Decline in lichen biodiversity on oak trunks due to urbanization

Biodiversity often suff ers from urbanization. In the present study, we focused on how the duration of urbanization aff ects therichness of 17 epiphytic lichen species and their cover on large oaks in urban environments in a city of 100 000 inhabitantsin southeast Sweden. We also surveyed trees in adjacent rural areas, selected to have similar distributions of tree trunkcircumference and surrounding oak density (within 300 m). Lichen richness and cover were lower on urban trees comparedto rural trees. Furthermore, richness and cover decreased with the length of time that urban trees had been surrounded byhouses. Most of the species that were analysed demonstrated a decline in occurrence with respect to the duration of housingdevelopment. Th e reduction in the probability of occurrence varied from 60% ( Calicium viride , Evernia prunastri ), 80%( Chrysothrix candelaris ) to 90% ( Ramalina spp.) during the considered 160-year period of urbanization. Th erefore, even ifvaluable trees survive over the course of development, their lichen biota is likely to become depleted over time.