The most mind-blowing part? The regenerating trees stabilized the riverbanks, causing the rivers to meander less and the channels to narrow.

One of the most fascinating concepts in ecology is the which shows how a single species can physically reshape an entire landscape.

With more trees came more birds and, crucially, beavers . Beavers built dams, which created habitats for otters, muskrats, ducks, and fish.

The classic example is the . It wasn't just about wolves eating elk; it triggered a chain reaction: