Data from: Decade-long avian monitoring in China reveals stable species richness but increasing biotic homogenization

China is undergoing rapid socio-economic growth and biodiversity loss. However, knowledge about the country’s biodiversity trends remains largely unknown because of a lack of a national-scale biodiversity monitoring program. Using a decade (2011-2020) of avian monitoring data from 202 sites and 896 species under the China Biodiversity Observation Network, we evaluate temporal trends in alpha and beta diversity at the taxonomic and functional facets and assess their drivers. We showed that species richness remained stable over 10 years, but functional richness increased significantly. Both taxonomic and functional multiple-site beta diversities decreased over time, indicating a trend towards biotic homogenization. Bird communities in regions with pronounced seasonality of precipitation exhibit larger increases in species richness, whereas those at higher elevations show greater biotic turnover. Our results reveal asynchronous changes in taxonomic and functional diversity, and decoupled trends in alpha and beta diversity, implying that stable species richness at the local scale may mask functional diversity trends and broader-scale biotic homogenization.