Change Analysis Of Vegetation Cover Along The Qinghai-Tibet Railway On The Southern And Northern Edge Of Permafrost Region In Qinghai Tibet Plateau

Qinghai-Tibet Railway(QTR) is located in the hinterland of Qinghai-Tibet Plateau. The full opening of the QTR promoted the social and economic development of Qinghai and Tibet provinces, in the meantime, the railway construction process and long-time operation caused inevitable disturbance to the fragile ecological environment of the permafrost along the railway.In this paper, our study area is the southern and northern edge of permafrost region along the QTR. With the help of VIPER Tools, we accomplished quantitative extraction of vegetation coverage of the study area based on Multiple Endmember Spectral Mixture Analysis(MESMA) model. According to the statistical results, we analyzed the spatial and temporal change pattern of vegetation coverage, and explored the influence of the QTR on vegetation coverage. The conclusions are as followings:(1) The extracted vegetation fraction based on MESMA model has a high coefficient with NDVI, proving that the MESMA model is applicable of extracting the vegetation on Tibetan Plateau.(2) From the multi-temporal extracted results, it can be concluded that the vegetation coverage change shows same trends in space: in northern permafrost edge region, the vegetation coverage increases gradually within 5km and holds steady from 5km away; in southern permafrost edge region, the vegetation coverage increases within 20 km and reduces in 20-50 km buffer zones.(3) The railway caused both decreased and increased influence on vegetation coverage around the railway, and the northern study region was greater affected than the southern region. The construction process had great positive influence on vegetation coverage change, in northern region the maximum value of influence is 9.33% which occurred in 0.5km; in the southern region the maximum value is 2.55%, and its influence erea is limited within 1km. The decreased influence of railway running is relatively small, in northern region, the influence area controls in less than 1.5km, and the maximum value 6.75% occurs in 0.5km, yet the southern area shows almost no influence.(4) The distribution and variety trends of vegetation coverage on east and west sides along the track are different in different region: in northern region, before the construction and operation of the railway, the vegetation coverage of east side is larger than the west side, but afterward the pattern turn into opposite, besides, the difference is gradually expanded(the biggest difference of 2000 is 2.11%, 2007 is 3.31%, 2013 is 6.36%); in southern region, the vegetation coverage of east side is all greater than the west in 1999, 2009 and 2013 year. In addition, the farther away the railway, the coverage difference between the east and west side is lager. Moreover, the difference is also increasing with the increasing year(the biggest difference of 1999 is 25.93%, 2009 is 37.92%, 2013 reaches 47.00%).(5) The influence of railway on west is larger than the east both in northern and southern region. This phenomenon is related to the difference of vegetation coverage on east and west side along the railway.