Sun breaks through clouds over the moraine. Aki and I have to ford a flooded section of the trail to one of our favorite lakes, a sign that the beavers are ahead of their human opponents in the struggle for glacier dominance. The energetic rodents spend each night building up the dams that back up water over the trails. Soon the human beaver patrol will start disassembling the dams. Meanwhile the beavers cut down the few remaining poplar trees and have even started to drop the less nourishing alders.

In school, children learn that beavers are energetic engineers—animals to admire. No one mentioned that they have no off switch. They log until there are no more edible trees standing. Then they must find other hardwood forests to ravage.