Beavers: Patagonia invaders

In 1940 twenty Canadian Beavers were brought to 'Tierra del Fuego' island in southern Patagonia for commercial fur production. However, beavers having no natural predators, quickly spread throughout the island, causing massive destruction of trees threatening the entire Patagonian forests rivers and species. Why wildlife conservationist are convinced that 150.000 beavers must be killed? Why some o…