Artificial tree holes as a tool to assess spatial and temporal diversity of cavity-dwelling invertebrates in urban forests

Tree cavities form over long periods of wood decay and represent important microhabitats that support diverse invertebrate assemblages in forest ecosystems. However, the structure and diversity of cavity-dwelling invertebrate communities in urban environments remain poorly understood. In this study, multiple artificial tree holes were installed in two types of urban forests that differed in size and structure, and the spatial and temporal patterns of cavity-dwelling invertebrate communities were analysed. Invertebrates inhabiting each artificial tree hole were periodically collected and recorded. We compared the community composition and α, β, and γ diversity while evaluating environmental factors influencing community assembly. Invertebrate communities in small urban forests exhibited slightly higher local within-cavity diversity (α diversity) and were dominated by a limited number of species adapted to urban environments. In contrast, large urban forests showed higher regional diversity (γ diversity) and greater among-cavity diversity (β diversity), with predators and omnivores contributing substantially to spatial community heterogeneity. Invertebrate communities within tree cavities changed dynamically over time following installation, and the abundance of xylophagous and omnivorous taxa increased with time after the installation of artificial tree holes. Although species richness and abundance were positively correlated with air temperature, invertebrate abundance was negatively correlated with tree density and diversity. These results demonstrate that artificial tree holes are an effective tool for assessing the diversity of cavity-dwelling invertebrate communities in urban forests and provide important insights into the effects of urbanisation on cavity ecosystems, with implications for the conservation and management of cavity resources.