Dogwoods in the north and east are succumbing to a disease (anthracnose) which causes die back. As the trees become infected, their limbs die back slowly until it reaches the trunk itself. Eventually it kills the tree. Dogwoods in the sun are not immune to the disease but seem to do better than those in shaded moist spots in the hollows or in deeply wooded areas on north slopes. There is no cure, from what I've read, and it's spreading. This photo of dogwood seeds was taken on an infected tree. It's very difficult to imaging a spring without the dogwoods flowers dressing up the forest.
For more information, see:

http://www.fs.fed.us/r8/foresthealth/hosf/dogwood.htm