Avian diversity changes in traditional agricultural landscapes of Japan over ten years

Abstract

Agricultural intensification is a leading cause of biodiversity loss worldwide. However, the traditional agroecosystems are often associated with high avian diversity because of their landscape heterogeneity, offering available niches to different bird species. Here, we focused on the temporal changes in taxonomic, functional, and phylogenetic diversity of avian communities from Satoyama traditional agricultural landscapes of Japan. We found significant temporal trends (e.g. increasing) in overall species richness, forest specialist species richness, phylogenetic diversity, and phylogenetic relatedness within avian assemblages, regardless of the land use composition surrounding the sites. The simultaneous increase in species richness and phylogenetic relatedness could highlight a process of biotic homogenization, typical of anthropized environments. Avian diversity was also significantly affected by the proportion of water bodies (e.g. increasing functional richness and dispersion, but decreasing functional evenness or redundancy) and other land use types (e.g. a negative association between species richness and the proportion of fields). The proportion of paddy fields affected each type of bird richness differently: an inverse U‐shape for forest generalists, negative for forest specialist species, and positive for open land specialists. When assessing the temporal stability of bird community composition, we found that such stability was significantly correlated with the proportion of grasslands, waterbodies, and urban landscapes. Specifically, avian communities surrounded by grasslands were characterized by higher species replacement over time. Additionally, very low or very high proportions of urban landscapes were associated with a relative instability of bird community composition. Our findings support the hypothesis that traditional farming systems represent valuable landscapes supporting avian diversity. However, the relative composition of land use types is crucial in shaping different taxonomic, functional, and phylogenetic diversity components in bird assemblages and their temporal stability.