Differential Responses and Mechanisms of Radial Growth Between Abies fargesii and Quercus mongolica in the Middle-Eastern Qinling Mountains Under Current Warming-Induced Aridification

As warming intensifies drying trends, tree species respond differently, especially across the conifer–broadleaf divide. Yet it remains unclear how these contrasting groups reorganise their relative composition under progressive aridification. Here, we investigated Abies fargesii and Quercus mongolica growing in the middle and eastern section of the Qinling Mountains, a transitional zone between the warm-temperate and subtropical climates, exploring the growth characteristics and tree growth-climate relationships before and after the climatic regime shift. The results indicated a wet-to-dry climate regime shift occurred in 1981 over the Qinling Mountains, causing a change in the tree growth trends as well as primary controlling factors for the tree growth of the two dominant tree species. Although the Basal Area Increment (BAI) of the Abies fargesii showed a continued decline trend in tree growth, BAI of Quercus mongolica represented a steadily increasing trend in tree growth, which implies that Quercus mongolica has stronger adaptability to the warming-induced aridification. For Abies fargesii, the dominant climate controlling factor shifted from temperature to a synergy of water and heat, whilst for Quercus mongolica, it shifted from water–heat coupling to precipitation dominance. In addition, the Abies fargesii chronology showed a significant teleconnection with ENSO events, whereas the Quercus mongolica chronology did not exhibit a similar response. Our findings suggest that Quercus mongolica exhibits greater tolerance to warming and drying conditions than Abies fargesii, providing important guidance for optimising regional forest composition and enhancing ecosystem resilience.