Bill Ripple and Rob Becheta's excellent new paper(click on pdf attachment in 2nd paragraph of article below) summarizes how Yellowstone is a healthier and more vibrant system 15 years after wolves were restored to the Park..........Everything from Willow and Aspen trees to Beaver to songbirds to ducks to foxes ravens and eagles...........The Wolves have reduced Elk grazers by 60 % and knocked Coyote populations in half................benefiting the list of species mentioned........... The authors mention the term "ecologically effective density" when it comes to predators like Wolves...........Top carnivores have to be present in sufficient numbers to fulfill their trophic role............Perhaps more wolves needed where bison herds in the Park are eating the grasses to the quick............In additon to Wolves impact on the system, factors such as fire suppression and warming temperatures will factor heavily into future equilibrium conditions for the Park

A LANDSCAPE TRANSFORMED FOR THE BETTER THROUGH TOP DOWN TROPHIC IMPACT FROM GRAY WOLVES--YELLOWSTONE 15 YEARS AFTER WOLF REWILDING


In 1995-1996 the grey wolf was reintroduced to Yellowstone National Park – after it had been hunted to extinction some 70 years earlier. Now, 15 years later, a new ecological balance is gradually forming between a stable number of wolves and a less dominant elk population – of which many plants and animals profit.

A special report (PDF) was released today by researchers of Oregon State University who have compared ecological changes between the late nineties and now for the Lamar River basin, which lies entirely in the national park

Most notable is the survival rate of sprouts of aspen trees. In 1998 still 100 percent of young aspen trees in the study area were being eaten by elk. Now that has reduced to 20 percent.
Apart from aspen trees, also cottonwood (another tree of the poplar family) and willow have recovered.

 Willow recovery has also led to a noticeable increase in songbird populations (such as that of the common yellowthroat, warbling vireo and song sparrow) as it provides nesting habitat.
Recovery of young deciduous trees has led to an increase of beaver populations around the Lamar River system from 1 in 1996 to 12 in 2009, which in turn has led to greater fish abundance. [Other research shows beaver ponds lead to a 75 times higher presence of duck species in Wyoming streams.]

The elk population has decreased from 15,000 in the early nineties to 6,100 in 2010 'and remaining elk now have different patterns of movement, vigilance, and other traits.'

Paradoxically many other predator species have benefited as well. This is because with the absence of wolves coyotes had grown to dominance in Yellowstone. The coyote numbers have again declined since the wolf's return, which means there is now more small prey left for species like the red fox, ravens and bald eagles.

After its reintroduction the wolf population has slowly increased to a peak of almost 100 individuals in 2003 and has since showed some variation, gradually declining to just over 40 wolves.
Development of various species numbers after wolf reintroduction in Yellowstone National Park.

However "these are still the early stages of recovery, and some of this may still take decades," says William Ripple, Oregon professor in the Department of Forest Ecosystems and Society. "But the signs are very encouraging."

Meanwhile an increase in the number of bisons in the Lamar Valley is impacting tree growth in that area – a development to which the wolf population may need to reply. "It may be necessary for wolves not only to be present but to have an ecologically effective density," says OSU co-author Robert Beschta, a professor emeritus of forestry.

He also notes it's not clear whether wolves can play their ecological role outside confined borders of national parks. "Mechanisms to deal with human and wolf conflicts also need to be improved."
A publication in Science earlier this year warned of worldwide ecosystem disturbances following large predator declines.
A resting grey wolf in snow-covered Yellowstone Park, judging the nutritional value of a photographer from afar. [Photos by Oregon State University.]

Meanwhile for many forest systems, ranging from tropical rainforests to temperate and boreal forests, it's not just overgrazing by dominant herbivores, there are other threats too – that wolves and other large predators can do little about, like fire. In Yellowstone's case this may still lead to an inevitable ecosystem shift halfway through the century, a special PNAS study stated last July.
There's only so much conservation measures can do to abate an environmental stress that is imposed from above…
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An ecosystem being transformed - Yellowstone 15 years after the return of wolves

CORVALLIS, Ore. – On the 15th anniversary of the return of wolves to Yellowstone National Park, a quiet but profound rebirth of life and ecosystem health is emerging, scientists conclude in a new report.

For the first time in 70 years, the over-browsing of young aspen and willow trees has diminished as elk populations in northern Yellowstone declined and their fear of wolf predation increased. Trees and shrubs have begun recovering along some streams, providing improved habitat for beaver and fish. Birds and bears also have more food.

"Yellowstone increasingly looks like a different place," said William Ripple, a professor in the Department of Forest Ecosystems and Society at Oregon State University, and lead author of the study.

"These are still the early stages of recovery, and some of this may still take decades," Ripple said. "But trees and shrubs are starting to come back and beaver numbers are increasing. The signs are very encouraging."

The findings of this report, based on a recent analysis done by OSU researchers and a review of many other studies as well, were just published in Biological Conservation, a professional journal. They outline an ecosystem renaissance that has taken place since wolves were restored to Yellowstone after being extirpated in the 1920s.

Along four streams studied in the Lamar River basin, 100 percent of the tallest young aspen sprouts were being browsed in 1998, compared to less than 20 percent last year. Heavy browsing by elk on this favorite food had caused new aspen tree recruitment to essentially grind to a halt in the mid-to-late 1900s, when wolves were absent, but new trees are now growing again in places.
Among the observations in this report:

• Since their reintroduction in 1995-96, the wolf population generally increased until 2003, forcing changes in both elk numbers and behavior due to what researchers call the "ecology of fear."
• The northern range elk populations decreased from more than 15,000 individuals in the early 1990s to about 6,000 last year, and remaining elk now have different patterns of movement, vigilance, and other traits.
• By 2006, some aspen trees had grown tall enough they were no longer susceptible to browsing by elk, and cottonwood and willow were also beginning to return in places.
• Improved willow growth is providing habitat that allows for a greater diversity and abundance of songbirds such as the common yellowthroat, warbling vireo and song sparrow.
• The number of beaver colonies in the same area increased from one in 1996 to 12 in 2009, with positive impacts on fish habitat.
• Increases in beaver populations have strong implications for riparian hydrology and biodiversity – Wyoming streams with beaver ponds have been found to have 75 times more abundant waterfowl than those without.
• The coyote population decreased with the increase in wolf numbers, potentially allowing more small mammals that provide food for other avian and mammalian predators, such as red foxes, ravens and bald eagles.

Evidence of improved ecosystem health following the return of wolves is "becoming increasingly persuasive," the scientists said in their report, though they also note that an increasing population of bison is continuing to impact young woody plants in the Lamar Valley."The wolves have made a major difference in Yellowstone," said Robert Beschta, a professor emeritus of forestry at OSU and co-author on the study.

"Whether similar recovery of plant communities can be expected in other areas, especially on public lands outside national parks, is less clear," Beschta said. "It may be necessary for wolves not only to be present but to have an ecologically effective density, and mechanisms to deal with human and wolf conflicts also need to be improved."

But at least in America's first national park, the return of this large predator is having an impact.
"Predation and predation risk associated with large predators appear to represent powerful ecological forces," the researchers concluded in their report, "capable of affecting the interactions of numerous animals and plants, as well as the structure and function of ecosystems."