A new study in Yellowstone National Park has revealed that since the reintroduction of wolves in the 1990s, its landscapes have undergone a dramatic transformation, particularly along its riverbanks.
According to the research, which spanned two decades from 2001–2020, there has been a 1,500% increase in the size of willow trees along these waterways.
Scientists from Oregon State University and the Conservation Biology Institute say that the wolves – and other large carnivores, such as cougars – have reshaped the park’s food chain, reducing elk browsing pressure and allowing plant life to recover, which in turn benefits many other species.
This 'trophic cascade' – an ecological process where predators limit the density or behaviour of their prey, and therefore enhance survival rates of the next lower trophic level – highlights the powerful role carnivores can play in restoring balance in nature, say the researchers, who published their findings in Global Ecology and Conservation.
Trophic cascade: the ripple effect of wolves
When wolves were wiped out from Yellowstone in the 1920s, elk numbers soared, leading to severe overgrazing. Trees such as willows, aspens and alders struggled to survive, resulting in a deterioration of habitats for birds, beavers and other wildlife.
Similar patterns were seen elsewhere on the content, for example at Banff National Park and Jasper National Park in Canada, where the loss of predators caused the health of the parks' ecosystems to fall.
However, since wolves were reintroduced to Yellowstone in 1995–96, the national park’s landscapes have been steadily recovering.
The study, led by Dr. William Ripple, is the first to analyse just how significant this change has been. The growth of willows – measured by their crown volume – shows that the effects of predator restoration in Yellowstone are among the strongest recorded anywhere in the world.
Although riverbanks cover only a small part of the landscape, they support more species than any other habitat type, say the researchers. Their recovery means healthier waterways, more food for wildlife, and improved living conditions for birds, fish and mammals.
Ripple says that not every area of Yellowstone has recovered at the same impressive rate, adding that restoring predators elsewhere could help revive struggling ecosystems, not just in Yellowstone but worldwide.
"Our findings show how predators act as nature’s architects,” says Ripple. “By controlling herbivore numbers, wolves have helped willows, aspens and berry-producing shrubs bounce back – proving just how interconnected wildlife truly is.”
Find out more about the study: The strength of the Yellowstone trophic cascade after wolf reintroduction
Main image: Yellowstone wolves/Getty
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