What is happening to this tree?
The tree is dying.  From what you say, it has no leaves wduring a time it should, it has saprophitic growth along the trunk; it looks like there's a crack in the bark on the right, and there are shoots coming up from the base of the trunk, the last hurrah from the tree to try to regenerate. 

Trees send up suckers as a reaction to stress (like slowly dying). If you cut the trunk in such a way as to discourage rot, it will likely be replaced by this shrubby growth if the roots are sound. Some loggers use this as a way to quick-start new lumber trees.