The species mostly occurs in boreal old-growth dry lichen dominated sandy forests of Scots pine (Pinus sylvestris) with the majority of the European localities known from Sweden and Finland and a possibly high number in Russia. In Fennoscandia is known from approx. 300 localities (50 in Norway, 100 in Sweden and 150 Finland). Not less than 100 localities are assumed to be in Russia. In North America the estimation is approx. 40 localities (GBIF 2019). There are then a total of 440 known localities, that with the not known localities could be five times more this number (2,200 localities globally estimated). The global population size is then calculated to be 22,000 (typically finding 10 mature individuals in each site).
Forest where it occurs are primarily threatened by clear-cutting and possibly it is also negatively affected by nitrogen fertilization of forests. The species seems to have poor ability to spread and establish in forest after clear-cutting. This is probably due to increasingly low proportion of old-growth-pine-forest where it occurs and hence lower likeliness of the species to re-establish from spores. It may also depend on that the species is considered to form long-lived individual mycelia, probably several decades and possibly several centuries old and that it evolutionary has been selected to have a slow population dynamics.
Historically, boreal forest fires commonly have been low-intense with a high degree of tree survival, and hence with a high likeliness for mycelia of ectomycorrhizal fungi to be very old. In Fennoscandia, old-growth pine forest is estimated to have declined >15% since 1960 during the last 50 years (Svensson et al. 2019 from Sweden, Kotiaho 2017 from Finland). Clear-cutting management was introduced in large scale in these countries around 1950 and on average 1% of the productive forest land is clear-cut annually. Boletopsis grisea is yet only rarely observed in forest resulting from clear-cutting, hence close to seed trees or retention trees.
Population Trend: decreasing
Boletopsis grisea forms ectomycorrhiza with Pinus spp., in particular Scots pine (Pinus sylvestris). It is common, but typically with only a few mycelia per stand in old-growth pine forests on sediment/sandy soils. Occurs predominately in open nutrient poor pine forests with lichens and ericaceous (Calluna and Vaccinium) undergrowth vegetation on dry acidic sandy soils. In Poland the fungus also was known to occur on inland sand dunes with pine. In France, it is reported in pine forests mixed with Cedrus.
The mycelium of the fungus is considered to be long-lived, potentially several decades to centuries, comparable to its host pine trees (Dahlberg and Mueller 2011). The mycelia of the fungus survive forest fires if their associated old tree survives.
Boletopsis grisea is primarily threatened by clear-cutting of old-growth pine forests (for decline of old-growth (pine) forests, see e.g. Svensson et al. 2019 from Sweden, Kotiaho 2017 from Finland). It is rarely observed in forest regenerated after clear-cutting. Hence conversion of old growth forests to managed forest, i.e. reduced amount of habitat, is the main cause of the decline. It is also negatively affected by nitrogen eutrophication of sandy pine forests, as well as by areal loss (expansion of urban settlements, military areas, roads etc.); see Brandrud and Bendiksen (2014) with references.
The major part of the potential pine habitat is in northern Europe and some parts of Russia. Around 1% of the forest is cut annually, so a conservative estimate of the potential decline of appropriate habitat is approximately 30% over 50 year period (three generations) taking into account uncertainties of numbers and size of subpopulations and rates of forest cutting in Russia and North America. It is possibly negatively affected by nitrogen fertilization of forests along with increased atmospheric nitrogen deposition (Dahlberg and Croneborg 2003).
Present in the Red Lists of Czechia NT, Denmark RE (2010), Finland NT (2010), Norway VU (2010), Poland EN (2006), Slovakia suggested to be nationally included in the Red List, Sweden VU (2010), Switzerland EN, 2010 and suggested to be included in the Red Lists in France, Germany and Slovakia. Also included in the Red Data Books of five regions of Russia. It is strictly protected by law in Poland.
Being an ectomycorrhizal fungus, B. grisea is dependent on its obligate association with pines. Although the sporocarps are short-lived, its soil-dwelling mycelia is perennial and potentially lives several decades or even centuries. With a continuity of mature Scots pine trees at a location, the mycelia can be older than the trees. It is not known why it appears not to colonize and establish in highly managed Scots pine plantations. Therefore, an appropriate conservation action is to maintain living trees and stands where it occurs to act as reserves. The fungus is adapted to withstand the regular, typically low intensity fires in boreal forests where a significant number of trees survive along with much of its the fungal mycelia that is associated with the trees.
Recommended Action: Set aside Scots pine forest reserves where the species have good subpopulations. At these forests, natural or prescribed burning should be considered to maintain desired forest dynamics.
It is possible that B. grisea can survive timber cutting if a sufficient number and density of retention trees are preserved in a managed forest. In this case it will be critical to ensure that as many retention trees as possible are located where the mycelia of the fungus are growing, e.g. where the sporocarps have been observed.
A better understanding of the specie’s population dynamic would facilitate a better management, e.g.at what conditions it may establish, the demographic structure within populations and the pattern (and causes) of individual mycelia. Also to what degree seed trees and retention trees in managed forest may maintain the species at locations. It is also recommended the establishment of new protected areas.