Assessment Notes

Justification

The forest woodwax Hygrophorus subviscifer is a rare, distinct and characteristic and well-investigated species that has decreased in many parts of Europe and is listed as threatened in many national Red Lists. It has it distribution in the northern part of Europe. Its main distribution is concentrated to Fennnoscandia. It forms ectomycorrhiza with Norway spruce (Picea abies) in old-growth, herb-rich coniferous forests usually on base-rich or calcareous soils. H. subviscifer is used as an indicator species of remnants of old spruce herb-rich forests on productive soils with long continuity of trees. These productive forest habitats are of high economic value and under heavy pressure from forestry. The prime cause for the decline of H. subviscifer is past and ongoing clear-cutting. The old-growth habitat of H. subviscifer is inferred to have decreased by more than 30% during the past 50 years in Fennoscandia, is ongoing and suspected to continue in the future. The habitat decline is suspected to correspond to a similar decline in population size.

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Taxonomic notes

The species was first described from Finland by Karsten as Agaricus subviscifer in 1878 and placed in the genus Hygrophorus by Harmaja in 1985. Was also described by M.M. Moser 1967 as Hygrophorus spodoleucus.

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Geographic range

Hygrophorus subviscifer is rare but has a wide distribution in boreal regions of northern Europe. In Russia there are a few observations from the Ural region (Sverdlovskaya Oblast) and Siberia (Tomskaya Oblast, Yamalo-Nenetsky Okrug (Tatyana Svetasheva pers. com.) It is also known from a few old reports from spruce forests in Switzerland, Estonia and Czechia (database records). In GBIF there are 210 occurrences from Europe between 1963-2016, mainly from Norway and Sweden, four of them from Estonia and two from Finland. There is one report from Czechia in 2004, but it has not been found there since then. The species does not seem to occur in North America and was not included in the monograph on North American species of Hygrophorus by Hesler and Smith 1963.

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Population and Trends

Hygrophorus subviscifer is known from approximately 200-250 localities in Fennoscandia and in the range of 25-50 localities in central Europe. The number of localities in Russia is unknown. The total number of localities (including undiscovered ones) may be estimated at less than 1000. It is nationally red-listed as threatened in several European countries (Austria CR, Norway VU, Sweden VU, Switzerland CR), but assessed as LC in Finland. 
The population of the species is declining due to forestry with clear cutting and fragmentation of older Norway spruce stands. There is considerable habitat loss of rich and calcareous spruce forests in the Nordic countries. The forest habitat, calcareous spruce forests, are red-listed as VU (Vulnerable) in Norway (Artsdatabanken 2018, Norsk rødliste for naturtyper 2018), EN in Finland (Kouki et al. 2018) and equally declining in Sweden. Old-growth forests not having been subjected to clear-cutting are estimated to have decreased by between 30-50% during the past 50 years (e.g. Kotiaho 2017 for Finland; Svensson et al. 2018 for Sweden). It is assumed to have declined by more than 50% over 100 years. Three generations in ectomycorrhizal fungi are estimated as 50 years (Dahlberg and Mueller 2011); the decline of population size over this timeframe is therefore suspected to be between 30 and 50 percent. The decline of sites with H. subviscifer is estimated to be in the same magnitude as the decline of its population size.

Population Trend: decreasing

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Habitat and Ecology

Hygrophorus subviscifer forms mycorrhiza with Norway spruce (Picea abies) and is mainly found in in old unmanaged spruce dominated forests, usually herb rich, and on nutrient rich or more calcareous soils (Larsson et al. 2010, von Bonsdorff et al. 2014). The mycelium of the fungus is long-lived and considered to potentially be as old as the trees or older (Dahlberg and Mueller 2011). It is only recorded in old growth forests that have not been affected by modern forestry with clear cutting.

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Threats

Hygrophorus subviscifer is today primarily found in old virgin forests, on more calcareous and nutrient rich soils. It is currently threatened by the decline and fragmentation of this suitable habitats. The forest type has declined by over 30 % in Fennoscandia during the last 50 years due to forestry (c.f. Kotiaho 2017, Svensson et al. 2018). The species seems to have poor ability to re-establish in managed forests after clear cutting. Rotation time in Fennoscandian managed forests is about 80-100 years.

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Conservation Actions

To prevent decline and fragmentation of rich spruce forests with good habitat quality for H. subvicifer, it is important to set aside reserves with productive coniferous forests as well as to identify suitable Woodland Key Habitats.  The detrimental effects of clearcutting for ectomycorrhizal fungi may be reduced by selective cutting or retention forestry, leaving much of the stand qualities intact. With continuity of the host-trees, the potentially long-lived mycelia of the species can survive.

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Use and Trade

The species is not used.

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Source and Citation

Larsson, E. 2019. Hygrophorus subviscifer. The IUCN Red List of Threatened Species 2019: e.T147323466A148008668. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T147323466A148008668.en .Accessed on 14 February 2024

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• Country occurrence