Most European grasslands are semi-natural and require proper management to preserve their high natural value. They are habitats for many rare and endangered species of plants and animals. The aim of the study was to determine patterns of changes in the flora of grasslands induced by the introduction of extensive mowing and grazing treatments and to answer the following questions: (1) Do species richness and the number and occurrence of ecological groups plants differ depending on management schemes? (2) Is grazing or mowing more beneficial for the conservation of plant diversity? (3) Is the duration of land management a determinant of flora characteristics? The study was carried out in permanent grasslands located in the buffer zone of Polesie National Park in 2015–2018. The flora comprised 189 vascular plant species representing six ecological groups. The most numerous groups were meadow species (M) – 85, grassland species (G) – 35, and segetal species (S) – 31. Trees and shrubs (T) – 10 made up the smallest share of the flora, followed by ruderal (R) – 13 and aquatic (W) – 17 vegetation. The study showed that extensive grazing and mowing induced quantitative and qualitative changes in the flora of the research plots and were the key determinants of the flora dynamics. The first two years of use were crucial for the dynamics of the flora present in the plots. During that time a significant increase in species richness and the emergence of ecological groups was noted. Stabilization of the features analysed was noted in subsequent years. Significant differences were noted in species richness (SR) and the number of meadow (M), grassland (G), segetal (S), ruderal (R), water (W) and tree and shrub (T) species in favour of the managed plots compared with the abandoned sites. Grazing significantly decreased the number of emerging trees and shrubs, while mowing facilitated the preservation and regeneration of water and waterside vegetation. The use of local cattle breeds for grazing in valuable nature areas protects meadow habitats, prevents succession of trees and shrubs, and preserves and protects farm animal genetic resources.