We established a standardized tree-ring width chronology using 46 Mongolian pine (Pinus sylvestris var. mongolica) tree-ring cores from the Tuqiang Forestry Bureau in the northern Greater Khingan Mountains (GKM). The average minimum temperature from May to July was significantly positively correlated with tree-ring width, indicating that it is the main climatic factor affecting tree growth in the study area. Based on this, the average minimum temperature sequence from May to July for the past 164 years in this region was reconstructed, and its reliability and stability were verified using the leave-one-out method. The reconstruction results revealed four warm periods and two cold periods in the northern GKM over the past 164 years. The four warm periods were from 1891 to 1897, 1902 to 1909, 1923 to 1931, and 2003 to 2023, and the two cold periods were from 1864 to 1880 and 1953 to 1992. The results of multi-window spectrum analysis and wavelet analysis showed that the reconstructed sequence had periodicities of 2.2–5.3 years, 11 years, 39 years, and 52 years, suggesting that the minimum temperature changes may be influenced by El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and solar sunspot activities.

Annual density chronologies of Pinus sylvestris var. mongolica L. at high and low elevations in the northern Greater Khingan Range were analyzed, and the responses of earlywood and latewood densities to climatic factors were examined. Significant elevational differentiation was observed in the growth response. At low elevation (630 m), earlywood density was positively correlated with temperatures in c4, c6, and c7 (c, current year) and negatively correlated with precipitation in p11 and c6 (p, previous year). Latewood density was negatively correlated with temperatures in c1–c5 and positively correlated with temperatures in c7–c8. At high elevation (1000 m), earlywood density was significantly negatively correlated with temperatures in p10, p11, c3, and c6, and with precipitation in p11, c2, c3, c5–c7, and c9; latewood density was significantly negatively correlated only with temperature in p11. Following an abrupt temperature shift in 1987, the low-elevation earlywood density chronology shifted from a decreasing to a strongly increasing trend, the low-elevation latewood chronology shifted from a strongly decreasing to a strongly increasing trend, and the high-elevation latewood chronology shifted from a strongly decreasing to an increasing trend. July temperature in the year of the shift drove the trend changes in the low-elevation earlywood and high-elevation latewood chronologies, and May temperature drove the trend change in the latewood density chronology at low-elevation, thereby explaining the shift in the latewood trend. Sliding-window correlation analyses further showed that low-elevation trees are more sensitive to climate fluctuations and exhibit lower growth stability, whereas high-elevation trees are less sensitive to climate fluctuations and show higher growth stability. Thus, the growth of low-elevation P. sylvestris var. mongolica is affected by combined water and heat stress, while the growth of high-elevation trees is primarily limited by temperature. Under ongoing warming, growth potential is likely to increase near the treeline but decline at low-elevation sites. These results provide a robust scientific basis for elucidating the response mechanisms of mountain forests in the Greater Khingan Range to climate change.