Cambium is the plant material just under the bark of the tree, and it is one of the beavers' preferred delicacies. At times they strip the bark from a tree not to fell it, but merely to access this delicious treat. Other times, it seems that the purpose of felling a tree is merely to ease the stripping of bark and eating of cambium as shown here:
We've also been meticulous enough to get a couple of before/after shots showing the process of felling a tree:
To be able to chew through a tree is spectacular enough, but doing so again and again results in dramatic changes to the river's edge.