Beavers in Tierra del Fuego: why they are a problem

Who brought beavers to Tierra del Fuego

The Argentine government, in 1946. Beavers were brought from Canada to create a wild population for the fur industry, and they were released in the area of Lake Fagnano (Khami), on the Claro River, northeast of the lake.

The fur business never took off, but the beavers did. Once that industry was abandoned, no one kept controlling the population, and they multiplied very quickly: in Tierra del Fuego they have no natural predators, like the bears of Canada, and they found plenty of resources.

How far they have spread

By 1960 beavers had already reached Tierra del Fuego National Park, where they now occupy much of its area, and they later moved into the Chilean side of the island and almost every river on Navarino Island. Today they occupy the whole of Isla Grande de Tierra del Fuego, other Chilean islands, islets in the Beagle Channel and parts of mainland Chile, because they crossed the Strait of Magellan. If they are not controlled, they could advance north along the Patagonian Andes, at least as far as Neuquén.

Why they are a problem: forests, rivers and peat bogs

Beavers change the landscape in two ways: they cut down trees and, with their dams, they flood the forest. They affect lenga, guindo and ñire forests, and a damaged lenga takes about 200 years to recover. The damage lasts so long because, unlike many North American trees, those in the south of the continent do not usually resprout when they are cut.

• Riverside forests: the dams reduce the “protection forests” that line the rivers.
• Rivers and roads: the dams flood areas of forest, kill the vegetation, alter watercourses and can break up or flood roads.
• Peat bogs: the beaver also affects what peat bogs do: regulate water, sustain biodiversity and store carbon.
• After the beaver: abandoned dams let light in and form soils where exotic grasses take hold.

Ecologist Christopher Anderson, of the University of Magallanes, summed it up this way: it is the largest change to the region’s forest landscape in about 10,000 years.

What a castorera (beaver dam) is

That is the local name for the structures beavers build with logs in rivers and streams. The beaver lives in lodges on the banks of rivers and lakes, about 4 m across and 1.5 m high, and around them it builds dams with logs and branches, sealed with leaves, mud and stones. It can cut trunks up to 30 cm in diameter with its incisors, and in the fall it fells trees and shrubs and stores them underwater for the winter. In the forests of Tierra del Fuego it feeds mainly on lenga and ñire.

The result is easy to recognize: the dammed water and, around it, the flooded forest with dead trees still standing, like the ones in this guide’s photo.

Can you see beavers?

Seeing the animal is hard: the beaver is nocturnal, lives in groups and spends a lot of time in the water. What you can see by day, and in many places, are its dams. To look for them we have a dedicated tour, beaver watching with dinner: it leaves at 4:30 p.m. and, at Estancia La Carmen, takes a guided interpretive walk of about 20 minutes to the beaver dams and their lodges. On our other tours, what the programs list are the beaver dams.

Where to see beaver dams on our tours

On the Laguna Esmeralda hike, the beaver dams appear on the first section, among lenga trees. Waterproof footwear that covers the ankle is mandatory there: the ground is sometimes boggy, with roots and peat. Lake Fagnano, where it all began, can be seen in the distance from the Garibaldi Pass viewpoint, on the way to Estancia La Carmen: more about the area in Garibaldi Pass and Lake Escondido.

Tierra del Fuego National Park also has beavers: they are among its exotic species, with a very significant negative impact on the environment, and the park has a trail called Castorera Turística, suitable for people with reduced mobility. Our hike and canoe tour does not include that trail in its program.

What is being done to control them

Argentina signed a Binational Agreement with Chile to stop the beaver from spreading to the mainland, control its populations and restore damaged ecosystems. Under the ENEEI project, work was carried out in eight pilot areas in the Argentine sector of Isla Grande, with intensive beaver removal to restore those habitats.

The journal Nature described it as the largest eradication project ever attempted. Sport hunting was not enough, because the pelts have little value on the local market, and that, culturally, the beaver is seen more as a likeable, dam-building herbivore than as an invader.

Further reading

What the trail is like, how far you walk and what to bring are in Laguna Esmeralda and in the guide to hiking in Ushuaia. For the park, see Tierra del Fuego National Park. And if you are taking the King Crab Route, king crab in Ushuaia explains what it is and where to try it.