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The Beavers that Dam the End of the World: An Analysis of the Impact of Castor canadensis in

Tierra del Fuego and Eradication Efforts

By Ben Gaiarin

10/17/16

Stanford University

Parks and Peoples in Patagonia: Dilemmas of Protected Area Conservation

Professor William Durham

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The Beavers that Dam the End of the World: An Analysis of the Impact of Castor canadensis in

Tierra del Fuego and Eradication Efforts

By Ben Gaiarin

Introduction: The Castor canadensis and Fuegian Struggles

The story of the North American beaver (Castor canadensis ) in the Patagonia region

begins in 1946, when 20 beavers were flown from Canada’s Manitoba Province to Tierra del

Fuego, a mountainous archipelago shared by Chile and Argentina that forms the southern tip of

South America. The Argentine government, under the rule of General Juan Perón, hoped to spark

a thriving fur industry to boost economic activity for the isolated Fuegian community living in

the southernmost landmass of Argentina situated at, as described by many who visit the island,

the end of the world . Under the guidance of the Secretary of the Navy and Secretary of

Agriculture, Tierra del Fuego’s first 20 beavers were released on the main island in the

Nothofagus forests that lie between Lago Yehuin and Lago Fagnano (Pietrek & Fasola 2014: 356

- 357). This is the point in time and space where the beaver’s spread, and subsequent

consequences, began.

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Fig. 1: The spread of the Castor canadensis. (Anderson et. al 2009)

The local Fuegians were not enticed by scanty economic promises to hunt the beavers

and kickstart a fur trade, allowing the semiaquatic rodents to proliferate practically untouched.

The last 70 years have seen the rise of the beaver population from a meager 20 beavers to an

astounding 60,000 - 100,000 beavers, with some estimates suggesting that the population

doubled in size between 1993 and 2014 (Pellettieri 2014: 3). The population has expanded (fig.

1) to consume the entire southern tip of the Tierra del Fuego island, and has reached as far north

as the continental mainland of Chile, mysteriously crossing the Strait of Magellan in 1994

(Pellettieri 2014: 7 & Anderson et. al 2009). The Castor canadensis now occupies an estimated

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90% of watershed areas within Tierra del Fuego’s Isla Grande, which includes river, streams,

ponds, and lakes in Tierra del Fuego National Park (Pellettieri 2014: 3).

Considering how the North American beaver is an invasive species not native to South

America, it is worth asking the question: how has the Castor canadensis managed to survive and

reproduce so well in Tierra del Fuego? The beavers in Tierra del Fuego have found an abundance

of material for their vegetarian diet and for constructing their lodges and dams in the

archipelago’s famous Nothofagus forests, developing a particular liking for three species of

deciduous Nothofagus trees: the guindo, lenga, and ñire (Soto & Soza-Amigo 2014). The beavers

have also benefitted from a low risk of predation, as the local minks take minimal interest in the

Castor and the local foxes express no interest at all (Anderson et. al 2009). Finally, the Fuegian

archipelago is home to a rich network of streams, rivers, lakes, and ponds that provide the

beavers–a species capable of reproducing and residing in a wide variety of freshwater

habitats–with enough potential lodging areas to expand and grow their population.

A sign about the ñire Nothofagus tree in Tierra del Fuego National Park.

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The Fuegian ecosystem and its people see this expansion of the invasive beaver

population as a serious threat that brings about grave ecological and economic impacts. Cost

estimates to repair roads and other infrastructure damaged by the beavers’ damming and flooding

of watershed areas reach an estimated $4 million USD per year (Parks et. al 2008: 6). Concerns

regarding the beaver’s impact on Nothofagus forests, native species, and vital watersheds have

garnered support from the Chilean and Argentine national governments as well as international

NGO’s, prompting Chile and Argentina to create a binational committee in 2006 dedicated to the

complete eradication of the invasive species (Worth 2014).

A museum sign titled “Kind but Problematic” in Tierra del Fuego National Park. The Castor canadensis

is pictured on the right, with a gnawed Nothofagus tree stump placed below.

