Temporal and spatial dynamic of Xilingol steppe based on MODIS NDVI in recent ten years

In the present study, the normalized difference vegetation index (NDVI) estimated from MODIS data were employed to analyze the temporal and spatial dynamic of different grassland types during growth season (April to October) in the recent 10 years (from 2003 to 2012) in Xilingol. The NDVI decreased from northeast to southwest in Xilingol in spatial. The maximum spatial differences occurred in 2005 and the minimum spatial differences occurred in 2007. The spatial variation of the same grassland type was similar during the study period. Temporal series analysis showed that the whole regional NDVI in 2012 was the maximum which followed by 2003. However, the minimum regional NDVI variations occurred in different period for different grasslands. For example, sandy grassland and desert steppe had minimum regional NDVI in 2005 and major NDVI fluctuations from 2004 to 2006, however, meadow steppe and typical steppe had minimum regional NDVI in 2007 and major NDVI fluctuations from 2007 to 2009. Spatial variation analysis showed the coefficient of variation (CV) of sandy grassland from 2003 to 2012 was less than 0.1 which indicated this type grassland was very stabilization. The CV of meadow steppe, typical steppe and desert steppe gradually increase which also was stable at 0.1 to 0.2. These results indicated that the ecological vulnerability of Xilingol was stabilization. The correlation analysis between main meteorological elements and NDVI indicated that there was a significant positive correlation between NDVI and precipitation which has a coefficient of 0.83. However, there was negative correlation between sunshine period and NDVI and no significant relationship between average temperature and NDVI.