Thursday, December 2, 2010

Diarrhena Grass Revisited

Every December, I’m newly amazed at the beauty of the Diarrhena Grass, Diarrhena americana, growing in the woods. Cold temperatures cause the grass to take on the color of golden honey. With the addition of sunlight, the whole hillside glows.

The Diarrhena Grass covers a large expanse of wooded hillside that was once extensively logged. This section was much more open 40 years ago. I’m wondering if the grass colonized the more open situation and now persists in the shade or if the grass was already here and just survived through the period of more sunlight.

It’s odd to see what looks like a prairie in the woods. It might appear that some clearing would be appropriate to bring sunlight to the grass, but the near 100 percent tree canopy cover makes this a true woodland. The grass actually thrives in the shade. It might even have some physical adaptation that keeps it from being covered by falling leaves. The tree leaves seem to filter naturally through the grass stalks to form a thick layer near the ground. Seed stalks remain standing free and tall.

I think Diarrhena Grass could be a valuable tool for woodland restoration. The grass grows on the steepest of areas and would provide perfect ground cover for an eroding woodland hillside. The grass would catch the falling leaves and the process of building stable hillside soil could begin.

There are still many questions concerning growth patterns and behavior of Diarrhena Grass that I would like to have answered. What is the mechanism for colonizing new areas and why do existing stands not spread across the entire woods? The hillside in the foreground has a thick cover of grass that has remained unchanged for the past 25 years, while the hillside beyond is free of Diarrhena Grass. What factors cause one hill to be covered while the other remains bare?

The functioning of a Diarrhena Grass ecosystem certainly deserves more study. I know that many spring wildflowers are found growing with the grass, but I haven’t done any counts to see how species numbers might differ from those in the non-grassy woodland. It seems that the added cover might be attractive to ground nesting bird species, but this is another thing I don’t know. There must be insect species that utilize all this grass. Maybe there’s even a rare species that’s Diarrhena dependent. Looks like a lot of material here for someone’s graduate thesis.


  1. I don't have any answers to your questions, but here is a pretty good brochure on this plant in Michigan where it is considered threatened.

  2. Thanks for the information, Ted. It appears that Michigan has variety obovata while I have variety americana. The Michigan populations occur in wooded floodplains and mine are located on dry ridges and upland slopes. The Michigan populations do have a large number of associated forest floor plant species, so it appears that the grass is not so aggressive as to preclude other species. That's good news from a management standpoint.