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If the Castor canadensis has been targeted as deserving of complete eradication, then

what, I ask, are the negative ecological impacts of the beaver population in Tierra del Fuego that

require their immediate cancellation? And if the beavers represent such a potent risk to the

Fuegian ecosystem and greater Patagonia region that they necessitate swift eradication, then why

has Argentina and Chile failed to send their population in decline thus far? I intend to address

these two questions in my paper, the former in significant detail and the latter in a brief

discussion, by providing testable hypotheses to explain the realities of the Castor canadensis in

Argentina and Chile. I will follow up my analyses with a short discussion of where academic and

political efforts can be directed within the scope of the invasion problem to best serve the

Fuegian ecosystem moving forward.

Analysis: Negative Ecological Impacts of the Beaver

Immediately upon looking into research on the environmental effects of beavers in Tierra

del Fuego I recognized that the destruction of Nothofagus forest is accumulating the most interest

from scholars and conservationists, as it represents the most visible effect of the invasive species

and the forests themselves represent a determinant of the ecological vitality of the Fuegian

region. As the forests attracted much of the spotlight, I also came across a wide variety of studies

focused on different ecological and chemical processes that the Castor canadensis and their

lodges are playing an adverse role in. Resulting from this division in impact discussions that I

witnessed in current research, I have formed two hypotheses to provide explanations for how the

beavers are injuring the Fuegian ecosystem:

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1) The destruction of the Nothofagus forests for the habitat construction and dietary needs

of the beaver carries severe ecological consequences.

2) Chemical and ecological imbalances caused by the construction of beaver dams brings

about negative ecological impacts.

I will begin by testing my first hypothesis with a discussion of how beavers are uprooting

Nothofagus forest, and why that creates disastrous effects to habitats and communities within the

archipelago.

One of the greatest consequences of beaver damming in Fuegian rivers and streams is the

subsequent flooding of the forests that reside around those water systems; 88% of

beaver-induced forest damage in Tierra del Fuego is caused by flooding, while the remaining

12% is due to gnawing and the dietary needs of the beavers (Parks et. al 2006: 16). Simanonok

et. al, conducting a comparison study of the effects of beavers and forestry on Nothofagus forest

in Tierra del Fuego in 2011, found the economic and environmental impacts of the beaver-led

forest destruction to be “relatively larger” than those of the local forestry industry. Their study

highlights the severity and size of the beavers’ forest impact, as well as the necessity to control

it.

Beaver-induced flooding also has long-lasting, negative ecological effects on watershed

areas even after the beaver residents have left for a new location. In 2006, Martinez et. al

published a study in Applied Vegetation Science that explores how the understorey, cover, and

biomass of Nothofagus forests change during succession after beavers abandon flooded river and

streams. They found understorey richness, cover, and biomass to be “significantly modified” by

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the beaver-induced flooding in all cases. They also noticed how ferns were the most negatively

affected group while grasses proliferated successfully during succession, suggesting that the

beavers, by flooding river and streams via the construction of dams, can convert Nothofagus

forest into grass and sedge dominated meadows. This connotes that the beavers can cause 180º

twists in habitat structure within an ecosystem, completely demolishing a forest and replacing it

with a meadow habitat that supports an entirely different array of species, and lacks the

necessary features for protecting and processing a healthy watershed ecosystem.

A grass and sedge dominated meadow by an abandoned streambed in Tierra del Fuego National Park.

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Equally important to the research of Martinez et. al is their discovery of how beavers

impede seed germination, making the destruction of Nothofagus a long-lasting effect. Normally,

Nothofagus trees are able to regenerate their populations around abandoned ponds after a short

period of time. However, the flooding caused by the beaver damming drowns seedlings, keeping

Nothofagus from springing up from the earth immediately following the start of succession.

More importantly, Martinez et. al found sediments left over from flooding to impede seed

germination within the original forest floor, requiring up to 20 years for Nothofagus populations

to completely regenerate.

