The North American beaver (Castor canadensis) is a large semi-aquatic rodent that has played a central role in shaping the Canadian boreal landscape, and colonial Canadian history. Exploitation of North American beaver populations to supply the European hat industry spurred the westward expansion of European explorers and traders into the continental interior. With intensive unregulated harvest, beavers virtually disappeared across much of their range; though populations are recovering, the species is only about 10% as abundant as it was before the fur trade took its toll. As a result, much of the recent ecological history of the Canadian boreal forest has occurred in the absence of this keystone ecosystem engineer, and the ecological state that we perceive as natural is in many regions quite different than it was a century ago.