The areas of the woods containing Diarrhena had periods in their history when the canopy was much more open. Perhaps additional sunlight helps this grass become established in new areas. Most of the Diarrhena is now growing beneath a near 100% canopy and appears to be thriving. There must be some limiting factor at work here or the Diarrhena would carpet the entire woodland floor.
Diarrhena Grass can reach a height of three feet and produce some fairly thick stands, but the individual stalks are not so tightly massed that other woodland plants are excluded from the area. Several species of woodland wildflowers will bloom here in the spring.
I think this grass would be excellent for use in restoration of heavily eroding woodland areas. Even a thin stand tends to capture and hold fallen leaves. This keeps the leaves in place on steep slopes, so they can begin decomposing and recreating the woodland soil ecosystem. Some young researcher may want to look into this. I bet it would make a great graduate research project.