Arthropod-based biotic integrity indices: A novel tool for evaluating the ecological condition of native forests in the Azores archipelago

•Conservation managers require accurate and efficient tools to urgently assess the biological quality of sites.•Considering biodiversity stratification in forests, canopy and understory strata are investigated separately.•Biological integrity indexes are developed, one for canopy and one for understory strata in Azorean native forests.•Abundance and species richness of endemic species are reliable parameters, consistently negatively related to disturbance.•Abundance and species richness of introduced species are reliable parameters, consistently positively related to disturbance.