Tricholoma apium is a characteristic and well-known, mainly European species of dry, pine forests. In Europe, the species is a representative and indicator species of old, dry, lichen-dominated sandy pine forests with a high conservation value, including a rich fungal biodiversity.
The sandy pine forests have been declining in most parts of Europe, and the species is included on most national redlists of this region. The decline is due to (i) eutrophication/heavy N-deposition in large parts of Europe, (ii) habitat-loss due to urbanization and (iii) reduced habitat qualities of remaining forests due to intensive forestry with clear-cuts (e.g. N Europe). The element of mycorrhizal fungi in dry sandy pine forests is probably among the most threatened and declining fungal elements of Europe.
A >30% decline in habitat quality and quantity (pine forest area) is considered, due to altered land-use/deforestation and intensive forestry, and eutrophication by heavy N-depositions. Evaluation period 50 years (= 3 generations according to the recommendation of Dahlberg & Mueller, 2011). In Fennoscandia, an ongoing population decline inferred from habitat change (forest statistics) is estimated to be approx 30%.
Global and European Red List assessment;
VU (A2c+3c+4c), with an estimated decline of >30% during evaluation period of 50 years.
The species has its core area in N Europe, in (E Norway-)Sweden-Finland(-Estonia), and probably also Russia. The species further has a wide but fragmented distribution in Western and Central Europe, and appears everywhere to be very rare, with only a few sites (some more in the Czech Republic). The species is in Europe found southwest to Spain and east to Turkey (in Cedrus forest). The species is not reported from Japan or other countries in E Asia. The species is furthermore widely distributed but rare in North America (known from the Pacific Northwest and Michigan-Masachusetts-Newfoundland).
Currently know from ca. 350-400 localities in Fennoscandia (50 sites in Norway, approx. 200 sites in Sweden). The real number of localities/sites may be 10x higher and are estimated to approx.. 3500-4000 in Fennoscandia, possibly approx. 5000 if Russia and Balticum are included. The numbers indicated from W and C Europe are very low (except for some more localities from the Czech Republic), approx. 100 altogether, making the estimates for the entire European populations to approx. 6000 sites, that is approx. 120.000 individuals. The species is rare and apparently not so widely distributed in North America, possibly constituting approx. one-fourth of the total population global population.
Due to various negative trends (areal loss, N-pollution/fertilization, clear-cutting), the dry (sandy) pine forests housing this species has had a considerable decline during 50 years in Europe (see under Why should the species be considered).
Probably some of the forest types in North America have had a similar decline due e.g. to modern forestry and in some areas also due to urbanization (e.g. in Massachusetts, where the forested area is now declining acc. to forest statistics).
The species are world-wide probably decreasing with more than 30% in 3 generations (50y) based on habitat-loss.
Tricholoma apium forms mycorrhiza with Scots pine (Pinus sylvestris) in Europe, whereas it is reported from various conifers in North America. In Europe, the species is mainly associated with dry, often lichen-dominated sandy pine forests with thin organic soils, on glacifluvial deposits, e.g. on flood-plains along the larger rivers and on eskers-ridges (formed from subglacial rivers). In C/W Europe, the species is reported also from coastal sand-dunes with pines. In S. Scandinavia, T. apium also occurs in calcareous pine forests without any sand deposits (but on mineralic soil with little humus). Also in N America, the species seems to occur mainly in sandy soils.
The species seems to be favored by some disturbance, such as small paths/openings in humus layer and probably also light forest fires with scattered surviving pine trees. The species is almost confined to old-growth forests, and is hardly observed in younger, even-aged forests that has been clear-cutted.
It is primarily threatened by clearcutting of old-growth pine forests, nitrogen fertilization of forests, and urbanization. The species appears more or less dependent on forest/tree/root continuity, and is one of the more vulnerable sandy pine forest species to modern forestry with clear-cuts.
To prevent decline and fragmentation of the old-growth sandy pine forests with natural dynamics it is important to set aside Scots pine forest reserves, preferentially larger, continuous areas, in regions where the species have good populations. In these forests, natural or prescribed burning should be considered to maintain desired forest dynamics. It is furthermore important to maintain other kinds of disturbance factors, such as (moderate) grazing, providing small openings in the humus layer.
Further studies are needed to document population dynamics, its dependence on old-growth forests with a slow turnover/root continuity and its dependence on moderate disturbance regimes with small paths or other kind of humus layer openings. The pylogeographic patterns of the species, especially the degree of differentiation between N American and European populations should be clarified. There is also a need to further document the apparent lack of the species in pine forests of E Asia, in sites where a number of otherwise co-occurring species are found.
Brandrud, T. E. & Bendiksen, E. 2014. Fungi of sandy pine forests in Norway, and a comparison of this threatened element elsewhere in Europe(-Asia). Agarica 35: 67-87.