Hygrocybe citrinovirens is one of the best indicators of species-rich semi-natural grasslands (so called waxcap grasslands) which were, for a long time, managed in a traditional way. These habitats are dependent on moderate grazing intensity and/or hand mowing without using artificial fertilizers and pesticides. They are rapidly disappearing worldwide due to changes in land use (agricultural intensification and decline of traditional farming practice) and increased use of fertilizers and pesticides, and as these habitats disappear so do the fungal species that rely on them.
This species is large, conspicuous and easy to recognize, but is only known from relatively few localities. The species is not known to occur outside of Europe (although it has close relatives in North America) and it is decreasing in all countries where it occurs. Decline in area and quality of available habitat has approached (or possibly exceeded) 30% over the last 50 years; the decline in population size over this time has probably been higher. This decline in habitat is expected to continue even more rapidly over the next 50 years (approximately three generations: one generation for H. citrinovirens is around 17 years). Currently the population size probably exceeds 20,000 mature individuals. The species is assessed Vulnerable because of a reduction in population size of more than 30% over the last 50 years, a decline suspected to continue and caused by habitat loss and degradation. This meets the threshold for VU A2c+3c+4c.
Hygrocybe virescens (Hesler & A.H. Sm.) Montoya & Bandala from North America is similar to this species and may be conspecific.
Hygrocybe citrinovirens is one of the best indicator species of species-rich semi-natural grasslands which were for a long time managed in a traditional way, so called waxcap grasslands. These habitats, dependent on moderate grazing intensity and/or hand mowing without using artificial fertilizers and pesticides, are rapidly disappearing worldwide and so do fungal species bound to them.
H. citrinovirens is a large, conspicuous and easy to recognize and have relatively low dark figures when it comes to number of localities. Its not known outside Europe (but have close relatives in North America) and its populations are decreasing in all countries where it occurs. Red-listed in seven European countries.
Hygrocybe citrinovirens is so far only known from the western Palearctic (eastwards to Georgia). It has been reported from most European countries with its stronghold occurrences probably in northwest Europe.
In North America, Hygrocybe virescens is similar to H. citrinovirens and may be conspecific. Hygrocybe virescens is considered rare, and is known only from Mexico, California and Washington.
The population size probably exceeds 20,000 mature individuals. The population is decreasing in all known countries of occurrence, caused by lack of small scale farming and traditional methods of grassland management. This decrease is inferred to be 30% over 30 years (past, future and ongoing) but may actually be as high as 50% over three generations (50 years; e.g., 1975-2025) and even higher over longer time-frames.
Population Trend: Decreasing
Hygrocybe citrinovirens is confined to seminatural, herb-rich grasslands, both on calcareous and more siliceous soils, Earlier considered to be saprotrophic but recent research have shown that some (and probably all) Hygrocybe species have arbuscular mycorrhiza connected to vascular plants.
The species is a representative of a fungal community with a large diversity other fungal species (Hygrocybe spp., Entoloma spp,, Clavaroid fungi, Geoglossaceae and many other fungi strictly dependent on habitats with low vegetation and limited availability of phosphorus and other nutrients due to long continuity of grazing and/or mowing. Added fertilizers or abandonment immediately changes vegetation cover in a way that is detrimental for the fungus community.
The species is more or less confined to the following habitats:
6210 NATURA 2000 - Semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco-Brometalia)
6230 NATURA 2000 - Species-rich Nardus grasslands, on siliceous substrates in mountain areas and submountain areas.
Like other species dependent on semi-natural grasslands Hygrocybe citrinovirens it is threatened by the loss of habitat due to decreasing small scale farming. The main reasons for decline are agricultural intensification (primarily the application of phosphorus) and the reduction of habitat areas and quality. Grassland neglect where the sward becomes rank and overgrown also restricts carpophore production, although it is not clear if this affects the mycelium under the ground. In urban/suburban environment, the application of lawn fertilisers, fungicides and moss killers can also affect the species (Mitchel 2000).
According to NATURA 2000 reports (Calaciura & Spinelli) grassland habitats is steadily decreasing, mainly due to abandonment or change in landuse. The total area of grassland in the EU fell by an average of 12% between 1975 and 1998, with increases in only very few areas. In the areas where the habitat is still present, the lack of management results in a continuing decrease in range of many species due to decrease in habitat quality.
According to FAO the area of grasslands in the EU declined by 12.8% from 1990 to 2003; only a few Member States managed to buck this trend. (Food and Agricultural Organisation of the United Nations 2006: FAO Statistical Yearbook. – FAOSTAT). Pressure caused by landuse changes on grassland habitats is steadily increasing. Some 60% of newly afforested areas in the EU was formerly used as permanent/seasonal grazing land or hay-production in natural meadows.
More than 75% of the grassland habitats in the EU are in an unfavourable conservation status, according to draft data provided by Member States under Article 17 of the Habitats Directive. Over the past decade, grassland butterflies have suffered large declines in Europe, with a reduction of abundance by almost 50%, with little sign of improvement (SEBI 2010 Biodiversity Indicators).
Site protection and management of habitats are very important conservation actions for this species. Some grasslands with high species diversity and conservation value (including grassland fungi such as Hygrocybe citrinovirens communities) are situated within national parks, nature monuments, or nature reserves. However, these grasslands need careful management plans, including grazing which is not always present even within strictly protected areas. This situation results in continual decrease of habitat quality even if sites are protected from exploitation.
This species is included in national Red Lists for seven European countries.
Distribution is not well known in south-eastern Europe.
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