Almost finalize, but text here does not match final assessment. Updated version will be published in IUCN´s Red List June or Nov 2019.
Grifola frondosa is a wood-inhabiting fungus with large annual fruitbodies forming at the trunk base of old and large trees, preferably Quercus spp. Except for veteran oak trees, its distinctive multipileate fruitbodies also occur on other old-growth deciduous hardwoods (Acer, Carpinus, Castanea, Fagus, Ulmus, etc.), with only a few known records on large conifers. The fungus usually grows on living or dying trees and subsequently continues fruiting at the base of dead trees and stumps. Being confined to old and large trees, this species is under threat of declining mainly due to deforestation and uncontrolled logging in mature forests.
The species is assessed under criterion A (Population reduction): population decline during the last 50 years is >20 %, and the decline is projected to continue in future in the next 50 years (which is the evaluation period, equal to three generations). Hence, the preliminary assessment is Near Threatened (A2c+A3c+4c). This assessment is based mostly on the European population trend while at the global level the species can be currently qualified as Least Concern.
The fungus was described from Britain in 1785. Despite morphological similarity of Grifola frondosa throughout its range, phylogenetic analysis demonstrated a strong support for species partition separating eastern North American and Asian isolates; moreover, although based on non-type European isolate, a distinct European lineage in G. frondosa was suggested (Shen et al., 2002). In this case, taxonomic revision would require the name G. frondosa to be applied to the European lineage, with different names for the North American and Asian populations. Since the North American and Asian material may not be regarded as conspecific with the European records, this assessment is based on the European populations.
Grifola frondosa is a lignicolous fungus confined to old and large trees, mainly oak but also other deciduous hardwoods. This conspicuous and rarely occurring fungus is declining globally from deforestation, particularly from large-scale logging of old-growth trees.
In Europe Grifola frondosa is native to temperate hardwood regions. If to consider it as conspecific with North American and Asian populations, it has a circumpolar range in the Northern hemisphere. In North America, it can be found in Eastern Canada, northeastern and mid-Atlantic states of the US, and rarely in northwestern or southeastern states (Chen et al., 2000). In Asia, it is known to occur in southwestern and northeastern China and northeastern Japan (Yamanaka, 1997; Chen et al., 2000). A few records have been reported in Australasia (Australia, New Zealand).
In Europe, the reported population trends of G. frondosa vary across the continent. In many countries the species is nationally red-listed under threatened categories (Estonia – CR; Bulgaria, Lithuania, Macedonia – EN; Austria, Finland, Germany, Latvia, Norway, Poland, Ukraine – VU, Sweden – NT) based on population decline. Some countries assessed its populations as stable (Netherlands, Slovak Republic). Recently reported increase in number of records (for example, in Ukraine) is due to more surveys in appropriate habitats by amateur mycologists rather than increasing population trend of the fungus. In Russia and Belarus it is assessed as Rare (category 3). In North America this fungus is presumably more widespread but its population trends are unclear. In Asia, population status and trends are poorly known.
Grifola frondosa is a well-known and conspicuous species that forms large fruit bodies and much looked after. In combination with its specialization on large and old trees, it is rarely overlooked. Typically it occurs at only one or a few trees per site (e.g. genetic distinct mycelial individuals).
The global population is estimated to exceed 20 000 mature individuals. Based on a long-term ongoing decline and degradation of coarse old oaks and other appropriate trees in Europe, it is estimated to have declined more than 20% since 1970, a decline that is projected to continue at about the same rate in the coming 50 years.Three generations length for G. frondosa is 50 years (Dahlberg & Mueller, 2011). Hence, at the European level, it would be classified as Near Threahened under criteria A2c+3c+4c. On a global scale, there is also an evidence of continuing degradation of habitat quality, decline of old growth forests and loss of large old trees. However, there is no recent data on the population trends of the species in North America and its current population status in Asia is unknown.
Population Trend: Decreasing
Grifola frondosa forms large fruit bodies on the ground at the trunk base of living and dying hardwoods or dead trunks and stumps. This species is found fruiting almost exclusively on large old-growth trees. G. frondosa is known to cause white rot and butt rot of trees (Ryvarden, Gilbertson, 1993). However, the fungus is apparently a xylosaprotroph rather than pathogen. Its long-lived mycelium may live in decaying heartwood or in submerged rotting roots of old trees for many decades. The fungus usually continues fruiting at the base of dead trees and stumps. Although mycelium persists in the substrate for many decades, large annual sporocarps may not form every year around the same tree. The species is mostly associated with Quercus spp. but has been also recorded on other hardwoods (Acer, Betula, Carpinus, Castanea, Eucalyptus, Fagus, Juglans, Populus, Ulmus) and occasionally on conifers (Pinus, Pseudotsuga, Larix) (Gilbertson, Ryvarden, 1986; Ryvarden, Melo, 2014). Occurrence on conifers has been reported only outside Europe: Pinus, Pseudotsuga, Larix – in North America, Abies – in China (Farr & Rossman, 2018).
Grifola frondosa occurs in broadleaf temperate (nemoral) forests as well as hemiboreal and mixed broadleaf-coniferous forests. The fungus prefers natural old-growth forests with minimum human influence but also can be occasionally found in parks and other plantations under old individual trees.
The main threat is habitat destruction. Old growth deciduous forests are highly vulnerable, particularly large size trees are declining. Forests dominated by slow-growing Quercus trees are under increasing threat. Many known and possible habitats have been destroyed by deforestation, uncontrolled logging for timber in mature forests, replacement of old growth forests by fast-growing trees.
In areas where picking wild mushrooms is traditional, collection of large edible fruit bodies is also a threat.
Habitat conservation is necessary as well as sustainable forest management to ensure harmless logging, regeneration and continuing growth of major host tree species (Quercus spp. and other Fagaceae). As G. frondosa is widely cultivated, a variety of its strains of diverse geographic origin is maintained in various culture collections, which can be regarded as a sort of ex situ conservation.
Molecular research, including expanded sampling of European isolates, is required in order to reveal possible distinct lineages within the species – European from North American and/or Asian. Surveys are needed to study population trends and to monitor habitat trends.
Grifola frondosa is an edible mushroom. It is commercially cultivated and marketed, particularly in Asia and the US (Yamanaka, 1997; Chen et al., 2000). It is also considered to have medicinal values and is widely used in traditional Chinese medicine (Mizuno, Zhuang, 1995).
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