Beyond native habitats: Indigenous arthropods adapted to mid-elevations find refuge in exotic forests

In island ecosystems, extensive land-use changes since human colonisation has transformed native habitats into agriculture and exotic forests, raising concerns about the long-term persistence of indigenous biodiversity. This study explores the distribution of relict populations of indigenous arthropod species in exotic forests on Terceira Island (Azores) and identifies the ecological and environmental drivers shaping their presence. Using standardized SLAM (Sea, Land, and Air Malaise) traps and pitfall traps data from native and exotic forest plots, we investigated the distribution and abundance of 85 indigenous arthropod species across 15 orders, of which 65 were recorded at least once in exotic forests. We modelled the effects of species traits and biogeographic variables on species abundance and presence in exotic forests. Elevation emerged as the dominant predictor in both models, with species associated with mid-elevation habitats (300 – 500 m a.s.l.) showing higher abundance and occurrence in exotic forests, while high-elevation specialists (above 500 m a.s.l.) were largely absent. Endemic species generally had lower relative abundances in exotic forests compared to native non-endemics, even when their overall elevational range was broad. These results suggest that species historically present in mid-elevation zones find refuge in exotic forests. While relict populations may offer a degree of resilience and restoration potential, their long-term persistence is uncertain, particularly under climate change scenarios that limit available habitat at higher elevations. Conservation strategies should therefore recognize the role of exotic forests as transitional refuges and prioritize their management and restoration of native forests, especially in non-protected and privately-owned landscapes.