Fungi spotlight: Piptoporus betulinus

Piptoporus betulinus (birch polypore) is almost exclusively confined to Betula spp., though it has been observed rarely on Fagus sylvatica. Its spores will gain entry via stem injury, then attack the tree’s sapwood and heartwood once the host is under stressed conditions. There is therefore a period of latency within the colonisation strategy of Piptoporus betulinus. As with most parasitic fungi, it may also act saprophytically.

The fungus induces a brown rot in principal branches and the main stem, as its mycelium secrets enzymes that digest the wood substrate, which soon causes wood to discolour to a reddish brown (in turn followed by the characteristic cubical rot of brown rotting fungi).

A rather large sporophore on a fallen stem of Betula pendula.

Because the wood progressively become more brittle, it will ultimately fracture due to such a weakened condition. By the time fruiting bodies appear it is usually too late for any remedial action however, given decay is rapid and loss of mass is therefore swift across the entire cross-section, in addition to the fact that fungal presence establishes and becomes extensive on an already weakened host. Decline can therefore be readily observed in infected hosts, though whether cause is fungal decay or general poor health remains uncertain.

This entire stem of a Betula pendula (still living) has been colonised.

Given weakened trees act as hosts, in addition to the swift decay caused by Piptoporus betulinus, treatment is likely to be ineffective and impractical. Removal is typically the preferred option, though depending upon the context (no significant target zone), retention for ecological reasons and subsequent routine inspections to determine decay extent are necessary (if even that, as colonised birch within woodlands, where the fungus is most common, may likely just be left standing). Limiting pruning wound size and ensuring potential hosts are not exposed to undesirable and adverse site conditions may aid with prevention, though as colonisation may be followed by a latent period, ascertaining when a potential host becomes infected is difficult. Research has also identified that cadmium application can reduce or entirely halt mycelium growth, though as cadmium disturbs tree processes, application to an already stressed host is likely to only aggravate the situation.

Some fresh sporophores found on a young Betula pendula during early autumn.

Suggested reading:

Baldrian, P. & Gabriel, J. (2002) Intraspecific variability in growth response to cadmium of the wood-rotting fungus Piptoporus betulinus. Mycologia. 94 (3). p428-436.

Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management (Research for Amenity Trees 7). London: HMSO.

Schmidt, O. (2006) Wood and Tree Fungi: Biology, Damage, Protection, and Use. Germany: Springer.

Terho, M., Hantula, J., & Hallaksela, A. (2007) Occurrence and decay patterns of common wood‐decay fungi in hazardous trees felled in the Helsinki City. Forest Pathology. 37 (6). p420-432.

Valášková, V. & Baldrian, P. (2006) Degradation of cellulose and hemicelluloses by the brown rot fungus Piptoporus betulinus–production of extracellular enzymes and characterization of the major cellulases. Microbiology. 152 (12). p3613-3622.

Watson, B. (2006) Trees – Their Use, Management, Cultivation, and Biology. India: The Crowood Press.

Watson, G. & Green, T (2011) Fungi on Trees: An Arborist’s Field Guide. UK: The Arboricultural Association.

Weber, K. & Mattheck, C. (2003) Manual of Wood Decays in Trees. UK: The Arboricultural Association.

Fungi spotlight: Piptoporus betulinus

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