Between 1995 and 1996, 67 wolves were reintroduced to Yellowstone National Park in Wyoming, USA. UU. This was necessary because the native wolves were completely exterminated by the federal government in the early decades of the twentieth century, at the time the policy was ofical kill any wolf found in the country, including nature reserves. Between 1924 and 1995 the natural ecosystem was altered substantially by the absence of wolves, although no one realized the magnitude of the change to its reintroduction in 1995.
After more than half a century and a great effort against the anti-environmentalist politicians, it was possible to re-introduce this relatively small number of wolves in the nearly 9,000 kilometers of territory that constitute Yellowstone National Park. In less than ten years, incredible effects were observed. Despite several setbacks with regard to the survival of wolves, their presence began a trophic cascade that reached to change the course of rivers in the park.
During the years that Yellowstone Park wolves remained, the populations of herbivores like deer had increased considerably, leaving large areas with sparse vegetation. In the absence of predators, government bodies charged with the care of the park had struggled to control the deer population in the park, however the existence of wolves had another completely unexpected effect. Although the number of wolves was little considering the vast area of the park and although several were killed illegally in the early years of the project, the presence of wolves was enough to change the behavior of deer, and this was the detail that allowed the amazing transformation of the entire ecosystem.
Due to the presence of wolves, deer began to avoid certain parts of the park – especially places where there was not enough vegetation to be able to hide – and thus allowed inadvertently vegetation growing again. Some of the areas that were left were frequented by deer valleys and canyons, which play an important role in determining the availability of water throughout the watershed. The result was impressive. bare lands became in some areas forests and trees grew up to 5 times its height in just 6 years. Several types of birds came to inhabit the new trees and biodiversity increased considerably. The new forests near water also attracted beavers; they build their prey with tree branches and these structures, in turn, provide habitat for fish, ducks, otters, reptiles and amphibians, among others. The park abounded in life.
All these effects were interesting and unexpected. However, the most impressive was how this chain of cause and effect that began with wolves ended up changing the form of the rivers. With the arrival of wolves and the consequent change deer behavior, rivers of Yellowstone Park became more consistent and deeper. erosion decreased and wells were formed, both of which promote biodiversity. But why they changed the rivers? When deer alter their behavior due to the presence of wolves, allowed the growth of trees and other vegetation in ravines and on the banks of the water. This vegetation was what stopped the erosion, stabilized the banks of the river and increased the amount of water retained by the entire ecosystem. It was so the presence of a few wolves changed the geography of the region and returned to heal the natural environment of Yellowstone National Park.