3.5. Distribution

All the local Usnea species have a more or less southern distribution in East Fennoscandia, although most of the species are widespread occurring both in western and eastern regions (III). Merely U. glabrata and U. longissima represent an eastern element in the area. U. hirta, U. lapponica and U. subfloridana are the only shrubby Usnea that have also been found rarely from the northernmost regions. The front of the frequent occurrence of the genus roughly follows the northern limit of the Middle Boreal bioclimatic zone (see Ahti et al. 1968).

Most of the British Columbia species have a coastal range, i.e. they are distributed in hypermaritime and/or maritime regions (IV, V). The northernmost Pacific range of U. ceratina, U. esperantiana, U. hesperina Motyka and U. rubicunda in North America is on the hypermaritime south-west coast of Vancouver Island. Solely hypermaritime taxa of British Columbia are also represented by U. nidulans s. lat. and U. fragilescens var. mollis. Other coastal species include U. chaetophora, U. cornuta s. lat. (incl. U. occidentalis Motyka), U. diplotypus, U. longissima, U. madeirensis, U. pacificana, U. rigida s. lat. and U. wirthii, and U. wasmuthii was found in three maritime localities from Washington and Oregon. U. filipendula Stirt. s. lat., U. glabrescens s. lat. (incl. U. fulvoreagens) and U. subfloridana have been collected from both the coast and the intermontane zone being more frequent in coastal areas. U. hirta, U. lapponica, U. trichodea Ach. (only one locality) and U. glabrata (rare in the maritime zone) represent the inland element. U. cavernosa Tuck., U. scabrata s. lat. and U. substerilis are the only species which occur throughout the entire province, but they are more common in inland regions.

All the East Fennoscandian Usneae also occur along the Pacific coast of North America, but the relatively low hygric oceanity of East Fennoscandia is indicated by the absence of hypermaritime Usnea species. Many species have different distribution patterns, however, when comparing their range in these two areas. For instance, U. hirta is one of the most common Usnea in East Fennoscandia and is distributed through­out Finland (I, III). Thus it is surprising that the species has been found so far only in a relatively small area in the southern parts of the intermontane regions in British Columbia (IV). The coast of the province is too humid for U. hirta, but the species could be present in northern intermontane areas and/or in the boreal zone.

Usnea longissima has a wide range along the coast of British Columbia even being locally common in hypermaritime regions (IV), while it has in total only four known localities in eastern Finland and the nearby areas of Russian Karelia (II). The climate is probably too dry to U. longissima in most parts of East Fennoscandia and the localities found are situated in areas with relatively high precipitation and a humid local climate. The species is regarded as extinct in Finland (Rassi et al. 1992), but it may be found, for instance, in the Koillismaa province in similar sites such as the nearby Paanajärvi locality in Russia. U. longissima, however, has an ineffective long-range dispersal (Esseen 1985, Gauslaa 1997) and the species often has a patchy occurrence, even in uniform habitats (Tønsberg et al. 1996). It is also probable that the four known East Fennoscandian sites are relicts of a former more frequent occurrence during a warmer post-glacial period when the present westernmost areas of Finland were covered by water.

Our studies have also had importance in the classification of threatened species. For example, based on our investigations (III), U. wasmuthii will be added to the list of threatened lichens of Finland (status “Nearly Threatened” and “in need of monitoring”). The other East Fennoscandian Red List Usnea species are U. barbata s. lat., U. glabrata and U. longissima (Kotiranta et. al. 1998). Only U. rigida s. lat. is reported as a threatened Usnea species in British Columbia (Goward 1996, IV), but there are also some other threatened Usneae in the province, e.g., U. ceratina and U. rubicunda which are very rare there.