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Beavers: Ecosystem Engineers

Study: Beaver-influenced wetlands make for good amphibian habitat

Beavers in Glacier National Park modify wetlands in a way that makes them better suited for the health of the park’s amphibian population, according to a study published this month.

The paper, published in the journal Biological Conservation, suggests that even though most amphibian populations are shrinking, the influence of beavers on their habitats can decrease the severity of the decline. While the influence isn’t enough to reverse the trend – many amphibians are falling prey to a fungus unrelated to the absence of beavers – they can mitigate it.

In 2002, Blake R. Hossack and six other researchers began studying the distribution of amphibians in Glacier, Yellowstone, Grand Teton, and Rocky Mountain national parks. The project was a joint monitoring program with the U.S. Geological Survey and the National Park Service.

For 10 summers, researchers surveyed wetlands for evidence of breeding in order to determine whether a population of amphibians was present. In Glacier, they studied Boreal toads, Columbia spotted frogs, and long-toed salamanders. They found that amphibians thrive in beaver-inhabited wetlands, and will move away from wetlands without beavers to find one that beavers have modified.

Beavers are a keyston­­e species, which means that other species in their ecosystem depend on them so heavily that the ecosystem would change drastically should they disappear. They significantly affect aquatic and riparian habitats by damming streams and creating new open wetlands, which retain more heat from the sun and maintain regular surface water levels through seasonal changes better than most other small wetlands.

The environments beavers create are just the type amphibians need – their larvae depend on heat from external sources to grow and develop. Beaver wetlands are important in seasons like this one, when the snow melts early and might otherwise dry up before the larvae can metamorphose into juveniles.

Beaver wetlands are especially critical in Glacier, where wetlands tend to be shallow, especially on the arid, eastern side of the park.

“I don’t think we would have amphibians [there] without beavers,” says Hossack.

Enhancing beaver populations might be a viable method for protecting these parks’ amphibian populations. Already, the reintroduction of beavers is being used as a tool in Oregon for the recovery of threatened frogs. For now, though, Hossack doesn’t think beavers are rare enough in Glacier to trigger a mobilization of management efforts.

More important is future research into population trends. The study confirmed that the boreal toad population is shrinking. It also revealed that the long-toed salamander is in decline, despite being the most popular toad in the park – a surprise to the researchers.

Another surprising result though, was that the Columbia spotted frogs are doing well. The one exception to the general trend across all four parks, they saw a population uptick during the study.

“It’s encouraging that at least one species seems to be stable,” says Hossack. “Future research efforts [will] in part focus on why some species in the region seem to be declining and others are doing OK.”