Epiphytic macrolichens as conservation indicators:: successional sequence in Populus tremula stands

We studied the species composition of epiphytic macrolichens in 18 aspen (Populus tremula) stands, in the boreal forest in Sweden. In total, 51 macrolichens were found, 15 of which were aspen specialists. Quantitative features, e.g. signal species, showed a stronger correlation than quantitative features, e.g. total number of species, with increasing stand age. Aspen specialists showed a significant difference in dispersal mode, early colonizers are mainly sexually dispersed and late colonizers are mainly asexually dispersed. Cyanolichens, were confined to late-successional stands, and did not occur in adjacent younger stands. It is concluded that late-successional aspen stands in the forest must be conserved to function as core habitats for dispersal to young stands. Thus, such young stands have to be continuously created in order to retain the unique lichen flora associated with aspen stands in the forest landscape. (C) 2000 Elsevier Science Ltd. All rights reserved.