Habitat and host specificity of epiphytic lichens in a rural landscape: cultural heritage habitats as refugia

Abstract

We hypothesize that many epiphytic lichens colonize trees in planted cultural heritage sites and persist as large-scale species meta-pools in historic rural landscape, while epiphytic biodiversity is threatened by the timber oriented forest management. We performed a stratified survey of epiphytic lichen species pools on ten common tree species in three contrasting habitat types across 19 Estonian landscapes. The meta-pools were examined at local and regional scales. The response differences between two ecological subsets—common forest-dwellers and conservation indicators—were assessed. Tree species in parks and corridors hosted more lichen species than they did in production forests. For common forest-dwelling lichens the local species pool size was similar in all habitat types, while their regional pool was larger in forests and parks. On the contrary, for conservation indicator lichens the local pool size was the largest in corridors and regional pool size was the same in all habitats. Habitat type and tree species equally shaped the composition of the regional pool. Lichens were the most host-tree-specific in forests and had the widest host-tree niche in corridors. Broad-leaved tree species supported the largest regional species pools only in forest, while Betula and Pinus with Larix did in corridors. Lichen pools on Populus tremula were consistently the smallest. As the habitat quality of contemporary forests is too low for epiphytic lichens, cultural heritage sites should be considered as refugia in biodiversity conservation networks. Forestry and rural greening should emphasise stand diversification, ensuring the continuity of micro-habitats. Indicator lichen classifications require forest-oriented refinements.