Reintroduction of wolves in Yellowstone national Park led to the restoration of willow thickets. According to the article in the journal Ecosphere, predators reduced the abundance of local deer and made them more cautious, the result of smaller herbivores eat willow and those can grow without interference. In turn, overgrown willow bushes make the entire ecosystem of the Park more sustainable and diverse.
Yellowstone national Park is not only one of the most famous protected areas in the world, but the arena of large-scale environmental experiment. It started in 1995 when the Park was brought wolves (Canis lupus) are destroyed here about 1930. According to the original plan, the wolves were just supposed to reduce the number of overly bred deer Wapiti (Cervus canadensis). In reality, however, their return had a profound effect on the entire ecosystem of Yellowstone, including its plant communities.
For example, it is believed that the reintroduction of wolves had a positive impact on Yellowstone willows (Salix spp.). When the number of ungulates in the Park was high, they eat willow, limiting their height and did not form thickets. The return of predators has reduced the pressure on the trees and allowed them to re-grow without interference. These findings, however, according to not all environmentalists. Some of them doubt that the number of herbivores decreased enough that it would affect the height of eve.
To understand the contentious issue decided Luke painter (Luke E. Painter) from the University of Oregon and his colleague Michael Tercek (Michael T. Tercek). The researchers compared data about the height of willows in Northern Yellowstone for the three period of time: from 1988 to 1993, 2001 to 2004 and from 2016 to 2018.
It turned out that the height and area of crowns of willows growing along the banks of rivers, has significantly increased over the twenty years that passed after the return of wolves. For 2016-2018 years overgrown with trees higher than three meters appeared in many places, where there was no early in the century. This process could not prevent any climate change or drought in Yellowstone in 2000-ies.
According to the authors, the state eve has improved due to the influence of wolves that have reduced the number of deer in the Northern part of the Park from 20,000 in 1995 to 4 149 in 2019. The reduction in the number of herbivores became evident by the early 2000s, and it was at this time began the process of recovery willow thickets. The appearance of predators also made the deer more cautious, so they began to spend less time on the grazing trees. The result is willow now can save most of the summer growth, which in the past has eaten. Previously, similar conclusions were made for Yellowstone aspens (Populus spp.), also benefited from the return of wolves.
Interestingly, the willows that grow in the meadows, and remained in a depressed condition. The fact that their heights are generally limited to bison (Bison bison), whose numbers in the Park have increased over the last decade despite the emergence of predators.
The researchers noted that the restoration of willow thickets is important for the entire Northern Yellowstone. These plants perform a number of important ecosystem services to curb erosion, to providing food of beavers (Castor canadensis). When willow feel good, the whole ecosystem becomes more resilient and diverse. Thus, the return of wolves has had a positive impact on the many species that inhabit Yellowstone.
In the absence of predators, herbivores often brood be a problem. For example, deer threaten the well-being of the largest living organism on Earth — ocinebrina clonal colony of poplar (Populus tremuloides) in Utah called Pando. Constantly herbivores they eat young trees, so they can not grow. In Pando result is aging, and its area is reduced.