Earlier spring in Seoul, Korea

In the present study, long-term changes in the first bloom date of shrub and tree species in Seoul (126.56 degrees E, 37.34 degrees N), Korea were examined using historical observational data for the period 1922-2004 (83 years). The study focused on two shrub species, golden-bell (Forsythia koreana) and azalea (Rhododendron mucronulatum), and three tree species, cherry (Prunus yedoensis), peach (Prunus persica), and American locust (Robinia pseudoacacia). The annual-mean temperature has increased by about 2 degrees C in Seoul over the 83 years analyzed. The temperature increase is significant during the winter and early spring and becomes less significant during late spring. As a result of this regional warming, all five species showed an advance in the first bloom date over this time period. The advanced date is particularly apparent in early-spring flowering species like golden-bell (-2.4 days 10-year(-1)), azalea (-2.4 days 10-year(-1)), cherry (-1.4 days 10-year(-1)), and peach (-1.4 days 10-year(-1)) as compared to late-spring flowering species like American locust (-0.5 days 10-year(-1)). The present results have demonstrated that the major factor for the determination of flower blooming is heat accumulation, i.e. a certain threshold of growing degree-days (GDD) index. In particular, early spring flowers were sensitive to the accumulation of warm temperature than late-spring flowers. Copyright (C) 2006 Royal Meteorological Society.