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| Research on change of vegetation fraction and its effect factors in Yanchi county,Ningxia Hui Autonomous Region |
| Zhang Kebin,Li Rui,Xia Zhaohua,Shen Yan |
| Key Lab.of Soil and Water Conservation and Desertification Combating, Ministry of Education,College of Soil and Water Conservation,Beijing Forestry University,100083,Beijing,China |
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Abstract Selecting 3 sceneries of Landsat TM image shot in Aug 1989,Aug 1999 and Aug 2003 in Yanchi County,Ningxia Hui Autonomous and basing on NDVI and the quantificational model of remote sensing,the grade maps of vegetation fraction were extracted.Through contrasting and analyzing the vegetation fraction of different grade in 3 phases,the result show that the variable tendency of the vegetation fraction is obvious,(especially) the vegetation of low and medium-high coverage.From 1989 to 2003 the area of the low and medium-high coverage vegetation increasing sharply 64.62% and 72.04%.From another angle,the change show that the reverse motion of desertification occurred in the period from 1989 to 2003 in Yanchi County.There are two reasons for vegetation improvement in Yanchi County,one is climate factor such as rainfall and evaporation,and another is artificial factor such as converting cropland to forests,closing and fencing and discontinuing farming and letting go out of cultivation,but the most important effect factors are rainfall and evaporation.The results of correlation analysis show that the correlation coefficient between the vegetation fraction and rainfall,evaporation are very high in Yanchi.The land use types of medium vegetation fraction mainly include(semi-fixed) sand land,deteriorated land and deteriorated grassland,it is the main types of vegetation fraction,and area of this type was 70.65% of total area in Yanchi in 2003.The area of medium vegetation fraction is large,its ecological structure is very fragile and it is the stress area of desertification prevention and cure in the(future.)
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Received: 28 November 2005
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