Does biological integrity respond to restoration? Testing the temporal sensitivity of an arthropod-based index as part of the LIFE BEETLES conservation project

Biological integrity indices (IBIs) combine multiple community attributes into a synthetic measure of ecological condition, but their sensitivity to short-term change during restoration remains poorly understood. Under the LIFE BEETLES conservation project (Bringing Environmental and Ecological Threats Lower To Endangered Species - LIFE18 NAT/PT/000864), we evaluated whether an arthropod-based IBI could detect temporal changes in Azorean native forests. Arthropods were monitored using SLAM (Sea, Land and Air Malaise) interception traps at sites on Flores, Pico and Terceira, Azores, from winter 2020 to autumn 2025. Adult abundances were standardised to 90-day sampling periods, and seasonal IBI values were calculated using metrics representing endemic, native non-endemic, introduced and saprophagous taxa. Temporal trends were assessed for complete seasonal time series and separately for cold (winter–spring) and warm (summer–autumn) periods using Seasonal Mann–Kendall and Mann–Kendall tests. Trends in individual IBI components were compared with those of the composite index. Composite IBI trends were uncommon and spatially inconsistent. In contrast, trends in individual components were more frequent and included changes in endemic, native non-endemic, introduced and saprophagous taxa. The arthropod-based IBI detected some temporal changes but showed limited and inconsistent short-term sensitivity to ecological change. Apparent stability in the composite index did not necessarily indicate stability in arthropod communities. Longer time series, explicit comparisons between restored and non-restored sites, and integration across forest strata will be necessary to determine whether LIFE BEETLES project interventions produce sustained improvements in biological integrity.