Tree-Ring-Based Analysis of Populus euphratica Radial Growth Response to Extreme Drought Across Lower Tarim River Sections, Xinjiang, China

The lower reaches of the Tarim River in Xinjiang, China are home to desert riparian vegetation dominated by Populus euphratica, which play an important role in windbreak and sand fixation, as well as maintaining the ecological balance of arid regions. Based on dendrochronology, this study analyzed the response of Populus euphratica radial growth to hydrothermal factors in the lower Tarim River region, assessed its resistance and resilience to extreme drought events, developed a multivariate regression model for resilience–hydrothermal factor relationships, and revealed the differential response of its ecological resilience to these factors. The results showed that the maximum, minimum, and mean temperatures and saturated water VPD (vapor pressure deficit) during the spring and growing season were the most significant and positively correlated with Populus euphratica growth. The radial growth of Populus euphratica was negatively correlated with maximum and mean summer temperatures. By region, Yingsu (YS) and Kaerdayi (KE) were more sensitive to seasonal climatic factors. The effect of groundwater on the radial growth of Populus euphratica was the strongest factor, with a highly significant negative correlation (p < 0.01), showing that the radial growth of Populus euphratica slowed with increasing depth of groundwater. The VPD, spring drought severity, and growing season groundwater variability all had a significant effect on Populus euphratica resistance, whereas Populus euphratica resilience was mainly significantly associated with growing season drought severity and summer groundwater variability. Radial growth was positively correlated with spring temperatures and the VPD and negatively correlated with summer temperatures (p < 0.01).