Cortinarius areni-silvae is a rare ectomycorrhizal fungus associated with Pinus sylvestris in the boreal parts of Europe to Western Siberia. It grows in dry and nutrient poor lichen - lingonberry dominated sandy, old, pine forests. This habitat has been and is being negatively impacted by clear cutting and threats leading to a reduction in the area of old-growth of Scots Pine outside protected areas. These forests have been and are seriously declining due to forestry but also due to roads, industry/settlements/military activities as well as gravel pits. It is suspected that this species has declined and is continuously declining at the global scale due to the decreasing area of old-growth pine forests and an apparent poor ability to spread and re-establish in managed forest after clear-cutting. The population is estimated to consist of c. 1,000 localities and c. 20,000 mature individuals. The decline in the major habitat of C. areni-silvae is considered to be in the magnitude of 25-30% in 50 years (three generations) and predicted to continue to decline. The population size is suspected to undergo a similar decline, approaching 30%. The species is thus assessed as Near Threatened (A2c+3c+4c).

Cortinarius areni-silvae is distributed in the boreal region of Eurasia, from Fennoscandia (mainly the eastern parts) to the east to Western Siberia (Altay) and probably also further east. The species has a few records in Denmark. It is reported to be rare in Russia.

The species is a rare species presently known from approx. 150 localities in the Nordic countries (six localities in Denmark, five localities in east Norway, c. 50 localities in Sweden and stated as rare but widespread in eastern Finland. It is reported as quite rare in Russia (T. Svetasheva, pers. comm). As the knowledge of the population size in Russia is poor, it is conservatively estimated that the number of sites may approach 1,000. According to Dahlberg and Mueller (2011), the number of individuals is estimated to approximately 20,000 (c.1,000 localities x c.20 mature individuals in each).

The species is nationally Red Listed in Denmark (EN; Moeslund et al. 2023), Norway (NT; Artsdatabanken 2021) and Sweden (NT; SLU Artdatabanken 2020). In Finland it is assessed as Least Concern. It is also noted as an indicator species for old-growth sandy Scots Pine forests in Finland (Bonsdorff et al. 2014), Norway (Brandrud and Bendiksen 2014) and in Sweden (Nitare et al. 2024, Björnström and Wikström 2024).

The decline of the major habitat of Cortinarius areni-silvae (older, dry, sandy pine forests) during the last 50 years (three generations) is estimated to be 25-30% in Fennoscandia (Brandrud and Bendiksen 2014) and thought to be similar in the Russian Siberian forests (Flintoff 2013, Kukavskaya et al. 2013). The species' population size is suspected to undergo a similar decline of c. 25% within this time frame, corresponding to three generations (see Dahlberg and Mueller 2011).

Cortinarius areni-silvae is a rare species within the group Phlegmacium of Cortinarius. It is a mycorrhizal fungus associating with Scots Pine (Pinus sylvestris) growing in nutrient-poor, dry and sandy old-growth forests with a vegetation of lichens and lingonberry (Vaccinium vitis-idaea) (Brandrud and Bendiksen 2014, Nitare 2023, Nitare et al. 2024). The species seems to favour sparse and light open forests with exposed sand and thin vegetation. Even in extensive areas of appropriate habitat, it is only rarely encountered, typically with single scattered sporocarps.

The species is primarily threatened by clear-cutting of old-growth pine forests (see e.g. Svensson et al. 2019 from Sweden, Kotiaho 2017 from Finland). It is rarely observed in regenerated forest after clear-cutting. Therefore, conversion of old-growth forests to managed forest, i.e. reduced amount of sandy old-growth pine forest, is the main cause of the decline. It is also negatively affected by area loss (expansion of urban settlements, military areas, roads, industry and gravel pits (see Brandrud and Bendiksen 2014).

The potential pine habitat is located in northern Europe and extending to western Siberia. Around 1% of the forest is cut annually in parts of its range, so a conservative estimate of the potential decline of appropriate habitat is approximately 30% over 50 year period taking into account uncertainties of forest cuttings and the population in Russia. The population size is suspected to undergo a similar decline, approaching 30% over 50 year period (three generations, see Dahlberg and Mueller 2011).

The species is not used.

Being an ectomycorrhizal fungus, Cortinarius areni-silvae is dependent on its obligate association with pines. Although the sporocarps are short-lived, the soil-dwelling mycelia are perennial and may potentially live several decades or even centuries. With a continuous presence of mature Scots Pine trees at a locality, the mycelia may potentially become as old as the trees. C. areni-silvae, as for most of this habitat's ectomycorrhizal fungi, has probably evolved to survive the historic typically low intensity fires in boreal forests. Key for its survival was that a significant number of trees survived the fires with much of its ectomycorrhizal community associated to its roots.

Site protection is recommended for sites where this species and other ectomycorrhizal fungi of conservation interest in this habitat have good populations. As forest fires have been an evolutionary important natural disturbance in this habitat, natural or prescribed burning should be considered to maintain desired forest dynamics and biodiversity.

A better understanding of the species' biology and population dynamics would facilitate better management, e.g. what conditions it may require for establishment, mycelial longevities and demographic structure within populations. Also such research should look into to what degree tree retention and alternative forestry in managed forests may maintain the species.