http://sandhillsexpress.com/local-news/nebraska-national-forest-near-halsey-continues-to-burn-thursday/This is where I spent my adolescence.
About the turn of the last century, a botanist from New York decided Nebraska needed trees, and so this forest was planted in the Sandhills. It is (was) the largest man-made forest in the world.
The terrain, the soil, the amount of rain, the weather, are inhospitable to trees; they shouldn't be there, and nature shoves them out.
Going back as far as I can remember, 1965, about every twenty years there's a big fire that levels the forest, after which new shoots are planted in between the charred branchless trunks.
This notion that Nebraska "needs" trees is nonsense; Nebraska has plenty of trees, alongside rivers. As Nebraska has more miles of river than the other 47 of the 48 lower states--surpassing even Texas, Montana, California, and somesuch--that means we have lots and lots of trees.