The destructive effect of Beavers in Patagonia.
These Northern Hemisphere animals (Castor canadiensis) were introduced to Tierra del Fuego Island by the Argentine navy, to kick-start the local fur industry. It was a failure so some tender hearted navy man, instead of killing off the twenty five pairs of beavers, set them loose in the wilderness.
They expanded quickly and adapted marvelously to the new environment. Nowadays they number between 35 and 50 thousand,  and their territory occupies a large portion of Tierra del Fuego Island and several smaller ones in both Chile and Argentina.
To make matters worse, beavers have left Tierra del Fuego and colonized the southern tip of the continent at Brunswick Peninsula. The Chilean government is working hard to errdicate this foothold and to create a buffer zone on the Island.
If beavers manage to gain a firm hold on the mainland, the whole ecosystem of the Andean Forests will be at risk.
The local forests made up mostly of Nothofagus (Southern Beech) have not co-evolved with beavers like the Northern Hemisphere's forests. They grow slowly and just can't keep up with the logging habits of beavers.
Furthermore, the guanaco feeds on the new saplings and the combination of flooded forests (beaver dams block the flow of rivers and flood the woods), tree foraging and slow growth / sapling destruction is taking its toll on the Fuegian forests.
Beavers, they can explain the monster at Lake Fagnano
Since beavers have spread along Lake Fagnano into Chile and it occupies the central part of their Fuegian habitat, they may help explain Fañanito, the lake creature that is said to live in it, and which has been described as follows:
[the] large head appeared suddenly and looked at him, and then submerged without leaving any trace. The man screamed, startling the people; the boat turned around but they did not see it again
For someone on a tourist excursion along the lake, a beaver head appearing on the surface would be a frightening experience. One that could easily be attributed to a lake cryptid.
 Lizarralde, M., Escobar, J. and Deferrari, G.Invader Species in Argentina: A review about the beaver (Castor canadiensis) Population Situation on Tierra del Fuego ecosystem.Interciencia Jul 2004. Vol. 29 pp. 356
 Parkes, J.; Paulson, J, Donlan, J.; Campbell, K. (2008). Control of North American beavers in Tierra del Fuego: feasibility of eradication and alternative management options. Landcare Research Contract Report LC0708/
 Photograph is copyright © by Alec Earnshaw, Fauna of Argentina, it has some beautiful photographs of the Fuegian Fauna.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia
2010 International Year of Biodiversity
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