Wolves, aspen, elk and fire - keys to healthy forests?

There are things one knows to be true in the natural world of the Waterton-Glacier International Peace Park. There are wolves, there are elk, elk are chased down and eaten by wolves, and elk do everything they can to avoid being eaten. It’s nature.

Add a wild card to the mix, like the huge wildfires that have grazed the landscape in the North Fork of the Flathead, and one sees something else — lush growth of new stands of aspen, a tree coveted not only for its aesthetics but as a food resource for elk.

Oregon state researcher and author Cristina Eisenberg has been studying the relationships between elk, aspens, wolves and fires for several years in the adjoining national parks. Over the years, she’s compared the density of elk and wolves in three different but similar regions — the North Fork, St. Mary and Waterton valleys. She talked about her findings at the Glacier National Park Community Hall on May 2.

All three landscapes have elk and, to varying degrees, wolves. In the North Fork, wolf populations have been well-established for more than two decades. Around St. Mary, wolves are a transient population — they exist but have a tenuous relationship outside Glacier Park, where they are often shot for killing livestock on the Blackfeet Indian Reservation.

A pack of wolves lives in the Waterton area, but they also are subject to being shot when they leave the national park. Alberta doesn’t protect wolves outside the national park’s boundaries.

In the North Fork, however, the hunting quota is low — just two wolves — and wolves were still protected under the Endangered Species Act when Eisenberg conducted her study.

Eisenberg explained that ecologists tend to think of food webs as either bottom up or top down. In the bottom-up model, the web starts with energy from the sun, which sustains plants. In turn, plants feed herbivores, and predators eat herbivores.

In the top-down theory, the top predators feed on the herbivores which impacts plant growth. Eisenberg has her own theory — the web runs in a circular fashion, everything is interconnected, and relationships in the food web all have an impact on one another.

For example, Eisenberg found that in the North Fork, new aspen growth wasn’t great where wolves existed and there was no fire compared to areas with both wolves and fire. In fact, in areas where the landscape had burned and wolves denned, new aspen growth was lush.

On the flip side, elk density was far lower in burned areas that had wolves. In the North Fork, study areas where there was no fire had about nine elk per square kilometer, while areas where there had been fire had about eight elk per square kilometer.

By contrast, the St. Mary Valley had 21 elk per square kilometer, and Waterton had 24 elk per square kilometer. Neither Waterton nor St. Mary has seen a fire since 1880.

Elk in the North Fork avoided the burned areas even though they had plenty of aspens — a favorite food. Why? The wolves, Eisenberg surmised.

Wolves have a twofold effect on elk — not only do they eat them, but they scare them. An elk browsing on aspen in wolf territory may eat a bud here or there and move on for fear of being eaten itself. But an elk with no fear of wolves or being eaten will stay in an aspen stand and eat to its heart’s content. This is known as the theory of ecology of fear.

The relationship between a top-down predator and its prey is called trophic cascades. Removing the top predator can have a profound impact on the landscape. In St. Mary, where wolves are transient and elk density is high, aspen stands are old and new growth is highly stunted — over browsed by elk and deer.

Eisenberg discusses these theories in her book, “A Wolf’s Tooth,” and she is working on another volume. But it’s just not elk and wolves and their relationship that appears to drive aspen health.

“You need the other keystone force, which is fire,” she said.

Fire rejuvenates the soil and stimulates new growth in aspens. Aspens reproduce primarily by cloning. A stand of aspen is usually made up of trees that are all related, one big organism. When aspen trees change colors in the fall, a group will turn all at once.

Eisenberg will continue her wolf-aspen-elk studies in Waterton this year where the park officials recently conducted controlled burns in aspens to gauge the effects. She also plans on doing more work in Yellowstone National Park, which also has elk, aspen and wolves, but where aspen trees are failing in some areas.

It’s a complex system, and there’s an inherent problem to studying trees and ecosystems, Eisenberg notes — trees live for hundreds of years while a human lives about 80.