Wetlands lead, but all ecosystems matter: quantifying conservation priorities for plant communities in agricultural landscapes

Agricultural landscapes are mosaics of different ecosystem types, each hosting distinct plant communities. Although the known role of ecosystem diversification in sustaining farmland biodiversity, quantitative large-scale assessments of how different plant communities contribute to overall biodiversity within these landscapes remain limited. Here, we identified conservation priorities for plant communities across multiple ecosystem types in agricultural landscapes by quantifying their contributions to plant diversity. We sampled vegetation in croplands, forests, grasslands, shrublands, and wetlands across 46 study sites in Italy using 230 quadrats of 25 m². We tested differences in plant community α-diversity, β-diversity, and species composition using multiple complementary metrics. Grasslands exhibited the highest species richness, whereas wetlands showed the lowest. However, wetlands displayed the highest Local Contribution to Beta Diversity (LCBD), reflecting their distinctive species composition. Wetland and woody species exhibited the highest Species Contribution to Beta Diversity (SCBD). Grasslands hosted the highest number of unique species, whereas wetlands showed the highest proportion of unique species. Although the number and proportion of red-listed species did not differ significantly among ecosystem types, wetlands consistently exhibited higher values. Croplands and grasslands were the richest in non-native species; however, invasion levels remained low across the dataset. Species composition differed significantly among all ecosystem types. Based on the assessed metrics, wetlands had the highest conservation priority for vascular plant diversity. However, all ecosystem types contributed to the conservation of unique plant species and communities. Maximizing vascular plant diversity therefore requires maintaining diversified agricultural landscapes integrating different ecosystem types within a spatially connected mosaic.