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

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: inverse u-shape for forest generalists,
negative for forest specialists species, and positive for open land
specialists. When assessing the temporal stability of bird community
composition, we found that such stability was significantly correlated to
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 plays a crucial role in shaping different components of
taxonomic, functional and phylogenetic diversity in bird assemblages, as
well as their temporal stability.