<p>Rapid climate warming has redistributed the climatic drivers of global tree growth. Understanding the long-term changes in tree growth synchrony is crucial for identifying the threshold of forest response to climate change and the newly formed threats faced by forests. However, the response of tree growth synchrony among different elevations in mountainous forests to climate change remains poorly understood. In this study, by using tree-ring data from five dominant species and 46 plots along the elevation gradients on the eastern Tibetan Plateau, we detect the changes in tree growth synchrony, and the relationships between synchrony pattern and growth-climate responses. Our results indicate that synchrony within low-elevation group (below 2850&#xa0;m) is greater than that at high-elevation sites (above 2850&#xa0;m), likely due to more pronounced drought constraints at lower elevations. Over recent decades, divergent trends in growth synchrony have emerged between high- and low-elevation forests. At high elevations, the growth limitations of partial trees have shifted from cold- to drought-constrained, showing a V-shaped variation in synchrony. Meanwhile, increased drought stress at low elevations has led to a significant enhancement in growth synchrony. Overall, tree growth synchrony is mediated by specific growth-climate relationships. With increasing drought sensitivity and synchrony, the vulnerability of regional forests to climate change could be escalating. These findings highlight a shift in the primary drivers of growth synchrony at higher elevations as warming continues, underscoring the growing threat of drought to forest stability in the region.</p>