Dog wood tree
Looks like quite of bit of the canopy is dead. I don't believe there is much that can be done for it expect removing it and replacing the trees.
Dogwoods planted in full sun, hot dry locations become stressed and begin to decline. Dogwoods have also been plagued with Anthracnose (a leaf fungal disease that effects the leaves in the spring). You might also look at the trunk for signs of wood borers.