Influence of the climatic factors on the mass flowering dates of Bulbocodium versicolor (Melanthiaceae) at the south-eastern border of its range

Under conditions of climate change, phenological studies of vegetation are of particular importance. Most of the current research are carried out in Protected Areas (PAs), network of phenological stations, agricultural lands, nurseries, and botanical gardens. Studies based on remote sensing data do not take into account the species diversity of the vegetation cover. This study is aimed to determine regularities of the timing of Bulbocodium versicolor mass flowering at the southeast border of its range. The studied B. versicolor population is located in the vicinity of the city Volgograd, which makes it available for research. At the same time, the B. versicolor population is under constant anthropogenic pressure. Understanding the phenological features of this species and regularities of the timing of mass flowering (the period of highest vulnerability) will allow us to organise the protection of the B. versicolor population during this period. The study is based on data about the beginning of mass flowering dates, obtained during surveys of 2007–2020 with a possible error of 2–7 days, as well as an archive of weather data of the Volgograd weather station. The average start date of mass flowering is 24 March ± 12 days. The range between the earliest and latest dates exceeds a month. We have found a statistically significant correlation between the start date of B. versicolor mass flowering and the date of snow cover destruction, as well as dates of stable transition of the maximum air temperature over 0°C, and the average daily temperature, over 0°C and over 3°C. Over the period 2007–2020, no statistically significant trends were found for either dates of B. versicolor mass flowering or dates of main meteorological phenomena. Almost every year, after the start of B. versicolor mass flowering, frosts occur on the soil and in the air, and snowfalls take place regularly. This may be one of the factors which cause a lower seed regeneration in this B. versicolor population compared to the ones located northward, since the temperature drop during the flowering period contributes to the depressive state of the B. versicolor population.