Assessment Notes

Justification

Cortinarius tiliae is a rare European ectomycorrhizal fungus strictly associated with calcareous Tilia cordata forests with its main occurrence in the Oslofjord area of south-east Norway. In total, the species has been recorded from 16 sites in Europe. The calcareous Tilia forests have severely declined in south-east Norway with a loss of area due to 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 estimated to have a total population of 800 mature individuals, distributed within a very small area. According to the C and B criteria (C2a(i)), B2ab(ii,iii,v)) the species fulfils the requirements to be listed as EN, based on a continuous decline, population size <2,500 mature individuals, small area and very small/isolated subpopulations.

---

Geographic range

Cortinarius tiliae occurs mainly in the Oslofjord district of south-east Norway, where it is known from 13 localities/sites in calcareous Tilia forests. The Norwegian sites are believed to be old, relic ones; that is being remnants of a formerly larger population of Tilia forests and C. tiliae in a Holocene climate optimum 5,000-8,000 years ago. Outside Norway, the species is extremely rare, verified from one locality in Czechia, one in Hungary and one in Italy (also in Tilia forests).

---

Population and Trends

Cortinarius tiliae is known from 13 localities/sites in the Oslofjord district. The habitat (calcareous lime forests) is very well investigated for fungi (including a specific monitoring programme), and the total number of localities in Norway is estimated to ca. 20, corresponding to 400 individuals. The total in Europe/globally as a whole is estimated to 40 sites, that is equivalent to 800 mature individuals (cf. Dahlberg and Mueller 2011).The calcareous Tilia forest type is Red Listed as EN in Norway, according to the national nature type redlist (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 tiliae is likewise Red Listed as EN in Norway, based on decline in habitat and a very small population.

Population Trend: decreasing

---

Habitat and Ecology

The species forms mycorrhiza exclusively with Tilia cordata in calcareous lime forests. The major populations in the Oslofjord districts occur on very dry, shallow-soil limestone outcrops 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, in the Holocene climate optimum, when the Tilia cordata forests were much more frequent than today. Subsequently, the species has probably been outcompeted by Fagus-Quercus-Carpinus species in forests nowadays dominated by these tree species and the species has been restricted to some Tilia forests of a relic nature, 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 in urban areas, including an increase in roads, and limestone quarries. Also there has been a "densification" due to increase in thickets e.g. of Fraxinus and Acer and invasion of Picea abies is 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

A couple of the Tilia forests with Cortinarius tiliae have recently become nature reserves, but more sites need to be set aside to prevent further declines and 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 is also important to identify sites where less strict conservation regime can be appropriate, e.g. woodland habitats or where non-destructive human activities can be allowed. Additionally, more mapping, surveying and monitoring of C. tiliae is desired, and more information on occurrences in fragments of calcareous Tilia cordata forests in various parts of Europe where this species potentially could occur would also be good.

---

Use and Trade

No use or trade is known.

---

Source and Citation

Brandrud, T.-E., Krisai-Greilhuber, I. & Saar, I. 2021. Cortinarius tiliae. The IUCN Red List of Threatened Species 2021: e.T204091900A204095095. https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T204091900A204095095.en .Accessed on 14 October 2023

---

• Country occurrence