Characteristics and causes of vegetation variation in the source regions of the Yellow River, China

摘要

The eco-environment in the source region of the Yellow River in western China has been experiencing deterioration in the past decades. Vegetation affected by climate variables and anthropogenic activities is indicative of eco-environment well-being. To quantify temporal and spatial variations of vegetation coverage and analyse potential causes for the variations, we analysed the normalized difference vege-tation index (NDVI), temperature and precipitation data from 2000 to 2007. We found that altitude and topographic aspects have a strong influence on vegetation coverage. Altitudes between 4500 and 4800 m and shady aspects provide more favourable environments for vegetation growth. Data show stronger vegetation growth within the temperature range of 4.5-5.5°C. Vegetation growth generally increases with precipitation. At higher elevations of 4800-5200 m, however, despite high precipitation rates, lower temperatures restrict growth. Local hydrology condi-tions are found to directly influence vegetation variations. Vegetation degradation increases with distance from surface water boundaries up to 4 km, but ground-water might serve as a reliable source for preventing vegetation from degrading. Finally, we found that the percentage of degradation decreases with increasing dis-tance from residential loci up to 24 km, which suggests that overgrazing can be a lead cause for localized vegetation degradation. Findings of this study may have a broad implication in assessing vegetation variation and grassland restoration.