Beaver battle plan: Orange line denotes forest edge once thought to be the boundary of beaver advance; yellow arrows show beaver incursions into tundra since 1999; white areas plot likely new advances; white crosses denote beaver encampments now far beyond tree line.

The streams and rivers of Arctic Alaska are slowly but steadily being transformed by a northward advance of beavers into the shrub lands of the tundra, according to a new study by a team of scientists led by Ken Tape from the University of Alaska Fairbanks.

Already the buck-tooth rodents are “dramatically altering numerous tundra streams on local to regional scales,” write Tape and colleagues from UAF, the U.S. Geological Survey and two Germany institutions.

As a result, waterways that once flowed freely to the ocean are being turned into stream-pond systems and wetlands with broad habitat and microclimate implications, says their peer-reviewed study published in Global Change Biology in May.

The rather provocative title is “Tundra be dammed: Beaver colonization of the Arctic.”

The spelling there is of the dam version, but given the broader implications for tundra habitats it might also be considered the damned version.

“Water bodies in permafrost regions cause the greatest (among all land cover classes) difference between ground temperatures and regional air temperatures, increasing sediment temperatures up to 10°C (50 degrees Farenheit) above the mean annual air temperatures and allowing permafrost under lakes to thaw, even in cold permafrost regions,” the study says.

New beaver works would be expected to speed permafrost melt and add to global warming, but there is debate about whether Arctic warming leads to more CO2 in the atmosphere or less. The debate hinges on the balance between CO2 escaping from melting permafrost and that being sucking up by new plants for photosynthesis. 

An examination of years of satellite imagery allowed scientists to spot beaver ponds that marked the steady advance of beaver nation from 1999 to today. An army of beavers is now re-engineering the Arctic in ways no one had thought of before, Tape said.

“The oasis/spring concept would seem to apply in all manner to beaver dams and their associated disturbances,” he messaged in response to some questions: “Permafrost thaw, warmer water, more unfrozen water in winter, more biodiversity in invertebrate communities and possibly fish, more and taller shrubs (and trees), more herbivores, more birds in ponds, etc. A large and seemingly determined team of beaver engineers are dotting the Arctic with these oases, and the exciting part is that we have caught them in the act.”

Not all bad

Given that the advance of the beavers is linked to climate change that allowed the willows on which the beaver feed to move farther north, and given that the work of the beavers is likely to accelerate global warming at least at the microclimate level, and given that most people believe global warming is bad, bad, bad, it might be only natural to look at this beaver-led re-engineering of Arctic waterways in a negative light.

But that presupposes that change is a bad thing. And change isn’t always a bad thing.

“New beaver ponds are moderating the stream thermal regime, varying aquatic thermal habitat, and likely increasing biodiversity, thus functioning like springs or oases in the Arctic,” the scientists write.

Tundra oases would be expected to increase the low, ecological productivity of the tundra in much the way desert oases increase the low, ecological productivity of the desert.

“…The increasing water temperatures and permafrost disturbance associated with beaver dams may enhance biological processes in the Arctic more so than in other
biomes. Many arctic freshwater species are limited by insufficient unfrozen water during winter,” the scientists note, “or by low water temperatures, suggesting that greater unfrozen water or elevated water temperatures associated with beaver activity will make conditions suitable for new freshwater species.”

But that’s only the precursor to what could be an even bigger ecological change: new salmon runs.

“Warmer water and substrate temperatures above and below beaver dams may promote successful salmon reproduction in arctic streams sooner than expected,” the paper concludes. “Pacific salmon, notably chum salmon and pink salmon have been observed in many rivers across the North Slope of Alaska. However, it appears that most arctic freshwater ecosystems are too cold for successful salmon reproduction and egg incubation; (salmon) juveniles are extremely rare.”

Clearly the salmon are ready and waiting to colonize new streams, but the environment isn’t cooperating as of yet. The beavers could change that. And who knows what the combination of two might do with growing numbers of salmon each year bringing back their body loads of nitrogen and phospohorous from the sea to fertilize the areas where they spawn and die.

Can you say accelerated Arctic greening? Not that the road forward will be smooth.

“Although we predict the net effect of beavers on salmon in the Arctic to be positive, we anticipate complex interactions and variable responses depending on the local attributes,” the study says.

“After beaver establishment in a tundra riparian corridor, we anticipate an immediate decline in shrub height and extent due to inundation or to beavers cutting them down for forage caches and to build dams. We predict that the longer term effects of beaver-induced disturbance, however, will actually enhance shrub growth.”

Moose, a newly arrived species in the far north, and the Alaska Hare, a long-established species limited to the tundra of Western Alaska, are likely to suffer in the competition with beavers for willow in the short-term, but “we believe that ultimately shrubs and shrub herbivores will thrive with the addition of disturbances like changing water levels and thawing permafrost,” the study says.

How quickly this change will take place is an unknown, but the beavers are now calculated to be advancing at an average rate of about 8 miles per year. And who knows but that advance might accelerate with the Arctic being the fastest warming part of Alaska.