Beavers invade

beaver battle plan

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.



9 replies »

  1. Was there any mention in the paper of new food sources(beaver) for predators,ie foxes, wolves, wolverine, and bears? I would assume that once beaver become abundant,predators would key in on the food source, thus delaying the beaver advancement and slowing down their effect on the landscape.

    • If the predators you reference used steel traps that would likely slow down the advancement. But natural predators are a different matter. In the Arctic they would consist of wolves, coyotes, some raptors, and maybe a wolverine or bear. Ever tried to take a Beaver? Ever tried to destroy their dams or homes? Not easy and they are quick to rebuild and reproduce. And they live off the materials they use to build with. And there is lots of that.

      • I have taken many of beavers. no i never distoryed a beaver house or dam. as it is illegal to destroy a hose and dams are frozen when i trap. You don’t have to worry about trappers in that part of the country as there are not many.

      • Al: I and others whom I know have been given DNR permits and ADF&G approvals to blow dams when they backed up spawning salmon or were causing unnecessary flooding. Beavers build their houses and live in these large dams. Large Beaver dams are almost untouchable with conventional methods. And certainly not easy to access by any predators. If they are set to take over an area in the Arctic there will be little impact by predators. Climate may play a bigger role. And you are correct, there is very little trapping in the Arctic compared to south of the Brooks Range.

    • Al, its my guess that those predators won’t wait till beavers become abundant and are already slowing down their effect on the landscape.
      Here is an observation by John Hyde in his book “Romeo, the Story of an Alaskan Wolf.”
      “The beaver was about 150 yards down the shoreline from me. As I reached for my binoculars to get a better view, a large black object streaked out of trees and leaped right on top of the beaver…..Before I knew it, the black wolf had pulled the limp body of the beaver out of the shallow water, and in about three or four strides had disappeared into the vegetation.”

      • Bill, i know the prey does not have to be abundant for predators to react, but when they do, they become more of their diet. Also when predators are not accustom to taking a prey species, they have to learn how and then pass that practice on to their young. this usually accrues when that prey specie is more abundant.

      • Al, I remember a conversation with Sandy Hamilton back in the 80s (Sandy flew biologists to the North Slope to study the prey of wolves there). He said that most wolves north of Brooks ate predominantly caribou but they did have one wolf that only ate moose meat (they weren’t sure if this wolf also killed its moose). They learned this from analyzing wolf scats.
        There was no mention of beaver meat in those wolves diet then but I wouldn’t be surprised if that’s changing today. There was also no mention of mice being in those wolves scats (thinking of Never Cry Wolf here, heheh).

      • Bill, one of my favorite greenie movies. Try to watch it once a year. Depending on how long the study was conducted. No rodent evidence in the scat could have been because at the time of the study, the rodents may have been at a low cycle.

      • Al, the dog team in that movie belonged to a good friend of mine (Dick Mahoney from Haines Junction then and Mayo, now). The scene of the team leaving with the old Native was actually filmed with Dick’s wife at the time (Polly) as the gear was too small for Dick. When the wolves were after the star under the canoe, those were Dick’s huskies sticking their noses under the canoe after pieces of cheese thrown there.

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