KOCKOVÁ, V.: Phenological studies on the generative organs (flowers) of manna ash (Fraxinus ornus L.) [Diploma thesis] – Technical University in Zvolen, Faculty of Ecology and Environmental Sciences, UNESCO Chair for the Ecological Awareness and Sustainable Development. Supervisor: Assoc. Prof. Ing. Branko Slobodník, PhD. Qualification Degree: „Ingenieur“ abbreviation „Ing.“. Zvolen: FEE TU, 2021, 67 s. Manna ash (Fraxinus ornus L.) is the morphologically androdioecious woody plant with the Northern limit of its natural distribution on the territory of Slovakia. At the same time, it has some expansive properties and is very tolerant to the high temperatures and drought. Therefore, there is some risk of its possible future spontaneous expansion due to the climate change. The course of the spring generative (flowering) phenology of the manna ash was studied on the locality Radvaň – Vartovka in Central Slovakia. This locality represents an artificial stand with its allochthonous occurrence. The manna ash was planted here for stabilizing erosive slope, but, even at present days, its artificial population is characterized by spontaneous expansion. The results of phenological research from 2020 confirm the more or less well-known facts that, under conditions of Central Slovakia, the flowering of this species is relatively late (anthesis starts usually in early May) and is characterized by some protogyny, i.e. certain phenological advance of female generative organs ‒ pistils, compared to the male generative structures ‒ anthers. Nevertheless, in 2020 the protogyny was very weak and we registered it only at the start of flowering. In context of the corresponding temperature conditions, the onset of spring 2020 was initially moderate, later colder and therefore, also relatively slower. The starting dates of the initial phenological phases were, compared to the previous years of investigations on this locality, usual and normal. The general flower bud burst started in April 15 (Julian day 106) and this date was common for both male individuals and hermaphrodites. The general butonization was observed in April 28 (Julian day 119) in male individuals and in May 6 (Julian day 128) in hermaphrodites. Due to the cold spring, the period of anthesis was relatively late and, in the both sexual types, the general flowering fell on the 15th May (Julian day 137). The analysis of the relationships between the dates of particular phenological phases and corresponding temperature values confirmed that the dates of the flower bud burst and butonization are in strong correlations (r = 0.65 ‒ 0.88) with the mean temperatures, measured in later winter and early spring (January to April). The high coefficients of correlation (r = 0.81 ‒ 0.90) were also calculated for the dates of general flowering and general flowering cessation. Nevertheless, these phenological phases correlated with the mean spring temperatures (April ‒ May). Contrariwise, the correlations between the dates of the spring generative phenophases and spring precipitations were only weak or even fully absented.