Vegetation responses to climate change in the Qilian Mountain Nature Reserve, Northwest China

摘要

Understanding the dynamics of vegetation responses to climate change can provide important information for environmental management. The Qilian Mountain Nature Reserve in Northwest China, a high-altitude mountainous region that is of critical ecological importance, has been affected by drastic climate change. However, the response of vegetation to climate change in this area has not been established. This study aims to address three unanswered questions. First, what is the relative importance of temperature and precipitation change in driving regional vegetation change? Second, how does this vegetation–climate relationship manifest itself across different timescales (e.g., seasonal)? Third, what is the spatial heterogeneity of the vegetation–climate relationship? Based on MODIS data and daily meteorological data from 41 stations within and adjacent to the reserve, we used Ensemble Empirical Mode Decomposition (EEMD), Theil-Sen median trend analysis, the Mann-Kendall nonparametric test, and Pearson correlation analysis to study the evolution of temperature, precipitation, and the normalized difference vegetation index (NDVI). The key results are as follows: (1) during 1985–2019, the temperature in the reserve has increased by an average of 0.048?°C/a, with the largest average annual increases occurring in spring (0.069?°C) and summer (0.056?°C); (2) during the same period, precipitation in the reserve increased by an average of 1.17?mm/a, with the largest annual increases occurring in autumn (0.669?mm) and summer (0.545?mm); (3) during 2001–2019, the NDVI increased by an average of 0.004/a; an average annual increase was experienced in all seasons, although the largest increase occurred in summer; (4) there is a statistically significant positive correlation (0.619) between the NDVI and temperature at the annual scale; (5) in contrast, the correlation between the NDVI and precipitation is weaker and not statistically significant (0.368), which indicates that temperature is the dominant factor affecting vegetation changes in the reserve; (6) there exist seasonal differences in the vegetation–climate relationship. The positive correlation between NDVI and temperature is strongest in spring whereas the positive correlation between NDVI and precipitation is strongest in summer; (7) the vegetation–climate relations demonstrate a degree of spatial heterogeneity driven by variability in climate factors and ecosystems. The value of this research is that it analyzes the response characteristics of vegetation to climate change using multiple methods and at multiple scales, providing a useful reference for understanding vegetation changes and their response to climate change in high-altitude mountain regions.