Looks like a bracket fungus to me
this is the "fruiting part" the miles of mycelia are inside the tree
People are quick to remove trees that are hollow inside, but remember engineers use hollow tubes to build very strong structures (think bicycle frames). Hollow tubes and hollow trees have far greater strength to weight ratios than solid forms. They transfer loads around the trunk to the other side, like an arch transfers loads. A study in the UK showed that hollow oak trees there faired better in storms than solid trees. In a wind storm a solid tree trunk creates greater tensile stresses on the windward side than a hollow tree. Arborists don't always know this or may not tell you, but many old, hollow trees (but not all) are very sound. So, the tree may be just fine, if it is otherwise healthy (good full canopy of healthy leaves, etc.), this keeps the tree building new strong outer layers to compensate for lost material inside.
Thanks for the information Brian. This growth has continued. Every year it eventually falls off and seasonally,it seems, a new one appears. For the last few years I've had several branches removed to allow more sunlight in the yard. Now bark near the ground appears to be seperating from the trunk. Perhaps it''s time to remove this tree. Also it's on a hill.
If it is bracket fungus, it is definitely not good for your hickory.
@Brian Campbell, Basswood Artisan Carpentry that is a very interesting concept re: load transfer. Where did you learn this?
@Becky H Forestry school at Colorado State, and Arborist Licensing. Think of snapping a branch in two by bending it over your knee... not too hard. Then try just bending a branch of the same size with your hands only... not so easy. Wood in the middle of a solid tree trunk works as a fulcrum, not unlike your knee in the example above, so the tensile strength of the wood is more easily exceeded. There are other factors at play, so this example has limits. A solid tree does have greater strength than a hollow tree, but it is also heavier and creates greater internal stresses, due to both greater weight, less flexibility and the "fulcrum thing". A solid tree IS stronger, but it has to be--if that makes sense. :) Hollow trees can certainly be too rotten to have much strength left, but most do just fine. Storms bring down about as many trees completely free of rot as hollow trees, maybe more.
Thank you @Brian Campbell, Basswood Artisan Carpentry for the explanation. I always like to learn something new and understand it.
Wood rot has very wide range. And depending on the "age" of the rot can be any where from lightly "splated" and firm and usable as furniture wood to a punky mess that you can push your fingers through.
Evidence of rot. Any other dead wood in tree? Was the tree damaged there in there in the past? Normally, a given for removal but if the rest of the tree looks good and no other fungus/mushroom areas then might just keep an eye on it.