Vegetation dynamics and its response to drought in the Inner Mongolia of northern China during 1998-2013

Vegetation plays a significant role in global terrestrial ecosystems and in combating desertification. Satellite-derived vegetation growth trend in the Inner Mongolia of northern China were analyzed by using the methods of slope of linear regression and Sen+Mann-Kendall analysis based on SPOT NDVI time series data from 1998 to 2013. The response of vegetation growth trend to drought indicated by the Standard Precipitation Evaporation Index (SPEI) also was explored in this paper. The results showed that vegetation in most of the study area had got rehabilitation to vary degrees from 1998 to 2013. Significant vegetation improvement had occurred in those regions such as most of the Horqin sandy land, the eastern Ordos Plateau including the Mu Us sandy land, the Hetao Plain, as well as the middle-northern Da Hinggan Ling Mountains. Vegetation degradation centrally distributed in Xilingol grassland close to the Sino-Mongolia border and the Yinshan Mountains in Ulanqab Meng, but the degradation trend is nonsignificant. Significant vegetation degradation area was very small, and mainly distributed around several prefecture-level cities where were disturbed by obvious urbanization. Huge variation of vegetation in the growing season (NDVI_gs) mainly occurred in those grasslands close to the precipitation isoline of 200 mm and the west part of Hulun Buir Sandy Land, but also variation of NDVI_gs greatly was attributed to the summer vegetation growth features (NDVI_su). Drought had significant influence on vegetation change of the most of the Inner Mongolia, except from the eastern Hunlun Buir Meng and the western Alxa Meng, whichever at 6-month scale or 12-month scale. Human beings had made great progress in improving local vegetation. But hazards caused by regional frequent droughts should be given further attention, especially in those grasslands or vegetated-dune fields with bigger vegetation variation, where grazing activities or reclamation must be strictly optimized or prohibited.

Key words: vegetation change; SPOT NDVI; linear regression; Mann-Kendall analysis; SPEI