Long-term changes in dry grasslands on rock outcrops in the Dyje/Thaya river valley, Czech Republic/Austria

Dry grasslands on rock outcrops in deep river valleys of the Bohemian Massif are typically small and difficult to access, forming isolated open patches surrounded by forests. Although probably partly maintained by historical low-intensity land use, these habitats have often been regarded as near-natural due to their extreme environmental conditions and long-term continuity. However, it remains unclear how strongly these habitats have responded to rapidly changing environmental conditions over recent decades. In 2020–2024, we repeated vegetation sampling conducted in the 1990s (42 semipermanent plots) to analyse long-term vegetation changes in dry grasslands in the Dyje/Thaya river valley. We revealed a decline in rare and xerophilous species, the expansion of ruderal and nutrient-demanding species, and the increased cover of dwarf shrubs and tree seedlings. These changes differed between areas located within the Podyjí/Thayatal National Park and those in less protected parts of the valley, reflecting differences in the surroundings, namely the proportion of woody vegetation, degree of anthropogenic disturbance, game management, and conservation interventions. This suggests that the state of grassland vegetation is strongly linked to the surrounding landscape conditions and the effects of conservation management. Our research provides evidence that even these environmentally extreme habitats are undergoing significant long-term vegetation changes. Shifts toward ruderalized vegetation were more pronounced at sites outside of national parks, whereas sites in national parks exhibited slower and less extensive vegetation change, likely reflecting both the establishment of strict protection and historically lower anthropogenic pressure.