Seasonal development of the pedunculate oak in the Prigorodnoye forestry area of the Voronezh region

The research was carried out on the basis of a series of phenological observations conducted on the territory of the special protected natural area “Amenity forest” of the All-Russian Research Institute of Forest Genetics, Breeding and Biotechnology, Voronezh. We studied the development of early and late phenological forms of pedunculate oak of vegetative origin. The study unfolded over three growing seasons (2019–2021) and showed that the time of the different phenological phases varies significantly and depends on the temperature conditions of the growing season. The difference in the beginning of the phenological phases between the early form and the late form of oak can reach 5–35 days, depending on the meteorological conditions of the season. We observed that for the early form 2–4 phenological phases (from bud swelling to leaf unfolding and the beginning of flowering) can fit in one month of April, while for the late form only bud swelling takes place in April. In May, the early form passes 4–5 phases of development (from bud swelling to the end of flowering), the late form – 3–6 phases (from bud swelling to the end of flowering). By June, the phenological development of both forms synchronizes. In July, only the late form continues its development to the fruits growth and development phase. To begin the development in spring the late form needs the 1.5–2 times bigger sum of effective temperatures than the early one. The duration (or the simultaneousness) of the beginning of a certain phase in the groups of trees of two phenoforms is influenced by the temperature conditions of the growing season. Using the method of factor analysis, we established that for the early form there is a strong linear relation (r = 0.67) between the sum of effective temperatures (more than +5 °C) and the beginning of the budburst phase, while the sum of positive temperatures (more than +8 °C) correlates with the beginning of shoot growth (r = 0.83). For the late form, there is a strong relation between the beginning of the shoot growth phase and the sum of temperatures over +8 °C (r = 0.92). The temperature factor amounts to 17.5 % of the variability of all characteristics.