The human impact on nature is enormous. And it is not always given to us to predict how it will respond in the surrounding space. Therefore, before you reshape the world to suit your desires, you should think about the consequences. Otherwise, it will take years of work to correct mistakes, as in Yellowstone National Park. By the beginning of the XX century, the US government decided that the presence of wolves in the park was superfluous.
By the 20s, the last flock was destroyed. An ecosystem that has existed for thousands of years has been significantly disrupted. For seventy years, deer reigned supreme in Yellowstone. By the 70s of the XX century, scientists began talking about the need to revive the wolf population. During the years of the absence of predators, herbivores have multiplied extraordinarily, which mercilessly trampled spaces and ate vegetation. 
Attempts to regulate their numbers by man did not bring success. Until 1995, scientific and practical training took place. Finally, everything was ready. The first 14 wolves were caught in Canada and released in the Lamar Valley of Yellowstone Park, but no one was prepared for what would happen next. In the following years, 17 more Canadian and 10 wolves were imported from Northwestern Montana. The population began to grow actively, as each group was released on its territory and already formed pairs went into nature.
A documentary was even made about one of the packs released on Druid Peak. Scientists hoped that wolves would bring the deer population to a reasonable limit. But the predators have done much more. Although everything happened gradually. Sensing the presence of predators, the deer began to choose open areas for pastures, where wolves could be noticed in advance and it was easier to run away on flat terrain. There were fewer ungulates, but the population was strengthening. 
Wolves “culled” old and sick individuals. The migration of deer to the plains made it possible to revive vegetation along the slopes of gorges and rivers. First the grass, then the willows, aspens and poplars appeared. Strengthening, they became a home for birds and a food base for beavers. Stronger competitors, wolves, have also reduced the number of coyotes by a third. It became easier for mice and rabbits to survive, which the new predator paid less attention to. But foxes, hawks and badgers were actively interested in them, whose populations began to grow.
The overgrown berry bushes, carrion and the opportunity to take away the finished prey from the wolf began to “attract” bears to the park. It became even more difficult for deer to live. During the 25 years of the wolf’s new presence in the park, the entire ecological system has changed significantly. Not only have new inhabitants appeared, but the physical geography has also changed. The shores were strengthened. Beavers took root, which began to build dams for their fodder and residential bases. The overgrown coastline and beaver structures have narrowed and in some places changed the riverbeds! 
Backwaters and rapids began to form. Water animals, waterfowl and frogs settled on the rivers. Now more than eight dozen predators live in the park, which still retain a protected status from the government. Almost the same number of individuals have settled in adjacent territories, where hunting has already been allowed for them since 2009. Scientists did not think in the distant 90s that only the first 14 individuals would mark the beginning of the revival and change of the national park.
But their idea turned out to be really saving. In the end, even for deer, which began to have enough food for the existing livestock. The story of Yellowstone Park is the brightest example of how a person can “trample” the surrounding world or revive it. And a clear signal to man is not to interfere with nature, which is the best regulator for his own existence.