Prairies/pastures are more than just grass, but actually an entire community of diverse broadleaf wildflowers as well. Several of these happen to provide excellent forage for bison. Quite a few native legumes such as purple or white prairie clover, Illinois bundleflower and daleas contribute nitrogen to the soil and serve as high protein fodder. Perennial sunflowers and goldenrods are commonly observed and nutritionally important to grazers. Compassplant is a personal favorite of mine. Of course, pollinators are definite fans of the wildflowers. There are literally hundreds of valuable native American broadleaf species available for beneficial uses.