Temperature Characteristics and Spring Frost Risk in the Sour Cherry (Prunus Cerasus L.) Blooming Period in 1985–2010

The aim of the paper is an attempt to present the relationships between sour cherry (Prunus cerasus L.) blooming time, climatic conditions and spring frost risk in western Poland (Great Poland Lowland). Air temperature indices from meteorological stations in Przybroda and Poznań for the period 1985-2010 representing contemporary climate warming were used. ‘English Morello’ sour cherry phenological records for the period 1985–2010 were collected at the Research Station of Poznań University of Life Sciences located in Przybroda. The earliest end of blooming was observed on 2nd of May 1999, and the latest one on 26th of May 1987. The average period of sour cherry blooming was between 30th April and 12th May. During 50% of the years the blooming period lasted from 11 to 15 days. Mean monthly temperature in Przybroda varied from -1.1ºC in January to 19.6ºC in July. A significant relationship between the beginning date of cherry blooming and the beginning of the thermal vegetation period was found. Variability of the index explained more than 50% of variability in the first dates of cherries blooming (coefficient of determination R2 = 0.505 is significant on the level p < 0.05). The beginning of blooming was also significantly (p < 0.05) correlated with mean April temperature, which could explain about 43% of variability in the dates of the first bloom. An increase in April temperature by 1.0ºC caused earlier blooming by about 2.8 days. During the period of 1985–2010 a significant increase in April temperature was observed (in Poznań 0.79ºC per decade). It had an effect on advanced dates of the beginning of sour cherry blooming of about 3 days per decade. In 26 of the years the last frost occurred 4 times (15% of seasons) during the blooming phenological phase or later in Przybroda. Frost occurred 10 days before blooming started and during blooming in 54% of the years