This is the damage done by beavers along most waterways in Canada. Even in the heart of the city. These trees are big around as you can stretch your arms and they're chewed through in a few days. Then once they're munched into manageable bits the beavers drag the pieces to their dams and build these massive homes.

This is why you'll see lots of trees with wire mesh "girdles" around their trunks. To protect them from hordes of ravenning, toothy beasts. .. Ok, they're cute as heck, but still..