The Castor canadensis , through skillful engineering and disastrous flooding, has not only

the ability to demolish entire forest species and the populations that depend on them for habitat

structures, but also to establish long-lasting conversions of forests to grass and sedge filled

meadows and impede the regeneration of old forests. But is there any way that this habitat

conversion could be a positive event? Guanacos, feral horses, and domesticated cattle have been

shown to make use of the newly-established grass meadows for grazing (Parks et. al 2008: 17),

but this only provides a slight expansion in habitat availability to a select group of species that is

by no means under concerning population stress in Tierra del Fuego, and does not provide a

strong counter to the negative results of flooding on forest. The support that Nothofagus forests

provide to watersheds and understorey ecosystems is crucial to the biodiversity of the Fuegian

archipelago, and their destruction is enough to require the immediate eradication of the Castor

canadensis.

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Two guanacos preparing to fight. Guanacos would benefit from a beaver-induced habitat conversion to

grass and sedge dominated meadows.

In addition to the negative ecological effects of flooding and the subsequent destruction

of Nothofagus forest, a significant body of research is dedicated towards exploring chemical and

ecological imbalances triggered by the construction and use of beaver lodges and dams. The

Castor canadensis is an engineer of two different types of lodging systems: bank lodges and

conical lodges. Bank lodges are lodge structures constructed on the side of deep and wide rivers

or lakes without the use of a damming system, while conical lodges are constructed in shallower,

narrower riverbeds and streambeds and include the construction of a dam. As a result of

damming the stream or river, the beaver, in constructing a conical lodging system, changes the

hydrology of the water from lotic (running) to lentic (still) (Menvielle et. al 2011: 11). Lizarralde

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et. al conducted a study in 1996 on the effects of this hydrological change on nutrient dynamics

in the beaver habitats. They found that beaver-induced hydrological change significantly affects

the nitrogen cycle in the river/streambed, specifically the processes of nitrification and

denitrification, and raises levels of organic carbon and phosphorus. Although the impact of these

chemical imbalances on native species and larger ecosystem interactions is relatively unclear, it

is nonetheless evident that the hydrological change caused by beaver damming does have

profound negative impacts on the chemical composition of watersheds.

By raising the nitrogen content in the water and submerging algae and other vegetation

by flooding at dam sites, the beaver converts its habitat into an environment that supports

numerous other invasive species. Lizarralde et. al found such beaver-induced alterations to

support invasive fish species like the Salmo truttafario (brown trout) and Oncorhynchus mykiss

(Rainbow trout), which, as shown in fig. 2, both respectively act as predators towards native

species, affect the original balance of the watershed food webs, and cause invasional meltdowns

(2004). This would suggest that the beaver supports other invasive species in Tierra del Fuego

that, in turn, also support other invasive species, contributing to an invasional meltdown (fig. 3)

that spans beyond the scope of the beaver problem.

Fig. 2: The brook trout and rainbow trout and their respective environmental impacts as invasive

species are highlighted above. (Valenzuela et. al 2014)

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Fig. 3: The beaver, as highlighted above, can cause invasional meltdown, in addition to changes

in habitat, nutrient cycling, and soil properties. (Valenzuela et. al 2014)

The beaver entices dangerous changes in the chemical, hydrological, and ecological

makeup of the rivers, lakes, ponds, and streams it resides in, which can impose disastrous effects

on the health and biodiversity of watershed areas. There are some ecological changes brought

forth by the beaver, however, that could potentially create positive effects for certain

communities. Anderson & Rosemond conducted a study in 2007 on the effects of beaver-led

engineering on in-stream diversity, and found increased levels of macroinvertebrate biomass and

production in benthic communities that reside with beavers. On the other hand, they also found

decreased levels of macroinvertebrate diversity, making the distinction between an overall

positive or negative effect unclear in this case.

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Overall, the chemical and ecological imbalances caused by the structure of beaver

habitats has overwhelmingly more negative effects on watershed ecosystems than positive, and

the potential for injury to native species and biodiversity is significant. More research, however,

will have to be conducted on measuring the effects of these imbalances on biodiversity and

ecosystem productivity.

A stream uninhabited by beavers in Tierra del Fuego National Park.

