of ponds and wetlands. As wetlands are formed and riparian habitats enlarged, aquatic plants colonize newly available watery habitat. Insect, invertebrate, fish, mammal, and bird diversities are also expanded. Effects of beaver recolonization on native and non-native species in streams where they have been historically absent, particularly dryland streams, is not well-researched. Relationship with humans As introduced non-native species 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