The species has earlier been included in different cetrarioid genera, such as Allocetraria, Cetraria and Tuckermannopsis (Randlane et al. 2013), however, according to the phylogenetic analyses it is not closely related to these three genera. Consequently, Usnocetraria, which was described by Lai et al. (2007) for several species of polyphyletic origin, was proposed later as being monotypic for U. oakesiana, a disjunct alpine species in the Northern Hemisphere (Thell et al. 2009).
Allocetraria oakesiana (Tuck.) Randlane & A. Thell in Thell, Randlane, Kärnefelt, Gao & Saag, Flechten Follmann, Contributions to Lichenology in Honour of Gerhard Follmann (Cologne): 363. 1995.
Cetraria bavarica Kremp., Flora 34: 273. 1851.
Cetraria oakesiana Tuck., Boston J. Nat. Hist. 3: 445. 1841.
Platysma ochrocarpum Eggerth, in Arnold, Lich. Exsicc. 1212. 1888.
Tuckermannopsis oakesiana (Tuck.) Hale in Egan, Bryologist 90: 164. 1987.
Usnocetraria oakesiana is an epiphyte on coniferous and deciduous trees in montane forests with dicjunct distribution in Europe, eastern areas of North America and in East Asia. In Europe the species is redlisted in all countries where it is recorded – in Austria (EN), Germany (category 1), Italy (VU), Norway (CR), Slovakia (RE), Switzerland (EN), Ukraine (Rare), and in several regional Red Lists of Russia; it is considered extinct also in Kaliningrad region of Russia (recorded in 19th c.). In North America the state of populations is stable. In Asian part of Russia the species is considered either rare or endangered (Urbanavichus & Urbanavichene 2015); records from other Asian countries are scarce and do not allow assessment of population trends.
Consequently, within its European range, Usnocetraria oakesiana is a lichen with clearly declining populations in the habitat which has been under severe pressure in the past century and continues to be threatened.
Assessment at European level.
A criterion: Population reduction in Europe during last 100 years is over 30% - extinct in Slovakkia and Kaliningrad region; population decline observed in Austria, Germany, Norway (20% of the Norwegian population was clearcut logged in 2013, data from Einar Timdal, 2015) and Switzerland. The species qualifies for the category VU according to A2c, A3c and A4c.
B criterium does not apply as EOO is wider than 20 000 km2.
C and D criteria: not applicable as relevant numbers of individuals are not available; E criterium: not applicable as no quantitative analyses have been carried out.
Assessment at global level.
A criterion: Population reduction globally is lower than 30% as in North America it is not threatened (state of populations is stable) and in Asia the state of populations is unclear due to the lack of information, although the decline in Europe is documented. The species is globally assessed as LC.
Other criteria are not applicable.
Decision: Usnocetraria oakesiana is assessed for the European Red List category VU according to the criteria A2c, A3c, A4c. Globally it is assessed as LC.
The species occurs in the Northern Hemisphere having disjunct distribution in Europe (mainly in its montane areas of Central Europe), eastern part of North America and East Asia. Europe: mainly in Central Europe – Austria; Germany; Greece – in Korfu Island; Italy – in 3 regions out of 20; Slovakia – extinct; Switzerland; Ukraine – only in its westernmost part of Eastern Carpathians; Norway – in a single recently found locality in Buskerud, southern Norway (Klepsland & Timdal 2010; Thell 2011); Russia – in Kaliningrad region (extinct), in Republics of Adygeya, Marii El & Bashkortostan (Urbanavichus & Urbanavichene 2015). North America: Canada – Ontario; USA – in its eastern states (Brodo et al. 2001). Asia: China – in two provinces, Hubei and Xizang (Randlane et al. 2001); Nepal; Russia – in Krasnoyarsk krai, Irkutsk region, Republic of Buryatia & Primorski krai (Urbanavichus 2010; Urbanavichus & Urbanavichene 2015); Turkey (Yazici & Aslan 2002).
Population trend in Europe is clearly declining – the species is considered extinct in Slovakia (recorded in 1960s) and in Kaliningrad region of Russia (recorded in 19th c.), declining in Austria, Germany, Italy and Switzerland, probably due to the deterioration of suitable habitats, while the populations are evaluated stable in North America. For example, in Italy it is recorded as ‘extremely rare’ in 3 regions of northern Italy, in montane and subalpine regions (Nimis & Martellos 2008). In Asian part of Russia the species is considered either rare or endangered (Urbanavichus & Urbanavichene 2015). Records from other Asian countries are scarce and do not allow assessment of population trends.
Usnocetraria oakesiana is an epiphyte on coniferous and deciduous trees in montane forests, sometimes on wood or rock; typically in humid shaded forests.
The northenmost, Norwegian locality, is in the southern boreal vegetation zone; the substrate trees were all in old-growth forest, however, several were rather young, some probably not more than 30–40 years of age, hence, the species does not seem to be dependent on old trees, but rather a stable, humid forest with a closed canopy (Klepsland & Timdal 2010).
Within its European range, Usnocetraria oakesiana is a lichen with narrow autecology in endangered habitat. Major threats include decline and destruction of typical habitat (montane forests, shaded damp forests in southern boreal vegetation zone) caused by human activities – tree cutting and forest fires. Recreational activity might locally also appear as an additional threat. The species is considered very sensitive to human disturbance (Nascimbene et al. 2013).
In most of European localities Usnocetraria oakesiana is represented by a few specimens only, and they are always sterile. This means that the species reproduces only vegetatively in this region which also contributes negatively to its distributional ability (in North America, the samples with apothecia have been recorded).
The northenmost, Norwegian locality, has been assessed as regionally worthy of protection (i.e., three points on a six point scale) according to a set of criteria used in the river gorge inventory project. It was also mapped as an important biodiversity locality in within a national mapping project (Klepsland & Timdal). Nevertheless, about 20% of the Norwegian population was clearcut logged in 2013 (comment by Einar Timdal in February, 2015).
In Russia some localities are situated in the protected areas, e.g. in Caucasus and Baikal Nature Reserves; however, in these reserves the habitats of Usnocetraria oakesiana still suffer from the human activities (Urbanavichus & Urbanavichene 2015).
Population studies, including the assessment of population size and number of individuals in subpopulations are needed. Studies about the genetic variation of this species in subpopulations of different parts of the world (Europe, Asia, and North America) may reveal genetically defined evolutionary significant units which might indicate to necessity of varying conservation activities in different areas.
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Lai, M. J., Qian, Z. G. & Xu, L. 2007. Synopsis of the cetrarioid lichen genera and species (Parmeliaceae, lichenized Ascomycotina) in China. Journal of the National Taiwan Museum 60: 45–61.
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Urbanavichus, G. P. 2010. A checklist of the lichen flora of Russia. St. Petersburg. 194 pp. (In Russian).
Urbanavichus, G. P. & Urbanavichene, I. N. 2015. Assessment of Usnocetraria oakesiana for the Red Data Book of Russia. (Manuscript received from the authors)
Yazici, K. & Aslan, A. 2002. New records for the lichen flora of Turkey. Turkish Journal of Botany 26: 117–118.