Tree-Ring Reconstruction of Minimum Temperature Changes in the Northern Greater Khingan Mountains

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.