Question

black fungus  

carbon chunk removed   Any idea what this might be?  Looks like ascomycete carbon balls writ large, but I removed a chunk and it did not appear to originate below the bark (second photo).  It is now brittle.  Not horticultural; on a flood plain in Clarke County (Piedmont Province), Georgia, USA - Feb. 08, 2016.

Answer
Bill:

This may be a fungus called Hypoxylon.  This fungus is mostly considered a secondary invader that sets up shop on declining trees.  It is very crusty on the tree. Unfortunately, there is no cure other than good cultural practices (appropiate fertilization/irrigation etc.) to promote vigorous tree growth.  

I expect that there is some level of internal decay within the lower portion of the tree.  Difficult to say what fungus/bacteria might have been the primary invader. These organisms often enter the tree thru wounds in the bark.  With good fert/irrigation regimes, the tree may persist for a number of years since many of the tree decay fungi are usually slow growers within the tree.  The internal decay will weaken the structural integrity of the tree. Thus, the tree may fail during a wind or ice storm.  Removal may become necessary, especially if this tree could fall on person or property.

Regards
Steve