R-L categories correct, but text here does not match final assessment. Updated version will be published in IUCN´s Red List.
This polypore is largely restricted to veteran oaks (Quercus spp. and usually Q. robur or Q. petraea) in temperate deciduous forests across Europe and Asia with a recently-discovered and DNA-verified presence in eastern USA (?introduction). It forms large annual sporophores (brackets) and, although widespread, it is rare throughout its entire distribution range. In Europe the countries with most reports are Sweden and the United Kingdom (where it is legally protected), probably due to the relatively large collections of ancient and veteran oak trees in these countries. The global stronghold for this species (>100 occupied trees) is probably in England on the Windsor Crown Estate, which was formerly a royal hunting forest. Its potential distribution area is large, but the scarceness of ancient Quercus trees in semi-open situations is a limiting factor for its presence. As ancient oak woodlands have disappeared to a large extent during the past 100 years, populations of B. quercinus have decreased similarly. A cautious estimate of this habitat loss is 30-50% in a 100y perspective across continental Europe. Furthermore, the survival of B. quercinus in future is challenged by the scarcity and long time-scale required for large ancient oak trees to fill in the generation-gaps which are present in many woodlands today.
The usual situation is that just a few ancient and veteran trees are occupied by reproductive individuals of B. quercinus in each locality. Small subpopulations and an increasingly fragmented distribution make the species very susceptible to local extinctions due to the generation-gap in older trees.
The total number of localities is estimated to be fewer than 500, corresponding to fewer than 5000 mature individuals. Considering an ongoing marked decline in both number and habitat quality of veteran oaks, it is assessed as Vulnerable.
This species is also known as Piptoporus quercinus (Schrad.) P. Karst, but its correct placement is in Buglossoporus, as it is not closely related to P. betulinus, the generic type as shown by molecular data (Binder et al. 2013). Indeed the genus Piptoporus has now become a synonym of Fomitopsis.
The species is distributed in temperate broadleaved forests of Europe, Asia and the eastern USA, strictly following the distribution of Quercus spp. In Europe the countries with most reports are Sweden and the United Kingdom, probably due to the relatively high numbers of large oak trees in these countries. The European, (global?) stronghold for this species is a former royal hunting forest in southern England (Crown Estate, Windsor) where 100 oaks are known to be occupied by this fungus (since 1998). This is roughly half the total number recorded for the UK as a whole (since 1960).
Buglossoporus quercinus is estimated to be present in ca. 350 localities in Europe (incl. estimated unrecorded localities). It is rare throughout its distribution range. The number of individuals estimated to exist in Europe is c. 3500. The global population is estimated not to exceed 500 locations. Its potential distribution area is large, but the scarceness of ancient Quercus trees in semi-open situations is a limiting factor for its presence. As ancient oak woodlands have disappeared to large extent during the past 100 years, populations of B. quercinus have decreased similarily. A cautious estimate of this habitat loss is 30-50% in a 100y perspective. Furthermore, the survivial of B. quercinus in future is challenged by the scarcity and long time-scale of large ancient oak trees able to fill in the generation-gap of veteran trees.
Population Trend: Decreasing
Buglossoporus quercinus is a polypore associated with a central brown heart rot of oak. Its basidiomata are frequently associated with large old oak trees (Quercus spp.) and it primarily occurs in relatively open habitats such as pasture woodland, parkland and other mosaic deciduous forests. Fruiting occurs on dead wood of living trees and on snags and fallen wood, especially on larger diameter elements. This species has been stated to fruit only on trees older than 250 years (Crockatt 2008), but it has been observed fruiting on younger trees with exposed heartwood (i.e. veteran but not necessarily ancient oaks) under special circumstances (i.e. in core populations with small oak pollards or oaks that have been damaged when young and surrounded by relatively large and thriving populations of the fungus).
The main threat to B. quercinus is the rapid decrease of suitable host trees (Quercus, usually Q. robur) by forestry or changes in land management. Most of the still existing large oak tree areas in Europe have historically been used as grazed woodlands (pasture woodland) resulting in a semi-open environment. Death of large oak trees is accelerated by the decrease of grazing in pastoral landscapes (dense growth of competing understory trees and shrubs), change of land use to agriculture (ploughing close to trees, damage and trampling due to animal stocking density), to conifer forestry or to use as golf courses. In some areas cessation of pollarding could result in hastened death of oak trees. Habitat fragmentation might well be an additional threat that is increasing. Small population size make the species very susceptible for random events and local extinctions due to generation-gap in suitable host trees.
Site protection and habitat management is urgently needed for localities. management plans must include proper clearing around veteran oaks harbouring B. quercinus in order to prolong the lifespan of oak trees. In some cases, a periodical pollarding can ensure a longer life of oak trees but caution is advised when starting to restore management of lapsed pollards. Fallen dead branches (often removed esp. in parks) should be left in situ or moved to less formally managed areas to allow the fungus to fruit. Focusing on demography of oak population is very important, i.e. favouring younger oaks of different age classes as B. quercinus requires a continuous supply of ancient and/or veteran host trees in order to fruit.
Further data are required to improve our knowledge regarding the rate of habitat decline. Population genetic research across Europe is needed as a preliminary limited study (using somatic incompatibility testing in UK) suggested that many genets may be genetically rather similar to each other (indicating a historical population bottleneck?). We need to test the hypothesis that each occupied oak tree is inhabited by a single genet which can then fragment to several ramets as occupied branches and trunks fall to the ground. Phylogenetic studies are desirable to investigate conspecificity of the Japanese population. At least some Japanese records were confused with Laccocephalum hartmanii (fide T. Hattori).
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