Effect of the landscape composition of artificial Robinia pseudoacacia forests on bird diversity in the Loess Plateau

Habitat degradation in recent years has resulted in substantial biodiversity loss and homogenization, with serious ecological and socioeconomic consequences. Afforestation is a globally adopted strategy to mitigate this environmental change. In China, for instance, a total of approximately 87.6 million hectares have been afforested since 1999. However, studies on the impacts of anthropogenically modified plantation ecosystems on biodiversity remain insufficient. This study assessed disparities in bird diversity across three landscape compositions: monoculture artificial forests, mixed tree-shrub artificial forests, and mixed tree-shrub-agricultural artificial forests in the Ansai region, a key area for the implementation of large-scale afforestation programs in China. The analysis focused on the effects of vegetation structures, microhabitat indicators, and anthropogenic disturbances on bird species and functional diversity. The findings revealed that the composition of artificial forest landscapes significantly influenced the taxonomic diversity of birds. Compared to monoculture tree plantations, mixed tree-shrub-agricultural plantations supported greater bird abundance and unique species. Agricultural land area significantly affected bird abundance, richness, and functional richness, driven largely by seasonal dynamics of farmland. This study emphasizes that microhabitat diversity, rather than abundance, is key to supporting bird species richness and functional richness. However, spatial aggregation of deadwood and large trees may lead to resource monopolization by certain functional groups, reducing functional evenness and divergence. Higher grazing intensity reduced bird functional richness while cutting intensity did not lower local bird abundance. To promote development while ensuring ecosystem stability and diversity, a mixed tree-shrub-agricultural plantation model is recommended as a sustainable and resource-efficient strategy.