Assessment Notes

Justification

Hapalopilus croceus (Orange Polypore) is a well-known, conspicuous and much searched for rare wood-inhabiting polypore restricted to veteran trees of Quercus and Castanea in old-growth forest, isolated trees in farmland, parks and pastures. It is globally widespread and present in eastern North America, Europe and eastern Asia. There are more records in Europe and Asia. It is very rare in North America. 
The population of the Orange Polypore has significantly declined during the last 200 years because coarse oaks and chestnuts have strongly declined and are now very rare and scattered. The reasons are cutting and agriculture development and in the US also that the American chestnuts (Castanea dentata) were wiped out in the early 1900s due to chestnut blight (Cryphonectria parasitica). Further, in Europe the age-structure of oaks show serious gaps, there are only a few old coarse veteran oaks (>400 yrs), few mature oaks (200-400 years) and many young oaks (< than 100 years ). Thus host trees in a suitable age for further transmitting of the species are more or less absent.

The decline of the old-growth oak forests in the evaluation period (last 100 years or three generations) is estimated to be at least of 30% (Hansen and Delatour 1999, Denman et al. 2014, Brandrud et al. 2011). This decline is ongoing and it is presumed to continue in the future. The species is therefore assessed as Vulnerable (A2c + 3c +4c). Better documentation on the habitat decline rate is recommended as it could reveal a higher threat category.

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Taxonomic notes

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Geographic range

Hapalopilus croceus is distributed in the temperate parts of Europe, eastern parts of North America, and the eastern parts of Asia.

In Europe it is widely spread, found in about 25 countries, but rare and scattered everywhere, following the distribution of oak (Quercus) from the Mediterranean Sea to the northern boundary of oak in southern Scandinavia. In Russia it is known from 17 regions of European and Asian parts. The largest populations occur in Sweden and Latvia.

It is present but rare in eastern USA and also has been reported from eastern Canada. It is widely distributed but not common in south-western to north-eastern China (the regions Sichuan, Hubei, Guangdon, Jilin and Heilongjiangin). It is not rare in Japan, distributed on deciduous coarse and old oaks, especially in northern Japan.

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Population and Trends

Oak forests in most of European countries have been severely exploited through the centuries, in particular since 1800. Because oak trees have been intensively utilized for several hundreds of years in Europe, the tree host of Hapalopilus croceus is in a long-term decline. Thus, this species is rare throughout Europe. Furthermore, it is limited to sites with veteran oaks. Today the felling of such trees has largely ceased inn protected areas. However, most places lack an intermediate generation of oaks, which creates a discontinuity and thus an ecological “bottleneck”. Decline of veteran oaks has happened in both forests and in the agricultural landscape including parks and cemeteries.

In eastern North America Hapalopilus croceus  is rare but widespread. It is considered to have largely declined due to cutting and conversion of forests to farmlands. In the past it also occurred on the American chestnut (Castanea dentata) until the beginning of 1900 when the introduction of chestnut blight (Cryphonectria parasitica) wiped out this source tree.

Hapalopilus croceus is nationally red-listed in 11 European countries. It is listed as CR in Norway, Finland, Sweden, Croatia, Germany, Denmark, Estonia, Austria; EN in Czechia, Latvia, Romania and Poland; and VU in Slovakia. In Russia is included in nine regional Red Data Books as VU, and recommended to be included in the national Red Data Book.

Population Trend: decreasing

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Habitat and Ecology

Hapalopilus croceus is a magnificent orange, fleshy wood-inhabiting polypore that grows on old and coarse veteran trees, mainly oak (Quercus) and more rarely on Chestnut (Castanea) in old growth forests, also on old oak trees in farmland, parks and pastures. It is a saprotroph and seems also to be a weak parasite on old and coarse oversized, living and dead trees. In Europe, most observations are from living, old, giant and hollow oaks, where the fruit bodies appear on dead parts of the tree, mostly on the lower part of the trunk, the tree’s base and in the cavity. It may also produce fruit bodies on fallen trunks for decades (Sunhede 1997, Sunhede and Vasiliauskas 2003). Each oak holds probably only one mycelium. Fruit bodies are annual, but the mycelium can be very long lived, many decades and potentially until the wood is completely rotten, which of oak may take several hundred years. At the only locality in Denmark, what is considered to be the same individual mycelium (genotype) has been fruiting for more than 70 years.

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Threats

The species is threatened by habitat loss, especially old growth oak-forest, habitat quality reduction by transformation of old growth oak forests into commercially productive forests, removing of its host tree and of coarse woody debris (thick standing and lying oak trunks), severe shortage of intermediate aged oaks to replace the old veteran oaks colonized by H. croceus.

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Conservation Actions

Old oaks colonized by H. croceus and other potential veteran oak trees must be protected. Entire stands of uneven-aged oak must be preserved in landscapes where H. croceus occurs.

A better knowledge of the species ecology, in particular its population biology; under what conditions does it establish, its potential to successfully disperse and colonize at low population densities. Research should also be conducted to investigate the potential to establish H. croceus by mycelial inoculation into oaks.

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Use and Trade

The species is inedible.

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Source and Citation

Dahlberg, A. 2019. Hapalopilus croceus. The IUCN Red List of Threatened Species 2019: e.T58521209A58521216. https://dx.doi.org/10.2305/IUCN.UK.2019-2.RLTS.T58521209A58521216.en .Accessed on 1 February 2024

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• Country occurrence