Effects of Spring Phenology on Grassland Growth in Qilian Mountains Across Multiple Spatiotemporal Scales

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AbstractInvestigating the differences in grassland growth and its response to advancing spring phenology and climate change across various spatiotemporal scales is crucial for the sustainable development of alpine mountain regions under a warming and wetting climate. This study analyzed the growth dynamics of grassland in the Qilian Mountains from 2000 to 2019 at seasonal and periodic scales. Using partial wavelet coherency and partial correlation analysis, we investigated the influence of temperature, precipitation, and spring phenology on grassland growth. Additionally, we quantified the dominant factors affecting grassland growth in different ecological zones and elevational gradient. The results indicated that the mean normalized difference vegetation index increased at an average rate of 1.1 and 2.8 × 10−3/year for grassland in spring and summer, respectively. Furthermore, the start of vegetation growing season (SOS) has advanced 6.0 days during 2000–2019. The dominant factor for grassland growth shifted from spring temperature to summer precipitation. The importance of SOS ranked second, significantly influencing 29.3% and 25.1% of grassland during spring and summer, respectively. Grasslands situated above 4,000 m above sea level (ASL) were more sensitive to climate change, with SOS exerting the greatest influence within the elevation range of 2,800–4,000 m ASL. Additionally, the phase difference in the time‐frequency scale of partial wavelet coherency revealed a lag effect of approximately 1 month for summer grassland growth to respond to precipitation. These findings can provide a scientific basis for optimizing global vegetation models and predicting the productivity of alpine mountain grasslands.