www.sciencenews.org | December 8, 2018 17
In a broad swath of northwestern Alaska, small groups of recent immigrants are hard at work. Like many residents of this remote area, they’re living off the land. But these industrious foreigners are neither prospecting for gold nor
trapping animals for their pelts. In fact, their own
luxurious fur was once a hot commodity. Say hello
to Castor canadensis, the American beaver.
Much like humans, beavers can have an oversized effect on the landscape (SN: 8/4/18, p. 28).
People who live near beaver habitat complain
of downed trees and flooded land. But in areas
populated mostly by critters, the effects can be
positive. Beaver dams broaden and deepen small
streams, forming new ponds and warming up local
waters. Those beaver-built enhancements create or expand habitats hospitable to many other
species — one of the main reasons that researchers
refer to beavers as ecosystem engineers.
Beavers’ tireless toils — to erect lodges that
provide a measure of security against land-based
predators and to build a larder of limbs, bark and
other vegetation to tide them over until spring
thaw — benefit the wildlife community.
A couple of decades ago, the dam-building
rodents were hard to find in northwestern Alaska.
“There’s a lot of beaver around here now, a lot of
lodges and dams,” says Robert Kirk, a long-time
resident of Noatak, Alaska — ground zero for much
of the recent beaver expansion. His village of less
than 600 people is the only human population
center in the Noatak River watershed.
Beavers may be infiltrating the region for the
first time in recent history as climate change makes
conditions more hospitable, says Ken Tape, an
ecologist at the University of Alaska Fairbanks. Or
maybe the expansion is a rebound after trapping
reduced beaver numbers to imperceptible levels
in the early 1900s, he says. Nobody knows for sure.
And the full range of changes the rodents are
generating in their new Arctic ecosystems hasn’t
been studied in detail. But from what Tape and a
few other researchers can tell so far, the effects
could be profound, and most of them will probably
be beneficial for other species.
In the areas newly colonized by beavers,
“some really interesting processes are unfold-
ing,” says John Benson, a wildlife ecologist at the
University of Nebraska–Lincoln who studies
wolves and coyotes, among other beaver preda-
tors. “I’d expect some pretty dramatic changes to
the areas they take over.”
Beavers’ biggest effects on Arctic ecosystems
may come from the added biodiversity within the
ponds they create, says James Roth, an ecologist at
the University of Manitoba in Winnipeg, Canada.
These “oases on the tundra” will not only provide
permanent habitat for fish and amphibians, they’ll
serve as seasonal stopover spots for migratory
waterfowl. Physical changes to the environment
could be just as dramatic, thawing permafrost
decades faster than climate change alone would.
The Arctic tundra isn’t the first place beavers
have made their mark. Changes seen in beaver-rich areas at lower latitudes may offer some clues
to the future of the Alaskan tundra, home to
moose, caribou and snowshoe hares.
North through Alaska
As Earth’s climate has warmed in recent years,
some plants and animals — such as the mountain-dwelling pika, a small mammal related to
rabbits — have fled the heat by moving to higher
altitudes (SN: 6/30/12, p. 16). Others, from moose
and snowshoe hares to bull sharks and bottle-nosed dolphins, have moved toward the poles to
take advantage of newly hospitable ecosystems
(SN: 5/26/18, p. 9).
Arctic environments have changed more than
most, Tape says. Polar regions are warming much
faster than other parts of the world, he says. Studies estimate that average temperatures in the
Arctic have risen about 1. 8 degrees Celsius since
1900, about 60 percent faster than the Northern
Hemisphere as a whole.
This warming is bringing great change to the
Alaskan tundra, Tape says. Winter snow cover
doesn’t persist as long as it used to. Streams freeze
later in the fall and melt earlier in the spring.
Permafrost, the perennially frozen ground, is
thawing, allowing shrubs to take hold. New species are moving in, few more noticeable than the
Beaver dams (arrows) convert a tundra stream in Alaska into a wetland, creating new
habitat and thawing underlying permafrost. A beaver’s protective lodge is shown, too.