Epiphytic lichen synusiae and functional trait groups of species in boreo-nemoral deciduous forests are influenced by host tree properties and environmental factors

13 November 2018

Juriado, Inga; Paal, Jaanus

Deciduous forests with temperate broad-leaved tree species, which are especially important in terms of biodiversity and its protection, are threatened habitats in northern Europe. We studied the effect of forest site type, environmental variables and host tree properties on epiphytic lichen synusiae and on the composition of functional traits, using multivariate analyses. Epiphytic lichens were examined on Acer platanoides, Fraxinus excelsior, Quercus robur, Tilia cordata, Ulmus glabra and U. laevis in Humulus site type floodplain forests and in Lunaria site type boreo-nemoral forests on the talus slope of the limestone escarpment (klint forests). Klint forests located near the seashore were under greater maritime influence compared to floodplain forests located in inland Estonia with stronger air temperature contrasts. In addition to stand level and climatic variables, also tree level factors (bark pH, trunk circumference, and cover of bryophytes) considerably affected the species composition of lichen synusiae. Overall, 137 lichen species were recorded, including 14 red-listed species characteristic of deciduous trees. We defined 13 lichen societies and showed their preference to forests of a specific site type and/or host tree properties. In forests of both site types, most of the epiphytic lichens were crustose, with the apothecia as the fruit bodies and with chlorococcoid algae as the photobiont. However, the proportion of lichens with a foliose or fruticose growth form, as well as the proportion of lichens with vegatative diaspores were higher in floodplain forests. In klint forests with a stronger influence of the wind, the proportion of the crustose species forming lichen synusiae was overhelming, while vegetative diaspores were not common and epiphytic lichens dispersed mostly sexually. In these forests, lichens with Trentepohlia as the photobiont were characteristic and lichens with lirellate ascomata were prevailing, indicating the great uniqueness of this site type forests for epiphytic lichens in the boreo-nemoral region.