Yellowstone wolves help the new generation of young aspen trees to join the forest canopy, taller.
Grey wolves (Cannis Loops) had disappeared from Yellowstone National Park by 1930 after extensive habitat loss, human hunting and government eradication programs. Without these best predators, the population of elk (Cervus canadensis) grew freely. At the peak of the population, an estimated 18,000 elks spread throughout the park, with grass, shrubs, leaves, twigs and bark whipping the bark of trees like aspen (Populus tremuloides). This stopped the seedlings from establishing themselves, and research in the 1990s found no aspen saplings.
“There was an old tree and nothing underneath it,” Luke Painter, an ecologist at Oregon State University and lead author of the new study, told Live Science.
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However, when wolves were reintroduced in 1995, photography began to change. As the number of wolves increased, the park’s elk population fell sharply, reaching around 2,000.
In a new study published on Tuesday (July 22) in the Journal Forest Ecology and Management, the painter and his colleagues investigated the aspen stand.
Related: Reintroduction of wolves in Yellowstone helped the entire ecosystem thrive, according to 20 years of research
The team returned to the three areas surveyed in 2012 to look at changes in aspen seedlings. Of the 87 aspen stands surveyed, a third has many tall aspen saplings throughout, indicating that the tree is healthy and growing. Another third of the stand had a patch of tall saplings.
“We’ve seen a significant new growth in young Aspen, which is the first time we’ve found on our plot,” Painter said. These are young aspen with trunks over 2 inches (5 centimeters) in diameter at chest height. He added that he hasn’t seen it since the 1940s.
“It doesn’t mean they won’t be killed or killed by anything, but getting a new tree is a pretty good sign,” Painter pointed out. “The bigger they get, the more resilient they become.”
Such trees are old enough to send new shoots from the roots at a considerable distance from the main tree or spread themselves through seed production, he said.
However, while Yellowstone’s trembling aspen is recovering, they have not yet left the forest. Moose populations have been decreasing, but in some regions in recent years the number of bison (bison bison) has been increasing.
Bisons are much more difficult for wolves to defeat, according to the painter, and as a new constraint on aspen in some areas, the increasing number of bisons may be on the rise.
The painter said that fluctuations in aspen’s recovery have the effect of reintroducing large predators at the top of the food chain, rather than, for example, changes in the overall climate.
The reappearance of aspen has a widespread effect, he told Live Science. “Aspen is an important species of biodiversity. The canopy is opener than coniferous trees and filters the light that creates habitat that supports many diverse plants.”
This means that the trees are the preferred food and building materials for semi-aquatic rodents, and boost the berries-like shrubs, insects, birds and beaver-like species that produce berries, along with grown cotton and cottonwoods close to the local waters.
There are also hints that the number of bears and cougars has been on the rise in the area since the introduction of wolves, but it is not clear why.
“This paper illustrates the important ecological benefits that arise from wolves’ restoration to Yellowstone National Park,” Dominic Splaklen, professor of biospheric atmospheric interactions at the University of Leeds, UK, who studied the potential impact of reintroducing wolves in Scotland, told Live Science.
“Ecosystems lacking large carnivorous animals are often out of balance,” Spracklen said. “While reintroduction of carnivorous animals presents a key challenge, centering on the coexistence of human life, this work highlights the important ecological benefits that such restoration efforts can bring.”
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