I read that book- I believe it is part of a trilogy by Conrad Richter: the trees, the forest, the fields ?
Anyway, the forest canopy, which kept out all direct sunlight, did cause people to go crazy.
And the work described in clearing a simple field is almost unbelievable. They were very strong people, those people who made the fields of America. They'd sure not think much of us today, I'm afraid.
You are right. They were strong; unlike the little green wimps of today.
Another related book is “Back from the Land: How Young Americans Went to Nature in the 1970s and Why They Came Back” by Eleanor Agnew - a woman who went with her family to the land, how it collapsed, and coming back to the real world, along with interviews of others in the same situation