Critical stage temperatures in early spring modulate the growing season onset of Pinus tabuliformis in Shenyang

Temperature modulating the growing season onset of trees is still not completely understood. We anatomically tracked the growing season onset development of Pinus tabuliformis annual cambium activities in Shenyang during 2019–2021, explored the influencing factors and their regularity on the pine growing season onset, determined the interannual trajectory of the onset date, and simulated the growing season onset trajectory by the physiological process-based tree-ring Vaganov–Shashkin model. We found that the growing season onset date of P. tabuliformis significantly advanced at a rate of 1.5 days/decade in Shenyang during 1951–2021, the mean of which was 6 days earlier in 1981–2021 than in 1951–1980. The April maximum temperature was extremely significantly correlated with the P. tabuliformis growing season onset date. The pine growing season onset is modulated by temperatures, including minimum, mean, maximum temperature and diurnal temperature range (DTR), with corresponding thresholds of 3.2 ± 1.1 °C, 11.4 ± 0.7 °C, 18.1 ± 0.8 °C and 13.0 ± 2.7 °C, respectively, during 11–12 days prior to the growing season onset date. A low DTR during this stage would delay the onset of the pine growing season. The finding of the critical stage, modulating climate variables and their thresholds may help to accurately predict the regional growing season onset of P. tabuliformis.