Spatiotemporal heterogeneities in vegetation phenophase responses to climate extremes in arid mountains of Central Asia

A comprehensive understanding of vegetation responses to climate extremes is essential for predicting ecological risks. The Tianshan Mountains, the world’s largest arid mountain system, are ecologically vulnerable to climate extremes, yet the spatiotemporal heterogeneity of vegetation responses is not well understood. To address this, we assessed changes in vegetation phenophases using the green-up date (GUD) and the monthly maximum vegetation index (MVI). Their relationship with climate extremes across seasons and geographic units was analyzed using Classification and Regression Tree and Principal Component Analysis. Results indicate that GUD advanced by 0.276 days/year, with MVI increasing in spring and decreasing in summer. On a yearly scale, nighttime heatwaves advanced GUD in all vegetation types at lower altitudes with higher snow cover, whereas daytime heatwaves delayed GUD in grasslands. On a monthly scale, early spring heatwaves generally benefitted vegetation, with positive effects decreasing from forests to grasslands: forests benefitted from March to May, forest-grassland from March to April, and grasslands only in March. By late summer, heatwaves were negatively correlated with MVI across all vegetation types. This study highlights the complex responses of vegetation to climate extremes and underscores the vulnerability of high-altitude, low snow-covered grasslands, which is crucial for guiding restoration efforts.