Weeeeeeelll,... kind've. Beavers eat bark, not wood. In any case, this would require Frontier to create a falling animation and model for every model of every tree in the game as well as animations for beavers pulling each of these and then figuring out a way to get beavers to assess the size and shape of each piece to form into a dam, and find a suitable place to build a dam and then to completely rework the water system so that it could respond to the presence of the dam...... its not going to happen.