°～15°region has increased, while the low and medium low vegetation coverage area ratio relative decline;45°～85°region, the vegetation coverage was further enhanced, high and medium high vegetation coverage area ratio was up to51.27%.From the aspect of view, high and high vegetation coverage mainly distributed in the east slope and the southern slope area, where the area ratio was67.46%and68.40%... |
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