I am no tree expert, but I though you wanted to clear away the grass from the trunk at least as far as the length of the limbs.
This is so the roots will not compete with the grass for water.

Also, the melting point for copper is about 1984 degrees Fahrenheit.
It would need to at least that hot to be a liquid.
How did you apply the copper?

Right now your are probably thinking you should ask a tree expert and not an engineer.
Good idea.