I’m struggling to identify this polypore bracket fungus but I’m going for Smoky Bracket, Bjerkandera adusta, a common fungus on the dead wood of deciduous trees. Having said that, this sawn-off poplar hasn’t quite given up the ghost: it’s putting out new green shoots from epicormic buds beneath the bark.
With bracket fungi, it’s important to know what species of tree they are growing on. This is poplar, which has distinctive diamond-shaped lenticels (right), so another possibility is that this is the Poplar Bracket, Oxyporus populinus.