Responses of Summer Shoots and Spring Phenology of Pinus koraiensis Seedlings to Increased Temperature and Decreased Precipitation

We investigated the changes in shoot growth and spring phenology of Pinus koraiensis seedlings under climate change. In 2016, 2-year-old seedlings were planted and treated with increased temperature and decreased precipitation. Temperature was elevated by 3 °C using infrared heaters and V-shaped panels covered 30% of plot area to block precipitation. Occurrence of summer shoots was measured in October 2017 and 2018. Spring phenology was observed in 2018 and 2019. Occurrence rate of summer shoots under increased temperature rose by 37.8% in 2018 but dropped by 14.3% in 2019 compared to the control. Occurrence rate of summer shoots was positively and negatively correlated with summer temperature in 2017 and 2018, respectively. Spring phenology advanced by 8.8 days under increased temperature in 2018 and 2019. The number of chilling days (daily mean temperature < 0 °C) decreased by 44.1% and growing-degree days in spring with a 0 °C base temperature increased by 15.6% under increased temperature in both years. Budburst date under increased temperature advanced with rapid and early warm temperature accumulation. Summer shoot development might not affect timing of growth cessation or spring phenology in the following year. Decreased precipitation treatment did not influence the summer shoots or spring phenology.