Hypoxylon vogesiacum is a decay fungus found on dead wood, in Europe mainly on Ulmus glabra, sometimes on Fraxinus excelsior, more rarely Acer, Quercus, Tilia and Pyrus. The substrate of H. vogesiacum is continuing to decline throughout its distribution area (Europe), as the populations of U. glabra and F. excelsior are declining in Europe. H. vogesiacum has its main area of occurrence in Norway and Sweden.

The population is considered to be suffering a decline approaching 30% over three generations (generation length estimated to 10 years, i.e. assessment period 30 years; present and future) because of declines in the host trees caused by fungal pathogens (Dutch Elm Disease and Ash Dieback), deer feeding killing elm, and competition from the invasive Acer pseudoplatanus. Therefore, H. vogesiacum is assessed as Near Threatened A3ce+4ce.

The former varieties of Hypoxylon vogesiacum are excluded as they are currently 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 known phylogenetically. Hypoxylon vogesiacum is reported from many continents, but molecular methods are needed to confirm whether they are truly conspecific or if more taxa are 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 2023). These observations from outside Europe 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 the 2,747 occurrences in GBIF, c.2,400 are from Norway and c.300 from Sweden (GBIF 2023). In other parts of its range, the species seems to be rare to very rare. Population trends in Norway and Sweden are thus the most important. Ulmus glabra and Fraxinus excelsior, the main European substrata of Hypoxylon vogesiacum, are declining because of fungal pathogens. U. glabra in Norway is estimated to face an ongoing decline of 30-50% in the next 90 years (in 2021 assessed as 50% decline in 100 years and Endangered; Artsdatabanken 2021). In Sweden, U. glabra is Critically Endangered (SLU Artdatabanken 2020). F. excelsior in Norway is estimated to face a decline of 65-85% in the coming 100 years, and is Endangered on the Norwegian Red List (Artsdatabanken 2021), while in Sweden it is evaluated as Critically Endangered (SLU Artdatabanken 2020, with an expected decline of 90% in the coming 100 years). Within Europe, populations of U. glabra declined at 10-40% in the past century, and are expected to decline by 30% in the current century; the species is assessed as Vulnerable in Europe (Rivers 2017), while F. excelsior is Near Threatened on a European and global scale, but that assessment was made before the full impact of ash dieback became obvious (Khela 2013, Khela and Oldfield 2018). Based on this, overall, H. vogesiacum is suspected to have an ongoing and future decline approaching 30% during over three generations (30 years).

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 substratum trees) 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 predicted, it reaches this region. In parts of western Norway, the vector of DED (the bark beetle Scolytus laevis) is already present and ready to spread DED. There is also a decline in available and suitable Ulmus logs in western Norway due to an increase in red deer numbers, with the deer killing old trees and affecting re-establishment by young trees, and because of competition from invasive Acer pseudoplatanus. Fraxinus excelsior, the second most important substratum tree, is seriously declining all over Europe because of ash dieback. In western Norway this species is also affected by red deer population and competition from invasive Acer pseudoplatanus.

The known sites are often very rich in (partly redlisted) epiphytic 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 spread of Dutch Elm Disease is important where DED is not yet present. Fighting DED and ash dieback are important measures for conserving H. vogesiacum.

Knowledge of 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.

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