Without specimen in hand, it's impossible to be sure.

But I would guess it _could_ be Daldinia concentrica or some similar
species of fungus. If so, you're have some significant damage to the
tree recently, either by colder than normal weather conditions, or by
something striking the tree.

Daldinia concentrica is just one of several related species, many of
which are little known at this time. It is also sometimes called "King
Alfred's Cakes", or "Cramp Balls".

Assuming that you have detached one of the things from your tree and
sliced it open, D. concentrica looks like a layered ball growing
outward from the wood. I have seen it growing on wood used to grow
shiitake (Lentinula edodes) as well as wood inoculated with Pleurotus
ostreatus (Oyster mushroom).

Let's hope it is not Phytopthora (Sudden Oak Death).

Daniel B. Wheeler
www.oregonwhitetruffles.com