干旱区生态环境知识资源中心

Grassland ecosystem degradation and desertification has been highly concerned in China for years because such degradation is perceived to directly relate with the occurrence of sandstorms invading into north China. In this study we intend to map the spatial-temporal variation of vegetation cover density from remote sensing data in Hulun Buir, a typical grassland ecosystem with the highest biomass productivity in Inner Mongolia of China. Since NDVI is a good indicator of vegetation, a practical approach had been developed in the study to map the spatial-temporal variation of the vegetation cover. The MODIS satellite data were used for the mapping. Results from our study indicated that the vegetation cover rate had been steadily decreasing in recent years, with relatively high spatial and temporal variation. Our study reveals that the rate on average has a trend of steadily decreasing in recent years. In 2000 the rate was above 80.6% on average, while it decreased to below 76.5% in 2006. Generally the west part of the region had much lower vegetation cover rate than the east part, probably due to the fact that the east part was dominated with forest ecosystem while the west part with fragile grassland. The counties of Xinbaerhuyou Banner and Manzhouli in the west part had the lowest vegetation cover rate among the 13 counties. As to the grassland types, lowland meadow had the highest vegetation cover rate while the temperate meadow and steppe had the lowest, indicating that ecosystem degradation was very serious in the temperate meadow and steppe, which were mainly distributed in the west part of the region. Though many factors might contribute to the decrease of vegetation cover, annual precipitation vibration had very good correspondence with the up-and-down change of vegetation cover in the region. In addition, overgrazing also played an important role in accelerating the degradation under the drought year. Therefore, we were able to conclude that the grassland ecosystem in Hulun Buir was under a very serious situation of degradation and desertification. Our study suggested that the change of vegetation cover rate could be an applicable indicator for grassland ecosystem monitoring required urgently to combat grassland degradation and desertification in arid and semiarid region.