Dynamic changes of grassland vegetation coverage from 2001 to 2011 in Gannan Prefecture

Vegetation coverage is an important indicator of grassland vegetation growth condition,and it has a crucial significance for evaluation and analysis of vegetation restoration.Using the Terra/MODIS product of MOD13A3 from May to October during 2001-2011,combined with ground observed data from 2006-2009,the inversion models of grassland vegetation coverage were established.Their precisions were compared and the characteristics of grassland vegetation coverage in the growing seasons of 2001-2011 were analyzed in Gannan Prefecture.The logarithmic function(y=33.658 ln x+112.65)of MODIS-EVI(enhanced vegetation index)best simulated grassland vegetation coverage in Gannan pastoral areas with aprecision of 93.31%.MODISEVI had more advantages in high vegetation coverage regions,and accurately reflected the spatial and temporal differences of vegetation coverage while reducing the effect of environmental factors to the maximum extent.In the recent 11 years,grassland vegetation coverage in Gannan Prefecture has shown an increasing trend.The grassland vegetation coverage was highest(78.43%)in 2005,and the vegetation coverage of 2001,2003,and2008 were lower than those in other years.The vegetation coverage in mid-west and southwest areas was better than that in the eastern area.Grassland vegetation was dominated by high,then higher vegetation coverage levels,while the proportion of other grassland vegetation coverage levels were small(6.98%)and stable.Overall,grassland in Gannan Prefecture for the 11 years was characterized by transformation from a high vegetation coverage into an even higher vegetation coverage.