In this diploma thesis I have dealt with the issue of climate and its influence on phenology, namely on the occurrence of phenological phases in the spring and autumn periods. I have more closely described the connection between phenology and climate, and the work includes a description of forest vegetation zones in Slovakia. The analysis of forest vegetation zones is elaborated in terms of climatic water balance and woody composition. In the last theoretical chapter I focus on the characteristics of beech forests in Slovakia, their light and thermal conditions. According to the practical part, we can see how the drought grading trend continues in selected vegetation zones in Slovakia and how it affects the phenological phases, namely their occurrence, course and termination. Nowadays, this issue is increasingly beginning to be in the forefront of interest, in order to solve this growing problem of drought in forest ecosystems and its impact on the occurrence, course and termination of phenological phases.