Analysis: Eradication Efforts

We have explored the negative ecological impacts induced by the beaver in Tierra del

Fuego. Many of these impacts have been injuring the region since the arrival of the first 20

beavers in 1946, and others have gradually appeared as the beaver population has proliferated

uncontrollably. Since the effects of the invasive species have been observed for 70 years now,

why, then, has Chile and Argentina failed to send the beaver population in decline thus far?

Upon beginning my investigation, I hypothesized that:

1) Opposition from local groups has significantly inhibited eradication efforts.

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My hypothesis was weakly supported by a number of individual cases in tourism, animal

rights, land ownership, and hunting. I found cases where beaver-watching tours and beaver hikes

offered by local Fuegian tourist groups (Pelletieri 2014: 6) were raising concerns for parties

working towards eradication, but I suspect that the extent to which these tourist groups are

actually hindering eradication efforts is negligible. I came across one animal rights group , the

American-based “Beavers: Wetlands & Wildlife” organization, (Pelletieri 2014: 6) that has been

publishing articles and speaking out against beaver eradication efforts in Tierra del Fuego and

arguing for sustainable control practices. Their impact on the issue in the political spheres of

Argentina and Chile is also doubtful. Argentina and Chile have operated bounty programs that

encourage harvesting beavers for their fur and meat by providing hunters with subsidies to

promote eradication, which Parks et. al argues is “counterproductive” as it encourages people to

value beavers (Parks et. al 2008: 6). However, no clear local opposition of hunters has been

formed to protect the source of their furs, meat, and subsidies as a result of the bounty program.

Finally, scholars have discussed the difficulty hunters have in reaching areas where beavers

reside (Loewy 2015), but I have not found any evidence that suggests the difficulty is in part

caused by the reluctance of private landowners to permit hunters and conservationists to enter

their property for eradication efforts.

I believe that the answer to why eradication efforts have been slow lies outside of local

opposition. The beavers have, in large part, proliferated because the natural Fuegian environment

has permitted them to: they experience extremely low risk of predation (Anderson et. al 2009),

and they take advantage of their ability to “reproduce in different habitats” (Loewy 2015)–lakes,

ponds, rivers and streams included–by spreading throughout the incredible abundance of

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potential beaver habitats that exist within the Fuegian archipelago. Chile and Argentina were also

late to take action; year-round beaver hunting was not legalized in Argentina until 1981 nor in

Chile until 1993 (Anderson et. al 2009). The national governments did not agree to complete

eradication and conduct a feasibility study until 2006 (Worth 2014). A slow eradication,

therefore, could best be explained by slow-moving political efforts and fast-proliferating beaver

populations.

The end of the southernmost road in the world in Tierra del Fuego National Park.

Recommendations for Further Research and Action

The invasive beaver species was certainly not been a priority for Chile and Argentina,

two countries riddled with many recent shifts in government and economic disasters. When the

problem finally surfaced to national and international attention, it came with its own set of

questions that have slowed the pace of the efforts. Where will the funding come from? How will

hunters and locals be mobilized to support the efforts? How do we access uninhabited,

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hard-to-reach areas in which some beaver populations reside? What is the best approach to

eradicating this invasive species?

All of these questions require more discussion, research, money, and time. There is a lot

more that both domestic and international researchers, conservationists, and conservation NGO’s

can do to help answer these questions and speed up current eradication efforts. A healthy amount

of research has been conducted on the ecological impacts of the beavers thus far, which has been

influential in emphasizing the necessity for a quick and efficient eradication process. I, however,

see a gap in the research when it comes to considering politics and policy. I identify a need for

researchers, particularly those experienced in certain fields of public policy, to investigate and

discuss current efforts to eradicate and control beavers in Tierra del Fuego. This would help

Chile, Argentina, and the international conservation community identify certain means of

organizing and mobilizing eradication efforts that would be most efficient.

There is also room for more international conservation organizations, especially those

like Tompkins Conservation that have a history of work in Patagonia, to step into the efforts with

funding and personnel support, as the funds for a complete effort are currently lacking and local

personnel is low in numbers.

