Overnight, a small pond has been transformed into a large one. Trees stand knee-deep in water, unable to wade to higher ground. This slow drowning will be only one of the costs the beavers will exact from this landscape, though they have made a home of startling beauty. Briefly, I contemplate pulling the sticks and branches and boughs from the culvert, but quickly I recognize I can’t do the math: How many trees is a beaver worth? And how many beavers, one tree?