Leptogium hibernicum Mitch ex. P.M. Jørg. sensu stricto has an amphi-Atlantic distribution encompassing eastern North America and Western Europe. Specimens from South America, southwestern North America and New Zealand are reported to be part of a species complex of different clades (Bjelland 2017, Stone et al 2016). The African specimens have been named a new species, Leptogium krogiae Bjelland, Frisch & Bendiksby.
The small, isolated, widely dispersed populations are restricted to northern hemisphere temperate highly humid oceanic/montane areas of Western Europe and Eastern North America. This species is reported from 9 temperate northern hemisphere countries. Over 85% of records come from the two countries where it is redlisted, Britain (Woods & Coppins, 2012) and Norway (Bjelland & Ihlen, 2013). Its low occurrence numbers, habitat limitations and widely separated populations make it vulnerable to decline. Its reestablishment chances are low. In some areas, forestry practices and human activity have negatively affected population numbers.
It is known from limited habitats in Eastern North America ( southern Appalachians, USA and Nova Scotia, Canada ) and oceanic/montane Western Europe i.e. western Ireland, western Scotland, Spain, Portugal, France, Greece (Muggia et al 2018)and Norway, with a recent discovery(Urbanavichus et al 2020) in the Caucasus Mountains near the Black Sea.
GBIF datasets list 256 occurrences in the northern hemisphere, 159 of which are human observation. Of the 256, 143 occur in Great Britain (123 are observations), where it is listed as Vulnerable. The The status of the global population is suspected to be unstable because some of the habitats where it occurs are under threat from human activity. In Norway, the cessation of practices such as pollarding and coppicing which provide the species’ apparent preferred microhabitat there, caused a 45% decline in population size (Bjelland & Ihlen 2013). The then estimate of a 45% decline may have changed since.
Regional population declines are difficult to estimate because site specific data over the last 50 years is not readily available. Herbarium collections and recorded human observations available report presence, not numbers of individuals at the given sites. Britain and Norway are the two countries where the species has been assessed and where the greatest number of records occurs (GBIF Species map, https://www.gbif.org/search?q=Leptogium hibernicum)(Note the maps include the aforementioned clades and species). It is assessed as Endangered in Norway and Near Threatened in Ireland and Scotland where it is most frequent; in each of the others, 7 or fewer locations have been reported. Collections made in France, Spain and Portugal in the 1980’s are not from the same locations as specimens or observations made since 2000, with one or two exceptions.
Forestry practices such as clearcutting and biomass harvesting and natural senescence of mature to old trees in as yet undisturbed forests will also limit or reduce current numbers and restrict the establishment of new occurrences. Small numbers of individuals are more susceptible to destruction from random events such as fire, windfall, and drought.
Leptogium hibernicum Mitch ex. P.M. Jørg. is a leafy epiphytic cyanolichen of temperate oceanic/montane occurrence usually inhabiting mature to old deciduous trees, frequently moss-covered, with neutral to basic bark. In Nova Scotia Canada, it also occurs on cedar ( Thuja occidentalis). It requires continual high humidity and moderate temperatures. It spreads by means of vegetative propagules (no known fertile specimens exist), but its known occurrences are small and widely distributed, suggesting that its habitat requirements are seldom met.
Habitat loss is the primary threat. In Eastern Canada (Nova Scotia), the four known locations are in the southwestern part of the province where they are under pressure from clearcutting and biomass harvesting which can not only change the required moisture regime, but which can limit the available habitat for new juveniles. In Norway it occurs mostly on pollarded trees, a practice no longer in much use and some of the older trees have fallen, limiting reestablishment.
Climate change alteration in moisture regimes by prolonged periods of drought or excessive rainfall would adversely affect its survival.
In eastern North America it is partially incidentally protected by parks and conservation organisation- owned lands. In Nova Scotia, two of the four sites are protected; one as a provincial Wilderness Area, the other by the Nova Scotia Nature Trust, in the US, the sites are in a National Park. Both sites contain fewer than 5 thalli. Incidental protection exists in a few sites in Portugal(Madeira), the Caucasus, Greece, Spain and France. Its redlist status in Scotland, Ireland and Norway function as protections in those countries.
more detailed data on existing sites.
Genetic similarity of Russian and Greek specimens
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