Animals Wildlife After Killing All the Wolves in Yellowstone, They Finally Brought Them Back – Here's What Happened Next By Melissa Breyer Melissa Breyer Editorial Director Hunter College F.I.T., State University of New York Cornell University Melissa Breyer is Treehugger’s editorial director. She is a sustainability expert and author whose work has been published by the New York Times and National Geographic, among others. Learn about our editorial process Updated October 11, 2018 Yellowstone National Park / NPS / Jacob W. Frank / Flickr / Public Domain Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species New research finds that the reintroduction of wolves to the National Park is helping to restore the ecosystem to its former glory. Wolves once roamed the continent freely ... but as more and more humans came along and gobbled up the land, as humans are wont to do, wolf populations began to dwindle. Wolves are not good for livestock – and hence, livestock owners have proven to be not good for wolves. Even in places like National Parks, their numbers suffered. In Yellowstone, because of federal and state efforts to reduce predators, the last of the park's gray wolves (Canis lupus) were killed in 1926. Reintroducing Wolves to Yellowstone Decades later – once people woke up, hello – the species became one of the first to be listed as endangered. At that point, Greater Yellowstone was named as one of three recovery areas and from 1995 to 1997, 41 wild wolves were released in the park. As of December 2016, there were at least 108 wolves in the park, according to the National Park Service. It hasn't been without controversy, but now a new study reveals some wonderful news. The reintroduction of wolves into the park has led to the recovery of quaking aspen (Populus tremuloides) in the area – a feat that the National Park Service has been trying to achieve for decades. “What we’re seeing in Yellowstone is the emergence of an ecosystem that is more normal for the region and one that will support greater biodiversity,” says Luke Painter, a wildlife ecologist at Oregon State University and lead author on the study. “Restoring aspen in northern Yellowstone has been a goal of the National Park Service for decades. Now they’ve begun to achieve that passively, by having the animals do it for them. It’s a restoration success story.” The large-scale study is the first to show that aspen is recovering inside of the park, and in areas around the park as well. And importantly, is a striking reminder of this: If you add to or remove something from an ecosystem, the domino effect can take its toll. How Wolves Brought Aspen Back to Yellowstone In the case of Yellowstone's wolves, once they were gone, the animals they eat began to thrive; namely, elk. In 1995, before wolves were reintroduced, there were nearly 20,000 elk in northern Yellowstone; in January of 2018, there were 7,579. Which may not be good news for the elk as far as they see it, but with elk numbers unchecked, the consumption of aspen skyrocketed. And aspen plays "an important ecological role in the American West," notes the study's authors. Among other things, aspen trees provide habitat for a wide variety of wildlife. The USDA Forest Service explains that, "the aspen ecosystem is rich in number and species of animals, especially in comparison to associated coniferous forest types." Oregon State University / William Ripple / Flickr / CC BY-SA 2.0 The study shows that the return of wolves to Yellowstone indeed could have a cascading effect on ecosystems, Painter says. As you can see in the photo above, which shows young aspen trees in the park which have been growing since the wolves were re-introduced. The older trees in the photo date to the last time there were wolves in the park. “We show that the recovery of aspen is real and significant, though patchy and in early stages, and occurring throughout the region where elk population densities have been reduced,” he says. “Our findings represent another piece of the puzzle as we’re trying to understand the role of predation in the ecology of the Rocky Mountain region,” Painter adds. “Much of the research ecologists have done has been in the absence of non-human predators. Before the reintroduction of wolves, most experts didn’t think it was going to make much difference for aspen. Wolves didn’t cause aspen recovery all by themselves, but it is safe to say it would not have happened without them.” The research was published in Ecosphere.