We studied the response in growth and phenology of naturally regenerated beech seedlings to changed ecological conditions over 14 and 19-years after cutting with different intensity. Five different types of stand densities were modelled: plot C - control plot - no cut, L - low intensity cut, M - medium intensity cut, H - high intensity cut and CC - clear cut, with 1, 8, 22, 53 and 100% of relative irradiation, and 66, 68, 78, 92 and 100% of through fall, respectively. We were focussing on tree height growth and leaf area. Our phenological observations were aimed at onset and course of two spring vegetative phenophases: bud-burst and leaf unfolding. Already in two-year-old beech seedlings we found significant differences in height growth; the differences in mean leaf area, however, were observed later. From the viewpoint of phenotypic plasticity, the height growth in beech seedlings represented more sensitive response to the environment than the leaf area. According to leaf area size and height growth in the beech seedlings on control plot, the stress conditions were indicated, primarily from the lacking light. With stand opening, the development of recruitment was getting better, and beginning with plot M the increase of seedlings height and leaf area became continuously related to the amount of radiation. The results of phenological observations showed that the spring phenophases in the seedlings start first on control plot. The start of spring phenophases on the clearcut was always observed the latest, even in comparison with the parent stand. Correlation analysis confirmed a significant correlation (P <0.05, r = -0.61) between the mean air temperature in March and April and start of the phenophase leafing in the individual years. Analysis of long-term research showed that the trend of leafing's onset observed in course of 18 years was significant (P <0.05), manifested a shift towards earlier dates.