Utah State University scientists report a
watershed-scale experiment in “highly degraded” streams within Oregon's John Day Basin
demonstrates building beaver dam analogs allows beavers to increase their dam
building activities, which benefits a threatened population of steelhead trout.
"Whether or not beaver dams are
beneficial to trout and salmon has been hotly debated," says ecologist
Nick Bouwes, owner of Utah-based Eco Logical Research, Inc. and adjunct
assistant professor in USU's Department of Watershed Sciences.
Billions of dollars are spent for varied river
restoration efforts each year in the United States, he says, but little
evidence is available to support the efficacy of beaver dams.
"This may be due to the small scale of
the limited research aimed at investigating restoration effects," Bouwes
says. "So, we conducted a large-scale experiment, where the effects of
restoration on a watershed were compared to another watershed that received no
Bouwes is lead author of a paper published
July 4, 2016, in the journal Nature's online, open access Scientific Reports
that details the seven-year experiment conducted in streams within north
central Oregon's Bridge Creek Watershed. Contributing authors are Bouwes' USU
colleagues Carl Saunders and Joe Wheaton, along with Nicholas Weber of Eco
Logical Research, Chris Jordan and Michael Pollock of NOAA's Northwest
Fisheries Science Center in Seattle, Ian Tattam of the Oregon Department of
Fish and Wildlife and Carol Volk of Washington's South Fork Research, Inc.
When Lewis and Clark made their way through
the Pacific Northwest in the early 19th century, the area's streams teemed with
steelhead and beaver, said Bouwes. But subsequent human activities, including
harvesting beaver to near extirpation, led to widespread degradation of fish
Bouwes says these activities may have also exacerbated
stream channel incision, meaning a rapid down-cutting of stream beds, which
disconnects a channel from its floodplain and near-stream vegetation from the
water table. He notes beavers build dams in the incised trenches, but because
of the lack of large, woody material, their dams typically fail within a year.
"It's an ubiquitous environmental problem
in the Columbia River Basin and throughout the world." Bouwes says.
"It sets a chain of ecological effects in motion that result in habitat
destruction, including declines in fish populations and other aquatic
To conduct the experiment, the researchers
built beaver dam analogs, known as "BDAs," by pounding wooden posts
into the stream bed, and weaving willow branches between the posts, throughout
the 32-kilometer study area.
"Our goal was to encourage beaver to
build on stable structures that would increase dam life spans, capture
sediment, raise the stream and reconnect the stream to its floodplain,"
Bouwes says. "We expected this would result in both an increase in
near-stream vegetation and better fish habitat."
Beavers quickly occupied the BDAs, resulting
in an increase in natural dam construction and longevity in Bridge Creek.
"What really impressed us was how quickly
the stream bed built up behind the dams and how water was spilling onto the
floodplain," Bouwes says.
The researchers also documented increases in
fish habitat quantity and quality in their study watershed relative to the
watershed that received no BDAs and saw little increase in beaver activity. The
changes in habitat in the watershed receiving BDAs resulted in a significant
uptick in juvenile steelhead numbers, survival and production.
"This is, perhaps, the only study to
demonstrate beaver-mediated restoration may be a viable and efficient strategy
to rehabilitate incised streams and to increase imperiled fish
populations," Bouwes says. "With so many streams that need help, we
need to look towards more cost-effective and proven means to restore streams,
and beavers may be able to do a lot of the heavy lifting for us."
-- CBB, March 4, 2016, “Council’s Science
Review Panel Looks At Broad Strategy To Restore John Day River Watershed” http://www.cbbulletin.com/436161.aspx
-- CBB, Feb. 5, 2016, “Study: Intensive,
Long-Term Monitoring Key To Determining Effects Of Habitat Restoration’ http://www.cbbulletin.com/435985.aspx