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Beavers are only endemic to North America and parts of Europe. So why does the rest of the world not overwhelmingly resemble the American southwest?

Good Q. Since there are many wetland plant species and willows that are beaverlike you could ask how would they become established in the first place, and how would their growing mass and persistence compare to a beaver's after a catastrophic event? And after all, why does the dry deep-gorge Southwest look like the Southwest anyway? THAT could be the outlier and its depth and dryness would seem the result of a 'jump start in erosion' bestowed over geologic time. I think even the Southwest may have been on course to be as green as the East and would have been -- had it not been for some truly horrific floods that eclipse anything in the modern era when the plugs for Glacial Lake Missoula and Bonneville gave way.

Drainage paths in the West ( https://i.dailymail.co.uk/i/pix/2016/10/21/16/3995911F000005... ) were more narrow and violent, the same in the East were not. A minimum of sudden deep erosion and therefore sideways diversion of blocked watercourses would be necessary for beavers to get established and shape the landscape so in the East they did. Other places in the world like the Amazon may have been shaped by vegetation impeding erosion more so than gnawing creatures.

> If it were not for beavers evolving beside us, the Eastern US and much of the world would very nearly resemble the driest American Southwest of today, with rain being gathered after a brief overland wash into deep river gorges, with little water left behind close to surface.

The rainfall patterns are very different in those two areas. I don't doubt that beavers have important erosion and sediment retention impacts that over time do have a massive impact on the ecosystem and landscape. However, sediment rention is far from only reason why the american SW looks so different from other parts of the country.

> the Eastern US

The eastern US pretty much wiped out beavers as most landowners view beavers as pests. Does not look anything like the southwest. If we introduce beavers to nevada, do you think nevada will look like upstate ny?

> much of the world would very nearly resemble the driest American Southwest of today

Most of the world doesn't have any beavers. Most of the world does not resemble the american southwest.

Rather than beavers creating the environment, it's the environment that created the beavers. Beavers exist in areas with plentiful rain/water for a reason. Look up rainfall patterns in the US and you'll see how illogical your argument is.

The only evidence of any animals activities visible from the Moon, is a clear cut 100miles by 150 miles in norther BC, as seen by humans on the moon..... There are two species of Beavers left, the well know aquatec version and a "woods beaver", rare. Beavers are making a comeback, and I see dams and lodges regularly, and hit a very large one driving, which I put in the back of the truck and took to a friend and we scun it, and he stretched the hide old style, easy to see why the fur was in such high demand, it's glorious, nothing synthetic can match the feel.The tails are a culenary delicacy. Not long ago Beavers and other species were still faceing an onslaught of human depredation, as there was a larger ,more vigerous rural human population, and guns and dynamite were hardware store items. Hyway departments still remove beaver dams where flooding threatens roads, but as flooding is becoming more damaging overall, the response is often to build MUCH larger drainage and bridge structures and then be able to let nature do it's thing.

By that logic, I'd vote for worms. Forestation is only possible after worms create enough humus to support trees.