The Giant Polypore and its Consequences

by Bill Welch.

A beech tree surrounded by Giant Polypore, Meripilus giganteus, in The Knoll, Hayes.

There are many mature beech trees, Fagus sylvatica, in the woods of Bromley borough. They are a common natural feature of mixed deciduous woodland, and they have also have been planted here and there as hedgerows, border markers, or as pleasant specimens in parks.

Young growth of Giant Polypore, Meripilus giganteus, on the exposed roots of a beech in The Knoll, Hayes.

Some of them, however, have an unwelcome additional feature. In late summer, large clumps of fungi appear around the base of the tree and along the length of any roots which have spread near the surface.

They mature into quite large clusters and then die off, leaving bunches of blackened and decomposing remains.

Giant Polypore, Meripilus giganteus, growing round a beech stump on West Wickham Common.

These are the fruiting bodies of the Giant Polypore, Meripilus giganteus, and it is a tree killer. It consumes the lignin in wood, leaving the lighter-coloured cellulose; this is known as a white rot. Some white rot fungi will only grow on dead wood, but the Giant Polypore is less discriminating.

Giant Polypore, Meripilus giganteus, by a stump on West Wickham Common.

The top photo shows M. giganteus around the base of a beech tree in The Knoll, a small park in Hayes, in November 2012. Here, it is a little past its peak. The next photo shows young growth on the same tree in late September 2012.

This fungus can often be seen growing around felled beech stumps. This is not a coincidence. Trees with a heavy infestation are felled by woodland and park managers so that in their weakened state they will not fall on passers-by.

Notice to fell a beech in The Knoll, Hayes. Photographed on 3 October 2013.

The next two photos show such a stump on West Wickham Common in October 2012. There is another felled beech not far away on Keston Common that I mentioned in a recent article about a fungus field trip, and a stump just off Layhams Road, near St John's Church, opposite Coney Hall recreation ground. All three have growths of Giant Polypore in season.

Fallen beech on The Knoll, Hayes, on 3 November 2013.

The beech in The Knoll was such a pleasant sight that I was disappointed to see that it had been marked for felling. But only a week or two later came the St Jude Storm of 28 October 2013, and then it was too late. The tree was blown over.

Underside of the root ball of a fallen beech in The Knoll, Hayes, on 3 November 2013.

The whole of the root ball was exposed. It was clear that the roots had broken off just below the base of the tree, and the effect of the fungus infestation could be seen very plainly. The main roots of this mature tree looked feeble. The outer surface still felt tough, but all of the insides had been turned into a soft whitish spongy material. I could crumble it quite easily with my hand, and it was useless against the force of a strong wind.

Exposed root of a fallen beech in The Knoll, Hayes, on 3 November 2013.

Looking at the state of those roots, I was surprised that the tree had stayed upright as long as it had.

You can also see a dark circle in the centre of the root mass. I think that this is probably material placed in a circular hole in the ground when the tree was planted, to help it to get established.

One lesson to be learned from this is to stay well clear of any trees infected with Giant Polypore during high winds. The same probably applies to trees with Honey Fungus, Armillaria species, around them. These are also tree-killers and cause a similar white rot.

Because I live near The Knoll, I have photographed this beech a few times, and there are several photos in my blog. This entry, Giant Polypore, has photos of the Giant Polypore, and this one, The Knoll, Hayes, has a couple of views of the tree.

In both entries, I predicted the tree's downfall. That did not require any unusual intelligence. The voracious Giant Polypore speaks plainly to all who know its habits.