With regard to the sections about beavers, I went to an event this year where a beaver scientist mentioned that many European settlers in North America showed up after beavers had been nearly extirpated by trappers. So they would come across open flat areas with a stream flowing through which had likely been dammed by beavers in the past. This caused problems with flooding and water damage, and problems as beavers have been reestablished in much of the US (and Canada?)