Trees are the only or main growth substrate for thousands of lichen species, including many endangered ones. The present study gives an overview of the diversity of red-listed (belonging to the IUCN categories CR, EN, VU and NT) lichens on Estonian trees based on nearly 1300 herbarium samples collected during ca. 150 years. According to the results, altogether 75 threatened and near-threatened lichen species are known from Estonian trees. The highest number of red-listed species are accounted for Fraxinus excelsior (34 red-listed species), followed by Quercus robur, Populus tremula, Betula spp., Picea abies and Acer platanoides (30 to 26 species per each host tree). In addition to the importance of different tree species as host trees for the red-listed lichens, we also discuss, taking into account the frequency of the tree species and predicted changes in the age structure of their stands in Estonia, the future perspectives of the epiphytes associated with them. Populus tremula can be considered as the best possible alternative phorophyte for the greatest part of threatened lichen species that are growing on temperate broadleaved trees.

Keywords: lichens; endangered species; biodiversity conservation; broadleaved trees; deciduous trees; conifers.