The lichen genus Usnea in Norway north of the Arctic Circle: biogeography and ecology

摘要

Six species of the lichen genus Usnea are reported from Norway north of the Arctic Circle (total study area of 97.000 km(2)). The distribution maps are based on herbarium records extensively supplemented by our own records. Usnea glabrescens and U. substerilis are reported for the first time from the study area, whereas U. lapponica is reported as new to Finnmark. The two former species and U. filipendula have their northern distribution limit in Tromso at 69 degrees 40'N. Usnea lapponica, U. hirta and U. subfloridana reach Finnmark, but none of them are common north or east of Tromso. Literature reports of U. barbata, U. chaetophora and U. florida from Nordland, and of U. filipendula from Finnmark are considered doubtful. Most site records of Usnea are from the middle boreal vegetation zone, and only 7% of the site records are from the northern boreal zone. The northern boreal populations are considered as casual occurrences originating from long-distance dispersal, and not as locally established, self-propagating populations. The weakly oceanic vegetation section is the most preferred section along the coast-inland gradient with 70% of all records. The abundance and population size of Usnea species vary considerably between sites. The density is generally below one thallus per 2500 m(2), but at some favourable sites we have counted up to 62 thalli per 2500 m(2). These sites are humid, relatively warm lowland areas close to sheltered sea surfaces.