Abstract
The land-cover change caused by desertification and re.-vegetation in Inner Mongolia from 1982 to 1999 was analyzed using a time series dataset of the normalized difference vegetation index (NDVI) derived from NOAA/AVHRR images. Comparison of the long-term change in NDVI with the actual reported vegetation change for four areas with typical vegetation cover showed good correlations. The areas consisted of stable forest cover at Daxing'anlin Diqu, in Heilongjiang Province, a large increase in vegetation cover at Aohan Banner in the city of Chifeng, a relative increase in vegetation cover at Yijinhuoluo Banner in the city of Ordos, and a decrease in sparse vegetation cover around the arid area at Ejina Banner, in Alxa League. After considering threshold values for identifying vegetation change, we concluded that the area of increased vegetation is much wider than the area of decreased vegetation in Inner Mongolia based on a map showing land-cover change using ΔNDVI, which is the difference in NDVI between 1982-1986 and 1995.1999. Aohan Banner in Chifeng showed the largest increase in vegetation cover, and parts of Xilingol League, Hohhot, and Bayannur also showed distinct increases. The total area in which vegetation increased was about 200,000 km2 in Inner Mongolia. The area of vegetation increase according to ΔNDVI in each prefecture-level municipality in Inner Mongolia was proportional to the sum of the re-vegetated and newly developed cultivated areas given in yearbooks. A constant increasing trend in NDVI, caused by global warming, has been reported in the higher latitudes of the northern hemisphere. The trend toward increased vegetation cover in Inner Mongolia is mainly attributed to the expansion of cultivated and re-vegetated areas. By contrast, areas with decreased vegetation cover are widely distributed in Horqin desert and in the western arid area around Alxa League, despite a slightly negative NDVI change; this has ensued from the progress of desertification.
