Ridge, perhaps what you say applies well to Nebraska or Kansas or even parts of Missouri (I’m not so familiar with those ecosystems). But my part of Illinois (much wetter than the above areas) was vast prairie land before it got plowed under with only scattered woodlands. But a funny thing happens. Leave pretty much ANY northern IL farm field unattended for 7-8 years and it turns into a brush jungle, and eventually turns into a woodland (cottonwoods, maples, black cherry, red oaks). There is nothing about the climate hereabouts unfriendly to woods. It was prairie hereabouts because of man!
There is a tendency to see man as NOT a part of nature, but that’s usually untrue. At least in my area, the vast prairies only stayed that way because Indians burned them off frequently, often as a technique to force buffalo to killing grounds before they had the horse.
I’m not sure why the various prairies were prairies. Undoubtedly some would have turned to woodland but for the Indians’ practice of burning them off annually. Some places just aren’t all that conducive to the development of woodland.
Of interest, I’m not sure we know the whole story yet. It might be too early. A great deal of the region in which I live is woodland, a good part of which was once grassland. But some of the species of trees are not well suited to the area and some start dying off after a time. But it can take a very long time to really know. In my area, probably the best suited, long-term, are white oak, shortleaf pine in the hilly land, and walnut and other fruit-producers in the valleys and hollows. But there are a lot of red oaks, ash and other species that do not well survive extended droughts when they get older, and are more vulnerable to ice storm damage and follow-on disease and pests. We’re just now realizing that old red oaks don’t survive the area’s cycles all that well, whereas white oaks and shortleaf pines do.
And, of course, plowing allows for introduction of woody plants. Initially, this area was largely cultivated, but is almost entirely woods and grassland now. Those old prairie sods were very thick and nearly impenetrable by any woody species trying to get established. Interestingly, perhaps, some of the best and latest grassland practices also are conducive to development of thick “sod protection” by grass species that build thick sods.
Truth is, I don’t think anybody really knows for sure why a lot of the land is the way it is or was the way it was. We might not really know for a long time yet. And we might never know for sure. I have long thought that no person presently living, or perhaps no person living within the last thousand or so years, really knows or knew what a “state of nature” was anywhere other than in the subarctic and arctic regions.
Let me add that a lot of the species that take over abandoned farmland are “opportunistic” but don’t stand the test of time. They establish easily and grow fast, but given time often don’t make it. With red oaks and some others in my part of the country, it has taken about 70-80 years for people to realize they don’t hold up. In a mixed forest with white oaks, the white oaks are more resistant to everything, and when the red oaks and ash die, one of two things seems to happen. Either the white oaks fill in with a canopy that prevents almost anything else from growing, or some kind of thick sod-building grass takes over.
I was astounded, once, on land my family owns, to find a patch of “tallgrass prairie” growing in a place where a couple of oaks had died and fallen. Some haw sprouts had tried to get started, but died. Nothing has encroached on it since. Tallgrass prairie species tend to prevent establishment of woody plants.