The things others are pointing out (esp. selective grazing) are all factors. Not sure how well-evidenced this is, but something I've heard from relevant resear

The things others are pointing out (esp. selective grazing) are all factors. Not sure how well-evidenced this is, but something I've heard from relevant researchers is that bison hooves are more scoop-link vs. cattle hooves. Bison more thoroughly till topsoil and activate microbial/fungal processes that promote floral diversity (among other things).