Widespread aspen trees were a common sight in Yellowstone National Park before wolves were removed. (Photo: Science Alert).
A new study has revealed a remarkable story of ecological restoration in Yellowstone National Park, where the return of gray wolves has helped revive disappearing aspen forests.
In the early 20th century, the decision to completely remove gray wolves from Yellowstone inadvertently set off a negative ecological chain reaction. Without a natural predator, the elk population exploded, becoming a serious threat to vegetation, especially young aspen trees.
They eat the tops, strip the bark and trample the forest floor, leaving many forests barren and bare. As a result, species that depend on the canopy, such as birds, beavers and insects, gradually disappear.
Ecologists have been documenting this severe degradation since 1934, but all attempts to intervene have had little apparent effect. The root cause lies not in the vegetation, but in the critical ecological link that has been severed: the absence of apex predators.
The wolf returns, the poplar forest revives
The turning point came in 1995, when gray wolves were reintroduced into Yellowstone from Jasper National Park, Canada. It was considered one of the most audacious restoration efforts in the United States. The wolves quickly adapted, established territories, and began to fulfill their natural role: controlling the elk population.
Two gray wolves stand on the carcass of a moose in Yellowstone National Park (Photo: Science Alert).
The presence of wolves forces deer to move more frequently, avoiding areas where they are most vulnerable to predators. This gives young plants that were previously eaten and trampled a chance to survive and thrive. This is a classic example of a “top-down chain effect,” where a predator at the top of the food chain has a ripple effect throughout the ecosystem below.
Nearly three decades after the reintroduction of wolves, scientists have observed a remarkable recovery. New research by a team led by Oregon State University Professor Luke Painter shows that about a third of the 87 aspen forests surveyed in Yellowstone now have a thriving sapling layer. This is the first generation of trees to form a canopy layer, something that hasn’t happened since the 1940s.
Specifically, 43% of the areas examined recorded saplings exceeding the 5cm stem diameter threshold, indicating long-term survival. The density of trees over 2m in height has increased 152-fold since the late 1990s. The landscape also varied significantly, with 30% of the forest area having dense trees and 32% having scattered trees.
To confirm the role of wolves, the team measured the rate of tree destruction by moose in each area. The results showed that forests with a regular wolf presence recorded much lower rates of tree destruction, while areas without wolves continued to destroy saplings and failed to develop into a forest floor.
Professor Painter said this was an amazing case of ecological restoration, where humans didn’t need to plant more trees or build more dams, but simply gave nature back its missing link. The return of wolves opened the door for aspen forests, and with them countless other species, to recover after decades of decline.
Source: https://dantri.com.vn/khoa-hoc/su-tro-lai-cua-loai-soi-giup-rung-yellowstone-hoi-sinh-the-nao-20250730084800356.htm
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