Fungi spotlight: Perenniporia fraxinea

Perhaps most renowned for the fact it was the cause of three deaths in Birmingham in December 1999, when the mature ash (weighing in at 15,000kg and estaimated to be 180 years old) that was host to this fungus failed and fell onto two cars waiting at traffic lights, Perenniporia fraxinea causes an intense white rot at the butt (lower stem and principal roots) of its host. However – on rare occassions – this fungus may be found further up the main stem, at sites of wounding.

According to current literature, this fungus can colonise – via either exposed sapwood or heartwood – species from the genus Fagus, Fraxinus, Laburnum, Platanus, Populus, Robinia, and Ulmus. It may more routinely, within the UK, be found colonising Fraxinus excelsior – particularly more mature specimens. Its preference for sporophore formation is however not fully understood, though I have seen it persist in an active state through to December.

As a result of its presence within the host, cavities may form (particularly in areas where decay is significant). Ultimately, the decayed wood from the lower stem and main roots is left increasingly prone to failure. In light of this, and in light of past events, it is advised that any tree colonised by this fungus is managed in a manner that reduces its risk to people and property. Of course, this may not mean pruning – the target zone, for example, could be fenced-off. This may be a particular avenue to pursue where the host tree is highly valued, or even as a means of studying the fungus.

Below are some images I have taken – all from mature ash trees close by to me – during the last month. Instead of describing its appearance to you, I would rather you look at some images.

At the base of a mature hedgerow ash, we can see a two-tiered arrangement. Note the white spore colour around the base of the brackets.

A closer inspection reveals, more discernibly, the white spore colour on the ivy leaves beneath the brackets. Also note the resemblance to Ganoderma spp. (which have brown spores) and Rigidoporus ulmarius (which causes a brown rot).

Factoring into the equation the fact my clipboard is A3 in size, we can really see how massive this bracket it. This ash was monolithed as a result of this decay, I strongly suspect. We can also see Daldinia concentrica above, which is a saprophytic fungus.

Further around the base of the monolithed ash tree, we can see a sporulating bracket. The white spore colour is very significant here.

Looking at a little closer at the underside of the bracket, the resemblance to Ganoderma spp. is understandable.

A new bracket forming on another monolithed ash tree close by. Again, we can see white spores upon the ivy leaves, which distinguishes this from Ganoderma spp.

Recommended reading list:

Forbes-Laird, J. (2009) Monograph on Perenniporia fraxinea. [Online] Available from: http://www.flac.uk.com/wp-content/uploads/2009/12/Monograph-on-Perenniporia-fraxinea.pdf [Accessed: 6th January 2016].

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

Mattheck C., Bethge, K., & Weber, K. (2015) The Body Language of Trees: Encyclopedia of Visual Tree Assessment. Germany: Karlsruhe Institute of Technology.

NTSG. (2011) Common Sense Risk Management of Trees. UK: HMSO.

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