A reintroduction has been defined by the International Union for the Conservation of Nature and Natural Resources (IUCN) as "the intentional movement of an organism into part of its native range from which it has disappeared or become extirpated in historic times as a result of human activities or natural catastrophe." Since extinctions in the wild continue and hence the number of species being potential candidates for reintroductions increases, it is a conservational tool of increasing importance.
The beaver population in Sweden is the result of one of the earliest reported successful attempts to bring back a species to its former range. The European beaver was historically found all over the Europe. Cultivation, deforestation, and grazing decreased the range of the beaver. However, habitat destruction was not the main cause behind the drastic decline in range and numbers. The main cause was overhunting. In the beginning of this century the beaver's range in Europe was restricted to a few small areas. The last well-documented observations of beaver from the original Swedish population are from the 1870's.
Between 1922 and 1939 about 80 beavers had been brought from Norway and released at 19 different sites in Sweden. In 1992, 70 years after the first reintroduction, the population was estimated at about 100,000 individuals. The population is still increasing and expanding its range.
Colonizing beaver have a great impact on stream morphology and hydrology by cutting wood and building dams, and ultimately influence plant and animal community composition and diversity. It is likely the most important key stone species in the northern hemisphere. Future management of the beaver population will have to balance the positive effects of beaver activity on biodiversity and its negative effects on forestry.
Key words: reintroduction, European beaver, Sweden.
Correspondence: Göran Hartman, Dept. Wildlife Biology, Box 7007, 75007 Uppsala, Sweden