I saw a show on either TLC or Discovery during the early 1990s. They used satellite imaging to examine soil reflectivity and infer what used to be there by the soil composition. They were also able to enhance the images to show travel routes. The travel routes corresponded to soil that would not form in a plain. There used to be forests there. The Indians chopped down the trees and turned it into the Great Plains.
It makes sense, really. Indians used wood for fuel, tools, and housing. They didn’t understand forestry, no matter how politically correct it is to say that they did. Ecology as science hadn’t been invented.
The PC police must not have liked it. I only saw it once.
This is absurd fantasy for some weird and unclear purpose. The fact is the Great Plains have been too arid to support forestation, in recorded history. Without irrigation and ample groundwaters they would be unpopulated deserts today.
Beyond that, the idea of Indians, without so much as iron tools, chopping down hundreds of thousands of square miles of forest is beyond ridiculous.
I hope you were being facetious and I just missed the humor in the lateness of the hour.