Direct and indirect ecological drivers of bird communities in intensively cultivated landscapes

Agriculture has played a pivotal role in shaping European mountain biodiversity. Traditional practices, characterized by low intensity and crop mosaics, have historically created complex, heterogeneous landscapes that supported a high biodiversity level. Agricultural intensification has turned these traditional crop systems into artificial habitats, leading to increased field sizes, habitat fragmentation, and decrease of habitat heterogeneity, contributing to the current farmland biodiversity crisis. We investigated the direct and indirect ecological drivers of bird communities in cultivated landscapes within the Alps. We aimed to disentangle the effects of biotic/abiotic factors on birds in permanent and annual crops (vineyards, apple orchards, arable lands). Using piecewise structural equation models, we analyzed bird indices and indicator species to explore the direct, indirect, and total effects of most relevant drivers, highlighting possible patterns due to degradation induced by intensification. Natural/near-natural habitats and compositional habitat heterogeneity positively influenced species richness and functional diversity. Conversely, structural habitat heterogeneity often had negative effects on bird communities. Topo-climatic variables were also relevant, with elevation promoting functional diversity and species richness, while steeper slopes increased near-natural habitats within the landscapes, indirectly supporting communities and species. These results highlighted the importance of maintaining and enhancing natural/near-natural habitats, usually removed by intensification processes, within intensively cultivated landscapes to support biodiversity. Landscape-scale conservation strategies that consider both direct and indirect ecological drivers are needed to effectively manage and conserve bird communities in the Alps under the pressures imposed by modern agriculture.