After decades of decline, the aspen forests of northern Yellowstone are finally making a comeback, and believe it or not, it’s all thanks to the return of certain carnivores.

A new long-term study has revealed a significant shift in the health of quaking aspen stands across northern Yellowstone National Park. Researchers found that 43% of the surveyed stands now contain a new generation of overstory aspen trees, something that hasn’t been seen since the 1940s.

These young trees are only 2 to 4 inches in diameter, yet they represent the first real sign that aspen forests are recovering after being suppressed for decades by overbrowsing from elk.

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How The Removal Of Wolves Killed The Yellowstone Aspen Trees

The root of the problem goes back nearly a century. By the 1930s, wolves had been eliminated from Yellowstone, and cougar populations were severely reduced. Without natural predators to keep elk numbers in check, the elk population soared.

During long winters, elk heavily browsed young aspen shoots, preventing them from growing tall enough to become mature trees. As older trees died off and no new ones took their place, aspen stands slowly thinned.

The reintroduction of wolves in 1995-96 marked a turning point. The return of gray wolves, along with more hunting and other predators like bears and cougars, caused elk numbers to drop and changed how they moved around. With fewer elk lingering in any one place, and overall browsing pressure reduced, young aspen finally had a chance to grow.

According to the new study, by 2020-21, tall aspen saplings (at least 6 feet high) reached an average density of 3,600 per acre. That’s a significant increase from 1998, when young aspen were almost completely absent in most stands.

However, the recovery isn’t uniform. In 2021, 30% of stands had consistent sapling recruitment, 32% had patchy growth, and 38% had few or no saplings. Areas with high rates of browsing, particularly from elk and increasingly from bison, still struggle to support new tree growth. In fact, researchers found that in stands with higher levels of browsing on shorter aspen, there were fewer tall saplings, reinforcing that herbivory remains the dominant factor limiting recovery.

Why Climate Change Isn't To Blame

Importantly, the study also ruled out climate as the primary driver of recent changes. Despite a warming and drying trend in the region, aspen recovery began even during drought years, and evidence suggests that browsing, not temperature or moisture, is the key influence on young tree growth.

While it may take decades for a full forest canopy to return, the presence of new trees signals a meaningful shift. These young aspen are not only proof of ecological resilience, but also a living example of how restoring apex predators can set off powerful ripple effects throughout an ecosystem.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.