Copper roofing nails hammered into the trunk do a pretty good job finishing off a tree as well. Copper is the arsenic of the plant world.
That's actually a myth
Yes too much copper is bad for most lifeforms, even us.
Some copper is needed but like most needed minerals too much is bad
But if you used alot of copper nails around the whole trunk you could maybe kill it that way
If you saw off a limb you can put in a few cooper nails and limb will be less likely to re-grow
Trees transport water and nutrients up and down in the area just under the bark/skin of the tree, the center area of a tree or larger branch is just for support
It you cut a 2" wide strip/ring around the trunk the tree will die
The copper nails take advantage of that transport system just under the surface, but because there are so many transport "tubes" one nail would only effect a small part of a tree, so multiple nails, one every inch or so, would be needed to poison most of the tree
Nails in a tree can be dangerous for the next poor bastard who might be cutting the tree down or cutting it up for firewood
Chainsaws and nails don't react well to each other, lol