Did the massacre of the American Bison Cause the dust bowl? It doesn't appear to be the only cause, but it's clearly a contributing factor.
The Dust Bowl was an ecological disaster in the early 20th century that devastated American agriculture, and was one of the major causes of the Great Depression. Millions of new settlers flooded into the Great Plains states after the Civil War, using farming techniques that were appropriate for smaller farms in wetter climates. Where they had come from, they had not needed to irrigate their fields, and they arrived in the Plains ignorant of the methods. To some extent, they benefited from a rare wet spell, and to a larger degree, from the immense Aquifer (the Ogallala Aquifer) reaches from South Dakota to Texas. They drilled thousands of wells into the aquifer and captured much of the few rivers that flowed across it. They believed a widespread myth that "Rain follows the plow", which was promoted by land speculators and others that profited from their settlement, but did not pay for the consequences of being wrong. When the wet spell ended in the 1920s, a lot of the land dried up and blew away. A lot of the landholders had mortgaged their farms, to buy equipment or other advances, which were now in arrears--a million or more "Okies" were forced to give up their farms, which had become the property of the bankers that had lended to them, and which were sold to Agribusinesses for very little.
At the same time, there was an effort to suppress the previous inhabitants of the land, called "Indians" and force them to live on reservations, leaving the best land for the new settlers. The army killed a lot of indians directly, but probably more indirectly, largely by the mass slaughter of their primary food source, the American Bison. Around 60 million Bison (sometimes called Buffalo) were killed and by 1889, there were just 541 bison left in the US. Active conservation has allowed these numbers to rebound to as many as 500,000 today, but the giant herds are gone, and existing agriculture is unlikely to allow them to return.
The Bison, it turns out, do a bunch of unique things that other large Ruminants do not. They tend to not stay in one place--they eat their favorite grasses down to where they're a little harder to reach, and then move on. One of the consequences of this is that the seeds from these preferred grasses adhere to the animals fur, and often pass through their guts, but survive and with a nice dollop of fresh fertilizer, are replanted in the new place that the Bison is feeding. This causes the preferred grasses to spread, and where possible, interbreed with whatever was already there, improving the quality of both. The great herds would trample the grass...this broke up the ground, and drove the seed below the surface where it was most likely to germinate. And perhaps most importantly, the Bison like to "Wallow", where they lie on their side and roll around, which digs great pits. This apparently helps to clean their fur, and helps them scratch itches. They also like to scratch against trees--they are huge animals and it's amazing to see a tree with the bark missing from one side, up to 9 feet high.
But the wallows have a wonderful secondary effect in the plains. They catch rainfall. Left to its own devices, or to regular cattle, any irregularities will tend to get flattened, and rainfall will flow downstream. Since a lot of this land is clay, it doesn't percolate well, and the water quickly runs off. But if millions of bison are creating millions of wallow pits every day, a lot of this water catches in the pits, and stays there until it evaporates or percolates in. That is probably a big part of how the Ogallala got to be there, and we almost completely removed this source in the late 1800s.
Can the the restoration of the Bison restore the Ogallala? Since the present population is less than 1% of what it was before the great slaughter, probably not. But it might go a long way toward helping.
