Semi-dry grasslands are among the most species-rich plant communities in the world, harbouring many specialised and threatened species. Most of these grasslands were traditionally maintained by grazing and hay-making. After traditional management ended, protected areas were established and conservation management was introduced to protect the most valuable grassland sites. However, recent changes in land use, eutrophication and climate warming are negatively impacting the biodiversity of these grasslands. In 2022, we resurveyed historical vegetation plots in the Central Moravian Carpathians (Czech Republic), first sampled in the 1980s, to test whether the plant species composition and richness of semi-dry grasslands are changing over time and, if so, whether the decline in habitat quality and plant diversity is absent or less severe in protected areas. We found significant changes in species composition. Species richness and the proportion of habitat specialists and Red-List species decreased, whereas competitively stronger species with higher moisture and nutrient requirements increased. These trends were more pronounced outside the protected areas but also occurred within protected areas. The main factor behind these changes appears to be the cessation of traditional management and natural succession supported by eutrophication.