Don't worry, when done correctly, it doesn't kill the tree.
Harvesting bark from the birch tree in a sustainable method can only be done for about three weeks out of the year, when the wild roses are in bloom in northern Minnesota. When done correctly only the outer bark is removed, leaving the inner bark intact. Throughout the rest of the summer and the fall it will form a scab, which the tree will use to overwinter and begin growing a new outer layer. The whole process takes around eight to ten years to complete.
Will Moore, of WTIP North Shore Community Radio, accompanied Beth and some others on a harvest near Grand Marais, MN. Recordings from the expedition were edited into a radio show, which can be played below.