Albert Dziekonski
Albert Dziekonski voted up HappyTwo BeHereTwo's answer

Beavers, mice, squirrels, porcupines, deer, bear...  It's a huge list!  This might help you identify your culprit.

http://www.forestry.gov.uk/fr/infd-6k4kaf

It's from the UK, brb with a US link.

Edit:  this one shows a picture of beaver damage where they just ate the bark.

https://www.americanforests.org/magazine/article/the-language-of-bark/

Albert Dziekonski
Albert Dziekonski voted up Ray Dart's answer

We've also seen that here in the UK by black and grey squirrels. We have very few beavers here, so most of the other damage is caused by deer (and then only in bad years when the grazing is bad).