It seemed like a good idea at the time.
Transplanting 25 pairs of Canadian beavers to Tierra del Fuego would provide raw material for a fur industry, bring jobs to a sparsely populated region and — as an advertisement in 1946 suggested — possibly attract tourists to this remote part of the hemisphere by "enriching the local fauna."
Seventy years later, the placement of the nonnative, wood-chewing mammals in Fagnano Lake along the Chile-Argentina border is viewed as a colossal mistake. On the Chilean side of Tierra fel Fuego alone, the beaver population has swelled to about 200,000, and the giant, semiaquatic rodents can be found near the wind-swept city of Punta Arenas, some 200 miles northwest from the lake.
Probably with human help, they even have crossed the Magellan Strait to inhabit several islands.
The problem is that the beavers, being beavers, have built hundreds of dams, and though beaver dams can invigorate some ecosystems, in Patagonia they are creating harmful floods that threaten the primeval forest of lenga trees and nearby lakes.
According to Wildlife Conservation Society figures, 25% of the forest and 95% of the archipelago basins have been affected by beaver dams, and thousands of old-growth trees are dead or dying, as well as bountiful peat bogs.
"Patagonian ecosystems are not prepared to the kind of changes that beavers bring," said Chilean biologist Giorgia Graells, who is part of a multidisciplinary team studying the local beaver population. "Magellanic forest regenerates from seed banks kept on the ground, so when an area is flooded, the seeds get covered by mud and water and die, and the forest won't recover."
To preserve the forests, the Chilean government this month is launching a $7.8-million population control project, funded in part with $2.1 million from the Global Environment Facility, an international aid-giving agency for developing countries. Part of the money will go to placing traps — think bear traps, but smaller — described as a means of providing a quick, humane kill.
"It would be too optimistic to think of extinguishing this invasive species in the short term, but we can expect a better control of it," Chilean Environment Minister Pablo Badenier said.
World history is full of examples of nonnative species that defy efforts to control them. In the United States, Africanized bees have reached California, Burmese pythons eat just about anything — including alligators — in Florida, and starlings, since their introduction in the U.S. in 1890, have spread to every state.
Chile has been trying to contain its beaver population since 2003 and, for many years, offered rewards for furs and tails. But the beavers, which have no natural predators in Chile such the wolves and bears that kill them in North America, have proved difficult to catch.
"Beavers are highly intelligent creatures. We set traps and sometimes they have activated them by placing branches" on them, said Mauricio Chacon, chief park ranger at Karukinka Natural Park, who makes his rounds with his .22-caliber Mauser rifle on his back. Beavers that do get their legs caught in a trap will gnaw them off to avoid capture, he said.
Scharon Zegarra, a female ranger at this park located more than 1,600 miles south of the Chilean capital of Santiago, said that nowadays "we took one out of its lodge and, soon after, a younger one takes its place. We haven't seen this before."
Beavers are also wildly reproducing on the Argentine side of Tierra del Fuego.
Argentina has been working with the Chilean government on the problem since 2005. Argentina has its own eradication project and aims to kill 100,000 beavers in the years to come — an initiative that has already received criticism from animal rights groups, which wish beavers could be returned to Canada.
This is a worrisome idea for Chilean biologists, who consider it not only expensive but impractical. And beavers aren't the only case of failed efforts to transplant foreign animals in nonnative habitats. German wild boars and American minks have also been transplanted here and are considered threats to Chile's biodiversity because they kill or crowd out native species.
"Invasive alien species are among the main issues against biodiversity in the planet, and the world is just waking up to it," said Barbara Saavedra, head of Chile's Wildlife Conservation Society, which owns the 1,160-square-mile private Karukinka Natural Park.
Located 161 miles from the nearest city, Porvenir in Chile, the park has little infrastructure but lush virgin forests and peat bogs. The government is trying to promote tourism to the region, but sees the out-of-control beaver population as more a nuisance than an attraction.
"Beavers won't devour the Patagonia, but they will destroy large amounts of forests and contaminate vast water sources," said Saavedra, looking at the Karukinka landscape. "So we want to stop them before they reach the Panama Canal. It's a sad but true joke."
Poblete is a special correspondent.