page_title: North American beaver
section_title: As introduced non-native species
hierarchical_section_title: North American beaver / Relationship with humans / As introduced non-native species
caption_attribution_description: English: Beaver damage to the forest on the north shore of Robalo Lake, Navarino Island, Chile. Español: Daño de los castores en el bosque a la costa norte del Lago Róbalo, Isla Navarino, Chile.
context_page_description: The North American beaver is one of two extant beaver species. It is native to North America and introduced in South America and Europe. In the United States and Canada, the species is often referred to simply as "beaver", though this causes some confusion because another distantly related rodent, Aplodontia rufa, is often called the "mountain beaver". Other vernacular names, including American beaver and Canadian beaver, distinguish this species from the other extant beaver species, Castor fiber, which is native to Eurasia. The North American beaver is an official animal symbol of Canada and is the official state mammal of Oregon and New York.
context_section_description: In the 1940s, beavers were brought to Tierra del Fuego in southern Chile and Argentina for commercial fur production and introduced near Fagnano Lake. Although the fur enterprise failed, 25 mating pairs of beavers were released into the wild. Having no natural predators in their new environment, they quickly spread throughout the main island, and to other islands in the archipelago, reaching a number of 100,000 individuals within just 50 years. Although they have been considered an invasive species, it has been more recently shown that the beaver have some beneficial ecological effects on native fish and should not be considered wholly detrimental. Although the dominant Lenga beech (Nothofagus pumilio) forest can regenerate from stumps, most of the newly created beaver wetlands are being colonized by the rarer native Antarctic beech (Nothofagus antarctica). It is not known whether the shrubbier Antarctic beech will be succeeded by the originally dominant and larger Lengo beech, however, and the beaver wetlands are readily colonized by non-native plant species. In contrast, areas with introduced beaver were associated with increased populations of the native catadromous puye fish (Galaxias maculatus). Furthermore, the beavers did not seem to have a highly beneficial impact on the exotic brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) which have negative impacts on native stream fishes in the Cape Horn Biosphere Reserve, Chile. They have also been found to cross saltwater to islands northward; and reached the Chilean mainland in the 1990s. On balance, because of their landscape-wide modifications to the Fuegian environment and because biologists want to preserve the unique biota of the region, most favor their removal.
  North American beavers were released in Finland in 1937, before it was realized that they formed a separate species; following this, 7 beavers expanded to a population of 12,000 within 64 years. Eurasian beavers had earlier been extirpated from the region, so the release was intended as a reintroduction project. By 1999, it was estimated that 90% of beavers in Finland were the American species. However, the species is not always considered invasive, as in Europe it has a similar keystone effect to European beavers, which have not recolonized the area. The beaver population has been controlled by issuing hunting licenses. A report in 2010 concluded that while the current population of American beavers was not problematic, as the species has larger litters than European beavers and builds somewhat larger dams, it could become a problem if its range continues expanding into Russia, but this does not seem to be taking place. 
  In Europe, significant invasive populations of Canadian beaver are only present in Finland and Karelia, as the boundary between species has somewhat stabilized, but smaller occurrences have been detected elsewhere. Ephemeral populations of C. canadensis in Germany and Poland were found from the 1950s to 1970s. Zoo escapes in 2006 created a small population of invasive C. canadensis in Luxembourg, Rhineland-Palatinate and Belgium. American beavers have not been detected in Sweden, Norway, or Denmark.
caption: Beaver damage on the north shore of Robalo Lake, Navarino Island, Chile
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