Martyn: What to say about the records from North America?
It appear widely spread in Russia to the east - is the estimate of total numbers of locations appropriate?
This oak polypore is largely restricted to veteran oaks and strictly following the distribution of Quercus robur in temperate decidious forests of Europe and West Asia. It is forming large annual fruitbodies and is rare throughout its distribution range. In Europe the countries with most reports are Sweden and the United Kingdom, probably due to the relatively high occurrences of large oak trees in these countries. The global stronghold for this species is probably the former royal hunting forest Windsor Crown Estate in England. 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.
The normal situation is that just a few veteran trees are colonised by by B. quercinus in each locality. Small subpopulation and more and more fragmented distribution make the species very susceptible for local extinctions due to generation-gap in suitable host trees.The total number of localities is estimated to be much less than 500, corresponding to less than 5000 mature individuals. Considering an ongoing marked decline in both amount of and habitat quality of veteran oaks, it is assessed as Vulnerable.
This species has been often referred to as Piptoporus quercinus (Schrad.) P. Karst, but its correct placement should be in Buglossoporus, as it is not closely related to P. betulinus, type of Piptoporus, as shown by molecular data (Binder et al. 2013). Buglossoporus quercinus is a polypore recognized by its fleshy and soft basidiomata, yellow and white pileus becoming brownish with age. Its fruiting populations are characteristic of large oak trees and medieval oak landscapes. It produces a brown rot.
The species is distributed in temperate decidious forests of Europe and West Asia (Palearctic region), strictly following the distribution of Quercus robur. In Europe the countries with most reports are Sweden and the United Kingdom, probably due to the relatively high occurrences of large oak trees in these countries. The European, (global?) stronghold for this species is definitely the former royal hunting forest in England (Windsor Crown Estate) 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: Deteriorating
Buglossoporus quercinus is associated with large old oak trees (Quercus robur), producing brown rot. It primarily occurs in relatively open habitats such as wood pastures, parklands and other mosaic decidious forests. Fruiting both on living trees and on logs and snags on dead wood some years after the death of the tree. 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 (veterans not ancients) 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.
Find figures as to the habitat decline. Species proposed as redlisted earlier on the European level. 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 (historical bottleneck?). Test the hypothesis that each occupied oak is inhabited by a single genet which can then fragment to several ramets as occupied branches and trunks fall to the ground.
Ainsworth, A.M. 2017. Non-lichenised fungi. In: Ancient oaks in the English landscape (A. Farjon), RBG Kew.
Binder, M.; Justo, A.; Riley, R.; Salamov, A.; Lopez-Giraldez, F.; Sjökvist, E.; Copeland, A.; Foster, B.; Sun, H.; Larsson, E.; Larsson, K.-H.; Townsend, J.; Grigoriev, I.V. & Hibbett, D.S. 2013. Phylogenetic and phylogenomic overview of the Polyporales. Mycologia 105(6):1350-73.
Calonge, F.D.; García, A.; Sanz, M.; Bastardo, J. 2003. Buglossoporus quercinus (Basidiomycotina, Coriolaceae), nueva cita para España. Bol. Soc. Micol. Madrid 27: 33-35.
Crockatt, M. 2008. Ecology of the rare oak polypore Piptoporus quercinus
and the tooth fungi Hericium cirrhatum. H. coralloides. and H. erinaceus in the UK. Ph. D. dissertation. Proquest. LLC. University of Cardiff.
Farjon, A. 2017. Ancient oaks in the English landscape. RBG Kew.
Sunhede, S. & Vasiliauskas, R. 2003. Hotade tickor på ek i Litauen. [Threatened polypores on oak in Lithuania.] – Svensk Bot. Tidskr. 97: 252–265. Uppsala. 0039-646X.