Change Trends of Grassland Coverage and Pasture Growth in the Northwest Area of Tibet

Based on the Normalized Difference Vegetation Index(NDVI) data(from 1981 to 2006),this paper revealed the dynamics of alpine grassland vegetation coverage and pasture growth in the northwest area of Tibet(NWT) by the method of remote sensing technique.The preliminary results were as follows: the alpine grassland vegetation coverage of NWT was very low that the average value was only 27.2% for many years.In terms of spatial distribution of grassland vegetation coverage,the eastern region had a relatively higher coverage of grassland vegetation;the western had the lowest vegetation coverage.During the period of 1981-2006,the average grassland vegetation coverage had a slight increasing trend,and most of the grassland area(60.7%) in NWT did not show a significant vegetation coverage change.The area with a significant decrease of vegetation coverage variation accounted for only 3.6% of the total grasslands surface,whereas that with a significant increase accounted for 35.7%.The grassland vegetation coverage in the western region had a marked rising trend while the coverage in the eastern regions had a decreasing tendency.