Three-dimensional dynamic characteristics of vegetation and its response to climatic factors in the Qilian Mountains

• The increase trend of NDVI in the northwest is greater than that in the southeast. • NDVI fluctuated greatly and the growth rate was greater at low-altitude. • Vegetation in the QLMs is mainly affected by the time-accumulation of PRE and the time-lag of TMP. • Compared with PRE, TMP was the dominant factor of the greening in the QLMs. Understanding the trend of vegetation change and its reaction to climate variation is important for revealing the mechanism of ecosystem behavior. However, current research rarely systematically analyzes the time effects of climate variation on vegetation dynamics (time-lag and time-accumulation effects), especially in arid and semi-arid mountainous terrain. The typical mountainous terrain—the Qilian Mountains was taken as the study area, and the spatiotemporal changes and vertical zonality distributions of the normalized vegetation index (NDVI) were explored. This study explored the time-lag and time-accumulation effects of the NDVI response to climate factors (precipitation, temperature), identified the main controlling factors that influence the variation of NDVI. The results show that in the growing season from 2000 to 2019, the NDVI represented an overall upward trend, especially in the northwest, and the growth rate of NDVI at low-altitude was greater. The time-accumulation effect of precipitation has an obvious effect on vegetation, especially on deserta and meadow; and the time-lag and time-accumulation effects of temperature have an obvious influence. Regarding the climate-vegetation response mechanism, this study finds that considering the optimal time effect is of great significance. In addition, compared with precipitation, the temperature has a more significant promotion effect on vegetation growth in the Qilian Mountains. The above results indicate that when the existing climate models study vegetation-climate interactions, considering the time effects of vegetation response to climate is of great significance for accurately monitoring vegetation dynamics under environmental changes.