Thank you for the responses!
The area is at the top of a slope. The grass was planted to slow erosion about 30 years ago. While clearing the debris we were reminded we had trimmed the grass probably 10 years ago, perhaps that caused the center to die. Also, it seems the ants decided this was a great place to live. Interesting though, two clumps in the row are unaffected, they're full and still growing.
We've decided to clear the debris and ant mounds and see what happens this growing season. If it doesn't appear promising, we will replace it next year with a native grass, perhaps indian grass.
Thanks again!
