If nails are nailed in to the trunk of a tree to hang something, does it damage the tree?

If it is a decent sized tree, it should not matter. Don't make a habit of this though as any wound on a tree makes it susceptible to harmful elements.





Sometimes I use huge cable zip ties (like the ones for electrical wires) hooked together to hang stuff on trees. I have ones that are 2 feet long from Home Depot.If nails are nailed in to the trunk of a tree to hang something, does it damage the tree?
Not really. but depends on the size and numbers of the nails!If nails are nailed in to the trunk of a tree to hang something, does it damage the tree?
Only if the tree is a sappling, otherwise the trunk is thick enough to protect the heartwood in the center.
This is not typically a problem with well established trees. I have seen many trees that had large nails (and sometimes even hooks) driven in to them in order to facilitate cleaning catfish.





I also know that it is very difficult in my location to find a sawmill that will take wild black walnut. Many of those trees grew along fence lines, and they often have nails and/or wire deeply embedded in them.





One time I tossed a chain up in a tree to get it out of my way when I was mowing. I did not need the chain for about a year. When I went to get it, the tree had grown around it. The tree is fine. My chain . . .





That said, I don't know what you are trying to hang, but you might not need a nail at all. I use bunge cords to hang bird feeders and plants from my trees. Works great!