4 minute read
Leave it to Beaver?
EMULATE: Leave it to Beaver?
In the face of climate change and increasing associated water scarcity, one promising restoration and resilience focus has emerged: beaver. Pre-colonial North American populations of Castor canadensis are estimated in a range up to 400 million individuals but were decimated to a mere estimated 100,000 individuals by the end of the beaver fashion epoch—a period from the sixteenth to the nineteenth centuries in which beaver hats and other garments using beaver pelt were in high fashion and extremely desirable. Thanks to the whims of fashion trends, the Castor genus—the last genus of what at one time was a 32 genera field—was saved from extinction. Two species remain within this genus: Castor canadensis, the North American beaver, and Castor fiber, the Eurasian beaver.
Today, scientists estimate there are between 6 and 12 million beaver across North America and hypothesize that they have an increasingly important role to play in conservation. Researchers in the state of Washington are applying beaver conservation assumptions to plans for salmon habitat restoration. These researchers are trapping “nuisance” beaver from urban environments and repopulating them in the uplands of a number of river systems and carefully measuring the impacts they have on the relocation grounds’ functionality. What these researchers are discovering is that the presence of beaver spell good things for otherwise plunging salmon populations; one study by Dr. Michael Pollock on the Stillaguamish River Basin estimated that at some point, the river basin provided crucial habitat to some 7.1 million juvenile coho annually, but in recent years that number had plummeted to 1 million. Lack of deep pools rich with associated riparian vegetation— which together provided juvenile coho with predatory protection and rich food supply—or, in other words, habitat destruction, is responsible for this decline. While these experiments are still being conducted, early outcomes are encouraging.
In a paper entitled “Reintegrating the North American beaver (Castor canadensis) in the urban landscape,” researchers from the University of Washington David Bailey, Ben Dittbrenner, and Ken Yocom share a compelling list of ecosystem services and benefits of beaver presence, which include: increasing groundwater levels, decreasing and retaining storm-water run-off, creating habitat for many species, most notably salmon, decreasing erosion and incision of streambeds, and increase in riparian vegetation. Ben Goldfarb, environmental journalist and author of Eager: The Surprising Secret Life of Beavers and Why They Matter, who has covered Bailey and Dittbrenner’s research extensively writes, “Beavers, by capturing surface water and elevating groundwater tables, keep our waterways hydrated in the face of climate-change fueled drought. Their wetlands dissipate floods and slow the onslaught of wildfires. They filter pollution. They store carbon. They reverse erosion. And, whereas our infrastructure is generally inimical to life, they terraform watery cradles for creatures from salmon to sawflies to salamanders. They heal the wounds we inflict.”
One study by Dittbrenner found that for every cubic meter of surface water that beaver trap in the deep pools that form behind their dams, another 2.5 cubic meters infiltrates, recharging groundwater. This process keeps streams running fuller and longer into the season. Further, as this water moves through the hyporheic zone beneath a stream bed, it cools. This cold water, which eventually reemerges downstream as surface flow, is crucial for salmon fry and other aquatic invertebrates that rely on oxygen rich water for their survival. As the snowpack in the Cascades decreases with climate change in the coming years, scientists like Dittbrenner hope the ecosystem services provided by beaver and their dam building might “make up an appreciable storage component of that lost snowpack.”
These researchers are now teaming up with Washington’s Tulalip Tribe to conduct their research and conservation work, and this collaboration is already having a ripple effect on other tribes’ approaches to salmon conservation. Similar research initiatives and relocation efforts are now underway to determine what effect beaver might have on bull trout populations on the Lewis River, in an initiative led by the Cowlitz Tribe.
Biohabitats’ Spring 2018 issue of Leaf Litter, focused on beaver, noted in its introduction that, “In building dams, beaver naturally achieve many of the goals those of us in conservation and restoration strive to achieve…In fact, the beaver’s impact on other animals and plants is so profound it is now considered a keystone species.”
So how can we set up conditions in which beaver can thrive and provide these crucial ecosystem services? In addition to reintroducing beaver to specific ecosystems and chronicling their impacts, scientists are also experimenting with beaver dam analogs in stream restoration work. These manmade structures mimic the effects of their “real” counterparts and can be used either to lure beaver to a site or to mimic their activities in places where they are not present. To aid the fledgling initiatives, in the latest edition of the Beaver Restoration Guidebook, Dr. Michael Pollock, a principal author, and his colleagues outline specific protocols for the location and installation of beaver dam analogs.
In his article “They Will Build It,” Ben Goldfarb documents a handful of current conservation measures relying on beaver for success ranging from encouraging the formation of beaver built wetlands to filter agricultural pollutants from areas that drain into Chesapeake Bay to mitigating flood damage by encouraging Castor fiber to engineer water systems that include deep ponds for the retention and infiltration of storm water in England.
While beaver aren’t a panacea for all environmental woes, they do provide an excellent example of and resource for environmental regeneration. Beaver researchers are wary of being as eager as their subject matter, but are more than cautiously optimistic that the comeback of this rodent that once dominated the North American watery landscape will play a major role in adjusting to pressing environmental stressors going forward. •
This article references the research presented in the following sources:
The writing of Ben Goldfarb, Beaver Believer, especially Eager: The Surprising, Secret Life of Beavers and Why They Matter. Chelsea Green Publishing, 2018.
David R. Bailey, Dittbrenner, B. and Yocom, K. “Reintigrating the North American Beaver (Castor canadensis) in the urban landscape.” University of Washington School of Environmental and Forest Sciences, 2017.
Biohabitats’ Leaf Litter, Spring Equinox 2018, Volume XVI, Edition 1, “Beaver.”
