Disturbances of any origin and size cause changes in species diversity and composition of plant communities. The aim of this study was to explain how the understorey vegetation responds to changes in environmental conditions after (i) an anthropogenic disturbance such as a clear-cut of forest stand and (ii) a natural disturbance such as a disintegration of an overstorey in the natural forest.We established parallel research plots on the andesite bedrock of the Poľana mountains in the Abieto-Fagetum site type (950–1200 m a.s.l.). We surveyed all age classes of the managed age-class forests as well as the natural unmanaged stands. We also restored permanent plots previously established in natural reserves of the old-growth fir-beech forests (Badínsky prales reserve, Dobročský prales reserve, Padva reserve and Zadná Poľana reserve) in the disintegration stage of the natural forest.We confirmed that both the species richness and alpha-diversity of the understorey are significantly higher in the natural forest than in the managed stands. Additionally, species composition and diversity of the understorey in the managed stands are significantly changing with stand age. Among the recorded environmental variables, the tree density (DBH ≥ 7 cm) had the highest influence on the understorey diversity. We also found that the species composition of clear-cut communities (i.e. managed stands up to 10 years after a clear-cut) significantly differs from the species composition of forest stands 11–40 years old. The species diversity of clear-cut communities culminates 6–7 years after a clear-cut and decreases afterwards. Managed beech stands reach their lowest species diversity values approximately 30 years after a clear-cut, spruce stands about 40 years after a timber harvesting. Clear-cut communities have a significantly higher cover of annual, biennial and shade-intolerant species, and also of species that were not present in the original fir-beech forests. Similarly, the species diversity in natural forests culminates 5–10 years after natural disintegration of a canopy. During 19 years after the natural disintegration the species diversity decreased in general. However, this trend was mostly insignificant. We found a decrease of the shade-intolerant species and also of “cs” and “csr” strategies after disintegration as well. Finally, we confirmed a significant correlation between canopy openness and frequencies of the understorey species.The comparison of vegetation dynamics in the natural and managed forest revealed that changes in the species diversity and composition of the understorey are greater and more rapid after a clear-cut than in the natural forests after spontaneous disintegration. Natural forests show high stability in the species diversity and composition during the small developmental cycle and higher spatial homogeneity.