Beavers, Castor canadensis, are semi-aquatic rodents who build dams. They are also the national animal of Canada. Beavers occur naturally in North America, where they have predators, including wolves and coyotes. And also, rodents were heavily hunted for their fur, which caused their number to dwindle rapidly. To prevent this, there was a ban imposed on hunting these creatures. Their number grew back to normal, but the fur industry took a big hit. In 1948, there was a need to boost the fur industry. So ten pairs were brought to Argentina and set free in Lake Fagnano. From there, they spread along the Beagle Channel, and now, a voracious beaver colony has been established on the Brunswick Peninsula in Chile, South America. While the pelt project for spurring trade never really took off, the beavers did. Since they were protected from hunting for the last 35 years and there were also no natural predators in South America, they sprouted rapidly. And the results are disastrous.
Beavers are the keystone species in South America
There are two types of beavers, one is present in Eurasia, Castor fiber, and the second the Castor canadensis, which is in North America was introduced in Canada in the 1940s. Beavers have been roaming North America for over 7 million years, a period long enough for native flora and fauna to know their teeth. Willow can now resprout its stems successfully, and Cottonwoods produce distasteful tannins to deter chewing.
In South America, beavers act as the keystone species, an organism that sustains the entire ecosystem. And, the presence or absence of that particular species would dramatically alter the food webs and affect the ecosystem.
Beavers are also known as the ecosystem engineers, which change landscapes by creating watery habitats for songbirds, fish, frogs, and trout by building dams. These animals take shelter and breed in these shallow, cold water ponds. These creatures use trees, especially their branches, to obstruct water flow and build a dam spanning many hectares. The beaver activity, when left unchecked, can cause a lot of damage to the trees in the area.
Factors that helped Canadian beavers to thrive in South America
The leafy giants of South America are grappling with the invasion of a flourishing army of furry beavers. Ten pairs of Canadian beavers introduced to Tierra del Fuego in 1946, primarily to give a boon to the fur industry, have boosted their population instead. This ill-conceived scheme resulted in a total of 200,000 million beavers dispersed across both Argentine and Chilean borders of Tierra del Fuego, chewing and gnawing their way through the pristine Patagonian forests.
“Drowned trunks, naked branches, and gnawed logs - it looks like a white ghost forest,” explained Chris Anderson, an ecologist at Chile’s Universidad de Magallanes and the lead author of a 2009 scientific paper.
Like most non-native invasions, the absence of native competitors or predators played a crucial role in rearranging these ecosystems. In the north, there are many predators of this animal that keeps its numbers in check. In stark contrast to North America, no natural predator is present in South America that wants beaver’s meat for dinner. Government laws protected them for 35 years from being hunted, and now they have grown to a massive level. They have become an invasive species. Beavers have started to damage the very place they were introduced.
In so doing, beavers have occupied some 27,027 square miles of territory and destroyed nearly 120 square miles of peat bogs, steppes, and forests. Many of these forests were centuries old, while others could only regenerate from dormant seeds in the ground. With the secondary effects of the beavers’ dam coming into play, we will go over this section soon, flooding disperses the seeds, and thus forests are lost forever. Anderson calls this “the largest landscape-level change in sub-antarctic forests since the last ice age.”
Beavers drill bank dens with underwater entrances beneath tree roots in large rivers. They constructed dams a short distance away from their lodges to increase the depth of the water surrounding the lodges and to discourage predators. Lodges are typically 10 feet tall and 20 feet across the base, though some can be as tall as 16 feet and 39 feet wide. During the winter, the wet walls of the lodge freeze, making it nearly impossible for predators to enter.
One more point in this is that they have an incredible ability to reproduce and survive in the new habitat. This particular trait has helped beavers survive the transition from North to South America. Each lodge houses an extended family of approximately eight beavers. An adult breeding pair, offspring of the year known as kits, and yearlings from the previous litter make up the family.
Beavers are the nature’s architects unleashed in South America
Let's see how they affect the habitat they have learned to thrive in. The trees in North America, such as American beech, cottonwood, or willow, have the ability to grow again after getting chewed or cut by beavers. These beaver-tolerant species can withstand flooded soils and produce unsavory defensive chemicals.
“As for the trees in South America, this is not the case,” explains Ben Goldfarb, the author of Eager: The Surprising, Secret Life of Beavers and Why They Matter. They are not well-equipped with the same defenses. So, once a tree is mowed down to build dams in rivers and lakes from their branches, it is not growing back.
The dams built by beavers reroute rivers and cause the flooding of nearby land. The trees in South America reproduce by seeds. They lie dormant in the earth and grow eventually. The trees regerminate much slower in this region compared to their native lands. But with flooding of the land, the seeds drown and die, delivering a critical blow to the growth of the forest. Their dam building has also destroyed roads and mixing of fresh and contaminated water. With beavers having reshaped up to 15% of the Tierra del Fuego landscapes and rerouted over 90 % of its rivers and streams, this poses a grave threat to the forests in the region.
The migration of fish like trout is also affected by the construction of beaver dams. It cannot swim freely around dams. As well, the dams can create bogs. Beavers contribute to climate change by cutting trees and releasing the carbon dioxide sequestered for centuries into the environment.
Biodiversity loss, the decline in wood production, and farming productivity due to flooding, damaged infrastructure, and flooded highways; these socio-economic impacts of beaver invasion cost Argentina and Chile a hundred million dollars every year.
On the other hand, the beaver invasion is more intriguing because, as one would expect from a keystone species, the rodent takeover has also benefited many species. The tree-gnawing, dam-building beavers, have aided native Magellanic woodpeckers by making trees more vulnerable to the wood-boring insects that the birds feed on. The slackwaters or low tidal zone behind dams also support native fish known as puye, four times more abundant around beaver impoundments than anywhere else in southern Chile.
Invasional meltdown as a result of beaver invasion
Researchers at the University of North Texas studied Navarino Island, Chile. They found that two other North American invasive species, Muskrat (Ondatra zibethicus) and American mink (Neovison vison), coexist with beavers at the southern tip of America. The research indicated that muskrats preferred beaver-modified wetlands while the weasel-like minks preyed on native mammals and fish. Although fish were mink’s primary prey in ponds around beaver dams, muskrats accounted for up to 50 % of the biomass of the mink diet. The researchers hypothesized this chain reaction as an “invasive meltdown process,” in which another invasive species exacerbate the negative impact caused by the first invasive species. Such novel ecosystems are the new normal.
Government plans the eradication of 100,000 beavers in Argentina and Chile
In some ways, the South American beaver story is very familiar: Humans introduce alien species; non-native species cause chaos, and humans futilely try to undo their mistakes. Both the governments of Argentina and Chile realized the problem in the 1990s. They tried to lure natives into beaver-hunting, but the low-priced furs, $20 at most, could motivate only a few.
Authorities also offered rewards to trappers who hunt critters, but that didn’t make a dent either. Not many people know how to trap rodents.
Now, what can be done about this invasive species? Well, the solution is simple, and it is not what most people would like to hear. Yes, you guessed it, it's culling. The governments of Argentina and Chile have decided to cull over 100,000 beavers over ten years.
But, this has given rise to cruelty concerns. With the compassionate conservation movement on the rise, some animal rights activists do not agree with this. They suggest that rather than being wiped out, Patagonia’s beavers should be trapped and sent back to Canada. But that is a very time-consuming process, and it also involves a quarantine period in which these beavers will be tested for any new disease that they might carry to the other side.
Nida Riaz is a freelance blogger based in Pakistan. She started writing about her passion for the environment when the world came to a stop in early 2020.