Question
One of my sisters cut a ring of bark from around a large pine tree branch. Soon the whole branch died. My dad said that the bark carries the nutrients in the tree. So if a lot of bark gets pulled off it will die. Is this true?

Eric

Answer
Under the bark is a layer of cells called the cambium layer. This is the living layer that moves food and water from the roots to the leaves. The cambium layers down wood toward the center of the tree and bark toward the outside. The bark is there to protect the cambium for outside damages. When you cut all the way around the tree or branch this cuts the cambium layer and the branch or in the case of the tree the Tree dies since it can not receive water from the root system. If the bark gets pulled off the cambium layer is exposed to insects and diseases and over time the tree could and usually does die. It is not from the bark damage but from the damage to the cambium layer.
Here is a web link that describes this in more detail.
http://www.backyardnature.net/woodtwi2.htm