Yellowstone National Park is a national park located primarily in the U.S. state of Wyoming, although it also extends into Montana and Idaho. It was established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872. Yellowstone, the first National Park in the U.S. and widely held to be the first national park in the world, is known for its wildlife and its many geothermal features, especially Old Faithful Geyser, one of the most popular features in the park. It has many types of ecosystems, but the subalpine forest is the most abundant. It is part of the Rockies ecoregion.


After the reintroduction of the gray wolf in 1995, researchers noticed drastic changes occurring. Elk, the primary prey of the gray wolf, became less abundant and changed their behavior, freeing riparian zones from constant grazing. The respite allowed willows and aspens to grow, creating habitat for beaver, moose, and scores of other species. In addition to the effects on prey species, the gray wolf’s presence also affected the park’s grizzly bear population. The bears, emerging from hibernation, chose to scavenge off wolf kills to gain needed energy and fatten up after fasting for months. Dozens of other species have been documented scavenging from wolf kills and are now flourishing.


Since the reintroduction of the grey wolf the vegitation of Yellowstone has flourished. Its eco-region is predominantly coniferous forest, dominated by lodgepole pine. Other trees include Engelmann spruce, Rocky Mountain fir, subalpine fir and trembling aspen. Whitebark pine is an important species at the upper tree line krummholz zone. This eco-region also contains mountain meadows, foothills grasslands, riparian woodlands, and alpine tundra. In some areas, geothermal activity creates distinct, warm habitats with unique floral communities.


The ecosystem is the largest remaining continuous stretch of mostly undeveloped pristine land in the continental United States, considered the world’s largest intact ecosystem in the northern temperate zone. With the successful wolf reintroduction program, which began in the 1990s, virtually all the original faunal species known to inhabit the region when white explorers first entered the area can still be found there. As a result, small animals, ground mice and rabbits also returned to the now growing meadows. The birds of prey such as the eagle returned to find a replenished source of food.


A century ago, wolves were not charismatic attractions for visitors to the park. They were perceived as a threat to the park and over time slowly removed from the protected from human-caused mortalities. Since their introduction to Yellowstone the park has experienced significant changes. The grazing habits of the deer and elk changed and as a result, the course of the rivers changed, as well. In 1973, the US Fish and Wildlife Service listed the northern Rocky Mountain wolf as an endangered species annually, from every corner of the globe and designated Greater Yellowstone as one of three recovery areas.


Rewilding is large-scale conservation aimed at restoring and protecting natural processes and core wilderness areas such as Yellowstone, providing connectivity between such areas, and protecting or reintroducing apex predators and keystone species. Rewilding projects may require ecological restoration or wilderness engineering, particularly to restore connectivity between fragmented protected areas, and reintroduction of predators where extirpated.