Land-use legacies drive post-disturbance responses of plant diversity and habitat conservation status in Alpine dry grasslands

Semi-natural grasslands are biodiversity hotspots of high conservation concern in Europe, recognized under the EU Habitats Directive 92/43/EEC. Their occurrence depended on historical low-intensity agro-pastoral management, which maintained open vegetation structures hosting habitat-typical plant species. In the Alps, widespread land abandonment represents the main threat for these habitats. This study focused on semi-natural dry grasslands within Susa Valley (NW Italian Alps), an area historically shaped by agro-pastoral practices abandoned since the 1950s, involved in a grazing reintroduction project in 2014 and later affected by a severe wildfire in autumn 2017. Here, we investigated the effects of historical and recent landscape structure and the short-term drivers of post-disturbance (i.e., grazing intensity and fire severity) responses in vegetation diversity and habitat conservation status. We detected land-cover changes through classifications of historical (1954) and recent (2015) aerial images, and characterized grassland communities before and after disturbance events through field surveys. Results revealed substantial grassland loss and fragmentation due to dense forest expansion. Current dry grassland biodiversity and conservation status are strongly associated with historical landscape structure: sites embedded in formerly long-standing and extensive open areas host more diverse and better preserved communities. Post-fire responses differed markedly according to pre-disturbance conditions — degraded grasslands exhibited significant increases in habitat-typical species, whereas well-preserved grasslands showed limited compositional changes, indicating higher resistance to disturbance. These findings highlight the importance of landscape and vegetation legacies in shaping grassland dynamics. Management strategies should integrate historical landscape knowledge with current vegetation conditions to effectively maintain these high conservation value habitats.