Dead areas in the crown of evergreen shrub

I have several Yaupon Holly shrubs that I have shaped in a rounded-crown shape. They are about 4 feet tall.

All of them have dead areas in their crowns. Each of these dead areas seem to be related to a single branch off the trunk of the shrub. In other words, it seems that single branches are dying.

The same condition existed several years ago. I severely pruned the shrubs the following winter, they grew back vigorously, and their new crowns looked good. Yet, a few years later, they have dead areas again.

These shrubs are probably about 30 years old. Could it be that they are just dying from old age, or could there be something that I could do to rejuvenate them? Any help would be appreciated !

[Newt]

Hi Joe,

I searched for info on the lifespan and couldn't find it easily. Since no one has answered your question, I suggest you ask these folks.

http://forums2.gardenweb.com/forums/trees/

Good luck,
Newt