Moving everyone in the US to Texas would only result in 0.2% of the population density of Manhattan (just checked with Wolfram alpha which is great for this kind of thing)
You might be thinking of moving the entire world's population to Texas, which would result in 56.7% of the Manhattan density (by 2017 estimates).
Of course we would still need to grow food in fields, which surely is the most space consumptious part of the population.
It is staggering only until you realize that the majority of land in the US is too arid to grow crops and was once called the Great American Desert -- basically most of the land west of the Mississippi. Such land grows primarily scrub and is ideal for livestock such as Bison and Cattle that are able to eat the vegetation that grows there naturally as a result of the limited rainfall available. That we have water intensive agriculture west of the Mississippi is only because we are depleting aquifers. It's not sustainable, and using this land for livestock is about the best thing that can be done with it. It's also what this land was used for prior to being settled -- large open plains on which Bison roamed.
The gist of your point is correct, but "West of the Mississippi" is the wrong dividing line. You have about a state and half of excellent land west of the Mississippi. It is all about the mountains - From when the mountains start just past the West coast, they cause clouds to dump their moisture on the west side. The east sides are arid, for a couple hundreds miles or more. And because we have multiples ranges of mountains, the western third of the nation is arid... with pockets of agriculture just west of each mountain range.
Indeed, calling the Dakotas/montana as "desert" is... misleading.
Tundra maybe, but its not really a desert. And the plains are a great spot for grazing critters like Bison. The land there is their old stomping grounds, they fit in there like jelly on peanut butter sandwiches.
It's not just "a couple hundred miles past the mountains". It's basically even with the western edge of the Gulf of Mexico. East of there, there's enough rain. West of there, there's not.
You are right that "West of the Mississippi" is not the actual boundary, which is why I said "majority of the land". The actual boundary curves, being farther west in the Gulf and almost touching the Mississippi in the North, but "Western half of the US" is as good a description as any.
Point being, a lot of people who grow up in the Eastern Half of the US think the Western half has a similar climate, when it really doesn't. It really is an arid climate and the difference between East and West is rather stark.
Here you can take a look at a map of precipitation:
Yep. In Texas, we have both FM (farm to market) roads, but also, as you head further west, toward the Mexican border and the landscape turns a beige-tan hue of brown, we also have RM (ranch to market) roads
Introduction of horses changed the landscape. They damage the roots when grazing. Bison and cows don't. Many of these desert scrub areas may have had much more grass cover pre-columbus.
According to Allan Savory and some other respectable scientists the problem arose because the plants evolved to support huge buffalo populations and depended on them to clean and fertilize the ground. As their population declined, there was no more mega-herds migrating annually through the prairies and smaller groups of animals had different grazing patterns. Plants couldn't adapt to the new situation quick enough and the balance got broken. Less cover meant more evaporation, drier soil, erosion and rain washing off the soil rich in organic matter, and it all spiraled down to the land turning into semi-deserts. Allan Savory thinks (and he proved this method successful in practice) that the solution is to have large flocks of grazing animals moving around periodically, which stimulates grass growth and grass protects the soil and helps other plants to colonize the area.
There is some evidence that the huge Buffalo herds did not exist until Indians died off after Columbus "discovered" America. Pre-Columbian indigenous societies hunted the Bison enough to keep their population in check.
One important point to keep in mind is that "land" varies a lot, and "pasture" can mean anything from dense grassy pasture with >1 cow per acre to arid pasture >100.
They aren't convertible to cropland in the same way. Even in terms of "rewinding," one acre doesn't equal another, for most interpretations of "wilderness value."
This is why the amazon-2-pastureland problem is so serious. Every acre of amazon rainforest reoresents a lot of habitat.
Are they counting BLM (federal) land where they allow cattle to graze? A lot of land is federally owned but the BLM allow ranchers to let cattle graze in the summer/warmer months.
You might be thinking of moving the entire world's population to Texas, which would result in 56.7% of the Manhattan density (by 2017 estimates).
Of course we would still need to grow food in fields, which surely is the most space consumptious part of the population.