Oddly, my mental picture of Rohan has been hugely influenced by the movies. Living in NE as I do, I always struggled to find good riding trails; too many young woods with no trails at all. The more I rode, the fewer fields I rode in.
Imagine riding on a golf course--
What a good way to die young.
But then, I can't picture Kentucky Bluegrass very well, either. It always has pristine white-board fences... not very rohirric.
Here in RI we have turf farms. Not very rohirric, either.
Perhaps something more like what the buffaloes run on out west...?