Hypoxylon vogesiacum is a decay fungus found on dead wood, in Europe mainly on Ulmus glabra, sometimes on Fraxinus excelsior, more rarely Acer and Pyrus. The substrate of H. vogesiacum is continuing to decline throughout its distribution area (Europe), as the populations of U. glabra and Fraxinus excelsior are declining in Europe (Rivers 2017, Khela 2013).  Hypoxylon vogesiacum is NT in Norway and VU in Sweden. The European population is considered to suffer from a decline of 15-30% during three generations (generation length estimated to 10 years, i.e. assessment period 30 years; present and future) because of decline in host trees caused by fungal pathogens (dutch elm disease and ash dieback), deer feeding killing elm (Norway), and competition from the invasive Acer pseudoplatanus (Norway). Ulmus glabra is VU both in Norway (2015, assessment period 100 years; where the largest known population of H. vogesiacum is) and in Europe as a whole, while it is CR in Sweden (2020, assessment period 100 years). Fraxinus excelsior is VU in Norway (2015) and EN in Sweden (2020) due to the ash dieback. In Europe and globally (Fraxinus excelsior is mainly a European species) it was assessed as NT before the complete picture of the ash dieback was available. Hypoxylon vogesiacum is assessed as NT A3ce, A4ce based on an estimated ongoing and future reduction in substrate and population of 15-30% in 30 years, especially based on knowledge of the Scandinavian populations.

The former varieties of Hypoxylon vogesiacum are excluded as they currently are regarded as other species (var. microsporum=H. fuscopurpureum, var. macrosporum=H. macrosporum; Granmo 1999). Hypoxylon vogesiacum belongs to a genus with many species, which are not sufficiently checked phylogenetically. Hypoxylon vogesiacum is reported from many continents, but there is a need of using molecular methods to see whether there are more taxa involved. Here we have chosen to exclude distribution data from outside Europe.

Hypoxylon vogesiacum is known mainly from Europe, with a few records from Asia, Australia and western USA (GBIF (https://www.gbif.org/species/5254781). These outside Europe observations are not verified by molecular methods and are here considered likely to be different taxa. In Europe, the main distribution area is Scandinavia with southern/western Norway and southern Sweden as most important. In Norway H. vogesiacum, is widely distributed in the warmest lowland parts of southern Norway north to Trøndelag, with its largest populations in western Norway. Further, there are reports from W Russia (GBIF and E. Popov pers. comm.), Austria and Czechia (see also Zibarova & Kout 2017). There is one recent record from southern Finland and two from Slovakia (Ivona Kautmanova pers. comm.). Holec (2008) reports the species from Ukraine. Hypoxylon vogesiacum was described from France and is also reported from Switzerland and northern Spain (Petrini 1985, Petrini & Miller 1986). It is known from Latvia (Inita Daniele pers. comm.). It has not been reported from Denmark or the UK.

We have chosen to exclude extra-european records as the few reports from India, Canada,  temperate Asia, and Australia are assumed to represent separate taxa. Among the1563 occurrences in GBIF, ca. 1350 are from Norway and ca. 200 from Sweden. Otherwise the species seems to be rare to very rare throughout its range. That means that the population trends in Norway and Sweden are most important. The main European hosts of Hypoxylon vogesiacum, Ulmus glabra and Fraxinus excelsior are declining due to fungal pathogenes. Ulmus glabra in Norway is estimated to have an ongoing decline of 30-50%  ongoing and future 90 years (2015, assessed as VU, in 2021 assessed to >50% decline in 100 years and EN). In Sweden Ulmus glabra is CR (2020). Fraxinus excelsior is in Norway is estimated to have a decline of 65-85% in the coming 100 years and is EN on the Norwegian red list (2021), in Sweden CR (2020, estimated to have a decline of >90% in the coming 100 years). Within Europe, the populations of U. glabra are declining (10-40% in the past century; >30% in the current century), and the species is assessed as VU in Europe (Rivers 2017). Globally Ulmus glabra is DD (Barstow & Rivers 2017. Fraxinus excelsior is NT on a European and global scale, but it was assessed before the full impact of the ash dieback was obvious (Khela 2013, Khela & Oldfield 2018). Based on this, H. vogesiacum is inferred to have an ongoing and future decline of 15-30% during 3 generations (30 years), in its main European (i.e. Scandinavian) population.

Hypoxylon vogesiacum is mainly found on wood of Ulmus glabra and (less commonly) on Fraxinus excelsior, rarely to very rarely also on Acer, Quercus, Tilia or Pyrus ((>80 % on Ulmus, 12% on Fraxinus in Norway according to Granmo 1999); Granmo 1999, Nordén et al. 2015). It occurs on coarse logs of old trees or on coarse fallen branches, or on dead parts of still living trees. The species (like its host) seems to prefer relatively warm summers and occurs especially in the hemiboreal regions of Northern Europe (Granmo 1999).

Hypoxylon vogesiacum depends on its hosts. Dutch elm disease (DED) is the most serious threat to Ulmus glabra in SE Norway, Sweden and other European countries. In Western Norway DED is not present, but will kill most Ulmus trees if, as is predicted, it will reach this region. In parts of western Norway, the vector of DED (the bark beetle Scolytus laevis) is already present and ready to spread the DED. There is a decline in available and suitable Ulmus logs also in western Norway due to an increase in red deer population, e.g. killing old trees and affecting re-establishments of young trees, and competion from the invasive Acer pseudoplatanus. Fraxinus excelsior is the second most important host, and is seriously declining all over Europe because of the ash dieback. In western Norway this species is also affected by red deer population and competition from the invasive Acer pseudoplatanus.

The known sites are often very rich in (partly redlisted) epifytic species on Ulmus or Fraxinus, and are in need of area-specific protection. Protecting the hosts elm and ash is very important. Monitoring and preventing the spread of Dutch Elm Disease is important where DED is still not present. Fighting DED and ash dieback are important measures for H. vogesiacum.

The knowledge of the host relationships, nutrient strategy and population dynamics of Hypoxylon vogesiacum has gaps which should be filled. Knowledge on how to fight DED and ash dieback is very important.

There is no use or trade of this species. Its host trees Ulmus glabra and Fraxinus excelsior were formerly used for pollarding (cutting branches for fodder), which was not a threat for H. vogesiacum. The timber of its host trees is strong, durable and water resistant, and has in Europe been used as material for different purposes (Rivers 2017, Khela 2013).

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