Arid Zone Research (干旱区研究) 2011/28:1 PP.10-16
Interannual and seasonal variations of vegetation activity in Xinjiang during the period from 1982 to 2006 were studied using the time series data of normalized difference vegetation index (NDVI) derived from remote sensing images (NOAA/AVHRR), information of vegetation distribution and observed climatic data. The results show that the NDVI in growth season (from April to October) increased significantly in 27% of the study area but decreased in 4% of the study area in recent 25 years. The area with a high NDVI (>0.3) in growth season was enlarged by 5% during the period of 2002-2006 compared with that in the 1980s (1982-1986), and the area with a low NDVI (<0.1) in growth season was reduced by 5%. Seasonal NDVI in Xinjiang increased significantly in spring, summer and autumn in recent 25 years. Seasonal variation of NDVI reveals that the NDVI increase in autumn was the most significant (P<0.01), and the mean increase rate was 0.57%. However, the seasonal NDVI varied from different vegetation types. NDVI of grasslands and desert vegetation increased significantly in spring, summer and autumn, that of crops increased significantly in summer and autumn, especially in summer (increased by 1%/a), but that of forests increased significantly only in autumn. Therefore, our study suggests that the overtime of growth season and acceleration of plant growth were the main factors resulting in the increase of vegetation activity in Xinjiang, and the increase of temperature, rainfall in summer and agricultural practices might be the important driving factors.
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