Yellowstone

A temperate forest and grassland ecosystem in the northern Rocky Mountains of the United States, centered on Yellowstone National Park, the world's first national park, and sitting atop one of the largest volcanic systems on Earth, whose underlying heat powers the ecosystem's geysers and hot springs. Yellowstone is one of the most complete large temperate ecosystems remaining in the continental United States, holding nearly all of the large mammal species present at the time of European settlement, and it is the site of one of conservation's best-known case studies: the reintroduction of the gray wolf in 1995, after the species had been eliminated from the park for seventy years, which reduced overgrazing by elk and allowed streamside vegetation, beaver and songbirds to recover across the following decades.