'Ecosystem engineers': Arctic foxes build gardens on tundra, biologists say

Winnipeg-based biologists working near Churchill have discovered Arctic foxes effectively grow gardens around their dens on the tundra.

Organic waste from the furry carnivores — and the remains of the animals they kill — allows almost three times as much vegetation to bloom around their dens compared to elsewhere on the tundra, according to research authored by University of Manitoba biologists James Roth, John Markham, Tazarve Gharajehdaghipour and Paul Fafard.

In a paper published earlier this spring in the academic journal Scientific Reports, the U of M biologists call Arctic foxes "ecosystem engineers" because their dens support green blooms of dune grasses, willows and wildflowers that stand out on the otherwise yellow tundra.

Those plants, in turn attract herbivores such as caribou, lemmings and hares, while the remains of geese killed by foxes attract scavengers such as polar bears, wolves, gulls and ravens.

• Report: 'Arctic foxes as ecosystem engineers'
• Feds to invest $6M in Manitoba national parks: Environment minister

The combined effect of all those animals urinating, defecating and rotting around fox dens drives up the nutrient levels in the tundra, allowing more plants to grow on these sites, said Roth, a U of M associate professor of biology, who has been studying the way Arctic foxes interact with other animals since 1994.

"It's really striking. You can see these dens in August as a bright green spot from a kilometre away," Roth said in an interview.

"It's such a dramatic contrast between the bright, green vegetation around the dens and the tundra around it."

Roth calls Arctic foxes "ecosystem engineers" because they physically modify their environment in a way that affects other species. He compares the carnivores to beavers, which build dams that create ponds that benefit other species.

Roth said there are about 100 fox dens scattered along the Hudson Bay coast from Cape Churchill to just south of Broad River, within Wapusk National Park. Some of the sites may be hundreds of years old, as foxes tend to use the same dens over and over because it takes a lot of energy to dig into the permafrost, Roth said.

Lemmings make nests atop predators' dens

In 2014, graduate student Gharajehdaghipour took half-metre-square samples of vegetation from 20 of these dens within Wapusk and compared the vegetation with plants from control samples of tundra located away from the fox dens.

The biologists found not only more vegetation within the den samples, but more nutrients within the plants, as well. Roth said this helps explain why dune grasses and willows that normally only grow near water can be found around fox dens located high up on beach ridges.

"They're bringing nutrients from the prey items all around and bringing them back to their nests to feed their pups," said Roth, adding there are about 10 pups in an Arctic fox litter. "You can tell which dens are successful in producing pups because of all the dead stuff on the dens."

The researchers also found that lemmings make nests in the snow right on top of dens inhabited by foxes — their primary predators.

"They live right above the creatures that eat them," Roth noted, adding the topic is worthy of additional study. "Why are we finding these winter nests on these fox dens."

​