There were no empty seats in the Pinery Room of the Portage County Library on Feb. 10, when Drs. Eric Larsen and Susan Talarico presented Larsen’s research on trophic cascades in Yellowstone National Park.
Titled “Aspen, Elk and Wolves on Yellowstone’s Northern Range,” the lecture was the latest installment of the community lecture series hosted by the University of Wisconsin-Stevens Point College of Letters and Science. Larsen is a professor of geography, and Talarico is an associate professor of mathematics. Both teach at UWSP.
Trophic cascades are a phenomena that occur when species are added to, or removed from, an ecosystem’s food chain. When predators limit their prey, an effect can be seen in lower food chain levels.
Larsen’s research aims to explain trophic relationships between aspen, elk and deer in Yellowstone. He is examining evidence that proves since wolves were re-introduced to the park in 1995, the number of elk have decreased dramatically, thus freeing young aspen trees from being eaten.
Wolf re-introduction and subsequent ecological changes are significant both historically and scientifically. During the beginning of the lecture, Talarico explained the park’s history and the troubled past of Yellowstone’s wolves.
Talarico said after the park was established in 1872, wolves and other animals “of fang and claw” were hunted heavily because they were seen as enemies to hunters and ranchers.
“The national park service in earnest went after wolves,” Talarico said. “By 1926 there were no wolves left. They were completely eradicated.”
Following wolf eradication, elk and bison were actively bred and grazed the land excessively for almost 70 years. During this time, elk were free from predation and browsing their food of choice, young aspen.
Talarico said with the wolves came controversy, but they are now established in the park and sightings are common again.
In the mid ’90s, when the wolf project was looking for support, Larsen was looking for a topic to guide his Ph.D dissertation. His research in the park began in 1996, one year after the wolves were brought back.
“When the wolves got re-introduced, I honestly wasn’t thinking about it much, but wolves eat elk,” Larsen said. “I said to myself, ‘this is a once in a lifetime opportunity right here.'”
Larsen began his research by obtaining background information on aspen stands in the park. He found strong evidence of elk browsing.
“I drilled increment cores, hundreds of increment cores,” he said. “After about 1930, nothing.”
Larsen said evidence indicated “it was really browsing that was suppressing aspen on the northern range.”
To put his research into context, Larsen needed to understand what the aspen forests and browsing levels were like while the wolves were still around. He began researching the growth history of aspen.
With Talarico’s help, he was able to use historical data from beaver studies and data of his own to mathematically model aspen forest conditions before wolves were eradicated.
Larsen’s research has continued in the park every summer, except one, since the project began. He noted that for almost 10 years, there was no clear evidence of increased aspen growth – a discouraging observation.
“How much time am I going to spend measuring a system that’s not changing?” Larsen said.
In 2005, dramatic growth improvements occurred on some of Larsen’s research areas. Larsen collaborated with a wolf researcher and compared wolf kill data to confirm elk were killed in the same areas aspen was growing. Growth continues to improve and browsing levels are down.
Larsen admits the trophic cascades in Yellowstone are not detached from other factors, and he reinforced the idea that unexpected things happen when species enter or leave ecosystems. He also mentioned that the increase in aspen growth coincided with Montana’s decision to lower the amount of wolves to be harvested.
“There is ‘the magic wolf,” Larsen said. “It’s not in isolation; a lot of things happened at the same time. It’s a story of making the world whole again as much as it is a story of science.”