Changes of the Flowering Time of Trees in Spring by Climate Change in Seoul,South Korea

Flowering onset has attracted much attention in ecological research as animportant indicator of climate change. Generally, warmer temperatures advanceflowering onset. The effect of climate warming on flowering onset is more pronounced in spring because the difference between atmospheric and water temperatures creates more rapid convection than in other seasons. We analyzed thecorrelation between 73 species of spring woody plants in Hongneung Arboretumin Seoul, South Korea and the spring minimum temperature and average precipitation over the past 50 years (1968–2018). The spring minimum temperature andaverage precipitation have increased over the past 50 years, resulting in the advanceof the first flowing date (FFD) in all 73 species by 8.5 days on average. A comparison of FFD changes over time by dividing the survey period into three time periodsconfirmed the advance of the FFD in 50 species (68% of investigated species) by11.1 days on average in both Period 2 (1999–2008) and Period 3 (2009–2018) relative to Period 1 (1968–1975). Additionally, a delay of the FFD by 3.2 days on average was observed in 8 species. The FFD of Lonicera chrysantha (Caprifoliaceae)advanced by over 40 days and was highly correlated with the increased spring minimum temperature. Analysis of the sensitivity of plant responses to climate changerevealed that a temperature rise of 1°C was associated with an FFD advance of1.2 days in all species. The species that was most sensitive to temperature changewas Spiraea pubescens for. leiocarpa (Rosaceae), whose FFD advanced by 4.7days per 1°C temperature rise. Each increase in precipitation by 1 mm was foundto result in a 0.1-day advance of the FFD of all species. Prunus tomentosa (Rosaceae) was the most sensitive species, that advanced by 2.6 days for each 1 mmincrease in precipitation. Thus, for all species, the FFD was more sensitive to thechange in temperature than in precipitation. Assuming that the current greenhousegas (GHGs) emission levels or atmospheric CO₂ concentration is maintained,Seoul’s spring minimum temperature is projected to rise by 2.7°C over the next50 years. Accordingly, considering only the global temperature change, the meanFFD of the study’s 73 species is projected to advance by an additional 3.4 days.