Just doing a google search for "copper nail" brought up an interesting possibility. Supposedly driving a copper nail into a tree will kill it.
Date: Tue Aug 25 14:02:58 1998
Posted By: Dr. Elson Silva, , Soil Scientist, Ph. D., Embrapa
Area of science: Agricultural Sciences
ID: 904063988.Ag
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Message:
Yes, if the nail is big enough to harm the base of the tree. It can open an
entry for infection and disease. You also need to consider how big is the
nail and the tree. Driving a copper nail has physical, chemical, and
biological actions playing together. If the tree dies, it will not be easy
to know precisely what the main cause was acting. Copper as a metallic form
is not harmfull to tree nutrition. It needs to oxidize, to solubilize and
then be absorbed. Absorption of copper at the bark level may not occur, while
high levels of copper ion in the soil rooting system may lead to toxicity. Many
species of trees also will respond differently to this stress related to
nails in their bases. In biology we do not play yes/no answer!