Spatial characteristic of vegetation change in the source regions of the Yangtze River, Yellow River and Lancang River in China
2007, 26 (3):
The source regions of the Yangtze River, Yellow River and Lancang River are located in the middle east of the Tibetan Plateau with a total area of about 198496 km2. In recent years, the risk of vegetation degradation in the regions has been keeping increasing, which led to many negative effects. This study assessed the trend and temporal-spatial distribution of vegetation index change, which is related with vegetation degradation, in the source regions of the three rivers using multi-temporal NOAA AVHRR NDVI data (8 km spatial resolution) from 1981 to 2001 provided by NASA, DEM data (1 km resolution), roads, residents, rivers data (1 ∶ 250000) and collected field data. Data types converting and reclassifying and zonal statistic analysis are completed in Arcgis 9.0 software. Results show that: ①The decrease, improved and the invariant vegetation index occupied 18.92%, 13.99% and 67.09% of the whole study area respectively. ②The decrease rates of brush, needle-leaf forest, alpine meadow, alpine sparse vegetation and alpine steppes are 22.15%, 20.75%, 18.83%, 18.73% and 18.6% respectively; on the different frozen soil types, the decrease rates differ insignificantly.The vegetation index decrease rates on permafrost and seasonal-frozen ground are 19.78% and 19.41% respectively; the decrease rates are relative to the population density and livelihoods. ③The decrease rates are different in space, which in the source regions of the Yangtze River, Yellow River and Lantcang River are 13.56%, 32.51% and 18.1% respectively. ④The nearer to the roads and water sources is, the higher the decrease rates are; but to the distance buffers of the residents, the decrease rates rise with distance expending, and reach the top when arriving at the 24 km. ⑤The trend of decrease rates is according to the settlements density in different elevation zones with the correlation coefficient of 0.78. ⑥The vegetation decrease is highly related with the activities of human beings in the source regions of the Yangtze River, Yellow River and Lancang River.
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