How Does Temperature Influence the Flowering Onset Date of Kerria japonica (Rosaceae)? Regional Comparison Based on Long-Term Observation Data in Japan

Abstract

Although it is known that flowering onset is strongly influenced by temperature in Rosaceae, there was a lack of research on whether the effects of temperature differ among regions within the same species. In this study, we used flowering records of Kerria japonica from four sites—Fukushima, Ibaraki, Toyama, and Yamagata—recorded between 2003 and 2020 by the Tsukuba Botanical Garden and the Japan Meteorological Agency to compare the correlation between flowering onset dates and cumulative temperature across regions. As a result, two key findings emerged: (1) flowering onset trends were inconsistent across sites, with advanced trends were observed only in Fukushima and Ibaraki, and (2) flowering onset at all sites was strongly correlated with cumulative temperature, but the accumulation periods varied, being longer in lower-latitude regions. It was suggested that meteorological differences and temperature requirements for flowering may affect the variability of flowering onset dates between sites.