After driving past this large red oak on multiple occasions, I thought I’d finally park up and have a more in-depth look at it. I’m glad I did, as there is a large (but very decayed) fungal sporophore at the base, within or around a buttress that ends up becoming a sort of girdling root (there are two large roots partially girdling the stem on this tree, as can be seen below). At first, I thought the fungus was a very old Pseudoinonotus dryadeus, though when I found an old remnant of the sporophore a few yards from the tree I noticed it had small segments of the characteristic lacquered appearance of Ganoderma resinaceum. Comparing the tube layer with existing photos I have from other samples, it also appears there are similarities in this regard, as are there similarities with the pore surface on the underside. For this reason, I’m running with Ganoderma resinaceum.
After sounding the tree with a nylon hammer, there was no indication of hollowing, and therefore one can suspect that the decay is well compartmentalised (or not at the stage where wood has become markedly degraded). As Ganoderma resinaceum can however infect principal roots in the location surrounding the stem base (according to literature), perhaps the girdling roots have lead to some localised decay just beneath the surface, from which this fungus has been feeding from. Of course, this is only a suspicion of mine, and I have no means of currently proving that.