system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does removing a circle of bark on a tree (Girdling) kill it?
gpt
The inner wood on a tree is generally dead wood that does not transport water and nutrients for the tree. Instead it is the outermost layers and the bark (to some extent) that feeds the tree from its roots. If you take off those outside layers then everything above the area of removed bark and outer wood will die due to lack of nutrients.