Rigidoporus ulmarius in a poplar cavity

I have been sharing a lot of stuff to do with wood-decay fungi lately, and thought I’d continue with that theme as it’s certainly a field that we need to understand, as arborists. After all, the presence of a fungal sporophore can dramatically alter how we perceive the tree we are looking at, and how we manage it. Plus, they’re damn cool!

In this instance, I came across a hybrid black poplar (Populus x canadensis) colonised by the fungus Rigidoporus ulmarius. However, unlike in most instances, one of the sporophores was within a fairly large cavity. I have seen this sort of thing before with this fungus (on a horse chestnut), though not with such a large sporophore. Therefore, it just goes to show that, when out inspecting trees, we must also check cavities for signs of fungi (beyond just the showcasing of wood decay).

Perhaps a sporophore within a cavity suggests effective compartmentalisation by the barrier zone, though this doesn’t mean the tree is out of the woods. Decay can still be very extensive, and potentially hazardous, if there is a target zone beneath.

And so, as always, here are a good few pictures to look at over a mug of coffee and some music.

Here we can see the poplar tree, sitting between a petrol station and the back garden fence of a row of houses. A target zone is therefore evident.

Looking at the base of the poplar, we can see a cavity. Most probably, this cavity formed after a stem failed and subsequently decayed. That may be why a new stem has grown out at such an odd angle, as it grew adventitiously from the site of failure. Of course, this is pure speculation on my part.

Peering within the cavity, we can spot quite a large sporophore that spreads, if we look at it as a clock face, from 9-3. Also note what looks like two exit holes of the poplar hornet moth (Sesia apiformis), just above the cavity. Perhaps a relationship between the two – does the moth prefer to exit in such decayed areas?

Closer still, here. I managed to break a bit off with my car keys, as I left my blade in the car.

Here’s the cross-section. We can see a few years’ worth of growth (or a few growth spurts, maybe not one per annum). Quite a large tube layer for the fungus, though perhaps the cramped setting caused that.

On the smaller stem, we can spot another sporophore around 2m up (and just to its lower left, another sporophore beginning to form from between a crack in the bark).

Upon closer viewing, we recognise the intricacies of the sporophore.

And a cross-section reveals the typical flesh and tube layer arrangement and colouration of Rigidoporus ulmarius.

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