Impact of warmer winters on the flowering display of Tokyo cherry (Cerasus ×yedoensis ‘Somei-yoshino’) at its southern range

With a warming climate, many temperate plants may not meet their winter chilling requirements and may not flower normally in spring. This effect may represent a particular problem for the culturally important Tokyo cherry (Cerasus ×yedoensis ‘Somei-yoshino’) at the southern limits of its range in Japan. We investigated the flowering period and dormant bud development of Tokyo cherry at study sites at the southern limits of the plant’s range in Kagoshima Prefecture, Japan and at sites in cooler parts of the plant’s range in Kumamoto Prefecture, Japan. We analyzed long-term observations collected at two sites during the years 1965–2024, and more detailed observations collected at 14 sites during the years 2021–2024. Cumulative chill units (cCU), a measure of winter chilling, showed strong negative correlations with full bloom date and flowering intensity, with milder winters associated with delayed spring flowering and lower proportions of flowers open at peak flowering. Trees experiencing mild winters with cCU values of less than 1,500 tended to exhibit development disorders for flowers and leaf buds. These effects were particularly pronounced in very mild winters with cCU values of less than 1,000. This study highlights how the lack of sufficient winter chilling threatens the flowering display of this culturally important tree at the southern edge of its range. Such threats will become more frequent and widespread as the climate continues to change. Managers need to consider alternative strategies to maintain flower displays during cherry blossom festivals, such as planting species with lower winter chilling requirements.