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Finally, it is also time to start thinking not only about how we can proceed with full

eradication, but also about how we can reverse the detrimental effects of the beavers’ presence in

Tierra del Fuego. How can we organize to replant damaged Nothofagus forest? How can we

identify native species that have been harmed by the beavers and restore their populations? These

are questions that researchers, conservationists, and politicians alike can bring to the discussion

table.

Protecting the vibrant biodiversity of the Fuegian archipelago is deserving of international

support.

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Works Cited

Anderson, C.B. and Rosemond, A.D., 2007. Ecosystem engineering by invasive exotic beavers

reduces in-stream diversity and enhances ecosystem function in Cape Horn,

Chile.Oecologia , 154 (1), pp.141-153.

Anderson, C.B., Pastur, G., Lencinas, M.V., Wallem, P.K., Moorman, M.C. and Rosemond,

A.D., 2009. Do introduced North American beavers Castor canadensis engineer

differently in southern South America? An overview with implications for restoration.

Mammal Review , 39 (1), pp.33-52.

Lizarralde, M., Deferrari, G., Alvarez, S.E. and Escobar, J., 1996. Effects of beaver (Castor

canadensis) on the nutrient dynamics of the Southern Beech forest of Tierra del Fuego

(Argentina). Ecología Austral , 6 , pp.101-105.

Lizarralde, M., Escobar, J. and Deferrari, G., 2004. Invader species in Argentina: a review about

the beaver (Castor canadensis) population situation on Tierra del Fuego ecosystem.

INTERCIENCIA-CARACAS- , 29 (7), pp.352-356.

Loewy, M. (2015). North American Beaver Invasion Occupies Forests and Steppes in Southern

Chile and Argentina . [online] Scientific American. Available at:

http://www.scientificamerican.com/article/north-american-beaver-invasion-occupies-fore

sts-and-steppes-in-southern-chile-and-argentina/ [Accessed 10 Sep. 2016].

Martínez Pastur, G., Lencinas, M.V., Escobar, J., Quiroga, P., Malmierca, L. and Lizarralde, M.,

2006. Understorey succession in Nothofagus forests in Tierra del Fuego (Argentina)

affected by Castor canadensis. Applied Vegetation Science ,9 (1), pp.143-154.

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Menvielle, M.F., Funes, M., Malmierca, L., Ramadori, D., Saavedra, B., Schiavini, A. and Soto

Volkart, N., 2010. American beaver eradication in the southern tip of South America:

main challenges of an ambitious project. Aliens Invasive Species Bull , 29 , pp.9-16.

Parks, J.P., Paulson, J., Donlan, C.J., & Campbell, K. 2008, March. Control of north american

beavers in tierra del fuego: Feasibility of eradication and alternative management

options (Research Report No. LC0708/084). Landcare Research New Zealand Ltd.

http://docplayer.es/1591343-Feasibility-of-eradication-and-alternative-management-op

tions.html

Pellettieri, L. 2014. As burgeoning beaver population disrupts ecosystem, Argentina prepares to

exterminate nonindigenous species. Global Press Journal . Retrieved from

https://globalpressjournal.com/americas/argentina/burgeoning-beaver-population-disrupts

Simanonok, M.P., Anderson, C.B., Pastur, G.M., Lencinas, M.V. and Kennedy, J.H., 2011. A

comparison of impacts from silviculture practices and North American beaver invasion

on stream benthic macroinvertebrate community structure and function in Nothofagus

forests of Tierra del Fuego.Forest Ecology and Management , 262 (2), pp.263-269.

Soto Simeone, A. and Soza-Amigo, S., 2014. Economic valuation of native forest affected by the

North American beaver (Castor canadensis) in Tierra del Fuego. BOSQUE , 35 (2),

pp.229-234.

Valenzuela, A.E., Anderson, C.B., Fasola, L. and Cabello, J.L., 2014. Linking invasive exotic

vertebrates and their ecosystem impacts in Tierra del Fuego to test theory and determine

action.Acta Oecologica , 54 , pp.110-118.

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Worth, K. 2014, March. Argentina and Chile Decide Not to Leave It to Beavers . Scientific

American . Retrieved 8 September 2016, from

http://www.scientificamerican.com/article/argentina-and-chile-decide-not-to-leave-it-to-b

eavers/