Assessment Notes

Justification

Cortinarius mariekristinae is a rare ectomycorrhizal fungus strictly associated with calcareous Tilia cordata forests, an exclusive forest type. The species is only known from eight sites in the Oslofjord area in Norway, one site in the Rhine valley, south-west Germany and two sites in Estonia. Calcareous Tilia forests have been seriously declining in south-east Norway due to a loss of area as a result of urbanization, roads, limestone quarries, forestry and in some places also due to increased growth of shrubs and spruce following ceased management with e.g. cattle grazing. The species is suspected to have a total population of 500 mature individuals, occupying a very small area. According to the C and B criteria (C2a(i), and B2ab(ii,iii,v)) the species fulfils the criteria for being red-listed as EN, based on a continuous decline, population size of <2,500 individuals, small area and very small/isolated subpopulations.

---

Taxonomic notes

The species was described in 2019 (Brandrud et al. 2019). Prior to that, the species was listed in the Norwegian Red List treated under the working name Cortinarius aff. humolens.

---

Geographic range

Cortinarius mariekristinae is known mainly from the Oslofjord district of south-east Norway, where it is recorded from eight localities/sites in calcareous Tilia forests. The species was described in 2019, but has been known for a long time from the Oslofjord area (Brandrud et al. 2019). The Norwegian sites are believed to be old, relic ones; that is being remnants of a formerly larger population of Tilia forests in the Holocene climate optimum 5,000-8,000 years ago. Outside of Norway, the species is extremely rare, so far verified from one locality in Tilia forest along the Rhine valley in south-west Germany and environmental samples at two localities in Estonia.

---

Population and Trends

Cortinarius mariekristinae is known from eight sites in the Oslofjord district. The habitat (calcareous lime forests) is very well investigated for fungi in Norway (including a specific monitoring programme), and the total number of localities is estimated to ca. 13, corresponding to 260 individuals. The total in Europe/globally as a whole is estimated to 25 sites, that is equivalent to 500 mature individuals (Dahlberg and Mueller, 2011). The calcareous Tilia forest type is Red Listed as EN in Norway, according to the national nature type Red List (Artsdatabanken 2018), due mainly to a loss of area from urbanization, road construction, lime quarries, etc. (see also Direktoratet for naturforvaltning 2011, Brandrud et al. 2011). Cortinarius mariekristinae was in 2015 Red Listed as CR in Norway, based on a decline in habitat and a very small population. In the new 2021 Red List, it is proposed to EN, since the updated (sub)population estimates exceed the threshold for CR.

Population Trend: decreasing

---

Habitat and Ecology

Cortinarius mariekristinae forms mycorrhiza with Tilia cordata, possibly also Corylus avellana, in calcareous lime forests. The major populations in the Oslofjord districts occur on very dry, shallow-soil limestone outcrops/shelves or small scree areas with limestone/shale gravel. It is probable that the species formerly had a wider European distribution associated with Tilia forests on calcareous ground, during the Holocene climate optimum, when Tilia cordata forests were more frequent than today. The species has probably been outcompeted by Fagus-Quercus-Carpinus species in forests nowadays dominated by these tree species and the species may only have survived in a few Tilia forests of a relic nature, mainly outside the distributional area of Fagus and Carpinus.

---

Threats

The calcareous Tilia forests of south-east Norway have been declining by >30% the last 50 years due to an increase of urban areas, including an increase in roads, and limestone quarries. Also there has been a "densification" due to an increase in thickets e.g. of Fraxinus and Acer and an invasion of Picea abies has been seen in many stands (due to loss of traditional management and increased seed pressure from adjacent Picea plantations), increasing the humification/acidification of the calcareous topsoil, and threatening the old, relic biodiversity of the Tilia forests (Direktoratet for naturforvaltning 2011, Brandrud et al. 2011, Artsdatabanken 2018).

---

Conservation Actions

One of the Norwegian Tilia forests containing Cortinarius mariekristinae is a nature reserve (the type site), but more sites need conservation, to prevent declines and further fragmentation of calcareous Tilia forests with good habitat quality. It is especially important to set aside reserves on calcareous lime forest hotspots, housing many rare/Red Listed, habitat-specific species. It may also be important to identify sites where a less strict conservation regime can be appropriate, e.g. woodland key biotopes, or where cautious extensive selective cutting may be acceptable. More mapping/surveying and monitoring of C. mariekristinae is desired as is more information on the ocurrence and status of calcareous Tilia cordata forests in various parts of Europe.

---

Use and Trade

This species is not used.

---

Source and Citation

Brandrud, T.-E., Krisai-Greilhuber, I. & Saar, I. 2021. Cortinarius mariekristinae. The IUCN Red List of Threatened Species 2021: e.T204091999A204094198. https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T204091999A204094198.en .Accessed on 25 September 2024

---

• Country occurrence