Copper nails driven into tree trunks do not kill the tree. In fact, the metal is an ingredient in many fungicides, which are used to protect trees.
In addition to the copper nail myth, many mistaken beliefs revolve around trees. Entire root systems do not burrow deep into the soil. While a few of a tree's roots extend down several feet, most are within a few inches of the surface. A cavity within a tree should be left alone. Concrete is not an appropriate filler, and it often harms the tree. Severe pruning is not good for trees. Though it stimulates growth, it also places a burden on the tree's energy resources and weakens its immune system.