Habitat loss, extinction debt and climate change threaten terricolous lichens in lowland open dry habitats

Habitat loss is the main driver of biodiversity decline worldwide. An immediate consequence can be extinction debt, i.e. time-delayed extinction of species following habitat loss. We tested extinction debt in terricolous lichen communities in 45 patches of lowland open dry habitats in the western Po Plain (northern Italy) considering richness of four species groups: total, red-listed, rare, and common species. The distance from the currently nearest patch and the annual precipitation correlated – negatively and positively, respectively – with all the groups. Total, red-listed, and rare species were positively related to the oldest available patch extent (1954). Common species were positively related to the current (2020) patch extent. Total and red-listed species were negatively related to the extent difference (1954–2020). Results reveal an extinction debt which has not yet been completely paid and that could be exacerbated by climate change. To counteract this trend, management should conserve habitat patches with the highest species richness, improve connectivity between habitat patches, and provide suitable microrefugia for species with different ecological requirements.